package sqlplaceholder

import (
	"strconv"
	"strings"
)

// ConvertQuestionToDollarPlaceholders converts '?' to '$1,$2,...' in SQL text.
// It skips quoted strings, quoted identifiers and comments.
func ConvertQuestionToDollarPlaceholders(query string) string {
	if query == "" || !strings.Contains(query, "?") {
		return query
	}

	const (
		stateNormal = iota
		stateSingleQuote
		stateDoubleQuote
		stateBacktick
		stateLineComment
		stateBlockComment
	)

	var b strings.Builder
	b.Grow(len(query) + 8)

	state := stateNormal
	index := 1

	for i := 0; i < len(query); i++ {
		c := query[i]

		switch state {
		case stateNormal:
			if c == '\'' {
				state = stateSingleQuote
				b.WriteByte(c)
				continue
			}
			if c == '"' {
				state = stateDoubleQuote
				b.WriteByte(c)
				continue
			}
			if c == '`' {
				state = stateBacktick
				b.WriteByte(c)
				continue
			}
			if c == '-' && i+1 < len(query) && query[i+1] == '-' {
				state = stateLineComment
				b.WriteByte(c)
				i++
				b.WriteByte(query[i])
				continue
			}
			if c == '/' && i+1 < len(query) && query[i+1] == '*' {
				state = stateBlockComment
				b.WriteByte(c)
				i++
				b.WriteByte(query[i])
				continue
			}
			if c == '?' {
				b.WriteByte('$')
				b.WriteString(strconv.Itoa(index))
				index++
				continue
			}
			b.WriteByte(c)

		case stateSingleQuote:
			b.WriteByte(c)
			if c == '\'' {
				// SQL escaped single quote: ''
				if i+1 < len(query) && query[i+1] == '\'' {
					i++
					b.WriteByte(query[i])
					continue
				}
				state = stateNormal
			}

		case stateDoubleQuote:
			b.WriteByte(c)
			if c == '"' {
				// escaped double quote: ""
				if i+1 < len(query) && query[i+1] == '"' {
					i++
					b.WriteByte(query[i])
					continue
				}
				state = stateNormal
			}

		case stateBacktick:
			b.WriteByte(c)
			if c == '`' {
				state = stateNormal
			}

		case stateLineComment:
			b.WriteByte(c)
			if c == '\n' {
				state = stateNormal
			}

		case stateBlockComment:
			b.WriteByte(c)
			if c == '*' && i+1 < len(query) && query[i+1] == '/' {
				i++
				b.WriteByte(query[i])
				state = stateNormal
			}
		}
	}

	return b.String()
}