#include "particle.h"
#include "types.h"
#include "shader.h"

#include <stdlib.h>
#include <float.h>

void respawn_particle(struct particle *particle, struct object object, v2 offset)
{
	f32 random = ((rand() % 100) - 50) / 10.0f;
	particle->pos = addf_v2(add_v2(object.pos, offset), random);
	particle->vel = scale_v2(object.vel, 0.1f);
	random = 0.5f + ((rand() % 100) / 100.0f);
	particle->color = (v4){random, random, random, 1.0f};
	particle->life = 1.0f;
}

i32 find_unused_particle(struct particle_generator generator)
{
	f32 min = FLT_MAX;
	i32 mini = 0;
	for (i32 i = 0; i < MAX_PARTICLES; i++) {
		f32 life = generator.particles[i].life;
		if (life <= 0.0f) {
			return i;
		} else if (life < min) {
			min = life;
			mini = i;
		}
	}
	return mini;
}

struct particle_generator init_generator(i32 new, u32 shader, u32 texture)
{
	struct particle_generator generator = {0};
	reset_particles(&generator);
	generator.new = new;
	generator.shader = shader;
	generator.texture = texture;
	f32 vertices[] = {
		0.0f, 0.0f, 0.0f, 0.0f,
		1.0f, 0.0f, 1.0f, 0.0f,
		0.0f, 1.0f, 0.0f, 1.0f,

		1.0f, 0.0f, 1.0f, 0.0f,
		1.0f, 1.0f, 1.0f, 1.0f,
		0.0f, 1.0f, 0.0f, 1.0f
	};
	u32 vao, vbo;
	glGenVertexArrays(1, &vao);
	glGenBuffers(1, &vbo);
	glBindBuffer(GL_ARRAY_BUFFER, vbo);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
	glBindVertexArray(vao);
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 4, GL_FLOAT, 0, 4 * sizeof(f32), 0);
	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindVertexArray(0);
	generator.vao = vao;
	return generator;
}

void update_particles(struct particle_generator *generator, struct object object, f32 dt, v2 offset)
{
	for (i32 i = 0; i < generator->new; i++) {
		i32 unused = find_unused_particle(*generator);
		respawn_particle(generator->particles + unused, object, offset);
	}
	for (i32 i = 0; i < MAX_PARTICLES; i++) {
		struct particle *particle = generator->particles + i;
		particle->life -= dt;
		if (particle->life > 0.0f) {
			particle->pos = sub_v2(particle->pos, scale_v2(particle->vel, dt));
			particle->color.w -= dt * 2.0f;
		}
	}
}

void render_particles(struct particle_generator generator)
{
	glBlendFunc(GL_SRC_ALPHA, GL_ONE);
	glUseProgram(generator.shader);
	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, generator.texture);
	glBindVertexArray(generator.vao);
	for (i32 i = 0; i < MAX_PARTICLES; i++) {
		struct particle *particle = generator.particles + i;
		if (particle->life > 0.0f) {
			uniform_v2(generator.shader, "offset", particle->pos);
			uniform_v4(generator.shader, "color", particle->color);
			glDrawArrays(GL_TRIANGLES, 0, 6);
		}
	}
	glBindVertexArray(0);
	glUseProgram(0);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}
	
void reset_particles(struct particle_generator *generator)
{
	for (i32 i = 0; i < MAX_PARTICLES; i++)
		generator->particles[i] = (struct particle)default_particle;
}