# Three-Line Strike

`D06-F04-A10` · Price Action and Candlesticks → Multi-Candle Patterns · archetype `record-transform` · difficulty 2/5 · verification **verified**

Full page: https://docs.thefintechbuilder.com/price-action-and-candlesticks/multi-candle-patterns/three-line-strike/
Agent skill: `npx skills add IslamBaraka90/Fintech-Algorithms-Library` — https://docs.thefintechbuilder.com/guides/agent-skill/

## Install and import

```bash
npm install fintech-algorithms
```

```ts
import { threeLineStrike } from "fintech-algorithms/price-action-and-candlesticks/multi-candle-patterns/three-line-strike";
```

## Signature

```ts
threeLineStrike(input)
```

Scans four-bar windows for three same-colour candles followed by one opposite candle whose body swallows the run from the first candle's body edge to the third's.

## Parameters

| Name | Type | Required | Notes |
| --- | --- | --- | --- |
| `input` | `TopicInput` | yes | `bars` is a chronologically ordered array of OHLCV rows; each needs a non-empty `timestamp` strictly greater than the previous row's and finite `open`, `high`, `low`, `close` and `volume`. The pattern family validates `tick_tolerance` (default 0.01, at least 0) and `doji_body_ratio` (default 0.05, within 0..1) on every call, but this topic's branch reads neither: every comparison is an exact body and colour test with no tolerance. |

## Returns

`TopicResult`

`series.matched` is the boolean verdict for the window ending at that index, and `series.label` is `"bearish-strike"` when three up candles are struck by a down candle, `"bullish-strike"` for the mirror case, and `"none"` otherwise. `latest` carries the last value of each. The warm-up is the three leading bars that cannot close a four-bar window.

## Warm-up

The first `3 bars` positions are `null`. The pattern needs a four-bar window, so both series hold null at indexes 0 through 2 and `ready_at` is 3. From index 3 onward `matched` is false or true, and false is a real verdict rather than a warm-up placeholder, so `ready_at` does not depend on any pattern ever firing. An input of one to three bars returns null throughout, with `ready_at` null and `state` "waiting".

## Errors

- When a bar has a non-finite price or volume, a negative volume, a `high` below its own open/low/close, a `low` above them, or a `timestamp` that does not advance — throws Error
- When `tick_tolerance` or `doji_body_ratio` is out of range, which the family validates before the branch runs even though this topic does not use either — throws Error
- When `input` is not an object, `input.parameters` is not an object, or `bars` is not an array holding at least one bar — throws Error

## Complexity

Time `O(n)`, space `O(n)`.

## Worked example

Captured by running this function on the input its own test provides. Real output of real code — but not asserted against a published figure.

### Input

`input`:

```json
{
  "bars": [
    {
      "timestamp": "2024-01-02",
      "basis": "synthetic-unadjusted",
      "open": 100,
      "high": 101.45,
      "low": 98.695,
      "close": 100,
      "volume": 750000,
      "benchmark": 200
    },
    {
      "timestamp": "2024-01-03",
      "basis": "synthetic-unadjusted",
      "open": 101.49111452,
      "high": 103.38381693,
      "low": 100.05480022,
      "close": 101.78791214,
      "volume": 795117,
      "benchmark": 200.56326135
    },
    {
      "timestamp": "2024-01-04",
      "basis": "synthetic-unadjusted",
      "open": 102.45519048,
      "high": 104.6701838,
      "low": 100.91147007,
      "close": 102.9549389,
      "volume": 840234,
      "benchmark": 201.11020913
    }
  ],
  "parameters": {}
}
```

### Call

```ts
threeLineStrike(input)
```

### Returns

object with 9 fields: topic_id, title, state, ready, ready_at, series, latest, parameters, …

```json
{
  "topic_id": "D06-F04-A10",
  "title": "Three-Line Strike",
  "state": "calculated",
  "ready": true,
  "ready_at": 3,
  "series": {
    "label": [null, null, null, "none", "none", "none"],
    "matched": [null, null, null, false, false, false]
  },
  "latest": {
    "label": "none",
    "matched": false
  },
  "parameters": {},
  "diagnostics": {
    "causal": true,
    "input_count": 96
  }
}
```

## Verification and provenance

Tier: **verified** (via E).

The worked example below is the figure published in this algorithm's article, replayed and asserted by the test suite on every build. The arithmetic cannot drift without the build failing.

Both tiers guarantee the signature. Full explanation: https://docs.thefintechbuilder.com/guides/verification/

Generated from the docs.json payload shipped inside fintech-algorithms@0.13.0.
The signature and parameter list are checked against the compiled implementation at build time,
so a description that contradicts the code fails the build rather than reaching this file.

## Links

- Article (how it works, step by step): https://thefintechbuilder.com/price-action-and-candlesticks/multi-candle-patterns/three-line-strike/
- Implementation source: https://github.com/IslamBaraka90/Fintech-Algorithms-Library/blob/main/src/price-action-and-candlesticks/multi-candle-patterns/three-line-strike/impl.ts
- Package on npm: https://www.npmjs.com/package/fintech-algorithms
- Domain index for agents: https://docs.thefintechbuilder.com/price-action-and-candlesticks/llms.txt