fix(grid): grid's update() now always returns a grid that iterates ov…

…er hexes in its store

Previously the grid returned from update() iterated over hexes in the grid instance where update()
was called on. These hexes may be different from those in the grid instance returned from update().

fixes #68

src/grid/grid.test.ts

@@ -167,17 +167,19 @@ describe('update()', () => {
   })
 
   test('creates a clone of the grid and passes it to the callback', () => {
+    const hexes = [createHex(hexPrototype, { q: 1, r: 2 }), createHex(hexPrototype, { q: 3, r: 4 })]
     const newStore = new Map()
     const callback = jest.fn((grid) => {
+      expect(grid.hexes()).toEqual(hexes)
       grid.store = newStore
       return grid
     })
-    const grid = new Grid(hexPrototype, [at({ q: 1, r: 2 }), at({ q: 3, r: 4 })])
+    const grid = new Grid(hexPrototype, () => hexes)
     const result = grid.update(callback)
 
     expect(callback).toBeCalledWith(expect.any(Grid))
     expect(callback.mock.calls[0][0]).not.toBe(grid)
-    expect(result.hexes()).toEqual(grid.hexes())
+    expect(result.hexes()).toEqual([])
     expect(result.store).not.toBe(grid.store)
     expect(result.store).toBe(newStore)
     expect(result).not.toBe(grid)
@@ -194,6 +196,26 @@ describe('update()', () => {
     expect(result.store).toBe(newStore)
     expect(result).not.toBe(grid)
   })
+
+  test('iterates over the hexes *in the store* of the cloned grid', () => {
+    interface TestHex extends Hex {
+      test: number
+    }
+    const hexPrototype = createHexPrototype<TestHex>()
+    const hex1 = createHex(hexPrototype, { q: 0, r: 0, test: 1 })
+    const hex2 = hex1.clone({ test: 2 })
+    const grid1 = new Grid(hexPrototype, () => [hex1]).filter((hex) => hex.test === 0)
+
+    const grid2 = grid1.update((grid) => {
+      grid.store.set(hex2.toString(), hex2)
+    })
+
+    grid2
+      .each((hex) => {
+        expect(hex).toEqual(hex2)
+      })
+      .run()
+  })
 })
 
 describe('each()', () => {

src/grid/grid.ts

@@ -53,8 +53,11 @@ export class Grid<T extends Hex> {
   }
 
   update(callback: (grid: Grid<T>) => Grid<T> | void) {
-    const nextGrid = this._clone(this._getPrevHexes)
-    return callback(nextGrid) || nextGrid
+    let nextGrid = this._clone(this._getPrevHexes)
+    nextGrid = callback(nextGrid) || nextGrid
+    // reset hex state to iterate over nextGrid's store (fixes issue #68)
+    nextGrid._getPrevHexes = () => Array.from(nextGrid.store.values())
+    return nextGrid
   }
 
   each(callback: Callback<T, void>) {