import type { Activity, MetricACWRData } from '@/types';

/**
 * Format date to YYYY-MM-DD in local timezone (not UTC)
 */
function formatDateLocal(date: Date): string {
    const year = date.getFullYear();
    const month = String(date.getMonth() + 1).padStart(2, '0');
    const day = String(date.getDate()).padStart(2, '0');
    return `${year}-${month}-${day}`;
}

/**
 * Calculate ACWR for a specific metric (distance, duration, or TSS)
 * @param activities - Array of activities
 * @param metricExtractor - Function to extract the metric value from an activity
 * @param dateRange - Optional date range to maintain consistency
 */
export function calculateMetricACWR(
    activities: Activity[],
    metricExtractor: (activity: Activity) => number | undefined,
    dateRange?: { start: Date; end: Date }
): MetricACWRData {
    if (activities.length === 0 && !dateRange) {
        return {
            dates: [],
            values: [],
            average7d: [],
            average28d: [],
            acwr: [],
        };
    }

    // Sort activities by date
    const sortedActivities = [...activities].sort((a, b) => a.date.getTime() - b.date.getTime());

    // Get date range
    const startDate = dateRange?.start || (sortedActivities.length > 0 ? new Date(sortedActivities[0].date) : new Date());
    const endDate = dateRange?.end || (sortedActivities.length > 0 ? new Date(sortedActivities[sortedActivities.length - 1].date) : new Date());

    // Create a map of date -> daily sum
    const dailyValues = new Map<string, number>();
    sortedActivities.forEach(activity => {
        const dateStr = formatDateLocal(activity.date);
        const value = metricExtractor(activity);
        if (value !== undefined) {
            dailyValues.set(dateStr, (dailyValues.get(dateStr) || 0) + value);
        }
    });

    const dates: string[] = [];
    const values: (number | null)[] = [];
    const average7d: (number | null)[] = [];
    const average28d: (number | null)[] = [];
    const acwr: (number | null)[] = [];

    // Generate all dates in range
    const allDates: Date[] = [];
    for (let d = new Date(startDate); d <= endDate; d.setDate(d.getDate() + 1)) {
        allDates.push(new Date(d));
    }

    // Calculate for each date
    allDates.forEach((date, index) => {
        const dateStr = formatDateLocal(date);
        dates.push(dateStr);

        // Get daily value
        const dailyValue = dailyValues.get(dateStr) || null;
        values.push(dailyValue);

        // Calculate 7-day rolling average (acute load)
        let acuteSum = 0;
        let acuteCount = 0;
        for (let i = Math.max(0, index - 6); i <= index; i++) {
            const checkDateStr = formatDateLocal(allDates[i]);
            const val = dailyValues.get(checkDateStr);
            if (val !== undefined) {
                acuteSum += val;
                acuteCount++;
            }
        }
        const acuteAvg = acuteCount > 0 ? acuteSum / 7 : null;
        average7d.push(acuteAvg);

        // Calculate 28-day rolling average
        let chronicSum = 0;
        let chronicCount = 0;
        for (let i = Math.max(0, index - 27); i <= index; i++) {
            const checkDateStr = formatDateLocal(allDates[i]);
            const val = dailyValues.get(checkDateStr);
            if (val !== undefined) {
                chronicSum += val;
                chronicCount++;
            }
        }
        const chronicAvg = chronicCount > 0 ? chronicSum / 28 : null;
        average28d.push(chronicAvg);

        // Calculate ACWR (need at least 28 days of data)
        if (index < 27) {
            acwr.push(null);
            return;
        }

        // For ACWR, use the full 28-day sum (not average)
        let acwrChronicSum = 0;
        for (let i = index - 27; i <= index; i++) {
            const checkDateStr = formatDateLocal(allDates[i]);
            const val = dailyValues.get(checkDateStr);
            if (val !== undefined) {
                acwrChronicSum += val;
            }
        }
        const acwrChronicAvg = acwrChronicSum / 28;

        // Calculate ACWR
        if (acwrChronicAvg > 0 && acuteAvg !== null) {
            acwr.push(acuteAvg / acwrChronicAvg);
        } else {
            acwr.push(null);
        }
    });

    return {
        dates,
        values,
        average7d,
        average28d,
        acwr,
    };
}