// Compile-only battery, built with the cross compiler so the target's 16-bit
// int is exercised. Two of this firmware's three numeric surfaces are decided
// entirely at compile time - the fan curve and the thermistor table - and the
// third, quarter-degrees to whole ones, is the arithmetic between them.

#include <cstdint>

#include "curve.hpp"
#include "thermistor.hpp"

namespace {

using app::thermistor::whole_degrees;

// Rounding to nearest, across zero. A negative quotient truncates toward zero
// in C, so a `(q + 2) / 4` reads -3.00 C as -2 and every case below the tie
// with it; the arithmetic shift floors, which is what these hold it to.
static_assert(whole_degrees(0) == 0);
static_assert(whole_degrees(1) == 0);  // +0.25
static_assert(whole_degrees(2) == 1);  // +0.50, the tie
static_assert(whole_degrees(3) == 1);  // +0.75
static_assert(whole_degrees(4) == 1);  // +1.00
static_assert(whole_degrees(-1) == 0); // -0.25
static_assert(whole_degrees(-2) == 0); // -0.50, the tie, toward zero
static_assert(whole_degrees(-3) == -1);
static_assert(whole_degrees(-4) == -1);
static_assert(whole_degrees(-12) == -3);
static_assert(whole_degrees(-160) == -40); // the table's own floor
static_assert(whole_degrees(500) == 125);  // and its ceiling

// The curve is held at zero below the temperature the fan starts at, and
// saturates inside the table's window rather than at its edge.
using app::curve::detail::duty_entry;
static_assert(duty_entry(app::curve::start_celsius - 1) == 0);
static_assert(duty_entry(app::curve::start_celsius) == 0);
static_assert(duty_entry(30) == 7);
static_assert(duty_entry(40) == 36);
static_assert(duty_entry(49) == 93);
static_assert(duty_entry(50) == 100);
static_assert(duty_entry(99) == 100);

// Monotone across the whole table: a warmer reading never asks for less air.
consteval bool curve_rises()
{
	for (std::int32_t t = 1; t < 100; ++t) {
		if (duty_entry(t) < duty_entry(t - 1)) {
			return false;
		}
	}
	return true;
}
static_assert(curve_rises());

// The thermistor table, anchored where the Beta equation fixes it rather than
// against numbers this file computed the same way: the divider reads the
// thermistor's nominal resistance at
// adc = full_scale * nominal / (series + nominal), and the equation's own
// definition puts that count at the nominal temperature.
using app::thermistor::detail::quarters_entry;

inline constexpr std::int32_t nominal_count =
    static_cast<std::int32_t>(app::thermistor::adc_full_scale * app::thermistor::nominal_resistance /
                              (app::thermistor::series_resistor + app::thermistor::nominal_resistance));
static_assert(quarters_entry(nominal_count / 4) >= 100);    // 25.00 C, in quarters
static_assert(quarters_entry(nominal_count / 4 + 1) < 100); // and the step below it

// Both clamps, at the ends the divider cannot leave.
static_assert(quarters_entry(0) == 125 * 4);
static_assert(quarters_entry(255) == -40 * 4);

// An NTC on this divider falls with the count: more counts is more resistance
// is a colder sensor, over every step of the table.
consteval bool thermistor_falls()
{
	for (std::int32_t i = 1; i < 256; ++i) {
		if (quarters_entry(i) > quarters_entry(i - 1)) {
			return false;
		}
	}
	return true;
}
static_assert(thermistor_falls());

} // namespace