/**
 * Parses an event by comparing old and new data to determine which fields have changed.
 *
 * @async
 * @function eventParser
 * @param {Object} params - The parameters for parsing the event.
 * @param {Object} params.oldData - The previous state of the data. If not provided, the data is considered new.
 * @param {Object} params.newData - The new state of the data.
 * @param {string} params.trigger - The trigger that caused the event.
 * @param {string} params.table - The name of the table where the event occurred.
 * @param {string} [params.jobIdField] - The field name or key path (e.g., "req.body.event.new.jobid") used to extract the job ID.
 * @returns {Promise<Object>} An object containing:
 *   - {@link changedFieldNames}: An array of field names that have changed.
 *   - {@link changedFields}: An object mapping changed field names to their new values (or `null` if the field was removed).
 *   - {boolean} isNew - Indicates if the event is for new data (i.e., no oldData exists).
 *   - {Object} data - The new data.
 *   - {string} trigger - The event trigger.
 *   - {string} table - The table name.
 *   - {string|null} jobId - The extracted job ID, if available.
 */
const eventParser = async ({ oldData, newData, trigger, table, jobIdField }) => {
  const isNew = !oldData;
  let changedFields = {};
  let changedFieldNames = [];

  if (isNew) {
    // If there's no old data, every field in newData is considered changed (new)
    changedFields = { ...newData };
    changedFieldNames = Object.keys(newData);
  } else {
    // Compare oldData with newData for changes
    for (const key in newData) {
      if (Object.prototype.hasOwnProperty.call(newData, key)) {
        // Check if the key exists in oldData and if values differ
        if (
          !Object.prototype.hasOwnProperty.call(oldData, key) ||
          JSON.stringify(oldData[key]) !== JSON.stringify(newData[key])
        ) {
          changedFields[key] = newData[key];
          changedFieldNames.push(key);
        }
      }
    }
    // Check for fields that were removed
    for (const key in oldData) {
      if (Object.prototype.hasOwnProperty.call(oldData, key) && !Object.prototype.hasOwnProperty.call(newData, key)) {
        changedFields[key] = null; // Indicate field was removed
        changedFieldNames.push(key);
      }
    }
  }
  // Extract jobId based on jobIdField
  let jobId = null;
  if (jobIdField) {
    // If the jobIdField is provided as a string like "req.body.event.new.jobid",
    // strip the prefix if it exists so we can use the property name.
    let keyName = jobIdField;
    const prefix = "req.body.event.new.";
    if (keyName.startsWith(prefix)) {
      keyName = keyName.slice(prefix.length);
    }
    // Attempt to retrieve the job id from newData first; if not available, try oldData.
    jobId = newData[keyName] || (oldData && oldData[keyName]) || null;
  }

  return {
    changedFieldNames,
    changedFields,
    isNew,
    data: newData,
    trigger,
    table,
    jobId
  };
};

module.exports = eventParser;