using System;
using System.Collections.Generic;
using System.Data;
using System.IO;
using System.Linq;
using System.Threading.Tasks;

using App.Metrics;

using Dapper;

using NodaTime;

using Npgsql;

using Serilog;

namespace PluralKit.Core
{
    internal class Database: IDatabase
    {
        private const string RootPath = "PluralKit.Core.Database"; // "resource path" root for SQL files
        private const int TargetSchemaVersion = 8;
        
        private readonly CoreConfig _config;
        private readonly ILogger _logger;
        private readonly IMetrics _metrics;
        private readonly DbConnectionCountHolder _countHolder;

        public Database(CoreConfig config, DbConnectionCountHolder countHolder, ILogger logger,
                        IMetrics metrics)
        {
            _config = config;
            _countHolder = countHolder;
            _metrics = metrics;
            _logger = logger;
        }
        
        public static void InitStatic()
        {
            DefaultTypeMap.MatchNamesWithUnderscores = true;
            
            // Dapper by default tries to pass ulongs to Npgsql, which rejects them since PostgreSQL technically
            // doesn't support unsigned types on its own.
            // Instead we add a custom mapper to encode them as signed integers instead, converting them back and forth.
            SqlMapper.RemoveTypeMap(typeof(ulong));
            SqlMapper.AddTypeHandler(new UlongEncodeAsLongHandler());
            SqlMapper.AddTypeHandler(new UlongArrayHandler());

            NpgsqlConnection.GlobalTypeMapper.UseNodaTime();
            // With the thing we add above, Npgsql already handles NodaTime integration
            // This makes Dapper confused since it thinks it has to convert it anyway and doesn't understand the types
            // So we add a custom type handler that literally just passes the type through to Npgsql
            SqlMapper.AddTypeHandler(new PassthroughTypeHandler<Instant>());
            SqlMapper.AddTypeHandler(new PassthroughTypeHandler<LocalDate>());
            
            // Add ID types to Dapper
            SqlMapper.AddTypeHandler(new NumericIdHandler<SystemId, int>(i => new SystemId(i)));
            SqlMapper.AddTypeHandler(new NumericIdHandler<MemberId, int>(i => new MemberId(i)));
            SqlMapper.AddTypeHandler(new NumericIdHandler<SwitchId, int>(i => new SwitchId(i)));
            SqlMapper.AddTypeHandler(new NumericIdArrayHandler<SystemId, int>(i => new SystemId(i)));
            SqlMapper.AddTypeHandler(new NumericIdArrayHandler<MemberId, int>(i => new MemberId(i)));
            SqlMapper.AddTypeHandler(new NumericIdArrayHandler<SwitchId, int>(i => new SwitchId(i)));
            
            // Register our custom types to Npgsql
            // Without these it'll still *work* but break at the first launch + probably cause other small issues
            NpgsqlConnection.GlobalTypeMapper.MapComposite<ProxyTag>("proxy_tag");
            NpgsqlConnection.GlobalTypeMapper.MapEnum<PrivacyLevel>("privacy_level");
        }
        
        public async Task<IPKConnection> Obtain()
        {
            // Mark the request (for a handle, I guess) in the metrics
            _metrics.Measure.Meter.Mark(CoreMetrics.DatabaseRequests);
            
            // Create a connection and open it
            // We wrap it in PKConnection for tracing purposes
            var conn = new PKConnection(new NpgsqlConnection(_config.Database), _countHolder, _logger, _metrics);
            await conn.OpenAsync();
            return conn;
        }
        
        public async Task ApplyMigrations()
        {
            // Run everything in a transaction
            await using var conn = await Obtain();
            await using var tx = await conn.BeginTransactionAsync();
            
            // Before applying migrations, clean out views/functions to prevent type errors
            await ExecuteSqlFile($"{RootPath}.clean.sql", conn, tx);

            // Apply all migrations between the current database version and the target version
            await ApplyMigrations(conn, tx);

            // Now, reapply views/functions (we deleted them above, no need to worry about conflicts)
            await ExecuteSqlFile($"{RootPath}.Views.views.sql", conn, tx);
            await ExecuteSqlFile($"{RootPath}.Functions.functions.sql", conn, tx);

            // Finally, commit tx
            await tx.CommitAsync();
        }
        
        private async Task ApplyMigrations(IPKConnection conn, IDbTransaction tx)
        {
            var currentVersion = await GetCurrentDatabaseVersion(conn);
            _logger.Information("Current schema version: {CurrentVersion}", currentVersion);
            for (var migration = currentVersion + 1; migration <= TargetSchemaVersion; migration++)
            {
                _logger.Information("Applying schema migration {MigrationId}", migration);
                await ExecuteSqlFile($"{RootPath}.Migrations.{migration}.sql", conn, tx);
            }
        }
        
        private async Task ExecuteSqlFile(string resourceName, IPKConnection conn, IDbTransaction tx = null)
        {
            await using var stream = typeof(Database).Assembly.GetManifestResourceStream(resourceName);
            if (stream == null) throw new ArgumentException($"Invalid resource name  '{resourceName}'");

            using var reader = new StreamReader(stream);
            var query = await reader.ReadToEndAsync();

            await conn.ExecuteAsync(query, transaction: tx);

            // If the above creates new enum/composite types, we must tell Npgsql to reload the internal type caches
            // This will propagate to every other connection as well, since it marks the global type mapper collection dirty.
            ((PKConnection) conn).ReloadTypes();
        }

        private async Task<int> GetCurrentDatabaseVersion(IPKConnection conn)
        {
            // First, check if the "info" table exists (it may not, if this is a *really* old database)
            var hasInfoTable =
                await conn.QuerySingleOrDefaultAsync<int>(
                    "select count(*) from information_schema.tables where table_name = 'info'") == 1;

            // If we have the table, read the schema version
            if (hasInfoTable)
                return await conn.QuerySingleOrDefaultAsync<int>("select schema_version from info");

            // If not, we return version "-1"
            // This means migration 0 will get executed, getting us into a consistent state
            // Then, migration 1 gets executed, which creates the info table and sets version to 1
            return -1;
        }

        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 = Array.ConvertAll(value, i => (long) i);

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

        private class NumericIdHandler<T, TInner>: SqlMapper.TypeHandler<T>
            where T: INumericId<T, TInner>
            where TInner: IEquatable<TInner>, IComparable<TInner>
        {
            private readonly Func<TInner, T> _factory;

            public NumericIdHandler(Func<TInner, T> factory)
            {
                _factory = factory;
            }

            public override void SetValue(IDbDataParameter parameter, T value) => parameter.Value = value.Value;

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

        private class NumericIdArrayHandler<T, TInner>: SqlMapper.TypeHandler<T[]>
            where T: INumericId<T, TInner>
            where TInner: IEquatable<TInner>, IComparable<TInner>
        {
            private readonly Func<TInner, T> _factory;

            public NumericIdArrayHandler(Func<TInner, T> factory)
            {
                _factory = factory;
            }

            public override void SetValue(IDbDataParameter parameter, T[] value) => parameter.Value = Array.ConvertAll(value, v => v.Value);

            public override T[] Parse(object value) => Array.ConvertAll((TInner[]) value, v => _factory(v));
        }
    }
}