import { emptySet, add, length, forEach, has, remove } from "../../structures/set.js";
import { getDepth, Slot } from "./value_slot.js";
import { compareSlot } from "./compare.js";
import { makeTypeParser } from "../../parser/type_parser.js";
import { newDynamic } from "../../primitives/dynamic.js";

const emptySetOfSlots = compareElems => emptySet(compareSlot(compareElems));

export const findLCA = compareElems => slotA => slotB => {
  console.log('compareSlot...', slotA, slotB);
  if (compareSlot(compareElems)(slotA)(slotB) === 0) {
    return slotA;
  }
  if (getDepth(slotA) > getDepth(slotB)) {
    // we can assume that slotA.variant === "write"
    return findLCA(compareElems)(slotA.value.slot)(slotB);
  }
  else {
    // we can assume that slotB.variant === "write"
    return findLCA(compareElems)(slotA)(slotB.value.slot);
  }
};

// returns
//  {slotA} if slotA is younger
//  {slotB} if slotB is younger
//  {slotA, slotB} if they are concurrent (conflicting)
export const merge = compareElems => slotA => slotB => {
  const lca = findLCA(compareElems)(slotA)(slotB);
  const emptySet = emptySetOfSlots(compareElems);
  if (compareSlot(compareElems)(lca)(slotA) === 0) {
    return add(emptySet)(slotB);
  }
  if (compareSlot(compareElems)(lca)(slotB) === 0) {
    return add(emptySet)(slotA);
  }
  const setWithA = add(emptySet)(slotA);
  const setWithAandB = add(setWithA)(slotB);
  return setWithAandB;
};

export const mergeN = compareElems => slots => {
  let result = slots;
  forEach(slots)(slotA => {
    forEach(slots)(slotB => {
      // compare all non-identical pairs
      if (compareSlot(compareElems)(slotA)(slotB) !== 0) {
        const m = merge(compareElems)(slotA)(slotB);
        if (length(m) === 1) {
          // if in the pair, one is an ancestor of the other,
          // only keep the other
          if (has(m)(slotA)) {
            result = remove(result)(slotB);
          }
        }
      }
    });
  });
  return result;
};

const mkType = makeTypeParser({
  extraBracketOperators: [
    [':=', ['=:', Slot]],
  ],
});

export const ModuleStaticMerge = [
  ["merge" , newDynamic(merge)(mkType(":=a=: -> :=a=: -> {:=a=:}"))],
  ["mergeN", newDynamic(merge)(mkType("{:=a=:} -> {:=a=:}"       ))],
];