// Copyright 2017 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package util

import (
	"bytes"
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"math/big"
	rand2 "math/rand/v2"
	"slices"
	"strconv"
	"strings"
	"sync"

	"code.gitea.io/gitea/modules/container"

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

// IsEmptyString checks if the provided string is empty
func IsEmptyString(s string) bool {
	return len(strings.TrimSpace(s)) == 0
}

// NormalizeEOL will convert Windows (CRLF) and Mac (CR) EOLs to UNIX (LF)
func NormalizeEOL(input []byte) []byte {
	var right, left, pos int
	if right = bytes.IndexByte(input, '\r'); right == -1 {
		return input
	}
	length := len(input)
	tmp := make([]byte, length)

	// We know that left < length because otherwise right would be -1 from IndexByte.
	copy(tmp[pos:pos+right], input[left:left+right])
	pos += right
	tmp[pos] = '\n'
	left += right + 1
	pos++

	for left < length {
		if input[left] == '\n' {
			left++
		}

		right = bytes.IndexByte(input[left:], '\r')
		if right == -1 {
			copy(tmp[pos:], input[left:])
			pos += length - left
			break
		}
		copy(tmp[pos:pos+right], input[left:left+right])
		pos += right
		tmp[pos] = '\n'
		left += right + 1
		pos++
	}
	return tmp[:pos]
}

// CryptoRandomInt returns a crypto random integer between 0 and limit, inclusive
func CryptoRandomInt(limit int64) int64 {
	rInt, err := rand.Int(rand.Reader, big.NewInt(limit))
	if err != nil {
		panic(err) // this should never happen
	}
	return rInt.Int64()
}

// CryptoRandomString generates a crypto random alphanumerical string, each byte is generated by [0,61] range
func CryptoRandomString(length int64) string {
	const alphanumericalChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	buf := make([]byte, length)
	limit := int64(len(alphanumericalChars))
	for i := range buf {
		num := CryptoRandomInt(limit)
		buf[i] = alphanumericalChars[num]
	}
	return string(buf)
}

// CryptoRandomBytes generates `length` crypto bytes
// This differs from CryptoRandomString, as each byte in CryptoRandomString is generated by [0,61] range
// This function generates totally random bytes, each byte is generated by [0,255] range
func CryptoRandomBytes(length int64) []byte {
	buf := make([]byte, length)
	if _, err := rand.Read(buf); err != nil {
		panic(err) // this should never happen, "rand.Read" never fails
	}
	return buf
}

var chaCha8RandPool = sync.OnceValue(func() *sync.Pool {
	return &sync.Pool{
		New: func() any {
			seed := CryptoRandomBytes(32)
			return rand2.NewChaCha8([32]byte(seed))
		},
	}
})

func FastCryptoRandomBytes(length int) []byte {
	// ChaCha8 is about 20x times faster than system's crypto/rand.
	// It is suitable for UUIDs, session IDs, etc
	pool := chaCha8RandPool()
	chaCha8Rand := pool.Get().(*rand2.ChaCha8)
	defer pool.Put(chaCha8Rand)
	buf := make([]byte, length)
	_, _ = chaCha8Rand.Read(buf)
	return buf
}

func FastCryptoRandomHex(length int) string {
	buf := FastCryptoRandomBytes(length / 2)
	return hex.EncodeToString(buf)
}

// ToLowerASCII returns s with all ASCII letters mapped to their lower case.
func ToLowerASCII(s string) string {
	b := []byte(s)
	for i, c := range b {
		if 'A' <= c && c <= 'Z' {
			b[i] += 'a' - 'A'
		}
	}
	return string(b)
}

// ToTitleCase returns s with all english words capitalized
func ToTitleCase(s string) string {
	// `cases.Title` is not thread-safe, do not use global shared variable for it
	return cases.Title(language.English).String(s)
}

// ToTitleCaseNoLower returns s with all english words capitalized without lower-casing
func ToTitleCaseNoLower(s string) string {
	// `cases.Title` is not thread-safe, do not use global shared variable for it
	return cases.Title(language.English, cases.NoLower).String(s)
}

// ToInt64 transform a given int into int64.
func ToInt64(number any) (int64, error) {
	var value int64
	switch v := number.(type) {
	case int:
		value = int64(v)
	case int8:
		value = int64(v)
	case int16:
		value = int64(v)
	case int32:
		value = int64(v)
	case int64:
		value = v

	case uint:
		value = int64(v)
	case uint8:
		value = int64(v)
	case uint16:
		value = int64(v)
	case uint32:
		value = int64(v)
	case uint64:
		value = int64(v)

	case float32:
		value = int64(v)
	case float64:
		value = int64(v)

	case string:
		var err error
		if value, err = strconv.ParseInt(v, 10, 64); err != nil {
			return 0, err
		}
	default:
		return 0, fmt.Errorf("unable to convert %v to int64", number)
	}
	return value, nil
}

// ToFloat64 transform a given int into float64.
func ToFloat64(number any) (float64, error) {
	var value float64
	switch v := number.(type) {
	case int:
		value = float64(v)
	case int8:
		value = float64(v)
	case int16:
		value = float64(v)
	case int32:
		value = float64(v)
	case int64:
		value = float64(v)

	case uint:
		value = float64(v)
	case uint8:
		value = float64(v)
	case uint16:
		value = float64(v)
	case uint32:
		value = float64(v)
	case uint64:
		value = float64(v)

	case float32:
		value = float64(v)
	case float64:
		value = v

	case string:
		var err error
		if value, err = strconv.ParseFloat(v, 64); err != nil {
			return 0, err
		}
	default:
		return 0, fmt.Errorf("unable to convert %v to float64", number)
	}
	return value, nil
}

// Iif is an "inline-if", it returns "trueVal" if "condition" is true, otherwise "falseVal"
func Iif[T any](condition bool, trueVal, falseVal T) T {
	if condition {
		return trueVal
	}
	return falseVal
}

// IfZero returns "def" if "v" is a zero value, otherwise "v"
func IfZero[T comparable](v, def T) T {
	var zero T
	if v == zero {
		return def
	}
	return v
}

func IfEmpty[T any](v, def []T) []T {
	if len(v) == 0 {
		return def
	}
	return v
}

// OptionalArg helps the "optional argument" in Golang:
//
//	func foo(optArg ...int) { return OptionalArg(optArg) }
//		calling `foo()` gets zero value 0, calling `foo(100)` gets 100
//	func bar(optArg ...int) { return OptionalArg(optArg, 42) }
//		calling `bar()` gets default value 42, calling `bar(100)` gets 100
//
// Passing more than 1 item to `optArg` or `defaultValue` is undefined behavior.
// At the moment only the first item is used.
func OptionalArg[T any](optArg []T, defaultValue ...T) (ret T) {
	if len(optArg) >= 1 {
		return optArg[0]
	}
	if len(defaultValue) >= 1 {
		return defaultValue[0]
	}
	return ret
}

type EnumConst[T comparable] interface {
	EnumValues() []T
}

// EnumValue returns the value if it's in the enum const's values,
// otherwise returns the first item of enums as default value.
func EnumValue[T comparable](val EnumConst[T]) (ret T, valid bool) {
	enums := val.EnumValues()
	if slices.Contains(enums, val.(T)) {
		return val.(T), true
	}
	return enums[0], false
}

func NormalizeStringEOL(input string) string {
	// Since the content is from a form which is a textarea, the line endings are \r\n.
	// It's a standard behavior of HTML.
	// But in most cases, we only want "\n" for EOL
	// * Text files: use "\n" by default because "\r\n" sometimes doesn't work in POSIX
	// * Actions values: store them as "\n" like what GitHub does.
	// And users are unlikely to really need the "\r".
	// Other than this, we should respect the original content, even leading or trailing spaces.
	return UnsafeBytesToString(NormalizeEOL(UnsafeStringToBytes(input)))
}

func DiffSlice[T comparable](oldSlice, newSlice []T) (added, removed []T) {
	oldSet := container.SetOf(oldSlice...)
	newSet := container.SetOf(newSlice...)

	addedSet, removedSet := container.Set[T]{}, container.Set[T]{}
	for _, v := range newSlice {
		if !oldSet.Contains(v) && addedSet.Add(v) {
			added = append(added, v)
		}
	}
	for _, v := range oldSlice {
		if !newSet.Contains(v) && removedSet.Add(v) {
			removed = append(removed, v)
		}
	}
	return added, removed
}