/* SPDX-License-Identifier: MIT */
/*
 * konparticles.c
 *
 * Copyright (c) 2026 KonAki
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "konparticles.h"

#include <math.h>
#include <string.h>

/*** random numbers ***/

static uint32_t next(kon_particles_t *ps)
{
	uint32_t x = ps->seed;

	x ^= x << 13;
	x ^= x >> 17;
	x ^= x << 5;
	ps->seed = x;
	return x;
}

/* 0 up to but not including 1 */
static float unit(kon_particles_t *ps)
{
	return (float)(next(ps) >> 8) * (1.0f / 16777216.0f);
}

static float between(kon_particles_t *ps, float a, float b)
{
	return a + (b - a) * unit(ps);
}

/* a number that cannot upset the maths below */
static float number(float v)
{
	return v == v && v - v == 0.0f ? v : 0.0f;
}

/*** particles ***/

void kon_particlesInit(kon_particles_t *ps, kon_particle_t *pool, int capacity, uint32_t seed)
{
	kon_particles_t zero = {0};
	int i;

	*ps = zero;
	ps->pool = pool;
	ps->capacity = pool && capacity > 0 ? capacity : 0;
	for (i = 0; i < ps->capacity; i++) memset(&pool[i], 0, sizeof pool[i]);
	ps->seed = seed ? seed : 0x9E3779B9u;
	ps->speedMin = ps->speedMax = 20.0f;
	ps->lifeMin = ps->lifeMax = 1.0f;
	ps->size0 = ps->size1 = 1.0f;
	ps->color0 = ps->color1 = 0xFFE4DDF0u;
	ps->blend = KON_BLEND_NORMAL;
}

static int spawn(kon_particles_t *ps)
{
	int i;

	for (i = 0; i < ps->capacity; i++) {
		kon_particle_t *p = &ps->pool[i];
		float angle, speed, life;

		if (p->life > 0.0f) continue;
		life = between(ps, number(ps->lifeMin), number(ps->lifeMax));
		if (!(life > 0.0f)) return 0;
		angle = number(ps->angle) + between(ps, -number(ps->spread), number(ps->spread));
		speed = between(ps, number(ps->speedMin), number(ps->speedMax));
		p->x = number(ps->x) + unit(ps) * number(ps->width);
		p->y = number(ps->y) + unit(ps) * number(ps->height);
		p->vx = cosf(angle) * speed;
		p->vy = sinf(angle) * speed;
		p->age = 0.0f;
		p->life = life;
		p->size0 = number(ps->size0);
		p->size1 = number(ps->size1);
		p->color0 = ps->color0;
		p->color1 = ps->color1;
		return 1;
	}
	return 0;
}

int kon_particlesBurst(kon_particles_t *ps, int count)
{
	int made = 0;

	while (made < count && spawn(ps)) made++;
	return made;
}

void kon_particlesUpdate(kon_particles_t *ps, float dt)
{
	int i;

	if (!(dt > 0.0f)) return;
	if (dt > 0.25f) dt = 0.25f;

	for (i = 0; i < ps->capacity; i++) {
		kon_particle_t *p = &ps->pool[i];

		if (!(p->life > 0.0f)) continue;
		p->vx += number(ps->ax) * dt;
		p->vy += number(ps->ay) * dt;
		p->x += p->vx * dt;
		p->y += p->vy * dt;
		p->age += dt;
		if (p->age >= p->life) p->life = 0.0f;
		if (ps->area.w > 0 && ps->area.h > 0 && (p->x < (float)ps->area.x || p->y < (float)ps->area.y ||
		    p->x >= (float)(ps->area.x + ps->area.w) || p->y >= (float)(ps->area.y + ps->area.h)))
			p->life = 0.0f;
	}

	if (number(ps->rate) > 0.0f) {
		ps->carry += number(ps->rate) * dt;
		while (ps->carry >= 1.0f) {
			ps->carry -= 1.0f;
			if (!spawn(ps)) {
				ps->carry = 0.0f;
				break;
			}
		}
	}
}

int kon_particlesCount(const kon_particles_t *ps)
{
	int i, n = 0;

	for (i = 0; i < ps->capacity; i++) {
		if (ps->pool[i].life > 0.0f) n++;
	}
	return n;
}

void kon_particlesClear(kon_particles_t *ps)
{
	int i;

	for (i = 0; i < ps->capacity; i++) ps->pool[i].life = 0.0f;
	ps->carry = 0.0f;
}

/*** drawing ***/

static uint32_t mix(uint32_t a, uint32_t b, float t)
{
	uint32_t out = 0;
	int shift;

	for (shift = 0; shift < 32; shift += 8) {
		float ca = (float)((a >> shift) & 0xFF), cb = (float)((b >> shift) & 0xFF);
		int v = (int)(ca + (cb - ca) * t + 0.5f);

		if (v < 0) v = 0;
		if (v > 255) v = 255;
		out |= (uint32_t)v << shift;
	}
	return out;
}

void kon_particlesDraw(const kon_particles_t *ps, kon_framebuffer_t *fb, int offsetX, int offsetY)
{
	static uint32_t white = 0xFFFFFFFFu;
	kon_framebuffer_t speck;
	const kon_image *image = ps->image;
	kon_rect_t src = {0, 0, 1, 1};
	int i;

	if (!fb) return;
	speck.width = speck.height = 1;
	speck.data = &white;
	speck.depth = NULL;
	if (image) {
		src = ps->src;
		if (src.w <= 0 || src.h <= 0) src = KON_RECT(0, 0, image->width, image->height);
		if (src.w <= 0 || src.h <= 0) return;
	} else {
		image = &speck;
	}

	for (i = 0; i < ps->capacity; i++) {
		const kon_particle_t *p = &ps->pool[i];
		float t, size, length, angle = 0.0f;

		if (!(p->life > 0.0f)) continue;
		t = p->age / p->life;
		if (t > 1.0f) t = 1.0f;
		size = p->size0 + (p->size1 - p->size0) * t;
		if (!(size > 1.0f)) size = 1.0f;
		length = size;
		if (!ps->image && number(ps->stretch) > 0.0f) {
			float speed = sqrtf(p->vx * p->vx + p->vy * p->vy);

			if (speed > 0.0f) {
				length = speed * ps->stretch;
				if (length < size) length = size;
				angle = atan2f(p->vy, p->vx);
			}
		}
		kon_drawImageBlend(fb, image, src, p->x + (float)offsetX + 0.5f, p->y + (float)offsetY + 0.5f,
		    (float)src.w * 0.5f, (float)src.h * 0.5f,
		    ps->image ? size / (float)src.w : length, ps->image ? size / (float)src.w : size, angle,
		    KON_FILTER_NEAREST, mix(p->color0, p->color1, t), ps->blend);
	}
}

/*** weather ***/

static void weatherBase(kon_particles_t *ps, int viewWidth, int viewHeight, int power)
{
	if (viewWidth < 0) viewWidth = 0;
	if (viewHeight < 0) viewHeight = 0;
	if (viewWidth > 16384) viewWidth = 16384;
	if (viewHeight > 16384) viewHeight = 16384;
	if (power < 1) power = 1;
	if (power > 9) power = 9;
	ps->rate = (float)power * (float)viewWidth * (float)viewHeight / 1800.0f;
	ps->image = NULL;
	ps->blend = KON_BLEND_NORMAL;
	ps->ax = ps->ay = 0.0f;
	ps->height = 0.0f;
	ps->area = KON_RECT(-96, -64, viewWidth + 192, viewHeight + 128);
}

void kon_weatherRain(kon_particles_t *ps, int viewWidth, int viewHeight, int power)
{
	viewWidth = viewWidth < 0 ? 0 : viewWidth > 16384 ? 16384 : viewWidth;
	viewHeight = viewHeight < 0 ? 0 : viewHeight > 16384 ? 16384 : viewHeight;
	float speed = 420.0f, margin = 24.0f;

	weatherBase(ps, viewWidth, viewHeight, power);
	ps->x = -margin;
	ps->width = (float)viewWidth + margin * 2.0f;
	ps->y = -16.0f;
	ps->angle = 1.35f; /* leaning a little with the wind */
	ps->spread = 0.03f;
	ps->speedMin = speed * 0.9f;
	ps->speedMax = speed * 1.1f;
	ps->lifeMin = ((float)viewHeight + 32.0f) / (speed * 1.1f);
	ps->lifeMax = ((float)viewHeight + 32.0f) / (speed * 0.9f);
	ps->size0 = ps->size1 = 1.0f;
	ps->color0 = ps->color1 = 0xA0B8C8E0u;
	ps->stretch = 0.035f;
}

void kon_weatherSnow(kon_particles_t *ps, int viewWidth, int viewHeight, int power)
{
	viewWidth = viewWidth < 0 ? 0 : viewWidth > 16384 ? 16384 : viewWidth;
	viewHeight = viewHeight < 0 ? 0 : viewHeight > 16384 ? 16384 : viewHeight;
	float speed = 36.0f, margin = 24.0f;

	weatherBase(ps, viewWidth, viewHeight, power);
	ps->rate *= 0.5f;
	ps->x = -margin;
	ps->width = (float)viewWidth + margin * 2.0f;
	ps->y = -8.0f;
	ps->angle = 1.5708f;
	ps->spread = 0.5f;
	ps->speedMin = speed * 0.6f;
	ps->speedMax = speed * 1.4f;
	ps->lifeMin = ((float)viewHeight + 16.0f) / (speed * 1.4f);
	ps->lifeMax = ((float)viewHeight + 16.0f) / (speed * 0.6f);
	ps->size0 = 2.0f;
	ps->size1 = 1.0f;
	ps->color0 = 0xF0E4DDF0u;
	ps->color1 = 0xC0E4DDF0u;
	ps->stretch = 0.0f;
}

void kon_weatherStorm(kon_particles_t *ps, int viewWidth, int viewHeight, int power)
{
	viewWidth = viewWidth < 0 ? 0 : viewWidth > 16384 ? 16384 : viewWidth;
	viewHeight = viewHeight < 0 ? 0 : viewHeight > 16384 ? 16384 : viewHeight;
	kon_weatherRain(ps, viewWidth, viewHeight, power);
	ps->rate *= 1.6f;
	ps->angle = 1.15f;
	ps->speedMin = 520.0f;
	ps->speedMax = 640.0f;
	ps->lifeMin = ((float)viewHeight + 32.0f) / 640.0f;
	ps->lifeMax = ((float)viewHeight + 32.0f) / 520.0f;
	ps->x = -(float)viewHeight * 0.5f;
	ps->width = (float)viewWidth + (float)viewHeight;
	ps->stretch = 0.045f;
	ps->area = KON_RECT(-viewHeight - 32, -64, viewWidth + viewHeight * 2 + 64, viewHeight + 128);
}