//! DID (Decentralized Identifier) types and validation for did:plc

use crate::encoding::is_valid_base32;
use crate::error::{PlcError, Result};
use serde::{Deserialize, Serialize};
use std::fmt;
use std::str::FromStr;

/// The prefix for all did:plc identifiers
pub const DID_PLC_PREFIX: &str = "did:plc:";

/// The length of the identifier portion (24 characters)
pub const IDENTIFIER_LENGTH: usize = 24;

/// The total length of a valid did:plc string (32 characters)
pub const TOTAL_LENGTH: usize = 32; // "did:plc:" (8) + identifier (24)

/// Represents a validated did:plc identifier.
///
/// A did:plc consists of the prefix "did:plc:" followed by exactly 24
/// lowercase base32 characters (using alphabet abcdefghijklmnopqrstuvwxyz234567).
///
/// # Examples
///
/// ```
/// use atproto_plc::Did;
///
/// let did = Did::parse("did:plc:ewvi7nxzyoun6zhxrhs64oiz")?;
/// assert_eq!(did.identifier(), "ewvi7nxzyoun6zhxrhs64oiz");
/// # Ok::<(), atproto_plc::PlcError>(())
/// ```
///
/// # Format
///
/// The identifier is derived from the SHA-256 hash of the genesis operation,
/// base32-encoded and truncated to 24 characters.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct Did {
    /// The full did:plc:xyz... string
    full: String,
    /// The 24-character identifier portion
    identifier: String,
}

impl Did {
    /// Parse and validate a DID string
    ///
    /// # Errors
    ///
    /// Returns `PlcError::InvalidDidFormat` if:
    /// - The string doesn't start with "did:plc:"
    /// - The total length isn't exactly 32 characters
    /// - The identifier portion contains invalid base32 characters
    ///
    /// # Examples
    ///
    /// ```
    /// use atproto_plc::Did;
    ///
    /// let did = Did::parse("did:plc:ewvi7nxzyoun6zhxrhs64oiz")?;
    /// assert!(did.is_valid());
    /// # Ok::<(), atproto_plc::PlcError>(())
    /// ```
    pub fn parse(s: &str) -> Result<Self> {
        Self::validate_format(s)?;

        let identifier = s[DID_PLC_PREFIX.len()..].to_string();

        Ok(Self {
            full: s.to_string(),
            identifier,
        })
    }

    /// Create a DID from a validated identifier (without the "did:plc:" prefix)
    ///
    /// # Errors
    ///
    /// Returns `PlcError::InvalidDidFormat` if the identifier is not exactly 24 characters
    /// or contains invalid base32 characters
    pub fn from_identifier(identifier: &str) -> Result<Self> {
        if identifier.len() != IDENTIFIER_LENGTH {
            return Err(PlcError::InvalidDidFormat(format!(
                "Identifier must be exactly {} characters, got {}",
                IDENTIFIER_LENGTH,
                identifier.len()
            )));
        }

        if !is_valid_base32(identifier) {
            return Err(PlcError::InvalidDidFormat(
                "Identifier contains invalid base32 characters".to_string(),
            ));
        }

        Ok(Self {
            full: format!("{}{}", DID_PLC_PREFIX, identifier),
            identifier: identifier.to_string(),
        })
    }

    /// Get the 24-character identifier portion (without "did:plc:" prefix)
    ///
    /// # Examples
    ///
    /// ```
    /// use atproto_plc::Did;
    ///
    /// let did = Did::parse("did:plc:ewvi7nxzyoun6zhxrhs64oiz")?;
    /// assert_eq!(did.identifier(), "ewvi7nxzyoun6zhxrhs64oiz");
    /// # Ok::<(), atproto_plc::PlcError>(())
    /// ```
    pub fn identifier(&self) -> &str {
        &self.identifier
    }

    /// Get the full DID string including "did:plc:" prefix
    ///
    /// # Examples
    ///
    /// ```
    /// use atproto_plc::Did;
    ///
    /// let did = Did::parse("did:plc:ewvi7nxzyoun6zhxrhs64oiz")?;
    /// assert_eq!(did.as_str(), "did:plc:ewvi7nxzyoun6zhxrhs64oiz");
    /// # Ok::<(), atproto_plc::PlcError>(())
    /// ```
    pub fn as_str(&self) -> &str {
        &self.full
    }

    /// Check if this DID is valid
    ///
    /// Since DIDs can only be constructed through validation,
    /// this always returns `true`
    pub fn is_valid(&self) -> bool {
        true
    }

    /// Validate the format of a DID string without constructing a Did instance
    ///
    /// # Errors
    ///
    /// Returns `PlcError::InvalidDidFormat` if validation fails
    fn validate_format(s: &str) -> Result<()> {
        // Check prefix
        if !s.starts_with(DID_PLC_PREFIX) {
            return Err(PlcError::InvalidDidFormat(format!(
                "DID must start with '{}', got '{}'",
                DID_PLC_PREFIX,
                s.chars().take(8).collect::<String>()
            )));
        }

        // Check exact length
        if s.len() != TOTAL_LENGTH {
            return Err(PlcError::InvalidDidFormat(format!(
                "DID must be exactly {} characters, got {}",
                TOTAL_LENGTH,
                s.len()
            )));
        }

        // Extract and validate identifier
        let identifier = &s[DID_PLC_PREFIX.len()..];

        if !is_valid_base32(identifier) {
            return Err(PlcError::InvalidDidFormat(format!(
                "Identifier contains invalid base32 characters. Valid alphabet: abcdefghijklmnopqrstuvwxyz234567"
            )));
        }

        Ok(())
    }
}

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

impl FromStr for Did {
    type Err = PlcError;

    fn from_str(s: &str) -> Result<Self> {
        Self::parse(s)
    }
}

impl Serialize for Did {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        serializer.serialize_str(&self.full)
    }
}

impl<'de> Deserialize<'de> for Did {
    fn deserialize<D>(deserializer: D) -> std::result::Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        let s = String::deserialize(deserializer)?;
        Self::parse(&s).map_err(serde::de::Error::custom)
    }
}

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

    #[test]
    fn test_valid_did() {
        let did = Did::parse("did:plc:ewvi7nxzyoun6zhxrhs64oiz").unwrap();
        assert_eq!(did.identifier(), "ewvi7nxzyoun6zhxrhs64oiz");
        assert_eq!(did.as_str(), "did:plc:ewvi7nxzyoun6zhxrhs64oiz");
        assert!(did.is_valid());
    }

    #[test]
    fn test_invalid_prefix() {
        assert!(Did::parse("did:web:example.com").is_err());
        assert!(Did::parse("DID:PLC:ewvi7nxzyoun6zhxrhs64oiz").is_err());
    }

    #[test]
    fn test_invalid_length() {
        assert!(Did::parse("did:plc:tooshort").is_err());
        assert!(Did::parse("did:plc:wayyyyyyyyyyyyyyyyyyyyyyytooooooolong").is_err());
    }

    #[test]
    fn test_invalid_characters() {
        // Contains 0, 1, 8, 9 which are not in base32 alphabet
        assert!(Did::parse("did:plc:012345678901234567890123").is_err());
        // Contains uppercase
        assert!(Did::parse("did:plc:EWVI7NXZYOUN6ZHXRHS64OIZ").is_err());
    }

    #[test]
    fn test_from_identifier() {
        let did = Did::from_identifier("ewvi7nxzyoun6zhxrhs64oiz").unwrap();
        assert_eq!(did.as_str(), "did:plc:ewvi7nxzyoun6zhxrhs64oiz");
    }

    #[test]
    fn test_display() {
        let did = Did::parse("did:plc:ewvi7nxzyoun6zhxrhs64oiz").unwrap();
        assert_eq!(format!("{}", did), "did:plc:ewvi7nxzyoun6zhxrhs64oiz");
    }

    #[test]
    fn test_serialization() {
        let did = Did::parse("did:plc:ewvi7nxzyoun6zhxrhs64oiz").unwrap();
        let json = serde_json::to_string(&did).unwrap();
        assert_eq!(json, "\"did:plc:ewvi7nxzyoun6zhxrhs64oiz\"");

        let deserialized: Did = serde_json::from_str(&json).unwrap();
        assert_eq!(did, deserialized);
    }
}