#nullable enable
using System;
using System.Data;
using System.Data.Common;
using System.Diagnostics.CodeAnalysis;
using System.Threading;
using System.Threading.Tasks;

using App.Metrics;

using NodaTime;

using Npgsql;

using Serilog;

namespace PluralKit.Core
{
    internal class PKConnection: DbConnection, IPKConnection
    {
        public NpgsqlConnection Inner { get; }
        public Guid ConnectionId { get; }

        private readonly DbConnectionCountHolder _countHolder;
        private readonly ILogger _logger;
        private readonly IMetrics _metrics;

        private bool _hasOpened;
        private bool _hasClosed;
        private Instant _openTime;

        public PKConnection(NpgsqlConnection inner, DbConnectionCountHolder countHolder, ILogger logger, IMetrics metrics)
        {
            Inner = inner;
            ConnectionId = Guid.NewGuid();
            _countHolder = countHolder;
            _logger = logger.ForContext<PKConnection>();
            _metrics = metrics;
        }
        
        public override Task OpenAsync(CancellationToken ct)
        {
            if (_hasOpened) return Inner.OpenAsync(ct);
            _countHolder.Increment();
            _hasOpened = true;
            _openTime = SystemClock.Instance.GetCurrentInstant();
            _logger.Verbose("Opened database connection {ConnectionId}, new connection count {ConnectionCount}", ConnectionId, _countHolder.ConnectionCount);       
            return Inner.OpenAsync(ct);
        }

        public override Task CloseAsync() => Inner.CloseAsync();

        protected override DbCommand CreateDbCommand() => new PKCommand(Inner.CreateCommand(), this, _logger, _metrics);
        
        public void ReloadTypes() => Inner.ReloadTypes();

        public new async ValueTask<IPKTransaction> BeginTransactionAsync(IsolationLevel level, CancellationToken ct = default) => new PKTransaction(await Inner.BeginTransactionAsync(level, ct));

        public NpgsqlBinaryImporter BeginBinaryImport(string copyFromCommand) => Inner.BeginBinaryImport(copyFromCommand);
        public NpgsqlBinaryExporter BeginBinaryExport(string copyToCommand) => Inner.BeginBinaryExport(copyToCommand);
        
        public override void ChangeDatabase(string databaseName) => Inner.ChangeDatabase(databaseName);
        public override Task ChangeDatabaseAsync(string databaseName, CancellationToken ct = default) => Inner.ChangeDatabaseAsync(databaseName, ct);
        protected override DbTransaction BeginDbTransaction(IsolationLevel isolationLevel) => throw SyncError(nameof(BeginDbTransaction));
        protected override async ValueTask<DbTransaction> BeginDbTransactionAsync(IsolationLevel level, CancellationToken ct) => new PKTransaction(await Inner.BeginTransactionAsync(level, ct));

        public override void Open() => throw SyncError(nameof(Open));
        public override void Close()
        {
            // Don't throw SyncError here, Dapper calls sync Close() internally so that sucks
            Inner.Close();
        }

        IDbTransaction IPKConnection.BeginTransaction() => throw SyncError(nameof(BeginTransaction));
        IDbTransaction IPKConnection.BeginTransaction(IsolationLevel level) => throw SyncError(nameof(BeginTransaction));

        [AllowNull]
        public override string ConnectionString
        {
            get => Inner.ConnectionString;
            set => Inner.ConnectionString = value;
        }

        public override string Database => Inner.Database!;
        public override ConnectionState State => Inner.State;
        public override string DataSource => Inner.DataSource;
        public override string ServerVersion => Inner.ServerVersion;
        
        protected override void Dispose(bool disposing)
        { 
            Inner.Dispose();
            if (_hasClosed) return;
            
            LogClose();
        }

        public override ValueTask DisposeAsync()
        {
            if (_hasClosed) return Inner.DisposeAsync();
            LogClose();
            return Inner.DisposeAsync();
        }
        
        private void LogClose()
        {
            _countHolder.Decrement();
            _hasClosed = true;
            
            var duration = SystemClock.Instance.GetCurrentInstant() - _openTime;
            _logger.Verbose("Closed database connection {ConnectionId} (open for {ConnectionDuration}), new connection count {ConnectionCount}", ConnectionId, duration, _countHolder.ConnectionCount);
        }

        private static Exception SyncError(string caller) => throw new Exception($"Executed synchronous IDbCommand function {caller}!");
    }
}