package app

import (
	"strings"
	"unicode"
)

func leadingSQLKeyword(query string) string {
	text := strings.TrimSpace(query)
	for len(text) > 0 {
		trimmed := strings.TrimLeft(text, " \t\r\n")
		if trimmed == "" {
			return ""
		}
		text = trimmed

		switch {
		case strings.HasPrefix(text, "--"):
			if idx := strings.IndexByte(text, '\n'); idx >= 0 {
				text = text[idx+1:]
				continue
			}
			return ""
		case strings.HasPrefix(text, "#"):
			if idx := strings.IndexByte(text, '\n'); idx >= 0 {
				text = text[idx+1:]
				continue
			}
			return ""
		case strings.HasPrefix(text, "/*"):
			if idx := strings.Index(text, "*/"); idx >= 0 {
				text = text[idx+2:]
				continue
			}
			return ""
		}
		break
	}

	if text == "" {
		return ""
	}
	for i, r := range text {
		if unicode.IsLetter(r) || unicode.IsDigit(r) || r == '_' {
			continue
		}
		if i == 0 {
			return ""
		}
		return strings.ToLower(text[:i])
	}
	return strings.ToLower(text)
}

func isReadOnlySQLQuery(dbType string, query string) bool {
	if strings.ToLower(strings.TrimSpace(dbType)) == "mongodb" && strings.HasPrefix(strings.TrimSpace(query), "{") {
		return true
	}

	switch leadingSQLKeyword(query) {
	case "select", "with", "show", "describe", "desc", "explain", "pragma", "values":
		return true
	default:
		return false
	}
}

func sanitizeSQLForPgLike(dbType string, query string) string {
	switch strings.ToLower(strings.TrimSpace(dbType)) {
	case "postgres", "kingbase", "highgo", "vastbase", "opengauss":
		// 有些情况下会出现多层重复引用（例如 """"schema"""" 或 ""schema"""），单次修复不一定收敛。
		// 这里做有限次数的迭代，直到输出不再变化。
		out := query
		for i := 0; i < 3; i++ {
			fixed := fixBrokenDoubleDoubleQuotedIdent(out)
			if fixed == out {
				break
			}
			out = fixed
		}
		return out
	default:
		return query
	}
}

// fixBrokenDoubleDoubleQuotedIdent fixes accidental identifiers like:
//
//	SELECT * FROM ""schema"".""table""
//
// which can be produced when a quoted identifier gets wrapped by quotes again.
//
// It is intentionally conservative:
// - only runs outside strings/comments/dollar-quoted blocks
// - does not touch valid escaped-quote sequences inside quoted identifiers (e.g. "a""b")
func fixBrokenDoubleDoubleQuotedIdent(query string) string {
	if !strings.Contains(query, `""`) {
		return query
	}

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

	inSingle := false
	inDoubleIdent := false
	inLineComment := false
	inBlockComment := false
	dollarTag := ""

	for i := 0; i < len(query); i++ {
		ch := query[i]
		next := byte(0)
		if i+1 < len(query) {
			next = query[i+1]
		}

		if inLineComment {
			b.WriteByte(ch)
			if ch == '\n' {
				inLineComment = false
			}
			continue
		}
		if inBlockComment {
			b.WriteByte(ch)
			if ch == '*' && next == '/' {
				b.WriteByte('/')
				i++
				inBlockComment = false
			}
			continue
		}
		if dollarTag != "" {
			if strings.HasPrefix(query[i:], dollarTag) {
				b.WriteString(dollarTag)
				i += len(dollarTag) - 1
				dollarTag = ""
				continue
			}
			b.WriteByte(ch)
			continue
		}
		if inSingle {
			b.WriteByte(ch)
			if ch == '\'' {
				// escaped single quote
				if next == '\'' {
					b.WriteByte('\'')
					i++
					continue
				}
				inSingle = false
			}
			continue
		}
		if inDoubleIdent {
			b.WriteByte(ch)
			if ch == '"' {
				// escaped quote inside identifier
				if next == '"' {
					b.WriteByte('"')
					i++
					continue
				}
				inDoubleIdent = false
			}
			continue
		}

		// --- Outside of all string/comment blocks ---
		if ch == '-' && next == '-' {
			b.WriteByte(ch)
			b.WriteByte('-')
			i++
			inLineComment = true
			continue
		}
		if ch == '/' && next == '*' {
			b.WriteByte(ch)
			b.WriteByte('*')
			i++
			inBlockComment = true
			continue
		}
		if ch == '\'' {
			b.WriteByte(ch)
			inSingle = true
			continue
		}
		if ch == '$' {
			if tag := parseDollarTag(query[i:]); tag != "" {
				b.WriteString(tag)
				i += len(tag) - 1
				dollarTag = tag
				continue
			}
		}

		if ch == '"' {
			// Fix: ""ident"" -> "ident" (only when it looks like a plain identifier)
			// Also handle variants like ""ident""" / """"ident"""" (extra quotes at either side).
			if next == '"' {
				if replacement, advance, ok := tryFixDoubleDoubleQuotedIdent(query, i); ok {
					b.WriteString(replacement)
					i = advance - 1
					continue
				}
			}

			b.WriteByte(ch)
			inDoubleIdent = true
			continue
		}

		b.WriteByte(ch)
	}

	return b.String()
}

func tryFixDoubleDoubleQuotedIdent(query string, start int) (replacement string, advance int, ok bool) {
	// start points at the first quote of a broken identifier, usually like:
	//   ""ident""  / ""ident""" / """"ident""""
	if start < 0 || start+1 >= len(query) {
		return "", 0, false
	}
	if query[start] != '"' || query[start+1] != '"' {
		return "", 0, false
	}
	if start > 0 && query[start-1] == '"' {
		return "", 0, false
	}

	runLen := 0
	for start+runLen < len(query) && query[start+runLen] == '"' {
		runLen++
	}
	if runLen < 2 || runLen%2 == 1 {
		// Odd run (e.g. """...) can be a valid quoted identifier with escaped quotes.
		return "", 0, false
	}

	contentStart := start + runLen
	j := contentStart
	for j < len(query) {
		if query[j] == '"' {
			endRunLen := 0
			for j+endRunLen < len(query) && query[j+endRunLen] == '"' {
				endRunLen++
			}
			if endRunLen >= 2 {
				content := strings.TrimSpace(query[contentStart:j])
				if looksLikeIdentifierContent(content) {
					return `"` + content + `"`, j + endRunLen, true
				}
				return "", 0, false
			}
		}
		// Fast abort: identifier-like content should not span lines.
		if query[j] == '\n' || query[j] == '\r' {
			break
		}
		j++
	}
	return "", 0, false
}

func looksLikeIdentifierContent(s string) bool {
	if strings.TrimSpace(s) == "" {
		return false
	}
	for _, r := range s {
		if r == '_' || r == '$' || r == '-' || unicode.IsLetter(r) || unicode.IsDigit(r) {
			continue
		}
		return false
	}
	return true
}

func parseDollarTag(s string) string {
	// Match: $tag$ where tag is [A-Za-z0-9_]* (can be empty => $$)
	if len(s) < 2 || s[0] != '$' {
		return ""
	}
	for i := 1; i < len(s); i++ {
		c := s[i]
		if c == '$' {
			return s[:i+1]
		}
		if !((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_') {
			return ""
		}
	}
	return ""
}