using System.Diagnostics;
using System.Text;

namespace JournalBot.Shared;

public sealed record BotResult(int ExitCode, string Output);

public sealed class BotRunner
{
    private readonly string _pythonExe;
    private readonly string _workingDir;

    public BotRunner(string pythonExe, string workingDir)
    {
        _pythonExe = pythonExe;
        _workingDir = workingDir;
    }

    // Runs `python -m journal_bot <command>`.
    public Task<BotResult> RunAsync(string command, CancellationToken ct = default)
        => RunRawAsync(new[] { "-m", "journal_bot", command }, ct);

    // Runs python with arbitrary args (used by tests and RunAsync).
    public async Task<BotResult> RunRawAsync(IReadOnlyList<string> args, CancellationToken ct = default)
    {
        var psi = new ProcessStartInfo
        {
            FileName = _pythonExe,
            WorkingDirectory = _workingDir,
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            UseShellExecute = false,
            CreateNoWindow = true,
            StandardOutputEncoding = Encoding.UTF8,
            StandardErrorEncoding = Encoding.UTF8,
        };
        foreach (var a in args) psi.ArgumentList.Add(a);

        var sb = new StringBuilder();
        var gate = new object();
        using var proc = new Process { StartInfo = psi };
        proc.OutputDataReceived += (_, e) => { if (e.Data is not null) { lock (gate) sb.AppendLine(e.Data); } };
        proc.ErrorDataReceived += (_, e) => { if (e.Data is not null) { lock (gate) sb.AppendLine(e.Data); } };
        if (!proc.Start())
            throw new InvalidOperationException($"Failed to start process: {_pythonExe}");
        proc.BeginOutputReadLine();
        proc.BeginErrorReadLine();
        try
        {
            await proc.WaitForExitAsync(ct);
        }
        catch (OperationCanceledException)
        {
            try { proc.Kill(entireProcessTree: true); } catch { /* already exited */ }
            throw;
        }
        return new BotResult(proc.ExitCode, sb.ToString());
    }
}