Packer (#172)

* introduce pako and add general packer interface

* add tests for packer

* use function API instead of class API for better tree shaking support

* refcatoring the rollup bundle config

src/packer/base.ts

@@ -0,0 +1,10 @@
+import { eventWithTime } from '../types';
+
+export type PackFn = (event: eventWithTime) => string;
+export type UnpackFn = (raw: string) => eventWithTime;
+
+export type eventWithTimeAndPacker = eventWithTime & {
+  v: string;
+};
+
+export const MARK = 'v1';

src/packer/index.ts

@@ -0,0 +1,2 @@
+export { pack } from './pack';
+export { unpack } from './unpack';

src/packer/pack.ts

@@ -0,0 +1,10 @@
+import { deflate } from 'pako/dist/pako_deflate';
+import { PackFn, MARK, eventWithTimeAndPacker } from './base';
+
+export const pack: PackFn = (event) => {
+  const _e: eventWithTimeAndPacker = {
+    ...event,
+    v: MARK,
+  };
+  return deflate(JSON.stringify(_e), { to: 'string' });
+};

src/packer/unpack.ts

@@ -0,0 +1,31 @@
+import { inflate } from 'pako/dist/pako_inflate';
+import { UnpackFn, eventWithTimeAndPacker, MARK } from './base';
+import { eventWithTime } from '../types';
+
+export const unpack: UnpackFn = (raw: string) => {
+  if (typeof raw !== 'string') {
+    return raw;
+  }
+  try {
+    const e: eventWithTime = JSON.parse(raw);
+    if (e.timestamp) {
+      return e;
+    }
+  } catch (error) {
+    // ignore and continue
+  }
+  try {
+    const e: eventWithTimeAndPacker = JSON.parse(
+      inflate(raw, { to: 'string' }),
+    );
+    if (e.v === MARK) {
+      return e;
+    }
+    throw new Error(
+      `These events were packed with packer ${e.v} which is incompatible with current packer ${MARK}.`,
+    );
+  } catch (error) {
+    console.error(error);
+    throw new Error('Unknown data format.');
+  }
+};