#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <math.h>
#include "display.h"

#define W 800
#define H 600

#ifndef PLATFORM_WEB
  #define FPS 120
#else
  #define FPS 60
#endif

#define SCALE 800
#define CYCLES 5

#define RFPS 1/FPS
#define PI 3.141592654
#define g -9.81f * SCALE

float s = 25;   // starting agnle
float l = 0.5;  // lenght
float m = 0.01; // mass in kg

float t;
float v;
float a;

float secs = 0.0f;
int swings = 2 * CYCLES;

int has_reached_starting_amp(float old_t)
{
    if(swings % 2 == 0 && t < 0) {
        if(old_t < t) return 1;
    } else if(swings % 2 == 1 && t > 0) {
        if(old_t > t) return 1;
    } return 0;
}

void update()
{
    if(secs == 0.0f) {
        printf("\nStarting angle: %f", s/(PI/180));
        printf("\nLenght:         %f", l/SCALE);
        printf("\nMass:           %f\n", m/SCALE);
    }

    float old_t = t;
    a = (g/l) * sinf(t);
    v += a * RFPS;
    t += v * RFPS;

    if(has_reached_starting_amp(old_t)) {
        swings += 1;
    }
    if(swings >= 2 * CYCLES) {
        printf("period: %f\n", secs/CYCLES);
        secs = 0.0f;
        swings = 0;
    }

    secs += (float)RFPS;

    float px = sinf(t) * l;
    float py = cosf(t) * l;
    dspl_draw_line(px, py, 0, 0, 0);
    dspl_draw_circle(px, py, m);
}

int main(int argc, char **argv)
{
    if(argc != 1 && argc != 4) {
        puts("Please provide either 0 or 3 arguments:\n\t1st is starting angle in degrees\n\t2nd is lenght in meters\n\t3rd is mass in kilograms");
        return 1;
    }

    float arg_s = strtof(argv[1], NULL);
    float arg_l = strtof(argv[2], NULL);
    float arg_m = strtof(argv[3], NULL);

    s = ((arg_s == 0.0f) ? s : arg_s) * PI/180;
    l = ((arg_l == 0.0f) ? l : arg_l) * SCALE;
    m = ((arg_m == 0.0f) ? m : arg_m) * SCALE;

    t = s;
    v = 0;
    a = 0;

    dspl_createinfo info = {0};
    info.width = W;
    info.height = H;
    info.name = "Pendulum";
    info.fps = FPS;
    info.update_func = &update;

    dspl_create(info);
    dspl_start();
    dspl_destroy();
    return 0;
}