How to get the final state from an array of objects representing changes-CodePudding

I have an array of changes (objects) and would like to get the final state after all the changes have been made.

For example, having this array of changes:

const today = new Date();
const yesterday = new Date(today);
yesterday.setDate(yesterday.getDate() - 1);
const tomorrow = new Date(today);
tomorrow.setDate(tomorrow.getDate()   1);

const item1 = {
  id: 'id1',
  timestamp: yesterday,
};
const item2 = {
  id: 'id2',
  timestamp: today,
};
const item3 = {
  id: 'id3',
  timestamp: tomorrow,
};

const changes = [
  {
    action: 'swap',
    item1,
    item2,
  },
  {
    action: 'swap',
    item1,
    item2: item3,
  },
]

I am expecting this array with the final state of each item:

const finalState = [
  {
    id: item1.id,
    timestamp: item3.timestamp,
  },
  {
    id: item2.id,
    timestamp: item1.timestamp,
  },
  {
    id: item3.id,
    timestamp: item2.timestamp,
  },
]

currently, the logic I am using is this one. However it is not working properly.

export const convertChangesToFinalState = ({
  changes,
}): FinalChanges => {
  const finalState: {
    [id: string]: FinalChange;
  } = {};

  for (const { item1, item2 } of changes) {
    finalState[item1.id] = {
      id: item1.id,
      timestamp: new Date(finalState[item2.id]?.timestamp ?? item2.timestamp),
    };

    finalState[item2.id] = {
      id: item2.id,
      timestamp: new Date(finalState[item1.id]?.timestamp ?? item1.timestamp),
      // timestamp: new Date(new Date(item2.timestamp).getTime() !== new Date(finalState[item1.id]?.timestamp).getTime()? finalState[item1.id]?.timestamp : item1.timestamp),
    };
  }

  return Object.values(finalState);
};

Could you please help me solve this?

Thank you in advance!

CodePudding user response：

When the item1 is stored in the finalChanges, you cannot read again this modified object, otherwise you will be accessing to the new updated value. You will need to create a copy of the non-modified object for each iteration, before modifying it.

If it doesn´t exist, just get the value we want to set from the main item.

export const convertChangesToFinalState = ({
  changes,
}): FinalChanges => {
  const finalState: {
    [id: string]: FinalChange;
  } = {};

  for (const { item1, item2 } of changes) {
    const notAlteredItem = { ...finalState };
    finalState[item1.id] = {
      id: item1.id,
      timestamp: new Date(finalState[item2.id]?.timestamp ?? item2.timestamp),
    };

    finalState[item2.id] = {
      id: item2.id,
      timestamp: notAlteredItem[item1.id]?.timestamp ?? item1.timestamp
    };
  }

  return Object.values(finalState);
};

Check this sandbox https://codesandbox.io/s/zen-johnson-dkxk0?file=/src/index.js