use crate::quantity::{Ohms, Volts};

/// Given the resistance of the second resistor in a resistive voltage divider, calculate the resistance of the first resistor.
pub fn solve_r1(
    voltage_src: Volts<f32>,
    voltage_read: Volts<f32>,
    r2: Ohms<f32>,
) -> Ohms<f32> {
    Ohms(r2.0 * (voltage_src.0 / voltage_read.0 - 1.0))
}

/// Given the resistance of the first resistor in a resistive voltage divider, calculate the resistance of the second resistor.
pub fn solve_r2(
    voltage_src: Volts<f32>,
    voltage_read: Volts<f32>,
    r1: Ohms<f32>,
) -> Ohms<f32> {
    Ohms((r1.0 * voltage_read.0) / (voltage_src.0 - voltage_read.0))
}

// ---------------------------------------------------------------------------------------------------------------------
// ----- Tests ------------------------
// ---------------------------------------------------------------------------------------------------------------------
#[cfg(test)]
mod tests {
    use crate::quantity::{OhmsVal, VoltsVal};
    use super::*;
    use float_cmp::assert_approx_eq;

    #[test]
    fn solve_r1_test() {
        let resistance = solve_r1(3.3.volts(), 2.0.volts(), 1_000.0.ohms());

        assert_approx_eq!(f32, 650.0, resistance.0);
    }

    #[test]
    fn solve_r2_test() {
        let resistance = solve_r2(3.3.volts(), 2.0.volts(), 1_000.0.ohms());

        assert_approx_eq!(f32, 1538.462, resistance.0);
    }
}