Reimplemented Pathfinder to use A* instead of spawning an entity

#closes 788

features/pathfinder/heap.lua

@@ -0,0 +1,77 @@
+
+local Heap = {}
+Heap.__index = Heap
+
+local function findLowest( a, b )
+    return a < b
+end
+
+local function newHeap( template, compare )
+    return setmetatable( {
+        Data = {},
+        Compare = compare or findLowest,
+        Size = 0
+    }, template )
+end
+
+local function sortUp( heap, index )
+    if index <= 1 then return end
+    local pIndex = index % 2 == 0 and index / 2 or ( index - 1 ) / 2
+
+    if not heap.Compare( heap.Data[pIndex], heap.Data[index] ) then
+        heap.Data[pIndex], heap.Data[index] = heap.Data[index], heap.Data[pIndex]
+        sortUp( heap, pIndex )
+    end
+end
+
+local function sortDown( heap, index )
+    local leftIndex, rightIndex, minIndex
+    leftIndex = index * 2
+    rightIndex = leftIndex + 1
+    if rightIndex > heap.Size then
+        if leftIndex > heap.Size then return
+        else minIndex = leftIndex end
+    else
+        if heap.Compare( heap.Data[leftIndex], heap.Data[rightIndex] ) then minIndex = leftIndex
+        else minIndex = rightIndex end
+    end
+
+    if not heap.Compare( heap.Data[index], heap.Data[minIndex] ) then
+        heap.Data[index], heap.Data[minIndex] = heap.Data[minIndex], heap.Data[index]
+        sortDown( heap, minIndex )
+    end
+end
+
+function Heap:Empty()
+    return self.Size == 0
+end
+
+function Heap:Clear()
+    self.Data, self.Size, self.Compare = {}, 0, self.Compare or findLowest
+    return self
+end
+
+function Heap:Push( item )
+    if item then
+        self.Size = self.Size + 1
+        self.Data[self.Size] = item
+        sortUp( self, self.Size )
+    end
+    return self
+end
+
+function Heap:Pop()
+    local root
+    if self.Size > 0 then
+        root = self.Data[1]
+        self.Data[1] = self.Data[self.Size]
+        self.Data[self.Size] = nil
+        self.Size = self.Size - 1
+        if self.Size > 1 then
+            sortDown( self, 1 )
+        end
+    end
+    return root
+end
+
+return setmetatable( Heap, { __call = function( self, ... ) return newHeap( self, ... ) end } )