// Package dht provides a driver for DHTXX family temperature and humidity sensors.
//
// [1] Datasheet DHT11: https://www.mouser.com/datasheet/2/758/DHT11-Technical-Data-Sheet-Translated-Version-1143054.pdf
// [2] Datasheet DHT22: https://cdn-shop.adafruit.com/datasheets/Digital+humidity+and+temperature+sensor+AM2302.pdf
// Adafruit C++ driver: https://github.com/adafruit/DHT-sensor-library

package dht // import "tinygo.org/x/drivers/dht"

import (
	"encoding/binary"
	"machine"
	"time"
)

// enum type for device type
type DeviceType uint8

// DeviceType specific parsing of information received from the sensor
func (d DeviceType) extractData(buf []byte) (temp int16, hum uint16) {
	if d == DHT11 {
		temp = int16(buf[2])
		if buf[3]&0x80 > 0 {
			temp = -1 - temp
		}
		temp *= 10
		temp += int16(buf[3] & 0x0f)
		hum = 10*uint16(buf[0]) + uint16(buf[1])
	} else {
		hum = binary.LittleEndian.Uint16(buf[0:2])
		temp = int16(buf[3])<<8 + int16(buf[2]&0x7f)
		if buf[2]&0x80 > 0 {
			temp = -temp
		}
	}
	return
}

// All functions return ErrorCode instance as error. This class can be used for more efficient error processing
type ErrorCode uint8

const (
	startTimeout = time.Millisecond * 200
	startingLow  = time.Millisecond * 20

	DHT11 DeviceType = iota
	DHT22

	ChecksumError ErrorCode = iota
	NoSignalError
	NoDataError
	UpdateError
	UninitializedDataError
)

// error interface implementation for ErrorCode
func (e ErrorCode) Error() string {
	switch e {
	case ChecksumError:
		// DHT returns ChecksumError if all the data from the sensor was received, but the checksum does not match.
		return "checksum mismatch"
	case NoSignalError:
		// DHT returns NoSignalError if there was no reply from the sensor. Check sensor connection or the correct pin
		// sis chosen,
		return "no signal"
	case NoDataError:
		// DHT returns NoDataError if the connection was successfully initialized, but not all 40 bits from
		// the sensor is received
		return "no data"
	case UpdateError:
		// DHT returns UpdateError if ReadMeasurements function is called before time specified in UpdatePolicy or
		// less than 2 seconds after past measurement
		return "cannot update now"
	case UninitializedDataError:
		// DHT returns UninitializedDataError if user attempts to access data before first measurement
		return "no measurements done"
	}
	// should never be reached
	return "unknown error"
}

// Update policy of the DHT device. UpdateTime cannot be shorter than 2 seconds. According to dht specification sensor
// will return undefined data if update requested less than 2 seconds before last usage
type UpdatePolicy struct {
	UpdateTime          time.Duration
	UpdateAutomatically bool
}

var (
	// timeout counter equal to number of ticks per 1 millisecond
	timeout counter
)

func init() {
	timeout = cyclesPerMillisecond()
}

func cyclesPerMillisecond() counter {
	freq := machine.CPUFrequency()
	freq /= 1000
	return counter(freq)
}