// Copyright 2018 The Periph Authors. All rights reserved.
// Use of this source code is governed under the Apache License, Version 2.0
// that can be found in the LICENSE file.

package as7262

import (
	"context"
	"encoding/binary"
	"errors"
	"fmt"
	"math"
	"sync"
	"time"

	"periph.io/x/conn/v3"
	"periph.io/x/conn/v3/gpio"
	"periph.io/x/conn/v3/i2c"
	"periph.io/x/conn/v3/physic"
)

// Opts holds the configuration options.
type Opts struct {
	InterruptPin gpio.PinIn
	Gain         Gain
}

// DefaultOpts are the recommended default options.
var DefaultOpts = Opts{
	InterruptPin: nil,
	Gain:         G1x,
}

// New opens a handle to an AS7262 sensor.
func New(bus i2c.Bus, opts *Opts) (*Dev, error) {
	// The nil or zero values for gain and interrupt are valid
	c := make(chan struct{})
	close(c)
	return &Dev{
		c:         &i2c.Dev{Bus: bus, Addr: 0x49},
		gain:      opts.Gain,
		interrupt: opts.InterruptPin,
		cancel:    func() {},
		done:      c,
	}, nil
}

var sensorTimeout = 200 * time.Millisecond

// waitForSensor is overridden in tests.
var waitForSensor = time.After

// Dev is a handle to the as7262 sensor.
type Dev struct {
	c         conn.Conn
	interrupt gpio.PinIn

	// Mutable
	mu   sync.Mutex
	gain Gain

	// cancelMu guards cancel and done.
	cancelMu sync.Mutex
	cancel   context.CancelFunc
	done     chan struct{}
}

// Spectrum is the reading from the sensor including the actual sensor state for
// the readings.
type Spectrum struct {
	Bands             []Band
	SensorTemperature physic.Temperature
	Gain              Gain
	LedDrive          physic.ElectricCurrent
	Integration       time.Duration
}

func (s Spectrum) String() string {
	str := fmt.Sprintf("Spectrum: Gain:%s, Led Drive %s, Sense Time: %s", s.Gain, s.LedDrive, s.Integration)
	for _, band := range s.Bands {
		str += "\n" + band.String()
	}
	return str
}

// Band has two types of measurement of relative spectral flux density.
//
// Value
//
// Value are the calibrated readings. The accuracy of the channel counts/μW/cm2
// is ±12%.
//
// Counts
//
// Counts are the raw readings, there are approximately 45 counts/μW/cm2 with a
// gain of 16 (Gx16).
//
// Wavelength
//
// Wavelength is the nominal center of a band, with a ±40nm bandwidth around the
// center. Wavelengths for the as7262 are: 450nm, 500nm, 550nm, 570nm, 600nm and
// 650nm.
type Band struct {
	Wavelength physic.Distance
	Value      float64
	Counts     uint16
	Name       string
}

func (b Band) String() string {
	return fmt.Sprintf("%s Band(%s) %7.1f counts", b.Name, b.Wavelength, b.Value)
}

// Sense preforms a reading of relative spectral radiance of all the sensor
// bands.
//
// Led Drive Current
//
// The AS7262 provides a current-limited integrated led drive circuit. Valid
// limits for the drive current are 0mA, 12.5mA, 25mA, 50mA and 100mA. If non
// valid values are given the next lowest valid value is used.
//
// Resolution
//
// For best resolution it is recommended that for a specific led drive
// current that the senseTime or gain is increased until at least one of the
// bands returns a count above 10000. The maximum senseTime time is 714ms
// senseTime will be quantised into intervals of of 2.8ms. Actual time taken to
// make a reading is twice the senseTime.
func (d *Dev) Sense(ledDrive physic.ElectricCurrent, senseTime time.Duration) (Spectrum, error) {

	d.mu.Lock()

	it, integration := calcSenseTime(senseTime)
	ctx, cancel := context.WithCancel(context.Background())
	d.cancelMu.Lock()
	d.cancel = cancel
	d.done = make(chan struct{})
	d.cancelMu.Unlock()

	defer func() {
		close(d.done)
		d.cancel()
		d.mu.Unlock()
	}()

	if err := d.writeVirtualRegister(ctx, integrationReg, it); err != nil {
		return Spectrum{}, err
	}
	led, drive := calcLed(ledDrive)

	if err := d.writeVirtualRegister(ctx, ledControlReg, led); err != nil {
		return Spectrum{}, err
	}

	if err := d.writeVirtualRegister(ctx, controlReg, allOneShot|uint8(d.gain)); err != nil {
		return Spectrum{}, err
	}

	if d.interrupt != nil {
		isEdge := make(chan bool)
		go func() {
			// TODO(NeuralSpaz): Test on hardware.
			isEdge <- d.interrupt.WaitForEdge(integration*2 + sensorTimeout)
		}()
		select {
		case edge := <-isEdge:
			if !edge {
				return Spectrum{}, errPinTimeout
			}
		case <-ctx.Done():
			return Spectrum{}, errHalted
		}
	} else {
		select {
		// WaitForSensor is time.After().
		case <-waitForSensor(integration * 2):
			if err := d.pollDataReady(ctx); err != nil {
				return Spectrum{}, err
			}
		case <-ctx.Done():
			return Spectrum{}, errHalted
		}

	}

	if err := d.writeVirtualRegister(ctx, ledControlReg, 0x00); err != nil {
		return Spectrum{}, err
	}

	raw := make([]byte, 12)
	if err := d.readVirtualRegister(ctx, rawBase, raw); err != nil {
		return Spectrum{}, err
	}

	cal := make([]byte, 24)
	if err := d.readVirtualRegister(ctx, calBase, cal); err != nil {
		return Spectrum{}, err
	}

	v := binary.BigEndian.Uint16(raw[0:2])
	b := binary.BigEndian.Uint16(raw[2:4])
	g := binary.BigEndian.Uint16(raw[4:6])
	y := binary.BigEndian.Uint16(raw[6:8])
	o := binary.BigEndian.Uint16(raw[8:10])
	r := binary.BigEndian.Uint16(raw[10:12])

	vcal := float64(math.Float32frombits(binary.BigEndian.Uint32(cal[0:4])))
	bcal := float64(math.Float32frombits(binary.BigEndian.Uint32(cal[4:8])))
	gcal := float64(math.Float32frombits(binary.BigEndian.Uint32(cal[8:12])))
	ycal := float64(math.Float32frombits(binary.BigEndian.Uint32(cal[12:16])))
	ocal := float64(math.Float32frombits(binary.BigEndian.Uint32(cal[16:20])))
	rcal := float64(math.Float32frombits(binary.BigEndian.Uint32(cal[20:24])))

	traw := make([]byte, 1)
	if err := d.readVirtualRegister(ctx, deviceTemperatureReg, traw); err != nil {
		return Spectrum{}, err
	}
	temperature := physic.Temperature(int8(traw[0]))*physic.Kelvin + physic.ZeroCelsius
	return Spectrum{
		Bands: []Band{
			{Wavelength: 450 * physic.NanoMetre, Counts: v, Value: vcal, Name: "V"},
			{Wavelength: 500 * physic.NanoMetre, Counts: b, Value: bcal, Name: "B"},
			{Wavelength: 550 * physic.NanoMetre, Counts: g, Value: gcal, Name: "G"},
			{Wavelength: 570 * physic.NanoMetre, Counts: y, Value: ycal, Name: "Y"},
			{Wavelength: 600 * physic.NanoMetre, Counts: o, Value: ocal, Name: "O"},
			{Wavelength: 650 * physic.NanoMetre, Counts: r, Value: rcal, Name: "R"},
		},
		SensorTemperature: temperature,
		Gain:              d.gain,
		LedDrive:          drive,
		Integration:       integration,
	}, nil
}

// Halt stops any pending operations. Repeated calls to Halt do nothing.
func (d *Dev) Halt() error {
	d.cancelMu.Lock()
	defer d.cancelMu.Unlock()
	d.cancel()
	// A receive can always proceed on a closed channel we can use that
	// to signal that the running process has been canceled correctly.
	<-d.done
	return nil
}

func (d *Dev) String() string {
	return "AMS AS7262 6 channel visible spectrum sensor"
}

// Gain is the sensor gain for all bands
type Gain int

const (
	// G1x is gain of 1
	G1x Gain = 0x00
	// G4x is gain of 3.7
	G4x Gain = 0x10
	// G16x is a gain of 16
	G16x Gain = 0x20
	// G64x us a gain of 64
	G64x Gain = 0x30
)

const (
	_GainG1x  = "1x"
	_GainG4x  = "3.7x"
	_GainG16x = "16x"
	_GainG64x = "64x"
)

func (g Gain) String() string {
	switch {
	case g == 0:
		return _GainG1x
	case g == 16:
		return _GainG4x
	case g == 32:
		return _GainG16x
	case g == 48:
		return _GainG64x
	default:
		return "bad gain value"
	}
}

// Gain sets the gain of the sensor. There are four levels of gain 1x, 3.7x, 16x,
// and 64x.
func (d *Dev) Gain(gain Gain) error {
	if gain != G1x && gain != G4x && gain != G16x && gain != G64x {
		return errGainValue
	}
	d.mu.Lock()
	defer d.mu.Unlock()

	if err := d.writeVirtualRegister(context.Background(), controlReg, uint8(gain)); err != nil {
		return err
	}
	d.gain = gain
	return nil
}

// AS7262 i2c protocol uses virtual registers. To write to a given register the
// MSB of the register must be set when writing the register to the write
// register, also status register must be checked for pending writes or data may
// be discarded.
func (d *Dev) writeVirtualRegister(ctx context.Context, register, data byte) error {

	// Check for pending writes.
	if err := d.pollStatus(ctx, writing); err != nil {
		return err
	}

	// Set virtual register that is being written to.
	if err := d.c.Tx([]byte{writeReg, register | 0x80}, nil); err != nil {
		return &IOError{"setting virtual register", err}
	}

	// Check for pending writes again.
	if err := d.pollStatus(ctx, writing); err != nil {
		return err
	}

	// Write data to register that is being written to.
	if err := d.c.Tx([]byte{writeReg, data}, nil); err != nil {
		return &IOError{"writing virtual register", err}
	}

	return nil
}

// AS7262 protocol uses virtual registers. To read a virtual register the
// pointer to the virtual register must be written to the write register. Status
// register must be checked for any pending reads or data may be invalid, then
// data maybe read from the read register.
func (d *Dev) readVirtualRegister(ctx context.Context, register byte, data []byte) error {
	rx := make([]byte, 1)
	for i := 0; i < len(data); i++ {
		// Check for pending reads.
		if err := d.pollStatus(ctx, clearBuffer); err != nil {
			return err
		}

		// Set virtual register that is being read from plus offset.
		if err := d.c.Tx([]byte{writeReg, register + byte(i)}, nil); err != nil {
			return &IOError{"setting virtual register", err}
		}

		// Check if read buffer is ready.
		if err := d.pollStatus(ctx, reading); err != nil {
			return err
		}

		// Read byte from register that is being read from into our buffer with
		// offset.
		if err := d.c.Tx([]byte{readReg}, rx); err != nil {
			return &IOError{"reading virtual register", err}
		}
		data[i] = rx[0]
	}
	return nil
}

// Polls the data ready bit in the control register(virtual)
func (d *Dev) pollDataReady(ctx context.Context) error {
	timeout := time.NewTimer(sensorTimeout)
	defer timeout.Stop()

	for {
		if err := d.pollStatus(ctx, clearBuffer); err != nil {
			return err
		}

		// Set virtual register that is being read from plus offset.
		if err := d.c.Tx([]byte{writeReg, controlReg}, nil); err != nil {
			return &IOError{"setting virtual register", err}
		}

		// Check if read buffer is ready.
		if err := d.pollStatus(ctx, reading); err != nil {
			return err
		}

		// Read byte from register that is being read from into our buffer with
		// offset.
		data := make([]byte, 1)
		if err := d.c.Tx([]byte{readReg}, data); err != nil {
			return &IOError{"reading virtual register", err}
		}
		if data[0]&0x02 > 0 {
			return nil
		}
		select {
		case <-time.After(5 * time.Millisecond):
			// Polling interval.
		case <-timeout.C:
			// Return error if it takes too long.
			return errStatusDeadline
		case <-ctx.Done():
			return errHalted
		}
	}
}

type direction byte

const (
	// Reading is a bit mask for the status register.
	reading direction = 1
	// Writing is a bit mask for the status register.
	writing direction = 2
	// ClearBuffer clears any data left in the buffer and then checks the reading
	clearBuffer direction = 3
)

// The as7262 registers are implemented as virtual registers pollStatus
// provides a way to repeatedly check if there are any pending reads or writes
// in the relevant buffer before a transaction while with a timeout.
// Direction is used to set which buffer is being polled to be ready.
func (d *Dev) pollStatus(ctx context.Context, dir direction) error {
	timeout := time.NewTimer(sensorTimeout)
	defer timeout.Stop()

	select {
	case <-ctx.Done():
		return errHalted
	default:
	}

	status := make([]byte, 1)
	for {
		// Read status register.
		err := d.c.Tx([]byte{statusReg}, status)
		if err != nil {
			return &IOError{"reading status register", err}
		}

		switch dir {
		case reading:
			// Bit 0: rx valid bit.
			//    0 → No data is ready to be read in READ register.
			//    1 → Data byte available in READ register.
			if status[0]&byte(dir) == 1 {
				return nil
			}
		case writing:
			// Bit 1: tx valid bit.
			//    0 → New data may be written to WRITE register.
			//    1 → WRITE register occupied. Do NOT write.
			if status[0]&byte(dir) == 0 {
				return nil
			}
		case clearBuffer:
			// If there is data left in the buffer read it.
			if status[0]&byte(reading) == 1 {
				discard := make([]byte, 1)
				if err := d.c.Tx([]byte{readReg}, discard); err != nil {
					return &IOError{"clearing buffer", err}
				}
			}
			if status[0]&byte(reading) == 0 {
				return nil
			}
		}

		select {
		case <-time.After(5 * time.Millisecond):
			// Polling interval.
		case <-timeout.C:
			// Return error if it takes too long.
			return errStatusDeadline
		case <-ctx.Done():
			return errHalted
		}
	}
}

const (
	maxSenseTime time.Duration = 714 * time.Millisecond
	minSenseTime               = 2800 * time.Microsecond
)

// calculateIntergrationTime converts a time.Duration into a value between 0 and
// 256
func calcSenseTime(t time.Duration) (uint8, time.Duration) {
	if t > maxSenseTime {
		return 255, maxSenseTime
	}
	if t < minSenseTime {
		return 1, minSenseTime
	}
	// Minimum step is 2.8ms
	quantizedTime := t / minSenseTime
	return uint8(quantizedTime), quantizedTime * minSenseTime
}

func calcLed(drive physic.ElectricCurrent) (uint8, physic.ElectricCurrent) {
	switch {
	case drive < 12500*physic.MicroAmpere:
		return 0x00, 0
	case drive >= 12500*physic.MicroAmpere && drive < 25*physic.MilliAmpere:
		return 0x08, 12500 * physic.MicroAmpere
	case drive >= 25*physic.MilliAmpere && drive < 50*physic.MilliAmpere:
		return 0x18, 25 * physic.MilliAmpere
	case drive >= 50*physic.MilliAmpere && drive < 100*physic.MilliAmpere:
		return 0x28, 50 * physic.MilliAmpere
	default:
		return 0x38, 100 * physic.MilliAmpere
	}
}

const (
	// allOneShot gets data from both banks once, and set the data ready bit in
	// the status control register when complete requires 2x the integration
	// time.
	allOneShot uint8 = 0x0c
)

// IOError is a I/O specific error.
type IOError struct {
	Op  string
	Err error
}

func (e *IOError) Error() string {
	if e.Err != nil {
		return "ioerror while " + e.Op + ": " + e.Err.Error()
	}
	return "ioerror while " + e.Op
}

var (
	errStatusDeadline = errors.New("deadline exceeded reading status register")
	errPinTimeout     = errors.New("timeout waiting for interrupt signal on pin")
	errHalted         = errors.New("received halt command")
	errGainValue      = errors.New("invalid gain value")
)

const (
	statusReg            = 0x00
	writeReg             = 0x01
	readReg              = 0x02
	hardwareVersion      = 0x00
	firmwareVersion      = 0x02
	controlReg           = 0x04
	integrationReg       = 0x05
	deviceTemperatureReg = 0x06
	ledControlReg        = 0x07
	// RawBase used as base for reading uint16 values, data must be sequentially.
	rawBase = 0x08
	rawVReg = 0x08
	rawBReg = 0x0a
	rawGReg = 0x0c
	rawYReg = 0x0e
	rawOReg = 0x10
	rawRReg = 0x12
	// CalBase used as base for reading float32 values, data must be sequentially.
	calBase        = 0x14
	calibratedVReg = 0x14
	calibratedBReg = 0x18
	calibratedGReg = 0x1c
	calibratedYReg = 0x20
	calibratedOReg = 0x24
	calibratedRReg = 0x28
)