package sqlruntime

import "strings"

// FingerprintSQL creates a normalized SQL fingerprint.
// mode controls literal masking; keepComments controls whether comments are preserved.
func FingerprintSQL(query string, mode int, keepComments bool) string {
	prepared := query
	if !keepComments {
		prepared = stripSQLComments(prepared)
	}

	normalized := normalizeSQL(prepared)
	if normalized == "" {
		return ""
	}

	if NormalizeFingerprintMode(mode) == fingerprintModeMaskLiterals {
		return maskSQLLiterals(normalized, keepComments)
	}
	return normalized
}

func normalizeSQL(query string) string {
	normalized := strings.ToLower(strings.TrimSpace(query))
	if normalized == "" {
		return ""
	}
	return strings.Join(strings.Fields(normalized), " ")
}

func stripSQLComments(query string) string {
	if query == "" {
		return ""
	}

	const (
		stateNormal = iota
		stateSingleQuote
		stateDoubleQuote
		stateBacktick
		stateLineComment
		stateBlockComment
	)

	var b strings.Builder
	b.Grow(len(query))
	state := stateNormal

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

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

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

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

	return b.String()
}

func maskSQLLiterals(query string, keepComments bool) string {
	if query == "" {
		return ""
	}

	const (
		stateNormal = iota
		stateSingleQuote
		stateDoubleQuote
		stateBacktick
		stateLineComment
		stateBlockComment
	)

	var b strings.Builder
	b.Grow(len(query))
	state := stateNormal

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

		switch state {
		case stateNormal:
			if c == '\'' {
				b.WriteByte('?')
				state = stateSingleQuote
				continue
			}
			if c == '"' {
				b.WriteByte(c)
				state = stateDoubleQuote
				continue
			}
			if c == '`' {
				b.WriteByte(c)
				state = stateBacktick
				continue
			}
			if c == '-' && i+1 < len(query) && query[i+1] == '-' {
				if keepComments {
					b.WriteByte(c)
					i++
					b.WriteByte(query[i])
				} else {
					b.WriteByte(' ')
					i++
				}
				state = stateLineComment
				continue
			}
			if c == '/' && i+1 < len(query) && query[i+1] == '*' {
				if keepComments {
					b.WriteByte(c)
					i++
					b.WriteByte(query[i])
				} else {
					b.WriteByte(' ')
					i++
				}
				state = stateBlockComment
				continue
			}
			if c == '$' {
				j := i + 1
				for j < len(query) && isDigit(query[j]) {
					j++
				}
				if j > i+1 {
					b.WriteByte('?')
					i = j - 1
					continue
				}
			}
			if c == '-' && i+1 < len(query) && isDigit(query[i+1]) && isNumberBoundaryBefore(query, i) {
				j := scanNumber(query, i+1)
				if isNumberBoundaryAfter(query, j) {
					b.WriteByte('?')
					i = j - 1
					continue
				}
			}
			if isDigit(c) && isNumberBoundaryBefore(query, i) {
				j := scanNumber(query, i)
				if isNumberBoundaryAfter(query, j) {
					b.WriteByte('?')
					i = j - 1
					continue
				}
			}
			b.WriteByte(c)

		case stateSingleQuote:
			if c == '\'' {
				if i+1 < len(query) && query[i+1] == '\'' {
					i++
					continue
				}
				state = stateNormal
			}

		case stateDoubleQuote:
			b.WriteByte(c)
			if c == '"' {
				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:
			if keepComments {
				b.WriteByte(c)
			}
			if c == '\n' {
				if !keepComments {
					b.WriteByte(' ')
				}
				state = stateNormal
			}

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

	return strings.Join(strings.Fields(b.String()), " ")
}

func isDigit(c byte) bool {
	return c >= '0' && c <= '9'
}

func isIdentifierChar(c byte) bool {
	return (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') || c == '_'
}

func isNumberBoundaryBefore(query string, index int) bool {
	if index <= 0 {
		return true
	}
	prev := query[index-1]
	return !isIdentifierChar(prev) && prev != '$' && prev != '.'
}

func isNumberBoundaryAfter(query string, index int) bool {
	if index >= len(query) {
		return true
	}
	next := query[index]
	return !isIdentifierChar(next) && next != '.'
}

func scanNumber(query string, start int) int {
	i := start
	for i < len(query) && isDigit(query[i]) {
		i++
	}
	if i < len(query) && query[i] == '.' {
		i++
		for i < len(query) && isDigit(query[i]) {
			i++
		}
	}
	if i < len(query) && (query[i] == 'e' || query[i] == 'E') {
		i++
		if i < len(query) && (query[i] == '+' || query[i] == '-') {
			i++
		}
		for i < len(query) && isDigit(query[i]) {
			i++
		}
	}
	return i
}