using FluentAssertions;
using System.Diagnostics;
using Vav1Player.Container;

namespace Vav1Player.Tests.Container;

public class Av1BitstreamParserPerformanceTests
{
    [Fact]
    public void ParseMp4Sample_WithLargeValidSample_ShouldCompleteWithinTimeLimit()
    {
        // Arrange - Create large but valid sample (5MB total)
        var obuCount = 100;
        var obuSize = 50_000; // 50KB per OBU
        var sampleData = CreateLargeSampleData(obuCount, obuSize);

        var stopwatch = Stopwatch.StartNew();

        // Act
        var result = Av1BitstreamParser.ParseMp4Sample(sampleData);

        // Assert
        stopwatch.Stop();

        result.Should().HaveCount(obuCount);
        result.All(obu => obu.Length == obuSize).Should().BeTrue();

        // Performance assertion - should complete within 100ms for 5MB
        stopwatch.ElapsedMilliseconds.Should().BeLessThan(100,
            "because parsing 5MB of valid OBU data should be fast");
    }

    [Fact]
    public void ParseMp4Sample_WithManySmallOBUs_ShouldScaleLinearly()
    {
        // Arrange - Test with different numbers of small OBUs
        var testCases = new[] { 100, 500, 1000 };
        var timings = new List<long>();

        foreach (var obuCount in testCases)
        {
            var sampleData = CreateLargeSampleData(obuCount, 100); // 100 bytes per OBU

            var stopwatch = Stopwatch.StartNew();

            // Act
            var result = Av1BitstreamParser.ParseMp4Sample(sampleData);

            stopwatch.Stop();
            timings.Add(stopwatch.ElapsedMilliseconds);

            // Assert correctness
            result.Should().HaveCount(obuCount);
        }

        // Performance assertion - should scale roughly linearly
        // Time for 1000 OBUs should be less than 10x time for 100 OBUs
        var ratio = (double)timings[2] / Math.Max(timings[0], 1);
        ratio.Should().BeLessThan(10.0,
            "because parsing should scale roughly linearly with OBU count");
    }

    [Fact]
    public void CombineOBUs_WithLargeDataSet_ShouldCompleteQuickly()
    {
        // Arrange - Create 1000 OBUs of 1KB each (headers without size field)
        var obuList = new List<byte[]>();
        for (int i = 0; i < 1000; i++)
        {
            var obu = new byte[1024];
            obu[0] = (byte)(i & 0xFC); // Ensure bit 1 (size field) is 0
            // Fill with pattern
            for (int j = 1; j < obu.Length; j++)
            {
                obu[j] = (byte)((i + j) & 0xFF);
            }
            obuList.Add(obu);
        }

        var stopwatch = Stopwatch.StartNew();

        // Act
        var result = Av1BitstreamParser.CombineOBUs(obuList);

        // Assert
        stopwatch.Stop();

        // Should be larger than original due to added size fields (~1MB + size fields)
        result.Length.Should().BeGreaterThan(1000 * 1024); // Original 1MB + size overhead

        // Performance assertion - should complete within 50ms for ~1MB
        stopwatch.ElapsedMilliseconds.Should().BeLessThan(50,
            "because combining 1MB of OBU data should be fast");
    }

    [Fact]
    public void ParseMp4Sample_WithMaxSizeLEB128_ShouldHandleEfficiently()
    {
        // Arrange - Create sample with maximum reasonable LEB128 values
        var samples = new List<byte[]>();

        // Test various LEB128 sizes: 1-byte, 2-byte, 3-byte
        samples.Add(CreateSampleWithLEB128Size(127, 1));           // 1-byte LEB128
        samples.Add(CreateSampleWithLEB128Size(16383, 2));         // 2-byte LEB128
        samples.Add(CreateSampleWithLEB128Size(2097151, 3));       // 3-byte LEB128

        foreach (var sampleData in samples)
        {
            var stopwatch = Stopwatch.StartNew();

            // Act
            var result = Av1BitstreamParser.ParseMp4Sample(sampleData);

            stopwatch.Stop();

            // Assert
            result.Should().HaveCount(1);

            // Performance assertion - even large LEB128 should parse quickly
            stopwatch.ElapsedMilliseconds.Should().BeLessThan(10,
                "because LEB128 parsing should be efficient regardless of size");
        }
    }

    [Fact]
    public void ParseMp4Sample_WithInvalidData_ShouldFailFast()
    {
        // Arrange - Various types of invalid data that should fail quickly
        var invalidSamples = new[]
        {
            new byte[] { 0x80, 0x80, 0x80, 0x80, 0x80 },  // Truncated LEB128
            new byte[] { 0xFF, 0xFF, 0xFF, 0xFF, 0x0F },  // Oversized LEB128
            new byte[] { 0x80, 0x00 },                     // Invalid multi-byte zero
            new byte[0],                                   // Empty data
            new byte[] { 0x10, 0x01, 0x02 }               // Length=16 but only 2 bytes
        };

        foreach (var invalidData in invalidSamples)
        {
            var stopwatch = Stopwatch.StartNew();

            // Act
            var result = Av1BitstreamParser.ParseMp4Sample(invalidData);

            stopwatch.Stop();

            // Assert
            result.Should().BeEmpty();

            // Performance assertion - should fail fast
            stopwatch.ElapsedMilliseconds.Should().BeLessThan(5,
                "because invalid data should be rejected quickly");
        }
    }

    [Fact]
    public void ParseMp4Sample_StressTest_ShouldHandleRepeatedParsing()
    {
        // Arrange - Medium-sized sample that will be parsed many times
        var sampleData = CreateLargeSampleData(50, 1000); // 50 OBUs of 1KB each
        const int iterations = 1000;

        var stopwatch = Stopwatch.StartNew();

        // Act - Parse the same data many times
        for (int i = 0; i < iterations; i++)
        {
            var result = Av1BitstreamParser.ParseMp4Sample(sampleData);
            result.Should().HaveCount(50); // Sanity check
        }

        // Assert
        stopwatch.Stop();

        var avgTimePerParse = stopwatch.ElapsedMilliseconds / (double)iterations;

        // Performance assertion - average parse time should be reasonable
        avgTimePerParse.Should().BeLessThan(1.0,
            "because repeated parsing of the same data should be consistently fast");
    }

    [Theory]
    [InlineData(10, 100)]      // Small: 10 OBUs × 100 bytes
    [InlineData(100, 1000)]    // Medium: 100 OBUs × 1KB
    [InlineData(50, 10000)]    // Large: 50 OBUs × 10KB
    public void ParseMp4Sample_VariousDataSizes_ShouldCompleteReasonably(int obuCount, int obuSize)
    {
        // Arrange
        var sampleData = CreateLargeSampleData(obuCount, obuSize);
        var totalSize = obuCount * obuSize;

        var stopwatch = Stopwatch.StartNew();

        // Act
        var result = Av1BitstreamParser.ParseMp4Sample(sampleData);

        // Assert
        stopwatch.Stop();

        result.Should().HaveCount(obuCount);

        // Performance target: should complete within reasonable time (less than 1 second for reasonable data sizes)
        stopwatch.ElapsedMilliseconds.Should().BeLessThan(1000,
            $"because parsing {totalSize} bytes should complete within 1 second (actual: {stopwatch.ElapsedMilliseconds}ms)");
    }

    private static byte[] CreateLargeSampleData(int obuCount, int obuSize)
    {
        var sampleList = new List<byte>();

        for (int i = 0; i < obuCount; i++)
        {
            // Add LEB128 length
            var lengthBytes = EncodeLEB128((uint)obuSize);
            sampleList.AddRange(lengthBytes);

            // Add OBU data with pattern
            for (int j = 0; j < obuSize; j++)
            {
                sampleList.Add((byte)((i + j) & 0xFF));
            }
        }

        return sampleList.ToArray();
    }

    private static byte[] CreateSampleWithLEB128Size(uint value, int expectedBytes)
    {
        var lengthBytes = EncodeLEB128(value);
        lengthBytes.Length.Should().Be(expectedBytes, $"LEB128 encoding of {value} should use {expectedBytes} bytes");

        var obuData = new byte[value];
        for (int i = 0; i < obuData.Length; i++)
        {
            obuData[i] = (byte)(i & 0xFF);
        }

        var result = new byte[lengthBytes.Length + obuData.Length];
        Array.Copy(lengthBytes, 0, result, 0, lengthBytes.Length);
        Array.Copy(obuData, 0, result, lengthBytes.Length, obuData.Length);

        return result;
    }

    private static byte[] EncodeLEB128(uint value)
    {
        var bytes = new List<byte>();

        while (value >= 0x80)
        {
            bytes.Add((byte)((value & 0x7F) | 0x80));
            value >>= 7;
        }
        bytes.Add((byte)(value & 0x7F));

        return bytes.ToArray();
    }
}