# Implementation Plan - Phase 1: Dungeon Generation

## Goal Description
Build a robust, data-driven procedural dungeon generator that supports campaign-specific requirements (custom exits vs. objective rooms). This logic will be decoupled from the 3D visualization to ensure testability.

## Architecture
The engine will consist of three main components:
1.  **Tile Registry**: Definitions of all available board sections (Rooms, Corridors, T-Junctions, Corners).
2.  **Dungeon Deck**: A deck manager that handles the probability of drawing specific room types.
3.  **Generator Core**: The state machine that places tiles on a virtual grid.

## User Review Required
> [!IMPORTANT]
> **Campaign Logic Deviation**: The rulebook specifies random dungeons. We are implementing a constrained "Mission" system where:
> *   Current functionality must support "Forced Exits" after X tiles for early campaign missions.
> *   Final missions revert to standard "Objective Room" search.

## Proposed Changes

### [NEW] `src/engine/dungeon/`
We will structure the engine purely in JS logic first.

#### [NEW] `TileDefinitions.js`
-   **Data Structure**:
    ```javascript
    {
        id: 'corridor_straight',
        type: 'corridor', // 'room', 'objective'
        width: 2,
        length: 5,
        exits: [ {x:0, y:0, dir:'N'}, ... ] // Local coords
    }
    ```

#### [NEW] `DungeonDeck.js`
-   Handles the stack of cards.
-   Methods: `draw()`, `shuffle()`, `insert(card, position)`.
-   **Campaign Injection**: Ability to inject specific "Events" or "Rooms" at certain deck depths (e.g., "After 10 cards, shuffle the Exit card into the top 3").

#### [NEW] `Generator.js`
-   **Grid System**: A virtual 2D array or Map `Map<"x,y", TileID>` to track occupancy.
-   **Algorithm**:
    1.  Place Entry Room at (0,0).
    2.  Add Entry Exits to `OpenExitsList`.
    3.  **Step**: 
        -   Pick an Exit from `OpenExitsList`.
        -   Draw Card from `DungeonDeck`.
        -   Attempt to place Tile at Exit.
        -   **IF Collision**: Discard and try alternative (or end path).
        -   **IF Success**: Register Tile, Remove used Exit, Add new Exits.

### Campaign Integration
-   **Mission Config Payload**:
    ```javascript
    {
        missionId: "campaign_1_mission_1",
        deckComposition: [ ... ],
        specialRules: {
            forceExitAfter: 10, // Logic: Treat specific room as 'Objective' for generation purposes
            exitType: "ladder_room"
        }
    }
    ```

## Verification Plan
### Automated Tests
-   **Unit Tests**: Verify `Generator` can place tiles without overlapping.
-   **Logic Tests**: Verify "Exit functionality" triggers correctly after N tiles.