export type ClockConnectTimeMode =
    | 'random'
    | 'whole-hour'
    | 'half-hour'
    | 'quarter-hour';

export interface ClockConnectProblem {
    hour: number;
    minute: number;
    /** 格式化后的时间文本，如 "6:00" */
    timeText: string;
}

export interface ClockConnectData {
    /** 左侧钟表列表（按原始顺序） */
    clocks: ClockConnectProblem[];
    /** 右侧时间文本列表（打乱顺序） */
    shuffledTimes: ClockConnectProblem[];
    timeMode: ClockConnectTimeMode;
}

export const CLOCK_CONNECT_PROBLEM_COUNT = 6;

const MINUTES_BY_MODE: Record<
    Exclude<ClockConnectTimeMode, 'random'>,
    readonly number[]
> = {
    'whole-hour': [0],
    'half-hour': [30],
    'quarter-hour': [15, 45],
};

function pickMinute(timeMode: ClockConnectTimeMode): number {
    if (timeMode === 'random') {
        const options = [0, 15, 30, 45];
        return options[Math.floor(Math.random() * options.length)];
    }
    const pool = MINUTES_BY_MODE[timeMode];
    return pool[Math.floor(Math.random() * pool.length)] ?? 0;
}

function formatTime(hour: number, minute: number): string {
    return `${hour}:${minute.toString().padStart(2, '0')}`;
}

/** Fisher-Yates shuffle */
function shuffle<T>(arr: T[]): T[] {
    const result = [...arr];
    for (let i = result.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        [result[i], result[j]] = [result[j], result[i]];
    }
    return result;
}

/** 生成一页 6 道时钟连线题，同一页内时刻不重复 */
export function generateClockConnectProblems(
    timeMode: ClockConnectTimeMode,
): ClockConnectProblem[] {
    const used = new Set<string>();
    const problems: ClockConnectProblem[] = [];
    let guard = 0;

    while (problems.length < CLOCK_CONNECT_PROBLEM_COUNT && guard < 500) {
        guard += 1;
        const hour = Math.floor(Math.random() * 12) + 1;
        const minute = pickMinute(timeMode);
        const key = `${hour}:${minute}`;
        if (used.has(key)) continue;
        used.add(key);
        problems.push({ hour, minute, timeText: formatTime(hour, minute) });
    }

    return problems;
}

export function buildClockConnectData(
    timeMode: ClockConnectTimeMode,
): ClockConnectData {
    const clocks = generateClockConnectProblems(timeMode);
    const shuffledTimes = shuffle(clocks);

    return {
        timeMode,
        clocks,
        shuffledTimes,
    };
}

export const CLOCK_CONNECT_TIME_MODE_OPTIONS = [
    { id: 'whole-hour' as const, label: '整点', subtitle: '如 3:00' },
    { id: 'half-hour' as const, label: '半点', subtitle: '如 6:30' },
    { id: 'quarter-hour' as const, label: '刻钟', subtitle: '如 2:15、7:45' },
    { id: 'random' as const, label: '随机', subtitle: '整点/半点/刻钟' },
];