feuerwerk/src/core/graph/stateMachine.ts

import { textOf } from '../model/Properties';
import { flatDef } from '../properties/PropertySchema';
import { edgesInto, type Graph, type GraphNode } from './Graph';
import type { MachineState, MachineTransition, StateMachine } from './lookup';
import type { NodeDef, PortDef, PortSource } from './NodeRegistry';

export const STATE = 'State';
export const STATE_MACHINE = 'StateMachine';
export const STATE_TRANSITION = 'StateTransition';
export const STATE_NAME_PARAM = 'name';
/** The input naming the machine on `State branch` and `Set state`. */
export const MACHINE_PORT = 'machine';
/** The setting naming the transition on `State transition`. */
export const TRANSITION_PARAM = 'transition';
/** The two ports a transition hangs on. A port is the only anchor an edge has – without one it
 *  cannot be drawn, selected or undone – so a state carries these, and the editor never draws
 *  them: a transition joins whole states, not sockets. */
export const STATE_IN = 'in';
export const STATE_OUT = 'out';

/**
 * One state of a state machine: a node whose name is its title. Its graph is the machine asset's,
 * never a behavior's – the palette leaves the `state` category out.
 */
export const State: NodeDef = {
  type: STATE,
  label: 'State',
  category: 'state',
  description: 'One state of a state machine.',
  inputs: [{ key: STATE_IN, label: '', type: 'exec' }],
  outputs: [{ key: STATE_OUT, label: '', type: 'exec' }],
  params: [flatDef(STATE_NAME_PARAM, 'text', { label: 'Name', value: 'State' })],
  transitionEdges: true,
  derivePorts: ({ node }) => ({ label: stateName(node) }),
};

export function isStateNode(node: GraphNode): boolean {
  return node.type === STATE;
}

export function stateName(node: GraphNode): string {
  return textOf(node.params[STATE_NAME_PARAM] ?? '') || State.label;
}

/** The states of a machine's graph in node order – what its ports and the runtime name. */
export function statesOf(graph: Graph): MachineState[] {
  return graph.nodes.filter(isStateNode).map((node) => ({ id: node.id, name: stateName(node) }));
}

/** The transitions of a machine's graph: every edge between two states, in edge order. */
export function transitionsOf(graph: Graph): MachineTransition[] {
  const states = new Set(graph.nodes.filter(isStateNode).map((n) => n.id));
  return graph.edges
    .filter((e) => states.has(e.from.node) && states.has(e.to.node))
    .map((e) => ({ from: e.from.node, to: e.to.node, name: e.label ?? '' }));
}

/**
 * Where `State transition` moves from `current`: along the transition of that name leaving it. The
 * name is matched against the current state alone, so one node asking for "alarm" moves every state
 * that has an "alarm". Nothing happens when the state has no such transition, or two of the name –
 * with nothing drawn to pick between them, choosing either would be a guess the graph never made.
 */
export function transitionTo(machine: StateMachine, current: string, name: string): string {
  const out = machine.transitions.filter((t) => t.from === current && t.name === name);
  const targets = [...new Set(out.map((t) => t.to))];
  return targets.length === 1 ? targets[0]! : '';
}

/** The names a machine's transitions carry, deduped and in edge order – what a node may ask for. */
export function transitionNames(machine: StateMachine | null): string[] {
  return [...new Set((machine?.transitions ?? []).map((t) => t.name).filter((name) => name))];
}

/** What a state placed from the palette is called: "State 3" for the third. */
export function nextStateName(graph: Graph): string {
  return `${State.label} ${statesOf(graph).length + 1}`;
}

/** The `machine` input; unconnected, it shows the machine picker. */
export const machinePort = (): PortDef => ({
  key: MACHINE_PORT,
  label: 'machine',
  type: 'string',
  field: flatDef(MACHINE_PORT, 'statemachine', { label: 'Machine' }),
});

/**
 * The machine a node's `machine` input names while the graph is drawn: the inline pick, or the
 * `State machine` literal an edge brings in. A port is derived from the graph, not from a running
 * value, so a variable or a list item feeding the input yields no state ports.
 */
export function machineOf({ node, graph, lookup }: PortSource): StateMachine | null {
  const edge = edgesInto(graph, node.id, MACHINE_PORT)[0];
  const source = edge && graph.nodes.find((n) => n.id === edge.from.node);
  const id = edge
    ? source?.type === STATE_MACHINE
      ? textOf(source.params.value ?? '')
      : ''
    : textOf(node.params[MACHINE_PORT] ?? '');
  return id ? lookup.machine(id) : null;
}

/** One exec port per state, keyed by the state's id – a rename keeps every edge. */
export function statePorts(machine: StateMachine | null): PortDef[] {
  return (machine?.states ?? []).map((state) => ({ key: state.id, label: state.name, type: 'exec' }));
}