package databaseHelpers

import (
	"bufio"
	"database/sql"
	"strings"
)

// ExecScript executes a multi-statement SQL script.
// It only requires that statements end with ';' and ignores '--' comments.
// (Good for simple DDL/DML. If you add routines/triggers, upgrade later.)
func ExecScript(tx *sql.Tx, script string) error {
	sc := bufio.NewScanner(strings.NewReader(script))
	sc.Split(splitStatements)

	for sc.Scan() {
		stmt := strings.TrimSpace(sc.Text())
		if stmt == "" {
			continue
		}
		if _, err := tx.Exec(stmt); err != nil {
			return err
		}
	}
	return sc.Err()
}

// splitStatements separates statements at ';'
// and strips whitespace and '--' comments.
func splitStatements(data []byte, atEOF bool) (advance int, token []byte, err error) {
	// skip whitespace and comments
	start := 0
	for {
		// whitespace
		for start < len(data) {
			switch data[start] {
			case ' ', '\t', '\n', '\r':
				start++
				continue
			}
			break
		}
		// '-- comment'
		if start+1 < len(data) && data[start] == '-' && data[start+1] == '-' {
			i := start + 2
			for i < len(data) && data[i] != '\n' {
				i++
			}
			if i >= len(data) {
				return len(data), nil, nil
			}
			start = i + 1
			continue
		}
		break
	}

	// detect semicolon termination
	for i := start; i < len(data); i++ {
		if data[i] == ';' {
			return i + 1, data[start:i], nil
		}
	}
	if atEOF && start < len(data) {
		return len(data), data[start:], nil
	}
	return 0, nil, nil
}