[link] store share links

apps/link/src/link-db.ts

@@ -0,0 +1,86 @@
+/**
+ * The `link` table (migrations/0001_link.sql): one row per share code minted by
+ * `POST /actionlink`.
+ */
+
+/**
+ * The code alphabet: upper-case letters and digits without the look-alikes (0/O, 1/I/L),
+ * since a player may read a code aloud or type it from a screenshot. 31 symbols, so six of
+ * them give ~887 million codes.
+ */
+const CODE_ALPHABET = 'ABCDEFGHJKMNPQRSTUVWXYZ23456789'
+export const CODE_LENGTH = 6
+
+/** How many fresh codes to try before giving up on a run of collisions. */
+const MAX_ATTEMPTS = 8
+
+/** A random code. Rejection-sampled so every symbol is equally likely. */
+export function randomCode(): string {
+	// The largest multiple of the alphabet size that fits in a byte.
+	const limit = 256 - (256 % CODE_ALPHABET.length)
+	let code = ''
+	while (code.length < CODE_LENGTH) {
+		for (const byte of crypto.getRandomValues(new Uint8Array(CODE_LENGTH * 2))) {
+			if (byte >= limit) continue
+			code += CODE_ALPHABET[byte % CODE_ALPHABET.length]
+			if (code.length === CODE_LENGTH) break
+		}
+	}
+	return code
+}
+
+export interface NewLink {
+	creatorAccountId: number
+	codeType: number
+	extraDataId: number | null
+	data: string | null
+	validHours: number
+}
+
+export interface LinkRow {
+	code: string
+	creator_account_id: number
+	code_type: number
+	extra_data_id: number | null
+	data: string | null
+	valid_hours: number
+	created_at: string
+	expires_at: string
+}
+
+/**
+ * Store a link under a fresh code and return the code. A code already taken is skipped
+ * (`ON CONFLICT DO NOTHING` returns no row) and another drawn.
+ */
+export async function createLink(db: D1Database, link: NewLink, now = new Date()): Promise<string> {
+	const createdAt = now.toISOString()
+	const expiresAt = new Date(now.getTime() + link.validHours * 3_600_000).toISOString()
+	for (let attempt = 0; attempt < MAX_ATTEMPTS; attempt++) {
+		const code = randomCode()
+		const row = await db
+			.prepare(
+				`INSERT INTO link (code, creator_account_id, code_type, extra_data_id, data, valid_hours, created_at, expires_at)
+				 VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8)
+				 ON CONFLICT (code) DO NOTHING
+				 RETURNING code`
+			)
+			.bind(
+				code,
+				link.creatorAccountId,
+				link.codeType,
+				link.extraDataId,
+				link.data,
+				link.validHours,
+				createdAt,
+				expiresAt
+			)
+			.first<{ code: string }>()
+		if (row) return row.code
+	}
+	throw new Error(`no free link code after ${MAX_ATTEMPTS} attempts`)
+}
+
+/** One link by code, or null. */
+export async function getLink(db: D1Database, code: string): Promise<LinkRow | null> {
+	return db.prepare('SELECT * FROM link WHERE code = ?1').bind(code).first<LinkRow>()
+}