# Story 2.4: Altitude Colour Bands & Aircraft Type Icons

Status: done

## Story

As the renderer,
I want pure functions mapping an aircraft's altitude to a display colour and its ADS-B category/callsign to an icon type,
So that every aircraft is consistently colour-coded and type-classified with all logic centralised.

## Acceptance Criteria

AC1: **Given** `altitude_ft` values at the exact boundaries in `ALTITUDE_BANDS_FT` **When** `altitude_to_colour(altitude_ft)` is called **Then** the correct `ALTITUDE_COLOURS` entry is returned for each boundary and above/below it — all 6 palette colours reachable

AC2: **Given** an `Aircraft` with `category="A1"` (light aircraft) **When** `classify_aircraft_type(aircraft)` is called **Then** it returns `AircraftType.GA_LIGHT`

AC3: **Given** an `Aircraft` with a BA callsign pattern (e.g. `"BAW123"`) and no category **When** `classify_aircraft_type(aircraft)` is called **Then** it returns `AircraftType.COMMERCIAL`

AC4: **Given** an `Aircraft` with `category="A7"` (helicopter) **When** `classify_aircraft_type(aircraft)` is called **Then** it returns `AircraftType.HELICOPTER`

AC5: **Given** an `Aircraft` with no category and `altitude_ft=5000` (< 10,000ft) **When** `classify_aircraft_type(aircraft)` is called **Then** it returns `AircraftType.GA_LIGHT` (altitude fallback)

AC6: **Given** an `Aircraft` with no category and `altitude_ft=18000` (10,000–30,000ft) **When** `classify_aircraft_type(aircraft)` is called **Then** it returns `AircraftType.PRIVATE_JET`

AC7: **Given** an `Aircraft` with no category and `altitude_ft=38000` (> 30,000ft) **When** `classify_aircraft_type(aircraft)` is called **Then** it returns `AircraftType.AIRLINER`

## Tasks / Subtasks

- [x] Task 1: Implement `altitude_to_colour()` in `src/planemapper/renderer/colours.py` (AC: #1)
  - [x] 1.1 Replace `# stub` with full implementation
  - [x] 1.2 Imports: `from planemapper.constants import ALTITUDE_BANDS_FT, ALTITUDE_COLOURS`
  - [x] 1.3 Signature: `def altitude_to_colour(altitude_ft: int) -> tuple[int, int, int]:`
  - [x] 1.4 Iterate `ALTITUDE_BANDS_FT` with `enumerate`; return `ALTITUDE_COLOURS[i]` for the first band where `altitude_ft <= band`

- [x] Task 2: Implement `AircraftType` enum and `classify_aircraft_type()` in `src/planemapper/renderer/icons.py` (AC: #2–#7)
  - [x] 2.1 Replace `# stub` with full implementation
  - [x] 2.2 Imports: `from enum import Enum`; `from planemapper.models import Aircraft`
  - [x] 2.3 Define `AircraftType` enum:
    ```python
    from enum import Enum
    class AircraftType(Enum):
        GA_LIGHT = "ga_light"
        COMMERCIAL = "commercial"
        PRIVATE_JET = "private_jet"
        AIRLINER = "airliner"
        HELICOPTER = "helicopter"
        MILITARY = "military"
        UNKNOWN = "unknown"
    ```
  - [x] 2.4 Define `AIRLINE_PREFIXES` as a `frozenset` of 3-letter ICAO codes: `{"BAW", "EIN", "RYR", "EZY", "THY", "DLH", "AFR", "IBE", "KLM", "UAE", "SWR"}`
  - [x] 2.5 Signature: `def classify_aircraft_type(aircraft: Aircraft) -> AircraftType:`
  - [x] 2.6 Implement priority logic (in order):
    1. `category == "A7"` → `HELICOPTER`
    2. `category` in `{"A1", "A2"}` → `GA_LIGHT`
    3. `category` in `{"A3", "A4", "A5"}` → `COMMERCIAL`
    4. Callsign starts with a known airline prefix (first 3 chars in `AIRLINE_PREFIXES`) → `COMMERCIAL`
    5. Altitude fallback (no category, no recognised callsign):
       - `altitude_ft < 10000` → `GA_LIGHT`
       - `10000 <= altitude_ft < 30000` → `PRIVATE_JET`
       - `altitude_ft >= 30000` → `AIRLINER`
    6. Default → `UNKNOWN`

- [x] Task 3: Write tests in `tests/test_colours.py` (AC: #1)
  - [x] 3.1 Replace `def test_placeholder(): pass` with real tests
  - [x] 3.2 Test boundary values: 0, 1500, 1501, 5000, 5001, 10000, 10001, 20000, 20001, 35000, 35001 — assert each returns the expected colour from `ALTITUDE_COLOURS`
    - `0` → `COLOUR_GREEN` (≤ 1500)
    - `1500` → `COLOUR_GREEN` (boundary inclusive)
    - `1501` → `COLOUR_BLUE` (≤ 5000)
    - `5000` → `COLOUR_BLUE` (boundary inclusive)
    - `5001` → `COLOUR_YELLOW` (≤ 10000)
    - `10000` → `COLOUR_YELLOW` (boundary inclusive)
    - `10001` → `COLOUR_RED` (≤ 20000)
    - `20000` → `COLOUR_RED` (boundary inclusive)
    - `20001` → `COLOUR_BLACK` (≤ 35000)
    - `35000` → `COLOUR_BLACK` (boundary inclusive)
    - `35001` → `COLOUR_WHITE` (≤ 99999, last band catches all)
  - [x] 3.3 Verify all 6 colours are reachable (assert the union of test return values equals the full `ALTITUDE_COLOURS` set)

- [x] Task 4: Write tests in `tests/test_icons.py` (AC: #2–#7)
  - [x] 4.1 Replace `def test_placeholder(): pass` with real tests
  - [x] 4.2 One test function per AC:
    - `test_category_a1_returns_ga_light` — `Aircraft(icao="X", lat=0.0, lon=0.0, category="A1")` → `AircraftType.GA_LIGHT` (AC2)
    - `test_ba_callsign_returns_commercial` — `Aircraft(icao="X", lat=0.0, lon=0.0, callsign="BAW123")` → `AircraftType.COMMERCIAL` (AC3)
    - `test_category_a7_returns_helicopter` — `Aircraft(icao="X", lat=0.0, lon=0.0, category="A7")` → `AircraftType.HELICOPTER` (AC4)
    - `test_no_category_low_altitude_returns_ga_light` — `Aircraft(icao="X", lat=0.0, lon=0.0, altitude_ft=5000)` → `AircraftType.GA_LIGHT` (AC5)
    - `test_no_category_mid_altitude_returns_private_jet` — `Aircraft(icao="X", lat=0.0, lon=0.0, altitude_ft=18000)` → `AircraftType.PRIVATE_JET` (AC6)
    - `test_no_category_high_altitude_returns_airliner` — `Aircraft(icao="X", lat=0.0, lon=0.0, altitude_ft=38000)` → `AircraftType.AIRLINER` (AC7)
  - [x] 4.3 Use `Aircraft(icao="X", lat=0.0, lon=0.0, ...)` to construct test aircraft; supply only the fields relevant to each AC

- [x] Task 5: Run quality gates
  - [x] 5.1 `python -m pytest tests/` — all tests pass
  - [x] 5.2 `python -m ruff check .` — zero violations
  - [x] 5.3 `python -m ruff format --check .` — no formatting issues

## Implementation Notes

### `altitude_to_colour()` boundary behaviour

`ALTITUDE_BANDS_FT = [1500, 5000, 10000, 20000, 35000, 99999]`

The function iterates the list and returns the colour for the **first** band where `altitude_ft <= band`. The final band `99999` is a catch-all, so values above 35000ft still map to `COLOUR_WHITE` (index 5). Values above 99999ft (if any) would also resolve to `COLOUR_WHITE` via the last band.

### `classify_aircraft_type()` priority

Category takes precedence over callsign, which takes precedence over altitude fallback. The `altitude_ft` field may be `None` on the `Aircraft` model; guard with `is not None` before numeric comparison in the altitude fallback branch.

### `AIRLINE_PREFIXES` frozenset

Using `frozenset` ensures O(1) membership testing and signals the constant is immutable:
```python
AIRLINE_PREFIXES: frozenset[str] = frozenset(
    {"BAW", "EIN", "RYR", "EZY", "THY", "DLH", "AFR", "IBE", "KLM", "UAE", "SWR"}
)
```

Callsign prefix matching: `aircraft.callsign and aircraft.callsign[:3].upper() in AIRLINE_PREFIXES`.
