// Courtesy of Claude :)

const atRules = new Set([
    "charset", "import", "namespace", "media", "supports", "page", "font-face",
    "keyframes", "counter-style", "font-feature-values", "property", "layer",
    "container", "scope"
]);

const pseudoClasses = new Set([
    "hover", "focus", "active", "visited", "link", "disabled", "enabled",
    "checked", "first-child", "last-child", "nth-child", "nth-last-child",
    "first-of-type", "last-of-type", "nth-of-type", "nth-last-of-type",
    "only-child", "only-of-type", "empty", "root", "target", "not", "is",
    "where", "has", "focus-within", "focus-visible"
]);

const pseudoElements = new Set([
    "before", "after", "first-line", "first-letter", "selection", "backdrop",
    "placeholder", "marker", "file-selector-button"
]);

const properties = new Set([
    "display", "position", "top", "right", "bottom", "left", "width", "height",
    "margin", "padding", "border", "background", "color", "font", "text",
    "flex", "grid", "transform", "transition", "animation", "opacity",
    "visibility", "overflow", "z-index", "content", "cursor", "pointer-events"
]);

const units = new Set([
    "px", "em", "rem", "ex", "ch", "vw", "vh", "vmin", "vmax", "%",
    "cm", "mm", "in", "pt", "pc", "deg", "rad", "grad", "turn",
    "s", "ms", "hz", "khz", "dpi", "dpcm", "dppx", "fr"
]);

const functions = new Set([
    "url", "calc", "min", "max", "clamp", "var", "rgb", "rgba", "hsl", "hsla",
    "linear-gradient", "radial-gradient", "conic-gradient", "repeating-linear-gradient",
    "repeating-radial-gradient", "translate", "rotate", "scale", "skew", "matrix",
    "cubic-bezier", "steps", "attr", "counter", "counters"
]);

export function tokenize(code) {
    const tokens = [];
    let i = 0;

    while (i < code.length) {
        const char = code[i];

        // Whitespace
        if (/\s/.test(char)) {
            const start = i;
            while (i < code.length && /\s/.test(code[i])) i++;
            tokens.push({ type: "whitespace", value: code.slice(start, i) });
            continue;
        }

        // Comments
        if (char === '/' && code[i + 1] === '*') {
            const start = i;
            i += 2;
            while (i < code.length - 1 && !(code[i] === '*' && code[i + 1] === '/')) i++;
            if (i < code.length - 1) i += 2;
            tokens.push({ type: "comment", value: code.slice(start, i) });
            continue;
        }

        // Strings
        if (char === '"' || char === '\'') {
            const stringToken = tokenizeString(code, i, char);
            tokens.push(stringToken.token);
            i = stringToken.newIndex;
            continue;
        }

        // URL function special case
        if (char === 'u' && code.slice(i, i + 4) === "url(") {
            const urlToken = tokenizeUrl(code, i);
            if (urlToken) {
                tokens.push(urlToken.token);
                i = urlToken.newIndex;
                continue;
            }
        }

        // At-rules
        if (char === '@') {
            const atRuleToken = tokenizeAtRule(code, i);
            tokens.push(atRuleToken.token);
            i = atRuleToken.newIndex;
            continue;
        }

        // Numbers (including units)
        if (/\d/.test(char) || (char === '.' && /\d/.test(code[i + 1]))) {
            const numberToken = tokenizeNumber(code, i);
            tokens.push(numberToken.token);
            i = numberToken.newIndex;
            continue;
        }

        // Hash values (colors, IDs)
        if (char === '#') {
            const hashToken = tokenizeHash(code, i);
            tokens.push(hashToken.token);
            i = hashToken.newIndex;
            continue;
        }

        // Identifiers, properties, values
        if (/[a-zA-Z_-]/.test(char)) {
            const identifierToken = tokenizeIdentifier(code, i);
            tokens.push(identifierToken.token);
            i = identifierToken.newIndex;
            continue;
        }

        // CSS variables
        if (char === '-' && code[i + 1] === '-') {
            const variableToken = tokenizeVariable(code, i);
            tokens.push(variableToken.token);
            i = variableToken.newIndex;
            continue;
        }

        // Pseudo-classes and pseudo-elements
        if (char === ':') {
            const pseudoToken = tokenizePseudo(code, i);
            tokens.push(pseudoToken.token);
            i = pseudoToken.newIndex;
            continue;
        }

        // Operators and punctuation
        if ("{}[](),.;:>+~*|^$=".includes(char)) {
            // Handle multi-character operators
            const twoChar = code.slice(i, i + 2);
            if (["~=", "|=", "^=", "$=", "*="].includes(twoChar)) {
                tokens.push({ type: "operator", value: twoChar });
                i += 2;
                continue;
            }

            const type = "{}[]()".includes(char) ? "punctuation" :
                        ",;".includes(char) ? "delimiter" : "operator";
            tokens.push({ type, value: char });
            i++;
            continue;
        }

        // Important declaration
        if (char === '!') {
            const importantToken = tokenizeImportant(code, i);
            if (importantToken) {
                tokens.push(importantToken.token);
                i = importantToken.newIndex;
                continue;
            }
        }

        // Unknown character
        tokens.push({ type: "unknown", value: char });
        i++;
    }

    return tokens;
}

function tokenizeString(code, start, quote) {
    let i = start;
    let value = "";

    value += code[i++]; // Opening quote

    while (i < code.length) {
        const char = code[i];

        if (char === quote) {
            value += char;
            i++;
            break;
        }

        if (char === '\\') {
            value += char;
            i++;
            if (i < code.length) {
                value += code[i];
                i++;
            }
            continue;
        }

        value += char;
        i++;
    }

    return { token: { type: "string", value }, newIndex: i };
}

function tokenizeUrl(code, start) {
    let i = start + 4; // Skip "url("
    let value = "url(";

    // Skip whitespace
    while (i < code.length && /\s/.test(code[i])) {
        value += code[i++];
    }

    // Handle quoted URLs
    if (code[i] === '"' || code[i] === '\'') {
        const quote = code[i];
        value += code[i++];
        while (i < code.length && code[i] !== quote) {
            if (code[i] === "\\") {
                value += code[i++];
                if (i < code.length) value += code[i++];
            } else {
                value += code[i++];
            }
        }
        if (i < code.length) value += code[i++]; // Closing quote
    } else {
        // Unquoted URL
        while (i < code.length && code[i] !== ')' && !/\s/.test(code[i])) {
            value += code[i++];
        }
    }

    // Skip whitespace
    while (i < code.length && /\s/.test(code[i])) {
        value += code[i++];
    }

    if (i < code.length && code[i] === ')') {
        value += code[i++];
    }

    return { token: { type: "url", value }, newIndex: i };
}

function tokenizeAtRule(code, start) {
    let i = start + 1; // Skip @
    let value = "@";

    while (i < code.length && /[a-zA-Z-]/.test(code[i])) {
        value += code[i++];
    }

    const ruleName = value.slice(1);
    const type = atRules.has(ruleName) ? "at-rule" : "unknown";

    return { token: { type, value }, newIndex: i };
}

function tokenizeNumber(code, start) {
    let i = start;
    let value = "";

    // Handle negative numbers
    if (code[i] === "-") {
        value += code[i++];
    }

    // Parse number part
    let hasDecimal = false;
    while (i < code.length && (/\d/.test(code[i]) || (code[i] === '.' && !hasDecimal))) {
        if (code[i] === '.') hasDecimal = true;
        value += code[i++];
    }

    // Check for unit
    const unitStart = i;
    while (i < code.length && /[a-zA-Z%]/.test(code[i])) {
        i++;
    }

    if (i > unitStart) {
        const unit = code.slice(unitStart, i);
        value += unit;
        const type = units.has(unit) ? "number-unit" : "unknown";
        return { token: { type, value }, newIndex: i };
    }

    return { token: { type: "number", value }, newIndex: i };
}

function tokenizeHash(code, start) {
    let i = start + 1; // Skip #
    let value = "#";

    while (i < code.length && /[a-fA-F0-9]/.test(code[i])) {
        value += code[i++];
    }

    const hashValue = value.slice(1);
    const isColor = /^([a-fA-F0-9]{3}|[a-fA-F0-9]{6}|[a-fA-F0-9]{8})$/.test(hashValue);
    const type = isColor ? "color" : "hash";

    return { token: { type, value }, newIndex: i };
}

function tokenizeIdentifier(code, start) {
    let i = start;
    let value = "";

    while (i < code.length && /[a-zA-Z0-9_-]/.test(code[i])) {
        value += code[i++];
    }

    // Check for function
    if (i < code.length && code[i] === '(') {
        const type = functions.has(value) ? "function" : "unknown";
        return { token: { type, value }, newIndex: i };
    }

    // Determine type
    let type = "identifier";
    if (properties.has(value)) type = "property";
    else if (value === "important") type = "important";

    return { token: { type, value }, newIndex: i };
}

function tokenizeVariable(code, start) {
    let i = start + 2; // Skip --
    let value = "--";

    while (i < code.length && /[a-zA-Z0-9_-]/.test(code[i])) {
        value += code[i++];
    }

    return { token: { type: "variable", value }, newIndex: i };
}

function tokenizePseudo(code, start) {
    let i = start + 1; // Skip first :
    let value = ":";

    // Check for double colon (pseudo-element)
    if (i < code.length && code[i] === ":") {
        value += code[i++];
    }

    while (i < code.length && /[a-zA-Z-]/.test(code[i])) {
        value += code[i++];
    }

    const pseudoName = value.replace(/^::?/, "");
    const isDoubleColon = value.startsWith("::");

    let type = "pseudo-class";
    if (isDoubleColon && pseudoElements.has(pseudoName)) {
        type = "pseudo-element";
    } else if (!isDoubleColon && pseudoClasses.has(pseudoName)) {
        type = "pseudo-class";
    } else {
        type = isDoubleColon ? "unknown" : "unknown";
    }

    return { token: { type, value }, newIndex: i };
}

function tokenizeImportant(code, start) {
    let i = start + 1; // Skip !

    // Skip whitespace
    while (i < code.length && /\s/.test(code[i])) i++;

    if (code.slice(i, i + 9) === "important") {
        return {
            token: { type: "important", value: code.slice(start, i + 9) },
            newIndex: i + 9
        };
    }

    return null;
}