/*

Gist accompanying https://alloca.space/blog/c-lang.html 

Build and Run
-------------

1. Install a C compiler and https://raylib.com on your system

2. Build and run with:

   cc main.c -lraylib -lGL -lm -lpthread -ldl -lrt -lX11 -o game && ./game

*/

#include <stdlib.h>
#include "raylib.h"

/* Constants */

#define FPS 60
#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480
#define BALL_SPEED 200
#define BALL_RADIUS 50

/* Data types */

typedef struct {
  int x;
  int y;
} V2;

typedef struct {
  V2 position;
  float radius;
  V2 direction;
  Color color;
} Ball;

/* Functions */

Ball* createBall();
void swing(int *position, int *direction, int min, int max);
void swingBall(Ball* ball);
void applyKeys(Ball* ball);
void updateBall(Ball* ball);
void initialize();

/* Main */

int main(void) {
  initialize();

  Ball* ball = createBall();
  Color background_color = { 0x08, 0x18, 0x29, 0xff };

  // Game loop
  while (!WindowShouldClose()) {
    // Update
    updateBall(ball);

    // Draw
    BeginDrawing();

      ClearBackground(background_color);
      DrawCircle((*ball).position.x, (*ball).position.y, (*ball).radius, (*ball).color);

    EndDrawing();
  }

  // De-Initialization
  free(ball);
  CloseWindow();

  return 0;
}

/* Initialize window */

void initialize() {
  SetConfigFlags(FLAG_MSAA_4X_HINT);
  InitWindow(SCREEN_WIDTH, SCREEN_HEIGHT, "alloca.space - The C Programming Language");
  SetTargetFPS(FPS);
}

/* Ball */

Ball* createBall() {
  Ball ball_value = {
    .position = {
      .x = SCREEN_WIDTH/3,
      .y = SCREEN_HEIGHT/3,
    },
    .radius = BALL_RADIUS,
    .direction = {
      .x = 1,
      .y = 1,
    },
    .color = { 0xf9, 0x92, 0x26, 0xff },
  };

  Ball* ball = (Ball*)malloc(sizeof(Ball));
  *ball = ball_value;

  return ball;
}

void updateBall(Ball* ball) {
  applyKeys(ball);
  swingBall(ball);
}

void applyKeys(Ball* ball) {
    if (IsKeyDown(KEY_D)) { (*ball).direction.x = 1; }
    if (IsKeyDown(KEY_A)) { (*ball).direction.x = -1; }
    if (IsKeyDown(KEY_S)) { (*ball).direction.y = 1; }
    if (IsKeyDown(KEY_W)) { (*ball).direction.y = -1; }
}

void swingBall(Ball* ball) {
    swing(&(*ball).position.x, &(*ball).direction.x, 0 + (*ball).radius, SCREEN_WIDTH - (*ball).radius);
    swing(&(*ball).position.y, &(*ball).direction.y, 0 + (*ball).radius, SCREEN_HEIGHT - (*ball).radius);
}

void swing(int *position, int *direction, int min, int max) {
  if (*position <= min) {
    *position = min;
    *direction = 1;
  }
  else if (*position >= max) {
    *position = max;
    *direction = -1;
  }
  float dt = GetFrameTime();
  *position += *direction * (BALL_SPEED * dt);
}