/**
 * Copyright 2004-present Facebook. All Rights Reserved.
 *
 * @providesModule diffRawProperties
 */
'use strict';

/**
 * diffRawProperties takes two sets of props and a set of valid attributes
 * and write to updatePayload the values that changed or were deleted
 *
 * @param {?object} updatePayload Overriden with the props that changed.
 * @param {!object} prevProps Previous properties to diff against current
 * properties. These properties are as supplied to component construction.
 * @param {!object} prevProps Next "current" properties to diff against
 * previous. These properties are as supplied to component construction.
 * @return {?object}
 */
function diffRawProperties(updatePayload, prevProps, nextProps, validAttributes) {
  var validAttributeConfig;
  var nextProp;
  var prevProp;
  var isScalar;
  var shouldUpdate;

  for (var propKey in nextProps) {
    validAttributeConfig = validAttributes[propKey];
    if (!validAttributeConfig) {
      continue; // not a valid native prop
    }
    prevProp = prevProps && prevProps[propKey];
    nextProp = nextProps[propKey];
    if (prevProp !== nextProp) {
      // If you want a property's diff to be detected, you must configure it
      // to be so - *or* it must be a scalar property. For now, we'll allow
      // creation with any attribute that is not scalar, but we should
      // eventually even reject those unless they are properly configured.
      isScalar = typeof nextProp !== 'object' || nextProp === null;
      shouldUpdate = isScalar ||
        !prevProp ||
        validAttributeConfig.diff &&
        validAttributeConfig.diff(prevProp, nextProp);

      if (shouldUpdate) {
        updatePayload = updatePayload || {};
        updatePayload[propKey] = nextProp;
      }
    }
  }

  // Also iterate through all the previous props to catch any that have been
  // removed and make sure native gets the signal so it can reset them to the
  // default.
  for (var propKey in prevProps) {
    validAttributeConfig = validAttributes[propKey];
    if (!validAttributeConfig) {
      continue; // not a valid native prop
    }
    if (updatePayload && updatePayload[propKey] !== undefined) {
      continue; // Prop already specified
    }
    prevProp = prevProps[propKey];
    nextProp = nextProps && nextProps[propKey];
    if (prevProp !== nextProp) {
      if (nextProp === undefined) {
        nextProp = null; // null is a sentinel we explicitly send to native
      }
      // If you want a property's diff to be detected, you must configure it
      // to be so - *or* it must be a scalar property. For now, we'll allow
      // creation with any attribute that is not scalar, but we should
      // eventually even reject those unless they are properly configured.
      isScalar = typeof nextProp !== 'object' || nextProp === null;
      shouldUpdate = isScalar && prevProp !== nextProp ||
        validAttributeConfig.diff &&
        validAttributeConfig.diff(prevProp, nextProp);
      if (shouldUpdate) {
        updatePayload = updatePayload || {};
        updatePayload[propKey] = nextProp;
      }
    }
  }
  return updatePayload;
}

module.exports = diffRawProperties;