package naming

import (
	"strings"
	"unicode"
)

// ToSnakeCase converts a string to snake_case
func ToSnakeCase(s string) string {
	var result []rune
	for i, r := range s {
		if unicode.IsUpper(r) {
			if i > 0 {
				result = append(result, '_')
			}
			result = append(result, unicode.ToLower(r))
		} else {
			result = append(result, r)
		}
	}
	return string(result)
}

// ToPascalCase converts snake_case to PascalCase
func ToPascalCase(s string) string {
	parts := strings.Split(s, "_")
	for i, part := range parts {
		if len(part) > 0 {
			parts[i] = strings.ToUpper(part[:1]) + part[1:]
		}
	}
	return strings.Join(parts, "")
}

// Singularize converts a plural word to singular
// Uses common English pluralization rules
func Singularize(word string) string {
	// Handle empty string
	if word == "" {
		return word
	}

	// Common irregular plurals
	irregulars := map[string]string{
		"people":     "person",
		"men":        "man",
		"women":      "woman",
		"children":   "child",
		"teeth":      "tooth",
		"feet":       "foot",
		"mice":       "mouse",
		"geese":      "goose",
		"oxen":       "ox",
		"sheep":      "sheep",
		"fish":       "fish",
		"deer":       "deer",
		"series":     "series",
		"species":    "species",
		"quizzes":    "quiz",
		"analyses":   "analysis",
		"diagnoses":  "diagnosis",
		"oases":      "oasis",
		"theses":     "thesis",
		"crises":     "crisis",
		"phenomena":  "phenomenon",
		"criteria":   "criterion",
		"data":       "datum",
	}

	lower := strings.ToLower(word)
	if singular, ok := irregulars[lower]; ok {
		return preserveCase(word, singular)
	}

	// Handle words ending in 'ies' -> 'y'
	if strings.HasSuffix(lower, "ies") && len(word) > 3 {
		return word[:len(word)-3] + "y"
	}

	// Handle words ending in 'ves' -> 'fe' or 'f'
	if strings.HasSuffix(lower, "ves") && len(word) > 3 {
		base := word[:len(word)-3]
		// Common words that end in 'fe'
		if strings.HasSuffix(strings.ToLower(base), "li") ||
		   strings.HasSuffix(strings.ToLower(base), "wi") ||
		   strings.HasSuffix(strings.ToLower(base), "kni") {
			return base + "fe"
		}
		return base + "f"
	}

	// Handle words ending in 'xes', 'ses', 'shes', 'ches' -> remove 'es'
	if strings.HasSuffix(lower, "xes") ||
	   strings.HasSuffix(lower, "ses") ||
	   strings.HasSuffix(lower, "shes") ||
	   strings.HasSuffix(lower, "ches") {
		if len(word) > 2 {
			return word[:len(word)-2]
		}
	}

	// Handle words ending in 'oes' -> 'o'
	if strings.HasSuffix(lower, "oes") && len(word) > 3 {
		return word[:len(word)-2]
	}

	// Handle simple 's' suffix
	if strings.HasSuffix(lower, "s") && len(word) > 1 {
		// Don't remove 's' from words that naturally end in 's'
		if !strings.HasSuffix(lower, "ss") &&
		   !strings.HasSuffix(lower, "us") &&
		   !strings.HasSuffix(lower, "is") {
			return word[:len(word)-1]
		}
	}

	return word
}

// Pluralize converts a singular word to plural
func Pluralize(word string) string {
	if word == "" {
		return word
	}

	// Common irregular plurals
	irregulars := map[string]string{
		"person":     "people",
		"man":        "men",
		"woman":      "women",
		"child":      "children",
		"tooth":      "teeth",
		"foot":       "feet",
		"mouse":      "mice",
		"goose":      "geese",
		"ox":         "oxen",
		"sheep":      "sheep",
		"fish":       "fish",
		"deer":       "deer",
		"series":     "series",
		"species":    "species",
		"quiz":       "quizzes",
		"analysis":   "analyses",
		"diagnosis":  "diagnoses",
		"oasis":      "oases",
		"thesis":     "theses",
		"crisis":     "crises",
		"phenomenon": "phenomena",
		"criterion":  "criteria",
		"datum":      "data",
	}

	lower := strings.ToLower(word)
	if plural, ok := irregulars[lower]; ok {
		return preserveCase(word, plural)
	}

	// Already plural (ends in 's' after a consonant, but not 'ss', 'us', 'is')
	// Skip this check if word ends in 'ss' (like 'class', 'glass')
	if strings.HasSuffix(lower, "s") &&
	   !strings.HasSuffix(lower, "ss") &&
	   !strings.HasSuffix(lower, "us") &&
	   !strings.HasSuffix(lower, "is") {
		return word
	}

	// Handle words ending in 'y' -> 'ies'
	if strings.HasSuffix(lower, "y") && len(word) > 1 {
		prevChar := rune(lower[len(lower)-2])
		if !isVowel(prevChar) {
			return word[:len(word)-1] + "ies"
		}
	}

	// Handle words ending in 'f' or 'fe' -> 'ves'
	if strings.HasSuffix(lower, "f") {
		return word[:len(word)-1] + "ves"
	}
	if strings.HasSuffix(lower, "fe") {
		return word[:len(word)-2] + "ves"
	}

	// Handle words ending in 'o' -> 'oes'
	if strings.HasSuffix(lower, "o") && len(word) > 1 {
		prevChar := rune(lower[len(lower)-2])
		if !isVowel(prevChar) {
			return word + "es"
		}
	}

	// Handle words ending in 'x', 's', 'sh', 'ch' -> add 'es'
	if strings.HasSuffix(lower, "x") ||
	   strings.HasSuffix(lower, "s") ||
	   strings.HasSuffix(lower, "sh") ||
	   strings.HasSuffix(lower, "ch") {
		return word + "es"
	}

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

// preserveCase preserves the case pattern of the original word
func preserveCase(original, replacement string) string {
	if len(original) == 0 {
		return replacement
	}

	if unicode.IsUpper(rune(original[0])) {
		return strings.ToUpper(replacement[:1]) + replacement[1:]
	}
	return replacement
}

// isVowel checks if a rune is a vowel
func isVowel(r rune) bool {
	vowels := "aeiouAEIOU"
	return strings.ContainsRune(vowels, r)
}

// SingularizeTableName converts a table name to its singular form
// Handles snake_case table names
func SingularizeTableName(tableName string) string {
	parts := strings.Split(tableName, "_")
	if len(parts) > 0 {
		// Only singularize the last part
		lastIdx := len(parts) - 1
		parts[lastIdx] = Singularize(parts[lastIdx])
	}
	return strings.Join(parts, "_")
}