export const fields = {
    G: { field: 'era', desc: 'Era' },
    y: { field: 'year', desc: 'Year' },
    Y: { field: 'year', desc: 'Year of "Week of Year"' },
    u: { field: 'year', desc: 'Extended year' },
    U: { field: 'year', desc: 'Cyclic year name' },
    r: { field: 'year', desc: 'Related Gregorian year' },
    Q: { field: 'quarter', desc: 'Quarter' },
    q: { field: 'quarter', desc: 'Stand-alone quarter' },
    M: { field: 'month', desc: 'Month in year' },
    L: { field: 'month', desc: 'Stand-alone month in year' },
    w: { field: 'week', desc: 'Week of year' },
    W: { field: 'week', desc: 'Week of month' },
    d: { field: 'day', desc: 'Day in month' },
    D: { field: 'day', desc: 'Day of year' },
    F: { field: 'day', desc: 'Day of week in month' },
    g: { field: 'day', desc: 'Modified julian day' },
    E: { field: 'weekday', desc: 'Day of week' },
    e: { field: 'weekday', desc: 'Local day of week' },
    c: { field: 'weekday', desc: 'Stand-alone local day of week' },
    a: { field: 'period', desc: 'AM/PM marker' },
    b: { field: 'period', desc: 'AM/PM/noon/midnight marker' },
    B: { field: 'period', desc: 'Flexible day period' },
    h: { field: 'hour', desc: 'Hour in AM/PM (1~12)' },
    H: { field: 'hour', desc: 'Hour in day (0~23)' },
    k: { field: 'hour', desc: 'Hour in day (1~24)' },
    K: { field: 'hour', desc: 'Hour in AM/PM (0~11)' },
    j: { field: 'hour', desc: 'Hour in preferred cycle' },
    J: { field: 'hour', desc: 'Hour in preferred cycle without marker' },
    C: { field: 'hour', desc: 'Hour in preferred cycle with flexible marker' },
    m: { field: 'min', desc: 'Minute in hour' },
    s: { field: 'sec', desc: 'Second in minute' },
    S: { field: 'sec-frac', desc: 'Fractional second' },
    A: { field: 'ms', desc: 'Milliseconds in day' },
    z: { field: 'tz', desc: 'Time Zone: specific non-location' },
    Z: { field: 'tz', desc: 'Time Zone' },
    O: { field: 'tz', desc: 'Time Zone: localized' },
    v: { field: 'tz', desc: 'Time Zone: generic non-location' },
    V: { field: 'tz', desc: 'Time Zone: ID' },
    X: { field: 'tz', desc: 'Time Zone: ISO8601 with Z' },
    x: { field: 'tz', desc: 'Time Zone: ISO8601' }
};
const isLetter = (char) => (char >= 'A' && char <= 'Z') || (char >= 'a' && char <= 'z');
function readFieldToken(src, pos) {
    const char = src[pos];
    let width = 1;
    while (src[++pos] === char)
        ++width;
    const field = fields[char];
    if (!field) {
        const msg = `The letter ${char} is not a valid field identifier`;
        return { char, error: new Error(msg), width };
    }
    return { char, field: field.field, desc: field.desc, width };
}
function readQuotedToken(src, pos) {
    let str = src[++pos];
    let width = 2;
    if (str === "'")
        return { char: "'", str, width };
    while (true) {
        const next = src[++pos];
        ++width;
        if (next === undefined) {
            const msg = `Unterminated quoted literal in pattern: ${str || src}`;
            return { char: "'", error: new Error(msg), str, width };
        }
        else if (next === "'") {
            if (src[++pos] !== "'")
                return { char: "'", str, width };
            else
                ++width;
        }
        str += next;
    }
}
function readToken(src, pos) {
    const char = src[pos];
    if (!char)
        return null;
    if (isLetter(char))
        return readFieldToken(src, pos);
    if (char === "'")
        return readQuotedToken(src, pos);
    let str = char;
    let width = 1;
    while (true) {
        const next = src[++pos];
        if (!next || isLetter(next) || next === "'")
            return { char, str, width };
        str += next;
        width += 1;
    }
}
/**
 * Parse an {@link http://userguide.icu-project.org/formatparse/datetime | ICU
 * DateFormat skeleton} string into a {@link DateToken} array.
 *
 * @remarks
 * Errors will not be thrown, but if encountered are included as the relevant
 * token's `error` value.
 *
 * @public
 * @param src - The skeleton string
 *
 * @example
 * ```js
 * import { parseDateTokens } from '@messageformat/date-skeleton'
 *
 * parseDateTokens('GrMMMdd', console.error)
 * // [
 * //   { char: 'G', field: 'era', desc: 'Era', width: 1 },
 * //   { char: 'r', field: 'year', desc: 'Related Gregorian year', width: 1 },
 * //   { char: 'M', field: 'month', desc: 'Month in year', width: 3 },
 * //   { char: 'd', field: 'day', desc: 'Day in month', width: 2 }
 * // ]
 * ```
 */
export function parseDateTokens(src) {
    const tokens = [];
    let pos = 0;
    while (true) {
        const token = readToken(src, pos);
        if (!token)
            return tokens;
        tokens.push(token);
        pos += token.width;
    }
}