feat(grid): add from() static method that accepts an iterable of hexe…

…s and returns a new grid

README.md

@@ -201,10 +201,10 @@ These methods exist in v3 and they need to be considered for v4.
 
 #### API
 
-- [ ] **Creation**:
+- [x] **Creation**:
   - [x] `new Grid<T extends Hex>(hexPrototype: T, traverserOrStore?: Traverser<T> | Map<string, T>)`: ~~can be traversed indefinitely, determine default traverser (spiral?) the default traverser doesn't emit hexes~~ A grid without hexes isn't very helpful, so it makes sense to pass a traverser or store (`Map`) to the constructor.
   - [x] ~~`Grid.of<T extends Hex>(/* same args as constructor */)`~~
-  - [ ] `Grid.from<T extends Hex>(iterable: Iterable<T>)`
+  - [x] `Grid.from<T extends Hex>(iterable: Iterable<T>)`
 - [ ] **Traversal**:
   - [x] `grid.rectangle(options)`
   - [ ] `grid.hexagon(options)`

src/grid/grid.test.ts

@@ -79,6 +79,41 @@ describe('creation', () => {
 
     expect(callback).not.toBeCalled()
   })
+
+  describe('Grid.from()', () => {
+    const hex = createHex(hexPrototype)
+    const store = new Map([[hex.toString(), hex]])
+
+    test('accepts a store', () => {
+      const grid = Grid.from(store)
+
+      expect(grid.store).toEqual(store)
+      expect(grid.hexPrototype).toBe(hexPrototype)
+
+      const callback = jest.fn()
+      grid.run(callback)
+
+      expect(callback.mock.calls).toEqual([[hex, grid]])
+    })
+
+    test('accepts an iterable', () => {
+      const iterable = store.values()
+      const grid = Grid.from(iterable)
+
+      expect(grid.store).toEqual(store)
+      expect(grid.hexPrototype).toBe(hexPrototype)
+
+      const callback = jest.fn()
+      grid.run(callback)
+
+      expect(callback.mock.calls).toEqual([[hex, grid]])
+    })
+
+    test('throws an error when passed an empty store or iterable', () => {
+      expect(() => Grid.from(new Map())).toThrowError(`Can't create grid from empty iterable: ${new Map()}`)
+      expect(() => Grid.from([])).toThrowError(`Can't create grid from empty iterable: ${[]}`)
+    })
+  })
 })
 
 test('implements toStringTag', () => {

src/grid/grid.ts

@@ -3,6 +3,25 @@ import { flatTraverse } from './functions'
 import { Callback, Traverser } from './types'
 
 export class Grid<T extends Hex> {
+  static from<T extends Hex>(iterable: Map<string, T> | Iterable<T>) {
+    let firstHex: T
+    let store: Map<string, T>
+
+    if (iterable instanceof Map) {
+      firstHex = iterable.values()[Symbol.iterator]().next().value
+      store = iterable
+    } else {
+      const array = Array.from(iterable)
+      firstHex = array[0]
+      store = new Map(array.map((hex) => [hex.toString(), hex]))
+    }
+
+    if (!firstHex) {
+      throw new Error(`Can't create grid from empty iterable: ${iterable}`)
+    }
+
+    return new Grid<T>(Object.getPrototypeOf(firstHex), store)
+  }
 
   get [Symbol.toStringTag]() {
     return 'Grid'