gno.land/r/moul/x/daily/rot13demo/v0⧉

1// Package rot13demo is a small gnoweb demo of the ROT13 / Caesar cipher2// provided by the [p/moul/x/daily/rot13](/p/moul/x/daily/rot13/v0) library: it3// renders an explanation, a worked ROT13 example, and interactive path-driven4// ROT13 and Caesar transforms.5//6// It contains no cipher logic of its own — everything comes from `rot13.Rot13`7// and `rot13.Caesar`. Render reads its input straight from the gnoweb path.8package rot13demo910import (11	"strconv"12	"strings"1314	"gno.land/p/moul/x/daily/rot13/v0"15)1617// hexNibble decodes a single hex digit, returning -1 if invalid.18func hexNibble(b byte) int {19	switch {20	case b >= '0' && b <= '9':21		return int(b - '0')22	case b >= 'a' && b <= 'f':23		return int(b-'a') + 1024	case b >= 'A' && b <= 'F':25		return int(b-'A') + 1026	}27	return -128}2930// percentDecode turns "%20"/"+" style path escapes back into readable text so31// gnoweb links with spaces or punctuation round-trip nicely. Invalid escapes32// are left verbatim.33func percentDecode(s string) string {34	var sb strings.Builder35	for i := 0; i < len(s); i++ {36		c := s[i]37		switch {38		case c == '+':39			sb.WriteByte(' ')40		case c == '%' && i+2 < len(s):41			hi, lo := hexNibble(s[i+1]), hexNibble(s[i+2])42			if hi >= 0 && lo >= 0 {43				sb.WriteByte(byte(hi<<4 | lo))44				i += 245			} else {46				sb.WriteByte(c)47			}48		default:49			sb.WriteByte(c)50		}51	}52	return sb.String()53}5455// Render is the gnoweb entry point (not a crossing call).56//57//	Render("")                 -> explanation + a worked example58//	Render("/Hello, Gno!")     -> the input and its ROT1359//	Render("/caesar/3/attack") -> a Caesar shift of 3 applied to "attack"60func Render(path string) string {61	p := strings.TrimPrefix(path, "/")6263	// Caesar sub-path: /caesar/<shift>/<text>64	if rest, ok := strings.CutPrefix(p, "caesar/"); ok {65		shiftStr, text, found := strings.Cut(rest, "/")66		if !found {67			return renderRoot() + "\n> Usage: `/caesar/<shift>/<text>` — e.g. `/caesar/3/attack%20at%20dawn`\n"68		}69		shift, err := strconv.Atoi(shiftStr)70		if err != nil {71			return renderRoot() + "\n> `" + shiftStr + "` is not a valid integer shift.\n"72		}73		text = percentDecode(text)74		return renderCaesar(text, shift)75	}7677	if p == "" {78		return renderRoot()79	}8081	return renderRot13(percentDecode(p))82}8384func renderRoot() string {85	var sb strings.Builder86	sb.WriteString("# ROT13\n\n")87	sb.WriteString("Demo of the [`p/moul/x/daily/rot13`](/p/moul/x/daily/rot13/v0) library — ")88	sb.WriteString("an on-chain port of Go's classic **ROT13** cipher, the standard-library ")89	sb.WriteString("`strings.Map` / `io.Reader` teaching example. Each ASCII letter is rotated ")90	sb.WriteString("13 places through the alphabet; everything else is left alone.\n\n")91	sb.WriteString("Because the alphabet has 26 letters and 13 is exactly half, **ROT13 is its ")92	sb.WriteString("own inverse** — encoding twice returns the original text.\n\n")9394	const demo = "Hello, Gno!"95	enc := rot13.Rot13(demo)96	sb.WriteString("## Example\n\n")97	sb.WriteString("| stage | text |\n|---|---|\n")98	sb.WriteString("| input | `" + demo + "` |\n")99	sb.WriteString("| ROT13 | `" + enc + "` |\n")100	sb.WriteString("| ROT13 again | `" + rot13.Rot13(enc) + "` |\n\n")101102	sb.WriteString("## Try it\n\n")103	sb.WriteString("- `Render(\"/Uryyb, Tab!\")` — decode any text (append it to the path).\n")104	sb.WriteString("- `Render(\"/caesar/3/attack at dawn\")` — a general Caesar shift.\n\n")105	sb.WriteString("Or call the library functions directly:\n\n")106	sb.WriteString("```go\n")107	sb.WriteString("rot13.Rot13(\"Hello, Gno!\")     // " + strconv.Quote(enc) + "\n")108	sb.WriteString("rot13.Caesar(\"attack\", 3)      // " + strconv.Quote(rot13.Caesar("attack", 3)) + "\n")109	sb.WriteString("rot13.Caesar(\"Hello\", 13)      // same as Rot13: " + strconv.Quote(rot13.Caesar("Hello", 13)) + "\n")110	sb.WriteString("```\n")111	return sb.String()112}113114func renderRot13(text string) string {115	enc := rot13.Rot13(text)116	var sb strings.Builder117	sb.WriteString("# ROT13\n\n")118	sb.WriteString("| stage | text |\n|---|---|\n")119	sb.WriteString("| input | `" + text + "` |\n")120	sb.WriteString("| ROT13 | `" + enc + "` |\n\n")121	sb.WriteString("_ROT13 is its own inverse — running it on the output above gives back the input._\n\n")122	sb.WriteString("[Back to overview](/r/moul/x/daily/rot13demo/v0:)\n")123	return sb.String()124}125126func renderCaesar(text string, shift int) string {127	enc := rot13.Caesar(text, shift)128	var sb strings.Builder129	sb.WriteString("# Caesar shift " + strconv.Itoa(shift) + "\n\n")130	sb.WriteString("| stage | text |\n|---|---|\n")131	sb.WriteString("| input | `" + text + "` |\n")132	sb.WriteString("| shifted | `" + enc + "` |\n\n")133	sb.WriteString("_Decode with the opposite shift: `/caesar/" + strconv.Itoa(-shift) + "/...`._\n\n")134	sb.WriteString("[Back to overview](/r/moul/x/daily/rot13demo/v0:)\n")135	return sb.String()136}137