# Module 12 reference engine (Rust)

The course's own engine as of the end of Module 12: Module 11's engine (Part I's card engine, Part II's grid engine with conditions, and SpellGrid joining them), with combat and the end of a turn in Part I. Every test from Modules 1–11 still passes. Module 11's reference was the starting point, so a diff between the two shows what this module adds. `course/11-conditions/reference/rust/README.md` and the READMEs it points to describe everything else.

- `cards/` and `levels/` (at the crate root; not in this directory): staged by `tools/verify-references.mjs` as for Module 11, plus `course/12-combat/cards/` (`Test Bell`).
- Part I (`src/engine/`):
  - `combat.rs` (new): `attack_error(world, attacker, defender)`, the legality rules (a minion in play attacks an enemy character in play, with more than 0 Attack, and a Taunt minion if the defender's side has one), and `TAUNT`.
  - `card.rs`: `Card::keywords`, compiled from keyword clauses. `TriggerOn::EndOfTurn` now fires.
  - `event.rs`: `Event::TurnEnded { player }`, which end of turn triggers answer. The course's log doesn't show it.
  - `queue.rs`: `Action::Damage` carries `hits`, each a target, an amount and a `Priority` (`hits(targets, amount)` builds the usual one-amount list). `react` takes the priority of each event's entries and sorts its Queue by priority, highest first, keeping the order it was filled in within one priority. `Action::Attack` builds one Damage action: the attacker's Attack to the defender at priority `DEFENDER`, and the defender's Attack (if more than 0) to the attacker at `NORMAL`. `Action::EndTurn` records `TurnEnded` and resolves the triggers that answer it.
- `src/harness.rs`: `order_attack(attacker, defender) -> Result<(), String>`, `can_attack(attacker, defender) -> Option<String>` and `end_turn(player)` on `Game`.
- Part II, Part III, `src/cli.rs` and `src/bin/spellgrid.rs`: unchanged from Module 11. SpellGrid doesn't attack. `tools/diff-tracks.mjs` uses this module's CLIs by default.

Run it with the module's tests: `node tools/verify-references.mjs 12` from the course repository.