/* Snowstorm - Particle effects in C
 *
 * Copyright (c) 2021 Evan Hemsley
 *
 * This software is provided 'as-is', without any express or implied warranty.
 * In no event will the authors be held liable for any damages arising from
 * the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not
 * claim that you wrote the original software. If you use this software in a
 * product, an acknowledgment in the product documentation would be
 * appreciated but is not required.
 *
 * 2. Altered source versions must be plainly marked as such, and must not be
 * misrepresented as being the original software.
 *
 * 3. This notice may not be removed or altered from any source distribution.
 *
 * Evan "cosmonaut" Hemsley <evan@moonside.games>
 *
 */

#include "Snowstorm.h"

#include <stdlib.h>
#include <time.h>

typedef struct Snowstorm_Vector2
{
	float x;
	float y;
} Snowstorm_Vector2;

static inline Snowstorm_Vector2 Vector2_Rotate(Snowstorm_Vector2 vector, float angle)
{
	Snowstorm_Vector2 rotated;
	rotated.x = vector.x * cosf(angle) - vector.y * sinf(angle);
	rotated.y = vector.x * sinf(angle) + vector.y * cosf(angle);
	return rotated;
}

static inline float Vector2_Magnitude(Snowstorm_Vector2 vector)
{
	return sqrtf(vector.x * vector.x + vector.y * vector.y);
}

static inline Snowstorm_Vector2 Vector2_Normalize(Snowstorm_Vector2 vector)
{
	float length = Vector2_Magnitude(vector);

	Snowstorm_Vector2 normalized;
	normalized.x = vector.x / length;
	normalized.y = vector.y / length;

	return normalized;
}

typedef struct Snowstorm_Particle
{
	float time;
	Snowstorm_Vector2 position;
	Snowstorm_Vector2 velocity;
	Snowstorm_Vector2 scale;
	float size;
	float rotation;
	float spin;

	float directionVariance;
	float speedVariance;
	Snowstorm_Vector2 catchup;
} Snowstorm_Particle;

typedef struct Snowstorm_Context
{
	Snowstorm_Particle** particles;
	uint32_t particleCount;

	Snowstorm_Vector2 wind;

	float directionChaos;
	float speedChaos;

	float leftBound;
	float topBound;
	float rightBound;
	float bottomBound;
} Snowstorm_Context;

static Snowstorm_Context* context = NULL;

static inline float Approach(float value, float target, float maxChange)
{
	return value + min(max(target - value, -maxChange), maxChange);
}

static inline float WrapWithOvershoot(float value, float min, float max)
{
	if (value < min)
	{
		value = max - (min - value);
	}
	if (value > max)
	{
		value = min + (value - max);
	}
	return value;
}

static inline float Random(float a)
{
	return (float)rand() / (float)(RAND_MAX / a);
}

static inline float RandomRange(float min, float max)
{
	return Random(max - min) + min;
}

void Snowstorm_Init()
{
	srand((unsigned int)time(NULL));

	context = malloc(sizeof(Snowstorm_Context));

	context->particles = NULL;
	context->particleCount = 0;

	context->leftBound = -10;
	context->rightBound = 490;
	context->topBound = -10;
	context->bottomBound = 280;

	context->wind.x = 0;
	context->wind.y = 0;

	context->directionChaos = 0;
	context->speedChaos = 0;
}

void Snowstorm_Update(double delta)
{
	uint32_t i;
	Snowstorm_Particle* particle = NULL;

	float deltaTime = (float)delta;

	for (i = 0; i < context->particleCount; i += 1)
	{
		particle = context->particles[i];

		if (particle != NULL)
		{
			particle->time += deltaTime;

			float speed = Vector2_Magnitude(particle->velocity);
			float rotation = sinf(particle->time / (speed * 100)) * particle->directionVariance;

			float windSpeed = Vector2_Magnitude(context->wind);
			Snowstorm_Vector2 wind = Vector2_Normalize(context->wind);
			wind.x *= (windSpeed + particle->speedVariance);
			wind.y *= (windSpeed + particle->speedVariance);

			wind = Vector2_Rotate(wind, rotation);

			particle->velocity.x = Approach(particle->velocity.x, wind.x, particle->catchup.x);
			particle->velocity.y = Approach(particle->velocity.y, wind.y, particle->catchup.y);

			particle->position.x = WrapWithOvershoot(particle->position.x + particle->velocity.x, context->leftBound, context->rightBound);
			particle->position.y = WrapWithOvershoot(particle->position.y + particle->velocity.y, context->topBound, context->bottomBound);

			particle->scale.y = particle->size * sinf(particle->time / 10);

			particle->rotation += particle->spin;
		}
	}
}

void Snowstorm_ApplyWind(double xSpeed, double ySpeed)
{
	uint32_t i;
	Snowstorm_Particle* particle;

	for (i = 0; i < context->particleCount; i += 1)
	{
		particle = context->particles[i];

		if (particle != NULL)
		{
			particle->directionVariance = RandomRange(-context->directionChaos, context->directionChaos);
			particle->speedVariance = RandomRange(-context->speedChaos, context->speedChaos);
		}
	}

	context->wind.x = (float)xSpeed;
	context->wind.y = (float)ySpeed;
}