export type SuggestionSource = {
	description: string;
	amountCents: number;
	accountId: number | null;
	date: string;
};

export type Suggestion = {
	key: string;
	description: string;
	/** Most common amount for this description (latest wins ties). */
	amountCents: number;
	/** Account used most recently with this description. */
	accountId: number | null;
	count: number;
	lastDate: string;
};

/** Past descriptions ranked by use, each with its usual amount and latest account. */
export function descriptionSuggestions(rows: SuggestionSource[], today: string): Suggestion[] {
	const groups = new Map<
		string,
		{
			description: string;
			amounts: Map<number, number>;
			accountId: number | null;
			count: number;
			lastDate: string;
			lastAmount: number;
		}
	>();
	for (const row of rows) {
		if (row.date > today) continue;
		const key = row.description.trim().toLowerCase();
		if (!key) continue;
		const group = groups.get(key) ?? {
			description: row.description.trim(),
			amounts: new Map(),
			accountId: row.accountId,
			count: 0,
			lastDate: '',
			lastAmount: row.amountCents
		};
		group.count++;
		group.amounts.set(row.amountCents, (group.amounts.get(row.amountCents) ?? 0) + 1);
		if (row.date >= group.lastDate) {
			group.lastDate = row.date;
			group.description = row.description.trim();
			group.accountId = row.accountId;
			group.lastAmount = row.amountCents;
		}
		groups.set(key, group);
	}
	return [...groups.entries()]
		.map(([key, group]) => {
			let amountCents = group.lastAmount;
			let best = group.amounts.get(amountCents) ?? 0;
			for (const [value, uses] of group.amounts)
				if (uses > best) {
					best = uses;
					amountCents = value;
				}
			return {
				key,
				description: group.description,
				amountCents,
				accountId: group.accountId,
				count: group.count,
				lastDate: group.lastDate
			};
		})
		.sort((a, b) => b.count - a.count || b.lastDate.localeCompare(a.lastDate));
}