import * as t from "@babel/types";

import {
  delayedInstanceFieldValue,
  semanticComputedMethodKey,
  semanticBranchMayBeSkipped,
  semanticIterationCardinality,
} from "./javascriptSemanticEvaluationOrder.js";

import {
  semanticStaticPropertyKey,
  unwrapJavaScriptExpression,
} from "./javascriptAstValues.js";
import type {
  JavaScriptSemanticBindingState,
  JavaScriptSemanticAnalysisState,
  JavaScriptSemanticEffectTiming,
} from "./javascriptSemanticState.js";

interface StatementPosition {
  readonly body: readonly t.Statement[];
  readonly index: number;
  readonly declaratorIndex: number;
}

interface BindingReadPosition {
  readonly position: StatementPosition | null;
  readonly repeating: boolean;
}

interface ExpressionSiblings {
  readonly common: t.Node;
  readonly earlier: t.Node;
  readonly later: t.Node;
}

interface ExpressionAncestry {
  readonly source: t.Node;
  readonly ancestors: ReadonlyMap<t.Node, t.Node | undefined>;
  readonly siblings: WeakMap<t.Node, ExpressionSiblings | null>;
}

/**
 * Initializer positions depend only on a node and its parent map, which one
 * analysis builds once and never changes. Different mutations and initializers
 * re-derive the same positions along shared ancestry, so retain the first
 * result for as long as its parent map is reachable.
 */
interface InitializerPositionCache {
  readonly direct: WeakMap<t.Node, StatementPosition | null>;
  readonly mutation: WeakMap<t.Node, StatementPosition | null>;
  readonly reference: WeakMap<t.Node, StatementPosition | null>;
  readonly read: WeakMap<t.Node, BindingReadPosition>;
  readonly evaluationChildren: WeakMap<
    t.Node,
    ReadonlyMap<t.Node, number> | null
  >;
  // One source context bounds retained ancestry facts to O(AST), even when
  // an expression contains many distinct writes. Reuse its descendant paths.
  expressionAncestry: ExpressionAncestry | undefined;
}

const initializerPositionCaches = new WeakMap<
  WeakMap<t.Node, t.Node>,
  InitializerPositionCache
>();

const initializerPositionCache = (
  parents: WeakMap<t.Node, t.Node>,
): InitializerPositionCache => {
  const cached = initializerPositionCaches.get(parents);
  if (cached !== undefined) return cached;
  const created: InitializerPositionCache = {
    direct: new WeakMap(),
    mutation: new WeakMap(),
    reference: new WeakMap(),
    read: new WeakMap(),
    evaluationChildren: new WeakMap(),
    expressionAncestry: undefined,
  };
  initializerPositionCaches.set(parents, created);
  return created;
};

const statementPosition = (
  statement: t.Statement,
  parents: WeakMap<t.Node, t.Node>,
  declarator?: t.VariableDeclarator,
): StatementPosition | null => {
  const directParent = parents.get(statement);
  const enclosing =
    (t.isExportNamedDeclaration(directParent) ||
      t.isExportDefaultDeclaration(directParent)) &&
    directParent.declaration === statement
      ? directParent
      : statement;
  const parent = parents.get(enclosing);
  if (!t.isProgram(parent) && !t.isBlockStatement(parent)) return null;
  const index = parent.body.indexOf(enclosing);
  return index < 0
    ? null
    : {
        body: parent.body,
        index,
        declaratorIndex:
          t.isVariableDeclaration(statement) && declarator !== undefined
            ? statement.declarations.indexOf(declarator)
            : -1,
      };
};

const positionPrecedes = (
  left: StatementPosition,
  right: StatementPosition,
): boolean =>
  left.body === right.body &&
  (left.index < right.index ||
    (left.index === right.index &&
      left.declaratorIndex >= 0 &&
      left.declaratorIndex < right.declaratorIndex));

/** Order effects only in a non-repeating top-level activation. */
export const semanticTopLevelEffectFollowsCapture = (
  capture: t.Node,
  effect: t.Node | undefined,
  parents: WeakMap<t.Node, t.Node>,
): boolean => {
  const position = (node: t.Node | undefined): StatementPosition | null => {
    let selected: StatementPosition | null = null;
    let declarator: t.VariableDeclarator | undefined;
    let child: t.Node | undefined;
    while (node !== undefined) {
      if (t.isFunction(node) || t.isLoop(node)) return null;
      if (delayedInstanceFieldValue(node, child)) return null;
      if (t.isVariableDeclarator(node)) declarator = node;
      if (t.isStatement(node)) {
        const enclosing = statementPosition(node, parents, declarator);
        if (enclosing !== null) selected = enclosing;
      }
      if (t.isProgram(node)) return selected;
      child = node;
      node = parents.get(node);
    }
    return null;
  };
  const before = position(capture);
  const after = position(effect);
  if (before === null || after === null) return false;
  if (positionPrecedes(before, after)) return true;
  if (
    before.body !== after.body ||
    before.index !== after.index ||
    before.declaratorIndex !== after.declaratorIndex
  )
    return false;
  return expressionEvaluationOrder(capture, effect, parents) === "before";
};

/** Include expression order when a write operation contains the read site. */
export const semanticEffectFollowsReference = (
  reference: t.Node,
  effect: t.Node | undefined,
  parents: WeakMap<t.Node, t.Node>,
): boolean => {
  if (reference === effect) return false;
  let current: t.Node | undefined = reference;
  let child: t.Node | undefined;
  while (current !== undefined && current !== effect) {
    if (t.isFunction(current)) break;
    child = current;
    current = parents.get(current);
  }
  const loopInput =
    (t.isForInStatement(effect) || t.isForOfStatement(effect)) &&
    child === effect.right;
  let once = current;
  child = undefined;
  while (once !== undefined) {
    const initialLoopInput =
      (t.isForStatement(once) && child === once.init) ||
      ((t.isForInStatement(once) || t.isForOfStatement(once)) &&
        child === once.right) ||
      (once === effect && loopInput);
    if (
      t.isFunction(once) ||
      (t.isLoop(once) && !initialLoopInput) ||
      delayedInstanceFieldValue(once, child)
    )
      break;
    child = once;
    once = parents.get(once);
  }
  return (
    (current === effect &&
      once === undefined &&
      (t.isAssignmentExpression(effect) ||
        t.isUpdateExpression(effect) ||
        t.isVariableDeclarator(effect) ||
        t.isCallExpression(effect) ||
        t.isOptionalCallExpression(effect) ||
        t.isNewExpression(effect))) ||
    (current === effect && once === undefined && loopInput) ||
    semanticTopLevelEffectFollowsCapture(reference, effect, parents)
  );
};

export const semanticEffectTiming = (
  site: t.Node,
  effect: t.Node | undefined,
  state: JavaScriptSemanticAnalysisState,
): JavaScriptSemanticEffectTiming => {
  if (effect === undefined) return "unknown";
  // Invocation receives arguments after their values have been selected.
  if (
    site === effect &&
    (t.isCallExpression(site) ||
      t.isOptionalCallExpression(site) ||
      t.isNewExpression(site))
  )
    return "after";
  const loop = semanticEnclosingIteration(effect, state);
  if (loop !== undefined) {
    const cardinality = semanticIterationCardinality(
      loop,
      state.prototypeEnumerationMayAffect,
    );
    if (cardinality === "empty") return "after";
    if (cardinality === "nonempty") {
      const loopParent = state.parentsByNode.get(loop);
      const crossesFunction = (node: t.Node): boolean => {
        let current: t.Node | undefined = node;
        while (current !== undefined) {
          if (t.isFunction(current)) return true;
          current = state.parentsByNode.get(current);
        }
        return false;
      };
      if (
        loopParent === state.program &&
        !crossesFunction(site) &&
        typeof loop.start === "number" &&
        typeof loop.end === "number" &&
        typeof site.start === "number"
      ) {
        if (site.start > loop.end) return "before";
        if (site.start < loop.start) return "after";
      }
    }
  }
  if (semanticEffectFollowsReference(site, effect, state.parentsByNode))
    return "after";
  if (semanticEffectFollowsReference(effect, site, state.parentsByNode))
    return "before";
  return "unknown";
};

const semanticEnclosingIteration = (
  node: t.Node,
  state: JavaScriptSemanticAnalysisState,
): t.ForInStatement | t.ForOfStatement | undefined => {
  let current: t.Node | undefined = node;
  while (current !== undefined) {
    if (t.isForInStatement(current) || t.isForOfStatement(current))
      return current;
    if (t.isFunction(current)) return undefined;
    current = state.parentsByNode.get(current);
  }
  return undefined;
};

/** Memoize descendant paths toward the currently compared source expression. */
const expressionSiblings = (
  earlier: t.Node,
  later: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): ExpressionSiblings | null => {
  const cache = initializerPositionCache(parents);
  let context = cache.expressionAncestry;
  if (context?.source !== earlier) {
    const ancestors = new Map<t.Node, t.Node | undefined>();
    let child: t.Node | undefined;
    for (
      let node: t.Node | undefined = earlier;
      node !== undefined;
      node = parents.get(node)
    ) {
      ancestors.set(node, child);
      child = node;
    }
    context = { source: earlier, ancestors, siblings: new WeakMap() };
    cache.expressionAncestry = context;
  }
  const path: t.Node[] = [];
  let result: ExpressionSiblings | null = null;
  for (
    let node: t.Node | undefined = later;
    node !== undefined;
    node = parents.get(node)
  ) {
    if (context.ancestors.has(node)) {
      const sourceChild = context.ancestors.get(node);
      const readChild = path.at(-1);
      if (sourceChild !== undefined && readChild !== undefined)
        result = { common: node, earlier: sourceChild, later: readChild };
      break;
    }
    const cached = context.siblings.get(node);
    if (cached !== undefined) {
      result = cached;
      break;
    }
    path.push(node);
  }
  for (const node of path) context.siblings.set(node, result);
  return result;
};

/** Index existing child arrays once; wide literals/calls need no repeated copies. */
const expressionChildIndices = (
  node: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): ReadonlyMap<t.Node, number> | null => {
  const cache = initializerPositionCache(parents).evaluationChildren;
  const cached = cache.get(node);
  if (cached !== undefined) return cached;
  const children = ((): readonly (t.Node | null)[] | null => {
    if (t.isSequenceExpression(node)) return node.expressions;
    if (t.isArrayExpression(node)) return node.elements;
    if (t.isObjectExpression(node)) return node.properties;
    if (t.isObjectProperty(node))
      return node.computed ? [node.key, node.value] : [node.value];
    if (
      t.isCallExpression(node) ||
      t.isOptionalCallExpression(node) ||
      t.isNewExpression(node)
    )
      return node.arguments;
    if (t.isBinaryExpression(node) || t.isLogicalExpression(node))
      return [node.left, node.right];
    if (t.isConditionalExpression(node)) return [node.test];
    return null;
  })();
  if (children === null) {
    cache.set(node, null);
    return null;
  }
  const indices = new Map<t.Node, number>();
  let index = 0;
  if (
    t.isCallExpression(node) ||
    t.isOptionalCallExpression(node) ||
    t.isNewExpression(node)
  )
    indices.set(node.callee, index++);
  for (const child of children) {
    if (child !== null) indices.set(child, index);
    index++;
  }
  cache.set(node, indices);
  return indices;
};

/** Unproved ordering stays distinct from proof that a write follows the read. */
const expressionEvaluationOrder = (
  earlier: t.Node,
  later: t.Node | undefined,
  parents: WeakMap<t.Node, t.Node>,
): "before" | "after" | "unresolved" => {
  if (later === undefined) return "unresolved";
  const siblings = expressionSiblings(earlier, later, parents);
  if (siblings === null) return "unresolved";
  const children = expressionChildIndices(siblings.common, parents);
  const earlierIndex = children?.get(siblings.earlier);
  const laterIndex = children?.get(siblings.later);
  if (
    earlierIndex === undefined ||
    laterIndex === undefined ||
    earlierIndex === laterIndex
  )
    return "unresolved";
  return earlierIndex < laterIndex ? "before" : "after";
};

const computeDirectInitializerPosition = (
  node: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): StatementPosition | null => {
  if (t.isClassDeclaration(node) && node.id !== null)
    return statementPosition(node, parents);
  if (
    (t.isAssignmentExpression(node) &&
      t.isIdentifier(unwrapJavaScriptExpression(node.left).node)) ||
    t.isUpdateExpression(node)
  )
    return directMutationPosition(node, parents);
  const parent = parents.get(node);
  if (t.isVariableDeclarator(parent) && parent.init === node) {
    const declaration = parents.get(parent);
    return t.isVariableDeclaration(declaration)
      ? statementPosition(declaration, parents, parent)
      : null;
  }
  if (
    t.isAssignmentExpression(parent) &&
    parent.right === node &&
    t.isIdentifier(parent.left)
  ) {
    return directMutationPosition(parent, parents);
  }
  return null;
};

const directInitializerPosition = (
  node: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): StatementPosition | null => {
  const cache = initializerPositionCache(parents);
  const cached = cache.direct.get(node);
  if (cached !== undefined) return cached;
  const computed = computeDirectInitializerPosition(node, parents);
  cache.direct.set(node, computed);
  return computed;
};

const computeDirectMutationPosition = (
  node: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): StatementPosition | null => {
  if (t.isForOfStatement(node)) return statementPosition(node, parents);
  if (t.isVariableDeclarator(node)) {
    const declaration = parents.get(node);
    return t.isVariableDeclaration(declaration)
      ? statementPosition(declaration, parents, node)
      : null;
  }
  if (t.isSpreadElement(node)) {
    const array = parents.get(node);
    return t.isArrayExpression(array)
      ? semanticCapturePosition(array, parents)
      : null;
  }
  if (
    !t.isAssignmentExpression(node) &&
    !t.isUpdateExpression(node) &&
    !t.isUnaryExpression(node, { operator: "delete" }) &&
    !t.isCallExpression(node) &&
    !t.isOptionalCallExpression(node) &&
    !t.isNewExpression(node) &&
    !t.isTaggedTemplateExpression(node)
  )
    return null;
  let current: t.Node = node;
  while (true) {
    const parent = parents.get(current);
    if (
      parent === undefined ||
      t.isFunction(parent) ||
      semanticBranchMayBeSkipped(parent, current)
    )
      return null;
    if (t.isStatement(parent)) return statementPosition(parent, parents);
    if (t.isVariableDeclarator(parent)) {
      const declaration = parents.get(parent);
      return t.isVariableDeclaration(declaration)
        ? statementPosition(declaration, parents, parent)
        : null;
    }
    current = parent;
  }
};

const directMutationPosition = (
  node: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): StatementPosition | null => {
  const cache = initializerPositionCache(parents);
  const cached = cache.mutation.get(node);
  if (cached !== undefined) return cached;
  const computed = computeDirectMutationPosition(node, parents);
  cache.mutation.set(node, computed);
  return computed;
};

/** Prove that an unconditional member replacement precedes this read. */
export const semanticDefiniteEffectPrecedesReference = (
  effect: t.Node,
  reference: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): boolean => {
  const before = directMutationPosition(effect, parents);
  const after = bindingReadPosition(reference, parents);
  if (before === null || after.position === null || after.repeating)
    return false;
  if (positionPrecedes(before, after.position)) return true;
  return (
    before.body === after.position.body &&
    before.index === after.position.index &&
    before.declaratorIndex === after.position.declaratorIndex &&
    expressionEvaluationOrder(effect, reference, parents) === "before"
  );
};

const computeReferenceInitializerPosition = (
  node: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): StatementPosition | null => {
  // Defaults live inside the declaration pattern rather than its initializer.
  let current = node;
  while (true) {
    const direct = directInitializerPosition(current, parents);
    if (direct !== null) return direct;
    const parent = parents.get(current);
    if (
      t.isAssignmentExpression(parent, { operator: "=" }) &&
      (t.isObjectPattern(parent.left) || t.isArrayPattern(parent.left))
    )
      return directMutationPosition(parent, parents);
    if (t.isFunction(parent))
      return t.isBlockStatement(parent.body)
        ? { body: parent.body.body, index: -1, declaratorIndex: -1 }
        : null;
    if (
      parent === undefined ||
      t.isStatement(parent) ||
      delayedInstanceFieldValue(parent, current)
    )
      return null;
    if (t.isVariableDeclarator(parent)) {
      const declaration = parents.get(parent);
      return t.isVariableDeclaration(declaration)
        ? statementPosition(declaration, parents, parent)
        : null;
    }
    current = parent;
  }
};

const referenceInitializerPosition = (
  node: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): StatementPosition | null => {
  const cache = initializerPositionCache(parents);
  const cached = cache.reference.get(node);
  if (cached !== undefined) return cached;
  const computed = computeReferenceInitializerPosition(node, parents);
  cache.reference.set(node, computed);
  return computed;
};

/** Parameter-to-body copies and ordinary expressions share one position owner. */
const initializerPosition = (
  initializer: JavaScriptSemanticBindingState["initializers"][number],
  parents: WeakMap<t.Node, t.Node>,
  reference = false,
): StatementPosition | null => {
  if (initializer.entryBody !== undefined)
    return { body: initializer.entryBody.body, index: -1, declaratorIndex: -1 };
  return reference
    ? referenceInitializerPosition(initializer.node, parents)
    : directInitializerPosition(initializer.node, parents);
};

/** Resolve origins at their use or capture, never at a later transitive effect. */
export const semanticMutationInitializers = (
  binding: JavaScriptSemanticBindingState,
  mutation: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): Pick<
  JavaScriptSemanticBindingState,
  "initializers" | "referenceInitializers" | "directOrigins"
> => {
  const mutationPosition =
    directMutationPosition(mutation, parents) ??
    referenceInitializerPosition(mutation, parents);
  if (mutationPosition === null) return binding;
  const origins = [
    ...binding.initializers.map((initializer) => ({
      initializer,
      position: initializerPosition(initializer, parents),
    })),
    ...binding.referenceInitializers.map((initializer) => ({
      initializer,
      position: initializerPosition(initializer, parents, true),
    })),
  ];
  if (
    origins.some(
      ({ position }) =>
        position === null || !positionPrecedes(position, mutationPosition),
    )
  )
    return binding;
  const { retained, replacesEntry } = retainedInitializerOrigins(
    origins,
    binding,
    parents,
  );
  return {
    // A proven earlier assignment replaces even an import-equals value. A
    // capture before or inside an uncertain assignment retains the full binding.
    directOrigins: replacesEntry ? [] : binding.directOrigins,
    initializers: binding.initializers.filter((initializer) =>
      retained.has(initializer),
    ),
    referenceInitializers: binding.referenceInitializers.filter((initializer) =>
      retained.has(initializer),
    ),
  };
};

/** Reuse immutable ancestry facts across reads nested in the same expression. */
const bindingReadPosition = (
  read: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): BindingReadPosition => {
  const cache = initializerPositionCache(parents).read;
  const path: t.Node[] = [];
  let current = read;
  let result: BindingReadPosition;
  while (true) {
    const cached = cache.get(current);
    if (cached !== undefined) {
      result = cached;
      break;
    }
    path.push(current);
    const parent = parents.get(current);
    if (t.isLoop(parent)) {
      result = { position: null, repeating: true };
      break;
    }
    if (
      parent === undefined ||
      (t.isFunction(parent) && !semanticComputedMethodKey(parent, current)) ||
      delayedInstanceFieldValue(parent, current)
    ) {
      result = { position: null, repeating: false };
      break;
    }
    current = parent;
  }
  for (let index = path.length - 1; index >= 0; index--) {
    const node = path[index];
    if (node === undefined) continue;
    const parent = parents.get(node);
    let position: StatementPosition | null = null;
    if (t.isVariableDeclarator(parent)) {
      const declaration = parents.get(parent);
      if (t.isVariableDeclaration(declaration))
        position = statementPosition(declaration, parents, parent);
    } else if (
      t.isStatement(parent) &&
      !t.isLoop(parent) &&
      !t.isFunction(parent)
    )
      position = statementPosition(parent, parents);
    if (position !== null && position !== result.position)
      result = { ...result, position };
    cache.set(node, result);
  }
  return result;
};

/** Select a local alias at its read, before any later straight-line reassignment. */
type SemanticBindingRead = {
  readonly status: "ordered" | "unresolved";
  /** A retained initializer executes on paths reaching this particular read. */
  readonly hasDefiniteInitializer: boolean;
  /** Unresolved reads retain all possible origins for conservative alias effects. */
  readonly binding: JavaScriptSemanticBindingState;
};

export const semanticBindingAtRead = (
  binding: JavaScriptSemanticBindingState,
  read: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): SemanticBindingRead => {
  if (
    binding.initializers.length === 0 &&
    binding.referenceInitializers.length === 0
  )
    return { status: "ordered", binding, hasDefiniteInitializer: false };
  const [soleInitializer] = binding.initializers;
  if (
    binding.initializers.length === 1 &&
    binding.referenceInitializers.length === 0 &&
    binding.declarationKinds.size === 0 &&
    binding.definitions.length === 1 &&
    binding.definitions[0]?.kind === "function" &&
    soleInitializer !== undefined &&
    t.isFunctionDeclaration(soleInitializer.node)
  )
    return { status: "ordered", binding, hasDefiniteInitializer: true };
  const initializer = binding.initializers[0];
  const reference = binding.referenceInitializers[0];
  const origin = initializer ?? reference;
  const sourcePosition =
    initializer === undefined
      ? reference === undefined
        ? null
        : initializerPosition(reference, parents, true)
      : initializerPosition(initializer, parents);
  const { position, repeating } = bindingReadPosition(read, parents);
  // Coverage and latest-value selection are independent. A preceding write
  // can cover entry even when another write's order remains unknown.
  const hasDefiniteInitializer =
    position !== null &&
    [
      ...binding.initializers,
      ...binding.referenceInitializers.filter(({ assignment }) => assignment),
    ].some((initializer) => {
      const source = initializerPosition(
        initializer,
        parents,
        binding.referenceInitializers.includes(initializer),
      );
      return (
        source !== null &&
        positionPrecedes(source, position) &&
        !initializerMayRetainEntry(initializer, binding, parents)
      );
    });
  if (
    !repeating &&
    origin !== undefined &&
    binding.initializers.length + binding.referenceInitializers.length === 1 &&
    sourcePosition !== null &&
    position !== null &&
    positionPrecedes(sourcePosition, position)
  )
    return {
      status: "ordered",
      binding,
      hasDefiniteInitializer,
    };
  const uncertainOrder =
    repeating ||
    sourcePosition === null ||
    position === null ||
    sourcePosition.body !== position.body;
  if (uncertainOrder)
    return { status: "unresolved", binding, hasDefiniteInitializer };
  const selected = selectInitializers(binding, position, read, parents);
  if (selected === undefined)
    return { status: "unresolved", binding, hasDefiniteInitializer };
  if (selected.binding === binding)
    return {
      status: "ordered",
      binding,
      hasDefiniteInitializer:
        hasDefiniteInitializer || selected.hasDefiniteInitializer,
    };
  return {
    status: "ordered",
    hasDefiniteInitializer:
      hasDefiniteInitializer || selected.hasDefiniteInitializer,
    binding: {
      ...binding,
      ...selected.binding,
      // Later assignment definitions do not describe the value captured here.
      definitions: binding.definitions.filter(
        ({ kind }) => kind !== "assignment",
      ),
    },
  };
};

const selectInitializers = (
  binding: JavaScriptSemanticBindingState,
  position: StatementPosition | null,
  read: t.Node,
  parents: WeakMap<t.Node, t.Node>,
):
  | {
      readonly binding: Pick<
        JavaScriptSemanticBindingState,
        "initializers" | "referenceInitializers"
      >;
      readonly hasDefiniteInitializer: boolean;
    }
  | undefined => {
  if (position === null) return undefined;
  const origins = [
    ...binding.initializers.map((initializer) => ({
      initializer,
      position: initializerPosition(initializer, parents),
    })),
    ...binding.referenceInitializers.map((initializer) => ({
      initializer,
      position: initializerPosition(initializer, parents, true),
    })),
  ];
  const preceding: typeof origins = [];
  for (const origin of origins) {
    const source = origin.position;
    if (source === null || source.body !== position.body) return undefined;
    if (positionPrecedes(source, position)) preceding.push(origin);
    else if (!positionPrecedes(position, source)) {
      if (
        source.index !== position.index ||
        source.declaratorIndex !== position.declaratorIndex
      )
        return undefined;
      const order = expressionEvaluationOrder(
        origin.initializer.node,
        read,
        parents,
      );
      // Failure to prove precedence is not proof that the write happens later.
      if (order === "unresolved") return undefined;
      if (order === "before") preceding.push(origin);
    }
  }
  const { retained, replacesEntry } = retainedInitializerOrigins(
    preceding,
    binding,
    parents,
  );
  // Preserve the owner's identity when selection removes no facts. Consumers
  // can then reuse the binding's dependency-aware provenance memo rather than
  // treating every equivalent read as a new temporal snapshot.
  if (
    binding.initializers.every((initializer) => retained.has(initializer)) &&
    binding.referenceInitializers.every((initializer) =>
      retained.has(initializer),
    )
  )
    return { binding, hasDefiniteInitializer: replacesEntry };
  return {
    hasDefiniteInitializer: replacesEntry,
    binding: {
      initializers: binding.initializers.filter((initializer) =>
        retained.has(initializer),
      ),
      referenceInitializers: binding.referenceInitializers.filter(
        (initializer) => retained.has(initializer),
      ),
    },
  };
};

/** Logical writes may keep prior aliases. An RHS fact alone does not prove an
 * empty local: the complete binding must exclude incoming/default/other writes.
 */
const initializerMayRetainEntry = (
  initializer: JavaScriptSemanticBindingState["initializers"][number],
  binding: JavaScriptSemanticBindingState,
  parents: WeakMap<t.Node, t.Node>,
): boolean => {
  const node = initializer.node,
    parent = parents.get(node);
  const assignment = t.isAssignmentExpression(node)
    ? node
    : t.isAssignmentExpression(parent) && parent.right === node
      ? parent
      : undefined;
  if (
    assignment === undefined ||
    !["&&=", "||=", "??="].includes(assignment.operator)
  )
    return false;
  const emptyLocal =
    node === assignment.right &&
    binding.kind === "variable" &&
    !binding.runtimeImport &&
    binding.initializers.length === 1 &&
    binding.initializers[0] === initializer &&
    binding.referenceInitializers.length === 0 &&
    binding.directOrigins.length === 0 &&
    binding.definitions.some(({ kind }) => kind === "variable") &&
    binding.definitions.every(
      ({ kind }) => kind === "variable" || kind === "assignment",
    );
  return !emptyLocal;
};

/** Certain writes replace prior origins; short-circuit writes retain both. */
const retainedInitializerOrigins = (
  origins: readonly {
    readonly initializer: JavaScriptSemanticBindingState["initializers"][number];
    readonly position: StatementPosition | null;
  }[],
  binding: JavaScriptSemanticBindingState,
  parents: WeakMap<t.Node, t.Node>,
) => {
  const latest = origins.reduce<StatementPosition | null>(
    (latest, { initializer, position }) =>
      position !== null &&
      !initializerMayRetainEntry(initializer, binding, parents) &&
      (latest === null || positionPrecedes(latest, position))
        ? position
        : latest,
    null,
  );
  return {
    replacesEntry: latest !== null,
    retained: new Set(
      origins
        .filter(
          ({ position }) =>
            latest === null ||
            (position?.index === latest.index &&
              position?.declaratorIndex === latest.declaratorIndex) ||
            (position !== null && positionPrecedes(latest, position)),
        )
        .map(({ initializer }) => initializer),
    ),
  };
};

/** Locate a capture only in an unconditional declaration or literal initializer. */
export const semanticCapturePosition = (
  node: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): StatementPosition | null => {
  let current = node;
  while (true) {
    const direct = directInitializerPosition(current, parents);
    if (direct !== null) return direct;
    const parent = parents.get(current);
    if (
      t.isObjectProperty(parent) &&
      parent.value === current &&
      semanticStaticPropertyKey(parent.key, parent.computed) !== null
    )
      current = parent;
    else if (t.isObjectExpression(parent) || t.isArrayExpression(parent))
      current = parent;
    else return null;
  }
};

/** Intermediate values must themselves have been initialized before capture. */
export const semanticBindingPrecedesCapture = (
  binding: JavaScriptSemanticBindingState,
  capture: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): boolean => {
  const initializer = binding.initializers[0];
  if (binding.initializers.length !== 1 || initializer === undefined)
    return false;
  const sourcePosition = initializerPosition(initializer, parents);
  const capturePosition = semanticCapturePosition(capture, parents);
  return (
    sourcePosition !== null &&
    capturePosition !== null &&
    positionPrecedes(sourcePosition, capturePosition)
  );
};

/** A preceding initializer and capture in one body precede its later effect. */
export const semanticBindingEffectFollowsCapture = (
  binding: JavaScriptSemanticBindingState,
  capture: t.Node,
  effect: t.Node,
  parents: WeakMap<t.Node, t.Node>,
): boolean => {
  if (!semanticBindingPrecedesCapture(binding, capture, parents)) return false;
  const captured = semanticCapturePosition(capture, parents);
  const written = directMutationPosition(effect, parents);
  return (
    captured !== null && written !== null && positionPrecedes(captured, written)
  );
};

/** Ignore later escapes only while reading earlier references in one activation. */
export const semanticEscapeFollowsCapture = (
  binding: JavaScriptSemanticBindingState,
  capture: t.Node,
  escape: t.Node | undefined,
  parents: WeakMap<t.Node, t.Node>,
): boolean => {
  const initializer = binding.initializers[0];
  if (
    escape === undefined ||
    initializer === undefined ||
    !semanticBindingPrecedesCapture(binding, capture, parents)
  )
    return false;
  // A literal allocates here. Aliases are evaluated at the same capture point,
  // so an outer/persistent origin still receives all of its own escape effects.
  const origin = unwrapJavaScriptExpression(initializer.node).node;
  if (
    !t.isObjectExpression(origin) &&
    !t.isArrayExpression(origin) &&
    !t.isIdentifier(origin) &&
    !t.isMemberExpression(origin) &&
    !t.isOptionalMemberExpression(origin)
  )
    return false;
  const capturePosition = semanticCapturePosition(capture, parents);
  const escapePosition = directMutationPosition(escape, parents);
  return (
    capturePosition !== null &&
    escapePosition !== null &&
    positionPrecedes(capturePosition, escapePosition)
  );
};