sporel-lib-core.maps/README.md

# lib-core.maps

Single tile-grid map implementation. Loads JSON map + tilemap files, registers maps by id, and provides tile-fetch + walkability + size queries with current-map sugar.

**Version:** 0.1.1  
**Lib-ID:** lib-core.maps  
**Requires:** (none)  
**Tags:** maps, tile-grid, walkability, tilemap

## Topology

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

## API

### `maps.load(path)`
**Syntax:** `maps.load(path: string) -> string`

**Example:**
```lua
local id = maps.load("maps/forest.json")
maps.set_current(id)
```

**Description:** Loads a JSON map-file from disk, resolves + loads its referenced tilemap (local module-tilemap-id or fully-qualified), validates the map-table, and registers it. Returns the map-id. Errors if the id is already registered.

### `maps.create(t)`
**Syntax:** `maps.create(t: {id: string, tilemap_table: table, ...}) -> string`

**Example:**
```lua
local id = maps.create({
    id = "test-tiny",
    size = { w = 4, h = 4 },
    tile_size = { w = 16, h = 16 },
    tilemap_table = my_tilemap,
    tiles = { 0,0,0,0, 0,1,1,0, 0,1,1,0, 0,0,0,0 },
})
```

**Description:** Programmatic creation for tests + procedural generators. Caller must supply a fully-built `tilemap_table` (not a path/id reference). Otherwise identical to `load`.

### `maps.size(map_id)`
**Syntax:** `maps.size(map_id: string | nil) -> {w: integer, h: integer}`

**Description:** Returns map-size in tiles. Falls back to current-map when `map_id` is nil. Errors if no current map.

### `maps.tile_size(map_id)`
**Syntax:** `maps.tile_size(map_id: string | nil) -> {w: integer, h: integer}`

**Description:** Returns tile-size in pixels. Falls back to current-map when nil.

### `maps.tile_at(a, b, c)`
**Syntax:** `maps.tile_at(map_id: string, tx: integer, ty: integer) -> table | nil` *(also: `maps.tile_at(tx, ty)` uses current-map)*

**Example:**
```lua
local tile = maps.tile_at(5, 3)
if tile then engine.print(tile.id) end
```

**Description:** Arity-flex sugar: `tile_at(tx, ty)` uses current-map; `tile_at(map_id, tx, ty)` is explicit. Returns the resolved tile-record from the tilemap, or `nil` if out-of-bounds.

### `maps.is_walkable(a, b, c)`
**Syntax:** `maps.is_walkable(map_id: string, tx: integer, ty: integer) -> bool` *(also: `is_walkable(tx, ty)` uses current-map)*

**Description:** Convenience: returns `true` iff the tile exists and has `walkable == true`. Out-of-bounds is `false`.

### `maps.tilemap_id(map_id)`
**Syntax:** `maps.tilemap_id(map_id: string | nil) -> string`

**Description:** Returns the fully-qualified tilemap-id referenced by a map.

### `maps.current()`
**Syntax:** `maps.current() -> string | nil`

**Description:** Returns the currently-active map-id, or `nil` if none.

### `maps.set_current(map_id)`
**Syntax:** `maps.set_current(map_id: string) -> void`

**Description:** Switches the current-map pointer. Errors if `map_id` is not registered.

### `maps.list()`
**Syntax:** `maps.list() -> string[]`

**Description:** Returns an array of all registered map-ids.

### `maps.state(map_id)`
**Syntax:** `maps.state(map_id: string) -> string`

**Description:** DEPRECATED-MVP stub. Always returns `"Active"` in v0.1.x. Full lifecycle (`Virgin`/`Inert`/`Passive`/`Active`/`Pinned`) lands in the multi-map slice.

### `maps.pin(map_id, reason)`
**Syntax:** `maps.pin(map_id: string, reason: string) -> void`

**Description:** DEPRECATED-MVP stub. Emits a warn in v0.1.x. Pinning prevents lifecycle-eviction in the multi-map slice.

## Conventions

- Pixel-coords + tile-coords kept distinct: `size`/`tiles` index in tile-units; `tile_size` is the conversion to pixels.
- Tilemap-ids may be local (`<this-module-id>.<name>`) or fully-qualified; `load()` resolves both.
- `tile_at` is bounds-checked: out-of-bounds returns `nil` (not error).
- Y-down-positive per ADR-0031.

## Consumer pattern

```lua
local maps = require("lib-core.maps")

local id = maps.load("maps/forest.json")
maps.set_current(id)

local sz = maps.size()
for ty = 0, sz.h - 1 do
    for tx = 0, sz.w - 1 do
        if not maps.is_walkable(tx, ty) then
            -- mark blocked cell
        end
    end
end
```

## CHANGELOG

### v0.1.1
- Tilemap-id resolution handles module-ids with dots (prefix-match instead of first-dot split).

### v0.1.0 (P.0)
- Initial release: load/create + tile_at + is_walkable + current-map management.

## References

- Spec v0.1.0 (P.0): `meta/docs/superpowers/specs/2026-05-09-p0-lib-maps-design.md`
- Architecture: `meta/docs/architecture/map-topology.md`
- ADR-0001 (engine knows verbs, libs bring nouns)
- ADR-0031 (pixel-convention: Y-down-positive)
- ADR-0038 (API-Doc-Convention)