DEV 1247: Add a new map generator interface (#71)

* reorganize code

* first draft of map generator interfaces

* add explicit random interface to board helpers

* implement standard map

* rename Generator to GameMap

* allow initializing snakes separately from placing them

* add random number generator to Settings

* updates to GameMap interface

* add helpers for creating and updating BoardState with maps

maps/game_map.go

@@ -0,0 +1,115 @@
+package maps
+
+import "github.com/BattlesnakeOfficial/rules"
+
+type GameMap interface {
+	// Return a unique identifier for this map.
+	ID() string
+
+	// Return non-functional metadata about this map.
+	Meta() Metadata
+
+	// Called to generate a new board. The map is responsible for placing all snakes, food, and hazards.
+	SetupBoard(initialBoardState *rules.BoardState, settings rules.Settings, editor Editor) error
+
+	// Called every turn to optionally update the board.
+	UpdateBoard(previousBoardState *rules.BoardState, settings rules.Settings, editor Editor) error
+}
+
+type Metadata struct {
+	Name        string
+	Author      string
+	Description string
+}
+
+// Editor is used by GameMap implementations to modify the board state.
+type Editor interface {
+	// Returns a random number generator. This MUST be used for any non-deterministic behavior in a GameMap.
+	Random() rules.Rand
+
+	// Clears all food from the board.
+	ClearFood()
+
+	// Clears all hazards from the board.
+	ClearHazards()
+
+	// Adds a food to the board. Does not check for duplicates.
+	AddFood(rules.Point)
+
+	// Adds a hazard to the board. Does not check for duplicates.
+	AddHazard(rules.Point)
+
+	// Removes all food from a specific tile on the board.
+	RemoveFood(rules.Point)
+
+	// Removes all hazards from a specific tile on the board.
+	RemoveHazard(rules.Point)
+
+	// Updates the body and health of a snake.
+	PlaceSnake(id string, body []rules.Point, health int32)
+}
+
+// An Editor backed by a BoardState.
+type BoardStateEditor struct {
+	*rules.BoardState
+	rand rules.Rand
+}
+
+func NewBoardStateEditor(boardState *rules.BoardState, rand rules.Rand) *BoardStateEditor {
+	return &BoardStateEditor{
+		BoardState: boardState,
+		rand:       rand,
+	}
+}
+
+func (editor *BoardStateEditor) Random() rules.Rand { return editor.rand }
+
+func (editor *BoardStateEditor) ClearFood() {
+	editor.Food = []rules.Point{}
+}
+
+func (editor *BoardStateEditor) ClearHazards() {
+	editor.Hazards = []rules.Point{}
+}
+
+func (editor *BoardStateEditor) AddFood(p rules.Point) {
+	editor.Food = append(editor.Food, rules.Point{X: p.X, Y: p.Y})
+}
+
+func (editor *BoardStateEditor) AddHazard(p rules.Point) {
+	editor.Hazards = append(editor.Hazards, rules.Point{X: p.X, Y: p.Y})
+}
+
+func (editor *BoardStateEditor) RemoveFood(p rules.Point) {
+	for index, food := range editor.Food {
+		if food.X == p.X && food.Y == p.Y {
+			editor.Food[index] = editor.Food[len(editor.Food)-1]
+			editor.Food = editor.Food[:len(editor.Food)-1]
+		}
+	}
+}
+
+func (editor *BoardStateEditor) RemoveHazard(p rules.Point) {
+	for index, food := range editor.Hazards {
+		if food.X == p.X && food.Y == p.Y {
+			editor.Hazards[index] = editor.Hazards[len(editor.Hazards)-1]
+			editor.Hazards = editor.Hazards[:len(editor.Hazards)-1]
+		}
+	}
+}
+
+func (editor *BoardStateEditor) PlaceSnake(id string, body []rules.Point, health int32) {
+	for index, snake := range editor.Snakes {
+		if snake.ID == id {
+			editor.Snakes[index].Body = body
+			editor.Snakes[index].Health = health
+			return
+		}
+	}
+
+	editor.Snakes = append(editor.Snakes, rules.Snake{
+		ID:     id,
+		Health: health,
+		Body:   body,
+	})
+}