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

namespace Paca.Tests.Core;

public class DynamicConcurrencyTunerGateTests
{
    [Fact]
    public void Gate237_DynamicConcurrencyTuner_Initializes_WithSensibleDefaults()
    {
        var tunerNormal = new DynamicConcurrencyTuner(isMetered: false);
        Assert.Equal(4, tunerNormal.CurrentConcurrency);
        Assert.Equal(16, tunerNormal.MaxConcurrency);

        var tunerMetered = new DynamicConcurrencyTuner(isMetered: true);
        Assert.Equal(2, tunerMetered.CurrentConcurrency);
        Assert.Equal(3, tunerMetered.MaxConcurrency);
    }

    [Fact]
    public void Gate238_DynamicConcurrencyTuner_ScalesUp_OnHighThroughputAndZeroErrors()
    {
        var tuner = new DynamicConcurrencyTuner(isMetered: false, initialConcurrency: 4);

        // Record 3 fast chunk completions without error (e.g. 10MB/s each)
        tuner.RecordChunkResult(bytesDownloaded: 5_000_000, durationMs: 500, isError: false);
        tuner.RecordChunkResult(bytesDownloaded: 5_000_000, durationMs: 480, isError: false);
        tuner.RecordChunkResult(bytesDownloaded: 5_000_000, durationMs: 450, isError: false);

        Assert.True(tuner.CurrentConcurrency > 4, $"Concurrency should scale up from 4, but is {tuner.CurrentConcurrency}");
    }

    [Fact]
    public void Gate239_DynamicConcurrencyTuner_ScalesDownImmediately_OnErrorOrRateLimit()
    {
        var tuner = new DynamicConcurrencyTuner(isMetered: false, initialConcurrency: 8);

        // Encounter network error or rate-limit
        tuner.RecordChunkResult(bytesDownloaded: 0, durationMs: 1000, isError: true, isRateLimited: true);

        Assert.True(tuner.CurrentConcurrency <= 4, $"Concurrency should be halved on error, but is {tuner.CurrentConcurrency}");
    }

    [Fact]
    public void Gate240_DynamicConcurrencyTuner_MeteredMode_StrictCap()
    {
        var tuner = new DynamicConcurrencyTuner(isMetered: true, initialConcurrency: 2);

        // Record 10 fast chunks
        for (int i = 0; i < 10; i++)
        {
            tuner.RecordChunkResult(bytesDownloaded: 10_000_000, durationMs: 200, isError: false);
        }

        Assert.True(tuner.CurrentConcurrency <= 3, $"Metered concurrency must not exceed 3, but is {tuner.CurrentConcurrency}");
    }
}