<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\RateLimiter\Policy;

use Symfony\Component\Lock\LockInterface;
use Symfony\Component\RateLimiter\Exception\MaxWaitDurationExceededException;
use Symfony\Component\RateLimiter\LimiterInterface;
use Symfony\Component\RateLimiter\RateLimit;
use Symfony\Component\RateLimiter\Reservation;
use Symfony\Component\RateLimiter\Storage\StorageInterface;

/**
 * @author Wouter de Jong <wouter@wouterj.nl>
 */
final class TokenBucketLimiter implements LimiterInterface
{
    use ResetLimiterTrait;

    private int $maxBurst;
    private Rate $rate;

    public function __construct(string $id, int $maxBurst, Rate $rate, StorageInterface $storage, ?LockInterface $lock = null)
    {
        $this->id = $id;
        $this->maxBurst = $maxBurst;
        $this->rate = $rate;
        $this->storage = $storage;
        $this->lock = $lock;
    }

    /**
     * Waits until the required number of tokens is available.
     *
     * The reserved tokens will be taken into account when calculating
     * future token consumptions. Do not use this method if you intend
     * to skip this process.
     *
     * @param int        $tokens  the number of tokens required
     * @param float|null $maxTime maximum accepted waiting time in seconds
     *
     * @throws MaxWaitDurationExceededException if $maxTime is set and the process needs to wait longer than its value (in seconds)
     * @throws \InvalidArgumentException        if $tokens is larger than the maximum burst size
     */
    public function reserve(int $tokens = 1, ?float $maxTime = null): Reservation
    {
        if ($tokens > $this->maxBurst) {
            throw new \InvalidArgumentException(sprintf('Cannot reserve more tokens (%d) than the burst size of the rate limiter (%d).', $tokens, $this->maxBurst));
        }

        $this->lock?->acquire(true);

        try {
            $bucket = $this->storage->fetch($this->id);
            if (!$bucket instanceof TokenBucket) {
                $bucket = new TokenBucket($this->id, $this->maxBurst, $this->rate);
            }

            $now = microtime(true);
            $availableTokens = $bucket->getAvailableTokens($now);

            if ($availableTokens >= $tokens) {
                // tokens are now available, update bucket
                $bucket->setTokens($availableTokens - $tokens);

                if (0 === $availableTokens) {
                    // This means 0 tokens where consumed (discouraged in most cases).
                    // Return the first time a new token is available
                    $waitDuration = $this->rate->calculateTimeForTokens(1);
                    $waitTime = \DateTimeImmutable::createFromFormat('U', floor($now + $waitDuration));
                } else {
                    $waitTime = \DateTimeImmutable::createFromFormat('U', floor($now));
                }

                $reservation = new Reservation($now, new RateLimit($bucket->getAvailableTokens($now), $waitTime, true, $this->maxBurst));
            } else {
                $remainingTokens = $tokens - $availableTokens;
                $waitDuration = $this->rate->calculateTimeForTokens($remainingTokens);

                if (null !== $maxTime && $waitDuration > $maxTime) {
                    // process needs to wait longer than set interval
                    $rateLimit = new RateLimit($availableTokens, \DateTimeImmutable::createFromFormat('U', floor($now + $waitDuration)), false, $this->maxBurst);

                    throw new MaxWaitDurationExceededException(sprintf('The rate limiter wait time ("%d" seconds) is longer than the provided maximum time ("%d" seconds).', $waitDuration, $maxTime), $rateLimit);
                }

                // at $now + $waitDuration all tokens will be reserved for this process,
                // so no tokens are left for other processes.
                $bucket->setTokens($availableTokens - $tokens);

                $reservation = new Reservation($now + $waitDuration, new RateLimit(0, \DateTimeImmutable::createFromFormat('U', floor($now + $waitDuration)), false, $this->maxBurst));
            }

            if (0 < $tokens) {
                $this->storage->save($bucket);
            }
        } finally {
            $this->lock?->release();
        }

        return $reservation;
    }

    public function consume(int $tokens = 1): RateLimit
    {
        try {
            return $this->reserve($tokens, 0)->getRateLimit();
        } catch (MaxWaitDurationExceededException $e) {
            return $e->getRateLimit();
        }
    }
}