using ClawdDotNet.App.Services;
using ClawdDotNet.Core.Config;
using Microsoft.Extensions.Logging.Abstractions;
using Shouldly;

namespace ClawdDotNet.App.Tests.Services;

/// <summary>
/// The daily backup, since it belongs to the instance (#528, stage 1).
///
/// <para>Switch, time, target folder and retention lived in the
/// application settings and thus applied to every instance. Two consequences: whoever
/// enabled the backup for one instance enabled it for all — and all
/// archives lay in one folder in which retention cleans up by the prefix
/// <c>backup_&lt;Instanzname&gt;_</c>. That a prefix is not a boundary is shown by
/// <see cref="In_the_shared_folder_retention_reaches_beyond_the_instance"/>.</para>
/// </summary>
public sealed class BackupSchedulerTests : IDisposable
{
    private readonly string _root = Path.Combine(
        Path.GetTempPath(), "clawd-tests", "backup-" + Guid.NewGuid().ToString("N")[..8]);

    public void Dispose()
    {
        try { Directory.Delete(_root, recursive: true); }
        catch { /* A leftover test folder does not turn a run red. */ }
    }

    /// <summary>An instance directory with enough content that a backup is worthwhile.</summary>
    private string NewInstance(string name)
    {
        var dir = Path.Combine(_root, "Instance-" + name);
        Directory.CreateDirectory(dir);
        File.WriteAllText(Path.Combine(dir, "InstanceSettings.json"), $$"""{"instanceName":"{{name}}"}""");
        return dir;
    }

    private static InstanceConfig Config(string name, string? backupDirectory = null, int keep = 14)
        => new()
        {
            InstanceName = name,
            WorkingDirectory = "",
            AutoBackupEnabled = true,
            AutoBackupTime = "03:00",
            BackupDirectory = backupDirectory ?? "",
            BackupKeepCount = keep
        };

    /// <summary>
    /// A clock standing at a time — the point in time decides whether
    /// <c>TickAsync</c> does anything.
    /// </summary>
    private sealed class FixedClock(DateTime jetzt) : TimeProvider
    {
        public override DateTimeOffset GetUtcNow() => new(jetzt, TimeSpan.Zero);
        public override TimeZoneInfo LocalTimeZone => TimeZoneInfo.Utc;
    }

    private static BackupScheduler Scheduler(string dir, InstanceConfig config, DateTime now)
        => new(dir, config, NullLogger.Instance, new FixedClock(now));

    private static DateTime AtNight(int tag) => new(2026, 9, tag, 4, 0, 0, DateTimeKind.Utc);

    // ─── The target folder ───

    [Fact]
    public async Task Without_value_the_backup_ends_up_in_the_instance_directory()
    {
        var dir = NewInstance("Allein");

        await Scheduler(dir, Config("Allein"), AtNight(1)).TickAsync();

        var ziel = Path.Combine(dir, "Backups");
        Directory.Exists(ziel).ShouldBeTrue();
        Directory.GetFiles(ziel, "*.zip").Length.ShouldBe(1);
    }

    [Fact]
    public async Task Two_instances_without_value_back_up_separately()
    {
        var a = NewInstance("Eins");
        var b = NewInstance("Zwei");

        await Scheduler(a, Config("Eins"), AtNight(1)).TickAsync();
        await Scheduler(b, Config("Zwei"), AtNight(1)).TickAsync();

        Directory.GetFiles(Path.Combine(a, "Backups"), "*.zip").Length.ShouldBe(1);
        Directory.GetFiles(Path.Combine(b, "Backups"), "*.zip").Length.ShouldBe(1);
    }

    // ─── The switch ───

    [Fact]
    public async Task Switched_off_nothing_happens()
    {
        var dir = NewInstance("Ruhig");
        var config = Config("Ruhig");
        config.AutoBackupEnabled = false;

        await Scheduler(dir, config, AtNight(1)).TickAsync();

        Directory.Exists(Path.Combine(dir, "Backups")).ShouldBeFalse();
    }

    [Fact]
    public async Task Before_the_configured_time_nothing_happens()
    {
        var dir = NewInstance("Frueh");

        await Scheduler(dir, Config("Frueh"), new DateTime(2026, 9, 1, 2, 0, 0, DateTimeKind.Utc))
            .TickAsync();

        Directory.Exists(Path.Combine(dir, "Backups")).ShouldBeFalse();
    }

    [Fact]
    public async Task Twice_on_the_same_day_backs_up_only_once()
    {
        var dir = NewInstance("Einmal");
        var scheduler = Scheduler(dir, Config("Einmal"), AtNight(1));

        await scheduler.TickAsync();
        await scheduler.TickAsync();

        Directory.GetFiles(Path.Combine(dir, "Backups"), "*.zip").Length.ShouldBe(1);
    }

    // ─── Retention ───

    [Fact]
    public async Task Retention_cleans_up_its_own_archives()
    {
        var dir = NewInstance("Alt");
        var ziel = Path.Combine(dir, "Backups");
        Directory.CreateDirectory(ziel);

        // Three archives from the past that are older than the one about to be created.
        foreach (var tag in new[] { 1, 2, 3 })
        {
            var datei = Path.Combine(ziel, $"backup_Alt_2026-08-0{tag}_0300.zip");
            File.WriteAllText(datei, "alt");
            File.SetLastWriteTime(datei, new DateTime(2026, 8, tag, 3, 0, 0));
        }

        await Scheduler(dir, Config("Alt", keep: 2), AtNight(1)).TickAsync();

        Directory.GetFiles(ziel, "*.zip").Length.ShouldBe(2);
    }

    [Fact]
    public async Task Retention_zero_keeps_everything()
    {
        var dir = NewInstance("Sammler");
        var ziel = Path.Combine(dir, "Backups");
        Directory.CreateDirectory(ziel);
        File.WriteAllText(Path.Combine(ziel, "backup_Sammler_2026-08-01_0300.zip"), "alt");

        await Scheduler(dir, Config("Sammler", keep: 0), AtNight(1)).TickAsync();

        Directory.GetFiles(ziel, "*.zip").Length.ShouldBe(2);
    }

    /// <summary>
    /// Why the target folder has to belong to the instance.
    ///
    /// <para>Retention looks for the prefix <c>backup_&lt;Instanzname&gt;_</c>,
    /// and a prefix is not a boundary: <c>backup_Test_2_….zip</c> — the archive of the
    /// instance <c>Test_2</c> — starts with <c>backup_Test_</c>. In the shared folder
    /// <c>Test</c> therefore counts it among its own and throws it away. Separate folders
    /// take away the effect of the naming question: the test here deliberately restores the old state
    /// by entering the same folder for both instances.</para>
    /// </summary>
    [Fact]
    public async Task In_the_shared_folder_retention_reaches_beyond_the_instance()
    {
        var shared = Path.Combine(_root, "Backups");
        Directory.CreateDirectory(shared);

        var foreign = Path.Combine(shared, "backup_Test_2_2026-08-01_0300.zip");
        File.WriteAllText(foreign, "gehoert Test_2");
        File.SetLastWriteTime(foreign, new DateTime(2026, 8, 1, 3, 0, 0));

        var dir = NewInstance("Test");
        await Scheduler(dir, Config("Test", shared, keep: 1), AtNight(1)).TickAsync();

        File.Exists(foreign).ShouldBeFalse(
            "Der alte Zustand ist damit belegt — im gemeinsamen Ordner räumt eine "
            + "Instanz über ihre eigenen Archive hinaus auf.");

        // And the counter-check: with separate folders they do not get in each other's way.
        var own = NewInstance("Test2");
        var ownArchive = Path.Combine(own, "Backups", "backup_Test2_2026-08-01_0300.zip");
        Directory.CreateDirectory(Path.GetDirectoryName(ownArchive)!);
        File.WriteAllText(ownArchive, "gehoert Test2");

        var dir2 = NewInstance("Test3");
        await Scheduler(dir2, Config("Test3", keep: 1), AtNight(2)).TickAsync();

        File.Exists(ownArchive).ShouldBeTrue();
    }
}