// src/ast/normalizeFilters.ts
import type { ASTNode } from "../types";

/**
 * Rebuilds  FILTER(array, include[, ifEmpty])
 * into     FILTER({array}, {include[]}[, {ifEmpty}])
 * and flattens boolean-AND masks:  (A=1)*(B>1) → [A=1, B>1]
 */

const normalised = new WeakSet<ASTNode>(); // guards the main walk
const clonedMemo = new WeakMap<ASTNode, ASTNode>(); // memoised deep-clone

export function normalizeFilters(node: ASTNode): ASTNode {
  if (normalised.has(node)) return node;
  normalised.add(node);

  if (node.type === "FILTER" && node.args.length >= 2) {
    const [arrayArg, includeRaw, ifEmptyRaw] = node.args;

    const includeClauses = flattenMultiplication(includeRaw).map(deepClone);

    const rebuilt: ASTNode[] = [
      {
        type: "array",
        name: "array",
        args: [deepClone(arrayArg)],
        loc: arrayArg.loc,
      },
      {
        type: "include",
        name: "include",
        args: includeClauses,
        loc: (includeClauses[0] ?? deepClone(includeRaw)).loc,
      },
    ];

    if (ifEmptyRaw) {
      rebuilt.push({
        type: "ifEmpty",
        name: "ifEmpty",
        args: [deepClone(ifEmptyRaw)],
        loc: ifEmptyRaw.loc,
      });
    }

    node.args = rebuilt;
  }

  // recurse
  for (const child of node.args) normalizeFilters(child);
  return node;
}

/* ───────────────────────── helpers ─────────────────────────────────────── */

/** Depth-first clone that memoises already-cloned nodes (breaks cycles). */
function deepClone(n: ASTNode): ASTNode {
  const found = clonedMemo.get(n);
  if (found) return found;

  const copy: ASTNode = { ...n, args: [] };
  clonedMemo.set(n, copy);

  if (n.args) copy.args = n.args.map(deepClone);
  return copy;
}

/** Flatten a “*” chain; guarded so a truly cyclic tree cannot loop. */
function flattenMultiplication(n: ASTNode | undefined): ASTNode[] {
  const seen = new WeakSet<ASTNode>();
  function inner(node: ASTNode | undefined): ASTNode[] {
    if (!node || seen.has(node)) return [];
    seen.add(node);

    if (node.type === "*" && node.args?.length === 2) {
      return [...inner(node.args[0]), ...inner(node.args[1])];
    }
    return [node];
  }
  return inner(n);
}