//! WHATWG URL parser.
//!
//! Implements the URL Standard (<https://url.spec.whatwg.org/>):
//! - URL record type with scheme, username, password, host, port, path, query, fragment
//! - State-machine parser following the spec
//! - Host parsing: domains, IPv4 addresses, IPv6 addresses
//! - Percent-encoding and decoding (UTF-8)
//! - Special scheme handling (http, https, ftp, ws, wss, file)
//! - Relative URL resolution via base URL
//! - URL serialization
//! - Origin derivation

use core::fmt;

// ---------------------------------------------------------------------------
// Error types
// ---------------------------------------------------------------------------

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum UrlError {
    /// Input is empty or contains only whitespace.
    EmptyInput,
    /// Invalid URL syntax.
    InvalidUrl,
    /// Invalid scheme.
    InvalidScheme,
    /// Invalid authority.
    InvalidAuthority,
    /// Invalid host.
    InvalidHost,
    /// Invalid port number.
    InvalidPort,
    /// Invalid IPv4 address.
    InvalidIpv4,
    /// Invalid IPv6 address.
    InvalidIpv6,
    /// Invalid percent-encoding.
    InvalidPercentEncoding,
    /// Relative URL without a base.
    RelativeWithoutBase,
    /// Missing scheme.
    MissingScheme,
}

impl fmt::Display for UrlError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::EmptyInput => write!(f, "empty input"),
            Self::InvalidUrl => write!(f, "invalid URL"),
            Self::InvalidScheme => write!(f, "invalid scheme"),
            Self::InvalidAuthority => write!(f, "invalid authority"),
            Self::InvalidHost => write!(f, "invalid host"),
            Self::InvalidPort => write!(f, "invalid port number"),
            Self::InvalidIpv4 => write!(f, "invalid IPv4 address"),
            Self::InvalidIpv6 => write!(f, "invalid IPv6 address"),
            Self::InvalidPercentEncoding => write!(f, "invalid percent-encoding"),
            Self::RelativeWithoutBase => write!(f, "relative URL without a base"),
            Self::MissingScheme => write!(f, "missing scheme"),
        }
    }
}

pub type Result<T> = core::result::Result<T, UrlError>;

// ---------------------------------------------------------------------------
// Host
// ---------------------------------------------------------------------------

/// A parsed URL host.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Host {
    /// A domain name (already lowercased).
    Domain(String),
    /// An IPv4 address.
    Ipv4(u32),
    /// An IPv6 address (128 bits as eight 16-bit pieces).
    Ipv6([u16; 8]),
}

impl Host {
    /// Serialize the host to a string.
    pub fn serialize(&self) -> String {
        match self {
            Host::Domain(d) => d.clone(),
            Host::Ipv4(addr) => serialize_ipv4(*addr),
            Host::Ipv6(pieces) => format!("[{}]", serialize_ipv6(pieces)),
        }
    }
}

impl fmt::Display for Host {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.serialize())
    }
}

// ---------------------------------------------------------------------------
// Origin
// ---------------------------------------------------------------------------

/// A URL origin (scheme, host, port).
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Origin {
    /// A tuple origin (scheme, host, port).
    Tuple(String, Host, Option<u16>),
    /// An opaque origin (unique, not equal to anything).
    Opaque,
}

// ---------------------------------------------------------------------------
// URL record
// ---------------------------------------------------------------------------

/// A parsed URL record per the WHATWG URL Standard.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Url {
    /// The scheme (e.g., "http", "https", "file").
    pub scheme: String,
    /// The username (percent-encoded).
    username: String,
    /// The password (percent-encoded).
    password: String,
    /// The host.
    pub host: Option<Host>,
    /// The port (None = default or absent).
    pub port: Option<u16>,
    /// Path segments. For non-opaque paths, these are the segments.
    /// For opaque paths (cannot-be-a-base URL), this is a single element.
    path: Vec<String>,
    /// Whether this URL has an opaque path (cannot-be-a-base URL).
    opaque_path: bool,
    /// The query string (without leading '?').
    pub query: Option<String>,
    /// The fragment (without leading '#').
    pub fragment: Option<String>,
}

impl Url {
    /// Parse a URL string.
    pub fn parse(input: &str) -> Result<Self> {
        parse_url(input, None)
    }

    /// Parse a URL string with a base URL for resolving relative references.
    pub fn parse_with_base(input: &str, base: &Url) -> Result<Self> {
        parse_url(input, Some(base))
    }

    /// Get the scheme.
    pub fn scheme(&self) -> &str {
        &self.scheme
    }

    /// Get the username (percent-encoded).
    pub fn username(&self) -> &str {
        &self.username
    }

    /// Get the password (percent-encoded).
    pub fn password(&self) -> &str {
        &self.password
    }

    /// Get the host.
    pub fn host(&self) -> Option<&Host> {
        self.host.as_ref()
    }

    /// Get the host as a string.
    pub fn host_str(&self) -> Option<String> {
        self.host.as_ref().map(|h| h.serialize())
    }

    /// Get the port.
    pub fn port(&self) -> Option<u16> {
        self.port
    }

    /// Get the port or the default port for the scheme.
    pub fn port_or_default(&self) -> Option<u16> {
        self.port.or_else(|| default_port(&self.scheme))
    }

    /// Get the path as a string.
    pub fn path(&self) -> String {
        if self.opaque_path {
            self.path.first().cloned().unwrap_or_default()
        } else {
            let mut s = String::new();
            for seg in &self.path {
                s.push('/');
                s.push_str(seg);
            }
            if s.is_empty() {
                s.push('/');
            }
            s
        }
    }

    /// Get the path segments.
    pub fn path_segments(&self) -> &[String] {
        &self.path
    }

    /// Get the query string.
    pub fn query(&self) -> Option<&str> {
        self.query.as_deref()
    }

    /// Get the fragment.
    pub fn fragment(&self) -> Option<&str> {
        self.fragment.as_deref()
    }

    /// Whether this URL has an opaque path (cannot-be-a-base).
    pub fn cannot_be_a_base(&self) -> bool {
        self.opaque_path
    }

    /// Whether this URL includes credentials.
    pub fn has_credentials(&self) -> bool {
        !self.username.is_empty() || !self.password.is_empty()
    }

    /// Derive the origin of this URL.
    pub fn origin(&self) -> Origin {
        match self.scheme.as_str() {
            "http" | "https" | "ws" | "wss" | "ftp" => {
                if let Some(host) = &self.host {
                    Origin::Tuple(self.scheme.clone(), host.clone(), self.port)
                } else {
                    Origin::Opaque
                }
            }
            _ => Origin::Opaque,
        }
    }

    /// Serialize this URL to a string (the href).
    pub fn serialize(&self) -> String {
        let mut output = String::new();
        output.push_str(&self.scheme);
        output.push(':');

        if self.host.is_some() {
            output.push_str("//");
            if self.has_credentials() {
                output.push_str(&self.username);
                if !self.password.is_empty() {
                    output.push(':');
                    output.push_str(&self.password);
                }
                output.push('@');
            }
            if let Some(ref host) = self.host {
                output.push_str(&host.serialize());
            }
            if let Some(port) = self.port {
                output.push(':');
                output.push_str(&port.to_string());
            }
        } else if !self.opaque_path && self.scheme == "file" {
            output.push_str("//");
        }

        output.push_str(&self.path());

        if let Some(ref query) = self.query {
            output.push('?');
            output.push_str(query);
        }
        if let Some(ref fragment) = self.fragment {
            output.push('#');
            output.push_str(fragment);
        }

        output
    }
}

impl fmt::Display for Url {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.serialize())
    }
}

// ---------------------------------------------------------------------------
// Special schemes
// ---------------------------------------------------------------------------

/// Whether a scheme is "special" per the URL standard.
fn is_special_scheme(scheme: &str) -> bool {
    matches!(scheme, "http" | "https" | "ftp" | "ws" | "wss" | "file")
}

/// Default port for a special scheme.
fn default_port(scheme: &str) -> Option<u16> {
    match scheme {
        "http" | "ws" => Some(80),
        "https" | "wss" => Some(443),
        "ftp" => Some(21),
        _ => None,
    }
}

// ---------------------------------------------------------------------------
// Percent encoding / decoding
// ---------------------------------------------------------------------------

/// The C0 control percent-encode set.
fn is_c0_control(c: char) -> bool {
    c <= '\u{001F}' || c > '\u{007E}'
}

/// The fragment percent-encode set.
fn is_fragment_encode(c: char) -> bool {
    is_c0_control(c) || c == ' ' || c == '"' || c == '<' || c == '>' || c == '`'
}

/// The query percent-encode set.
fn is_query_encode(c: char) -> bool {
    is_c0_control(c) || c == ' ' || c == '"' || c == '#' || c == '<' || c == '>'
}

/// The special query percent-encode set.
fn is_special_query_encode(c: char) -> bool {
    is_query_encode(c) || c == '\''
}

/// The path percent-encode set.
fn is_path_encode(c: char) -> bool {
    is_query_encode(c) || c == '?' || c == '`' || c == '{' || c == '}'
}

/// The userinfo percent-encode set.
fn is_userinfo_encode(c: char) -> bool {
    is_path_encode(c)
        || c == '/'
        || c == ':'
        || c == ';'
        || c == '='
        || c == '@'
        || c == '['
        || c == '\\'
        || c == ']'
        || c == '^'
        || c == '|'
}

/// Percent-encode a string using the given encode set predicate.
fn percent_encode(input: &str, should_encode: fn(char) -> bool) -> String {
    let mut out = String::with_capacity(input.len());
    for c in input.chars() {
        if should_encode(c) {
            for b in c.to_string().as_bytes() {
                out.push('%');
                out.push(to_hex_upper(b >> 4));
                out.push(to_hex_upper(b & 0x0F));
            }
        } else {
            out.push(c);
        }
    }
    out
}

fn to_hex_upper(n: u8) -> char {
    if n < 10 {
        (b'0' + n) as char
    } else {
        (b'A' + n - 10) as char
    }
}

/// Percent-decode a byte string.
pub fn percent_decode(input: &str) -> Vec<u8> {
    let bytes = input.as_bytes();
    let mut out = Vec::with_capacity(bytes.len());
    let mut i = 0;
    while i < bytes.len() {
        if bytes[i] == b'%' && i + 2 < bytes.len() {
            if let (Some(hi), Some(lo)) = (hex_val(bytes[i + 1]), hex_val(bytes[i + 2])) {
                out.push(hi << 4 | lo);
                i += 3;
                continue;
            }
        }
        out.push(bytes[i]);
        i += 1;
    }
    out
}

/// Percent-decode to a UTF-8 string (lossy).
pub fn percent_decode_string(input: &str) -> String {
    String::from_utf8_lossy(&percent_decode(input)).into_owned()
}

fn hex_val(b: u8) -> Option<u8> {
    match b {
        b'0'..=b'9' => Some(b - b'0'),
        b'a'..=b'f' => Some(b - b'a' + 10),
        b'A'..=b'F' => Some(b - b'A' + 10),
        _ => None,
    }
}

// ---------------------------------------------------------------------------
// IPv4 parsing
// ---------------------------------------------------------------------------

fn parse_ipv4(input: &str) -> Result<u32> {
    let parts: Vec<&str> = input.split('.').collect();
    if parts.len() < 2 || parts.len() > 4 {
        return Err(UrlError::InvalidIpv4);
    }
    let mut numbers: Vec<u64> = Vec::with_capacity(parts.len());
    for part in &parts {
        if part.is_empty() {
            return Err(UrlError::InvalidIpv4);
        }
        let n = parse_ipv4_number(part)?;
        numbers.push(n);
    }
    let last = numbers.len() - 1;
    for (i, &n) in numbers.iter().enumerate() {
        if i < last && n > 255 {
            return Err(UrlError::InvalidIpv4);
        }
    }
    if numbers[last] >= 256u64.pow((4 - last) as u32) {
        return Err(UrlError::InvalidIpv4);
    }

    let mut ipv4 = numbers[last] as u32;
    for (i, &n) in numbers.iter().enumerate().take(last) {
        ipv4 += (n as u32) << (8 * (3 - i));
    }
    Ok(ipv4)
}

fn parse_ipv4_number(input: &str) -> Result<u64> {
    if input.is_empty() {
        return Err(UrlError::InvalidIpv4);
    }
    let (s, radix) = if input.starts_with("0x") || input.starts_with("0X") {
        (&input[2..], 16)
    } else if input.len() > 1 && input.starts_with('0') {
        (&input[1..], 8)
    } else {
        (input, 10)
    };
    if s.is_empty() {
        return Ok(0);
    }
    u64::from_str_radix(s, radix).map_err(|_| UrlError::InvalidIpv4)
}

fn serialize_ipv4(addr: u32) -> String {
    format!(
        "{}.{}.{}.{}",
        (addr >> 24) & 0xFF,
        (addr >> 16) & 0xFF,
        (addr >> 8) & 0xFF,
        addr & 0xFF
    )
}

// ---------------------------------------------------------------------------
// IPv6 parsing
// ---------------------------------------------------------------------------

fn parse_ipv6(input: &str) -> Result<[u16; 8]> {
    let mut pieces = [0u16; 8];
    let mut piece_index: usize = 0;
    let mut compress: Option<usize> = None;
    let chars: Vec<char> = input.chars().collect();
    let len = chars.len();
    let mut pointer = 0;

    if pointer < len && chars[pointer] == ':' {
        if pointer + 1 >= len || chars[pointer + 1] != ':' {
            return Err(UrlError::InvalidIpv6);
        }
        pointer += 2;
        piece_index += 1;
        compress = Some(piece_index);
    }

    while pointer < len {
        if piece_index >= 8 {
            return Err(UrlError::InvalidIpv6);
        }

        if chars[pointer] == ':' {
            if compress.is_some() {
                return Err(UrlError::InvalidIpv6);
            }
            pointer += 1;
            piece_index += 1;
            compress = Some(piece_index);
            continue;
        }

        let mut value: u16 = 0;
        let mut length = 0;
        while length < 4 && pointer < len && chars[pointer].is_ascii_hexdigit() {
            value = value * 0x10 + hex_val(chars[pointer] as u8).unwrap() as u16;
            pointer += 1;
            length += 1;
        }

        if pointer < len && chars[pointer] == '.' {
            // IPv4-mapped IPv6.
            if length == 0 {
                return Err(UrlError::InvalidIpv6);
            }
            pointer -= length;
            if piece_index > 6 {
                return Err(UrlError::InvalidIpv6);
            }
            let mut numbers_seen = 0;
            while pointer < len {
                let mut ipv4_piece: Option<u16> = None;
                if numbers_seen > 0 {
                    if chars[pointer] == '.' && numbers_seen < 4 {
                        pointer += 1;
                    } else {
                        return Err(UrlError::InvalidIpv6);
                    }
                }
                if pointer >= len || !chars[pointer].is_ascii_digit() {
                    return Err(UrlError::InvalidIpv6);
                }
                while pointer < len && chars[pointer].is_ascii_digit() {
                    let number = (chars[pointer] as u8 - b'0') as u16;
                    match ipv4_piece {
                        None => ipv4_piece = Some(number),
                        Some(0) => return Err(UrlError::InvalidIpv6), // leading zero
                        Some(v) => ipv4_piece = Some(v * 10 + number),
                    }
                    if ipv4_piece.unwrap_or(0) > 255 {
                        return Err(UrlError::InvalidIpv6);
                    }
                    pointer += 1;
                }
                pieces[piece_index] =
                    pieces[piece_index] * 0x100 + ipv4_piece.ok_or(UrlError::InvalidIpv6)?;
                numbers_seen += 1;
                if numbers_seen == 2 || numbers_seen == 4 {
                    piece_index += 1;
                }
            }
            if numbers_seen != 4 {
                return Err(UrlError::InvalidIpv6);
            }
            break;
        }

        if pointer < len && chars[pointer] == ':' {
            pointer += 1;
            if pointer >= len {
                // Trailing single colon after a piece — only valid with compress.
            }
        } else if pointer < len {
            return Err(UrlError::InvalidIpv6);
        }

        if piece_index >= 8 {
            return Err(UrlError::InvalidIpv6);
        }
        pieces[piece_index] = value;
        piece_index += 1;
    }

    if let Some(comp) = compress {
        let mut swaps = piece_index - comp;
        piece_index = 7;
        while piece_index != 0 && swaps > 0 {
            let swap_index = comp + swaps - 1;
            pieces.swap(piece_index, swap_index);
            piece_index -= 1;
            swaps -= 1;
        }
    } else if piece_index != 8 {
        return Err(UrlError::InvalidIpv6);
    }

    Ok(pieces)
}

fn serialize_ipv6(pieces: &[u16; 8]) -> String {
    // Find the longest run of consecutive zeros for :: compression.
    let mut best_start = None;
    let mut best_len = 0usize;
    let mut cur_start = None;
    let mut cur_len = 0usize;

    for (i, &p) in pieces.iter().enumerate() {
        if p == 0 {
            if cur_start.is_none() {
                cur_start = Some(i);
                cur_len = 1;
            } else {
                cur_len += 1;
            }
        } else {
            if cur_len > best_len && cur_len >= 2 {
                best_start = cur_start;
                best_len = cur_len;
            }
            cur_start = None;
            cur_len = 0;
        }
    }
    if cur_len > best_len && cur_len >= 2 {
        best_start = cur_start;
        best_len = cur_len;
    }

    let mut out = String::new();
    let mut i = 0;
    while i < 8 {
        if Some(i) == best_start {
            out.push_str("::");
            i += best_len;
            continue;
        }
        if !out.is_empty() && !out.ends_with(':') {
            out.push(':');
        }
        out.push_str(&format!("{:x}", pieces[i]));
        i += 1;
    }
    out
}

// ---------------------------------------------------------------------------
// Host parsing
// ---------------------------------------------------------------------------

fn parse_host(input: &str, is_special: bool) -> Result<Host> {
    if input.is_empty() {
        if is_special {
            return Err(UrlError::InvalidHost);
        }
        return Ok(Host::Domain(String::new()));
    }

    // IPv6
    if input.starts_with('[') {
        if !input.ends_with(']') {
            return Err(UrlError::InvalidIpv6);
        }
        let inner = &input[1..input.len() - 1];
        let pieces = parse_ipv6(inner)?;
        return Ok(Host::Ipv6(pieces));
    }

    if !is_special {
        let encoded = percent_encode(input, is_c0_control);
        return Ok(Host::Domain(encoded));
    }

    // Domain — percent-decode then lowercase.
    let decoded = percent_decode_string(input);
    let lowered = decoded.to_ascii_lowercase();

    // Check if it's an IPv4 address.
    if ends_with_number(&lowered) {
        match parse_ipv4(&lowered) {
            Ok(addr) => return Ok(Host::Ipv4(addr)),
            Err(_) => return Err(UrlError::InvalidHost),
        }
    }

    // Validate domain characters.
    for c in lowered.chars() {
        if c == '\0'
            || c == '\t'
            || c == '\n'
            || c == '\r'
            || c == ' '
            || c == '#'
            || c == '/'
            || c == ':'
            || c == '<'
            || c == '>'
            || c == '?'
            || c == '@'
            || c == '['
            || c == '\\'
            || c == ']'
            || c == '^'
            || c == '|'
        {
            return Err(UrlError::InvalidHost);
        }
    }

    Ok(Host::Domain(lowered))
}

/// Check if a domain string ends with a number (suggesting IPv4).
fn ends_with_number(input: &str) -> bool {
    let last_part = match input.rsplit('.').next() {
        Some(p) => p,
        None => return false,
    };
    if last_part.is_empty() {
        return false;
    }
    if last_part.starts_with("0x") || last_part.starts_with("0X") {
        return last_part[2..].chars().all(|c| c.is_ascii_hexdigit());
    }
    last_part.chars().all(|c| c.is_ascii_digit())
}

// ---------------------------------------------------------------------------
// Shorten path helper
// ---------------------------------------------------------------------------

fn shorten_path(scheme: &str, path: &mut Vec<String>) {
    if scheme == "file" && path.len() == 1 {
        if let Some(first) = path.first() {
            if is_normalized_windows_drive_letter(first) {
                return;
            }
        }
    }
    path.pop();
}

fn is_normalized_windows_drive_letter(s: &str) -> bool {
    let bytes = s.as_bytes();
    bytes.len() == 2 && bytes[0].is_ascii_alphabetic() && bytes[1] == b':'
}

fn starts_with_windows_drive_letter(s: &str) -> bool {
    let bytes = s.as_bytes();
    if bytes.len() < 2 {
        return false;
    }
    if !bytes[0].is_ascii_alphabetic() {
        return false;
    }
    if bytes[1] != b':' && bytes[1] != b'|' {
        return false;
    }
    if bytes.len() >= 3 {
        matches!(bytes[2], b'/' | b'\\' | b'?' | b'#')
    } else {
        true
    }
}

// ---------------------------------------------------------------------------
// URL parser
// ---------------------------------------------------------------------------

fn parse_url(input: &str, base: Option<&Url>) -> Result<Url> {
    // Strip leading/trailing C0 controls and spaces.
    let input = input.trim_matches(|c: char| c <= '\u{0020}');

    if input.is_empty() {
        if let Some(base) = base {
            return parse_relative("", base);
        }
        return Err(UrlError::EmptyInput);
    }

    // Remove tab and newline characters.
    let input: String = input
        .chars()
        .filter(|&c| c != '\t' && c != '\n' && c != '\r')
        .collect();

    let chars: Vec<char> = input.chars().collect();
    let len = chars.len();

    let mut pointer = 0;

    // Try to parse a scheme.
    let mut scheme = String::new();
    let mut has_scheme = false;

    if pointer < len && chars[pointer].is_ascii_alphabetic() {
        let mut temp = String::new();
        temp.push(chars[pointer].to_ascii_lowercase());
        let mut p = pointer + 1;
        while p < len
            && (chars[p].is_ascii_alphanumeric()
                || chars[p] == '+'
                || chars[p] == '-'
                || chars[p] == '.')
        {
            temp.push(chars[p].to_ascii_lowercase());
            p += 1;
        }
        if p < len && chars[p] == ':' {
            scheme = temp;
            has_scheme = true;
            pointer = p + 1; // skip the ':'
        }
    }

    if !has_scheme {
        if let Some(base) = base {
            return parse_relative(&input, base);
        }
        return Err(UrlError::MissingScheme);
    }

    let is_special = is_special_scheme(&scheme);

    let mut url = Url {
        scheme: scheme.clone(),
        username: String::new(),
        password: String::new(),
        host: None,
        port: None,
        path: Vec::new(),
        opaque_path: false,
        query: None,
        fragment: None,
    };

    let remaining: String = chars[pointer..].iter().collect();

    if scheme == "file" {
        return parse_file_url(&remaining, base, url);
    }

    if let Some(after_slashes) = remaining.strip_prefix("//") {
        parse_authority_and_path(&mut url, after_slashes, is_special)?;
    } else if is_special {
        if let Some(base) = base {
            if base.scheme == url.scheme {
                return parse_relative_special(&remaining, base, url);
            }
        }
        if let Some(after_slash) = remaining.strip_prefix('/') {
            parse_authority_and_path(&mut url, after_slash, is_special)?;
        } else {
            parse_authority_and_path(&mut url, &remaining, is_special)?;
        }
    } else {
        parse_opaque_or_path(&mut url, &remaining)?;
    }

    Ok(url)
}

fn parse_authority_and_path(url: &mut Url, input: &str, is_special: bool) -> Result<()> {
    let authority_end = input
        .find(|c: char| c == '/' || c == '?' || c == '#' || (is_special && c == '\\'))
        .unwrap_or(input.len());

    let authority = &input[..authority_end];
    let rest = &input[authority_end..];

    let (userinfo_part, hostport) = if let Some(at_pos) = authority.rfind('@') {
        (&authority[..at_pos], &authority[at_pos + 1..])
    } else {
        ("", authority)
    };

    if !userinfo_part.is_empty() {
        if let Some(colon_pos) = userinfo_part.find(':') {
            url.username = percent_encode(&userinfo_part[..colon_pos], is_userinfo_encode);
            url.password = percent_encode(&userinfo_part[colon_pos + 1..], is_userinfo_encode);
        } else {
            url.username = percent_encode(userinfo_part, is_userinfo_encode);
        }
    }

    let (host_str, port_str) = split_host_port(hostport);

    url.host = Some(parse_host(host_str, is_special)?);

    if let Some(port_s) = port_str {
        if !port_s.is_empty() {
            let port: u16 = port_s.parse().map_err(|_| UrlError::InvalidPort)?;
            if default_port(&url.scheme) != Some(port) {
                url.port = Some(port);
            }
        }
    }

    parse_path_query_fragment(url, rest, is_special)
}

fn split_host_port(input: &str) -> (&str, Option<&str>) {
    if input.starts_with('[') {
        if let Some(bracket_end) = input.find(']') {
            let host = &input[..bracket_end + 1];
            let after = &input[bracket_end + 1..];
            if let Some(port_str) = after.strip_prefix(':') {
                return (host, Some(port_str));
            }
            return (host, None);
        }
        return (input, None);
    }

    if let Some(colon_pos) = input.rfind(':') {
        let port_part = &input[colon_pos + 1..];
        if port_part.is_empty() || port_part.chars().all(|c| c.is_ascii_digit()) {
            return (&input[..colon_pos], Some(port_part));
        }
    }
    (input, None)
}

fn parse_path_query_fragment(url: &mut Url, input: &str, is_special: bool) -> Result<()> {
    let mut remaining = input;

    let path_end = remaining.find(['?', '#']).unwrap_or(remaining.len());
    let path_str = &remaining[..path_end];
    remaining = &remaining[path_end..];

    parse_path_into(url, path_str, is_special);

    if let Some(after_q) = remaining.strip_prefix('?') {
        remaining = after_q;
        let query_end = remaining.find('#').unwrap_or(remaining.len());
        let query_str = &remaining[..query_end];
        remaining = &remaining[query_end..];

        let encode_fn = if is_special {
            is_special_query_encode
        } else {
            is_query_encode
        };
        url.query = Some(percent_encode(query_str, encode_fn));
    }

    if let Some(after_hash) = remaining.strip_prefix('#') {
        url.fragment = Some(percent_encode(after_hash, is_fragment_encode));
    }

    Ok(())
}

fn parse_path_into(url: &mut Url, path: &str, is_special: bool) {
    if path.is_empty() {
        if is_special {
            url.path = vec![String::new()];
        }
        return;
    }

    let segments: Vec<&str> = if is_special {
        path.split(['/', '\\']).collect()
    } else {
        path.split('/').collect()
    };

    for (i, seg) in segments.iter().enumerate() {
        if i == 0 && seg.is_empty() {
            continue;
        }

        let decoded = *seg;
        if decoded == "." || decoded.eq_ignore_ascii_case("%2e") {
            if i == segments.len() - 1 {
                url.path.push(String::new());
            }
        } else if decoded == ".."
            || decoded.eq_ignore_ascii_case(".%2e")
            || decoded.eq_ignore_ascii_case("%2e.")
            || decoded.eq_ignore_ascii_case("%2e%2e")
        {
            shorten_path(&url.scheme, &mut url.path);
            if i == segments.len() - 1 {
                url.path.push(String::new());
            }
        } else {
            url.path.push(percent_encode(decoded, is_path_encode));
        }
    }
}

fn parse_opaque_or_path(url: &mut Url, input: &str) -> Result<()> {
    let mut remaining = input;

    let path_end = remaining.find(['?', '#']).unwrap_or(remaining.len());
    let path_str = &remaining[..path_end];
    remaining = &remaining[path_end..];

    if path_str.starts_with('/') {
        url.opaque_path = false;
        parse_path_into(url, path_str, false);
    } else {
        url.opaque_path = true;
        url.path = vec![percent_encode(path_str, is_c0_control)];
    }

    if let Some(after_q) = remaining.strip_prefix('?') {
        remaining = after_q;
        let query_end = remaining.find('#').unwrap_or(remaining.len());
        let query_str = &remaining[..query_end];
        remaining = &remaining[query_end..];
        url.query = Some(percent_encode(query_str, is_query_encode));
    }

    if let Some(after_hash) = remaining.strip_prefix('#') {
        url.fragment = Some(percent_encode(after_hash, is_fragment_encode));
    }

    Ok(())
}

// ---------------------------------------------------------------------------
// Relative URL parsing
// ---------------------------------------------------------------------------

fn parse_relative(input: &str, base: &Url) -> Result<Url> {
    let mut url = Url {
        scheme: base.scheme.clone(),
        username: base.username.clone(),
        password: base.password.clone(),
        host: base.host.clone(),
        port: base.port,
        path: base.path.clone(),
        opaque_path: base.opaque_path,
        query: base.query.clone(),
        fragment: None,
    };

    let is_special = is_special_scheme(&url.scheme);

    if input.is_empty() {
        return Ok(url);
    }

    let chars: Vec<char> = input.chars().collect();

    if chars[0] == '/' || (is_special && chars[0] == '\\') {
        if input.starts_with("//") || (is_special && input.starts_with("\\/")) {
            let after_slashes = &input[2..];
            url.username = String::new();
            url.password = String::new();
            url.path = Vec::new();
            url.query = None;
            parse_authority_and_path(&mut url, after_slashes, is_special)?;
            return Ok(url);
        }
        url.path = Vec::new();
        url.query = None;
        parse_path_query_fragment(&mut url, input, is_special)?;
        return Ok(url);
    }

    if let Some(after_q) = input.strip_prefix('?') {
        url.query = None;
        url.fragment = None;
        let query_end = after_q.find('#').unwrap_or(after_q.len());
        let query_str = &after_q[..query_end];
        let after = &after_q[query_end..];

        let encode_fn = if is_special {
            is_special_query_encode
        } else {
            is_query_encode
        };
        url.query = Some(percent_encode(query_str, encode_fn));

        if let Some(frag) = after.strip_prefix('#') {
            url.fragment = Some(percent_encode(frag, is_fragment_encode));
        }
        return Ok(url);
    }

    if let Some(frag) = input.strip_prefix('#') {
        url.fragment = Some(percent_encode(frag, is_fragment_encode));
        return Ok(url);
    }

    // Path-relative.
    if !url.opaque_path {
        shorten_path(&url.scheme, &mut url.path);
    }
    url.query = None;
    url.fragment = None;

    parse_path_query_fragment(&mut url, &format!("/{input}"), is_special)?;
    Ok(url)
}

fn parse_relative_special(remaining: &str, base: &Url, mut url: Url) -> Result<Url> {
    url.username = base.username.clone();
    url.password = base.password.clone();
    url.host = base.host.clone();
    url.port = base.port;
    url.path = base.path.clone();
    url.query = base.query.clone();

    let is_special = true;

    if remaining.is_empty() {
        return Ok(url);
    }

    if remaining.starts_with('/') || remaining.starts_with('\\') {
        url.path = Vec::new();
        url.query = None;
        parse_path_query_fragment(&mut url, remaining, is_special)?;
        return Ok(url);
    }

    if let Some(rest) = remaining.strip_prefix('?') {
        url.query = None;
        url.fragment = None;
        let query_end = rest.find('#').unwrap_or(rest.len());
        url.query = Some(percent_encode(&rest[..query_end], is_special_query_encode));
        if query_end < rest.len() {
            url.fragment = Some(percent_encode(&rest[query_end + 1..], is_fragment_encode));
        }
        return Ok(url);
    }

    if let Some(frag) = remaining.strip_prefix('#') {
        url.fragment = Some(percent_encode(frag, is_fragment_encode));
        return Ok(url);
    }

    shorten_path(&url.scheme, &mut url.path);
    url.query = None;
    parse_path_query_fragment(&mut url, &format!("/{remaining}"), is_special)?;
    Ok(url)
}

// ---------------------------------------------------------------------------
// File URL parsing
// ---------------------------------------------------------------------------

fn parse_file_url(input: &str, base: Option<&Url>, mut url: Url) -> Result<Url> {
    url.host = Some(Host::Domain(String::new()));

    let remaining = if let Some(after) = input.strip_prefix("//") {
        after
    } else if let Some(after) = input.strip_prefix('/') {
        after
    } else if let Some(base) = base {
        if base.scheme == "file" {
            url.host = base.host.clone();
            url.path = base.path.clone();

            if let Some(rest) = input.strip_prefix('?') {
                url.query = None;
                url.fragment = None;
                let query_end = rest.find('#').unwrap_or(rest.len());
                url.query = Some(percent_encode(&rest[..query_end], is_query_encode));
                if query_end < rest.len() {
                    url.fragment = Some(percent_encode(&rest[query_end + 1..], is_fragment_encode));
                }
                return Ok(url);
            }

            if let Some(frag) = input.strip_prefix('#') {
                url.fragment = Some(percent_encode(frag, is_fragment_encode));
                return Ok(url);
            }

            shorten_path(&url.scheme, &mut url.path);
            url.query = None;
            parse_path_query_fragment(&mut url, &format!("/{input}"), false)?;
            return Ok(url);
        } else {
            input
        }
    } else {
        input
    };

    let path_start = remaining
        .find(['/', '\\', '?', '#'])
        .unwrap_or(remaining.len());

    let potential_host = &remaining[..path_start];
    let rest = &remaining[path_start..];

    if starts_with_windows_drive_letter(remaining) {
        url.host = Some(Host::Domain(String::new()));
        parse_path_query_fragment(&mut url, &format!("/{remaining}"), false)?;
        return Ok(url);
    }

    if !potential_host.is_empty() {
        let host = parse_host(potential_host, false)?;
        if host != Host::Domain(String::new()) {
            url.host = Some(host);
        }
    }

    parse_path_query_fragment(&mut url, rest, false)?;

    // Normalize Windows drive letters in path.
    if let Some(first) = url.path.first_mut() {
        if first.len() == 2 {
            let bytes = first.as_bytes();
            if bytes[0].is_ascii_alphabetic() && bytes[1] == b'|' {
                let mut normalized = String::new();
                normalized.push(bytes[0] as char);
                normalized.push(':');
                *first = normalized;
            }
        }
    }

    Ok(url)
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;

    // -------------------------------------------------------------------
    // Basic absolute URL parsing
    // -------------------------------------------------------------------

    #[test]
    fn parse_simple_http() {
        let url = Url::parse("http://example.com").unwrap();
        assert_eq!(url.scheme(), "http");
        assert_eq!(url.host_str(), Some("example.com".into()));
        assert_eq!(url.port(), None);
        assert_eq!(url.path(), "/");
        assert_eq!(url.query(), None);
        assert_eq!(url.fragment(), None);
    }

    #[test]
    fn parse_https_with_path() {
        let url = Url::parse("https://example.com/foo/bar").unwrap();
        assert_eq!(url.scheme(), "https");
        assert_eq!(url.host_str(), Some("example.com".into()));
        assert_eq!(url.path(), "/foo/bar");
    }

    #[test]
    fn parse_full_url() {
        let url =
            Url::parse("https://user:pass@example.com:8080/path/to/page?q=1&r=2#frag").unwrap();
        assert_eq!(url.scheme(), "https");
        assert_eq!(url.username(), "user");
        assert_eq!(url.password(), "pass");
        assert_eq!(url.host_str(), Some("example.com".into()));
        assert_eq!(url.port(), Some(8080));
        assert_eq!(url.path(), "/path/to/page");
        assert_eq!(url.query(), Some("q=1&r=2"));
        assert_eq!(url.fragment(), Some("frag"));
    }

    #[test]
    fn parse_default_port_omitted() {
        let url = Url::parse("http://example.com:80/").unwrap();
        assert_eq!(url.port(), None);
        assert_eq!(url.port_or_default(), Some(80));
    }

    #[test]
    fn parse_non_default_port() {
        let url = Url::parse("http://example.com:8080/").unwrap();
        assert_eq!(url.port(), Some(8080));
    }

    #[test]
    fn parse_https_default_port() {
        let url = Url::parse("https://example.com:443/").unwrap();
        assert_eq!(url.port(), None);
    }

    #[test]
    fn parse_ftp_default_port() {
        let url = Url::parse("ftp://files.example.com:21/readme.txt").unwrap();
        assert_eq!(url.port(), None);
        assert_eq!(url.port_or_default(), Some(21));
    }

    // -------------------------------------------------------------------
    // Scheme handling
    // -------------------------------------------------------------------

    #[test]
    fn scheme_is_lowercased() {
        let url = Url::parse("HTTP://EXAMPLE.COM").unwrap();
        assert_eq!(url.scheme(), "http");
    }

    #[test]
    fn non_special_scheme() {
        let url = Url::parse("custom://host/path").unwrap();
        assert_eq!(url.scheme(), "custom");
        assert_eq!(url.host_str(), Some("host".into()));
        assert_eq!(url.path(), "/path");
    }

    #[test]
    fn data_uri() {
        let url = Url::parse("data:text/html,<h1>Hello</h1>").unwrap();
        assert_eq!(url.scheme(), "data");
        assert!(url.cannot_be_a_base());
    }

    #[test]
    fn javascript_uri() {
        let url = Url::parse("javascript:alert(1)").unwrap();
        assert_eq!(url.scheme(), "javascript");
        assert!(url.cannot_be_a_base());
    }

    #[test]
    fn mailto_uri() {
        let url = Url::parse("mailto:user@example.com").unwrap();
        assert_eq!(url.scheme(), "mailto");
        assert!(url.cannot_be_a_base());
    }

    // -------------------------------------------------------------------
    // Host parsing
    // -------------------------------------------------------------------

    #[test]
    fn host_is_lowercased() {
        let url = Url::parse("http://EXAMPLE.COM/").unwrap();
        assert_eq!(url.host_str(), Some("example.com".into()));
    }

    #[test]
    fn ipv4_host() {
        let url = Url::parse("http://127.0.0.1/").unwrap();
        assert_eq!(url.host(), Some(&Host::Ipv4(0x7F000001)));
        assert_eq!(url.host_str(), Some("127.0.0.1".into()));
    }

    #[test]
    fn ipv4_host_all_zeros() {
        let url = Url::parse("http://0.0.0.0/").unwrap();
        assert_eq!(url.host(), Some(&Host::Ipv4(0)));
    }

    #[test]
    fn ipv6_host() {
        let url = Url::parse("http://[::1]/").unwrap();
        assert_eq!(url.host(), Some(&Host::Ipv6([0, 0, 0, 0, 0, 0, 0, 1])));
    }

    #[test]
    fn ipv6_full() {
        let url = Url::parse("http://[2001:db8:85a3:0:0:8a2e:370:7334]/").unwrap();
        assert_eq!(
            url.host(),
            Some(&Host::Ipv6([
                0x2001, 0x0db8, 0x85a3, 0, 0, 0x8a2e, 0x0370, 0x7334
            ]))
        );
    }

    #[test]
    fn ipv6_serialization_compressed() {
        let url = Url::parse("http://[2001:db8::1]/").unwrap();
        assert_eq!(url.host_str(), Some("[2001:db8::1]".into()));
    }

    #[test]
    fn ipv6_all_zeros() {
        let url = Url::parse("http://[::]/").unwrap();
        assert_eq!(url.host(), Some(&Host::Ipv6([0; 8])));
        assert_eq!(url.host_str(), Some("[::]".into()));
    }

    #[test]
    fn ipv6_loopback() {
        let pieces = parse_ipv6("::1").unwrap();
        assert_eq!(pieces, [0, 0, 0, 0, 0, 0, 0, 1]);
    }

    #[test]
    fn ipv6_with_ipv4() {
        let pieces = parse_ipv6("::ffff:192.168.1.1").unwrap();
        assert_eq!(pieces, [0, 0, 0, 0, 0, 0xffff, 0xc0a8, 0x0101]);
    }

    // -------------------------------------------------------------------
    // IPv4 parsing
    // -------------------------------------------------------------------

    #[test]
    fn ipv4_basic() {
        assert_eq!(parse_ipv4("192.168.1.1").unwrap(), 0xC0A80101);
    }

    #[test]
    fn ipv4_hex() {
        assert_eq!(parse_ipv4("0xC0.0xA8.0x01.0x01").unwrap(), 0xC0A80101);
    }

    #[test]
    fn ipv4_octal() {
        assert_eq!(parse_ipv4("0300.0250.01.01").unwrap(), 0xC0A80101);
    }

    #[test]
    fn ipv4_single_number() {
        assert!(parse_ipv4("3232235777").is_err());
    }

    #[test]
    fn ipv4_two_parts() {
        // Two parts: first is top 8 bits, second is bottom 24 bits.
        // 192.168.1.1 => 168*65536 + 1*256 + 1 = 11010305
        assert_eq!(parse_ipv4("192.11010305").unwrap(), 0xC0A80101);
    }

    #[test]
    fn ipv4_reject_overflow() {
        assert!(parse_ipv4("256.0.0.0").is_err());
    }

    #[test]
    fn ipv4_reject_empty_part() {
        assert!(parse_ipv4("1..1.1").is_err());
    }

    // -------------------------------------------------------------------
    // Percent encoding/decoding
    // -------------------------------------------------------------------

    #[test]
    fn percent_decode_basic() {
        assert_eq!(percent_decode_string("%48%65%6C%6C%6F"), "Hello");
    }

    #[test]
    fn percent_decode_mixed() {
        assert_eq!(percent_decode_string("Hello%20World"), "Hello World");
    }

    #[test]
    fn percent_decode_passthrough() {
        assert_eq!(percent_decode_string("no-encoding"), "no-encoding");
    }

    #[test]
    fn percent_decode_partial() {
        assert_eq!(percent_decode_string("100%"), "100%");
        assert_eq!(percent_decode_string("%2"), "%2");
    }

    #[test]
    fn percent_encode_userinfo() {
        let encoded = percent_encode("user@host", is_userinfo_encode);
        assert_eq!(encoded, "user%40host");
    }

    #[test]
    fn percent_encode_path() {
        let encoded = percent_encode("hello world", is_path_encode);
        assert_eq!(encoded, "hello%20world");
    }

    // -------------------------------------------------------------------
    // Path parsing and dot segments
    // -------------------------------------------------------------------

    #[test]
    fn path_dot_removal() {
        let url = Url::parse("http://example.com/a/b/../c").unwrap();
        assert_eq!(url.path(), "/a/c");
    }

    #[test]
    fn path_dot_current() {
        let url = Url::parse("http://example.com/a/./b").unwrap();
        assert_eq!(url.path(), "/a/b");
    }

    #[test]
    fn path_multiple_dots() {
        let url = Url::parse("http://example.com/a/b/c/../../d").unwrap();
        assert_eq!(url.path(), "/a/d");
    }

    #[test]
    fn path_trailing_slash() {
        let url = Url::parse("http://example.com/a/b/").unwrap();
        assert_eq!(url.path(), "/a/b/");
    }

    #[test]
    fn path_empty() {
        let url = Url::parse("http://example.com").unwrap();
        assert_eq!(url.path(), "/");
    }

    #[test]
    fn path_double_dot_at_root() {
        let url = Url::parse("http://example.com/../a").unwrap();
        assert_eq!(url.path(), "/a");
    }

    // -------------------------------------------------------------------
    // Relative URL resolution
    // -------------------------------------------------------------------

    #[test]
    fn relative_path() {
        let base = Url::parse("http://example.com/a/b/c").unwrap();
        let url = Url::parse_with_base("d", &base).unwrap();
        assert_eq!(url.path(), "/a/b/d");
        assert_eq!(url.host_str(), Some("example.com".into()));
    }

    #[test]
    fn relative_path_with_dots() {
        let base = Url::parse("http://example.com/a/b/c").unwrap();
        let url = Url::parse_with_base("../d", &base).unwrap();
        assert_eq!(url.path(), "/a/d");
    }

    #[test]
    fn relative_absolute_path() {
        let base = Url::parse("http://example.com/a/b/c").unwrap();
        let url = Url::parse_with_base("/d/e", &base).unwrap();
        assert_eq!(url.path(), "/d/e");
        assert_eq!(url.host_str(), Some("example.com".into()));
    }

    #[test]
    fn relative_query_only() {
        let base = Url::parse("http://example.com/a/b?old=1").unwrap();
        let url = Url::parse_with_base("?new=2", &base).unwrap();
        assert_eq!(url.path(), "/a/b");
        assert_eq!(url.query(), Some("new=2"));
    }

    #[test]
    fn relative_fragment_only() {
        let base = Url::parse("http://example.com/a/b#old").unwrap();
        let url = Url::parse_with_base("#new", &base).unwrap();
        assert_eq!(url.path(), "/a/b");
        assert_eq!(url.fragment(), Some("new"));
    }

    #[test]
    fn relative_authority_override() {
        let base = Url::parse("http://example.com/a/b").unwrap();
        let url = Url::parse_with_base("//other.com/c", &base).unwrap();
        assert_eq!(url.scheme(), "http");
        assert_eq!(url.host_str(), Some("other.com".into()));
        assert_eq!(url.path(), "/c");
    }

    #[test]
    fn absolute_url_ignores_base() {
        let base = Url::parse("http://example.com/a").unwrap();
        let url = Url::parse_with_base("https://other.com/b", &base).unwrap();
        assert_eq!(url.scheme(), "https");
        assert_eq!(url.host_str(), Some("other.com".into()));
        assert_eq!(url.path(), "/b");
    }

    #[test]
    fn relative_empty_string() {
        let base = Url::parse("http://example.com/a/b?q=1#f").unwrap();
        let url = Url::parse_with_base("", &base).unwrap();
        assert_eq!(url.path(), "/a/b");
        assert_eq!(url.query(), Some("q=1"));
        assert_eq!(url.fragment(), None);
    }

    // -------------------------------------------------------------------
    // Serialization
    // -------------------------------------------------------------------

    #[test]
    fn serialize_simple() {
        let url = Url::parse("http://example.com/path").unwrap();
        assert_eq!(url.serialize(), "http://example.com/path");
    }

    #[test]
    fn serialize_with_credentials() {
        let url = Url::parse("http://user:pass@example.com/").unwrap();
        assert_eq!(url.serialize(), "http://user:pass@example.com/");
    }

    #[test]
    fn serialize_with_port() {
        let url = Url::parse("http://example.com:8080/").unwrap();
        assert_eq!(url.serialize(), "http://example.com:8080/");
    }

    #[test]
    fn serialize_with_query_fragment() {
        let url = Url::parse("http://example.com/path?q=1#frag").unwrap();
        assert_eq!(url.serialize(), "http://example.com/path?q=1#frag");
    }

    #[test]
    fn serialize_data_uri() {
        let url = Url::parse("data:text/html,hello").unwrap();
        assert_eq!(url.serialize(), "data:text/html,hello");
    }

    #[test]
    fn roundtrip_full_url() {
        let input = "https://user:pass@example.com:8080/a/b?q=1#frag";
        let url = Url::parse(input).unwrap();
        assert_eq!(url.serialize(), input);
    }

    #[test]
    fn roundtrip_ipv4() {
        let url = Url::parse("http://192.168.1.1/path").unwrap();
        assert_eq!(url.serialize(), "http://192.168.1.1/path");
    }

    #[test]
    fn roundtrip_ipv6() {
        let url = Url::parse("http://[::1]/path").unwrap();
        assert_eq!(url.serialize(), "http://[::1]/path");
    }

    // -------------------------------------------------------------------
    // Origin
    // -------------------------------------------------------------------

    #[test]
    fn origin_http() {
        let url = Url::parse("http://example.com:8080/path").unwrap();
        match url.origin() {
            Origin::Tuple(scheme, host, port) => {
                assert_eq!(scheme, "http");
                assert_eq!(host, Host::Domain("example.com".into()));
                assert_eq!(port, Some(8080));
            }
            _ => panic!("expected tuple origin"),
        }
    }

    #[test]
    fn origin_https_default_port() {
        let url = Url::parse("https://example.com/").unwrap();
        match url.origin() {
            Origin::Tuple(scheme, host, port) => {
                assert_eq!(scheme, "https");
                assert_eq!(host, Host::Domain("example.com".into()));
                assert_eq!(port, None);
            }
            _ => panic!("expected tuple origin"),
        }
    }

    #[test]
    fn origin_data_is_opaque() {
        let url = Url::parse("data:text/html,hello").unwrap();
        assert_eq!(url.origin(), Origin::Opaque);
    }

    // -------------------------------------------------------------------
    // File URLs
    // -------------------------------------------------------------------

    #[test]
    fn file_url_unix() {
        let url = Url::parse("file:///home/user/file.txt").unwrap();
        assert_eq!(url.scheme(), "file");
        assert_eq!(url.host_str(), Some("".into()));
        assert_eq!(url.path(), "/home/user/file.txt");
    }

    #[test]
    fn file_url_windows_drive() {
        let url = Url::parse("file:///C:/Windows/system32").unwrap();
        assert_eq!(url.scheme(), "file");
        assert_eq!(url.path(), "/C:/Windows/system32");
    }

    #[test]
    fn file_url_with_host() {
        let url = Url::parse("file://server/share/file.txt").unwrap();
        assert_eq!(url.scheme(), "file");
        assert_eq!(url.host_str(), Some("server".into()));
        assert_eq!(url.path(), "/share/file.txt");
    }

    // -------------------------------------------------------------------
    // Edge cases
    // -------------------------------------------------------------------

    #[test]
    fn empty_input_fails() {
        assert_eq!(Url::parse(""), Err(UrlError::EmptyInput));
    }

    #[test]
    fn whitespace_only_fails() {
        assert_eq!(Url::parse("   "), Err(UrlError::EmptyInput));
    }

    #[test]
    fn missing_scheme_fails() {
        assert!(Url::parse("example.com").is_err());
    }

    #[test]
    fn leading_whitespace_stripped() {
        let url = Url::parse("  http://example.com  ").unwrap();
        assert_eq!(url.host_str(), Some("example.com".into()));
    }

    #[test]
    fn tab_newline_stripped() {
        let url = Url::parse("http://exa\tmple\n.com/").unwrap();
        assert_eq!(url.host_str(), Some("example.com".into()));
    }

    #[test]
    fn query_with_special_chars() {
        let url = Url::parse("http://example.com/?key=val ue&foo=bar").unwrap();
        assert!(url.query().unwrap().contains("key=val%20ue"));
    }

    #[test]
    fn fragment_with_special_chars() {
        let url = Url::parse("http://example.com/#sec tion").unwrap();
        assert!(url.fragment().unwrap().contains("sec%20tion"));
    }

    #[test]
    fn username_only() {
        let url = Url::parse("http://user@example.com/").unwrap();
        assert_eq!(url.username(), "user");
        assert_eq!(url.password(), "");
        assert!(url.has_credentials());
    }

    #[test]
    fn no_credentials() {
        let url = Url::parse("http://example.com/").unwrap();
        assert!(!url.has_credentials());
    }

    #[test]
    fn port_overflow_fails() {
        assert!(Url::parse("http://example.com:99999/").is_err());
    }

    #[test]
    fn ws_scheme() {
        let url = Url::parse("ws://example.com/chat").unwrap();
        assert_eq!(url.scheme(), "ws");
        assert_eq!(url.port_or_default(), Some(80));
    }

    #[test]
    fn wss_scheme() {
        let url = Url::parse("wss://example.com/chat").unwrap();
        assert_eq!(url.scheme(), "wss");
        assert_eq!(url.port_or_default(), Some(443));
    }

    #[test]
    fn cannot_be_a_base() {
        let url = Url::parse("data:text/html,hello").unwrap();
        assert!(url.cannot_be_a_base());
    }

    #[test]
    fn http_can_be_a_base() {
        let url = Url::parse("http://example.com/").unwrap();
        assert!(!url.cannot_be_a_base());
    }

    // -------------------------------------------------------------------
    // Display/ToString
    // -------------------------------------------------------------------

    #[test]
    fn display_matches_serialize() {
        let url = Url::parse("https://example.com:8443/path?q=1#f").unwrap();
        assert_eq!(format!("{url}"), url.serialize());
    }

    // -------------------------------------------------------------------
    // Multiple path segments
    // -------------------------------------------------------------------

    #[test]
    fn path_segments() {
        let url = Url::parse("http://example.com/a/b/c").unwrap();
        assert_eq!(url.path_segments(), &["a", "b", "c"]);
    }

    #[test]
    fn path_segments_trailing_slash() {
        let url = Url::parse("http://example.com/a/b/").unwrap();
        assert_eq!(url.path_segments(), &["a", "b", ""]);
    }

    // -------------------------------------------------------------------
    // Host type
    // -------------------------------------------------------------------

    #[test]
    fn host_serialize_domain() {
        let h = Host::Domain("example.com".into());
        assert_eq!(h.serialize(), "example.com");
    }

    #[test]
    fn host_serialize_ipv4() {
        let h = Host::Ipv4(0x7F000001);
        assert_eq!(h.serialize(), "127.0.0.1");
    }

    #[test]
    fn host_serialize_ipv6() {
        let h = Host::Ipv6([0, 0, 0, 0, 0, 0, 0, 1]);
        assert_eq!(h.serialize(), "[::1]");
    }

    // -------------------------------------------------------------------
    // IPv6 serialization
    // -------------------------------------------------------------------

    #[test]
    fn ipv6_serialize_full() {
        let pieces = [
            0x2001, 0x0db8, 0x85a3, 0x0001, 0x0002, 0x8a2e, 0x0370, 0x7334,
        ];
        assert_eq!(serialize_ipv6(&pieces), "2001:db8:85a3:1:2:8a2e:370:7334");
    }

    #[test]
    fn ipv6_serialize_compress() {
        let pieces = [0x2001, 0x0db8, 0, 0, 0, 0, 0, 1];
        assert_eq!(serialize_ipv6(&pieces), "2001:db8::1");
    }

    #[test]
    fn ipv6_serialize_all_zeros() {
        let pieces = [0u16; 8];
        assert_eq!(serialize_ipv6(&pieces), "::");
    }

    #[test]
    fn ipv6_serialize_no_compress_single_zero() {
        let pieces = [1, 0, 2, 0, 3, 0, 4, 0];
        assert_eq!(serialize_ipv6(&pieces), "1:0:2:0:3:0:4:0");
    }

    // -------------------------------------------------------------------
    // Percent encoding edge cases
    // -------------------------------------------------------------------

    #[test]
    fn percent_encode_preserves_unreserved() {
        let encoded = percent_encode("hello-world_test.page~1", is_path_encode);
        assert_eq!(encoded, "hello-world_test.page~1");
    }

    #[test]
    fn percent_encode_multibyte_utf8() {
        let encoded = percent_encode("café", is_path_encode);
        assert_eq!(encoded, "caf%C3%A9");
    }
}