using System.Text.Json;

namespace VideoDownloader.Core.Update;

/// <summary>GitHub 릴리스의 설치 자산 하나.</summary>
public sealed record UpdateAsset(string Name, string DownloadUrl);

/// <summary>업데이트 확인 결과. LatestVersion 은 태그의 v 접두를 뗀 정규형.</summary>
public sealed record UpdateCheckResult(bool IsNewer, string CurrentVersion, string LatestVersion, string ReleaseUrl, UpdateAsset? Asset);

/// <summary>
/// DEPLOYMENT_PLAN §6 자동 업데이트 v1 — GitHub Releases latest 태그 폴링(무의존·전 OS 공통).
/// 설치를 자동 적용하지 않고 릴리스/자산 URL 만 돌려준다(설치는 사람 관문).
/// </summary>
public sealed class UpdateChecker
{
    private readonly HttpClient _http;

    public UpdateChecker(HttpMessageHandler? handler = null)
    {
        _http = handler == null ? new HttpClient() : new HttpClient(handler);
        _http.DefaultRequestHeaders.UserAgent.ParseAdd("VideoDownloader-UpdateCheck"); // GitHub API 는 UA 필수
        _http.Timeout = TimeSpan.FromSeconds(15);
    }

    /// <summary>"v1.2.3"/"1.2.3.0" 을 관대하게 비교. 어느 쪽이든 파싱 불가면 false(갱신 아님).</summary>
    public static bool IsNewer(string current, string latest) =>
        TryParse(current, out var cur) && TryParse(latest, out var lat) && lat > cur;

    private static bool TryParse(string s, out Version version)
    {
        s = s.Trim().TrimStart('v', 'V');
        if (!s.Contains('.')) s += ".0"; // Version.TryParse 는 최소 2파트 요구
        return Version.TryParse(s, out version!);
    }

    /// <summary>RID(win-x64 등)에 맞는 설치 자산 선택. "x64" 판정에서 arm64 를 먼저 배제한다.</summary>
    public static UpdateAsset? SelectAsset(IEnumerable<UpdateAsset> assets, string rid)
    {
        var parts = rid.Split('-');
        var os = parts[0];
        var arch = parts[^1];
        foreach (var asset in assets)
        {
            var name = asset.Name.ToLowerInvariant();
            var isArm = name.Contains("arm64");
            if (arch == "arm64" ? !isArm : isArm || !name.Contains(arch)) continue;
            var osMatch = os switch
            {
                "win" => name.EndsWith(".exe") || name.EndsWith(".msi"),
                "linux" => name.EndsWith(".tar.gz") || name.EndsWith(".appimage") || name.EndsWith(".deb"),
                "osx" => name.EndsWith(".dmg"),
                _ => false,
            };
            if (osMatch) return asset;
        }
        return null;
    }

    /// <summary>repo("owner/repo")의 latest 릴리스를 조회한다. API 실패는 HttpRequestException 으로 드러난다.</summary>
    public async Task<UpdateCheckResult> CheckAsync(string repo, string currentVersion, string rid, CancellationToken ct = default)
    {
        using var res = await _http.GetAsync($"https://api.github.com/repos/{repo}/releases/latest", ct);
        res.EnsureSuccessStatusCode();
        using var doc = JsonDocument.Parse(await res.Content.ReadAsStringAsync(ct));
        var root = doc.RootElement;

        var tag = root.GetProperty("tag_name").GetString() ?? "";
        var releaseUrl = root.TryGetProperty("html_url", out var h) ? h.GetString() ?? "" : "";
        var assets = new List<UpdateAsset>();
        if (root.TryGetProperty("assets", out var arr) && arr.ValueKind == JsonValueKind.Array)
        {
            foreach (var a in arr.EnumerateArray())
            {
                assets.Add(new UpdateAsset(
                    a.GetProperty("name").GetString() ?? "",
                    a.GetProperty("browser_download_url").GetString() ?? ""));
            }
        }

        return new UpdateCheckResult(
            IsNewer(currentVersion, tag), currentVersion, tag.TrimStart('v', 'V'), releaseUrl, SelectAsset(assets, rid));
    }
}