using System;
using System.Collections.Generic;
using System.Data.Common;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.Extensions.Logging;

namespace Microsoft.EntityFrameworkCore
{
	/// <summary>
	/// Extensions for the <see cref="DatabaseFacade"/>.
	/// </summary>
	public static class DatabaseFacadeExtensions
	{
		/// <summary>
		/// Applies migration files to the database.
		/// </summary>
		/// <param name="database">The database connection.</param>
		/// <param name="optionsAction">An action to set additional options.</param>
		/// <param name="cancellationToken">The cancellation token.</param>
		/// <returns>true on success, otherwise false or an exception is thrown.</returns>
		public static async Task<bool> ApplyMigrationsAsync(this DatabaseFacade database, Action<DatabaseMigrationOptions> optionsAction, CancellationToken cancellationToken = default)
		{
			if (database == null)
				throw new ArgumentNullException(nameof(database));

			var options = new DatabaseMigrationOptions();
			optionsAction?.Invoke(options);

			if (string.IsNullOrWhiteSpace(options.MigrationsTableName))
				throw new ArgumentNullException(nameof(options.MigrationsTableName), $"The property {nameof(options.MigrationsTableName)} of the {nameof(options)} parameter is required.");

			if (string.IsNullOrWhiteSpace(options.Path))
				throw new ArgumentNullException(nameof(options.Path), $"The property {nameof(options.Path)} of the {nameof(options)} parameter is required.");

			var connection = database.GetDbConnection();
			try
			{
				await connection.OpenAsync(cancellationToken);
				if (!await connection.CreateMigrationsTable(options, cancellationToken))
					return false;

				return await connection.Migrate(options, cancellationToken);
			}
			finally
			{
				connection.Close();
			}
		}

		private static DatabaseProvider GetProviderType(this DbConnection connection)
		{
			string provider = connection.GetType().FullName;

			if (provider.Contains("mysql", StringComparison.OrdinalIgnoreCase))
				return DatabaseProvider.MySQL;
			if (provider.Contains("oracle", StringComparison.OrdinalIgnoreCase))
				return DatabaseProvider.Oracle;
			if (provider.Contains("npgsql", StringComparison.OrdinalIgnoreCase))
				return DatabaseProvider.PostgreSQL;
			if (provider.Contains("sqlite", StringComparison.OrdinalIgnoreCase))
				return DatabaseProvider.SQLite;
			if (provider.Contains("sqlclient", StringComparison.OrdinalIgnoreCase))
				return DatabaseProvider.SQLServer;

			throw new DatabaseProviderException($"The database provider '{provider}' is unknown");
		}

		private static async Task<bool> CreateMigrationsTable(this DbConnection connection, DatabaseMigrationOptions options, CancellationToken cancellationToken)
		{
			try
			{
				using var command = connection.CreateCommand();

#pragma warning disable CS8524 // missing default case
				command.CommandText = connection.GetProviderType() switch
#pragma warning restore CS8524 // missing default case
				{
					DatabaseProvider.MySQL => $@"CREATE TABLE IF NOT EXISTS `{options.MigrationsTableName}` (
	`id` INT NOT NULL AUTO_INCREMENT,
	`schema_file` VARCHAR(250) NOT NULL,
	`installed_at` VARCHAR(16) NOT NULL,
	PRIMARY KEY (`id`)
);",
					DatabaseProvider.Oracle => $@"DECLARE ncount NUMBER;
BEGIN
	SELECT count(*) INTO ncount FROM dba_tables WHERE table_name = '{options.MigrationsTableName}';
	IF (ncount <= 0)
	THEN
		EXECUTE IMMEDIATE 'CREATE TABLE ""{options.MigrationsTableName}"" (
	""id"" NUMBER GENERATED by default on null as IDENTITY,
	""schema_file"" VARCHAR2(250) NOT NULL,
	""installed_at"" VARCHAR2(16) NOT NULL,
	PRIMARY KEY (""id""),
	CONSTRAINT uq_schema_file UNIQUE (""schema_file"")
)';
	END IF;
END;",
					DatabaseProvider.PostgreSQL => $@"CREATE TABLE IF NOT EXISTS ""{options.MigrationsTableName}"" (
	""id"" SERIAL4 PRIMARY KEY,
	""schema_file"" VARCHAR(250) NOT NULL,
	""installed_at"" VARCHAR(16) NOT NULL,
	CONSTRAINT ""uq_schema_file"" UNIQUE (""schema_file"")
);",
					DatabaseProvider.SQLite => $@"CREATE TABLE IF NOT EXISTS ""{options.MigrationsTableName}"" (
	""id"" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
	""schema_file"" TEXT(250) NOT NULL,
	""installed_at"" TEXT(16) NOT NULL,
	CONSTRAINT ""uq_schema_file"" UNIQUE (""schema_file"")
);",
					DatabaseProvider.SQLServer => $@"IF NOT EXISTS (SELECT * FROM [sysobjects] WHERE [name] = '{options.MigrationsTableName}' AND [xtype] = 'U')
BEGIN
	CREATE TABLE [{options.MigrationsTableName}] (
		[id] int IDENTITY(1,1) NOT NULL PRIMARY KEY,
		[schema_file] varchar(250) NOT NULL,
		[installed_at] varchar(16) NOT NULL,
		CONSTRAINT uq_schema_file UNIQUE (schema_file)
	)
END;"
				};

				await command.ExecuteNonQueryAsync(cancellationToken);
				return true;
			}
			catch (Exception ex)
			{
				options.Logger?.LogCritical(ex, $"Creating migrations table '{options.MigrationsTableName}' failed: {ex.InnerException?.Message ?? ex.Message}");
				return false;
			}
		}

		private static async Task<bool> Migrate(this DbConnection connection, DatabaseMigrationOptions options, CancellationToken cancellationToken)
		{
			try
			{
				List<string> availableMigrationFiles;
				if (options.SourceAssembly == null)
				{
					availableMigrationFiles = Directory.GetFiles(options.Path)
						.Where(f => f.ToLower().StartsWith(options.Path.ToLower()))
						.Where(f => f.ToLower().EndsWith(".sql"))
						.ToList();
				}
				else
				{
					availableMigrationFiles = options.SourceAssembly
						.GetManifestResourceNames()
						.Where(f => f.ToLower().StartsWith(options.Path.ToLower()))
						.Where(f => f.ToLower().EndsWith(".sql"))
						.ToList();
				}

				if (!availableMigrationFiles.Any())
					return true;

				using var command = connection.CreateCommand();

				var migratedFiles = new List<string>();
				command.CommandText = connection.GetProviderType() switch
				{
					DatabaseProvider.MySQL => $"SELECT `schema_file` FROM `{options.MigrationsTableName}`;",
					DatabaseProvider.SQLServer => $"SELECT [schema_file] FROM [{options.MigrationsTableName}];",
					_ => $@"SELECT ""schema_file"" FROM ""{options.MigrationsTableName}"";",
				};
				using (var reader = await command.ExecuteReaderAsync(cancellationToken))
				{
					while (await reader.ReadAsync(cancellationToken))
						migratedFiles.Add(reader.GetString(0));
				}

				int pathLength = options.Path.Length + 1;
				foreach (string migrationFile in availableMigrationFiles)
				{
					// remove path including the separator
					string fileName = migrationFile.Replace(options.Path, "")[1..];
					using var transaction = await connection.BeginTransactionAsync(cancellationToken);
					try
					{
						// max length in the database: 250 chars
						string trimmedFileName = fileName;
						if (trimmedFileName.Length > 250)
							fileName = fileName[..250];

						if (migratedFiles.Contains(trimmedFileName))
						{
							options.Logger?.LogDebug($"	Migrating file '{fileName}' done");
							continue;
						}

						string sqlScript = null;
						if (options.SourceAssembly == null)
						{
							sqlScript = await File.ReadAllTextAsync(migrationFile, cancellationToken);
						}
						else
						{
							using var stream = options.SourceAssembly.GetManifestResourceStream(migrationFile);
							using var sr = new StreamReader(stream);
							sqlScript = await sr.ReadToEndAsync();
						}

						if (string.IsNullOrWhiteSpace(sqlScript))
							continue;

						options.Logger?.LogDebug($"	Migrating file '{fileName}' started");
						command.Transaction = transaction;

						await command.ExecuteScript(sqlScript, cancellationToken);

						command.CommandText = connection.GetProviderType() switch
						{
							DatabaseProvider.MySQL => $"INSERT INTO `{options.MigrationsTableName}` (`schema_file`, `installed_at`) VALUES ('{trimmedFileName.Replace("'", "\\'")}', '{DateTime.UtcNow:yyyy-MM-dd HH:mm}');",
							DatabaseProvider.SQLServer => $"INSERT INTO [{options.MigrationsTableName}] ([schema_file], [installed_at]) VALUES ('{trimmedFileName.Replace("'", "\\'")}', '{DateTime.UtcNow:yyyy-MM-dd HH:mm}');",
							_ => $@"INSERT INTO ""{options.MigrationsTableName}"" (""schema_file"", ""installed_at"") VALUES ('{trimmedFileName.Replace("'", "\\'")}', '{DateTime.UtcNow:yyyy-MM-dd HH:mm}');",
						};
						await command.ExecuteNonQueryAsync(cancellationToken);

						await transaction.CommitAsync(cancellationToken);
						command.Transaction = null;
						options.Logger?.LogDebug($"	Migrating file '{fileName}' successful");
					}
					catch (Exception ex)
					{
						await transaction.RollbackAsync(cancellationToken);
						options.Logger?.LogError($"Migrating file '{fileName}' failed: {ex.InnerException?.Message ?? ex.Message}");
						return false;
					}
				}

				return true;
			}
			catch (Exception ex)
			{
				options.Logger?.LogCritical(ex, $"Migrating the database failed ({ex.GetType().Name}): {ex.InnerException?.Message ?? ex.Message}");
				return false;
			}
		}

		private static async Task<int> ExecuteScript(this DbCommand command, string text, CancellationToken cancellationToken)
		{
			if (command.Connection.GetProviderType() == DatabaseProvider.Oracle)
			{
				int affectedRows = 0;
				// Split script by a single slash in a line
				string[] parts = Regex.Split(text, @"\r?\n[ \t]*/[ \t]*\r?\n");
				foreach (string part in parts)
				{
					// Make writable copy
					string pt = part;

					// Remove the trailing semicolon from commands where they're not supported
					// (Oracle doesn't like semicolons. To keep the semicolon, it must be directly
					// preceeded by "end".)
					pt = Regex.Replace(pt.TrimEnd(), @"(?<!end);$", "", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant);

					// Execute all non-empty parts as individual commands
					if (!string.IsNullOrWhiteSpace(pt))
					{
						command.CommandText = pt;
						affectedRows += await command.ExecuteNonQueryAsync(cancellationToken);
					}
				}
				return affectedRows;
			}
			else
			{
				command.CommandText = text;
				return await command.ExecuteNonQueryAsync(cancellationToken);
			}
		}

		private enum DatabaseProvider
		{
			MySQL = 1,
			Oracle = 2,
			PostgreSQL = 3,
			SQLite = 4,
			SQLServer = 5
		}
	}
}