From b45a77f76d318e09ec973638085ac2f2fbc58c9b Mon Sep 17 00:00:00 2001
From: Tim Wundenberg <tim@wundenbergs.de>
Date: Wed, 23 Jul 2025 17:04:19 +0200
Subject: [PATCH] feat: implement game logic

---
 src/game.zig | 149 +++++++++++++++++++++++++++++++++------------------
 src/main.zig |   7 ++-
 2 files changed, 101 insertions(+), 55 deletions(-)

diff --git a/src/game.zig b/src/game.zig
index c474ab8..32a5a74 100644
--- a/src/game.zig
+++ b/src/game.zig
@@ -1,78 +1,125 @@
 const std = @import("std");
+const testing = std.testing;
 
 const Direction = enum {
     up,
     down,
     left,
     right,
+
+    fn vector(self: Direction) Vec2 {
+        return switch (self) {
+            Direction.up => Vec2{ 0, -1 },
+            Direction.down => Vec2{ 0, 1 },
+            Direction.left => Vec2{ -1, 0 },
+            Direction.right => Vec2{ 1, 0 },
+        };
+    }
 };
 
 /// x, y
-const Vec2 = @Vector(2, u32);
+const Vec2 = @Vector(2, i32);
 
-const Element = struct {
-    position: Vec2,
-
-    prev: ?Element,
-    next: ?Element,
-
-    pub fn hasPrev(self: Element) bool {
-        return self.prev != null;
-    }
-    pub fn hasNext(self: Element) bool {
-        return self.next != null;
-    }
+const State = enum {
+    running,
+    lost,
+    won,
 };
 
-const GameState = struct {
+const Game = struct {
     playFieldSize: Vec2,
-
     food: Vec2,
+    direction: Direction,
+    body: std.ArrayList(Vec2),
+    state: State,
 
-    headDirection: Direction,
+    pub fn create(allocator: std.mem.Allocator) !Game {
+        var body = try std.ArrayList(Vec2).initCapacity(allocator, 1000);
+        try body.append(Vec2{ 10, 10 });
+        try body.append(Vec2{ 9, 10 });
+        try body.append(Vec2{ 8, 10 });
 
-    head: Element,
-    tail: Element,
-
-    pub fn create() GameState {
-        const pos1 = Element{
-            .position = Vec2{ 10, 10 },
-            .prev = null,
-            .next = null,
-        };
-        const pos2 = Element{
-            .position = Vec2{ 9, 10 },
-            .prev = pos1,
-            .next = null,
-        };
-        const pos3 = Element{
-            .position = Vec2{ 8, 10 },
-            .prev = pos2,
-            .next = null,
-        };
-
-        pos1.next = pos2;
-        pos2.next = pos3;
-
-        return GameState{
+        return Game{
             .playFieldSize = Vec2{ 20, 20 },
             .food = Vec2{ 2, 5 },
-            .headDirection = Direction.left,
-            .head = pos1,
-            .tail = pos3,
+            .direction = Direction.right,
+            .body = body,
+            .state = State.running,
         };
     }
 
-    pub fn tick() void {}
+    pub fn deinit(self: *Game) void {
+        self.body.deinit();
+    }
 
-    fn calculateSnakePositions(self: GameState, allocator: std.Allocator) []Vec2 {
-        var array = std.ArrayList(u8).initCapacity(allocator, 1000);
-
-        var current = self.head;
-        while (current.hasNext()) {
-            array.add(current.position);
+    pub fn setDirection(self: *Game, newDirection: Direction) void {
+        if (self.direction == newDirection) {
+            return;
         }
 
-        return array;
+        const headPos = self.body.items[0];
+        const firstBodyPart = self.body.items[1];
+
+        if (std.meta.eql(headPos + newDirection.vector(), firstBodyPart)) {
+            return;
+        }
+
+        self.direction = newDirection;
+    }
+
+    pub fn tick(self: *Game) !void {
+        if (self.state != State.running) {
+            return;
+        }
+
+        const newHead = self.body.items[0] + self.direction.vector();
+        try self.body.insert(0, newHead);
+        _ = self.body.pop();
     }
 };
+
+test "should initialize game" {
+    const allocator = testing.allocator;
+
+    var game = try Game.create(allocator);
+    defer game.deinit();
+    const actual = game.body.items;
+    const expected = [_]Vec2{ Vec2{ 10, 10 }, Vec2{ 9, 10 }, Vec2{ 8, 10 } };
+
+    try testing.expectEqualSlices(Vec2, &expected, actual);
+    try testing.expectEqual(Direction.right, game.direction);
+    try testing.expectEqual(Vec2{ 20, 20 }, game.playFieldSize);
+    try testing.expectEqual(State.running, game.state);
+}
+
+test "should move down" {
+    const allocator = testing.allocator;
+
+    var game = try Game.create(allocator);
+    defer game.deinit();
+
+    game.setDirection(Direction.down);
+    try testing.expectEqual(Direction.down, game.direction);
+
+    try game.tick();
+    const expected = [_]Vec2{ Vec2{ 10, 11 }, Vec2{ 10, 10 }, Vec2{ 9, 10 } };
+    try testing.expectEqualSlices(Vec2, &expected, game.body.items);
+}
+
+test "should not be able to change direction to the previous position" {
+    const allocator = testing.allocator;
+
+    var game = try Game.create(allocator);
+    defer game.deinit();
+
+    game.setDirection(Direction.left);
+    try testing.expectEqual(Direction.right, game.direction);
+}
+
+test "should loose if exiting playField" {}
+test "should loose if eating itself" {}
+test "should grow if eating food" {}
+test "should win if no space is left" {}
+test "should tick if running" {}
+test "should fail tick if lost" {}
+test "should fail tick if won" {}
diff --git a/src/main.zig b/src/main.zig
index 9facc36..f6c7684 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,5 +1,8 @@
 const std = @import("std");
 const rl = @import("raylib");
+comptime {
+    _ = @import("game.zig");
+}
 
 pub fn main() anyerror!void {
     const alloc = std.heap.page_allocator;
@@ -25,7 +28,3 @@ pub fn main() anyerror!void {
         rl.drawRectangle(10, 10, 10, 10, .black);
     }
 }
-
-test "should initialize game" {
-    try std.testing.expect(42 == 42);
-}