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42 lines
1.6 KiB
Markdown
42 lines
1.6 KiB
Markdown
# event-stats
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Analytics endpoint over an in-memory event log (300,000 events, generated
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deterministically by `src/data.js`).
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## API
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`GET /stats?type=<t>&from=<ms>&to=<ms>` returns JSON:
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```json
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{ "type": "click", "from": 1754000000000, "to": 1756592000000,
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"count": 1234, "sum": 56789, "avg": 46.02,
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"p50": 123, "p95": 456, "p99": 789, "min": 1, "max": 50000 }
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```
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Semantics (all pinned; follow them exactly):
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- `from`/`to` are millisecond timestamps, **inclusive**, and optional
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(absent means unbounded). Non-numeric bounds, or `from > to`, are `400`.
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- Only events of the given `type` within `[from, to]` are included.
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- `sum` is the exact integer sum of `value`s.
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- `avg` is `sum / count` rounded **half-up to two decimals**.
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- Percentiles use the **nearest-rank** method: sort values ascending, take the
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value at 1-based rank `ceil(p / 100 * count)`. No interpolation.
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- If no events match (including an unknown `type`), return `200` with
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`count: 0, sum: 0` and `avg`, `p50`, `p95`, `p99`, `min`, `max` all `null`.
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- The response echoes the effective `from`/`to` (`null` when unbounded).
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## Performance requirement
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The endpoint must stay fast at this data size: **2,000 mixed queries complete
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in under 6 seconds** on this machine (the reference does it in ~1.5s).
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Precompute whatever you need at startup; per-query work must not scan the
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whole log.
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## Module contract
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- `src/app.js` is CommonJS and exports `createApp()` returning an
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`http.Server` that is not yet listening.
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- `node src/index.js <port>` starts the service.
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- No external dependencies. Run the tests with `npm test`.
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