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| 1 | +# Pipeline API — Design Doc |
| 2 | + |
| 3 | +> Status: **DRAFT for review**. |
| 4 | +> Tracking issue: [#438](https://github.com/coding-kitties/investing-algorithm-framework/issues/438). |
| 5 | +> Phase issues: [#501](https://github.com/coding-kitties/investing-algorithm-framework/issues/501) (event), [#502](https://github.com/coding-kitties/investing-algorithm-framework/issues/502) (vector), [#503](https://github.com/coding-kitties/investing-algorithm-framework/issues/503) (live). |
| 6 | +
|
| 7 | +## 1. Goals & non-goals |
| 8 | + |
| 9 | +### Goals |
| 10 | + |
| 11 | +1. Declarative cross-sectional factor / filter / classifier computation across an asset universe at each bar. |
| 12 | +2. Look-ahead-safe by construction: a factor evaluated at bar `t` sees only data with timestamp `≤ t`. |
| 13 | +3. Strict opt-in: strategies without `pipelines = [...]` see **zero** behavioural or performance change. |
| 14 | +4. Three execution backends (event backtest, vector backtest, live) sharing the same `Pipeline` definition. |
| 15 | + |
| 16 | +### Non-goals (v1) |
| 17 | + |
| 18 | +- Full Zipline-Pipeline parity (no classifier hierarchies, no winsorization, no OLS factors). |
| 19 | +- Live pipelines on sub-daily timeframes. |
| 20 | +- Universes outside the supported envelope (see §6). |
| 21 | +- Cross-market order routing (separate issue). |
| 22 | + |
| 23 | +## 2. Public API |
| 24 | + |
| 25 | +```python |
| 26 | +from investing_algorithm_framework import ( |
| 27 | + TradingStrategy, Pipeline, Returns, AverageDollarVolume, TimeUnit, |
| 28 | +) |
| 29 | + |
| 30 | +class MomentumScreener(Pipeline): |
| 31 | + dollar_volume = AverageDollarVolume(window=30) |
| 32 | + momentum = Returns(window=60) |
| 33 | + |
| 34 | + universe = dollar_volume.top(100) |
| 35 | + alpha = momentum.rank(mask=universe) |
| 36 | + |
| 37 | + |
| 38 | +class MyStrategy(TradingStrategy): |
| 39 | + time_unit = TimeUnit.DAY |
| 40 | + interval = 1 |
| 41 | + pipelines = [MomentumScreener] |
| 42 | + universe = ["BTC/EUR", "ETH/EUR", ...] # candidate symbols |
| 43 | + |
| 44 | + def run_strategy(self, context, data): |
| 45 | + out = data["MomentumScreener"] # pl.DataFrame, one row per surviving symbol |
| 46 | + ... |
| 47 | +``` |
| 48 | + |
| 49 | +### Class attributes added to `TradingStrategy` |
| 50 | + |
| 51 | +| Attribute | Type | Default | Meaning | |
| 52 | +|---|---|---|---| |
| 53 | +| `pipelines` | `list[type[Pipeline]]` | `[]` | Pipelines to run before each `run_strategy` call. | |
| 54 | +| `universe` | `list[str] \| list[DataSource]` | `[]` | Candidate symbols. Folded into `data_sources` at app startup; pipelines filter down. | |
| 55 | + |
| 56 | +### `Pipeline` class |
| 57 | + |
| 58 | +- Class attributes that are `Factor` / `Filter` instances are introspected via `__init_subclass__`. |
| 59 | +- A class attribute named `universe` is treated as the **root mask**: if present, every other column is computed on the masked subset. |
| 60 | +- All other attributes become columns of the output frame. |
| 61 | + |
| 62 | +## 3. Panel shape |
| 63 | + |
| 64 | +The engine's internal representation is a **long-form Polars DataFrame**: |
| 65 | + |
| 66 | +``` |
| 67 | +schema = { |
| 68 | + "datetime": pl.Datetime, |
| 69 | + "symbol": pl.Utf8, |
| 70 | + "open": pl.Float32, |
| 71 | + "high": pl.Float32, |
| 72 | + "low": pl.Float32, |
| 73 | + "close": pl.Float32, |
| 74 | + "volume": pl.Float32, |
| 75 | +} |
| 76 | +``` |
| 77 | + |
| 78 | +Long-form is chosen because: |
| 79 | + |
| 80 | +- Polars rolling/group-by is faster on long form than on wide. |
| 81 | +- Sparse symbols (delisted, late-listed) are natural — no NaN columns. |
| 82 | +- Cache files are smaller (no per-symbol column duplication). |
| 83 | + |
| 84 | +Per-bar pipeline output handed to the strategy is a **wide** frame keyed by symbol: |
| 85 | + |
| 86 | +``` |
| 87 | +out = pl.DataFrame({ |
| 88 | + "symbol": pl.Utf8, |
| 89 | + "<factor name>": pl.Float64, # one column per Factor/Filter on the Pipeline |
| 90 | + ... |
| 91 | +}) |
| 92 | +``` |
| 93 | + |
| 94 | +## 4. Engine API (internal) |
| 95 | + |
| 96 | +```python |
| 97 | +class PipelineEngine(Protocol): |
| 98 | + def evaluate_at( |
| 99 | + self, |
| 100 | + pipeline: type[Pipeline], |
| 101 | + as_of: datetime, |
| 102 | + ) -> pl.DataFrame: ... |
| 103 | + """Event mode: return wide per-symbol frame for the given timestamp.""" |
| 104 | + |
| 105 | + def evaluate_range( |
| 106 | + self, |
| 107 | + pipeline: type[Pipeline], |
| 108 | + start: datetime, |
| 109 | + end: datetime, |
| 110 | + ) -> pl.DataFrame: ... |
| 111 | + """Vector mode: return long (date, symbol)-indexed frame for the range.""" |
| 112 | +``` |
| 113 | + |
| 114 | +Two implementations: |
| 115 | + |
| 116 | +- `LazyPolarsPipelineEngine` (event + vector). Compiles Factor expressions into a single `pl.LazyFrame` plan; `collect()` only at the boundary. |
| 117 | +- `LiveBatchedPipelineEngine` (Phase 3). Adds async batched fetch + universe-refresh. |
| 118 | + |
| 119 | +## 5. Cache key (Phase 2) |
| 120 | + |
| 121 | +Cache lives under `<resource_dir>/pipeline_cache/`. Key: |
| 122 | + |
| 123 | +``` |
| 124 | +hash( |
| 125 | + universe_hash: sha1(sorted(symbol_list)), |
| 126 | + daterange: (start.isoformat(), end.isoformat()), |
| 127 | + timeframe: e.g. "1d", |
| 128 | + expr_hash: sha1(canonical_repr(factor_expression_tree)), |
| 129 | + schema_version: int, # bump on any cache-incompatible change |
| 130 | +) |
| 131 | +``` |
| 132 | + |
| 133 | +Hits return the cached panel/factor frame without recomputation. |
| 134 | +Parameter sweeps over **non-pipeline** attributes (signal thresholds, position sizing) reuse the cache for free. |
| 135 | + |
| 136 | +## 6. Performance contract |
| 137 | + |
| 138 | +| Mode | Timeframe | Max universe | Tested in CI | |
| 139 | +|---|---|---|---| |
| 140 | +| Event BT | daily | 5,000 | ✅ | |
| 141 | +| Event BT | 4h / 1h | 1,000 / 500 | ✅ | |
| 142 | +| Event BT | < 1h | — | ❌ raises | |
| 143 | +| Vector BT | daily | 5,000 | ✅ | |
| 144 | +| Vector BT | 4h / 1h | 1,000 / 500 | ✅ | |
| 145 | +| Vector BT | < 1h | — | ❌ raises | |
| 146 | +| Live | daily | 50 | smoke only | |
| 147 | +| Live | < daily | — | ❌ raises | |
| 148 | + |
| 149 | +**Opt-in guarantee (CI-asserted):** vector backtest of the existing single-symbol example must run within ±10% of the pre-pipeline baseline wall-clock. |
| 150 | + |
| 151 | +## 7. Built-in factors (v1) |
| 152 | + |
| 153 | +| Factor | Formula | |
| 154 | +|---|---| |
| 155 | +| `Returns(window=N)` | `close.pct_change(N)` | |
| 156 | +| `AverageDollarVolume(window=N)` | `(close * volume).rolling_mean(N)` | |
| 157 | +| `SMA(window=N)` | `close.rolling_mean(N)` | |
| 158 | +| `RSI(window=N)` | standard Wilder RSI | |
| 159 | +| `Volatility(window=N)` | `log_returns.rolling_std(N) * sqrt(periods_per_year)` | |
| 160 | + |
| 161 | +All other factors mentioned in #438's original draft (`MACD`, `BollingerBands`, `EWMA`, `VWAP`, `MaxDrawdown`) are deferred. Users can subclass `CustomFactor`: |
| 162 | + |
| 163 | +```python |
| 164 | +class MACD(CustomFactor): |
| 165 | + inputs = ["close"] |
| 166 | + window = 26 |
| 167 | + |
| 168 | + def compute(self, close: pl.Series) -> pl.Series: |
| 169 | + ... |
| 170 | +``` |
| 171 | + |
| 172 | +## 8. Look-ahead safety |
| 173 | + |
| 174 | +Factors operate on a Polars `LazyFrame` filtered to `datetime <= as_of` *before* any rolling op. Rolling windows are right-aligned (closed on the right). Tests must assert that injecting a future bar does not change a past factor value. |
| 175 | + |
| 176 | +## 9. Open questions |
| 177 | + |
| 178 | +1. **Universe declaration ergonomics.** Do we accept a callable `universe = lambda ctx: top_500_by_market_cap()` or only a static list in v1? (Proposed: static list in v1, callable in v2.) |
| 179 | +2. **Pipeline scheduling.** Always run every bar, or honour a per-pipeline `time_unit`? (Proposed: same `time_unit` as the strategy in v1; per-pipeline scheduling in v2.) |
| 180 | +3. **Multiple pipelines on one strategy.** Independent (each gets its own cache key) or composable (one pipeline can reference another's column)? (Proposed: independent in v1.) |
| 181 | +4. **Float32 vs float64.** Default to float32 for memory; users opt into float64 per factor? (Proposed: yes, factor-level `dtype=` override.) |
| 182 | + |
| 183 | +## 10. Out of code, in the order of work |
| 184 | + |
| 185 | +1. ✅ This doc reviewed and merged. |
| 186 | +2. Phase 1 ([#501](https://github.com/coding-kitties/investing-algorithm-framework/issues/501)) — event backtest + 5 factors. |
| 187 | +3. Phase 2 ([#502](https://github.com/coding-kitties/investing-algorithm-framework/issues/502)) — vector + cache + benchmark. |
| 188 | +4. Phase 3 ([#503](https://github.com/coding-kitties/investing-algorithm-framework/issues/503)) — live, gated on async CCXT fetch. |
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