package string

import (
	"fmt"
	"math/rand"
	"regexp"
	"strconv"
	"strings"
	"time"
	"unicode"
	"unicode/utf8"

	luajit "git.sharkk.net/Sky/LuaJIT-to-Go"
	"golang.org/x/text/cases"
	"golang.org/x/text/language"
)

const (
	maxStringLength = 10_000_000 // 10MB limit for safety
	maxRepeatCount  = 1_000_000  // Prevent excessive memory usage
	maxRandomLength = 100_000    // Reasonable limit for random strings
)

func validateStringLength(s string) error {
	if len(s) > maxStringLength {
		return fmt.Errorf("string too large (max %d bytes)", maxStringLength)
	}
	return nil
}

func GetStringFunctions() map[string]luajit.GoFunction {
	return map[string]luajit.GoFunction{
		"string_split": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_split: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_split: first argument must be a string")
			}
			sep, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_split: second argument must be a string")
			}

			if err := validateStringLength(str); err != nil {
				return s.PushError("string_split: %v", err)
			}

			// Handle empty separator - split into characters
			if sep == "" {
				runes := []rune(str)
				parts := make([]string, len(runes))
				for i, r := range runes {
					parts[i] = string(r)
				}
				if err := s.PushValue(parts); err != nil {
					return s.PushError("string_split: failed to push result: %v", err)
				}
				return 1
			}

			parts := strings.Split(str, sep)
			if err := s.PushValue(parts); err != nil {
				return s.PushError("string_split: failed to push result: %v", err)
			}
			return 1
		},

		"string_join": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_join: %v", err)
			}
			arr, err := s.SafeToTable(1)
			if err != nil {
				return s.PushError("string_join: first argument must be a table")
			}
			sep, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_join: second argument must be a string")
			}

			var parts []string
			switch v := arr.(type) {
			case []string:
				parts = v
			case []any:
				parts = make([]string, len(v))
				for i, val := range v {
					if val == nil {
						parts[i] = ""
					} else {
						parts[i] = fmt.Sprintf("%v", val)
					}
				}
			case map[string]any:
				if len(v) == 0 {
					parts = []string{}
				} else {
					return s.PushError("string_join: first argument must be an array, not a map")
				}
			default:
				return s.PushError("string_join: first argument must be an array")
			}

			result := strings.Join(parts, sep)
			if err := validateStringLength(result); err != nil {
				return s.PushError("string_join: result %v", err)
			}

			s.PushString(result)
			return 1
		},

		"string_trim": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_trim: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_trim: argument must be a string")
			}
			s.PushString(strings.TrimSpace(str))
			return 1
		},

		"string_trim_left": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_trim_left: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_trim_left: first argument must be a string")
			}

			if s.GetTop() >= 2 && !s.IsNil(2) {
				cutset, err := s.SafeToString(2)
				if err != nil {
					return s.PushError("string_trim_left: second argument must be a string")
				}
				s.PushString(strings.TrimLeft(str, cutset))
			} else {
				s.PushString(strings.TrimLeftFunc(str, unicode.IsSpace))
			}
			return 1
		},

		"string_trim_right": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_trim_right: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_trim_right: first argument must be a string")
			}

			if s.GetTop() >= 2 && !s.IsNil(2) {
				cutset, err := s.SafeToString(2)
				if err != nil {
					return s.PushError("string_trim_right: second argument must be a string")
				}
				s.PushString(strings.TrimRight(str, cutset))
			} else {
				s.PushString(strings.TrimRightFunc(str, unicode.IsSpace))
			}
			return 1
		},

		"string_upper": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_upper: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_upper: argument must be a string")
			}
			s.PushString(strings.ToUpper(str))
			return 1
		},

		"string_lower": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_lower: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_lower: argument must be a string")
			}
			s.PushString(strings.ToLower(str))
			return 1
		},

		"string_title": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_title: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_title: argument must be a string")
			}
			caser := cases.Title(language.English, cases.NoLower)
			s.PushString(caser.String(str))
			return 1
		},

		"string_contains": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_contains: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_contains: first argument must be a string")
			}
			substr, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_contains: second argument must be a string")
			}
			s.PushBoolean(strings.Contains(str, substr))
			return 1
		},

		"string_starts_with": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_starts_with: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_starts_with: first argument must be a string")
			}
			prefix, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_starts_with: second argument must be a string")
			}
			s.PushBoolean(strings.HasPrefix(str, prefix))
			return 1
		},

		"string_ends_with": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_ends_with: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_ends_with: first argument must be a string")
			}
			suffix, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_ends_with: second argument must be a string")
			}
			s.PushBoolean(strings.HasSuffix(str, suffix))
			return 1
		},

		"string_replace": func(s *luajit.State) int {
			if err := s.CheckExactArgs(3); err != nil {
				return s.PushError("string_replace: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_replace: first argument must be a string")
			}
			old, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_replace: second argument must be a string")
			}
			new, err := s.SafeToString(3)
			if err != nil {
				return s.PushError("string_replace: third argument must be a string")
			}

			if old == "" {
				return s.PushError("string_replace: cannot replace empty string")
			}

			result := strings.ReplaceAll(str, old, new)
			if err := validateStringLength(result); err != nil {
				return s.PushError("string_replace: result %v", err)
			}

			s.PushString(result)
			return 1
		},

		"string_replace_n": func(s *luajit.State) int {
			if err := s.CheckExactArgs(4); err != nil {
				return s.PushError("string_replace_n: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_replace_n: first argument must be a string")
			}
			old, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_replace_n: second argument must be a string")
			}
			new, err := s.SafeToString(3)
			if err != nil {
				return s.PushError("string_replace_n: third argument must be a string")
			}
			n, err := s.SafeToNumber(4)
			if err != nil || n != float64(int(n)) || n < 0 {
				return s.PushError("string_replace_n: fourth argument must be a non-negative integer")
			}

			if old == "" {
				return s.PushError("string_replace_n: cannot replace empty string")
			}

			result := strings.Replace(str, old, new, int(n))
			s.PushString(result)
			return 1
		},

		"string_index": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_index: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_index: first argument must be a string")
			}
			substr, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_index: second argument must be a string")
			}

			if substr == "" {
				s.PushNumber(1) // Empty string found at position 1
				return 1
			}

			index := strings.Index(str, substr)
			if index == -1 {
				s.PushNumber(0) // Not found
			} else {
				s.PushNumber(float64(index + 1)) // Convert to 1-indexed
			}
			return 1
		},

		"string_last_index": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_last_index: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_last_index: first argument must be a string")
			}
			substr, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_last_index: second argument must be a string")
			}

			if substr == "" {
				s.PushNumber(float64(utf8.RuneCountInString(str) + 1)) // Empty string at end
				return 1
			}

			index := strings.LastIndex(str, substr)
			if index == -1 {
				s.PushNumber(0) // Not found
			} else {
				s.PushNumber(float64(index + 1)) // Convert to 1-indexed
			}
			return 1
		},

		"string_count": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_count: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_count: first argument must be a string")
			}
			substr, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("string_count: second argument must be a string")
			}

			if substr == "" {
				// Empty string matches at every position including boundaries
				s.PushNumber(float64(utf8.RuneCountInString(str) + 1))
				return 1
			}

			count := strings.Count(str, substr)
			s.PushNumber(float64(count))
			return 1
		},

		"string_repeat": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("string_repeat: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_repeat: first argument must be a string")
			}
			count, err := s.SafeToNumber(2)
			if err != nil || count < 0 || count != float64(int(count)) {
				return s.PushError("string_repeat: second argument must be a non-negative integer")
			}

			n := int(count)
			if n == 0 {
				s.PushString("")
				return 1
			}

			// Check for potential overflow
			if len(str) > 0 && n > maxRepeatCount/len(str) {
				return s.PushError("string_repeat: result would be too large")
			}

			result := strings.Repeat(str, n)
			s.PushString(result)
			return 1
		},

		"string_reverse": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_reverse: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_reverse: argument must be a string")
			}

			if !utf8.ValidString(str) {
				return s.PushError("string_reverse: invalid UTF-8 string")
			}

			runes := []rune(str)
			for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
				runes[i], runes[j] = runes[j], runes[i]
			}
			s.PushString(string(runes))
			return 1
		},

		"string_length": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_length: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_length: argument must be a string")
			}
			s.PushNumber(float64(utf8.RuneCountInString(str)))
			return 1
		},

		"string_byte_length": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_byte_length: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_byte_length: argument must be a string")
			}
			s.PushNumber(float64(len(str)))
			return 1
		},

		"string_lines": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_lines: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_lines: argument must be a string")
			}

			// Handle different line endings
			str = strings.ReplaceAll(str, "\r\n", "\n")
			str = strings.ReplaceAll(str, "\r", "\n")
			lines := strings.Split(str, "\n")

			if err := s.PushValue(lines); err != nil {
				return s.PushError("string_lines: failed to push result: %v", err)
			}
			return 1
		},

		"string_words": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_words: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_words: argument must be a string")
			}
			words := strings.Fields(str)
			if err := s.PushValue(words); err != nil {
				return s.PushError("string_words: failed to push result: %v", err)
			}
			return 1
		},

		"string_pad_left": func(s *luajit.State) int {
			if err := s.CheckMinArgs(2); err != nil {
				return s.PushError("string_pad_left: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_pad_left: first argument must be a string")
			}
			width, err := s.SafeToNumber(2)
			if err != nil || width != float64(int(width)) || width < 0 {
				return s.PushError("string_pad_left: second argument must be a non-negative integer")
			}

			padChar := " "
			if s.GetTop() >= 3 && !s.IsNil(3) {
				if p, err := s.SafeToString(3); err == nil && utf8.RuneCountInString(p) > 0 {
					runes := []rune(p)
					padChar = string(runes[0])
				}
			}

			currentLen := utf8.RuneCountInString(str)
			targetLen := int(width)
			if currentLen >= targetLen {
				s.PushString(str)
				return 1
			}

			padLen := targetLen - currentLen
			if padLen > maxRepeatCount {
				return s.PushError("string_pad_left: padding too large")
			}

			padding := strings.Repeat(padChar, padLen)
			s.PushString(padding + str)
			return 1
		},

		"string_pad_right": func(s *luajit.State) int {
			if err := s.CheckMinArgs(2); err != nil {
				return s.PushError("string_pad_right: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_pad_right: first argument must be a string")
			}
			width, err := s.SafeToNumber(2)
			if err != nil || width != float64(int(width)) || width < 0 {
				return s.PushError("string_pad_right: second argument must be a non-negative integer")
			}

			padChar := " "
			if s.GetTop() >= 3 && !s.IsNil(3) {
				if p, err := s.SafeToString(3); err == nil && utf8.RuneCountInString(p) > 0 {
					runes := []rune(p)
					padChar = string(runes[0])
				}
			}

			currentLen := utf8.RuneCountInString(str)
			targetLen := int(width)
			if currentLen >= targetLen {
				s.PushString(str)
				return 1
			}

			padLen := targetLen - currentLen
			if padLen > maxRepeatCount {
				return s.PushError("string_pad_right: padding too large")
			}

			padding := strings.Repeat(padChar, padLen)
			s.PushString(str + padding)
			return 1
		},

		"string_slice": func(s *luajit.State) int {
			if err := s.CheckMinArgs(2); err != nil {
				return s.PushError("string_slice: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_slice: first argument must be a string")
			}
			start, err := s.SafeToNumber(2)
			if err != nil || start != float64(int(start)) {
				return s.PushError("string_slice: second argument must be an integer")
			}

			if !utf8.ValidString(str) {
				return s.PushError("string_slice: invalid UTF-8 string")
			}

			runes := []rune(str)
			length := len(runes)
			startIdx := int(start) - 1 // Convert from 1-indexed to 0-indexed

			// Handle negative start index
			if startIdx < 0 {
				startIdx = 0
			}
			if startIdx >= length {
				s.PushString("")
				return 1
			}

			endIdx := length
			if s.GetTop() >= 3 && !s.IsNil(3) {
				end, err := s.SafeToNumber(3)
				if err == nil && end == float64(int(end)) {
					endIdx = int(end)
					// Handle negative end index (from end of string)
					if endIdx < 0 {
						endIdx = length + endIdx + 1
					}
					if endIdx < 0 {
						endIdx = 0
					}
					if endIdx > length {
						endIdx = length
					}
				}
			}

			if startIdx >= endIdx {
				s.PushString("")
				return 1
			}

			s.PushString(string(runes[startIdx:endIdx]))
			return 1
		},

		"regex_match": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("regex_match: %v", err)
			}
			pattern, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("regex_match: first argument must be a string")
			}
			str, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("regex_match: second argument must be a string")
			}

			re, err := regexp.Compile(pattern)
			if err != nil {
				s.PushBoolean(false)
				return 1
			}

			s.PushBoolean(re.MatchString(str))
			return 1
		},

		"regex_find": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("regex_find: %v", err)
			}
			pattern, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("regex_find: first argument must be a string")
			}
			str, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("regex_find: second argument must be a string")
			}

			re, err := regexp.Compile(pattern)
			if err != nil {
				s.PushNil()
				return 1
			}

			match := re.FindString(str)
			if match == "" {
				s.PushNil()
			} else {
				s.PushString(match)
			}
			return 1
		},

		"regex_find_all": func(s *luajit.State) int {
			if err := s.CheckExactArgs(2); err != nil {
				return s.PushError("regex_find_all: %v", err)
			}
			pattern, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("regex_find_all: first argument must be a string")
			}
			str, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("regex_find_all: second argument must be a string")
			}

			re, err := regexp.Compile(pattern)
			if err != nil {
				// Return empty array for invalid patterns
				if err := s.PushValue([]string{}); err != nil {
					return s.PushError("regex_find_all: failed to push result: %v", err)
				}
				return 1
			}

			matches := re.FindAllString(str, -1)
			if matches == nil {
				matches = []string{} // Return empty array instead of nil
			}

			if err := s.PushValue(matches); err != nil {
				return s.PushError("regex_find_all: failed to push result: %v", err)
			}
			return 1
		},

		"regex_replace": func(s *luajit.State) int {
			if err := s.CheckExactArgs(3); err != nil {
				return s.PushError("regex_replace: %v", err)
			}
			pattern, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("regex_replace: first argument must be a string")
			}
			str, err := s.SafeToString(2)
			if err != nil {
				return s.PushError("regex_replace: second argument must be a string")
			}
			replacement, err := s.SafeToString(3)
			if err != nil {
				return s.PushError("regex_replace: third argument must be a string")
			}

			re, err := regexp.Compile(pattern)
			if err != nil {
				// Return original string for invalid patterns
				s.PushString(str)
				return 1
			}

			result := re.ReplaceAllString(str, replacement)
			s.PushString(result)
			return 1
		},

		"string_to_number": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_to_number: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_to_number: argument must be a string")
			}

			// Trim whitespace for more lenient parsing
			str = strings.TrimSpace(str)

			// Try float first for more general parsing
			if num, err := strconv.ParseFloat(str, 64); err == nil {
				s.PushNumber(num)
				return 1
			}

			s.PushNil()
			return 1
		},

		"string_is_numeric": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_is_numeric: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_is_numeric: argument must be a string")
			}

			str = strings.TrimSpace(str)
			if str == "" {
				s.PushBoolean(false)
				return 1
			}

			_, err1 := strconv.ParseFloat(str, 64)
			s.PushBoolean(err1 == nil)
			return 1
		},

		"string_is_alpha": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_is_alpha: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_is_alpha: argument must be a string")
			}

			if len(str) == 0 {
				s.PushBoolean(false)
				return 1
			}

			for _, r := range str {
				if !unicode.IsLetter(r) {
					s.PushBoolean(false)
					return 1
				}
			}
			s.PushBoolean(true)
			return 1
		},

		"string_is_alphanumeric": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_is_alphanumeric: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_is_alphanumeric: argument must be a string")
			}

			if len(str) == 0 {
				s.PushBoolean(false)
				return 1
			}

			for _, r := range str {
				if !unicode.IsLetter(r) && !unicode.IsDigit(r) {
					s.PushBoolean(false)
					return 1
				}
			}
			s.PushBoolean(true)
			return 1
		},

		"random_string": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("random_string: %v", err)
			}
			length, err := s.SafeToNumber(1)
			if err != nil || length != float64(int(length)) || length < 0 {
				return s.PushError("random_string: first argument must be a non-negative integer")
			}

			charset := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
			if s.GetTop() >= 2 && !s.IsNil(2) {
				if custom, err := s.SafeToString(2); err == nil && len(custom) > 0 {
					charset = custom
				}
			}

			n := int(length)
			if n == 0 {
				s.PushString("")
				return 1
			}
			if n > maxRandomLength {
				return s.PushError("random_string: length too large (max %d)", maxRandomLength)
			}

			// Validate charset for UTF-8
			if !utf8.ValidString(charset) {
				return s.PushError("random_string: charset must be valid UTF-8")
			}

			charsetRunes := []rune(charset)
			if len(charsetRunes) == 0 {
				return s.PushError("random_string: charset cannot be empty")
			}

			result := make([]rune, n)
			rnd := rand.New(rand.NewSource(time.Now().UnixNano()))
			for i := range result {
				result[i] = charsetRunes[rnd.Intn(len(charsetRunes))]
			}

			s.PushString(string(result))
			return 1
		},

		"string_is_valid_utf8": func(s *luajit.State) int {
			if err := s.CheckMinArgs(1); err != nil {
				return s.PushError("string_is_valid_utf8: %v", err)
			}
			str, err := s.SafeToString(1)
			if err != nil {
				return s.PushError("string_is_valid_utf8: argument must be a string")
			}
			s.PushBoolean(utf8.ValidString(str))
			return 1
		},
	}
}