strcase.go

/*
 * Copyright (c) 2023 Maple Wu <justmaplewu@gmail.com>
 *   National Electronics and Computer Technology Center, Thailand
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package zcore

import (
	"strings"
)

/*
this file is referred from github.com/stoewer/go-strcase

The MIT License (MIT)

Copyright (c) 2017, Adrian Stoewer <adrian.stoewer@rz.ifi.lmu.de>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

// SnakeCase converts a string into snake case.
func SnakeCase(s string) string {
	return delimiterCase(s, '_', false)
}

// UpperSnakeCase converts a string into snake case with capital letters.
func UpperSnakeCase(s string) string {
	return delimiterCase(s, '_', true)
}

// UpperCamelCase converts a string into camel case starting with a upper case letter.
func UpperCamelCase(s string) string {
	return camelCase(s, true)
}

// LowerCamelCase converts a string into camel case starting with a lower case letter.
func LowerCamelCase(s string) string {
	return camelCase(s, false)
}

// KebabCase converts a string into kebab case.
func KebabCase(s string) string {
	return delimiterCase(s, '-', false)
}

// UpperKebabCase converts a string into kebab case with capital letters.
func UpperKebabCase(s string) string {
	return delimiterCase(s, '-', true)
}

// isLower checks if a character is lower case. More precisely it evaluates if it is
// in the range of ASCII character 'a' to 'z'.
func isLower(ch rune) bool {
	return ch >= 'a' && ch <= 'z'
}

// toLower converts a character in the range of ASCII characters 'A' to 'Z' to its lower
// case counterpart. Other characters remain the same.
func toLower(ch rune) rune {
	if ch >= 'A' && ch <= 'Z' {
		return ch + 32
	}
	return ch
}

// isLower checks if a character is upper case. More precisely it evaluates if it is
// in the range of ASCII characters 'A' to 'Z'.
func isUpper(ch rune) bool {
	return ch >= 'A' && ch <= 'Z'
}

// toLower converts a character in the range of ASCII characters 'a' to 'z' to its lower
// case counterpart. Other characters remain the same.
func toUpper(ch rune) rune {
	if ch >= 'a' && ch <= 'z' {
		return ch - 32
	}
	return ch
}

// isSpace checks if a character is some kind of whitespace.
func isSpace(ch rune) bool {
	return ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r'
}

// isDelimiter checks if a character is some kind of whitespace or '_' or '-'.
func isDelimiter(ch rune) bool {
	return ch == '-' || ch == '_' || isSpace(ch)
}

// iterFunc is a callback that is called fro a specific position in a string. Its arguments are the
// rune at the respective string position as well as the previous and the next rune. If curr is at the
// first position of the string prev is zero. If curr is at the end of the string next is zero.
type iterFunc func(prev, curr, next rune)

// stringIter iterates over a string, invoking the callback for every single rune in the string.
func stringIter(s string, callback iterFunc) {
	var prev rune
	var curr rune
	for _, next := range s {
		if curr == 0 {
			prev = curr
			curr = next
			continue
		}

		callback(prev, curr, next)

		prev = curr
		curr = next
	}

	if len(s) > 0 {
		callback(prev, curr, 0)
	}
}

// delimiterCase converts a string into snake_case or kebab-case depending on the delimiter passed
// as second argument. When upperCase is true the result will be UPPER_SNAKE_CASE or UPPER-KEBAB-CASE.
func delimiterCase(s string, delimiter rune, upperCase bool) string {
	s = strings.TrimSpace(s)
	buffer := make([]rune, 0, len(s)+3)

	adjustCase := toLower
	if upperCase {
		adjustCase = toUpper
	}

	var prev rune
	var curr rune
	for _, next := range s {
		if isDelimiter(curr) {
			if !isDelimiter(prev) {
				buffer = append(buffer, delimiter)
			}
		} else if isUpper(curr) {
			if isLower(prev) || (isUpper(prev) && isLower(next)) {
				buffer = append(buffer, delimiter)
			}
			buffer = append(buffer, adjustCase(curr))
		} else if curr != 0 {
			buffer = append(buffer, adjustCase(curr))
		}
		prev = curr
		curr = next
	}

	if len(s) > 0 {
		if isUpper(curr) && isLower(prev) && prev != 0 {
			buffer = append(buffer, delimiter)
		}
		buffer = append(buffer, adjustCase(curr))
	}

	return string(buffer)
}

func camelCase(s string, upper bool) string {
	s = strings.TrimSpace(s)
	buffer := make([]rune, 0, len(s))

	stringIter(s, func(prev, curr, next rune) {
		if !isDelimiter(curr) {
			if isDelimiter(prev) || (upper && prev == 0) {
				buffer = append(buffer, toUpper(curr))
			} else if isLower(prev) {
				buffer = append(buffer, curr)
			} else if isUpper(prev) && isUpper(curr) && isLower(next) {
				// Assume a case like "R" for "XRequestId"
				buffer = append(buffer, curr)
			} else {
				buffer = append(buffer, toLower(curr))
			}
		}
	})

	return string(buffer)
}