package main

import (
	"context"
	"database/sql"
	"fmt"
	"hash/crc32"
	"os"
	"strconv"
	"strings"

	"github.com/lib/pq"
)

const (
	nilVersion         int  = -1
	migrationsTable         = "schema_migrations"
	advisoryLockIDSalt uint = 1486364155
)

type migrateDB struct {
	conn       *sql.Conn
	db         *sql.DB
	schemaName string
	dbName     string
	lockID     string
	isLocked   bool
}

func openDatabase(connStr string, schemaName string) (*migrateDB, error) {
	db, err := sql.Open("postgres", connStr)
	if err != nil {
		return nil, fmt.Errorf("failed to open database: %w", err)
	}

	if err := db.Ping(); err != nil {
		db.Close()
		return nil, fmt.Errorf("failed to connect to database: %w", err)
	}

	conn, err := db.Conn(context.Background())
	if err != nil {
		db.Close()
		return nil, fmt.Errorf("failed to acquire connection: %w", err)
	}

	mdb := &migrateDB{
		conn: conn,
		db:   db,
	}

	// get actual database name
	if err := conn.QueryRowContext(context.Background(), "SELECT current_database()").Scan(&mdb.dbName); err != nil {
		mdb.close()
		return nil, fmt.Errorf("failed to get database name: %w", err)
	}

	// determine schema name
	if schemaName != "" {
		mdb.schemaName = schemaName
	} else {
		if err := conn.QueryRowContext(context.Background(), "SELECT current_schema()").Scan(&mdb.schemaName); err != nil {
			mdb.close()
			return nil, fmt.Errorf("failed to get schema name: %w", err)
		}
	}

	mdb.lockID = generateAdvisoryLockID(mdb.dbName, mdb.schemaName)

	// ensure the schema_migrations table exists
	if err := mdb.ensureVersionTable(); err != nil {
		mdb.close()
		return nil, err
	}

	return mdb, nil
}

func (d *migrateDB) close() error {
	var connErr, dbErr error
	if d.conn != nil {
		connErr = d.conn.Close()
	}
	if d.db != nil {
		dbErr = d.db.Close()
	}
	if connErr != nil {
		return connErr
	}
	return dbErr
}

func (d *migrateDB) ensureVersionTable() error {
	if err := d.lock(); err != nil {
		return err
	}
	defer d.unlock()

	// check if table already exists
	var count int
	query := `SELECT COUNT(1) FROM information_schema.tables WHERE table_schema = $1 AND table_name = $2 LIMIT 1`
	if err := d.conn.QueryRowContext(context.Background(), query, d.schemaName, migrationsTable).Scan(&count); err != nil {
		return fmt.Errorf("failed to check for migrations table: %w", err)
	}

	if count > 0 {
		return nil
	}

	// create the table
	createQuery := `CREATE TABLE IF NOT EXISTS ` +
		pq.QuoteIdentifier(d.schemaName) + `.` + pq.QuoteIdentifier(migrationsTable) +
		` (version bigint NOT NULL PRIMARY KEY, dirty boolean NOT NULL)`

	if _, err := d.conn.ExecContext(context.Background(), createQuery); err != nil {
		return fmt.Errorf("failed to create migrations table: %w", err)
	}

	return nil
}

// generateAdvisoryLockID replicates golang-migrate's lock ID generation.
// Internally: strings.Join(append([]string{schemaName, tableName}, databaseName), "\x00")
// Result: "schemaName\x00tableName\x00databaseName"
// Then: CRC32(result) * 1486364155
func generateAdvisoryLockID(dbName, schemaName string) string {
	combined := strings.Join([]string{schemaName, migrationsTable, dbName}, "\x00")
	sum := crc32.ChecksumIEEE([]byte(combined))
	sum = sum * uint32(advisoryLockIDSalt)
	return fmt.Sprint(sum)
}

func (d *migrateDB) lock() error {
	if d.isLocked {
		return fmt.Errorf("database already locked")
	}

	query := `SELECT pg_advisory_lock($1)`
	if _, err := d.conn.ExecContext(context.Background(), query, d.lockID); err != nil {
		return fmt.Errorf("failed to acquire advisory lock: %w", err)
	}

	d.isLocked = true
	return nil
}

func (d *migrateDB) unlock() error {
	if !d.isLocked {
		return nil
	}

	query := `SELECT pg_advisory_unlock($1)`
	if _, err := d.conn.ExecContext(context.Background(), query, d.lockID); err != nil {
		return fmt.Errorf("failed to release advisory lock: %w", err)
	}

	d.isLocked = false
	return nil
}

func (d *migrateDB) version() (int, bool, error) {
	query := `SELECT version, dirty FROM ` +
		pq.QuoteIdentifier(d.schemaName) + `.` + pq.QuoteIdentifier(migrationsTable) +
		` LIMIT 1`

	var version int
	var dirty bool
	err := d.conn.QueryRowContext(context.Background(), query).Scan(&version, &dirty)

	switch {
	case err == sql.ErrNoRows:
		return nilVersion, false, nil
	case err != nil:
		if e, ok := err.(*pq.Error); ok {
			if e.Code.Name() == "undefined_table" {
				return nilVersion, false, nil
			}
		}
		return 0, false, fmt.Errorf("failed to get migration version: %w", err)
	default:
		return version, dirty, nil
	}
}

func (d *migrateDB) setVersion(version int, dirty bool) error {
	tx, err := d.conn.BeginTx(context.Background(), &sql.TxOptions{})
	if err != nil {
		return fmt.Errorf("failed to begin transaction: %w", err)
	}

	truncateQuery := `TRUNCATE ` +
		pq.QuoteIdentifier(d.schemaName) + `.` + pq.QuoteIdentifier(migrationsTable)

	if _, err := tx.Exec(truncateQuery); err != nil {
		tx.Rollback()
		return fmt.Errorf("failed to truncate migrations table: %w", err)
	}

	// re-write the schema version for nil dirty versions to prevent
	// empty schema version for failed down migration on the first migration
	if version >= 0 || (version == nilVersion && dirty) {
		insertQuery := `INSERT INTO ` +
			pq.QuoteIdentifier(d.schemaName) + `.` + pq.QuoteIdentifier(migrationsTable) +
			` (version, dirty) VALUES ($1, $2)`

		if _, err := tx.Exec(insertQuery, version, dirty); err != nil {
			tx.Rollback()
			return fmt.Errorf("failed to insert migration version: %w", err)
		}
	}

	if err := tx.Commit(); err != nil {
		return fmt.Errorf("failed to commit version update: %w", err)
	}

	return nil
}

func (d *migrateDB) run(filePath string) error {
	content, err := os.ReadFile(filePath)
	if err != nil {
		return fmt.Errorf("failed to read migration file %s: %w", filePath, err)
	}

	query := string(content)
	if strings.TrimSpace(query) == "" {
		return nil
	}

	if _, err := d.conn.ExecContext(context.Background(), query); err != nil {
		if pgErr, ok := err.(*pq.Error); ok {
			message := fmt.Sprintf("migration failed: %s", pgErr.Message)
			if pgErr.Position != "" {
				if pos, parseErr := strconv.ParseUint(pgErr.Position, 10, 64); parseErr == nil {
					line, col, ok := computeLineFromPos(query, int(pos))
					if ok {
						message = fmt.Sprintf("%s (line %d, column %d)", message, line, col)
					}
				}
			}
			if pgErr.Detail != "" {
				message = fmt.Sprintf("%s, %s", message, pgErr.Detail)
			}
			return fmt.Errorf("%s", message)
		}
		return fmt.Errorf("migration failed: %w", err)
	}

	return nil
}

func (d *migrateDB) drop() error {
	// Drop tables.
	tableQuery := `SELECT table_name FROM information_schema.tables WHERE table_schema=$1 AND table_type='BASE TABLE'`
	rows, err := d.conn.QueryContext(context.Background(), tableQuery, d.schemaName)
	if err != nil {
		return fmt.Errorf("failed to query tables: %w", err)
	}
	defer rows.Close()

	var tableNames []string
	for rows.Next() {
		var tableName string
		if err := rows.Scan(&tableName); err != nil {
			return fmt.Errorf("failed to scan table name: %w", err)
		}
		if len(tableName) > 0 {
			tableNames = append(tableNames, tableName)
		}
	}
	if err := rows.Err(); err != nil {
		return fmt.Errorf("failed to iterate tables: %w", err)
	}

	for _, t := range tableNames {
		dropQuery := `DROP TABLE IF EXISTS ` + pq.QuoteIdentifier(d.schemaName) + `.` + pq.QuoteIdentifier(t) + ` CASCADE`
		if _, err := d.conn.ExecContext(context.Background(), dropQuery); err != nil {
			return fmt.Errorf("failed to drop table %s: %w", t, err)
		}
	}

	// Drop views.
	viewQuery := `SELECT table_name FROM information_schema.views WHERE table_schema=$1`
	viewRows, err := d.conn.QueryContext(context.Background(), viewQuery, d.schemaName)
	if err != nil {
		return fmt.Errorf("failed to query views: %w", err)
	}
	defer viewRows.Close()

	var viewNames []string
	for viewRows.Next() {
		var viewName string
		if err := viewRows.Scan(&viewName); err != nil {
			return fmt.Errorf("failed to scan view name: %w", err)
		}
		viewNames = append(viewNames, viewName)
	}
	if err := viewRows.Err(); err != nil {
		return fmt.Errorf("failed to iterate views: %w", err)
	}

	for _, v := range viewNames {
		dropQuery := `DROP VIEW IF EXISTS ` + pq.QuoteIdentifier(d.schemaName) + `.` + pq.QuoteIdentifier(v) + ` CASCADE`
		if _, err := d.conn.ExecContext(context.Background(), dropQuery); err != nil {
			return fmt.Errorf("failed to drop view %s: %w", v, err)
		}
	}

	// Drop custom types (enums, composites, domains, ranges). typtype 'b' (base)
	// already excludes Postgres' auto-generated array types, so no further
	// filtering by name is needed.
	typeQuery := `
        SELECT t.typname
        FROM pg_type t
        JOIN pg_namespace n ON n.oid = t.typnamespace
        WHERE n.nspname = $1
          AND t.typtype IN ('e', 'c', 'd', 'r')
          AND NOT EXISTS (
              SELECT 1 FROM pg_class c
              WHERE c.reltype = t.oid AND c.relkind IN ('r', 'v', 'm', 'f', 'p')
          )
    `
	typeRows, err := d.conn.QueryContext(context.Background(), typeQuery, d.schemaName)
	if err != nil {
		return fmt.Errorf("failed to query types: %w", err)
	}
	defer typeRows.Close()

	var typeNames []string
	for typeRows.Next() {
		var typeName string
		if err := typeRows.Scan(&typeName); err != nil {
			return fmt.Errorf("failed to scan type name: %w", err)
		}
		typeNames = append(typeNames, typeName)
	}
	if err := typeRows.Err(); err != nil {
		return fmt.Errorf("failed to iterate types: %w", err)
	}

	for _, tn := range typeNames {
		dropQuery := `DROP TYPE IF EXISTS ` + pq.QuoteIdentifier(d.schemaName) + `.` + pq.QuoteIdentifier(tn) + ` CASCADE`
		if _, err := d.conn.ExecContext(context.Background(), dropQuery); err != nil {
			return fmt.Errorf("failed to drop type %s: %w", tn, err)
		}
	}

	return nil
}

func computeLineFromPos(s string, pos int) (line uint, col uint, ok bool) {
	s = strings.ReplaceAll(s, "\r\n", "\n")
	runes := []rune(s)
	if pos > len(runes) {
		return 0, 0, false
	}
	sel := runes[:pos]
	line = uint(runesCount(sel, '\n') + 1)
	col = uint(pos - 1 - runesLastIndex(sel, '\n'))
	return line, col, true
}

func runesCount(input []rune, target rune) int {
	var count int
	for _, r := range input {
		if r == target {
			count++
		}
	}
	return count
}

func runesLastIndex(input []rune, target rune) int {
	for i := len(input) - 1; i >= 0; i-- {
		if input[i] == target {
			return i
		}
	}
	return -1
}