using System.Diagnostics;
using System.Net;
using System.Net.Http.Headers;
using System.Reflection;
using System.Security.Cryptography;
using System.Text.Json;
using System.Text.Json.Serialization;
using KronaStaffTerminal.Models;

namespace KronaStaffTerminal.Services;

public sealed record AvailableUpdate(
    Version Version,
    string DisplayVersion,
    string ReleaseName,
    string ReleaseNotes,
    Uri ReleasePage,
    Uri InstallerUrl,
    Uri ChecksumUrl,
    string InstallerFileName);

public interface IUpdateSource
{
    Task<AvailableUpdate?> FindUpdateAsync(TerminalSettings settings, CancellationToken cancellationToken);
    Task<string> DownloadAndVerifyAsync(
        AvailableUpdate update,
        TerminalSettings settings,
        IProgress<double>? progress,
        CancellationToken cancellationToken);
}

public sealed class ForgejoUpdateSource : IUpdateSource
{
    private const string InstallerPrefix = "KronaStaffTerminal-Setup-";
    private static readonly HttpClient HttpClient = CreateHttpClient();

    public async Task<AvailableUpdate?> FindUpdateAsync(
        TerminalSettings settings,
        CancellationToken cancellationToken)
    {
        if (!Uri.TryCreate(settings.UpdateFeedUrl, UriKind.Absolute, out var feedUri) ||
            feedUri.Scheme != Uri.UriSchemeHttps)
        {
            throw new InvalidOperationException(
                "Адрес обновлений должен быть защищённым HTTPS-адресом Forgejo.");
        }

        using var request = CreateRequest(HttpMethod.Get, feedUri, settings.UpdateAccessToken);
        using var response = await HttpClient.SendAsync(
            request,
            HttpCompletionOption.ResponseHeadersRead,
            cancellationToken);
        if (response.StatusCode is HttpStatusCode.Unauthorized or
            HttpStatusCode.Forbidden or
            HttpStatusCode.NotFound)
        {
            throw new InvalidOperationException(
                "Нет доступа к обновлениям. Укажите токен чтения приватного репозитория в настройках.");
        }
        response.EnsureSuccessStatusCode();

        await using var stream = await response.Content.ReadAsStreamAsync(cancellationToken);
        var release = await JsonSerializer.DeserializeAsync<ForgejoRelease>(
                          stream,
                          cancellationToken: cancellationToken)
                      ?? throw new InvalidDataException("Forgejo вернул пустое описание релиза.");
        if (!TryParseVersion(release.TagName, out var releaseVersion) ||
            releaseVersion <= CurrentVersion)
        {
            return null;
        }

        var installer = release.Assets.FirstOrDefault(asset =>
            asset.Name.StartsWith(InstallerPrefix, StringComparison.OrdinalIgnoreCase) &&
            asset.Name.EndsWith(".exe", StringComparison.OrdinalIgnoreCase));
        var checksum = release.Assets.FirstOrDefault(asset =>
            string.Equals(asset.Name, installer?.Name + ".sha256", StringComparison.OrdinalIgnoreCase));
        if (installer is null ||
            checksum is null ||
            !Uri.TryCreate(installer.BrowserDownloadUrl, UriKind.Absolute, out var installerUri) ||
            !Uri.TryCreate(checksum.BrowserDownloadUrl, UriKind.Absolute, out var checksumUri) ||
            !Uri.TryCreate(release.HtmlUrl, UriKind.Absolute, out var releasePage))
        {
            throw new InvalidDataException(
                "В релизе нет установщика Windows или файла контрольной суммы.");
        }

        return new AvailableUpdate(
            releaseVersion,
            releaseVersion.ToString(3),
            string.IsNullOrWhiteSpace(release.Name)
                ? $"Krona Staff {releaseVersion.ToString(3)}"
                : release.Name,
            release.Body ?? "",
            releasePage,
            installerUri,
            checksumUri,
            installer.Name);
    }

    public async Task<string> DownloadAndVerifyAsync(
        AvailableUpdate update,
        TerminalSettings settings,
        IProgress<double>? progress,
        CancellationToken cancellationToken)
    {
        var updateDirectory = Path.Combine(
            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
            "Krona",
            "StaffTerminal",
            "updates",
            update.DisplayVersion);
        Directory.CreateDirectory(updateDirectory);
        var installerPath = Path.Combine(
            updateDirectory,
            Path.GetFileName(update.InstallerFileName));
        var temporaryPath = installerPath + ".download";

        using var checksumRequest = CreateRequest(
            HttpMethod.Get,
            update.ChecksumUrl,
            settings.UpdateAccessToken);
        using var checksumResponse = await HttpClient.SendAsync(
            checksumRequest,
            cancellationToken);
        checksumResponse.EnsureSuccessStatusCode();
        var checksumText = await checksumResponse.Content.ReadAsStringAsync(cancellationToken);
        var expectedHash = checksumText
            .Split((char[]?)null, StringSplitOptions.RemoveEmptyEntries)
            .FirstOrDefault();
        if (expectedHash is null ||
            expectedHash.Length != 64 ||
            expectedHash.Any(character => !Uri.IsHexDigit(character)))
        {
            throw new InvalidDataException(
                "Файл контрольной суммы обновления повреждён.");
        }

        using var installerRequest = CreateRequest(
            HttpMethod.Get,
            update.InstallerUrl,
            settings.UpdateAccessToken);
        using var installerResponse = await HttpClient.SendAsync(
            installerRequest,
            HttpCompletionOption.ResponseHeadersRead,
            cancellationToken);
        installerResponse.EnsureSuccessStatusCode();
        var totalBytes = installerResponse.Content.Headers.ContentLength;
        await using (var source = await installerResponse.Content.ReadAsStreamAsync(cancellationToken))
        await using (var destination = new FileStream(
                         temporaryPath,
                         FileMode.Create,
                         FileAccess.Write,
                         FileShare.None,
                         81920,
                         FileOptions.Asynchronous))
        {
            var buffer = new byte[81920];
            long received = 0;
            int count;
            while ((count = await source.ReadAsync(buffer, cancellationToken)) > 0)
            {
                await destination.WriteAsync(buffer.AsMemory(0, count), cancellationToken);
                received += count;
                if (totalBytes is > 0)
                {
                    progress?.Report((double)received / totalBytes.Value);
                }
            }
            await destination.FlushAsync(cancellationToken);
        }

        await using var downloaded = File.OpenRead(temporaryPath);
        var actualHash = Convert.ToHexString(
            await SHA256.HashDataAsync(downloaded, cancellationToken));
        if (!CryptographicOperations.FixedTimeEquals(
                Convert.FromHexString(expectedHash),
                Convert.FromHexString(actualHash)))
        {
            File.Delete(temporaryPath);
            throw new InvalidDataException(
                "Контрольная сумма обновления не совпала. Установка отменена.");
        }

        File.Move(temporaryPath, installerPath, true);
        return installerPath;
    }

    public static Version CurrentVersion =>
        Assembly.GetExecutingAssembly().GetName().Version ?? new Version(0, 0, 0);

    public static void LaunchInstaller(string installerPath) =>
        Process.Start(new ProcessStartInfo
        {
            FileName = installerPath,
            UseShellExecute = true
        });

    private static HttpRequestMessage CreateRequest(
        HttpMethod method,
        Uri uri,
        string token)
    {
        var request = new HttpRequestMessage(method, uri);
        if (!string.IsNullOrWhiteSpace(token))
        {
            request.Headers.Authorization =
                new AuthenticationHeaderValue("token", token.Trim());
        }
        return request;
    }

    private static HttpClient CreateHttpClient()
    {
        var client = new HttpClient { Timeout = TimeSpan.FromMinutes(10) };
        client.DefaultRequestHeaders.UserAgent.ParseAdd("KronaStaffTerminal/0.2");
        return client;
    }

    private static bool TryParseVersion(string? value, out Version version)
    {
        var normalized = (value ?? "")
            .Trim()
            .TrimStart('v', 'V')
            .Split('-', '+')[0];
        if (Version.TryParse(normalized, out var parsed))
        {
            version = parsed;
            return true;
        }
        version = new Version(0, 0, 0);
        return false;
    }

    private sealed class ForgejoRelease
    {
        [JsonPropertyName("tag_name")]
        public string TagName { get; set; } = "";

        [JsonPropertyName("name")]
        public string Name { get; set; } = "";

        [JsonPropertyName("body")]
        public string? Body { get; set; }

        [JsonPropertyName("html_url")]
        public string HtmlUrl { get; set; } = "";

        [JsonPropertyName("assets")]
        public List<ForgejoAsset> Assets { get; set; } = [];
    }

    private sealed class ForgejoAsset
    {
        [JsonPropertyName("name")]
        public string Name { get; set; } = "";

        [JsonPropertyName("browser_download_url")]
        public string BrowserDownloadUrl { get; set; } = "";
    }
}