const fs = require("fs");
const { leads } = JSON.parse(fs.readFileSync("./leads.json"));

// index records by ID for easy lookup
const leadsById = {};
// index IDs by email for easy lookup
const leadIdssByEmail = {};

const collisions = [];

for (const currentLead of leads) {
  const { _id, email } = currentLead;
  const collidingLeadIdByEmail = leadIdssByEmail[email];
  const collidingLead = collidingLeadIdByEmail
    ? leadsById[collidingLeadIdByEmail]
    : leadsById[_id];

  if (collidingLead) {
    const collision = {
      left: collidingLead,
      right: currentLead,
      collidingField: collidingLeadIdByEmail ? "email" : "_id",
    };
    collisions.push(collision);
    const lDate = new Date(collision.left.entryDate);
    const rDate = new Date(collision.right.entryDate);
    if (lDate > rDate) {
      // existing lead is newer than current lead
      // discard current lead by doing nothing with it
      collision.took = "left";
    } else {
      // current lead is newer than existing lead, or both leads have the same date
      // either way, take the current lead over the existing one
      collision.took = "right";
      if (collision.collidingField === "_id") {
        // colliding ID - replace ID index, delete old email in email index
        delete leadIdssByEmail[collision.left.email];
        leadIdssByEmail[email] = _id;
        leadsById[_id] = currentLead;
      } else {
        // colliding email - replace ID in email index, delete old ID index
        leadIdssByEmail[email] = _id;
        delete leadsById[collision.left._id];
        leadsById[_id] = currentLead;
      }
    }
  } else {
    // no collision
    leadsById[currentLead._id] = currentLead;
    leadIdssByEmail[currentLead.email] = currentLead._id;
  }
}

console.log("collisions", collisions);
console.log("leadsById", leadsById);

console.log('records processed:', leads.length)
console.log('collisions:', collisions.length)
console.log('output leads:', Object.keys(leadsById).length)