feat: give bots access to the previous other players state + a few re…

…lated fixes & improvements (#70)

## How does this PR impact the user?

https://www.loom.com/share/b8bfff4f10f047fabc83fcb9bb275536

## Description

- [x] give bots access to the previous other players state
- [x] fix bug where the bot that doesn't move can't eat anyone
- [x] optimize collision detection a bit
- [x] switch game from turn-by-turn logic (chess-like) to "all players
make moves simultaneously and then the engine computes collisions"

## Limitations

N/A

## Checklist

- [x] my PR is focused and contains one wholistic change
- [x] I have added screenshots or screen recordings to show the changes

other/__snapshots__/prepareBotCode.spec.ts.snap

@@ -1,10 +1,41 @@
 // Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
 
+exports[`correctly saves values for a different previous state 1`] = `
+"
+global._player = {"x":0,"y":0,"radius":5,"username":"yurij"};
+global._otherPlayers = [{"x":10,"y":10,"radius":5,"username":"danil"},{"x":20,"y":20,"radius":5,"username":"andrey"}];
+global._food = [{"x":30,"y":30,"radius":5},{"x":40,"y":40,"radius":5}];
+global._previousOtherPlayersState = [{"x":11,"y":12,"radius":4,"username":"danil"},{"x":22,"y":40,"radius":5,"username":"andrey"}];
+global._worldWidth = 100;
+global._worldHeight = 100;
+
+console.log('hello world');
+
+console.log('hello bot api');
+"
+`;
+
+exports[`handles the case when the bot was not in the previous bot state 1`] = `
+"
+global._player = {"x":0,"y":0,"radius":5,"username":"yurij"};
+global._otherPlayers = [{"x":10,"y":10,"radius":5,"username":"danil"},{"x":20,"y":20,"radius":5,"username":"andrey"}];
+global._food = [{"x":30,"y":30,"radius":5},{"x":40,"y":40,"radius":5}];
+global._previousOtherPlayersState = [];
+global._worldWidth = 100;
+global._worldHeight = 100;
+
+console.log('hello world');
+
+console.log('hello bot api');
+"
+`;
+
 exports[`prepares bot code correctly when there are three bots and some food in the world 1`] = `
 "
 global._player = {"x":0,"y":0,"radius":5,"username":"yurij"};
 global._otherPlayers = [{"x":10,"y":10,"radius":5,"username":"danil"},{"x":20,"y":20,"radius":5,"username":"andrey"}];
 global._food = [{"x":30,"y":30,"radius":5},{"x":40,"y":40,"radius":5}];
+global._previousOtherPlayersState = [{"x":10,"y":10,"radius":5,"username":"danil"},{"x":20,"y":20,"radius":5,"username":"andrey"}];
 global._worldWidth = 100;
 global._worldHeight = 100;
 
@@ -19,6 +50,7 @@ exports[`prepares bot code correctly when there are two bots in the world 1`] =
 global._player = {"x":0,"y":0,"radius":5,"username":"yurij"};
 global._otherPlayers = [{"x":10,"y":10,"radius":5,"username":"danil"}];
 global._food = [];
+global._previousOtherPlayersState = [{"x":10,"y":10,"radius":5,"username":"danil"}];
 global._worldWidth = 100;
 global._worldHeight = 100;
 
@@ -33,6 +65,7 @@ exports[`prepares bot code correctly when there is one bot in the world 1`] = `
 global._player = {"x":0,"y":0,"radius":5,"username":"yurij"};
 global._otherPlayers = [];
 global._food = [];
+global._previousOtherPlayersState = [];
 global._worldWidth = 100;
 global._worldHeight = 100;
 

other/defaultCode.ts

@@ -6,6 +6,8 @@ export const jsdoc = `/**
  *   Information about your player.
  * @property {Player[]} otherPlayers
  *   Information about other players.
+ * @property {Player[]} previousOtherPlayersState
+ *   Information about the other players in the previous frame.
  * @property {Food[]} food
  *   Information about the not yet eaten food.
  * @property {MoveTowards} moveTowards

other/prepareBotCode.spec.ts

@@ -20,7 +20,7 @@ it("prepares bot code correctly when there is one bot in the world", () => {
 
   const botApi = "console.log('hello bot api');";
 
-  const preparedCode = prepareBotCode({ bot, botCodes, state, botApi });
+  const preparedCode = prepareBotCode({ bot, botInfo: botCodes, state, prevBotState: state.bots, botApi });
 
   expect(preparedCode).toMatchSnapshot();
 });
@@ -55,7 +55,7 @@ it("prepares bot code correctly when there are two bots in the world", () => {
 
   const botApi = "console.log('hello bot api');";
 
-  const preparedCode = prepareBotCode({ bot, botCodes, state, botApi });
+  const preparedCode = prepareBotCode({ bot, botInfo: botCodes, state, prevBotState: state.bots, botApi });
 
   expect(preparedCode).toMatchSnapshot();
 });
@@ -97,7 +97,97 @@ it("prepares bot code correctly when there are three bots and some food in the w
 
   const botApi = "console.log('hello bot api');";
 
-  const preparedCode = prepareBotCode({ bot, botCodes, state, botApi });
+  const preparedCode = prepareBotCode({ bot, botInfo: botCodes, state, prevBotState: state.bots, botApi });
+
+  expect(preparedCode).toMatchSnapshot();
+});
+
+it("handles the case when the bot was not in the previous bot state", () => {
+  const bot = {
+    id: "1",
+    code: "console.log('hello world');",
+    username: "yurij",
+    userId: 1,
+  };
+
+  const botCodes = {
+    1: bot,
+    2: {
+      id: "2",
+      code: "console.log('hello world');",
+      username: "danil",
+      userId: 2,
+    },
+    3: {
+      id: "3",
+      code: "console.log('hello world');",
+      username: "andrey",
+      userId: 3,
+    },
+  };
+
+  const state = {
+    bots: new Map([
+      ["1", { x: 0, y: 0, radius: 5, botId: "1", color: "#00FF00", spawnId: "s1" }],
+      ["2", { x: 10, y: 10, radius: 5, botId: "2", color: "#00FF00", spawnId: "s2" }],
+      ["3", { x: 20, y: 20, radius: 5, botId: "3", color: "#00FF00", spawnId: "s3" }],
+    ]),
+    food: [{ x: 30, y: 30, radius: 5 }, { x: 40, y: 40, radius: 5 }],
+    width: 100,
+    height: 100,
+  };
+
+  const botApi = "console.log('hello bot api');";
+
+  const preparedCode = prepareBotCode({ bot, botInfo: botCodes, state, prevBotState: new Map(), botApi });
+
+  expect(preparedCode).toMatchSnapshot();
+});
+
+it("correctly saves values for a different previous state", () => {
+  const bot = {
+    id: "1",
+    code: "console.log('hello world');",
+    username: "yurij",
+    userId: 1,
+  };
+
+  const botCodes = {
+    1: bot,
+    2: {
+      id: "2",
+      code: "console.log('hello world');",
+      username: "danil",
+      userId: 2,
+    },
+    3: {
+      id: "3",
+      code: "console.log('hello world');",
+      username: "andrey",
+      userId: 3,
+    },
+  };
+
+  const state = {
+    bots: new Map([
+      ["1", { x: 0, y: 0, radius: 5, botId: "1", color: "#00FF00", spawnId: "s1" }],
+      ["2", { x: 10, y: 10, radius: 5, botId: "2", color: "#00FF00", spawnId: "s2" }],
+      ["3", { x: 20, y: 20, radius: 5, botId: "3", color: "#00FF00", spawnId: "s3" }],
+    ]),
+    food: [{ x: 30, y: 30, radius: 5 }, { x: 40, y: 40, radius: 5 }],
+    width: 100,
+    height: 100,
+  };
+
+  const prevBotState = new Map([
+    ["1", { x: 2, y: 4, radius: 3, botId: "1", color: "#00FF00", spawnId: "s1" }],
+    ["2", { x: 11, y: 12, radius: 4, botId: "2", color: "#00FF00", spawnId: "s2" }],
+    ["3", { x: 22, y: 40, radius: 5, botId: "3", color: "#00FF00", spawnId: "s3" }],
+  ]);
+
+  const botApi = "console.log('hello bot api');";
+
+  const preparedCode = prepareBotCode({ bot, botInfo: botCodes, state, prevBotState, botApi });
 
   expect(preparedCode).toMatchSnapshot();
 });

other/prepareBotCode.ts

@@ -1,21 +1,20 @@
-import type { BotCode, BotCodes } from "~/other/botCodeStore";
+import type { BotCode } from "~/other/botCodeStore";
 import type { WorldState } from "~/other/world";
 
 type PrepareBotCodeArgs = {
   bot: BotCode;
-  botCodes: BotCodes;
+  botInfo: Record<string, { username: string }>;
   state: Pick<WorldState, "bots" | "food" | "width" | "height">;
+  prevBotState: WorldState["bots"];
   botApi: string;
 };
 
-export default function prepareBotCode({ bot, botCodes, state, botApi }: PrepareBotCodeArgs): string | undefined {
+export default function prepareBotCode({ bot, botInfo, state, prevBotState, botApi }: PrepareBotCodeArgs): string {
   const { code, username } = bot;
 
   const botObject = [...state.bots.values()].find(b => bot.id === b.botId);
   if (!botObject) {
-    // TODO(yurij): handle this better
-    console.error(`Bot with id ${bot.id} not found in the world`);
-    return;
+    throw new Error(`Bot with id ${bot.id} not found in the world`);
   }
 
   const me = { x: botObject.x, y: botObject.y, radius: botObject.radius, username };
@@ -25,14 +24,19 @@ export default function prepareBotCode({ bot, botCodes, state, botApi }: Prepare
       x: b.x,
       y: b.y,
       radius: b.radius,
-      username: botCodes[b.botId]?.username,
+      username: botInfo[b.botId]?.username,
     }));
   const food = state.food.map(f => ({ x: f.x, y: f.y, radius: f.radius }));
 
+  const prevOtherPlayers = [...prevBotState.values()]
+    .filter(b => b.botId !== bot.id)
+    .map(b => ({ x: b.x, y: b.y, radius: b.radius, username: botInfo[b.botId]?.username }));
+
   const preparedCode = `
 global._player = ${JSON.stringify(me)};
 global._otherPlayers = ${JSON.stringify(otherPlayers)};
 global._food = ${JSON.stringify(food)};
+global._previousOtherPlayersState = ${JSON.stringify(prevOtherPlayers)};
 global._worldWidth = ${state.width};
 global._worldHeight = ${state.height};
 

other/world.spec.ts

@@ -18,7 +18,7 @@ it("correctly removes the smaller bot when the bigger bot eats it", () => {
   bot2.x = 10;
   bot2.y = 10;
 
-  world.checkCollisions("1");
+  world.checkCollisions();
 
   expect(world.hasBot("1")).toBe(true);
   expect(world.hasBot("2")).toBe(false);
@@ -41,7 +41,7 @@ it("correctly removes food when the bot eats it", () => {
   food.x = 10;
   food.y = 10;
 
-  world.checkCollisions("1");
+  world.checkCollisions();
 
   // @ts-expect-error - world.food is private
   expect(world.food.length).toBeLessThan(100);
@@ -69,7 +69,7 @@ it("shouldn't crash when bot eats two food items and one of them with the last i
   food2.x = 10;
   food2.y = 10;
 
-  world.checkCollisions("1");
+  world.checkCollisions();
 
   // @ts-expect-error - world.food is private
   expect(world.food.length).toBeLessThan(100);
@@ -94,6 +94,7 @@ it("doesn't allow the bot to go outside the world with large x and y", () => {
   expect(botFromStateBeforeMove.y).toBe(100);
 
   world.moveBot("1", 101, 101);
+  world.checkCollisions();
 
   const worldStateAfterMove = world.getState();
   const botsAfterMove = [...worldStateAfterMove.bots.values()];
@@ -124,6 +125,7 @@ it("doesn't allow the bot to go outside the world with negative x and y", () =>
   expect(botFromStateBeforeMove.y).toBe(0);
 
   world.moveBot("1", -1, -1);
+  world.checkCollisions();
 
   const worldStateAfterMove = world.getState();
   const botsAfterMove = [...worldStateAfterMove.bots.values()];