using System.Diagnostics;
using System.Text;

namespace ClaudeDo.Data.Git;

public sealed class GitService
{
    public async Task<bool> IsGitRepoAsync(string dir, CancellationToken ct = default)
    {
        var (exitCode, _, _) = await RunGitAsync(dir, ["rev-parse", "--git-dir"], ct);
        return exitCode == 0;
    }

    public async Task<string> RevParseHeadAsync(string dir, CancellationToken ct = default)
    {
        var (exitCode, stdout, stderr) = await RunGitAsync(dir, ["rev-parse", "HEAD"], ct);
        if (exitCode != 0)
            throw new InvalidOperationException($"git rev-parse HEAD failed (exit {exitCode}): {stderr}");
        return stdout.Trim();
    }

    public async Task WorktreeAddAsync(string repoDir, string branchName, string worktreePath, string baseCommit, CancellationToken ct = default)
    {
        var (exitCode, _, stderr) = await RunGitAsync(repoDir,
            ["worktree", "add", "-b", branchName, worktreePath, baseCommit], ct);
        if (exitCode != 0)
            throw new InvalidOperationException($"git worktree add failed (exit {exitCode}): {stderr}");
    }

    public async Task<bool> HasChangesAsync(string worktreePath, CancellationToken ct = default)
    {
        var (exitCode, stdout, stderr) = await RunGitAsync(worktreePath, ["status", "--porcelain"], ct);
        if (exitCode != 0)
            throw new InvalidOperationException($"git status --porcelain failed (exit {exitCode}): {stderr}");
        return !string.IsNullOrWhiteSpace(stdout);
    }

    public async Task AddAllAsync(string worktreePath, CancellationToken ct = default)
    {
        var (exitCode, _, stderr) = await RunGitAsync(worktreePath, ["add", "-A"], ct);
        if (exitCode != 0)
            throw new InvalidOperationException($"git add -A failed (exit {exitCode}): {stderr}");
    }

    public async Task CommitAsync(string worktreePath, string message, CancellationToken ct = default)
    {
        // Use -F - (read message from stdin) to handle multi-line messages safely.
        var (exitCode, _, stderr) = await RunGitAsync(worktreePath, ["commit", "-F", "-"], ct, stdinData: message);
        if (exitCode != 0)
            throw new InvalidOperationException($"git commit failed (exit {exitCode}): {stderr}");
    }

    public async Task<string> DiffStatAsync(string worktreePath, string baseCommit, string headCommit, CancellationToken ct = default)
    {
        var (exitCode, stdout, stderr) = await RunGitAsync(worktreePath,
            ["diff", "--stat", $"{baseCommit}..{headCommit}"], ct);
        if (exitCode != 0)
            throw new InvalidOperationException($"git diff --stat failed (exit {exitCode}): {stderr}");
        return stdout.Trim();
    }

    public async Task WorktreeRemoveAsync(string repoDir, string worktreePath, bool force = false, CancellationToken ct = default)
    {
        var args = new List<string> { "worktree", "remove" };
        if (force) args.Add("--force");
        args.Add(worktreePath);

        var (exitCode, _, stderr) = await RunGitAsync(repoDir, args, ct);
        if (exitCode != 0)
            throw new InvalidOperationException($"git worktree remove failed (exit {exitCode}): {stderr}");
    }

    public async Task BranchDeleteAsync(string repoDir, string branchName, bool force = false, CancellationToken ct = default)
    {
        var flag = force ? "-D" : "-d";
        var (exitCode, _, stderr) = await RunGitAsync(repoDir, ["branch", flag, branchName], ct);
        if (exitCode != 0)
            throw new InvalidOperationException($"git branch {flag} failed (exit {exitCode}): {stderr}");
    }

    public async Task MergeFfOnlyAsync(string repoDir, string branchName, CancellationToken ct = default)
    {
        var (exitCode, _, stderr) = await RunGitAsync(repoDir, ["merge", "--ff-only", branchName], ct);
        if (exitCode != 0)
            throw new InvalidOperationException($"Fast-forward merge of '{branchName}' failed. Manual merge required. git stderr: {stderr}");
    }

    private static async Task<(int ExitCode, string Stdout, string Stderr)> RunGitAsync(
        string workDir, IEnumerable<string> args, CancellationToken ct, string? stdinData = null)
    {
        var psi = new ProcessStartInfo
        {
            FileName = "git",
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            RedirectStandardInput = stdinData is not null,
            UseShellExecute = false,
            CreateNoWindow = true,
        };
        psi.ArgumentList.Add("-C");
        psi.ArgumentList.Add(workDir);
        foreach (var a in args) psi.ArgumentList.Add(a);

        using var proc = new Process { StartInfo = psi };
        proc.Start();

        if (stdinData is not null)
        {
            await proc.StandardInput.WriteAsync(stdinData.AsMemory(), ct);
            proc.StandardInput.Close();
        }

        var stdoutTask = proc.StandardOutput.ReadToEndAsync(ct);
        var stderrTask = proc.StandardError.ReadToEndAsync(ct);

        await proc.WaitForExitAsync(ct);

        var stdout = await stdoutTask;
        var stderr = await stderrTask;

        return (proc.ExitCode, stdout.TrimEnd(), stderr.TrimEnd());
    }
}