<?php
// SPDX-License-Identifier: GPL-3.0-or-later
declare(strict_types=1);

namespace Aiwend\Pricing;

/**
 * The cost of one measured request, or the reason it cannot be priced faithfully. Provider rules:
 *  - OpenAI and Gemini report cached input as a PART of the input tokens: the cached part is priced at the cached rate instead of the
 *    input rate (never in addition), and the cached count must be reported.
 *  - Anthropic's input tokens EXCLUDE cache reads and writes, which are priced separately; those are an "other category" this price
 *    list does not price, so a request that used them (or did not say) is unknown, not cheaper.
 *  - Reasoning tokens are part of the output tokens and are paid as output, so they never appear here.
 *  - Other categories (OpenAI cache writes, Gemini tool-use prompt tokens, Anthropic cache reads and writes) make a request unknown.
 *  - Only the standard processing tier is priced; priority, flex, batch or an unreported tier is unknown.
 */
final class CostCalculator
{
    public const MODEL_UNKNOWN = 'model_unknown';
    public const DETAILS_MISSING = 'details_missing';
    public const DETAILS_INVALID = 'details_invalid';
    public const NO_CACHED_RATE = 'no_cached_rate';
    public const OTHER_CATEGORIES = 'other_categories';
    public const TIER_UNKNOWN = 'tier_unknown';
    public const TIER_NOT_PRICED = 'tier_not_priced';

    /** The processing tier each provider reports for ordinary, standard-priced requests (the only tier the bundled list prices). */
    private const STANDARD_TIER = ['openai' => 'default', 'anthropic' => 'standard', 'gemini' => 'standard'];

    /** @return array{0:?Amount, 1:?string} the exact cost, or null and the reason */
    public static function price(Rate $rate, int $inputTokens, int $outputTokens, ?int $cachedInputTokens, ?int $otherTokens, ?string $processingTier): array
    {
        if ($inputTokens < 0 || $outputTokens < 0 || ($otherTokens !== null && $otherTokens < 0)) {
            return [null, self::DETAILS_INVALID];
        }
        // The list prices standard processing only: priority, flex, batch or any other tier is billed differently, and an unreported tier
        // cannot be assumed to be the standard one.
        if ($processingTier === null || $processingTier === '') {
            return [null, self::TIER_UNKNOWN];
        }
        if ($processingTier !== (self::STANDARD_TIER[$rate->provider] ?? '')) {
            return [null, self::TIER_NOT_PRICED];
        }
        if ($otherTokens !== null && $otherTokens > 0) {
            return [null, self::OTHER_CATEGORIES];
        }
        $out = Amount::ofTokens($outputTokens, $rate->outputMicro);
        if ($rate->provider === 'anthropic') {
            return $otherTokens === null ? [null, self::DETAILS_MISSING] : [Amount::ofTokens($inputTokens, $rate->inputMicro)->plus($out), null];
        }
        if ($cachedInputTokens === null) {
            return [null, self::DETAILS_MISSING];
        }
        if ($cachedInputTokens < 0 || $cachedInputTokens > $inputTokens) {
            return [null, self::DETAILS_INVALID];
        }
        if ($cachedInputTokens > 0 && $rate->cachedInputMicro === null) {
            return [null, self::NO_CACHED_RATE];
        }
        $in = Amount::ofTokens($inputTokens - $cachedInputTokens, $rate->inputMicro)->plus(Amount::ofTokens($cachedInputTokens, (int) $rate->cachedInputMicro));
        return [$in->plus($out), null];
    }
}