package gapr

import (
	"strings"
	"unicode"
)

type KeyMapper interface {
	MapKey(orig string) string
}

type KeyMapperFunc func(orig string) string

func (f KeyMapperFunc) MapKey(orig string) string {
	return f(orig)
}

var (
	identityKeyMapper KeyMapper = KeyMapperFunc(func(orig string) string {
		return orig
	})
	LowercaseKeyMapper KeyMapper = KeyMapperFunc(func(orig string) string {
		return strings.ToLower(orig)
	})

	UppercaseKeyMapper KeyMapper = KeyMapperFunc(func(orig string) string {
		return strings.ToUpper(orig)
	})

	CamelCaseKeyMapper = genericFirstKeyMapper(unicode.ToLower)

	PascalCaseKeyMapper = genericFirstKeyMapper(unicode.ToUpper)
)

func genericFirstKeyMapper(m func(r rune) rune) KeyMapperFunc {
	return func(orig string) string {
		if len(orig) < 1 {
			return ""
		}

		mapped := make([]byte, 1, len(orig))
		mapped[0] = byte(m(rune(orig[0])))

		if len(orig) > 1 {
			mapped = append(mapped, orig[1:]...)
		}

		return string(mapped)
	}
}