package postgres

import (
	"context"
	"database/sql"
	"fmt"
	"strconv"
	"strings"

	"github.com/pkg/errors"

	_ "github.com/lib/pq"
	"github.com/mattermost/morph/drivers"
	"github.com/mattermost/morph/models"
)

var (
	driverName              = "postgres"
	defaultMigrationMaxSize = 10 * 1 << 20 // 10 MB
	configParams            = []string{
		"x-migration-max-size",
		"x-migrations-table",
		"x-statement-timeout",
	}
)

// The format is morph: followed by a comma separated list of values.
// For now, we are taking the whole string in a single constant.
// Later, if we need more values, we can split "morph:" to a separate constant.
const nonTransactionalPrefix = "morph:nontransactional"

type driverConfig struct {
	drivers.Config
	databaseName   string
	schemaName     string
	closeDBonClose bool
}

type postgres struct {
	conn   *sql.Conn
	db     *sql.DB
	config *driverConfig
}

func WithInstance(dbInstance *sql.DB) (drivers.Driver, error) {
	conn, err := dbInstance.Conn(context.Background())
	if err != nil {
		return nil, &drivers.DatabaseError{Driver: driverName, Command: "grabbing_connection", OrigErr: err, Message: "failed to grab connection to the database"}
	}

	driverConfig := getDefaultConfig()
	if driverConfig.databaseName, err = currentDatabaseNameFromDB(conn, driverConfig); err != nil {
		return nil, err
	}

	if driverConfig.schemaName, err = currentSchema(conn, driverConfig); err != nil {
		return nil, err
	}

	return &postgres{
		conn:   conn,
		db:     dbInstance,
		config: driverConfig,
	}, nil
}

func Open(connURL string) (drivers.Driver, error) {
	customParams, err := drivers.ExtractCustomParams(connURL, configParams)
	if err != nil {
		return nil, &drivers.AppError{Driver: driverName, OrigErr: err, Message: "failed to parse custom parameters from url"}
	}

	sanitizedConnURL, err := drivers.RemoveParamsFromURL(connURL, configParams)
	if err != nil {
		return nil, &drivers.AppError{Driver: driverName, OrigErr: err, Message: "failed to sanitize url from custom parameters"}
	}

	driverConfig, err := mergeConfigWithParams(customParams, getDefaultConfig())
	if err != nil {
		return nil, &drivers.AppError{Driver: driverName, OrigErr: err, Message: "failed to merge custom params to driver config"}
	}

	db, err := sql.Open(driverName, sanitizedConnURL)
	if err != nil {
		return nil, &drivers.DatabaseError{Driver: driverName, Command: "opening_connection", OrigErr: err, Message: "failed to open connection with the database"}
	}

	conn, err := db.Conn(context.Background())
	if err != nil {
		return nil, &drivers.DatabaseError{Driver: driverName, Command: "grabbing_connection", OrigErr: err, Message: "failed to grab connection to the database"}
	}

	if driverConfig.databaseName, err = extractDatabaseNameFromURL(connURL); err != nil {
		return nil, &drivers.AppError{Driver: driverName, OrigErr: err, Message: "failed to extract database name from connection url"}
	}

	if driverConfig.schemaName, err = currentSchema(conn, driverConfig); err != nil {
		return nil, err
	}

	driverConfig.closeDBonClose = true

	return &postgres{
		db:     db,
		config: driverConfig,
		conn:   conn,
	}, nil
}

func currentSchema(conn *sql.Conn, config *driverConfig) (string, error) {
	query := "SELECT CURRENT_SCHEMA()"

	ctx, cancel := drivers.GetContext(config.StatementTimeoutInSecs)
	defer cancel()

	var schemaName string
	if err := conn.QueryRowContext(ctx, query).Scan(&schemaName); err != nil {
		return "", &drivers.DatabaseError{
			OrigErr: err,
			Driver:  driverName,
			Message: "failed to fetch current schema",
			Command: "current_schema",
			Query:   []byte(query),
		}
	}
	return schemaName, nil
}

func mergeConfigWithParams(params map[string]string, config *driverConfig) (*driverConfig, error) {
	var err error

	for _, configKey := range configParams {
		if v, ok := params[configKey]; ok {
			switch configKey {
			case "x-migration-max-size":
				if config.MigrationMaxSize, err = strconv.Atoi(v); err != nil {
					return nil, errors.New(fmt.Sprintf("failed to cast config param %s of %s", configKey, v))
				}
			case "x-migrations-table":
				config.MigrationsTable = v
			case "x-statement-timeout":
				if config.StatementTimeoutInSecs, err = strconv.Atoi(v); err != nil {
					return nil, errors.New(fmt.Sprintf("failed to cast config param %s of %s", configKey, v))
				}
			}
		}
	}

	return config, nil
}

func (pg *postgres) Ping() error {
	ctx, cancel := drivers.GetContext(pg.config.StatementTimeoutInSecs)
	defer cancel()

	return pg.conn.PingContext(ctx)
}

func (pg *postgres) createSchemaTableIfNotExists() (err error) {
	ctx, cancel := drivers.GetContext(pg.config.StatementTimeoutInSecs)
	defer cancel()

	createTableIfNotExistsQuery := fmt.Sprintf("CREATE TABLE IF NOT EXISTS %s (version bigint not null primary key, name varchar not null)", pg.config.MigrationsTable)
	if _, err = pg.conn.ExecContext(ctx, createTableIfNotExistsQuery); err != nil {
		return &drivers.DatabaseError{
			OrigErr: err,
			Driver:  driverName,
			Message: "failed while executing query",
			Command: "create_migrations_table_if_not_exists",
			Query:   []byte(createTableIfNotExistsQuery),
		}
	}

	return nil
}

func (postgres) DriverName() string {
	return driverName
}

func (pg *postgres) Close() error {
	if pg.conn != nil {
		if err := pg.conn.Close(); err != nil {
			return &drivers.DatabaseError{
				OrigErr: err,
				Driver:  driverName,
				Message: "failed to close database connection",
				Command: "pg_conn_close",
				Query:   nil,
			}
		}
	}

	if pg.db != nil && pg.config.closeDBonClose {
		if err := pg.db.Close(); err != nil {
			return &drivers.DatabaseError{
				OrigErr: err,
				Driver:  driverName,
				Message: "failed to close database",
				Command: "pg_db_close",
				Query:   nil,
			}
		}
		pg.db = nil
	}

	pg.conn = nil
	return nil
}

func (pg *postgres) Apply(migration *models.Migration, saveVersion bool) (err error) {
	query := migration.Query()

	ctx, cancel := drivers.GetContext(pg.config.StatementTimeoutInSecs)
	defer cancel()

	nonTransactional := strings.HasPrefix(query, "-- "+nonTransactionalPrefix)
	// We wrap with a transaction only when there is no non-transactional prefix.
	if !nonTransactional {
		transaction, err := pg.conn.BeginTx(ctx, nil)
		if err != nil {
			return &drivers.DatabaseError{
				OrigErr: err,
				Driver:  driverName,
				Message: "error while opening a transaction to the database",
				Command: "begin_transaction",
			}
		}

		if err = executeQuery(ctx, transaction, query); err != nil {
			return err
		}

		if saveVersion {
			if err = executeQuery(ctx, transaction, pg.addMigrationQuery(migration)); err != nil {
				return err
			}
		}

		err = transaction.Commit()
		if err != nil {
			return &drivers.DatabaseError{
				OrigErr: err,
				Driver:  driverName,
				Message: "error while committing a transaction to the database",
				Command: "commit_transaction",
			}
		}
	} else {
		_, err := pg.conn.ExecContext(ctx, query)
		if err != nil {
			return &drivers.DatabaseError{
				OrigErr: err,
				Driver:  driverName,
				Message: "failed to execute migration",
				Command: "executing_query",
				Query:   []byte(query),
			}
		}

		if saveVersion {
			_, err = pg.conn.ExecContext(ctx, pg.addMigrationQuery(migration))
			if err != nil {
				return &drivers.DatabaseError{
					OrigErr: err,
					Driver:  driverName,
					Message: "failed to save version",
					Command: "executing_query",
					Query:   []byte(query),
				}
			}
		}
	}

	return nil
}

func (pg *postgres) AppliedMigrations() (migrations []*models.Migration, err error) {
	if pg.conn == nil {
		return nil, &drivers.AppError{
			OrigErr: errors.New("driver has no connection established"),
			Message: "database connection is missing",
			Driver:  driverName,
		}
	}

	if err := pg.createSchemaTableIfNotExists(); err != nil {
		return nil, err
	}

	query := fmt.Sprintf("SELECT version, name FROM %s", pg.config.MigrationsTable)
	ctx, cancel := drivers.GetContext(pg.config.StatementTimeoutInSecs)
	defer cancel()
	var appliedMigrations []*models.Migration
	var version uint32
	var name string

	rows, err := pg.conn.QueryContext(ctx, query)
	if err != nil {
		return nil, &drivers.DatabaseError{
			OrigErr: err,
			Driver:  driverName,
			Message: "failed to fetch applied migrations",
			Command: "select_applied_migrations",
			Query:   []byte(query),
		}
	}
	defer rows.Close()

	for rows.Next() {
		if err := rows.Scan(&version, &name); err != nil {
			return nil, &drivers.DatabaseError{
				OrigErr: err,
				Driver:  driverName,
				Message: "failed to scan applied migration row",
				Command: "scan_applied_migrations",
			}
		}

		appliedMigrations = append(appliedMigrations, &models.Migration{
			Name:      name,
			Version:   version,
			Direction: models.Up,
		})
	}

	return appliedMigrations, nil
}

func (pg *postgres) addMigrationQuery(migration *models.Migration) string {
	if migration.Direction == models.Down {
		return fmt.Sprintf("DELETE FROM %s WHERE (Version=%d AND NAME='%s')", pg.config.MigrationsTable, migration.Version, migration.Name)
	}
	return fmt.Sprintf("INSERT INTO %s (version, name) VALUES (%d, '%s')", pg.config.MigrationsTable, migration.Version, migration.Name)
}

func executeQuery(ctx context.Context, transaction *sql.Tx, query string) error {
	if _, err := transaction.ExecContext(ctx, query); err != nil {
		if txErr := transaction.Rollback(); txErr != nil {
			err = errors.Wrap(errors.New(err.Error()+txErr.Error()), "failed to execute query in migration transaction")

			return &drivers.DatabaseError{
				OrigErr: err,
				Driver:  driverName,
				Command: "rollback_transaction",
			}
		}

		return &drivers.DatabaseError{
			OrigErr: err,
			Driver:  driverName,
			Message: "failed to execute migration",
			Command: "executing_query",
			Query:   []byte(query),
		}
	}

	return nil
}

func currentDatabaseNameFromDB(conn *sql.Conn, config *driverConfig) (string, error) {
	query := "SELECT CURRENT_DATABASE()"

	ctx, cancel := drivers.GetContext(config.StatementTimeoutInSecs)
	defer cancel()

	var databaseName string
	if err := conn.QueryRowContext(ctx, query).Scan(&databaseName); err != nil {
		return "", &drivers.DatabaseError{
			OrigErr: err,
			Driver:  driverName,
			Message: "failed to fetch database name",
			Command: "current_database",
			Query:   []byte(query),
		}
	}
	return databaseName, nil
}

func (pg *postgres) SetConfig(key string, value interface{}) error {
	if pg.config != nil {
		switch key {
		case "StatementTimeoutInSecs":
			n, ok := value.(int)
			if ok {
				pg.config.StatementTimeoutInSecs = n
				return nil
			}
			return fmt.Errorf("incorrect value type for %s", key)
		case "MigrationsTable":
			n, ok := value.(string)
			if ok {
				pg.config.MigrationsTable = n
				return nil
			}
			return fmt.Errorf("incorrect value type for %s", key)
		}
	}

	return fmt.Errorf("incorrect key name %q", key)
}