using System.IO;
using System.Net.Http;
using System.Text.Json;

namespace DeskCore;

public record UpdateInfo(Version Version, string Tag, string PageUrl, string? SetupUrl, string? Notes);

/// <summary>Fragt das neueste Release auf Gitea ab (https://git.viper.ipv64.net/M_Viper/DeskCore/releases).</summary>
public static class UpdateChecker
{
    private const string Host = "git.viper.ipv64.net";
    private const string LatestApi = $"https://{Host}/api/v1/repos/M_Viper/DeskCore/releases/latest";
    public const string ReleasesPage = $"https://{Host}/M_Viper/DeskCore/releases";
    private const string SetupAsset = "DeskCore-Setup.exe";

    public static Version Current
    {
        get
        {
            var v = typeof(UpdateChecker).Assembly.GetName().Version ?? new Version(1, 0, 0);
            return new Version(v.Major, v.Minor, Math.Max(0, v.Build));
        }
    }

    private static HttpClient NewClient(TimeSpan timeout)
    {
        var http = new HttpClient { Timeout = timeout };
        http.DefaultRequestHeaders.UserAgent.ParseAdd($"DeskCore/{Current}");
        return http;
    }

    /// <summary>Neuere Version oder null. Wirft bei Netzwerk-/Serverfehlern.</summary>
    public static async Task<UpdateInfo?> CheckAsync(CancellationToken ct = default)
    {
        using var http = NewClient(TimeSpan.FromSeconds(15));
        using var resp = await http.GetAsync(LatestApi, ct);
        if (resp.StatusCode == System.Net.HttpStatusCode.NotFound)
            throw new InvalidOperationException("Es ist noch kein Release veröffentlicht (oder das Repository ist nicht öffentlich).");
        resp.EnsureSuccessStatusCode();

        using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync(ct));
        var root = doc.RootElement;
        var tag = root.GetProperty("tag_name").GetString() ?? "";
        if (!TryParseVersion(tag, out var version) || version <= Current) return null;

        string? setupUrl = null;
        if (root.TryGetProperty("assets", out var assets))
            foreach (var a in assets.EnumerateArray())
                if (string.Equals(a.GetProperty("name").GetString(), SetupAsset, StringComparison.OrdinalIgnoreCase))
                    setupUrl = a.GetProperty("browser_download_url").GetString();

        // Nur Downloads vom eigenen Server zulassen
        if (setupUrl is not null && !IsTrusted(setupUrl)) setupUrl = null;

        var page = root.TryGetProperty("html_url", out var h) ? h.GetString() : null;
        return new UpdateInfo(version, tag, page is not null && IsTrusted(page) ? page : ReleasesPage, setupUrl,
            root.TryGetProperty("body", out var b) ? b.GetString() : null);
    }

    /// <summary>Lädt den Installer in den Temp-Ordner und gibt den Pfad zurück.</summary>
    public static async Task<string> DownloadSetupAsync(UpdateInfo info, Action<long, long>? progress, CancellationToken ct)
    {
        if (info.SetupUrl is null) throw new InvalidOperationException("Im Release fehlt die Datei DeskCore-Setup.exe.");
        using var http = NewClient(TimeSpan.FromMinutes(10));
        using var resp = await http.GetAsync(info.SetupUrl, HttpCompletionOption.ResponseHeadersRead, ct);
        resp.EnsureSuccessStatusCode();
        long total = resp.Content.Headers.ContentLength ?? 0;

        var path = Path.Combine(Path.GetTempPath(), $"DeskCore-Setup-{info.Version}.exe");
        await using (var input = await resp.Content.ReadAsStreamAsync(ct))
        await using (var output = File.Create(path))
        {
            var buffer = new byte[81920];
            long done = 0;
            int read;
            while ((read = await input.ReadAsync(buffer, ct)) > 0)
            {
                await output.WriteAsync(buffer.AsMemory(0, read), ct);
                done += read;
                progress?.Invoke(done, total);
            }
        }
        return path;
    }

    private static bool IsTrusted(string url) =>
        Uri.TryCreate(url, UriKind.Absolute, out var u) && u.Scheme == Uri.UriSchemeHttps &&
        string.Equals(u.Host, Host, StringComparison.OrdinalIgnoreCase);

    public static bool TryParseVersion(string tag, out Version version)
    {
        var t = tag.Trim().TrimStart('v', 'V');
        if (Version.TryParse(t, out var v))
        {
            version = new Version(v.Major, v.Minor, Math.Max(0, v.Build));
            return true;
        }
        version = new Version(0, 0, 0);
        return false;
    }
}