1 files changed, 209 insertions, 0 deletions
diff --git a/server/shared.ts b/server/shared.ts
new file mode 100644
index 0000000..b3fad21
--- /dev/null
+++ b/server/shared.ts
@@ -0,0 +1,209 @@
+import { createHmac, timingSafeEqual } from "crypto";
+import { songs } from "./data/songs";
+
+function getSalt(): string {
+  return process.env.VITE_HEARDLE_SALT ?? "changeme";
+}
+
+function getSigningSecret(): string {
+  return process.env.HEARDLE_SIGNING_SECRET ?? getSalt();
+}
+
+export type Song = (typeof songs)[number];
+
+export type GuessResult = "Correct" | "PartiallyCorrect" | "Incorrect" | "Skipped";
+
+export type GuessEntry = {
+  song?: {
+    artist: string;
+    name: string;
+  };
+  state: GuessResult;
+};
+
+export type SignedState = {
+  date: string;
+  currentTry: number;
+  didGuess: boolean;
+  guesses: GuessEntry[];
+};
+
+export function getObfuscationKey(date = getUtcDate()): Buffer {
+  return Buffer.from(getSalt() + date);
+}
+
+export function xorBuffer(data: Buffer, key: Buffer): Buffer {
+  const output = Buffer.alloc(data.length);
+  for (let i = 0; i < data.length; i++) {
+    output[i] = data[i] ^ key[i % key.length];
+  }
+  return output;
+}
+
+export function getUtcDate(): string {
+  return new Date().toISOString().slice(0, 10);
+}
+
+function hashString(str: string): number {
+  let hash = 0;
+  for (let i = 0; i < str.length; i++) {
+    hash = (hash * 31 + str.charCodeAt(i)) >>> 0;
+  }
+  return hash;
+}
+
+export function getDailySong(date: string): Song {
+  const seed = hashString(date);
+  const index = seed % songs.length;
+  return songs[index];
+}
+
+function signValue(prefix: string, value: string): string {
+  return createHmac("sha256", getSigningSecret())
+    .update(`${prefix}:${value}`)
+    .digest("hex");
+}
+
+function safeEqualHex(a: string, b: string): boolean {
+  try {
+    const left = Buffer.from(a, "hex");
+    const right = Buffer.from(b, "hex");
+    if (left.length !== right.length) return false;
+    return timingSafeEqual(left, right);
+  } catch {
+    return false;
+  }
+}
+
+export function buildSessionToken(date: string): string {
+  const payload = Buffer.from(JSON.stringify({ date }), "utf8").toString("base64url");
+  const sig = signValue("session", payload);
+  return `${payload}.${sig}`;
+}
+
+export function verifySessionToken(token: unknown, expectedDate: string): boolean {
+  if (typeof token !== "string") return false;
+  const [payload, sig] = token.split(".");
+  if (!payload || !sig) return false;
+
+  const expectedSig = signValue("session", payload);
+  if (!safeEqualHex(sig, expectedSig)) return false;
+
+  try {
+    const decoded = JSON.parse(Buffer.from(payload, "base64url").toString("utf8")) as {
+      date?: unknown;
+    };
+
+    return typeof decoded.date === "string" && decoded.date === expectedDate;
+  } catch {
+    return false;
+  }
+}
+
+function normalizeGuessEntry(entry: unknown): GuessEntry | null {
+  if (!entry || typeof entry !== "object" || Array.isArray(entry)) return null;
+
+  const maybeState = (entry as { state?: unknown }).state;
+  if (
+    maybeState !== "Correct" &&
+    maybeState !== "PartiallyCorrect" &&
+    maybeState !== "Incorrect" &&
+    maybeState !== "Skipped"
+  ) {
+    return null;
+  }
+
+  const maybeSong = (entry as { song?: unknown }).song;
+
+  if (maybeState === "Skipped") {
+    return { state: "Skipped" };
+  }
+
+  if (!maybeSong || typeof maybeSong !== "object" || Array.isArray(maybeSong)) {
+    return null;
+  }
+
+  const artist = (maybeSong as { artist?: unknown }).artist;
+  const name = (maybeSong as { name?: unknown }).name;
+
+  if (typeof artist !== "string" || typeof name !== "string") {
+    return null;
+  }
+
+  return {
+    song: { artist, name },
+    state: maybeState,
+  };
+}
+
+export function normalizeSignedState(input: unknown): SignedState | null {
+  if (!input || typeof input !== "object" || Array.isArray(input)) return null;
+
+  const date = (input as { date?: unknown }).date;
+  const currentTryRaw = (input as { currentTry?: unknown }).currentTry;
+  const didGuessRaw = (input as { didGuess?: unknown }).didGuess;
+  const guessesRaw = (input as { guesses?: unknown }).guesses;
+
+  if (typeof date !== "string") return null;
+  if (!Array.isArray(guessesRaw)) return null;
+  if (typeof currentTryRaw !== "number" || !Number.isFinite(currentTryRaw)) return null;
+
+  const currentTry = Math.floor(currentTryRaw);
+  if (currentTry < 0 || currentTry > 6) return null;
+
+  const guesses: GuessEntry[] = [];
+  for (const entry of guessesRaw) {
+    const normalized = normalizeGuessEntry(entry);
+    if (!normalized) return null;
+    guesses.push(normalized);
+  }
+
+  if (guesses.length > 6) return null;
+  if (guesses.length !== currentTry) return null;
+
+  const didGuess = !!didGuessRaw;
+  if (didGuess && !guesses.some((guess) => guess.state === "Correct")) {
+    return null;
+  }
+
+  return {
+    date,
+    currentTry,
+    didGuess,
+    guesses,
+  };
+}
+
+function canonicalState(state: SignedState): string {
+  return JSON.stringify({
+    date: state.date,
+    currentTry: state.currentTry,
+    didGuess: state.didGuess,
+    guesses: state.guesses.map((guess) => ({
+      state: guess.state,
+      song: guess.song
+        ? {
+            artist: guess.song.artist,
+            name: guess.song.name,
+          }
+        : null,
+    })),
+  });
+}
+
+export function signState(state: SignedState): string {
+  return signValue("state", canonicalState(state));
+}
+
+export function verifyStateSignature(state: SignedState, sig: unknown): boolean {
+  if (typeof sig !== "string") return false;
+  const expectedSig = signState(state);
+  return safeEqualHex(sig, expectedSig);
+}
+
+export function obfuscateSong(song: Song, date?: string): string {
+  const obfuscationKey = getObfuscationKey(date);
+  const songJson = JSON.stringify(song);
+  const obfuscatedData = xorBuffer(Buffer.from(songJson, "utf8"), obfuscationKey);
+  return obfuscatedData.toString("hex");
+}