package utini

import (
	"strings"
	"unicode"
)

type characterCasing int

const (
	undefinedCase characterCasing = iota
	lowerCase
	upperCase
)

func camelCaseToSnakeCase(name string) string {
	segments := strings.Split(name, ".")
	if len(segments) > 1 {
		for i, segment := range segments {
			segments[i] = camelCaseToSnakeCase(segment)
		}
		return strings.Join(segments, ".")
	}

	var words []string
	runes := []rune(name)
	if len(runes) == 0 {
		return ""
	}
	n := len(runes)
	end := n
	casing := undefinedCase
	for i := range runes {
		j := n - i - 1
		r := runes[j]

		if unicode.IsLower(r) {
			if casing == upperCase {
				words = append(words, strings.ToLower(string(runes[j+1:end])))
				end = j + 1
				casing = undefinedCase
			} else {
				casing = lowerCase
			}
		} else if r == '_' {
			if end-j > 1 {
				words = append(words, strings.ToLower(string(runes[j+1:end])))
				end = j
			}
			casing = undefinedCase
		} else if unicode.IsDigit(r) { // acts like either upper or lowercase depending on which character was following.
		} else {
			if casing == lowerCase {
				words = append(words, strings.ToLower(string(runes[j:end])))
				end = j
				casing = undefinedCase
			} else {
				casing = upperCase
			}
		}
	}
	if end > 0 {
		words = append(words, strings.ToLower(string(runes[:end])))
	}

	// reverse order of words
	last := len(words) - 1
	for i := 0; i < len(words)/2; i++ {
		words[i], words[last-i] = words[last-i], words[i]
	}

	return strings.Join(words, "_")
}

func snakeCaseToCamelCase(name string) string {
	words := strings.Split(name, `_`)
	for i, word := range words {
		runes := []rune(word)
		first := strings.IndexFunc(word, unicode.IsLetter)
		if first > -1 {
			runes[first] = unicode.ToUpper(runes[first])
		}
		words[i] = string(runes)
	}
	return strings.Join(words, ``)
}