using MongoDB.Driver;
using QuestionsApi.Models;

namespace QuestionsApi.Services;

public sealed record UserNotepadUpdateResult(UserNotepad? Note, UserNotepad? Current)
{
    public bool Succeeded => Note is not null;
}

public sealed class UserNotepadStore
{
    private readonly IMongoCollection<UserNotepad> _notes;

    public UserNotepadStore(MongoDatabaseProvider mongo)
    {
        _notes = mongo.Database.GetCollection<UserNotepad>("UserNotepads");
        _notes.Indexes.CreateOne(new CreateIndexModel<UserNotepad>(
            Builders<UserNotepad>.IndexKeys.Ascending(note => note.UserId),
            new CreateIndexOptions { Unique = true, Name = "user_notepad_unique_user" }));
    }

    public async Task<UserNotepad?> GetAsync(string userId) =>
        await _notes.Find(note => note.UserId == userId).FirstOrDefaultAsync();

    public async Task<UserNotepadUpdateResult> UpdateAsync(
        string userId,
        string content,
        long expectedRevision)
    {
        var now = DateTime.UtcNow;
        if (expectedRevision == 0)
        {
            var created = new UserNotepad
            {
                UserId = userId,
                Content = content,
                Revision = 1,
                CreatedUtc = now,
                UpdatedUtc = now
            };
            try
            {
                await _notes.InsertOneAsync(created);
                return new UserNotepadUpdateResult(created, null);
            }
            catch (MongoWriteException exception) when (
                exception.WriteError?.Category == ServerErrorCategory.DuplicateKey)
            {
                return new UserNotepadUpdateResult(null, await GetAsync(userId));
            }
        }

        var updated = await _notes.FindOneAndUpdateAsync(
            note => note.UserId == userId && note.Revision == expectedRevision,
            Builders<UserNotepad>.Update
                .Set(note => note.Content, content)
                .Set(note => note.UpdatedUtc, now)
                .Inc(note => note.Revision, 1),
            new FindOneAndUpdateOptions<UserNotepad> { ReturnDocument = ReturnDocument.After });

        return updated is not null
            ? new UserNotepadUpdateResult(updated, null)
            : new UserNotepadUpdateResult(null, await GetAsync(userId));
    }
}