package string

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

	luajit "git.sharkk.net/Sky/LuaJIT-to-Go"
)

const (
	maxStringLength = 10_000_000 // 10MB limit for safety
	maxRandomLength = 100_000    // Reasonable limit for random strings
)

func GetFunctionList() map[string]luajit.GoFunction {
	return map[string]luajit.GoFunction{
		"string_split":         string_split,
		"string_join":          string_join,
		"string_slice":         string_slice,
		"string_reverse":       string_reverse,
		"string_length":        string_length,
		"string_byte_length":   string_byte_length,
		"regex_match":          regex_match,
		"regex_find":           regex_find,
		"regex_find_all":       regex_find_all,
		"regex_replace":        regex_replace,
		"random_string":        random_string,
		"string_is_valid_utf8": string_is_valid_utf8,
	}
}

func string_split(s *luajit.State) int {
	str := s.ToString(1)
	sep := s.ToString(2)

	if len(str) > maxStringLength {
		s.PushNil()
		s.PushString("string too large")
		return 2
	}

	// 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)
		}
		s.PushValue(parts)
		return 1
	}

	parts := strings.Split(str, sep)
	s.PushValue(parts)
	return 1
}

func string_join(s *luajit.State) int {
	arr, err := s.ToValue(1)
	if err != nil {
		s.PushNil()
		s.PushString("invalid array")
		return 2
	}
	sep := s.ToString(2)

	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] = s.ToString(-1) // Convert via Lua
			}
		}
	case map[string]any:
		// Empty table {} from Lua becomes map[string]any{}
		if len(v) == 0 {
			parts = []string{} // Empty array
		} else {
			s.PushNil()
			s.PushString("not an array")
			return 2
		}
	default:
		s.PushNil()
		s.PushString("not an array")
		return 2
	}

	result := strings.Join(parts, sep)
	if len(result) > maxStringLength {
		s.PushNil()
		s.PushString("result too large")
		return 2
	}

	s.PushString(result)
	return 1
}

func string_slice(s *luajit.State) int {
	str := s.ToString(1)
	start := int(s.ToNumber(2))

	if !utf8.ValidString(str) {
		s.PushNil()
		s.PushString("invalid UTF-8")
		return 2
	}

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

	if startIdx < 0 {
		startIdx = 0
	}
	if startIdx >= length {
		s.PushString("")
		return 1
	}

	endIdx := length
	if s.GetTop() >= 3 && !s.IsNil(3) {
		end := int(s.ToNumber(3))
		if end < 0 {
			endIdx = length + end + 1
		} else {
			endIdx = end
		}
		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
}

func string_reverse(s *luajit.State) int {
	str := s.ToString(1)

	if !utf8.ValidString(str) {
		s.PushNil()
		s.PushString("invalid UTF-8")
		return 2
	}

	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
}

func string_length(s *luajit.State) int {
	str := s.ToString(1)
	s.PushNumber(float64(utf8.RuneCountInString(str)))
	return 1
}

func string_byte_length(s *luajit.State) int {
	str := s.ToString(1)
	s.PushNumber(float64(len(str)))
	return 1
}

func regex_match(s *luajit.State) int {
	pattern := s.ToString(1)
	str := s.ToString(2)

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

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

func regex_find(s *luajit.State) int {
	pattern := s.ToString(1)
	str := s.ToString(2)

	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
}

func regex_find_all(s *luajit.State) int {
	pattern := s.ToString(1)
	str := s.ToString(2)

	re, err := regexp.Compile(pattern)
	if err != nil {
		s.PushValue([]string{})
		return 1
	}

	matches := re.FindAllString(str, -1)
	if matches == nil {
		matches = []string{}
	}

	s.PushValue(matches)
	return 1
}

func regex_replace(s *luajit.State) int {
	pattern := s.ToString(1)
	str := s.ToString(2)
	replacement := s.ToString(3)

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

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

func random_string(s *luajit.State) int {
	length := int(s.ToNumber(1))
	if length < 0 || length > maxRandomLength {
		s.PushNil()
		s.PushString("invalid length")
		return 2
	}

	charset := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	if s.GetTop() >= 2 && !s.IsNil(2) {
		charset = s.ToString(2)
	}

	if length == 0 {
		s.PushString("")
		return 1
	}

	if !utf8.ValidString(charset) {
		s.PushNil()
		s.PushString("invalid charset")
		return 2
	}

	charsetRunes := []rune(charset)
	if len(charsetRunes) == 0 {
		s.PushNil()
		s.PushString("empty charset")
		return 2
	}

	result := make([]rune, length)
	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
}

func string_is_valid_utf8(s *luajit.State) int {
	str := s.ToString(1)
	s.PushBoolean(utf8.ValidString(str))
	return 1
}