// Copyright 2015 The Gogs Authors. All rights reserved.
// Copyright 2019 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package git

import (
	"encoding/hex"
	"fmt"
	"regexp"
	"strings"
)

// EmptySHA defines empty git SHA (undefined, non-existent)
const EmptySHA = "0000000000000000000000000000000000000000"

// EmptyTreeSHA is the SHA of an empty tree, the root of all git repositories
const EmptyTreeSHA = "4b825dc642cb6eb9a060e54bf8d69288fbee4904"

// SHAFullLength is the full length of a git SHA
const SHAFullLength = 40

// SHAPattern can be used to determine if a string is an valid sha
var shaPattern = regexp.MustCompile(`^[0-9a-f]{4,40}$`)

// IsValidSHAPattern will check if the provided string matches the SHA Pattern
func IsValidSHAPattern(sha string) bool {
	return shaPattern.MatchString(sha)
}

type ErrInvalidSHA struct {
	SHA string
}

func (err ErrInvalidSHA) Error() string {
	return fmt.Sprintf("invalid sha: %s", err.SHA)
}

// MustID always creates a new SHA1 from a [20]byte array with no validation of input.
func MustID(b []byte) SHA1 {
	var id SHA1
	copy(id[:], b)
	return id
}

// NewID creates a new SHA1 from a [20]byte array.
func NewID(b []byte) (SHA1, error) {
	if len(b) != 20 {
		return SHA1{}, fmt.Errorf("Length must be 20: %v", b)
	}
	return MustID(b), nil
}

// MustIDFromString always creates a new sha from a ID with no validation of input.
func MustIDFromString(s string) SHA1 {
	b, _ := hex.DecodeString(s)
	return MustID(b)
}

// NewIDFromString creates a new SHA1 from a ID string of length 40.
func NewIDFromString(s string) (SHA1, error) {
	var id SHA1
	s = strings.TrimSpace(s)
	if len(s) != SHAFullLength {
		return id, fmt.Errorf("Length must be 40: %s", s)
	}
	b, err := hex.DecodeString(s)
	if err != nil {
		return id, err
	}
	return NewID(b)
}