// Copyright (C) 2024  Umorpha Systems
// SPDX-License-Identifier: AGPL-3.0-or-later

package gitcache

import (
	"fmt"
	"regexp"
	"strings"
)

func URL2NS(url string) string {
	// > Clients MUST strip a trailing `/`, if present, from the
	// > user supplied `$GIT_URL` string
	// -- gitprotocol-http(5)
	url = strings.TrimRight(url, "/")

	var id strings.Builder
	id.Grow(len(url))
	for _, r := range url {
		switch {
		case r == '!', // our own escape
			// see: git-check-ref-format(1)
			r <= ' ', r == '\x7F', // never: ASCII control characters
			r == '~', r == '^', r == ':', // never: gitrevision meaning
			r == '?', r == '*', r == '[', // never: refspec pattern
			r == '\\',                    // never: backslash
			r == '.', r == '@', r == '/': // sometimes: special rules
			fmt.Fprintf(&id, "!%02x", r)
		default:
			id.WriteRune(r)
		}
	}
	return id.String()
}

var reEsc = regexp.MustCompile("![0-9a-f]{2}")

func hex2int(h byte) byte {
	switch {
	case '0' <= h && h <= '9':
		return h - '0'
	case 'a' <= h && h <= 'f':
		return h - 'a'
	default:
		panic("should not happen")
	}
}

func NS2URL(id string) string {
	return reEsc.ReplaceAllStringFunc(id, func(esc string) string {
		r := rune(hex2int(esc[1]))<<4 | rune(hex2int(esc[2]))
		return string([]rune{r})
	})
}