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

package gitcache

import (
	"strings"
)

func needsEscaped(b byte) bool {
	switch {
	case b == '!', // our own escape
		// see: git-check-ref-format(1)
		b <= ' ', b == '\x7F', // never: ASCII control characters
		b == '~', b == '^', b == ':', // never: gitrevision meaning
		b == '?', b == '*', b == '[', // never: refspec pattern
		b == '\\',                    // never: backslash
		b == '.', b == '@', b == '/': // sometimes: special rules
		return true
	default:
		return false
	}
}

func URL2NS(url string) (string, bool) {
	url, ok := NormalizeURL(url)
	if !ok {
		return "", false
	}

	l := len(url)
	for i := 0; i < len(url); i++ {
		if needsEscaped(url[i]) {
			l += 2
		}
	}
	var ns strings.Builder
	ns.Grow(l)
	var buf [3]byte
	buf[0] = '!'
	const digits = "0123456789abcdef"
	for i := 0; i < len(url); i++ {
		b := url[i]
		if needsEscaped(b) {
			buf[1] = digits[b>>4]
			buf[2] = digits[b&0xf]
			ns.Write(buf[:])
		} else {
			ns.WriteByte(b)
		}
	}
	return ns.String(), true
}

func hex2int(h byte) (byte, bool) {
	switch {
	case '0' <= h && h <= '9':
		return h - '0', true
	case 'a' <= h && h <= 'f':
		return h - 'a' + 0xa, true
	default:
		return 0, false
	}
}

func NS2URL(ns string) (string, bool) {
	l := len(ns) - (strings.Count(ns, "!") * 2)
	if l < 0 {
		return "", false
	}
	var url strings.Builder
	url.Grow(l)
	for i := 0; i < len(ns); i++ {
		b := ns[i]
		if b == '!' {
			if i+2 >= len(ns) {
				return "", false
			}
			h, hOK := hex2int(ns[i+1])
			l, lOK := hex2int(ns[i+2])
			if !hOK || !lOK {
				return "", false
			}
			b = h<<4 | l
			i += 2
		}
		url.WriteByte(b)
	}
	return url.String(), true
}