2 files changed, 92 insertions, 0 deletions
diff --git a/src/lib/Effect/authCookie.test.ts b/src/lib/Effect/authCookie.test.ts
new file mode 100644
index 00000000..2a27f0ce
--- /dev/null
+++ b/src/lib/Effect/authCookie.test.ts
@@ -0,0 +1,47 @@
+import { describe, expect, it } from "vitest";
+import { Result } from "effect";
+import {
+	decodeAuthCookieEither,
+	decodeAuthCookieOrThrow,
+} from "$lib/Effect/authCookie";
+
+describe("decodeAuthCookie", () => {
+	it("decodes a valid user cookie payload", () => {
+		const payload = JSON.stringify({
+			token_type: "Bearer",
+			expires_in: 3600,
+			access_token: "access-token",
+			refresh_token: "refresh-token",
+		});
+		const decoded = decodeAuthCookieEither(payload);
+
+		expect(Result.isSuccess(decoded)).toBe(true);
+
+		if (Result.isSuccess(decoded))
+			expect(decoded.success).toEqual({
+				tokenType: "Bearer",
+				expiresIn: 3600,
+				accessToken: "access-token",
+				refreshToken: "refresh-token",
+			});
+	});
+
+	it("returns a left when cookie JSON is invalid", () => {
+		const decoded = decodeAuthCookieEither("{oops");
+
+		expect(Result.isFailure(decoded)).toBe(true);
+	});
+
+	it("returns a left when required fields are missing", () => {
+		const payload = JSON.stringify({
+			token_type: "Bearer",
+		});
+		const decoded = decodeAuthCookieEither(payload);
+
+		expect(Result.isFailure(decoded)).toBe(true);
+	});
+
+	it("throws on invalid payload through decodeAuthCookieOrThrow", () => {
+		expect(() => decodeAuthCookieOrThrow("{oops")).toThrowError();
+	});
+});
diff --git a/src/lib/Effect/authCookie.ts b/src/lib/Effect/authCookie.ts
new file mode 100644
index 00000000..e716f5e9
--- /dev/null
+++ b/src/lib/Effect/authCookie.ts
@@ -0,0 +1,45 @@
+import type { AniListAuthorisation } from "$lib/Data/AniList/identity";
+import { Effect, Result, Schema } from "effect";
+
+const UserCookieSchema = Schema.Struct({
+	token_type: Schema.String,
+	expires_in: Schema.Number,
+	access_token: Schema.String,
+	refresh_token: Schema.String,
+});
+
+export const decodeAuthCookieEffect = (cookie: string) =>
+	Effect.gen(function* () {
+		const parsedCookie = yield* Effect.try({
+			try: () => JSON.parse(cookie) as unknown,
+			catch: (cause) => new Error("Invalid user cookie JSON", { cause }),
+		});
+		const decodedCookie = yield* Effect.try({
+			try: () => Schema.decodeUnknownSync(UserCookieSchema)(parsedCookie),
+			catch: (cause) => new Error("Invalid user cookie payload", { cause }),
+		});
+
+		return {
+			tokenType: decodedCookie.token_type,
+			expiresIn: decodedCookie.expires_in,
+			accessToken: decodedCookie.access_token,
+			refreshToken: decodedCookie.refresh_token,
+		} as AniListAuthorisation;
+	});
+
+export const decodeAuthCookieEither = (cookie: string) =>
+	Result.try({
+		try: () => Effect.runSync(decodeAuthCookieEffect(cookie)),
+		catch: (cause) =>
+			cause instanceof Error
+				? cause
+				: new Error("Failed to decode user cookie", { cause }),
+	});
+
+export const decodeAuthCookieOrThrow = (
+	cookie: string,
+): AniListAuthorisation => {
+	const decoded = decodeAuthCookieEither(cookie);
+
+	return Result.getOrThrow(decoded);
+};