From 37eeccaa731b521c4962b9d9485dc72f40e80fe7 Mon Sep 17 00:00:00 2001
From: Aaron Johnon <amjohnson@skyfall.tech>
Date: Mon, 2 Sep 2024 02:02:32 -0500
Subject: [PATCH] Added decoder

---
 nsdecode.go | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 nsdecode.go

diff --git a/nsdecode.go b/nsdecode.go
new file mode 100644
index 0000000..4b6f4e0
--- /dev/null
+++ b/nsdecode.go
@@ -0,0 +1,74 @@
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+// Function to decode number pairs into characters
+func decodePair(pair string) rune {
+	alphabet := " ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+	num, err := strconv.Atoi(pair)
+	if err != nil || num < 0 || num >= len(alphabet) {
+		return rune(-1) // Return -1 if pair is not valid
+	}
+	return rune(alphabet[num])
+}
+
+// Function to apply the reverse shift and wrap around
+func applyReverseShift(value, shift int) int {
+	shifted := (value - shift) % 37
+	if shifted < 0 {
+		shifted += 37
+	}
+	return shifted
+}
+
+func main() {
+	// Define command-line flags
+	shift := flag.Int("s", 0, "Shift amount for the cipher")
+	flag.Parse()
+
+	// Read all input from stdin
+	reader := bufio.NewReader(os.Stdin)
+	inputBytes, _ := io.ReadAll(reader)
+	input := string(inputBytes)
+
+	// Remove all spaces and line breaks
+	input = strings.ReplaceAll(input, " ", "")
+	input = strings.ReplaceAll(input, "\n", "")
+	input = strings.TrimSpace(input)
+
+	var decoded strings.Builder
+
+	// Decode the input string
+	for i := 0; i < len(input); i += 2 {
+		if i+1 >= len(input) {
+			break // If there's an odd number of characters, break out
+		}
+
+		pair := input[i : i+2]
+		num, err := strconv.Atoi(pair)
+		if err != nil {
+			continue // Skip invalid pairs
+		}
+
+		shiftedValue := applyReverseShift(num, *shift)
+		char := decodePair(fmt.Sprintf("%02d", shiftedValue))
+		if !unicode.IsPrint(char) || char == rune(-1) {
+			continue // Skip invalid characters
+		}
+
+		decoded.WriteRune(char)
+	}
+
+	// Output the decoded string
+	fmt.Println(decoded.String())
+}
+