feat(email-renderer): generate bounded animated countdown images

packages/email-renderer/src/countdown.ts

@@ -0,0 +1,54 @@
+import { createRequire } from "node:module";
+
+const { GIFEncoder } = createRequire(import.meta.url)("gifenc") as {
+  GIFEncoder(): {
+    writeFrame(pixels: Uint8Array, width: number, height: number, options: {
+      palette: number[][]; delay: number; repeat: number;
+    }): void;
+    finish(): void;
+    bytes(): Uint8Array;
+  };
+};
+
+const glyphs: Record<string, string> = {
+  "0": "111101101101111", "1": "010110010010111", "2": "111001111100111",
+  "3": "111001111001111", "4": "101101111001001", "5": "111100111001111",
+  "6": "111100111101111", "7": "111001001001001", "8": "111101111101111",
+  "9": "111101111001111", ":": "000010000010000", " ": "000000000000000",
+  D: "110101101101110", H: "101101111101101", M: "101111111101101", S: "111100111001111",
+};
+
+export function countdownLabel(deadline: number, now: number): string {
+  if (!Number.isFinite(deadline) || !Number.isFinite(now)) throw new Error("Invalid countdown time.");
+  const seconds = Math.max(0, Math.ceil((deadline - now) / 1000));
+  const days = Math.floor(seconds / 86400);
+  if (days > 999) throw new Error("Countdown cannot exceed 999 days.");
+  const pair = (value: number) => String(value).padStart(2, "0");
+  return `${String(days).padStart(3, "0")}D ${pair(Math.floor(seconds / 3600) % 24)}H ${pair(Math.floor(seconds / 60) % 60)}M ${pair(seconds % 60)}S`;
+}
+
+/** A bounded, non-looping animation. The caller injects its clock for deterministic rendering. */
+export function renderCountdownGif(deadline: number, now: number, frames = 60): Uint8Array {
+  if (!Number.isInteger(frames) || frames < 1 || frames > 60) throw new Error("Countdown requires 1–60 frames.");
+  countdownLabel(deadline, now);
+  const width = 320, height = 64, scale = 4;
+  const encoder = GIFEncoder();
+  const count = Math.min(frames, Math.max(1, Math.ceil((deadline - now) / 1000) + 1));
+  for (let frame = 0; frame < count; frame++) {
+    const label = countdownLabel(deadline, now + frame * 1000);
+    const pixels = new Uint8Array(width * height);
+    const left = Math.floor((width - label.length * 4 * scale) / 2);
+    for (let character = 0; character < label.length; character++) {
+      const glyph = glyphs[label[character]!]!;
+      for (let row = 0; row < 5; row++) for (let col = 0; col < 3; col++) {
+        if (glyph[row * 3 + col] !== "1") continue;
+        for (let y = 0; y < scale; y++) for (let x = 0; x < scale; x++) {
+          pixels[(22 + row * scale + y) * width + left + character * 4 * scale + col * scale + x] = 1;
+        }
+      }
+    }
+    encoder.writeFrame(pixels, width, height, { palette: [[17, 24, 39], [255, 255, 255]], delay: 1000, repeat: -1 });
+  }
+  encoder.finish();
+  return encoder.bytes();
+}