# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Project

`kiln` is a ZZT-inspired game-making system written in Rust (edition 2024). The goal is a system where players can create games using a scripting language, similar to the classic DOS game ZZT. It uses **Rhai** for scripting (WASM-compatible, sandboxed, pure Rust).

## Code style

- Add `///` rustdoc comments to every `pub` type, field, and function. The user reads rustdoc in their IDE to understand the code while making changes.
- Add inline `//` comments inside non-trivial function bodies to explain the *why* of each logical step — especially in `update` loops, rendering math, and conversion logic.
- Keep comments accurate: update them when the code they describe changes.

## Finishing an epic

When the user says **"finish the epic"**, do all of the following in order:
1. Update `CLAUDE.md` to reflect any new modules, types, or behaviors added during the session.
2. Update `ARCHITECTURE.md` to reflect the same.
3. Run the `/simplify` skill on changed code.
4. Commit everything with a summary message.

## Commands

```bash
cargo build          # compile
cargo run            # build and run (loads maps/start.toml)
cargo test           # run all tests
cargo test <name>    # run a single test by name (substring match)
cargo clippy         # lint
cargo fmt            # format
```

## Architecture

The game is a single Rust binary using **eframe 0.33 / egui 0.33** for the GUI. eframe drives a retained-mode UI: the `App::update` method is called every frame and is responsible for both drawing and responding to input.

`update` is structured in phases:
- Input handling — arrow keys move the player (Play mode only)
- `egui::TopBottomPanel::top` — menu bar (File → Exit, Play/Edit mode toggle)
- `editor::show_editor_panel` — archetype palette panel (Edit mode only; declared before CentralPanel)
- `egui::CentralPanel::default` — game viewport; rendered with `render::draw_board`; click-to-paint in Edit mode
- `glyph_picker::show` — floating picker dialog (Edit mode only, when open)

### Modules

**`src/game.rs`** — all core game types:
- `Glyph` (`Copy`, `Eq`, `Hash`) — per-cell visual: `tile: u32` (tilesheet index), `fg/bg: Color32`. `Glyph::player()` is a `const fn`; all other glyphs come from the map file. Derives `Hash` so boards can deduplicate glyphs into a palette.
- `FontSpec` — optional per-board bitmap font override: `path: String`, `tile_w: u32`, `tile_h: u32`. When `None`, the app default font is used.
- `Behavior` — plain data struct of runtime behavioral properties: `passable: bool`, `opaque: bool`. Returned by `Archetype::behavior()`; new properties added here require no match arms elsewhere.
- `Archetype` (`Copy`, `PartialEq`) — enum of named element types: `Empty`, `Wall`, `ErrorBlock`. Each variant provides `behavior()`, `name()` (used in map files), and `default_glyph()` (used by the editor when stamping a cell). `ErrorBlock` is a sentinel for unknown archetype names — renders as yellow `?` on red.
- `ALL_ARCHETYPES: &[Archetype]` — ordered list of valid editor choices (excludes `ErrorBlock`).
- `Board` — the complete game unit (ZZT-style "board"): `width`, `height`, `cells: Vec<(Glyph, Archetype)>` (row-major; each cell owns its visual and behavioral class directly), `player: Player`, `objects: Vec<ObjectDef>`, `portals: Vec<PortalDef>`, `font: Option<FontSpec>`. `cells` is `pub(crate)`. `is_passable(x, y)` checks objects before the grid cell: an impassable object blocks even over a passable floor tile.
- `Player` — `x: i32, y: i32`
- `ObjectDef` — scripted object placed on the board: `x`, `y`, `glyph: Glyph`, `passable: bool`, `opaque: bool`, `script_name: Option<String>`. `passable` defaults `false` and `opaque` defaults `true` in map files. Scripts not yet runtime-wired.
- `PortalDef` — parsed from map files, stored on Board; not yet runtime-wired
- `GameState` — holds `board: Board`; `try_move(dx, dy)` checks passability before moving the player

**`src/font.rs`** — bitmap font loading and UV mapping:
- `BitmapFont` — wraps an egui `TextureHandle` (preprocessed to opaque-white / transparent) plus tile dimensions. The top-left pixel of the source PNG defines the "background" color; those pixels become `TRANSPARENT`, all others become `WHITE`. At render time, `painter.image(…, tile_uv, fg_color)` tints white pixels to `fg` and transparent pixels reveal the `bg` fill behind.
- `BitmapFont::load(ctx, path, tile_w, tile_h)` — loads from disk
- `BitmapFont::from_bytes(ctx, bytes, tile_w, tile_h, label)` — loads from embedded bytes
- `BitmapFont::create_placeholder(ctx)` — 16×16 grid of 8×8 procedural tiles (bit-pattern bars), used as fallback when no font file is present
- `BitmapFont::tile_uv(tile)` — returns a UV `Rect` for the given tile index (left-to-right, top-to-bottom). Unit-tested via `compute_tile_uv`.
- `BitmapFont::tile_cols()`, `tile_count()`, `img_w()`, `img_h()` — geometry helpers used by the glyph picker and font dialog

**`src/font_dialog.rs`** — font picker dialog:
- `FontDialogState` — in-progress edit: `path: String`, `tile_w/tile_h: u32`, `preview: Option<BitmapFont>`
- `FontDialogState::from_spec(spec)` — initializes from an existing `FontSpec` or defaults (8×16, empty path)
- `show(ctx, open, state, font_spec)` — floating dialog with file browser (`rfd::FileDialog`), tile dimension `DragValue` controls, scrollable tilesheet preview with grid overlay, and Apply / Use default buttons. Uses a `should_close` flag to avoid the egui `.open()` borrow conflict.

**`src/map_file.rs`** — map file loading:
- `MapFile` and friends — serde `Deserialize` types for TOML map files
- `TileIndex` — `#[serde(untagged)]` enum accepting either `Num(u32)` or `Chr(char)`; lets map files use `tile = " "` (char) or `tile = 32` (integer) interchangeably
- `FontHeader` — deserializes the optional `[font]` section (`path`, `tile_w`, `tile_h`)
- `impl From<MapFile> for Board` — converts a parsed file into a ready-to-use `Board`; unknown archetype names produce `ErrorBlock`
- `pub fn load(path: &str) -> Result<Board, Box<dyn std::error::Error>>` — reads and converts a `.toml` map file
- `pub fn save(board: &Board, path: &Path) -> Result<(), Box<dyn std::error::Error>>` — serializes `Board` back to TOML and writes to disk

**`src/main.rs`** — app entry point and frame loop:
- `AppMode` enum (`Play` | `Edit`) — gates arrow-key input; toggles the side panel and viewport mode
- `App` holds `GameState`, `AppMode`, `EditorState`, `default_font: BitmapFont`, and `board_font: Option<BitmapFont>`
- `App::new(board, egui_ctx)` — loads `assets/vga-font-8x16.png` as the default font (falls back to `create_placeholder`); loads per-board font from `board.font` if present
- Font change detection: `font_spec_before` is snapshotted before `show_editor_panel`; if changed, `apply_font_spec` reloads `board_font`
- Borrow split: `let active_font = self.board_font.as_ref().unwrap_or(&self.default_font)` is extracted before mutable borrows of `editor` and `board.font` to satisfy the borrow checker
- **Play mode**: arrow keys move player; `render::board_origin` centers or player-tracks the viewport
- **Edit mode**: `ScrollArea::both()` wraps the board; click-to-paint stamps `(editor.glyph, editor.selected)`; calls `editor::show_editor_panel` and `glyph_picker::show`

**`src/render.rs`** — cell rendering and drawing primitives:
- Window sizing constants (`DEFAULT_WINDOW_W = 840`, `DEFAULT_WINDOW_H = 524`, `MIN_WINDOW_W/H`); no fixed `CELL_W/H` — cell size comes from the active `BitmapFont`
- `paint_glyph(painter, rect, glyph, font)` — `rect_filled` with `glyph.bg`, then `painter.image` tinted by `glyph.fg`
- `draw_glyph(painter, origin, x, y, glyph, font)` — sizes cell from `font.tile_w/tile_h`, delegates to `paint_glyph`
- `draw_board(painter, origin, board, font)` — draws all cells then player overlay
- `draw_object_overlays(painter, origin, board, font, selected)` — highlights all object cells in the Objects editor tab; the selected object gets a brighter border
- `board_origin(available, board_w, board_h, player, font)` — centers board or clamps to player with no empty space
- `pos_to_cell(origin, pos, tile_w, tile_h) -> (i32, i32)` — pixel → cell coordinates; negatives signal out-of-bounds

**`src/editor.rs`** — editor state and side panel:
- `EditorTab` enum (`Palette` | `Board` | `Objects` | `World`) — which tab is active
- `EditorState` — holds `selected: Archetype`, `glyph: Glyph`, `glyph_picker_open: bool`, `tab: EditorTab`, `font_dialog_open: bool`, `font_dialog_state: FontDialogState`, `selected_object: Option<usize>`, `object_glyph_picker_open: bool`, `object_editing_glyph: Glyph`, `placing_object: bool`; selecting a new archetype resets `glyph` to that archetype's default
- `show_editor_panel(ctx, editor, board, active_font)` — resizable right-side panel (default 200 px); Palette tab shows archetype list and glyph preview button; Board tab shows current font path and "Font…" button; Objects tab lists all board objects with click-to-select, glyph preview, **Passable/Opaque checkboxes**, and script combobox; World tab is a placeholder

**`src/glyph_picker.rs`** — floating glyph picker dialog:
- `show(ctx, open, glyph, board_cells, font)` — takes `open: &mut bool` and `glyph: &mut Glyph` directly; no dependency on `EditorState`
- Three sections: board palette (unique glyphs deduped via `HashSet<Glyph>`, click to select), FG/BG color pickers, scrollable tile grid (all tiles in the active font at `tile_w × tile_h` per cell)

### Map file format (`maps/*.toml`)

XPM-inspired: a `[palette]` maps single characters to `(Glyph, Archetype)` definitions; `[grid] content` is a TOML multi-line string where each character indexes the palette.

**Keep this example in sync with `map_file.rs` whenever the format changes.**

```toml
[map]
name = "Room Name"
width = 60
height = 25
player_start = [30, 12]

# Optional: override the default font for this board.
[font]
path = "assets/my_font.png"
tile_w = 8
tile_h = 16

[palette]
" " = { archetype = "empty", tile = " ", fg = "#000000", bg = "#000000" }
"#" = { archetype = "wall",  tile = 35,  fg = "#808080", bg = "#606060" }

[grid]
content = """
############################################################
#                                                          #
############################################################
"""

[[objects]]          # optional; parsed but not yet runtime-wired
x = 10
y = 5
script = """
  on_touch(|| { send_message("open"); });
"""

[[portals]]          # optional; parsed but not yet runtime-wired
x = 59
y = 12
target_map = "cave"
target_entry = "west_door"
```

Colors are `"#RRGGBB"` hex strings. `player_start` is a header field — the player is not a board cell. The `tile` field accepts either a single-character string (`tile = " "`) or an integer (`tile = 35`); both are valid and existing char-style map files continue to work. The grid multi-line string's leading newline is trimmed by TOML; trailing newline is handled correctly by `str::lines()`. Unknown archetype names produce an `ErrorBlock` cell and a logged warning.

### Key design decisions

- **`Behavior` and `Archetype` are separate types** — `Archetype` is the named class of a thing (`Wall`, `Empty`, `Object`); `Behavior` is its runtime properties (`passable`, `opaque`). Adding a new property means adding a field to `Behavior`, not a match arm at every call site.
- **`cells: Vec<(Glyph, Archetype)>`** — each cell owns its visual and behavioral class directly; there is no per-board element palette or integer indirection. `Archetype` is `Copy` so this is efficient.
- **Archetypes are referenced by name in map files** — so `ALL_ARCHETYPES` can be reordered or extended without breaking saved games.
- **`Board` is the complete unit** — grid, player, objects, and portals all live on `Board`, matching how ZZT treats a "board". No separate wrapper struct.
- **Glyph (visual) and Archetype (behavior) are decoupled** — each cell has its own `Glyph` (so colors can vary per-cell, e.g. fire flickering) while sharing an `Archetype` with other cells of the same type.
- **File loading happens in `main()`** before the window is created, so board dimensions are available for window sizing.

eframe runs on its own event loop thread; do not assume single-threaded execution.