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

export interface ClockProblem {
    hour: number;
    minute: number;
}

export interface ClockReadingData {
    problems: ClockProblem[];
    timeMode: ClockReadingTimeMode;
}

export const CLOCK_PROBLEM_COUNT = 12;

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

function pickMinute(timeMode: ClockReadingTimeMode): number {
    if (timeMode === 'random') {
        return Math.floor(Math.random() * 60);
    }
    const pool = MINUTES_BY_MODE[timeMode];
    return pool[Math.floor(Math.random() * pool.length)] ?? 0;
}

/** 生成一页 12 道钟表题，同一页内时刻不重复 */
export function generateClockProblems(
    timeMode: ClockReadingTimeMode,
): ClockProblem[] {
    const used = new Set<string>();
    const problems: ClockProblem[] = [];
    let guard = 0;

    while (problems.length < CLOCK_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 });
    }

    return problems;
}

export function buildClockReadingData(
    timeMode: ClockReadingTimeMode,
): ClockReadingData {
    return {
        timeMode,
        problems: generateClockProblems(timeMode),
    };
}

export const CLOCK_TIME_MODE_OPTIONS = [
    { id: 'random' as const, label: '随机', subtitle: '0–59 分均可' },
    { 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' },
];