/*
 * Copyright (C) 2019 Jordan Halase <jordan@halase.me>
 *
 * Permission to use, copy, modify, and/or distribute this software for any 
 * purpose with or without fee is hereby granted, provided that the above 
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY 
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION 
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <math.h>

#include <SDL2/SDL.h>

#define SCREEN_WIDTH	800
#define SCREEN_HEIGHT	600
#define RENDER_SCALE	16.0f
#define SCREEN_WIDTH_F	(SCREEN_WIDTH/RENDER_SCALE)
#define SCREEN_HEIGHT_F	(SCREEN_HEIGHT/RENDER_SCALE)
#define SCREEN_CENTER_X	(SCREEN_WIDTH_F/2)
#define SCREEN_CENTER_Y	(SCREEN_HEIGHT_F/2)
#define TWOPI		6.283185307f
#define PIOVER2		1.570796327f
#define INVSQRT2	0.707106781f

void fatal_sdl()
{
	fprintf(stderr, "%s\n", SDL_GetError());
	SDL_ShowSimpleMessageBox(
		SDL_MESSAGEBOX_ERROR,
		"Fatal Error",
		SDL_GetError(),
		NULL
	);
	exit(1);
}

#define CHECK_SDL(f) do { if ((f) < 0) { fatal_sdl(); } } while (0)

typedef struct vec2 {
	float x, y;
} vec2;

#define vec2(x, y)	((vec2){(x), (y)})
#define vadd(a, b)	vec2((a).x+(b).x, (a).y+(b).y)
#define vscale(v, s)	vec2((v).x*(s), (v).y*(s))
#define vcomplex(a, b)	vec2((a).x*(b).x-(a).y*(b).y, (a).x*(b).y+(a).y*(b).x)
#define vdot(a, b)	((a).x*(b).x + (a).y*(b).y)
#define vdotself(v)	vdot(v, v)
#define viszero(v)	((v).x == 0.0f && (v).y == 0.0f)

enum CollisionType {
	COLLISION_TYPE_NONE		= 0x0,
	COLLISION_TYPE_PLAYER		= 0x1,
	COLLISION_TYPE_ASTEROID		= 0x2,
	COLLISION_TYPE_UFO		= 0x4,
	COLLISION_TYPE_PLAYER_BULLET	= 0x8,
	COLLISION_TYPE_UFO_BULLET	= 0x10
};

struct Bullet {
	vec2 position;
	vec2 velocity;		// Zero velocity bullets are vacant
};

#define MAX_BULLETS	8

/* Zero is initialization */
struct BulletPool {
	uint32_t used;		// Number of bullets currently in use
	uint32_t index;		// Index of possibly vacant bullet
	struct Bullet bullets[MAX_BULLETS];
};

struct BulletPool player_bullets;

bool bullets_shoot(struct BulletPool *pool, const vec2 position, const vec2 velocity)
{
	if (pool->used >= MAX_BULLETS) {
		return false;
	}
	uint32_t i;
	for (i = pool->index; i < MAX_BULLETS; ++i) {
		if (viszero(pool->bullets[i].velocity)) {
			goto found;
		}
	}
	for (i = 0; i < pool->index; ++i) {
		if (viszero(pool->bullets[i].velocity)) {
			goto found;
		}
	}
	return false;
found:
	pool->bullets[i].position = position;
	pool->bullets[i].velocity = velocity;
	pool->index = (pool->index + 1) % MAX_BULLETS;
	++pool->used;
	return true;
}

static bool is_point_in_screen(const vec2 position)
{
	if (position.x > SCREEN_WIDTH_F || position.y > SCREEN_HEIGHT_F ||
	    position.x < 0.0f || position.y < 0.0f) {
		return false;
	}
	return true;
}

void bullets_integrate(struct BulletPool *pool)
{
	for (uint32_t i = 0; i < MAX_BULLETS; ++i) {
		if (!viszero(pool->bullets[i].velocity)) {
			pool->bullets[i].position = vadd(pool->bullets[i].position, pool->bullets[i].velocity);
			if (!is_point_in_screen(pool->bullets[i].position)) {
				pool->bullets[i].velocity = vec2(0.0f, 0.0f);
				--pool->used;
				pool->index = i;
			}
		}
	}
}

void bullets_draw(const struct BulletPool *pool, SDL_Renderer *ren)
{
	uint32_t num_bullets = 0;
	SDL_Point points[MAX_BULLETS];
	for (uint32_t i = 0; i < MAX_BULLETS; ++i) {
		if (!viszero(pool->bullets[i].velocity)) {
			const vec2 v = vscale(pool->bullets[i].position, RENDER_SCALE);
			points[num_bullets].x = lroundf(v.x);
			points[num_bullets].y = lroundf(v.y);
			++num_bullets;
		}
	}
	SDL_RenderDrawPoints(ren, points, num_bullets);
}

struct KinematicBody {
	vec2 position;
	vec2 velocity;
	vec2 acceleration;
	float angle;
	float angular_velocity;
	float k_max_speed;
	float collision_radius;
	uint16_t collision_listen_mask;
	uint16_t collision_create_mask;
};

struct Player {
	struct KinematicBody body;
	vec2 direction;
	float k_acceleration;
	float k_angular_speed;
	bool can_shoot;
	bool is_thrusting;
	bool show_thrust;
	uint8_t thrust_counter;
};

#define PLAYER_RENDER_RADIUS	INVSQRT2

void player_create(struct Player *player, const vec2 position, const float update_rate)
{
	*player = (struct Player){
		.body = {
			.position = position,
			.angle = -PIOVER2,
			.collision_radius = PLAYER_RENDER_RADIUS,
			.k_max_speed = 0.375f
		},
		.direction = vec2(0.0f, -1.0f),
		.k_acceleration = 0.375f/update_rate,
		.k_angular_speed = TWOPI/update_rate,		// 1 revolution per second
		.can_shoot = true
	};
}

void player_input(struct Player *player, const Uint8 *keys)
{
	struct KinematicBody *body = &player->body;
	bool update_direction = false;
	if (keys[SDL_SCANCODE_LEFT] && !keys[SDL_SCANCODE_RIGHT]) {
		body->angular_velocity = -player->k_angular_speed;
		update_direction = true;
	} else if (keys[SDL_SCANCODE_RIGHT] && !keys[SDL_SCANCODE_LEFT]) {
		body->angular_velocity = player->k_angular_speed;
		update_direction = true;
	} else {
		body->angular_velocity = 0.0f;
	}
	if (keys[SDL_SCANCODE_UP]) {
		body->acceleration = vscale(player->direction, player->k_acceleration);
		player->is_thrusting = true;
	} else {
		body->acceleration = vec2(0.0f, 0.0f);
		player->is_thrusting = false;
	}
	if (keys[SDL_SCANCODE_Z]) {
		if (player->can_shoot) {
			// TODO
			const vec2 nose = vec2(INVSQRT2, 0.0f);	// Fire out the nose of the ship
			const vec2 pos = vadd(vcomplex(nose, player->direction), body->position);
			if (bullets_shoot(&player_bullets, pos, vadd(vscale(player->direction, 0.375f), body->velocity))) {
				// Successful fire
			}
			player->can_shoot = false;
		}
	} else {
		player->can_shoot = true;
	}
	if (update_direction) {
		player->direction.x = cosf(body->angle);
		player->direction.y = sinf(body->angle);
	}
}

void kinematic_integrate(struct KinematicBody *body)
{
	body->angle += body->angular_velocity;
	while (body->angle < 0.0f) body->angle += TWOPI;
	while (body->angle >= TWOPI) body->angle -= TWOPI;

	body->velocity = vadd(body->velocity, body->acceleration);
	if (body->velocity.x > body->k_max_speed) {
		body->velocity.x = body->k_max_speed;
	} else if (-body->velocity.x > body->k_max_speed) {
		body->velocity.x = -body->k_max_speed;
	}
	if (body->velocity.y > body->k_max_speed) {
		body->velocity.y = body->k_max_speed;
	} else if (-body->velocity.y > body->k_max_speed) {
		body->velocity.y = -body->k_max_speed;
	}
	body->position = vadd(body->position, body->velocity);
}

void kinematic_wrap(struct KinematicBody *body)
{
	while (body->position.x > SCREEN_WIDTH_F + body->collision_radius) {
		body->position.x -= SCREEN_WIDTH_F;
	}
	while (body->position.x < -body->collision_radius) {
		body->position.x += SCREEN_WIDTH_F;
	}
	while (body->position.y > SCREEN_HEIGHT_F + body->collision_radius) {
		body->position.y -= SCREEN_HEIGHT_F;
	}
	while (body->position.y < -body->collision_radius) {
		body->position.y += SCREEN_HEIGHT_F;
	}
}

/* Exact center of mass to set the origin of the player 1 - 1/sqrt(2) */
#define PLAYER_ORIGIN		0.292893219f

static const vec2 player_lines[] = {
	vec2(1.0f - PLAYER_ORIGIN,  0.0f), vec2(-0.25f - PLAYER_ORIGIN, -0.5f),
	vec2(1.0f - PLAYER_ORIGIN,  0.0f), vec2(-0.25f - PLAYER_ORIGIN,  0.5f),
	vec2(0.0f - PLAYER_ORIGIN, -0.4f), vec2( 0.0f  - PLAYER_ORIGIN,  0.4f),
	vec2(0.0f - PLAYER_ORIGIN, -0.2f), vec2(-0.75f, 0.0f),
	vec2(0.0f - PLAYER_ORIGIN,  0.2f), vec2(-0.75f, 0.0f)
};

static void player_draw(struct Player *player, SDL_Renderer *const ren)
{
	struct KinematicBody *body = &player->body;
	const int num_points = player->is_thrusting && player->show_thrust ? 10 : 6;
	for (int i = 0; i < num_points; i += 2) {
		const vec2 v1 = vscale(vadd(vcomplex(player_lines[i], player->direction), body->position), RENDER_SCALE);
		const vec2 v2 = vscale(vadd(vcomplex(player_lines[i+1], player->direction), body->position), RENDER_SCALE);
		SDL_RenderDrawLine(
			ren,
			lroundf(v1.x),
			lroundf(v1.y),
			lroundf(v2.x),
			lroundf(v2.y)
		);
	}
	if (++player->thrust_counter > 1) {
		player->thrust_counter = 0;
		player->show_thrust = !player->show_thrust;
	}
}

int main(int argc, char **argv)
{
	(void)argc;
	(void)argv;
	CHECK_SDL(SDL_Init(SDL_INIT_EVERYTHING));
	SDL_Window *win = SDL_CreateWindow(
		"Asteroids Clone",
		SDL_WINDOWPOS_CENTERED,
		SDL_WINDOWPOS_CENTERED,
		SCREEN_WIDTH,
		SCREEN_HEIGHT,
		0
	);
	if (!win) fatal_sdl();
	SDL_Renderer *ren = SDL_CreateRenderer(
		win,
		-1,
		SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC
	);
	if (!ren) fatal_sdl();

	struct Player player;
	player_create(&player, vec2(SCREEN_CENTER_X, SCREEN_CENTER_Y), 60.0f);

	SDL_Event e;
	for (;;) {
		while(SDL_PollEvent(&e)) {
			if (e.type == SDL_QUIT) goto quit;
			if (e.type == SDL_KEYDOWN &&
			    e.key.keysym.sym == SDLK_ESCAPE) {
				goto quit;
			}
		}
		const Uint8 *keys = SDL_GetKeyboardState(NULL);
		player_input(&player, keys);
		kinematic_integrate(&player.body);
		bullets_integrate(&player_bullets);
		kinematic_wrap(&player.body);
		SDL_SetRenderDrawColor(ren, 0, 0, 0, 255);
		SDL_RenderClear(ren);
		SDL_SetRenderDrawColor(ren, 255, 255, 255, 255);
		player_draw(&player, ren);
		bullets_draw(&player_bullets, ren);
		SDL_RenderPresent(ren);
	}
quit:
	SDL_DestroyRenderer(ren);
	SDL_DestroyWindow(win);
	SDL_Quit();
	return 0;
}