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const DiffSequence = {};\n\nconst hasOwn = Object.prototype.hasOwnProperty;\n\nfunction isObjEmpty(obj) {\n  for (let key in Object(obj)) {\n    if (hasOwn.call(obj, key)) {\n      return false;\n    }\n  }\n  return true;\n}\n\n// ordered: bool.\n// old_results and new_results: collections of documents.\n//    if ordered, they are arrays.\n//    if unordered, they are IdMaps\nDiffSequence.diffQueryChanges = function (ordered, oldResults, newResults,\n                                              observer, options) {\n  if (ordered)\n    DiffSequence.diffQueryOrderedChanges(\n      oldResults, newResults, observer, options);\n  else\n    DiffSequence.diffQueryUnorderedChanges(\n      oldResults, newResults, observer, options);\n};\n\nDiffSequence.diffQueryUnorderedChanges = function (oldResults, newResults,\n                                                       observer, options) {\n  options = options || {};\n  var projectionFn = options.projectionFn || EJSON.clone;\n\n  if (observer.movedBefore) {\n    throw new Error(\"_diffQueryUnordered called with a movedBefore observer!\");\n  }\n\n  newResults.forEach(function (newDoc, id) {\n    var oldDoc = oldResults.get(id);\n    if (oldDoc) {\n      if (observer.changed && !EJSON.equals(oldDoc, newDoc)) {\n        var projectedNew = projectionFn(newDoc);\n        var projectedOld = projectionFn(oldDoc);\n        var changedFields =\n              DiffSequence.makeChangedFields(projectedNew, projectedOld);\n        if (! isObjEmpty(changedFields)) {\n          observer.changed(id, changedFields);\n        }\n      }\n    } else if (observer.added) {\n      var fields = projectionFn(newDoc);\n      delete fields._id;\n      observer.added(newDoc._id, fields);\n    }\n  });\n\n  if (observer.removed) {\n    oldResults.forEach(function (oldDoc, id) {\n      if (!newResults.has(id))\n        observer.removed(id);\n    });\n  }\n};\n\nDiffSequence.diffQueryOrderedChanges = function (old_results, new_results,\n                                                     observer, options) {\n  options = options || {};\n  var projectionFn = options.projectionFn || EJSON.clone;\n\n  var new_presence_of_id = {};\n  new_results.forEach(function (doc) {\n    if (new_presence_of_id[doc._id])\n      Meteor._debug(\"Duplicate _id in new_results\");\n    new_presence_of_id[doc._id] = true;\n  });\n\n  var old_index_of_id = {};\n  old_results.forEach(function (doc, i) {\n    if (doc._id in old_index_of_id)\n      Meteor._debug(\"Duplicate _id in old_results\");\n    old_index_of_id[doc._id] = i;\n  });\n\n  // ALGORITHM:\n  //\n  // To determine which docs should be considered \"moved\" (and which\n  // merely change position because of other docs moving) we run\n  // a \"longest common subsequence\" (LCS) algorithm.  The LCS of the\n  // old doc IDs and the new doc IDs gives the docs that should NOT be\n  // considered moved.\n\n  // To actually call the appropriate callbacks to get from the old state to the\n  // new state:\n\n  // First, we call removed() on all the items that only appear in the old\n  // state.\n\n  // Then, once we have the items that should not move, we walk through the new\n  // results array group-by-group, where a \"group\" is a set of items that have\n  // moved, anchored on the end by an item that should not move.  One by one, we\n  // move each of those elements into place \"before\" the anchoring end-of-group\n  // item, and fire changed events on them if necessary.  Then we fire a changed\n  // event on the anchor, and move on to the next group.  There is always at\n  // least one group; the last group is anchored by a virtual \"null\" id at the\n  // end.\n\n  // Asymptotically: O(N k) where k is number of ops, or potentially\n  // O(N log N) if inner loop of LCS were made to be binary search.\n\n\n  //////// LCS (longest common sequence, with respect to _id)\n  // (see Wikipedia article on Longest Increasing Subsequence,\n  // where the LIS is taken of the sequence of old indices of the\n  // docs in new_results)\n  //\n  // unmoved: the output of the algorithm; members of the LCS,\n  // in the form of indices into new_results\n  var unmoved = [];\n  // max_seq_len: length of LCS found so far\n  var max_seq_len = 0;\n  // seq_ends[i]: the index into new_results of the last doc in a\n  // common subsequence of length of i+1 <= max_seq_len\n  var N = new_results.length;\n  var seq_ends = new Array(N);\n  // ptrs:  the common subsequence ending with new_results[n] extends\n  // a common subsequence ending with new_results[ptr[n]], unless\n  // ptr[n] is -1.\n  var ptrs = new Array(N);\n  // virtual sequence of old indices of new results\n  var old_idx_seq = function(i_new) {\n    return old_index_of_id[new_results[i_new]._id];\n  };\n  // for each item in new_results, use it to extend a common subsequence\n  // of length j <= max_seq_len\n  for(var i=0; i<N; i++) {\n    if (old_index_of_id[new_results[i]._id] !== undefined) {\n      var j = max_seq_len;\n      // this inner loop would traditionally be a binary search,\n      // but scanning backwards we will likely find a subseq to extend\n      // pretty soon, bounded for example by the total number of ops.\n      // If this were to be changed to a binary search, we'd still want\n      // to scan backwards a bit as an optimization.\n      while (j > 0) {\n        if (old_idx_seq(seq_ends[j-1]) < old_idx_seq(i))\n          break;\n        j--;\n      }\n\n      ptrs[i] = (j === 0 ? -1 : seq_ends[j-1]);\n      seq_ends[j] = i;\n      if (j+1 > max_seq_len)\n        max_seq_len = j+1;\n    }\n  }\n\n  // pull out the LCS/LIS into unmoved\n  var idx = (max_seq_len === 0 ? -1 : seq_ends[max_seq_len-1]);\n  while (idx >= 0) {\n    unmoved.push(idx);\n    idx = ptrs[idx];\n  }\n  // the unmoved item list is built backwards, so fix that\n  unmoved.reverse();\n\n  // the last group is always anchored by the end of the result list, which is\n  // an id of \"null\"\n  unmoved.push(new_results.length);\n\n  old_results.forEach(function (doc) {\n    if (!new_presence_of_id[doc._id])\n      observer.removed && observer.removed(doc._id);\n  });\n\n  // for each group of things in the new_results that is anchored by an unmoved\n  // element, iterate through the things before it.\n  var startOfGroup = 0;\n  unmoved.forEach(function (endOfGroup) {\n    var groupId = new_results[endOfGroup] ? new_results[endOfGroup]._id : null;\n    var oldDoc, newDoc, fields, projectedNew, projectedOld;\n    for (var i = startOfGroup; i < endOfGroup; i++) {\n      newDoc = new_results[i];\n      if (!hasOwn.call(old_index_of_id, newDoc._id)) {\n        fields = projectionFn(newDoc);\n        delete fields._id;\n        observer.addedBefore && observer.addedBefore(newDoc._id, fields, groupId);\n        observer.added && observer.added(newDoc._id, fields);\n      } else {\n        // moved\n        oldDoc = old_results[old_index_of_id[newDoc._id]];\n        projectedNew = projectionFn(newDoc);\n        projectedOld = projectionFn(oldDoc);\n        fields = DiffSequence.makeChangedFields(projectedNew, projectedOld);\n        if (!isObjEmpty(fields)) {\n          observer.changed && observer.changed(newDoc._id, fields);\n        }\n        observer.movedBefore && observer.movedBefore(newDoc._id, groupId);\n      }\n    }\n    if (groupId) {\n      newDoc = new_results[endOfGroup];\n      oldDoc = old_results[old_index_of_id[newDoc._id]];\n      projectedNew = projectionFn(newDoc);\n      projectedOld = projectionFn(oldDoc);\n      fields = DiffSequence.makeChangedFields(projectedNew, projectedOld);\n      if (!isObjEmpty(fields)) {\n        observer.changed && observer.changed(newDoc._id, fields);\n      }\n    }\n    startOfGroup = endOfGroup+1;\n  });\n\n\n};\n\n\n// General helper for diff-ing two objects.\n// callbacks is an object like so:\n// { leftOnly: function (key, leftValue) {...},\n//   rightOnly: function (key, rightValue) {...},\n//   both: function (key, leftValue, rightValue) {...},\n// }\nDiffSequence.diffObjects = function (left, right, callbacks) {\n  Object.keys(left).forEach(key => {\n    const leftValue = left[key];\n    if (hasOwn.call(right, key)) {\n      callbacks.both && callbacks.both(key, leftValue, right[key]);\n    } else {\n      callbacks.leftOnly && callbacks.leftOnly(key, leftValue);\n    }\n  });\n\n  if (callbacks.rightOnly) {\n    Object.keys(right).forEach(key => {\n      const rightValue = right[key];\n      if (! hasOwn.call(left, key)) {\n        callbacks.rightOnly(key, rightValue);\n      }\n    });\n  }\n};\n\nDiffSequence.diffMaps = function (left, right, callbacks) {\n  left.forEach(function (leftValue, key) {\n    if (right.has(key)){\n      callbacks.both && callbacks.both(key, leftValue, right.get(key));\n    } else {\n      callbacks.leftOnly && callbacks.leftOnly(key, leftValue);\n    }\n  });\n\n  if (callbacks.rightOnly) {\n    right.forEach(function (rightValue, key) {\n      if (!left.has(key)){\n        callbacks.rightOnly(key, rightValue);\n      }\n    });\n  }\n};\n\n\nDiffSequence.makeChangedFields = function (newDoc, oldDoc) {\n  var fields = {};\n  DiffSequence.diffObjects(oldDoc, newDoc, {\n    leftOnly: function (key, value) {\n      fields[key] = undefined;\n    },\n    rightOnly: function (key, value) {\n      fields[key] = value;\n    },\n    both: function (key, leftValue, rightValue) {\n      if (!EJSON.equals(leftValue, rightValue))\n        fields[key] = rightValue;\n    }\n  });\n  return fields;\n};\n\nDiffSequence.applyChanges = function (doc, changeFields) {\n  Object.keys(changeFields).forEach(key => {\n    const value = changeFields[key];\n    if (typeof value === \"undefined\") {\n      delete doc[key];\n    } else {\n      doc[key] = value;\n    }\n  });\n};\n\n"]}