/**
 * Price usage records from configured rates.
 *
 * `createPricer` owns the two things that must not be rebuilt per record: the
 * matching rates and the timezone formatter. Both currencies price a record
 * from `rates` and `peak` when a key matches. They differ only for a model no
 * key matches: `USD` adds Pi's recorded dollar amount (its catalog is already
 * per model), while `CNY` adds nothing and counts the record as unpriced, so the
 * session can say what its total leaves out.
 */

import { zeroUsage } from "../../../../lib/usage.ts";
import type { ByteflyConfig, ModelRates } from "./types.ts";
import type { PricedUsage, UsageRecord } from "../types.ts";
import { createRateLookup } from "./rates.ts";
import { isPeak, peakFormatter } from "./schedule.ts";

const TOKENS_PER_MILLION = 1_000_000;

/** The cost of one record's tokens at `rates`, which are per million tokens. */
function tokenCost(record: UsageRecord, rates: ModelRates): number {
	return (
		(record.input * rates.input +
			record.output * rates.output +
			record.cacheRead * rates.cacheRead +
			record.cacheWrite * rates.cacheWrite) /
		TOKENS_PER_MILLION
	);
}

/**
 * Build a pricer for one config.
 *
 * The returned function totals tokens as well as cost, so the bar's meters and
 * its price always describe the same set of records.
 */
export function createPricer(config: ByteflyConfig): (records: readonly UsageRecord[]) => PricedUsage {
	// Both currencies price from `rates` and the tariff; they differ only in what
	// an unmatched model falls back to, and Pi's recorded cost is already dollars.
	const dollars = config.currency.code === "USD";
	// Both are built once per config, never per record: the table splits every key
	// and remembers the last match, and the formatter is the expensive part.
	const lookup = createRateLookup(config.rates);
	const format = config.peak.windows.length > 0 ? peakFormatter(config.peak.timezone) : null;

	return (records) => {
		const totals: PricedUsage = { ...zeroUsage(), unpriced: 0 };
		for (const record of records) {
			totals.input += record.input;
			totals.output += record.output;
			totals.cacheRead += record.cacheRead;
			totals.cacheWrite += record.cacheWrite;
			const rates = lookup(record.provider, record.model);
			if (rates !== undefined) {
				totals.cost += ratedCost(config, format, record, rates);
				continue;
			}
			// No rate: USD still has Pi's own per-model amount, CNY has nothing to add
			// and only a count to report.
			if (dollars) totals.cost += record.recordedCost;
			else totals.unpriced += 1;
		}
		return totals;
	};
}

/** One record's cost at its matched rates, after the peak schedule. */
function ratedCost(
	config: ByteflyConfig,
	format: Intl.DateTimeFormat | null,
	record: UsageRecord,
	rates: ModelRates,
): number {
	const cost = tokenCost(record, rates);
	// An undated record is never discounted: we cannot tell which tariff applied.
	if (format === null || record.at === null) return cost;
	return isPeak(config.peak, record.at, format) ? cost : cost * rates.offPeakMultiplier;
}