using System.Text;
using SQLInsight.Licensing;
using SQLInsight.Rules.Lifecycle;

namespace SQLInsight.Updates;

public sealed record CheckedManifest(UpdateManifest Manifest, string Token);

/// <summary>
/// The unprivileged half of updating, run by the agent: reads the signed manifest, installs newer rule packs, and
/// downloads and stages application packages. It never replaces program files; <see cref="UpdateApplier"/> does that.
/// </summary>
public sealed class UpdateChecker(UpdateFeed feed, TrustedKeys keys, UpdateDirectories directories, string channel, TimeProvider time)
{
    public string Channel { get; } = channel;

    public async Task<CheckedManifest> FetchAsync(CancellationToken cancellationToken)
    {
        var token = await feed.ReadManifestAsync(Channel, cancellationToken).ConfigureAwait(false);
        var manifest = ManifestVerifier.Verify(token, keys, Channel, time.GetUtcNow(), directories.LastManifest(Channel));
        directories.RememberManifest(Channel, manifest.PublishedAt);
        return new CheckedManifest(manifest, token);
    }

    /// <summary>Downloads the manifest's rule pack if it is newer than <paramref name="current"/>. Returns the new pack or null.</summary>
    public async Task<RulePack?> UpdateRulePackAsync(CheckedManifest source, RulePack current, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(source);
        ArgumentNullException.ThrowIfNull(current);
        if (source.Manifest.RulePack is not { } reference || !Version.TryParse(reference.Version, out var offered) || offered <= current.Version)
        {
            return null;
        }

        var bytes = await feed.DownloadAsync(reference.File, cancellationToken).ConfigureAwait(false);
        RulePack pack;
        try
        {
            pack = RulePack.Parse(bytes, $"regelpakke fra {source.Manifest.Channel}-kanalen, {source.Manifest.PublishedAt:yyyy-MM-dd}");
        }
        catch (InvalidDataException ex)
        {
            throw new UpdateException(ex.Message, ex);
        }

        if (pack.Version != offered)
        {
            throw new UpdateException($"Regelpakkens version ({pack.Version}) svarer ikke til manifestet ({offered}).");
        }

        new RulePackStore(directories).Save(bytes, source.Token);
        return pack;
    }

    /// <summary>The release in the manifest if it is newer than the running version, otherwise null.</summary>
    public static AppRelease? NewerRelease(UpdateManifest manifest, AppVersion installed)
    {
        ArgumentNullException.ThrowIfNull(manifest);
        return manifest.Release is { } release && AppVersion.Parse(release.Version) > installed ? release : null;
    }

    /// <summary>
    /// Downloads the package for this platform into the pending folder, where the privileged updater picks it up.
    /// Returns false if there is nothing newer than <paramref name="installed"/>.
    /// </summary>
    public async Task<bool> StageAsync(CheckedManifest source, AppVersion installed, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(source);
        if (NewerRelease(source.Manifest, installed) is not { } release)
        {
            return false;
        }

        var asset = release.Assets.FirstOrDefault(a => string.Equals(a.Platform, Platform.Current, StringComparison.OrdinalIgnoreCase))
            ?? throw new UpdateException($"Version {release.Version} har ingen pakke til {Platform.Current}.");

        var package = Path.Combine(directories.Pending, "package.zip");
        var manifestFile = Path.Combine(directories.Pending, UpdateFeed.ManifestFile);
        if (File.Exists(package) && File.Exists(manifestFile) && await File.ReadAllTextAsync(manifestFile, cancellationToken).ConfigureAwait(false) == source.Token)
        {
            return true;
        }

        Directory.CreateDirectory(directories.Pending);
        File.Delete(manifestFile);
        var download = package + ".download";
        await feed.DownloadToFileAsync(asset.File, download, cancellationToken).ConfigureAwait(false);
        File.Move(download, package, overwrite: true);
        UpdateDirectories.WriteAtomic(manifestFile, Encoding.UTF8.GetBytes(source.Token));
        return true;
    }
}