playground: most of the logic for both frontend and backend is implemented, some bugs remain

frontend/tools/b66.ts

@@ -0,0 +1,54 @@
+// B66 encoding and decoding functions for compact url query parameter values. https://gist.github.com/danneu/6755394
+const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789.-_~";
+
+export function b66Encode(data: Uint8Array): string {
+    let result = "";
+    let bits = 0;
+    let value = 0;
+
+    for (let byte of data) {
+        value = (value << 8) | byte;
+        bits += 8;
+
+        while (bits >= 6) {
+            bits -= 6;
+            result += alphabet[(value >> bits) & 0x3F];
+        }
+    }
+
+    if (bits > 0) {
+        result += alphabet[(value << (6 - bits)) & 0x3F];
+    }
+
+    return result;
+}
+
+export function b66Decode(encoded: string): Uint8Array {
+    let result = [];
+    let bits = 0;
+    let value = 0;
+
+    for (let char of encoded) {
+        const index = alphabet.indexOf(char);
+        if (index === -1) {
+            throw new Error(`Invalid character '${char}' in B66 encoded string.`);
+        }
+
+        value = (value << 6) | index;
+        bits += 6;
+
+        while (bits >= 8) {
+            bits -= 8;
+            result.push((value >> bits) & 0xFF);
+        }
+    }
+
+    if (bits > 0) {
+        // If there are leftover bits, they should not be present in a valid B66 encoding.
+        if (value << (8 - bits)) {
+            throw new Error("Invalid B66 encoding: leftover bits.");
+        }
+    }
+
+    return new Uint8Array(result);
+}