plug_battery_windows.cpp

#include <iostream>
#include <stdio.h>   // snprintf
#include <windows.h>

/// @example Termux Battery Info JSON Format
/// health      - "COLD" | "DEAD" | "GOOD" | "OVERHEAT" | "OVER_VOLTAGE" |
///		  "UNKNOWN" | "UNSPECIFIED_FAILURE" | integer
/// percentage  - integer
/// plugged     - "UNPLUGGED" | "PLUGGED_AC" | "PLUGGED_USB" |
///               "PLUGGED_WIRELESS" | "PLUGGED_".integer
/// status      - "CHARGING" | "DISCHARGING" | "FULL" | "NOT_CHARGING" |
///               "UNKNOWN"
/// temperature - integer. 

/// @group JSON Serialize functions
/// @{

/// @brief All Windows flags.
/// @see https://docs.microsoft.com/en-gb/windows/desktop/api/winbase/ns-winbase-_system_power_status
enum battery_flags {
	battery_flag_charge_status_high     = 0x1,
	battery_flag_charge_status_low      = 0x2,
	battery_flag_status_critical        = 0x4,
	battery_flag_charge_status_charging = 0x8,
	battery_flag_no_battery             = 0x80,
	battery_flag_unknown_status         = 0xff
};

/// @brief simple struct for easy printing to avoid the C++17 variants.
struct variant_for_poormen { 
	union {
		const char *str;
		int number;
	};
	bool is_string;
};

std::ostream &operator <<(std::ostream &os, const variant_for_poormen &var)
{
	if (var.is_string) {
		os << var.str;
	} else {
		os << var.number;
	}
	return os;
}

#define CHECK_FLAG(value, flag) ( ((value) & (flag)) == (flag) )

const char *getHealthString(SYSTEM_POWER_STATUS &status)
{
	auto battery_flag = status.BatteryFlag;
	if (CHECK_FLAG(battery_flag, battery_flag_unknown_status)) {
		// we could return "UNKNOWN", but we will use it for no_battery flag.
		return "UNSPECIFIED_FAILURE";
	}

	if (CHECK_FLAG(battery_flag, battery_flag_status_critical)) {
		return "DEAD";
	}

	if (CHECK_FLAG(battery_flag, battery_flag_no_battery)) {
		return "UNKNOWN";
	}

	return "GOOD";
}

size_t getPercentageNumber(SYSTEM_POWER_STATUS &status)
{
	return status.BatteryLifePercent;
}

const char *getPluggedString(SYSTEM_POWER_STATUS &status)
{
	// Windows can't say us which kind of AC charge it used, so return PLUGGED_AC.
	// Assume that 255 (unknown status) is "UNPLUGGED".
	return status.ACLineStatus == 1 ? "PLUGGED_AC" : "UNPLUGGED";
}

const char *getStatusString(SYSTEM_POWER_STATUS &status)
{
	auto battery_flag = status.BatteryFlag;
	if (CHECK_FLAG(battery_flag, battery_flag_unknown_status)) {
		return "UNKNOWN";
	}
	if (CHECK_FLAG(battery_flag, battery_flag_charge_status_charging)) {
		return "CHARGING";
	}
	if (status.BatteryLifePercent == 100) {
		return "FULL";
	}
	if (status.ACLineStatus == 1) {
		return "NOT_CHARGING";
	}
	return "DISCHARGING";
}

size_t getTemperatureNumber(SYSTEM_POWER_STATUS &status)
{
	// this API does not support temperature, we should send ioctl to device
	// for getting its temperature. it's in TODO.
	return 0;
}

/// @}

/// @brief Flushes battery info in Termux-compatible JSON format.
// 
int main()
{
	struct json_power_entry {
		const char *key;
		const char *(*value_str)(SYSTEM_POWER_STATUS&);
		size_t (*value_number)(SYSTEM_POWER_STATUS&);
	};
	SYSTEM_POWER_STATUS status;
	BOOL result = GetSystemPowerStatus(&status);
	if (!result) {
		return 1;
	}

	const json_power_entry serialize_entries[] = {
		{ "health"     , getHealthString               },
		{ "percentage" , nullptr, getPercentageNumber  },
		{ "plugged"    , getPluggedString              },
		{ "status"     , getStatusString               },
		{ "temperature", nullptr, getTemperatureNumber }
	};

	char delims[3] = "{\n";
	for (auto &entry : serialize_entries) {
		std::cout << delims;
		delims[0] = ','; // replace to comma for next line delim
		std::cout << "\t\"" << entry.key << "\": ";
		if (entry.value_str) {
			std::cout << "\"" << entry.value_str(status) << "\"";
		} else {
			std::cout << entry.value_number(status);
		}
	}
	std::cout << "\n}";
	return 0;
}