// Mostly stolen from SebLague's plane game
// thanks

use log::debug;
use nalgebra::{vector, Vector2};
use crate::orbit::newtonian::solve_kepler_with_newtonian;
use crate::orbit::vis_viva::vis_viva;
use crate::planet::GRAVITY;

pub fn calculate_vector_of_orbit(periapsis: f64, apoapsis: f64, t: f64, mass_of_bigger: f64, current_x_vel: f64, current_y_vel: f64, delta_t: f64, mass_of_orbiter: f64) -> Vector2<f64> {
    let semi_major_length = (apoapsis + periapsis) / 2.0;
    let linear_eccentricity = semi_major_length - periapsis; // distance between center and focus

    let distances = calculate_point_on_orbit(periapsis, apoapsis, t);
    let distance_x = distances[0];
    let distance_y = distances[1];

    let distance = (distance_x * distance_x + distance_y * distance_y).sqrt();

    let velocity = vis_viva(distance, semi_major_length, GRAVITY, mass_of_bigger);

    let ellipse_center_x = -linear_eccentricity;
    let ellipse_center_y = apoapsis - semi_major_length;

    let theta = (ellipse_center_x / ellipse_center_y).atan() - std::f64::consts::PI / 2.0;

    let x_vel = velocity * theta.sin();
    let y_vel = velocity * theta.cos();

    let x_accel = current_x_vel - x_vel / delta_t;
    let y_accel = current_y_vel - y_vel / delta_t;

    let x_force = mass_of_orbiter * x_accel;
    let y_force = mass_of_orbiter * y_accel;

    vector![x_force, y_force]
}

pub fn calculate_point_on_orbit(periapsis: f64, apoapsis: f64, t: f64) -> Vector2<f64> {
    let semi_major_length = (apoapsis + periapsis) / 2.0;
    let linear_eccentricity = semi_major_length - periapsis; // distance between center and focus
    let eccentricity = linear_eccentricity / semi_major_length; // 0: circle. 1: parabola. in between: ellipse
    let semi_minor_length = (semi_major_length * semi_major_length - linear_eccentricity * linear_eccentricity).sqrt();

    let mean_anomaly = t * std::f64::consts::PI * 2.0;
    let eccentric_anomaly = solve_kepler_with_newtonian(mean_anomaly, eccentricity, 100);

    let ellipse_center_x = -linear_eccentricity;
    let point_x = eccentric_anomaly.cos() * semi_major_length + ellipse_center_x;
    let point_y = eccentric_anomaly.sin() * semi_minor_length;

    vector![point_x, point_y]
}

pub fn calculate_world_position_of_orbit(point: Vector2<f64>, orbiting_on: Vector2<f64>) -> Vector2<f64> {
    // i have no idea if this is actually right or not
    // we'll find out
    vector![point[0] + orbiting_on[0], point[1] + orbiting_on[1]]
}