529 lines
21 KiB
Rust
529 lines
21 KiB
Rust
//! Rhai scripting runtime for board objects.
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//!
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//! [`ScriptHost`] owns the Rhai [`Engine`], the compiled scripts referenced by a
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//! board's objects, and a persistent per-object [`Scope`]. It drives the optional
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//! lifecycle hooks on each scripted object:
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//!
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//! - `init()` — run once after the whole map is loaded (see [`ScriptHost::run_init`]).
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//! - `tick(dt)` — run every frame with the elapsed seconds (see [`ScriptHost::run_tick`]).
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//! - `bump(id)` — run when another mover steps into this object's cell, with the
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//! bumper's object index (`-1` for the player); see [`ScriptHost::run_bump`].
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//!
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//! ## Actions, queues, and rate limiting
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//!
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//! Scripts don't mutate the world directly. Each write host function (`move`,
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//! `set_tile`, `log`) appends an [`Action`] to the issuing object's **output
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//! queue** (a per-object FIFO). Actions leave that queue one batch at a time via
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//! [`ScriptHost::pump`], which promotes them onto the shared **board queue**:
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//!
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//! - A [`pump`](ScriptHost::pump) pulls the leading run of zero-cost actions plus at
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//! most one action with a time cost (currently only [`Action::Move`], 250 ms).
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//! - Pulling a timed action arms the object's **ready timer**; while it is running no
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//! further actions are pulled (this is what caps an object's speed). [`tick`] ticks
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//! the timer down via [`advance_timers`](ScriptHost::advance_timers).
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//!
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//! [`crate::game::GameState`] drains the board queue ([`take_board_queue`]) and applies
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//! each action *after* the script batch, preserving the borrow discipline (scripts only
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//! ever read the board during execution). Which object issued an action is read from the
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//! per-call **tag** (set to the object index in [`ScriptHost::run`]).
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//!
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//! [`tick`]: ScriptHost::run_tick
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//! [`take_board_queue`]: ScriptHost::take_board_queue
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//! [`GameState`]: crate::game::GameState
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use crate::game::Board;
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use crate::log::LogLine;
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use rhai::{AST, CallFnOptions, Engine, FuncArgs, ImmutableString, NativeCallContext, Scope};
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use std::cell::RefCell;
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use std::collections::{HashMap, HashSet, VecDeque};
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use std::rc::Rc;
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/// How long a move occupies an object before it can act again, in seconds.
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pub const MOVE_COST: f64 = 0.25;
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/// One deferred mutation emitted by a script, applied by [`crate::game::GameState`]
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/// after it is promoted onto the board queue.
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pub enum Action {
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/// Move the source object one cell in a direction (subject to passability).
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Move(Direction),
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/// Set the source object's glyph tile index.
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SetTile(u32),
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/// Append a plain (uncolored) line to the game log.
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Log(LogLine),
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}
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impl Action {
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/// How long performing this action keeps the object busy, in seconds.
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///
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/// Only [`Action::Move`] has a cost ([`MOVE_COST`]); zero-cost actions can be
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/// drained several-per-pump and never arm the ready timer.
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pub fn time_cost(&self) -> f64 {
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match self {
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Action::Move(_) => MOVE_COST,
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Action::SetTile(_) | Action::Log(_) => 0.0,
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}
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}
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}
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/// An action promoted from an object's output queue onto the board queue, tagged
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/// with the object that issued it.
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pub struct BoardAction {
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/// The object that issued the action.
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// TODO: `source` is an index into `Board::objects`, which is a stopgap — it
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// breaks under object spawn/destroy/reorder. Replace with a monotonically
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// increasing unique object id, with objects stored keyed by it (e.g.
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// `BTreeMap<ObjectId, ObjectDef>`). Mirrored on `ObjectRuntime::object_index`.
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pub source: usize,
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/// The action to apply.
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pub action: Action,
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}
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/// A cardinal movement direction.
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#[derive(Clone, Copy)]
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pub enum Direction {
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North,
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South,
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East,
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West,
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}
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impl From<Direction> for (i32, i32) {
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/// The `(dx, dy)` cell delta for a direction (screen coordinates: +y down).
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fn from(d: Direction) -> Self {
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match d {
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Direction::North => (0, -1),
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Direction::South => (0, 1),
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Direction::East => (1, 0),
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Direction::West => (-1, 0),
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}
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}
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}
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/// A read-only handle to the world, exposed to scripts as `Board`. Holds a shared
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/// reference to the [`Board`]; only getters are registered, so it is
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/// read-only by construction.
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type BoardRef = Rc<RefCell<Board>>;
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/// A single object's output queue, shared between the host (which pumps it between
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/// script calls) and the script (which reads/mutates it through the `Queue` object).
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type ObjQueue = Rc<RefCell<VecDeque<Action>>>;
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/// The board queue: actions promoted from object queues, awaiting resolution. Shared
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/// so the `blocked` host function can scan pending moves during script execution.
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type BoardQueue = Rc<RefCell<Vec<BoardAction>>>;
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/// Maps an object index to its output queue, so the global write host functions can
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/// route an emitted action to the right object via the per-call tag.
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type QueueMap = Rc<RefCell<HashMap<usize, ObjQueue>>>;
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/// Channel for engine/compile/runtime errors, surfaced straight to the game log
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/// (errors never go through the action queues).
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type ErrorSink = Rc<RefCell<Vec<LogLine>>>;
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/// A compiled script plus which lifecycle hooks it defines.
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struct CompiledScript {
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/// The compiled Rhai AST (function definitions plus any top-level code).
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ast: AST,
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/// Whether the script defines `fn init()` (zero parameters).
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has_init: bool,
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/// Whether the script defines `fn tick(dt)` (one parameter).
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has_tick: bool,
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/// Whether the script defines `fn bump(id)` (one parameter).
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has_bump: bool,
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}
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/// The runtime state of one scripted object: which script it runs, its persistent
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/// Rhai scope, its pending actions, and its cooldown timer.
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struct ObjectRuntime {
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/// Index into [`crate::game::Board::objects`]; passed to scripts as the
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/// per-call tag so host functions know which object issued an action.
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// TODO: see [`BoardAction::source`] — array indices should become stable ids.
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object_index: usize,
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/// Key into [`ScriptHost::scripts`] naming this object's compiled script.
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script_name: String,
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/// Per-object scope (holds the `Board`/`Queue` views + direction constants, and
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/// can hold object-local state in the future). Persists across calls.
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scope: Scope<'static>,
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/// This object's output queue (shared with its scope's `Queue` object).
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output_queue: ObjQueue,
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/// Seconds remaining before this object may pull another action. While `> 0`
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/// nothing is pulled from [`output_queue`](Self::output_queue).
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ready_timer: f64,
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}
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/// Owns the Rhai engine and per-object script state for a board.
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pub struct ScriptHost {
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/// The Rhai engine, with the read getters and write host functions registered.
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engine: Engine,
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/// Compiled scripts, keyed by script name; compiled once per referenced name.
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scripts: HashMap<String, CompiledScript>,
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/// One entry per object that has a successfully compiled script.
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objects: Vec<ObjectRuntime>,
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/// Actions promoted from object queues, drained by [`Self::take_board_queue`].
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board_queue: BoardQueue,
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/// Errors collected during compile/run, drained by [`Self::take_errors`].
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errors: ErrorSink,
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}
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impl ScriptHost {
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/// Builds a host for the board behind `board_cell`: registers the read/write API,
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/// compiles every script referenced by an object (once each), and creates a fresh
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/// scope and output queue per scripted object. Compile errors and references to
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/// unknown scripts are queued onto the error sink (retrievable via
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/// [`Self::take_errors`]); no script is run here.
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pub fn new(board_cell: &BoardRef) -> Self {
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let board_queue: BoardQueue = Rc::new(RefCell::new(Vec::new()));
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let queues: QueueMap = Rc::new(RefCell::new(HashMap::new()));
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let errors: ErrorSink = Rc::new(RefCell::new(Vec::new()));
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let mut engine = Engine::new();
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register_read_api(&mut engine, board_cell, &board_queue);
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register_write_api(&mut engine, &queues);
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register_queue_api(&mut engine);
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let board = board_cell.borrow();
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// Compile each referenced script once; attribute failures to the first
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// object that references the script.
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let mut scripts: HashMap<String, CompiledScript> = HashMap::new();
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let mut failed: HashSet<String> = HashSet::new();
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for obj in board.objects.iter() {
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let Some(name) = obj.script_name.as_ref() else {
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continue;
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};
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if scripts.contains_key(name) || failed.contains(name) {
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continue;
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}
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match board.scripts.get(name) {
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Some(src) => match engine.compile(src) {
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Ok(ast) => {
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// Detect the optional hooks by name and arity.
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let defines = |n: &str, params: usize| {
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ast.iter_functions()
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.any(|f| f.name == n && f.params.len() == params)
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};
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let compiled = CompiledScript {
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has_init: defines("init", 0),
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has_tick: defines("tick", 1),
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has_bump: defines("bump", 1),
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ast,
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};
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scripts.insert(name.clone(), compiled);
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}
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Err(err) => {
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failed.insert(name.clone());
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errors.borrow_mut().push(LogLine::raw(format!(
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"script '{name}' failed to compile: {err}"
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)));
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}
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},
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None => {
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failed.insert(name.clone());
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errors.borrow_mut().push(LogLine::raw(format!(
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"object references unknown script '{name}'"
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)));
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}
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}
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}
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// One runtime (independent scope + output queue) per object whose script
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// compiled. The queue is registered in `queues` so host functions can find
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// it by the object's index, and shared into the scope as the `Queue` object.
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let mut objects = Vec::new();
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for (i, obj) in board.objects.iter().enumerate() {
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let Some(name) = obj.script_name.as_ref() else {
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continue;
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};
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if !scripts.contains_key(name) {
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continue;
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}
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let queue: ObjQueue = Rc::new(RefCell::new(VecDeque::new()));
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queues.borrow_mut().insert(i, queue.clone());
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objects.push(ObjectRuntime {
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object_index: i,
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script_name: name.clone(),
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scope: new_object_scope(board_cell, &queue),
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output_queue: queue,
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ready_timer: 0.0,
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});
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}
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drop(board);
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Self {
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engine,
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scripts,
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objects,
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board_queue,
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errors,
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}
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}
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/// Calls `init()` on every scripted object that defines it, pumping each object's
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/// queue afterward.
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pub fn run_init(&mut self) {
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self.run("init", |c| c.has_init, ());
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}
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/// Calls `tick(dt)` on every scripted object that defines it, passing the elapsed
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/// seconds, then pumps each object's queue.
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pub fn run_tick(&mut self, dt: f64) {
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self.run("tick", |c| c.has_tick, (dt,));
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}
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/// Calls `bump(id)` on the object at `object_index`, if it defines the hook.
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///
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/// `bumper` is the index of the object that moved into it, or `-1` for the player.
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/// Does **not** pump: any actions the hook emits wait for the next tick's pump, so
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/// a bump can't cascade within the same resolution pass.
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pub fn run_bump(&mut self, object_index: usize, bumper: i64) {
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let Self {
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engine,
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scripts,
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objects,
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errors,
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..
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} = self;
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let Some(obj) = objects.iter_mut().find(|o| o.object_index == object_index) else {
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return;
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};
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let Some(compiled) = scripts.get(&obj.script_name) else {
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return;
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};
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if !compiled.has_bump {
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return;
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}
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let options = CallFnOptions::default().with_tag(object_index as i64);
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if let Err(err) = engine.call_fn_with_options::<()>(
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options,
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&mut obj.scope,
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&compiled.ast,
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"bump",
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(bumper,),
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) {
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errors.borrow_mut().push(LogLine::raw(format!(
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"script '{}' bump error: {err}",
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obj.script_name
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)));
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}
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}
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/// Counts every object's ready timer down by `dt` (floored at zero). Call once per
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/// frame before [`run_tick`](Self::run_tick).
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pub fn advance_timers(&mut self, dt: f64) {
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for obj in &mut self.objects {
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obj.ready_timer = (obj.ready_timer - dt).max(0.0);
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}
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}
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/// Removes and returns the actions promoted onto the board queue.
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pub fn take_board_queue(&mut self) -> Vec<BoardAction> {
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std::mem::take(&mut self.board_queue.borrow_mut())
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}
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/// Removes and returns the errors collected since the last drain.
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pub fn take_errors(&mut self) -> Vec<LogLine> {
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std::mem::take(&mut self.errors.borrow_mut())
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}
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/// Promotes ready actions from object `i`'s output queue onto the board queue.
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///
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/// While the object's ready timer is running, nothing is pulled. Otherwise the
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/// leading run of zero-cost actions is promoted, followed by at most one timed
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/// action (which arms the timer and ends the pump). The board-queue guard keeps a
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/// second pump in the same tick from double-promoting.
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fn pump(&mut self, i: usize) {
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let oid = self.objects[i].object_index;
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// Don't re-promote if this object already has actions awaiting resolution.
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if self.board_queue.borrow().iter().any(|ba| ba.source == oid) {
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return;
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}
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loop {
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// A running cooldown blocks all further pulls (timed or not).
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if self.objects[i].ready_timer > 0.0 {
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break;
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}
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let queue = self.objects[i].output_queue.clone();
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let cost = match queue.borrow().front() {
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Some(action) => action.time_cost(),
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None => break, // queue drained
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};
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let action = queue.borrow_mut().pop_front().expect("front checked above");
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if cost > 0.0 {
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self.objects[i].ready_timer = cost;
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}
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self.board_queue.borrow_mut().push(BoardAction {
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source: oid,
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action,
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});
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// A timed action ends the pump; zero-cost ones keep draining.
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if cost > 0.0 {
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break;
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}
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}
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}
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/// Shared driver for `init`/`tick`: for each object, call the hook if its script
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/// `defined` it (tagging the call with the object index so host functions know the
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/// source), then pump that object so backlogged actions drain and later objects'
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/// `blocked` checks can see earlier movers. Runtime errors are captured rather than
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/// aborting the batch.
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fn run<A: FuncArgs + Copy>(
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&mut self,
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hook: &str,
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defined: fn(&CompiledScript) -> bool,
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args: A,
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) {
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for i in 0..self.objects.len() {
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// Scope the split borrow so it ends before the `pump` reborrow below.
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{
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let Self {
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engine,
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scripts,
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objects,
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errors,
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..
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} = self;
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let obj = &mut objects[i];
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if let Some(compiled) = scripts.get(&obj.script_name)
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&& defined(compiled)
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{
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// The tag carries this object's index to the host functions.
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let options = CallFnOptions::default().with_tag(obj.object_index as i64);
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if let Err(err) = engine.call_fn_with_options::<()>(
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options,
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&mut obj.scope,
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&compiled.ast,
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hook,
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args,
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) {
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errors.borrow_mut().push(LogLine::raw(format!(
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"script '{}' {hook} error: {err}",
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obj.script_name
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)));
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}
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}
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}
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self.pump(i);
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}
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}
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}
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/// Registers the read-only `Board` API (getters plus the `blocked` query).
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///
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/// The getters operate on the `Board` value in scope; `blocked` instead captures a
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/// clone of the world and the board queue, so it can resolve the caller's position and
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/// scan pending moves.
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fn register_read_api(engine: &mut Engine, board: &BoardRef, board_queue: &BoardQueue) {
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engine.register_type_with_name::<BoardRef>("Board");
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engine.register_get("player_x", |b: &mut BoardRef| b.borrow().player.x as i64);
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engine.register_get("player_y", |b: &mut BoardRef| b.borrow().player.y as i64);
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engine.register_get("width", |b: &mut BoardRef| b.borrow().width as i64);
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engine.register_get("height", |b: &mut BoardRef| b.borrow().height as i64);
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let b = board.clone();
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let bq = board_queue.clone();
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engine.register_fn("blocked", move |ctx: NativeCallContext, dir: Direction| {
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is_blocked(&b, &bq, source_of(&ctx), dir)
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});
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}
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/// Whether the object at `source` would bump something by moving in `dir`.
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///
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/// Returns `true` if the target cell is off the board, already holds a solid, or is
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/// the destination of any pending move on the board queue. The caller's own move is
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/// never on the queue yet (its pump runs after its script), so it can't block itself.
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///
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/// Pending moves are matched by their *immediate* target cell only; a queued move that
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/// would push a chain of solids into the cell is not accounted for (an approximation).
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fn is_blocked(board: &BoardRef, board_queue: &BoardQueue, source: usize, dir: Direction) -> bool {
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let board = board.borrow();
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let Some(obj) = board.objects.get(source) else {
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return true;
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};
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let (dx, dy): (i32, i32) = dir.into();
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let target = (obj.x as i32 + dx, obj.y as i32 + dy);
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if !board.in_bounds(target) {
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return true;
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}
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let (tx, ty) = (target.0 as usize, target.1 as usize);
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if board.solid_at(tx, ty).is_some() {
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return true;
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}
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// Any pending move whose immediate target is this cell would put a solid here.
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board_queue.borrow().iter().any(|ba| {
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if let Action::Move(d) = &ba.action
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&& let Some(mover) = board.objects.get(ba.source)
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{
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let (mdx, mdy): (i32, i32) = (*d).into();
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return (mover.x as i32 + mdx, mover.y as i32 + mdy) == target;
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}
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false
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})
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}
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/// Registers the write API: the `Direction` type and the `move`/`set_tile`/`log` host
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/// functions, each appending an [`Action`] to the issuing object's output queue.
|
|
fn register_write_api(engine: &mut Engine, queues: &QueueMap) {
|
|
engine.register_type_with_name::<Direction>("Direction");
|
|
|
|
let q = queues.clone();
|
|
engine.register_fn("move", move |ctx: NativeCallContext, dir: Direction| {
|
|
emit(&q, source_of(&ctx), Action::Move(dir));
|
|
});
|
|
|
|
let q = queues.clone();
|
|
engine.register_fn("set_tile", move |ctx: NativeCallContext, tile: i64| {
|
|
emit(&q, source_of(&ctx), Action::SetTile(tile as u32));
|
|
});
|
|
|
|
let q = queues.clone();
|
|
engine.register_fn(
|
|
"log",
|
|
move |ctx: NativeCallContext, msg: ImmutableString| {
|
|
emit(
|
|
&q,
|
|
source_of(&ctx),
|
|
Action::Log(LogLine::raw(msg.to_string())),
|
|
);
|
|
},
|
|
);
|
|
}
|
|
|
|
/// Registers the `Queue` object: a handle to an object's output queue with `length()`
|
|
/// and `clear()`. Safe to mutate from a script because the host only touches these
|
|
/// queues between script calls (during [`ScriptHost::pump`]).
|
|
fn register_queue_api(engine: &mut Engine) {
|
|
engine.register_type_with_name::<ObjQueue>("Queue");
|
|
engine.register_fn("length", |q: &mut ObjQueue| q.borrow().len() as i64);
|
|
engine.register_fn("clear", |q: &mut ObjQueue| q.borrow_mut().clear());
|
|
}
|
|
|
|
/// Appends `action` to the output queue of the object identified by `source`.
|
|
fn emit(queues: &QueueMap, source: usize, action: Action) {
|
|
if let Some(queue) = queues.borrow().get(&source) {
|
|
queue.borrow_mut().push_back(action);
|
|
}
|
|
}
|
|
|
|
/// Reads the issuing object's index from the call tag (set in [`ScriptHost::run`]).
|
|
fn source_of(ctx: &NativeCallContext) -> usize {
|
|
ctx.tag()
|
|
.and_then(|t| t.as_int().ok())
|
|
.and_then(|n| usize::try_from(n).ok())
|
|
.unwrap_or(0)
|
|
}
|
|
|
|
/// Builds a fresh per-object scope, seeded with the read-only `Board` view, this
|
|
/// object's `Queue`, and the four direction constants (`North`/`South`/`East`/`West`).
|
|
fn new_object_scope(board: &BoardRef, queue: &ObjQueue) -> Scope<'static> {
|
|
let mut scope = Scope::new();
|
|
scope.push_constant("Board", board.clone());
|
|
scope.push_constant("Queue", queue.clone());
|
|
scope.push_constant("North", Direction::North);
|
|
scope.push_constant("South", Direction::South);
|
|
scope.push_constant("East", Direction::East);
|
|
scope.push_constant("West", Direction::West);
|
|
scope
|
|
}
|