package mysql

import (
	"errors"
	"strings"
)

// splitSQL supports ordinary migration statements, quoted values and comments.
// Stored routines and DELIMITER scripts are intentionally unsupported.
func splitSQL(src string) ([]string, error) {
	var out []string
	var b strings.Builder
	var quote byte
	lineComment, blockComment := false, false
	flush := func() error {
		s := strings.TrimSpace(b.String())
		b.Reset()
		if s == "" {
			return nil
		}
		if strings.HasPrefix(strings.ToUpper(s), "DELIMITER") {
			return errors.New("DELIMITER scripts are unsupported")
		}
		out = append(out, s)
		return nil
	}
	for i := 0; i < len(src); i++ {
		c := src[i]
		if lineComment {
			if c == '\n' {
				lineComment = false
				b.WriteByte(' ')
			}
			continue
		}
		if blockComment {
			if c == '*' && i+1 < len(src) && src[i+1] == '/' {
				blockComment = false
				i++
				b.WriteByte(' ')
			}
			continue
		}
		if quote != 0 {
			b.WriteByte(c)
			if c == '\\' && i+1 < len(src) {
				i++
				b.WriteByte(src[i])
				continue
			}
			if c == quote {
				if i+1 < len(src) && src[i+1] == quote {
					i++
					b.WriteByte(src[i])
				} else {
					quote = 0
				}
			}
			continue
		}
		if c == '#' || c == '-' && i+2 < len(src) && src[i+1] == '-' && src[i+2] <= ' ' {
			lineComment = true
			if c == '-' {
				i++
			}
			continue
		}
		if c == '/' && i+1 < len(src) && src[i+1] == '*' {
			if i+2 < len(src) && src[i+2] == '!' {
				return nil, errors.New("executable SQL comments are unsupported")
			}
			blockComment = true
			i++
			continue
		}
		if c == '\'' || c == '"' || c == '`' {
			quote = c
			b.WriteByte(c)
			continue
		}
		if c == ';' {
			if err := flush(); err != nil {
				return nil, err
			}
			continue
		}
		b.WriteByte(c)
	}
	if quote != 0 || blockComment {
		return nil, errors.New("unterminated SQL quote or comment")
	}
	if err := flush(); err != nil {
		return nil, err
	}
	if len(out) == 0 {
		return nil, errors.New("empty migration")
	}
	return out, nil
}