using System;
using Paca.Mobile.Core;
using Xunit;

namespace Paca.Tests.Core;

public class DownloadTokenBucketRateLimiterGateTests
{
    [Fact]
    public void Gate453_DownloadTokenBucketRateLimiter_AllowsImmediateConsumption_WhenBucketFull()
    {
        var now = DateTime.UtcNow;
        var limiter = new DownloadTokenBucketRateLimiter(rateBytesPerSec: 1_000_000, burstCapacityBytes: 2_000_000, initialTime: now);

        var decision = limiter.Request(500_000, now);

        Assert.True(decision.IsAllowedImmediately);
        Assert.Equal(TimeSpan.Zero, decision.DelayRequired);
        Assert.Equal(1_500_000, limiter.AvailableTokens, 1);
    }

    [Fact]
    public void Gate454_DownloadTokenBucketRateLimiter_CalculatesRequiredDelay_WhenTokensExhausted()
    {
        var now = DateTime.UtcNow;
        var limiter = new DownloadTokenBucketRateLimiter(rateBytesPerSec: 1_000_000, burstCapacityBytes: 1_000_000, initialTime: now);

        // Exhaust all tokens
        limiter.Request(1_000_000, now);

        // Request another 500KB immediately (needs 500ms refill)
        var decision = limiter.Request(500_000, now);

        Assert.False(decision.IsAllowedImmediately);
        Assert.Equal(TimeSpan.FromMilliseconds(500), decision.DelayRequired);
    }

    [Fact]
    public void Gate455_DownloadTokenBucketRateLimiter_RefillsTokensOverTime_UpToCapacity()
    {
        var now = DateTime.UtcNow;
        var limiter = new DownloadTokenBucketRateLimiter(rateBytesPerSec: 1_000_000, burstCapacityBytes: 2_000_000, initialTime: now);

        // Consume everything
        limiter.Request(2_000_000, now);
        Assert.Equal(0, limiter.AvailableTokens, 1);

        // Advance time by 3 seconds (3MB generated, capped at 2MB burst)
        var future = now.AddSeconds(3);
        var decision = limiter.Request(1, future);

        Assert.True(decision.IsAllowedImmediately);
        Assert.Equal(2_000_000 - 1, limiter.AvailableTokens, 1);
    }

    [Fact]
    public void Gate456_DownloadTokenBucketRateLimiter_DynamicRateAdjustment_PreservesTokens()
    {
        var now = DateTime.UtcNow;
        var limiter = new DownloadTokenBucketRateLimiter(rateBytesPerSec: 1_000_000, burstCapacityBytes: 2_000_000, initialTime: now);

        limiter.Request(1_000_000, now);
        Assert.Equal(1_000_000, limiter.AvailableTokens, 1);

        // Adjust rate to 5 MB/s
        limiter.SetRate(5_000_000, now);
        Assert.Equal(1_000_000, limiter.AvailableTokens, 1);
        Assert.Equal(5_000_000, limiter.RateBytesPerSec);
    }
}