import type { Dayjs, ManipulateType, OptionType } from 'dayjs';
import dayjs from 'dayjs';
import customParseFormat from 'dayjs/plugin/customParseFormat.js';
import duration from 'dayjs/plugin/duration.js';
import isSameOrBefore from 'dayjs/plugin/isSameOrBefore.js';
import weekday from 'dayjs/plugin/weekday.js';

dayjs.extend(customParseFormat);
dayjs.extend(duration);
dayjs.extend(isSameOrBefore);
dayjs.extend(weekday);

/**
 * Defines a pattern for semantic date keywords.
 */
interface KeywordDefinition {
    /**
     * Regular expression to match the keyword (e.g., "Yesterday", "Monday", "周一").
     */
    regExp: RegExp;
    /**
     * Factory function to calculate the base date (start of day) relative to the current time.
     */
    calc: () => Dayjs;
}

/**
 * Defines a pattern for extracting time units from a string.
 */
interface UnitPattern {
    /**
     * The unit of time manipulation (e.g., 'days', 'hours').
     */
    unit: ManipulateType;
    /**
     * Regular expression to match value and unit in the input string.
     */
    regExp: RegExp;
}

// === Pre-compiled Regular Expressions ===

const REGEX_JUST_NOW = /^(?:just\s?now|刚刚|剛剛)$/i;
const REGEX_AGO = /(.*)(?:ago|[之以]?前)$/i;
const REGEX_IN = /^(?:in\s*)(.*)|(.*)(?:\s*later|\s*after|[之以]?[后後])$/i;
const REGEX_STICKY_AMPM = /(\d+)\s*(a|p)m$/i;
const REGEX_IS_PM = /(?:下午|晚上|晚|pm|p\.m\.)/i;
const REGEX_IS_AM = /(?:上午|凌晨|早|晨|am|a\.m\.)/i;

const UNIT_PATTERNS: UnitPattern[] = [
    { unit: 'years', regExp: /(\d+)\s*(?:年|y(?:ea)?rs?)/i },
    { unit: 'months', regExp: /(\d+)\s*(?:[个個]?月|months?)/i },
    { unit: 'weeks', regExp: /(\d+)\s*(?:周|[个個]?星期|weeks?)/i },
    { unit: 'days', regExp: /(\d+)\s*(?:天|日|d(?:ay)?s?)/i },
    { unit: 'hours', regExp: /(\d+)\s*(?:[个個]?(?:小?时|時|点|點)|h(?:(?:ou)?r)?s?)/i },
    { unit: 'minutes', regExp: /(\d+)\s*(?:分[鐘钟]?|m(?:in(?:ute)?)?s?)/i },
    { unit: 'seconds', regExp: /(\d+)\s*(?:秒[鐘钟]?|s(?:ec(?:ond)?)?s?)/i },
];

const CN_NUM_MAP: Record<string, string> = {
    一: '1',
    二: '2',
    两: '2',
    三: '3',
    四: '4',
    五: '5',
    六: '6',
    七: '7',
    八: '8',
    九: '9',
    十: '10',
};

/**
 * Calculates the date of the most recent occurrence of a specific weekday.
 *
 * If the target weekday is the same as today or occurs later in the current week,
 * it returns the date from the previous week.
 *
 * @param targetDay - The day index: 1 (Monday) to 7 (Sunday).
 * @returns A Dayjs object representing the start of that day.
 */
const getLastWeekday = (targetDay: number): Dayjs => {
    const today = dayjs();
    const currentDayIndex = today.day(); // 0 (Sun) - 6 (Sat)

    // Normalize input (7=Sun) to Day.js standard (0=Sun)
    const targetDayIndex = targetDay === 7 ? 0 : targetDay;

    // Calculate difference
    let daysToAdd = targetDayIndex - currentDayIndex;

    // If the target day is today or in the future (within the standard week cycle),
    // backtrack 7 days to find the previous occurrence.
    if (daysToAdd >= 0) {
        daysToAdd -= 7;
    }

    return today.add(daysToAdd, 'day').startOf('day');
};

// Semantic Keywords configuration
const KEYWORDS: KeywordDefinition[] = [
    {
        regExp: /^(?:今[天日早晨晚]|to?day?)/i,
        calc: () => dayjs().startOf('day'),
    },
    {
        regExp: /^(?:昨[天日早晨晚]|y(?:ester)?day?)/i,
        calc: () => dayjs().subtract(1, 'days').startOf('day'),
    },
    {
        regExp: /^(?:前天|(?:the)?d(?:ay)?b(?:eforeyesterda)?y)/i,
        calc: () => dayjs().subtract(2, 'days').startOf('day'),
    },
    {
        regExp: /^(?:明[天日早晨晚]|t(?:omorrow)?)/i,
        calc: () => dayjs().add(1, 'days').startOf('day'),
    },
    {
        regExp: /^(?:[后後][天日]|(?:the)?d(?:ay)?a(?:fter)?t(?:omrrow)?)/i,
        calc: () => dayjs().add(2, 'days').startOf('day'),
    },
    // Weekdays (English + Chinese)
    { regExp: /^(?:mon(?:day)?|(?:周|星期)[1一])/i, calc: () => getLastWeekday(1) },
    { regExp: /^(?:tue(?:sday)?|(?:周|星期)[2二两])/i, calc: () => getLastWeekday(2) },
    { regExp: /^(?:wed(?:nesday)?|(?:周|星期)[3三])/i, calc: () => getLastWeekday(3) },
    { regExp: /^(?:thu(?:rsday)?|(?:周|星期)[4四])/i, calc: () => getLastWeekday(4) },
    { regExp: /^(?:fri(?:day)?|(?:周|星期)[5五])/i, calc: () => getLastWeekday(5) },
    { regExp: /^(?:sat(?:urday)?|(?:周|星期)[6六])/i, calc: () => getLastWeekday(6) },
    { regExp: /^(?:sun(?:day)?|(?:周|星期)[7日天])/i, calc: () => getLastWeekday(7) },
];

/**
 * Normalizes the input string to a format suitable for parsing.
 *
 * Operations performed:
 * - Lowercasing and trimming.
 * - Converting English articles/quantifiers ('a', 'an', 'x') to numbers.
 * - Converting Chinese numerals and quantifiers to Arabic numbers.
 * - Removing punctuation (commas).
 *
 * @param date - The raw date string to normalize.
 * @returns The normalized string.
 */
const normalize = (date: string): string => {
    let str = date.toLowerCase().trim();

    if (REGEX_JUST_NOW.test(str)) {
        return 'just now';
    }

    // 1. Quantifiers: 'a'/'an' -> '1'
    str = str.replaceAll(/(^|\s)an?(\s)/g, '$11$2');

    // 2. Vague 'x' (English needs boundary)
    str = str.replaceAll(/(^|\s)x(\s|$)/g, '$13$2');

    // 3. Vague Chinese '几/数' (No boundary needed)
    str = str.replaceAll(/几|幾|数/g, '3');

    // 4. Chinese numerals
    str = str.replaceAll(/[一二两三四五六七八九十]/g, (match) => CN_NUM_MAP[match] || match);

    // 5. Remove commas
    str = str.replaceAll(',', '');

    return str;
};

/**
 * Parses a string to extract the total duration based on predefined unit patterns.
 *
 * @param str - The string containing time units (e.g., "1 hour 30 mins").
 * @returns A Dayjs Duration object representing the total time.
 */
const parseDuration = (str: string): plugin.Duration => {
    let totalDuration = dayjs.duration(0);
    // Remove spaces for regex unit matching
    const cleanStr = str.replaceAll(/\s+/g, '');

    for (const { unit, regExp } of UNIT_PATTERNS) {
        const match = regExp.exec(cleanStr);
        if (match) {
            const val = Number.parseInt(match[1], 10);
            if (!Number.isNaN(val)) {
                totalDuration = totalDuration.add(val, unit);
            }
        }
    }
    return totalDuration;
};

/**
 * A wrapper around `dayjs()` to parse standard date formats.
 *
 * @param date - The date input (string, number, or Date object).
 * @param options - Optional Day.js configuration (e.g., format string).
 * @returns A native JavaScript Date object.
 */
export const parseDate = (date: string | number | Date, ...options: OptionType[]): Date => dayjs(date, ...options).toDate();

/**
 * Processes a date string composed of a semantic keyword and an optional time component.
 *
 * @param baseTime - The calculated base date (start of day).
 * @param timePart - The string segment containing the time info (e.g., "3pm", "10:00").
 * @param originalContext - The original normalized string for context detection (AM/PM modifiers).
 * @returns The resolved Date object.
 */
const processSemanticKeyword = (baseTime: Dayjs, timePart: string, originalContext: string): Date => {
    if (!timePart) {
        return baseTime.toDate();
    }

    const isPM = REGEX_IS_PM.test(originalContext);
    const isAM = REGEX_IS_AM.test(originalContext);

    // Normalize formats like "3pm" to "3 pm" to separate digits from text
    const fixTimePart = timePart.replace(REGEX_STICKY_AMPM, '$1 $2m');

    // Attempt 1: Parse as a duration (e.g., "8点" -> 8 hours from start of day)
    const extraDuration = parseDuration(fixTimePart);
    let addedMillis = extraDuration.asMilliseconds();

    // Attempt 2: Handle cases where duration regex fails (e.g., "3 pm" doesn't match standard units)
    const stickyMatch = REGEX_STICKY_AMPM.exec(timePart);
    if (addedMillis === 0 && stickyMatch) {
        addedMillis = Number.parseInt(stickyMatch[1], 10) * 60 * 60 * 1000;
    }

    if (addedMillis > 0) {
        const hours = dayjs.duration(addedMillis).asHours();
        // Adjust for 12-hour clock context
        if (isPM && hours < 12) {
            addedMillis += 12 * 60 * 60 * 1000;
        } else if (isAM && hours === 12) {
            addedMillis -= 12 * 60 * 60 * 1000;
        }
        return baseTime.add(addedMillis, 'ms').toDate();
    }

    // Attempt 3: Parse as a standard time string using Day.js formats
    const composedDateStr = `${baseTime.format('YYYY-MM-DD')} ${fixTimePart}`;
    const tried = dayjs(composedDateStr, ['YYYY-MM-DD HH:mm:ss', 'YYYY-MM-DD HH:mm', 'YYYY-MM-DD H:m', 'YYYY-MM-DD h:m a', 'YYYY-MM-DD h a']);

    if (tried.isValid()) {
        let result = tried;
        // Manual adjustment if the parser missed 12-hour context (e.g., "下午" stripped earlier)
        if (isPM && result.hour() < 12) {
            result = result.add(12, 'hours');
        }
        return result.toDate();
    }

    return baseTime.toDate();
};

/**
 * Parses a relative or semantic date string into a JavaScript Date object.
 *
 * This function handles a variety of natural language date formats, including:
 *
 * 1. **Immediate Time**:
 *    - `Just now`, `刚刚`
 *
 * 2. **Relative Durations**:
 *    - Past: `10 minutes ago`, `an hour ago`, `x days ago`, `几分钟前`
 *    - Future: `in 10 minutes`, `2 hours later`, `10分钟后`
 *
 * 3. **Semantic Keywords**:
 *    - `Today`, `Yesterday`, `Tomorrow`, `TDA`, `今天`, `昨天`, `明天`
 *    - `Monday`, `Tuesday`... (Always resolves to the previous occurrence if ambiguous)
 *    - `周一`, `星期三`, `前天`
 *
 * 4. **Combined Semantic Expressions** (Date + Time + Context):
 *    - Explicit Time: `Yesterday 10:00`, `Monday 3pm`
 *    - Contextual Modifiers: `Today 3pm`, `昨晚8点` (Yesterday Evening), `明早8点` (Tomorrow Morning)
 *    - Mixed Formats: `周五下午3点`, `Today 3 p.m.`
 *
 * 5. **Fallback**:
 *    - Any format not matched above is passed to Day.js with the provided options.
 *
 * @param date - The relative or absolute date string to parse.
 * @param options - Optional configuration passed to Day.js for fallback parsing.
 * @returns A parsed JavaScript Date object.
 */
export const parseRelativeDate = (date: string, ...options: OptionType[]): Date => {
    if (!date) {
        return new Date();
    }

    const normalized = normalize(date);

    // Strategy 1: Immediate Time
    if (normalized === 'just now') {
        return dayjs().subtract(3, 'seconds').toDate();
    }

    // Strategy 2: Relative Duration
    const agoMatch = REGEX_AGO.exec(normalized);
    if (agoMatch) {
        const duration = parseDuration(agoMatch[1]);
        if (duration.asMilliseconds() > 0) {
            return dayjs().subtract(duration).toDate();
        }
    }

    const inMatch = REGEX_IN.exec(normalized);
    if (inMatch) {
        const duration = parseDuration(inMatch[1] || inMatch[2]);
        if (duration.asMilliseconds() > 0) {
            return dayjs().add(duration).toDate();
        }
    }

    // Strategy 3: Semantic Keywords extraction and processing
    const cleanStr = normalized.replaceAll(/\s+/g, '');
    for (const word of KEYWORDS) {
        const match = word.regExp.exec(cleanStr);
        if (match) {
            const baseTime = word.calc();
            const timePart = cleanStr.replace(word.regExp, '');
            return processSemanticKeyword(baseTime, timePart, normalized);
        }
    }

    // Strategy 4: Fallback to standard Day.js parsing
    return parseDate(date, ...options);
};