module sim

pub struct SimState {
pub mut:
    position Vector3D
    velocity Vector3D
    accel    Vector3D
}

pub fn new_state(state SimState) SimState {
    return SimState{
        ...state
    }
}

pub fn (mut state SimState) satisfy_rope_constraint(params SimParams) {
    mut rope_vector := params.get_rope_vector(state)
    rope_vector = rope_vector.scale(params.rope_length / rope_vector.norm())
    state.position = vector(z: params.rope_length) + rope_vector
}

pub fn (mut state SimState) increment(delta_t f64, params SimParams) {
    // 1. add up all forces
    // 2. get an acceleration
    // 3. add to velocity
    // 4. ensure rope constraint is satisfied

    // sum up all forces
    forces_sum := params.get_forces_sum(state)

    // get the acceleration
    accel := forces_sum.scale(1.0 / params.bearing_mass)
    state.accel = accel

    // update the velocity
    state.velocity = state.velocity + accel.scale(delta_t)

    // update the position
    state.position = state.position + state.velocity.scale(delta_t)

    // ensure the position satisfies rope constraint
    state.satisfy_rope_constraint(params)
}

pub fn (state SimState) done() bool {
    return state.velocity.norm() < 0.05 && state.accel.norm() < 0.01
}