using MeetingAssistant.Transcription;
using MeetingAssistant.MeetingNotes;
using Microsoft.Extensions.Options;
using System.Collections.Concurrent;

namespace MeetingAssistant.Recording;

public sealed class VaultTranscriptStore : ITranscriptStore
{
    private readonly MeetingAssistantOptions options;
    private readonly ILogger<VaultTranscriptStore> logger;
    private readonly ConcurrentDictionary<string, SemaphoreSlim> fileGates = new(StringComparer.OrdinalIgnoreCase);

    public VaultTranscriptStore(IOptions<MeetingAssistantOptions> options, ILogger<VaultTranscriptStore> logger)
    {
        this.options = options.Value;
        this.logger = logger;
    }

    public async Task<TranscriptSession> CreateSessionAsync(CancellationToken cancellationToken)
    {
        return await CreateSessionAsync(options, DateTimeOffset.Now, cancellationToken);
    }

    public async Task<TranscriptSession> CreateSessionAsync(
        MeetingAssistantOptions options,
        DateTimeOffset startedAt,
        CancellationToken cancellationToken)
    {
        var folder = VaultPath.Resolve(options.Vault, options.Vault.TranscriptsFolder);
        Directory.CreateDirectory(folder);

        var fileName = MeetingArtifactFileNames.Create(startedAt, MeetingArtifactFileNames.Transcript);
        var path = Path.Combine(folder, fileName);
        await File.WriteAllTextAsync(path, $"# Meeting Transcript{Environment.NewLine}{Environment.NewLine}", cancellationToken);
        logger.LogInformation("Created meeting transcript file {TranscriptPath}", path);

        return new TranscriptSession(path);
    }

    public async Task<TranscriptLineReference> AppendLineAsync(
        TranscriptSession session,
        string line,
        CancellationToken cancellationToken)
    {
        return await WithFileGateAsync(
            session.TranscriptPath,
            () => AppendToBodyAsync(session.TranscriptPath, line, cancellationToken),
            cancellationToken);
    }

    public async Task ReplaceLineAsync(
        TranscriptSession session,
        TranscriptLineReference lineReference,
        string replacementLine,
        CancellationToken cancellationToken)
    {
        await WithFileGateAsync(
            session.TranscriptPath,
            async () =>
            {
                if (!File.Exists(session.TranscriptPath))
                {
                    return;
                }

                var content = await File.ReadAllTextAsync(session.TranscriptPath, cancellationToken);
                var (frontmatter, body) = MeetingArtifactFrontmatterRenderer.Split(content);
                var lines = SplitLines(body);
                if (lineReference.BodyLineIndex < 0 ||
                    lineReference.BodyLineIndex >= lines.Count ||
                    !string.Equals(lines[lineReference.BodyLineIndex], lineReference.OriginalLine, StringComparison.Ordinal))
                {
                    logger.LogWarning(
                        "Could not replace transcript line in {TranscriptPath} at body line {BodyLineIndex} because the original line no longer matched",
                        session.TranscriptPath,
                        lineReference.BodyLineIndex);
                    return;
                }

                lines[lineReference.BodyLineIndex] = replacementLine;
                await WriteBodyAsync(session.TranscriptPath, frontmatter, string.Join(Environment.NewLine, lines), cancellationToken);
            },
            cancellationToken);
    }

    public Task ReplaceLinesAsync(
        TranscriptSession session,
        IReadOnlyList<string> replacementLines,
        CancellationToken cancellationToken)
    {
        return WithFileGateAsync(
            session.TranscriptPath,
            async () =>
            {
                var existing = File.Exists(session.TranscriptPath)
                    ? File.ReadAllText(session.TranscriptPath)
                    : "";
                var (frontmatter, _) = MeetingArtifactFrontmatterRenderer.Split(existing);
                var body = "# Meeting Transcript"
                    + Environment.NewLine
                    + Environment.NewLine
                    + string.Concat(replacementLines.Select(line => line + Environment.NewLine));
                await WriteBodyAsync(session.TranscriptPath, frontmatter, body, cancellationToken);
            },
            cancellationToken);
    }

    public async Task UpdateMetadataAsync(
        TranscriptSession session,
        MeetingSessionArtifacts artifacts,
        MeetingNote meetingNote,
        CancellationToken cancellationToken)
    {
        await WithFileGateAsync(
            session.TranscriptPath,
            async () =>
            {
                var body = File.Exists(session.TranscriptPath)
                    ? MeetingArtifactFrontmatterRenderer.Split(await File.ReadAllTextAsync(session.TranscriptPath, cancellationToken)).Body
                    : "# Meeting Transcript" + Environment.NewLine + Environment.NewLine;
                var frontmatter = MeetingArtifactFrontmatterRenderer.Create(
                    artifacts,
                    meetingNote,
                    MeetingArtifactFrontmatterRenderer.DefaultTitle(meetingNote, "Meeting Transcript"),
                    session.TranscriptPath);

                await File.WriteAllTextAsync(
                    session.TranscriptPath,
                    MeetingArtifactFrontmatterRenderer.Render(frontmatter, body),
                    cancellationToken);
            },
            cancellationToken);
    }

    private static async Task<TranscriptLineReference> AppendToBodyAsync(
        string path,
        string line,
        CancellationToken cancellationToken)
    {
        if (!File.Exists(path))
        {
            await File.AppendAllTextAsync(path, line + Environment.NewLine, cancellationToken);
            return new TranscriptLineReference(path, 0, line);
        }

        var content = await File.ReadAllTextAsync(path, cancellationToken);
        var (frontmatter, body) = MeetingArtifactFrontmatterRenderer.Split(content);
        var bodyLineIndex = GetAppendBodyLineIndex(body);
        if (string.IsNullOrWhiteSpace(frontmatter))
        {
            await File.AppendAllTextAsync(path, line + Environment.NewLine, cancellationToken);
            return new TranscriptLineReference(path, bodyLineIndex, line);
        }

        await WriteBodyAsync(path, frontmatter, body + line + Environment.NewLine, cancellationToken);
        return new TranscriptLineReference(path, bodyLineIndex, line);
    }

    private async Task WithFileGateAsync(
        string path,
        Func<Task> action,
        CancellationToken cancellationToken)
    {
        await WithFileGateAsync(
            path,
            async () =>
            {
                await action();
                return true;
            },
            cancellationToken);
    }

    private async Task<T> WithFileGateAsync<T>(
        string path,
        Func<Task<T>> action,
        CancellationToken cancellationToken)
    {
        var gate = fileGates.GetOrAdd(path, static _ => new SemaphoreSlim(1, 1));
        await gate.WaitAsync(cancellationToken);
        try
        {
            return await action();
        }
        finally
        {
            gate.Release();
        }
    }

    private static async Task WriteBodyAsync(
        string path,
        string frontmatter,
        string body,
        CancellationToken cancellationToken)
    {
        var content = string.IsNullOrWhiteSpace(frontmatter)
            ? body
            : "---" + Environment.NewLine + frontmatter + Environment.NewLine + "---" + Environment.NewLine + Environment.NewLine + body;
        await File.WriteAllTextAsync(path, content, cancellationToken);
    }

    private static int GetAppendBodyLineIndex(string body)
    {
        var lines = SplitLines(body);
        return lines.Count > 0 && lines[^1].Length == 0
            ? lines.Count - 1
            : lines.Count;
    }

    private static List<string> SplitLines(string text)
    {
        return text
            .Replace("\r\n", "\n", StringComparison.Ordinal)
            .Split('\n')
            .ToList();
    }
}