package template

import (
	"strings"
	"unicode"

	"golang.org/x/text/cases"
	"golang.org/x/text/language"
)

// ToUpper converts a string to uppercase
func ToUpper(s string) string {
	return strings.ToUpper(s)
}

// ToLower converts a string to lowercase
func ToLower(s string) string {
	return strings.ToLower(s)
}

// ToCamelCase converts snake_case to camelCase
// Examples: user_name → userName, http_request → httpRequest
func ToCamelCase(s string) string {
	if s == "" {
		return ""
	}

	parts := strings.Split(s, "_")
	for i, part := range parts {
		if i == 0 {
			parts[i] = strings.ToLower(part)
		} else {
			parts[i] = capitalize(part)
		}
	}
	return strings.Join(parts, "")
}

// ToPascalCase converts snake_case to PascalCase
// Examples: user_name → UserName, http_request → HTTPRequest
func ToPascalCase(s string) string {
	if s == "" {
		return ""
	}

	parts := strings.Split(s, "_")
	for i, part := range parts {
		parts[i] = capitalize(part)
	}
	return strings.Join(parts, "")
}

// ToSnakeCase converts PascalCase/camelCase to snake_case
// Examples: UserName → user_name, HTTPRequest → http_request
func ToSnakeCase(s string) string {
	if s == "" {
		return ""
	}

	var result strings.Builder
	var prevUpper bool
	var nextUpper bool

	runes := []rune(s)
	for i, r := range runes {
		isUpper := unicode.IsUpper(r)

		if i+1 < len(runes) {
			nextUpper = unicode.IsUpper(runes[i+1])
		} else {
			nextUpper = false
		}

		if i > 0 && isUpper {
			// Add underscore before uppercase letter if:
			// 1. Previous char was lowercase, OR
			// 2. Next char is lowercase (end of acronym)
			if !prevUpper || (!nextUpper && i+1 < len(runes)) {
				result.WriteRune('_')
			}
		}

		result.WriteRune(unicode.ToLower(r))
		prevUpper = isUpper
	}

	return result.String()
}

// ToKebabCase converts snake_case or PascalCase/camelCase to kebab-case
// Examples: user_name → user-name, UserName → user-name
func ToKebabCase(s string) string {
	// First convert to snake_case, then replace underscores with hyphens
	snakeCase := ToSnakeCase(s)
	return strings.ReplaceAll(snakeCase, "_", "-")
}

// Title capitalizes the first letter of each word
func Title(s string) string {
	caser := cases.Title(language.English)
	src := []byte(s)
	dest := []byte(s)
	_, _, _ = caser.Transform(dest, src, true)
	return string(dest)
}

// Pluralize converts a singular word to plural
// Basic implementation with common English rules
func Pluralize(s string) string {
	if s == "" {
		return ""
	}

	// Special cases
	irregular := map[string]string{
		"person":   "people",
		"child":    "children",
		"tooth":    "teeth",
		"foot":     "feet",
		"man":      "men",
		"woman":    "women",
		"mouse":    "mice",
		"goose":    "geese",
		"ox":       "oxen",
		"datum":    "data",
		"medium":   "media",
		"analysis": "analyses",
		"crisis":   "crises",
		"status":   "statuses",
	}

	if plural, ok := irregular[strings.ToLower(s)]; ok {
		return plural
	}

	// Already plural (ends in 's' but not 'ss' or 'us')
	if strings.HasSuffix(s, "s") && !strings.HasSuffix(s, "ss") && !strings.HasSuffix(s, "us") {
		return s
	}

	// Words ending in s, x, z, ch, sh
	if strings.HasSuffix(s, "s") || strings.HasSuffix(s, "x") ||
		strings.HasSuffix(s, "z") || strings.HasSuffix(s, "ch") ||
		strings.HasSuffix(s, "sh") {
		return s + "es"
	}

	// Words ending in consonant + y
	if len(s) >= 2 && strings.HasSuffix(s, "y") {
		prevChar := s[len(s)-2]
		if !isVowel(prevChar) {
			return s[:len(s)-1] + "ies"
		}
	}

	// Words ending in f or fe
	if strings.HasSuffix(s, "f") {
		return s[:len(s)-1] + "ves"
	}
	if strings.HasSuffix(s, "fe") {
		return s[:len(s)-2] + "ves"
	}

	// Words ending in consonant + o
	if len(s) >= 2 && strings.HasSuffix(s, "o") {
		prevChar := s[len(s)-2]
		if !isVowel(prevChar) {
			return s + "es"
		}
	}

	// Default: add 's'
	return s + "s"
}

// Singularize converts a plural word to singular
// Basic implementation with common English rules
func Singularize(s string) string {
	if s == "" {
		return ""
	}

	// Special cases
	irregular := map[string]string{
		"people":   "person",
		"children": "child",
		"teeth":    "tooth",
		"feet":     "foot",
		"men":      "man",
		"women":    "woman",
		"mice":     "mouse",
		"geese":    "goose",
		"oxen":     "ox",
		"data":     "datum",
		"media":    "medium",
		"analyses": "analysis",
		"crises":   "crisis",
		"statuses": "status",
	}

	if singular, ok := irregular[strings.ToLower(s)]; ok {
		return singular
	}

	// Words ending in ies
	if strings.HasSuffix(s, "ies") && len(s) > 3 {
		return s[:len(s)-3] + "y"
	}

	// Words ending in ves
	if strings.HasSuffix(s, "ves") {
		return s[:len(s)-3] + "f"
	}

	// Words ending in ses, xes, zes, ches, shes
	if strings.HasSuffix(s, "ses") || strings.HasSuffix(s, "xes") ||
		strings.HasSuffix(s, "zes") || strings.HasSuffix(s, "ches") ||
		strings.HasSuffix(s, "shes") {
		return s[:len(s)-2]
	}

	// Words ending in s (not ss)
	if strings.HasSuffix(s, "s") && !strings.HasSuffix(s, "ss") {
		return s[:len(s)-1]
	}

	// Already singular
	return s
}

// Trim trims whitespace from both ends
func Trim(s string) string {
	return strings.TrimSpace(s)
}

// TrimPrefix removes the prefix from the string if present
func TrimPrefix(s, prefix string) string {
	return strings.TrimPrefix(s, prefix)
}

// TrimSuffix removes the suffix from the string if present
func TrimSuffix(s, suffix string) string {
	return strings.TrimSuffix(s, suffix)
}

// Replace replaces occurrences of old with new (n times, or all if n < 0)
func Replace(s, old, newstr string, n int) string {
	return strings.Replace(s, old, newstr, n)
}

// StringContains checks if substr is within s
func StringContains(s, substr string) bool {
	return strings.Contains(s, substr)
}

// HasPrefix checks if string starts with prefix
func HasPrefix(s, prefix string) bool {
	return strings.HasPrefix(s, prefix)
}

// HasSuffix checks if string ends with suffix
func HasSuffix(s, suffix string) bool {
	return strings.HasSuffix(s, suffix)
}

// Split splits string by separator
func Split(s, sep string) []string {
	return strings.Split(s, sep)
}

// Join joins string slice with separator
func Join(parts []string, sep string) string {
	return strings.Join(parts, sep)
}

// capitalize capitalizes the first letter and handles common acronyms
func capitalize(s string) string {
	if s == "" {
		return ""
	}

	upper := strings.ToUpper(s)

	// Handle common acronyms
	acronyms := map[string]bool{
		"ID":    true,
		"UUID":  true,
		"GUID":  true,
		"URL":   true,
		"URI":   true,
		"HTTP":  true,
		"HTTPS": true,
		"API":   true,
		"JSON":  true,
		"XML":   true,
		"SQL":   true,
		"HTML":  true,
		"CSS":   true,
		"RID":   true,
	}

	if acronyms[upper] {
		return upper
	}

	// Capitalize first letter
	runes := []rune(s)
	runes[0] = unicode.ToUpper(runes[0])
	return string(runes)
}

// isVowel checks if a byte is a vowel
func isVowel(c byte) bool {
	c = byte(unicode.ToLower(rune(c)))
	return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'
}