reverse-engineering-anything/src/domain/javascript/javascriptSemanticMutationValues.ts

import type {
  JavaScriptSemanticProperty,
  JavaScriptSemanticValue,
} from "./javascriptSemanticValueTypes.js";
import {
  semanticPropertyPathKeyMatches,
  type JavaScriptSemanticPropertyPath,
} from "./javascriptSemanticPropertyPaths.js";

/** Invalidate escaped object references without rewriting their containing slots. */
export const invalidateSemanticEscapedPath = (
  value: JavaScriptSemanticValue,
  path: JavaScriptSemanticPropertyPath,
): JavaScriptSemanticValue => {
  if (value.status !== "object" && value.status !== "array") return value;
  const [key, ...remaining] = path;
  if (key === undefined)
    return {
      status: "unknown",
      reason: "This object reference may have been mutated by a call.",
    };
  const invalidateChild = (
    property: JavaScriptSemanticProperty,
  ): JavaScriptSemanticProperty =>
    semanticPropertyPathKeyMatches(key, property.name)
      ? {
          ...property,
          value: invalidateSemanticEscapedPath(property.value, remaining),
        }
      : property;
  return value.status === "object"
    ? { ...value, properties: value.properties.map(invalidateChild) }
    : { ...value, items: value.items.map(invalidateChild) };
};

/**
 * Invalidate only slots that explicit mutations can affect, as if applying each
 * path in order. Paths are grouped per slot so that many writes to one object
 * cost one pass over its slots rather than one pass per write.
 */
export const invalidateSemanticMutationPaths = (
  value: JavaScriptSemanticValue,
  paths: readonly JavaScriptSemanticPropertyPath[],
): JavaScriptSemanticValue => {
  if (paths.length === 0) return value;
  // An unknown key or a replaced value leaves nothing that a later path can
  // restore, wherever it occurs in the sequence.
  if (
    (value.status !== "object" && value.status !== "array") ||
    paths.some(([key]) => key === undefined || key === null)
  )
    return {
      status: "unknown",
      reason: "This property may have been mutated.",
    };
  // Writing an array length discards every item known before it.
  const reset =
    value.status === "array"
      ? paths.findLastIndex(([key]) => key === "length")
      : -1;
  const base: typeof value =
    reset < 0
      ? value
      : { status: "array", items: [], unknownItems: true, omittedItems: null };
  const slots = base.status === "object" ? base.properties : base.items;
  const slotsByName = new Map<string, number[]>();
  slots.forEach((property, index) => {
    const indexes = slotsByName.get(property.name) ?? [];
    indexes.push(index);
    slotsByName.set(property.name, indexes);
  });
  const slotPaths = new Map<number, JavaScriptSemanticPropertyPath[]>();
  const replacedSlots = new Set<number>();
  const select = (index: number, remaining: JavaScriptSemanticPropertyPath) => {
    const selected = slotPaths.get(index) ?? [];
    selected.push(remaining);
    slotPaths.set(index, selected);
    if (remaining.length === 0) replacedSlots.add(index);
  };
  // An added slot is already unknown, so later paths that select it are inert.
  const added = new Set<string>();
  for (const [key, ...remaining] of paths.slice(reset + 1)) {
    if (key === undefined || key === null) continue;
    if (typeof key === "object") {
      slots.forEach((property, index) => {
        if (semanticPropertyPathKeyMatches(key, property.name))
          select(index, remaining);
      });
      continue;
    }
    const indexes = slotsByName.get(String(key));
    if (indexes === undefined) added.add(String(key));
    else for (const index of indexes) select(index, remaining);
  }
  const properties: JavaScriptSemanticProperty[] = slots.map(
    (property, index) => {
      const selected = slotPaths.get(index);
      return selected === undefined
        ? property
        : {
            ...property,
            ...(replacedSlots.has(index)
              ? { presence: "unknown-coverage" as const }
              : {}),
            value: invalidateSemanticMutationPaths(property.value, selected),
          };
    },
  );
  for (const name of added)
    properties.push({
      name,
      value: {
        status: "unknown",
        reason: "This property may have been mutated.",
      },
      presence: "unknown-coverage",
    });
  return base.status === "object"
    ? { ...base, properties }
    : { ...base, items: properties };
};