// Copyright (C) 2021-present sam (starshines.gay)
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

using System.Data;
using System.Text.Json;
using System.Text.Json.Serialization;
using Catalogger.Backend.Database.Models;
using Dapper;
using NodaTime;
using Npgsql;

namespace Catalogger.Backend.Database.Dapper;

public class DatabasePool
{
    private readonly ILogger _rootLogger;
    private readonly ILogger _logger;
    private readonly NpgsqlDataSource _dataSource;

    private static int _openConnections;
    public static int OpenConnections => _openConnections;

    public DatabasePool(Config config, ILogger logger, ILoggerFactory? loggerFactory)
    {
        _rootLogger = logger;
        _logger = logger.ForContext<DatabasePool>();

        var connString = new NpgsqlConnectionStringBuilder(config.Database.Url)
        {
            Timeout = config.Database.Timeout ?? 5,
            MaxPoolSize = config.Database.MaxPoolSize ?? 50,
        }.ConnectionString;

        var dataSourceBuilder = new NpgsqlDataSourceBuilder(connString);
        dataSourceBuilder.EnableDynamicJson().UseNodaTime();
        if (config.Logging.LogQueries)
            dataSourceBuilder.UseLoggerFactory(loggerFactory);
        _dataSource = dataSourceBuilder.Build();
    }

    public async Task<DatabaseConnection> AcquireAsync(CancellationToken ct = default)
    {
        return new DatabaseConnection(
            LogOpen(),
            _rootLogger,
            await _dataSource.OpenConnectionAsync(ct)
        );
    }

    public DatabaseConnection Acquire()
    {
        return new DatabaseConnection(LogOpen(), _rootLogger, _dataSource.OpenConnection());
    }

    private Guid LogOpen()
    {
        var connId = Guid.NewGuid();
        _logger.Debug("Opening database connection {ConnId}", connId);
        IncrementConnections();
        return connId;
    }

    public async Task ExecuteAsync(
        Func<DatabaseConnection, Task> func,
        CancellationToken ct = default
    )
    {
        await using var conn = await AcquireAsync(ct);
        await func(conn);
    }

    public async Task<T> ExecuteAsync<T>(
        Func<DatabaseConnection, Task<T>> func,
        CancellationToken ct = default
    )
    {
        await using var conn = await AcquireAsync(ct);
        return await func(conn);
    }

    public async Task<IAsyncEnumerable<T>> ExecuteAsync<T>(
        Func<DatabaseConnection, Task<IAsyncEnumerable<T>>> func,
        CancellationToken ct = default
    )
    {
        await using var conn = await AcquireAsync(ct);
        return await func(conn);
    }

    internal static void IncrementConnections() => Interlocked.Increment(ref _openConnections);

    internal static void DecrementConnections() => Interlocked.Decrement(ref _openConnections);

    /// <summary>
    /// Configures Dapper's SQL mapping, as it handles several types incorrectly by default.
    /// Most notably, ulongs and arrays of ulongs.
    /// </summary>
    public static void ConfigureDapper()
    {
        DefaultTypeMap.MatchNamesWithUnderscores = true;

        SqlMapper.RemoveTypeMap(typeof(ulong));
        SqlMapper.AddTypeHandler(new UlongEncodeAsLongHandler());
        SqlMapper.AddTypeHandler(new UlongArrayHandler());

        SqlMapper.AddTypeHandler(new PassthroughTypeHandler<Instant>());
        SqlMapper.AddTypeHandler(new JsonTypeHandler<Guild.ChannelConfig>());
    }

    // Copied from PluralKit:
    // https://github.com/PluralKit/PluralKit/blob/4bf60a47d76a068fa0488bf9be96cdaf57a6fe50/PluralKit.Core/Database/Database.cs#L116
    // Thanks for not working with common types by default, Dapper. Really nice of you.
    private class PassthroughTypeHandler<T> : SqlMapper.TypeHandler<T>
    {
        public override void SetValue(IDbDataParameter parameter, T? value) =>
            parameter.Value = value;

        public override T Parse(object value) => (T)value;
    }

    private class UlongEncodeAsLongHandler : SqlMapper.TypeHandler<ulong>
    {
        public override ulong Parse(object value) =>
            // Cast to long to unbox, then to ulong (???)
            (ulong)(long)value;

        public override void SetValue(IDbDataParameter parameter, ulong value) =>
            parameter.Value = (long)value;
    }

    private class UlongArrayHandler : SqlMapper.TypeHandler<ulong[]>
    {
        public override void SetValue(IDbDataParameter parameter, ulong[]? value) =>
            parameter.Value = value != null ? Array.ConvertAll(value, i => (long)i) : null;

        public override ulong[] Parse(object value) =>
            Array.ConvertAll((long[])value, i => (ulong)i);
    }

    public class JsonTypeHandler<T> : SqlMapper.TypeHandler<T>
    {
        public override T Parse(object value)
        {
            string json = (string)value;
            return JsonSerializer.Deserialize<T>(json)
                ?? throw new CataloggerError("JsonTypeHandler<T> returned null");
        }

        public override void SetValue(IDbDataParameter parameter, T? value)
        {
            parameter.Value = JsonSerializer.Serialize(value);
        }
    }
}

public static class ServiceCollectionDatabaseExtensions
{
    public static IServiceCollection AddDatabasePool(this IServiceCollection serviceCollection) =>
        serviceCollection
            .AddSingleton<DatabasePool>()
            .AddScoped<DatabaseConnection>(services =>
                services.GetRequiredService<DatabasePool>().Acquire()
            );
}