rea/src/domain/javascript/javascriptSemanticAliasSelections.ts

import type { JavaScriptSemanticPropertyPath } from "./javascriptSemanticPropertyPaths.js";
import { SEMANTIC_ALIAS_SELECTION_LIMIT } from "./javascriptSemanticResourceLimits.js";

type PropertyKey = JavaScriptSemanticPropertyPath[number];

/** Finite alternatives retain selected keys without admitting unrelated slots. */
export type SemanticAliasSelection =
  | PropertyKey
  | { readonly alternatives: readonly PropertyKey[] };

export type SemanticAliasSelectionPath = readonly SemanticAliasSelection[];

export const semanticAliasSelectionChoices = (
  key: SemanticAliasSelection,
): readonly PropertyKey[] =>
  key !== null && typeof key === "object" && "alternatives" in key
    ? key.alternatives
    : [key];

const selection = (choices: readonly PropertyKey[]): SemanticAliasSelection => {
  if (choices.includes(null)) return null;
  const alternatives = [
    ...new Map(choices.map((choice) => [JSON.stringify(choice), choice])),
  ]
    .sort(([left], [right]) => (left < right ? -1 : left > right ? 1 : 0))
    .map(([, choice]) => choice);
  return alternatives.length === 1 ? alternatives[0]! : { alternatives };
};

const selectionCovers = (
  prior: SemanticAliasSelection,
  next: SemanticAliasSelection,
): boolean => {
  if (prior === null) return true;
  const choices = new Set(
    semanticAliasSelectionChoices(prior).map((key) => JSON.stringify(key)),
  );
  return semanticAliasSelectionChoices(next).every((key) =>
    choices.has(JSON.stringify(key)),
  );
};

const pathCovers = (
  prior: SemanticAliasSelectionPath,
  next: SemanticAliasSelectionPath,
): boolean =>
  prior.every(
    (key, index) =>
      next[index] !== undefined && selectionCovers(key, next[index]!),
  );

/** Only one differing selector can be joined without inventing crossed paths. */
const joinSelections = (
  prior: SemanticAliasSelectionPath,
  next: SemanticAliasSelectionPath,
): SemanticAliasSelectionPath | undefined => {
  let changed = -1;
  for (let index = 0; index < prior.length; index++) {
    if (JSON.stringify(prior[index]) === JSON.stringify(next[index])) continue;
    if (changed !== -1) return undefined;
    changed = index;
  }
  return prior.map((key, index) =>
    index === changed
      ? selection([
          ...semanticAliasSelectionChoices(key),
          ...semanticAliasSelectionChoices(next[index]!),
        ])
      : key,
  );
};

/** Preserve correlated selector alternatives while coalescing complete grids. */
export class SemanticAliasSelections {
  #paths = new WeakMap<object, Map<number, SemanticAliasSelectionPath[]>>();
  #calls = 0;
  #limited = false;

  constructor(readonly onLimit: () => void) {}

  get limited(): boolean {
    return this.#limited;
  }

  normalize(
    node: object,
    next: SemanticAliasSelectionPath,
  ): SemanticAliasSelectionPath {
    if (this.#limited) return next.map(() => null);
    const existing = this.#paths.get(node);
    const byDepth = existing ?? new Map<number, SemanticAliasSelectionPath[]>();
    const paths = [...(byDepth.get(next.length) ?? [])];
    let candidate = next.map((key) =>
      selection(semanticAliasSelectionChoices(key)),
    );
    const covered = paths.find((prior) => pathCovers(prior, candidate));
    if (covered !== undefined) return covered;
    if (
      existing !== undefined &&
      ++this.#calls > SEMANTIC_ALIAS_SELECTION_LIMIT
    ) {
      this.#limited = true;
      this.#paths = new WeakMap();
      this.onLimit();
      return next.map(() => null);
    }
    for (let index = 0; index < paths.length;) {
      const prior = paths[index]!;
      if (pathCovers(prior, candidate)) return prior;
      const joined = pathCovers(candidate, prior)
        ? candidate
        : joinSelections(prior, candidate);
      if (joined === undefined) {
        index++;
        continue;
      }
      candidate = [...joined];
      paths.splice(index, 1);
      index = 0;
    }
    paths.push(candidate);
    byDepth.set(candidate.length, paths);
    this.#paths.set(node, byDepth);
    return candidate;
  }
}