export type BucketUsageBucket = {
    tags: string[];
    necessity: "NECESSARY" | "BOTH" | "UNNECESSARY";
    windowDays: number;
};

export type BucketUsageEntry = {
    amountDollars: number;
    occurredAt: string | Date;
    necessity: "NECESSARY" | "BOTH" | "UNNECESSARY";
    tags: string[];
    isRecurring: boolean;
    entryType?: "SPENDING" | "INCOME";
};

const MS_PER_DAY = 24 * 60 * 60 * 1000;

function toDateOnly(value: string | Date) {
    if (value instanceof Date) {
        return new Date(Date.UTC(value.getUTCFullYear(), value.getUTCMonth(), value.getUTCDate()));
    }
    if (!value) return null;
    const parsed = new Date(`${value}T00:00:00Z`);
    if (Number.isNaN(parsed.getTime())) return null;
    return parsed;
}

function daysBetween(today: Date, occurred: Date) {
    return Math.floor((today.getTime() - occurred.getTime()) / MS_PER_DAY);
}

function hasAllTags(bucketTags: string[], entryTags: string[]) {
    if (!bucketTags.length) return true;
    if (!entryTags.length) return false;
    const entrySet = new Set(entryTags.map(tag => tag.toLowerCase()));
    return bucketTags.every(tag => entrySet.has(tag.toLowerCase()));
}

export function calculateBucketUsage(bucket: BucketUsageBucket, entries: BucketUsageEntry[], today: string | Date) {
    const windowDays = Number(bucket.windowDays || 0);
    if (!Number.isFinite(windowDays) || windowDays <= 0)
        return { totalUsage: 0, matchedCount: 0 };

    const todayDate = toDateOnly(today);
    if (!todayDate) return { totalUsage: 0, matchedCount: 0 };

    const bucketNecessity = bucket.necessity;
    let totalUsage = 0;
    let matchedCount = 0;

    entries.forEach(entry => {
        if (entry.entryType && entry.entryType !== "SPENDING") return;
        if (entry.isRecurring) return;
        if (!hasAllTags(bucket.tags || [], entry.tags || [])) return;

        const occurred = toDateOnly(entry.occurredAt);
        if (!occurred) return;
        const diffDays = daysBetween(todayDate, occurred);
        if (diffDays < 0 || diffDays > windowDays - 1) return;

        const entryNecessity = entry.necessity;
        if (bucketNecessity !== "BOTH") {
            if (entryNecessity === "BOTH") {
                totalUsage += entry.amountDollars / 2;
                matchedCount += 1;
                return;
            }
            if (entryNecessity !== bucketNecessity) return;
        }

        totalUsage += entry.amountDollars;
        matchedCount += 1;
    });

    return { totalUsage, matchedCount };
}