using System.Text.RegularExpressions;

namespace AcDream.App.Tests.Diagnostics;

/// <summary>
/// Keeps <c>docs/launch-options.md</c> honest: every environment variable the
/// shipped client reads must have a documented row, and every documented row
/// must name a variable something actually reads.
/// </summary>
/// <remarks>
/// <para>
/// A hand-maintained list of ~170 flags goes stale within a week. #432 is what
/// that costs: <c>ACDREAM_AUTOMATION_ARTIFACT_DIR</c> read like an output-path
/// setting but also constructed a per-frame diagnostics referee worth ~6 MB and
/// ~14 ms every frame, and three days of measurements were taxed before anyone
/// noticed. The same audit found CLAUDE.md still advertising
/// <c>ACDREAM_RUN_SKILL</c> / <c>ACDREAM_JUMP_SKILL</c> after their read sites
/// were deleted. Both directions of drift are failures, so both fail here.
/// </para>
/// <para>
/// Scope is <c>src/</c> only. Test-owned variables, shader-compiler macro
/// tokens under <c>tools/</c>, and historical mentions in dated research
/// documents are deliberately out of scope — the doc describes what a launched
/// client reads today.
/// </para>
/// </remarks>
public sealed class LaunchOptionsDocumentationTests
{
    private const string DocRelativePath = "docs/launch-options.md";

    /// <summary>
    /// Structure rule 5 wants runtime flags behind diagnostic owner classes and
    /// rule 4 wants startup configuration in <c>RuntimeOptions</c>. These files
    /// still read the environment directly, with the exact number of distinct
    /// flags each one reads today.
    /// </summary>
    /// <remarks>
    /// The counts are FROZEN, not merely the file names: promoting a stray to
    /// its subsystem's owner lowers a number (update it here), and adding a new
    /// direct read raises one and fails. A file that reaches zero leaves the
    /// table entirely.
    /// </remarks>
    private static readonly IReadOnlyDictionary<string, int> DirectReadDebt =
        new Dictionary<string, int>(StringComparer.Ordinal)
        {
            ["src/AcDream.App/Physics/LiveEntityNetworkUpdateController.cs"] = 2,
            ["src/AcDream.App/Physics/RemoteServerControlledVelocityCycle.cs"] = 1,
            ["src/AcDream.App/Platform/GraphicalWindowBackendSelection.cs"] = 1,
            ["src/AcDream.App/Rendering/GameWindow.cs"] = 1,
            ["src/AcDream.App/Rendering/PortalVisibilityBuilder.cs"] = 1,
            ["src/AcDream.App/Rendering/Sky/SkyRenderer.cs"] = 1,
            ["src/AcDream.App/Rendering/TextureCache.cs"] = 1,
            ["src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs"] = 2,
            ["src/AcDream.Core/Physics/TransitionTypes.cs"] = 2,
            ["src/AcDream.Core/Vfx/PhysicsScriptRunner.cs"] = 1,
            ["src/AcDream.Core/World/SkyDescLoader.cs"] = 2,
            ["src/AcDream.Core.Net/GameEventWiring.cs"] = 1,
            ["src/AcDream.Core.Net/Messages/PlayerDescriptionParser.cs"] = 1,
            ["src/AcDream.Core.Net/Messages/UpdateMotion.cs"] = 1,
            ["src/AcDream.Core.Net/WorldSession.cs"] = 3,
            ["src/AcDream.Platform/ApplicationPathSet.cs"] = 3,
            ["src/AcDream.Platform/BakePublicationGuardPaths.cs"] = 1,
            ["src/AcDream.Runtime/Physics/RuntimeRemotePhysicsUpdater.cs"] = 1,
            ["src/AcDream.UI.Abstractions/Settings/QualityPreset.cs"] = 6,
        };

    /// <summary>
    /// Any <c>ACDREAM_*</c> string literal in <c>src/</c>. Matching the literal
    /// rather than a <c>GetEnvironmentVariable</c> call is deliberate: the
    /// startup path reads through an injected <c>env</c> delegate
    /// (<c>RuntimeOptions.Parse</c>) so a call-shaped pattern silently missed
    /// ACDREAM_LIVE, ACDREAM_PAK_PATH and every other production flag. Comment
    /// mentions (shader macros such as ACDREAM_SAMPLE_2D, prefix fragments)
    /// carry no quotes and stay out.
    /// </summary>
    private static readonly Regex EnvironmentRead = new(
        @"""(ACDREAM_[A-Z0-9_]+)""",
        RegexOptions.Compiled);

    private static readonly Regex DocumentedRow = new(
        @"^\|\s*`(ACDREAM_[A-Z0-9_]+)`",
        RegexOptions.Compiled | RegexOptions.Multiline);

    [Fact]
    public void EveryEnvironmentVariableTheClientReadsIsDocumented()
    {
        IReadOnlySet<string> read = ReadFlags();
        IReadOnlySet<string> documented = DocumentedFlags();

        List<string> undocumented = read.Except(documented).Order(StringComparer.Ordinal).ToList();
        Assert.True(
            undocumented.Count == 0,
            $"{DocRelativePath} is missing a row for flags the client reads: "
            + string.Join(", ", undocumented)
            + ". Add the row in the same commit that adds the read site.");
    }

    [Fact]
    public void EveryDocumentedEnvironmentVariableStillExists()
    {
        IReadOnlySet<string> read = ReadFlags();
        IReadOnlySet<string> documented = DocumentedFlags();

        List<string> phantom = documented.Except(read).Order(StringComparer.Ordinal).ToList();
        Assert.True(
            phantom.Count == 0,
            $"{DocRelativePath} documents flags nothing in src/ reads: "
            + string.Join(", ", phantom)
            + ". Delete the row (or move it to the retired section with its "
            + "removal commit) in the same commit that deletes the read site.");
    }

    [Fact]
    public void DirectEnvironmentReadsOutsideOwnerClassesDoNotGrow()
    {
        Dictionary<string, int> actual = SourceFiles()
            .Where(file => !IsOwnerClass(file.RelativePath))
            .Select(file => (
                file.RelativePath,
                Count: DistinctFlagsRead(File.ReadAllText(file.Path))))
            .Where(file => file.Count > 0)
            .ToDictionary(file => file.RelativePath, file => file.Count, StringComparer.Ordinal);

        List<string> problems = [];
        foreach ((string path, int count) in actual.OrderBy(pair => pair.Key, StringComparer.Ordinal))
        {
            if (!DirectReadDebt.TryGetValue(path, out int frozen))
            {
                problems.Add(
                    $"{path} reads {count} ACDREAM_* variable(s) directly but is "
                    + "not an owner class. Add the property to the subsystem's "
                    + "diagnostics owner (or RuntimeOptions) and read it there.");
            }
            else if (count > frozen)
            {
                problems.Add(
                    $"{path} grew from {frozen} to {count} direct reads. New "
                    + "flags belong in an owner class, not here.");
            }
        }

        foreach ((string path, int frozen) in DirectReadDebt.OrderBy(pair => pair.Key, StringComparer.Ordinal))
        {
            int count = actual.GetValueOrDefault(path, 0);
            if (count < frozen)
            {
                problems.Add(
                    $"{path} is down to {count} direct read(s) from {frozen}. "
                    + "Lower the frozen count (or drop the entry at zero) so the "
                    + "debt cannot silently grow back.");
            }
        }

        Assert.True(problems.Count == 0, string.Join("\n", problems));
    }

    private static bool IsOwnerClass(string relativePath)
    {
        // The intended homes for environment reads: one static diagnostics
        // class per subsystem, the typed startup options objects, the
        // executables' own entry points, and the single-purpose probe/capture
        // owners (a file that exists only to own one probe already satisfies
        // the rule the *Diagnostics.cs suffix encodes).
        string name = Path.GetFileName(relativePath);
        return name.EndsWith("Diagnostics.cs", StringComparison.Ordinal)
            || name.EndsWith("Options.cs", StringComparison.Ordinal)
            || name.EndsWith("Probe.cs", StringComparison.Ordinal)
            || name.EndsWith("Capture.cs", StringComparison.Ordinal)
            || name == "Program.cs";
    }

    private static int DistinctFlagsRead(string source)
    {
        var flags = new HashSet<string>(StringComparer.Ordinal);
        foreach (Match match in EnvironmentRead.Matches(source))
            flags.Add(match.Groups[1].Value);
        return flags.Count;
    }

    private static IReadOnlySet<string> ReadFlags()
    {
        var flags = new HashSet<string>(StringComparer.Ordinal);
        foreach ((string path, _) in SourceFiles())
        {
            foreach (Match match in EnvironmentRead.Matches(File.ReadAllText(path)))
                flags.Add(match.Groups[1].Value);
        }

        Assert.True(
            flags.Count > 100,
            $"Only found {flags.Count} environment reads in src/; the scanner "
            + "is probably broken rather than the codebase suddenly clean.");
        return flags;
    }

    private static IReadOnlySet<string> DocumentedFlags()
    {
        string doc = Path.Combine(FindRepoRoot(), DocRelativePath.Replace('/', Path.DirectorySeparatorChar));
        Assert.True(File.Exists(doc), $"{DocRelativePath} is missing.");

        string text = File.ReadAllText(doc);
        // Rows below the retired marker describe flags that are deliberately
        // gone; they document history and must not resurrect the read-site
        // requirement.
        int retired = text.IndexOf("<!-- retired -->", StringComparison.Ordinal);
        if (retired >= 0)
            text = text[..retired];

        var flags = new HashSet<string>(StringComparer.Ordinal);
        foreach (Match match in DocumentedRow.Matches(text))
            flags.Add(match.Groups[1].Value);
        return flags;
    }

    private static IEnumerable<(string Path, string RelativePath)> SourceFiles()
    {
        string root = FindRepoRoot();
        string src = Path.Combine(root, "src");
        foreach (string path in Directory.EnumerateFiles(src, "*.cs", SearchOption.AllDirectories))
        {
            string relative = Path.GetRelativePath(root, path).Replace('\\', '/');
            if (relative.Contains("/bin/", StringComparison.Ordinal)
                || relative.Contains("/obj/", StringComparison.Ordinal))
            {
                continue;
            }

            yield return (path, relative);
        }
    }

    private static string FindRepoRoot()
    {
        DirectoryInfo? directory = new(AppContext.BaseDirectory);
        while (directory is not null)
        {
            if (File.Exists(Path.Combine(directory.FullName, "AcDream.slnx")))
                return directory.FullName;
            directory = directory.Parent;
        }

        throw new DirectoryNotFoundException("Could not find AcDream.slnx.");
    }
}