using AcDream.Launcher.Core.Installation;
using AcDream.Launcher.Core.Integrity;
using AcDream.Launcher.Core.Launching;
using AcDream.Platform;

namespace AcDream.Launcher.Core.Tests.Installation;

/// <summary>
/// LU1. Ordinary startup used to SHA-256 the whole installed package before
/// the launcher window was constructed. That package is ~28 GiB in practice
/// and the hash measured 24.1 s, so the launcher took roughly half a minute
/// to appear while re-confirming a digest that had not changed since the
/// install wrote it.
///
/// <para>These tests pin the replacement: the cheap facts (size, last-write
/// time) still run on every startup, the hash is skipped only when a previous
/// full hash of that same file agreed with the install record, and every way
/// that agreement can be false falls back to hashing.</para>
/// </summary>
[Collection(WorkingDirectoryCollection.Name)]
public sealed class PreparedAssetVerificationCacheTests : IDisposable
{
    private const string PackageContent = "verified package";

    private readonly string _root = Path.Combine(
        Path.GetTempPath(),
        "acdream-verification-cache-tests",
        Guid.NewGuid().ToString("N"));
    private readonly ApplicationPathSet _paths;
    private readonly string _dats;
    private int _hashCount;

    public PreparedAssetVerificationCacheTests()
    {
        _paths = new ApplicationPathSet(
            Path.Combine(_root, "config"),
            Path.Combine(_root, "data"),
            Path.Combine(_root, "cache"),
            null);
        _dats = Path.Combine(_root, "retail-dats");
        Directory.CreateDirectory(_dats);
        foreach (string fileName in DatDirectoryLocator.RequiredFileNames)
        {
            File.WriteAllText(Path.Combine(_dats, fileName), "fixture");
        }
    }

    public void Dispose()
    {
        if (Directory.Exists(_root))
        {
            Directory.Delete(_root, recursive: true);
        }
    }

    [Fact]
    public async Task SecondStartupSkipsTheHashEntirely()
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();

        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(1, _hashCount);

        // The whole point of the slice: nothing is read from the package the
        // second time around.
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(1, _hashCount);
    }

    [Fact]
    public async Task ForcedFullVerificationHashesEvenWithAValidCache()
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(1, _hashCount);

        Assert.True((await store.LoadAndVerifyAsync(forceFullVerification: true))
            .IsVerified);
        Assert.Equal(2, _hashCount);
    }

    [Fact]
    public async Task ATouchedPackageIsHashedAgain()
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(1, _hashCount);

        // Same bytes, new write time: the cheap facts no longer match, so the
        // expensive one has to run. It still verifies, because the content is
        // in fact unchanged.
        File.SetLastWriteTimeUtc(
            store.PreparedAssetPath,
            File.GetLastWriteTimeUtc(store.PreparedAssetPath).AddMinutes(5));

        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(2, _hashCount);
    }

    [Fact]
    public async Task ASilentlyCorruptedPackageOfTheSameSizeStillFailsAndDropsTheCache()
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);

        // Identical length, so only the write time can betray it. Moved
        // explicitly rather than trusting the clock: see the companion test
        // below for why "the write just happened" is not the same as "the
        // write time changed".
        DateTime before = File.GetLastWriteTimeUtc(store.PreparedAssetPath);
        await File.WriteAllTextAsync(
            store.PreparedAssetPath,
            new string('x', PackageContent.Length));
        File.SetLastWriteTimeUtc(store.PreparedAssetPath, before.AddSeconds(1));

        InstallRecordVerification verification = await store.LoadAndVerifyAsync();

        Assert.False(verification.IsVerified);
        Assert.Contains("SHA-256", verification.Status, StringComparison.Ordinal);
        Assert.False(File.Exists(CachePath));
    }

    /// <summary>
    /// The honest limit of a size + write-time check, and why "Verify files"
    /// exists.
    ///
    /// <para>A modification that preserves BOTH the size and the write time is
    /// invisible to the startup check. That is not a theoretical hole: the
    /// Linux CI runner's /tmp is ZFS, whose timestamp granularity is coarse
    /// enough that 141 of 200 measured same-size rewrites produced an
    /// identical mtime. This test originally asserted that startup catches
    /// such a change, and it correctly failed there.</para>
    ///
    /// <para>So the contract is stated as two facts instead of one wrong one:
    /// startup does not catch it, and a forced full verification does. The
    /// launcher's Verify files button is that forced verification.</para>
    /// </summary>
    [Fact]
    public async Task CorruptionPreservingSizeAndWriteTimeIsCaughtOnlyByFullVerification()
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);

        DateTime original = File.GetLastWriteTimeUtc(store.PreparedAssetPath);
        await File.WriteAllTextAsync(
            store.PreparedAssetPath,
            new string('x', PackageContent.Length));
        File.SetLastWriteTimeUtc(store.PreparedAssetPath, original);

        // Startup trusts the remembered digest — nothing cheap can tell the
        // difference, and reading 28 GiB on every launch is the cost this
        // whole mechanism exists to avoid.
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);

        InstallRecordVerification forced =
            await store.LoadAndVerifyAsync(forceFullVerification: true);

        Assert.False(forced.IsVerified);
        Assert.Contains("SHA-256", forced.Status, StringComparison.Ordinal);
        Assert.False(File.Exists(CachePath));
    }

    [Fact]
    public async Task AResizedPackageIsRejectedWithoutHashingIt()
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(1, _hashCount);

        await File.WriteAllTextAsync(store.PreparedAssetPath, PackageContent + "!");

        InstallRecordVerification verification = await store.LoadAndVerifyAsync();

        Assert.False(verification.IsVerified);
        Assert.Contains("size changed", verification.Status, StringComparison.Ordinal);
        Assert.Equal(1, _hashCount);
    }

    [Fact]
    public async Task ACacheWhoseDigestDisagreesWithTheRecordIsIgnored()
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(1, _hashCount);

        // A cache entry that matches the FILE but not the RECORD must never
        // satisfy verification — otherwise a stale entry could vouch for a
        // package the current record does not describe.
        await File.WriteAllTextAsync(
            CachePath,
            (await File.ReadAllTextAsync(CachePath)).Replace(
                await FileIntegrity.ComputeSha256HexAsync(store.PreparedAssetPath),
                new string('a', 64),
                StringComparison.OrdinalIgnoreCase));

        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(2, _hashCount);
    }

    [Theory]
    [InlineData("")]
    [InlineData("{ not json")]
    [InlineData("{\"version\":9999}")]
    public async Task AnUnreadableCacheDegradesToHashingRatherThanFailing(string content)
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(1, _hashCount);

        await File.WriteAllTextAsync(CachePath, content);

        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(2, _hashCount);
    }

    [Fact]
    public async Task BackupRecoveryHashesTheBackupEvenWhenTheLiveCacheIsValid()
    {
        LauncherInstallRecordStore store = await CreateInstalledStoreAsync();
        Assert.True((await store.LoadAndVerifyAsync()).IsVerified);
        Assert.Equal(1, _hashCount);

        // Crash shape: the verified package was moved aside and what sits in
        // its place is wrong. The cache still describes the ORIGINAL bytes, so
        // if recovery trusted it the launcher would accept a bad package.
        string backup = LauncherInstallRecordStore.GetBackupPath(store.PreparedAssetPath);
        File.Move(store.PreparedAssetPath, backup);
        await File.WriteAllTextAsync(
            store.PreparedAssetPath,
            new string('z', PackageContent.Length));

        InstallRecordVerification verification = await store.LoadAndVerifyAsync();

        Assert.True(verification.IsVerified);
        Assert.Equal(PackageContent, await File.ReadAllTextAsync(store.PreparedAssetPath));
        Assert.False(File.Exists(backup));
        // Live package hashed (and failed), then the backup hashed.
        Assert.Equal(3, _hashCount);
    }

    private string CachePath => Path.Combine(
        Path.GetFullPath(_paths.DataDirectory),
        "install.verification.json");

    private async Task<LauncherInstallRecordStore> CreateInstalledStoreAsync()
    {
        var store = new LauncherInstallRecordStore(
            _paths,
            datDirectories: null,
            computeSha256: (path, cancellationToken) =>
            {
                Interlocked.Increment(ref _hashCount);
                return FileIntegrity.ComputeSha256HexAsync(path, cancellationToken);
            });

        Directory.CreateDirectory(Path.GetDirectoryName(store.PreparedAssetPath)!);
        await File.WriteAllTextAsync(store.PreparedAssetPath, PackageContent);
        var info = new FileInfo(store.PreparedAssetPath);
        await store.SaveAtomicallyAsync(new LauncherInstallRecord(
            Path.GetFullPath(_dats),
            Path.GetFullPath(store.PreparedAssetPath),
            await FileIntegrity.ComputeSha256HexAsync(store.PreparedAssetPath),
            info.Length,
            LauncherInstallRecordStore.CurrentBakeToolVersion));
        return store;
    }
}