# lib-core.input

P.0 action-mapping lib. Decouples physical keys from logical actions.
Polling-based (`is_action_down`) + edge-based (`was_action_pressed`, `was_action_released`).
Direction-vector helper composes 4 actions into `{x, y}` in {-1, 0, +1}^2.

| Field | Value |
|---|---|
| Version | 0.4.0 |
| Lib-ID | lib-core.input |
| Requires | (none) |
| Tags | input, action-mapping |

<!-- topology:start (auto-generated; do not edit) -->
```mermaid
graph LR
  this["lib-core.input"]
  engine["engine.*"]
  this --> engine
```
<!-- topology:end -->

## API

### `input.bind(action_name, keys)`
**Syntax:** `input.bind(action_name: string, keys: string[]) -> void`

**Example:**
```lua
input.bind("move_left", { "a", "left" })
```

**Description:** Bindet einen logischen Action-Namen an ein Array von Key-Names. Atomic: wenn ein Key invalid ist, fehlt der gesamte Bind ohne partial state. Lua `error(...)` für `bind()` misuse (caller-bug fast-fail).

### `input.unbind(action_name)`
**Syntax:** `input.unbind(action_name: string) -> void`

**Example:**
```lua
input.unbind("move_left")
```

**Description:** Entfernt eine Action-Binding. No-op wenn Action nicht gebunden.

### `input.is_action_down(action) -> bool`
**Syntax:** `input.is_action_down(action: string) -> bool`

**Example:**
```lua
if input.is_action_down("move_left") then ... end
```

**Description:** Returns true wenn irgendein gebundener Key der Action gerade gedrückt ist. Silent-false für undefined actions.

### `input.was_action_pressed(action) -> bool`
**Syntax:** `input.was_action_pressed(action: string) -> bool`

**Example:**
```lua
if input.was_action_pressed("quit") then engine.exit(0) end
```

**Description:** Press-Edge — true für genau einen Frame pro Key-Down-Event. Triggers einmal pro Press-Release-Cycle.

### `input.was_action_released(action) -> bool`
**Syntax:** `input.was_action_released(action: string) -> bool`

**Example:**
```lua
if input.was_action_released("attack") then finish_swing() end
```

**Description:** Release-Edge — true für genau einen Frame pro Key-Up-Event. v0.4.0+. Triggers einmal pro Press-Release-Cycle.

### `input.direction(left, right, up, down)`
**Syntax:** `input.direction(left: string, right: string, up: string, down: string) -> {x: int, y: int}`

**Example:**
```lua
local d = input.direction("move_left", "move_right", "move_up", "move_down")
-- d.x, d.y in {-1, 0, +1}
```

**Description:** Komponiert 4 Actions in einen Direction-Vector. Y-down-positive per ADR-0031.

### `input.action_count() -> number`
**Syntax:** `input.action_count() -> number`

**Description:** Returns Anzahl der gebundenen Actions. Debug-friendly.

## Key-Names

Strict-lowercase. Engine-internal `engine.input.KEY_*` integer-args are rejected.

| Category | Names |
|---|---|
| Letters | `a`, `b`, ..., `z` |
| Numbers | `0`, `1`, ..., `9` |
| Arrows | `left`, `right`, `up`, `down` |
| Whitespace + control | `space`, `tab`, `enter`, `backspace`, `escape` |
| Modifiers (left-side) | `shift` (= `lshift`), `ctrl` (= `lctrl`), `alt` (= `lalt`) |
| Console-toggle | `^` (DE: Zirkumflex / US: backtick) |
| Mouse | `mouse_left`, `mouse_right`, `mouse_middle` (v0.3.0+) |

Right-modifier-aliases (`rshift`, `rctrl`, `ralt`) + function-keys (`f1`..`f12`) + special-keys (`delete`, `insert`, ...) are **forthcoming**.

Unknown key-names raise a Lua-error with hint to this README.

## Conventions

- Y-down-positive per Sporel pixel-convention (ADR-0031).
- Multi-key per action (e.g., `{"a", "left"}` for both A and Left-Arrow).
- Silent-false for undefined actions (debug-friendly).
- Lua `error(...)` for `bind()` misuse (caller-bug fast-fail). Atomic.

## Consumer pattern

```lua
local input = require("lib-core.input")
input.bind("quit",       { "escape" })
input.bind("move_left",  { "a", "left" })
input.bind("move_right", { "d", "right" })
input.bind("move_up",    { "w", "up" })
input.bind("move_down",  { "s", "down" })

function update(ctx, dt)
    if input.was_action_pressed("quit") then engine.exit(0) end
    local d = input.direction("move_left", "move_right", "move_up", "move_down")
    -- d.x, d.y in {-1, 0, +1}
end
```

## Migration v0.1.0 -> v0.2.0

`bind()` switched from integer `engine.input.KEY_*` arguments to lowercase string-keys (per P.2.6). Reason: stop leaking engine-internal namespace into modules.

| v0.1.0 | v0.2.0 |
|---|---|
| `bind("quit", { engine.input.KEY_ESCAPE })` | `bind("quit", { "escape" })` |

## CHANGELOG

### v0.4.0 (P.3.10, 2026-05-15)
- Added `was_action_released(action_name)` — release-edge detection per action.

### v0.3.0 (P.3.3, 2026-05-12)
- `bind()` now accepts unified key+mouse strings via BIND_MAP with kind-tagged entries.

### v0.2.0 (P.2.6, 2026-05-11)
- `bind()` accepts string-key-names only.

### v0.1.0 (P.0)
- Initial release.

## References

- Spec v0.4.0 (P.3.10): `meta/docs/superpowers/specs/2026-05-15-p3-housekeeping-design.md`
- Spec v0.3.0 (P.3.3): `meta/docs/superpowers/specs/2026-05-12-p3-3-mouse-input-design.md`
- Spec v0.2.0 (P.2.6): `meta/docs/superpowers/specs/2026-05-11-engine-input-symbolic-keys-design.md`
- Spec v0.1.0 (P.0): `meta/docs/superpowers/specs/2026-05-09-p0-lib-input-design.md`
- ADR-0001 (engine knows verbs, libs bring nouns)
- ADR-0031 (pixel-convention: Y-down-positive)
- ADR-0038 (API-Doc-Convention)