using System.Text;
using System.Text.Json;
using System.Runtime.CompilerServices;
using Xunit;

namespace StellaOps.TestKit.Assertions;

/// <summary>
/// Provides snapshot testing assertions for golden master testing.
/// Snapshots are stored in the test project's `Snapshots/` directory.
/// </summary>
/// <remarks>
/// Usage:
/// <code>
/// [Fact]
/// public void TestSbomGeneration()
/// {
///     var sbom = GenerateSbom();
///
///     // Snapshot will be stored in Snapshots/TestSbomGeneration.json
///     SnapshotAssert.MatchesSnapshot(sbom, snapshotName: "TestSbomGeneration");
/// }
/// </code>
///
/// To update snapshots (e.g., after intentional changes), set environment variable:
/// UPDATE_SNAPSHOTS=1 dotnet test
/// </remarks>
public static class SnapshotAssert
{
    private static readonly bool UpdateSnapshotsMode =
        global::System.Environment.GetEnvironmentVariable("UPDATE_SNAPSHOTS") == "1";

    /// <summary>
    /// Resolves the default snapshot directory for a caller.
    /// </summary>
    /// <remarks>
    /// If the caller source file lives inside a <c>Snapshots</c> directory, that directory is used so
    /// snapshots stay source-controlled and deterministic across environments.
    /// Otherwise the legacy runtime path (<c>current working directory/Snapshots</c>) is used.
    /// </remarks>
    public static string ResolveDefaultSnapshotsDirectory([CallerFilePath] string callerFilePath = "")
    {
        if (!string.IsNullOrWhiteSpace(callerFilePath))
        {
            var callerDirectory = Path.GetDirectoryName(callerFilePath);
            if (!string.IsNullOrWhiteSpace(callerDirectory))
            {
                if (string.Equals(
                    Path.GetFileName(callerDirectory),
                    "Snapshots",
                    StringComparison.OrdinalIgnoreCase))
                {
                    return callerDirectory;
                }

                var siblingSnapshots = Path.Combine(callerDirectory, "Snapshots");
                if (Directory.Exists(siblingSnapshots))
                {
                    return siblingSnapshots;
                }
            }
        }

        return Path.Combine(Directory.GetCurrentDirectory(), "Snapshots");
    }

    /// <summary>
    /// Asserts that the value matches the stored snapshot. If UPDATE_SNAPSHOTS=1, updates the snapshot.
    /// </summary>
    /// <param name="value">The value to snapshot (will be JSON-serialized).</param>
    /// <param name="snapshotName">The snapshot name (filename without extension).</param>
    /// <param name="snapshotsDirectory">Optional directory for snapshots (default: "Snapshots" in test project).</param>
    public static void MatchesSnapshot<T>(
        T value,
        string snapshotName,
        string? snapshotsDirectory = null,
        [CallerFilePath] string callerFilePath = "")
    {
        snapshotsDirectory ??= ResolveDefaultSnapshotsDirectory(callerFilePath);
        Directory.CreateDirectory(snapshotsDirectory);

        string snapshotPath = Path.Combine(snapshotsDirectory, $"{snapshotName}.json");

        // Serialize to pretty JSON for readability
        string actualJson = JsonSerializer.Serialize(value, new JsonSerializerOptions
        {
            WriteIndented = true,
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase
        });

        if (UpdateSnapshotsMode)
        {
            // Update snapshot
            File.WriteAllText(snapshotPath, actualJson, Encoding.UTF8);
            return; // Don't assert in update mode
        }

        // Verify snapshot exists
        Assert.True(File.Exists(snapshotPath),
            $"Snapshot '{snapshotName}' not found at {snapshotPath}. Run with UPDATE_SNAPSHOTS=1 to create it.");

        // Compare with stored snapshot
        string expectedJson = File.ReadAllText(snapshotPath, Encoding.UTF8);

        Assert.Equal(expectedJson, actualJson);
    }

    /// <summary>
    /// Asserts that the text matches the stored snapshot.
    /// </summary>
    public static void MatchesTextSnapshot(
        string value,
        string snapshotName,
        string? snapshotsDirectory = null,
        [CallerFilePath] string callerFilePath = "")
    {
        snapshotsDirectory ??= ResolveDefaultSnapshotsDirectory(callerFilePath);
        Directory.CreateDirectory(snapshotsDirectory);

        string snapshotPath = Path.Combine(snapshotsDirectory, $"{snapshotName}.txt");

        if (UpdateSnapshotsMode)
        {
            File.WriteAllText(snapshotPath, value, Encoding.UTF8);
            return;
        }

        Assert.True(File.Exists(snapshotPath),
            $"Snapshot '{snapshotName}' not found at {snapshotPath}. Run with UPDATE_SNAPSHOTS=1 to create it.");

        string expected = File.ReadAllText(snapshotPath, Encoding.UTF8);
        Assert.Equal(expected, value);
    }

    /// <summary>
    /// Asserts that binary data matches the stored snapshot.
    /// </summary>
    public static void MatchesBinarySnapshot(
        byte[] value,
        string snapshotName,
        string? snapshotsDirectory = null,
        [CallerFilePath] string callerFilePath = "")
    {
        snapshotsDirectory ??= ResolveDefaultSnapshotsDirectory(callerFilePath);
        Directory.CreateDirectory(snapshotsDirectory);

        string snapshotPath = Path.Combine(snapshotsDirectory, $"{snapshotName}.bin");

        if (UpdateSnapshotsMode)
        {
            File.WriteAllBytes(snapshotPath, value);
            return;
        }

        Assert.True(File.Exists(snapshotPath),
            $"Snapshot '{snapshotName}' not found at {snapshotPath}. Run with UPDATE_SNAPSHOTS=1 to create it.");

        byte[] expected = File.ReadAllBytes(snapshotPath);
        Assert.Equal(expected, value);
    }
}