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gaia/shared/js/binary_search.js

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+'use strict';
+/* exported utils */
+var utils = window.utils || {};
+
+/**
+ * This function performs a binary search over an already sorted array
+ * target is the target item to search for
+ * array is the sorted array
+ * options is an optional object which may contain
+ * the start and end position (from, to)
+ * an optional arrayField which indicates the object property that contains the
+ * comparable item and transform and compare functions
+ *
+ * Returns an array with the positions on which the target item was found
+ *
+ */
+utils.binarySearch = function(target, array, options) {
+  var arrayField = options.arrayField,
+      transformFunction = options.transformFunction,
+      compareFunction = options.compareFunction;
+
+  // Obtains the comparable item by transforming if necessary
+  function getItem(array, index) {
+    var item = array[index];
+    if (arrayField) {
+      item = item[arrayField];
+      if (typeof transformFunction === 'function') {
+        item = transformFunction(item);
+      }
+    }
+    return item;
+  }
+
+  // Compares the target with an array item
+  function compare(target, item) {
+    var out;
+    if (typeof compareFunction === 'function') {
+      out = compareFunction(target, item);
+    }
+    else {
+      if (typeof target === 'string') {
+         out = target.localeCompare(item);
+      }
+      else {
+        out = target.toString().localeCompare(item);
+      }
+    }
+
+    return out;
+  }
+
+  var from = options.from;
+  if (typeof from === 'undefined') {
+    from = 0;
+  }
+  var to = options.to;
+  if (typeof to === 'undefined') {
+    to = array.length - 1;
+  }
+
+  if (to < from) {
+    // Not found
+    return [];
+  }
+
+  var middleIndex = Math.floor((to - from) / 2);
+  var item = getItem(array, from + middleIndex);
+
+  var compareResult = compare(target, item);
+
+  if (compareResult === 0) {
+    // Once a result is found let's iterate in both directions to get the rest
+    // Just in case there are more than one result
+    var results = [from + middleIndex];
+
+    var next = from + middleIndex + 1;
+    var finish = false;
+    while (next <= (array.length - 1) && !finish) {
+      item = getItem(array, next);
+
+      if (compare(target, item) === 0) {
+        results.push(next);
+      }
+      else {
+        finish = true;
+      }
+      next++;
+    }
+
+    finish = false;
+    next = from + middleIndex - 1;
+
+    while (next >= 0 && !finish) {
+      item = getItem(array, next);
+
+      if (compare(target, item) === 0) {
+        results.push(next);
+      }
+      else {
+        finish = true;
+      }
+      next--;
+    }
+    return results;
+  }
+  else if (compareResult < 0) {
+    return utils.binarySearch(target, array, {
+      from: from,
+      to: to - middleIndex - 1,
+      arrayField: arrayField,
+      transformFunction: transformFunction,
+      compareFunction: compareFunction
+    });
+  }
+  else {
+    return utils.binarySearch(target, array, {
+      from: from + middleIndex + 1,
+      to: to,
+      arrayField: arrayField,
+      transformFunction: transformFunction,
+      compareFunction: compareFunction
+    });
+  }
+};