// Package epd7in3e drives the Waveshare 7.3" e-Paper (E) "Spectra 6"
// panel (epd7in3e, 800x480, 6 colours) over SPI on a Raspberry Pi.
package epd7in3e

import (
	"context"
	"errors"
	"fmt"
	"image"
	"sync"
	"time"
)

// DefaultBusyTimeout bounds each waitIdle when Opts.BusyTimeout is zero.
const DefaultBusyTimeout = 60 * time.Second

// ErrAsleep is returned by Display, DisplayRaw and Clear when the
// panel is in deep sleep.
var ErrAsleep = errors.New("epd7in3e: device is asleep; call Init before displaying")

// ErrBusyTimeout is returned by WaitIdle when the BUSY pin stays low
// until the busy timeout elapses.
var ErrBusyTimeout = errors.New("epd7in3e: panel still busy after the busy timeout")

// ErrBadColor is returned by Clear for a value that is not one of the
// six panel colours (code 0x4 does not exist on this panel).
var ErrBadColor = errors.New("epd7in3e: not one of the six panel colours (code 0x4 does not exist)")

// Opts configures a Dev.
type Opts struct {
	// BusyTimeout bounds each waitIdle; zero uses DefaultBusyTimeout.
	BusyTimeout time.Duration
	// Rotate180 rotates packed frames 180 degrees.
	Rotate180 bool
	// Dither enables Floyd-Steinberg dithering in Display. Dithering
	// is on by default; pass Dither false to select nearest-colour
	// quantisation.
	Dither bool
	// Verbose logs every command, data write and busy-wait duration
	// to stderr.
	Verbose bool
}

// Dev drives one epd7in3e panel. Methods are serialised by a mutex
// and are safe to call from multiple goroutines.
type Dev struct {
	mu     sync.Mutex
	b      bus
	o      Opts
	asleep bool
}

func newDev(b bus, o *Opts) *Dev {
	d := &Dev{b: b}
	if o != nil {
		d.o = *o
	} else {
		d.o.Dither = true
	}
	if d.o.BusyTimeout <= 0 {
		d.o.BusyTimeout = DefaultBusyTimeout
	}
	return d
}

func (c Color) isPanelColour() bool {
	return c <= Green && c != 4
}

// reg is one command/data pair of the Init register sequence.
type reg struct {
	cmd  byte
	data []byte
}

var initRegisters = []reg{
	{0xAA, []byte{0x49, 0x55, 0x20, 0x08, 0x09, 0x18}},
	{0x01, []byte{0x3F}},
	{0x00, []byte{0x5F, 0x69}},
	{0x03, []byte{0x00, 0x54, 0x00, 0x44}},
	{0x05, []byte{0x40, 0x1F, 0x1F, 0x2C}},
	{0x06, []byte{0x6F, 0x1F, 0x17, 0x49}},
	{0x08, []byte{0x6F, 0x1F, 0x1F, 0x22}},
	{0x30, []byte{0x03}},
	{0x50, []byte{0x3F}},
	{0x60, []byte{0x02, 0x00}},
	{0x61, []byte{0x03, 0x20, 0x01, 0xE0}}, // 800, 480 big-endian
	{0x84, []byte{0x01}},
	{0xE3, []byte{0x2F}},
	{0x04, nil}, // power on, no data
}

// secondBoost is the second 0x06 booster setting sent between
// power-on and the refresh command.
var secondBoost = []byte{0x6F, 0x1F, 0x17, 0x49}

// Init puts the panel out of deep sleep and initialises it. It is
// required before the first Display and after every Sleep.
func (d *Dev) Init(ctx context.Context) error {
	d.mu.Lock()
	defer d.mu.Unlock()
	if err := d.initLocked(ctx); err != nil {
		return err
	}
	d.asleep = false
	return nil
}

func (d *Dev) initLocked(ctx context.Context) error {
	if err := d.b.Power(true); err != nil {
		return fmt.Errorf("epd7in3e: init: power on: %w", err)
	}
	if err := d.b.Reset(); err != nil {
		return fmt.Errorf("epd7in3e: init: reset: %w", err)
	}
	if err := d.waitIdle(ctx, "init"); err != nil {
		return err
	}
	d.b.Sleep(30 * time.Millisecond)
	for _, r := range initRegisters {
		if err := d.b.Cmd(r.cmd); err != nil {
			return fmt.Errorf("epd7in3e: init: command 0x%02X: %w", r.cmd, err)
		}
		if len(r.data) > 0 {
			if err := d.b.Data(r.data); err != nil {
				return fmt.Errorf("epd7in3e: init: data for 0x%02X: %w", r.cmd, err)
			}
		}
	}
	return d.waitIdle(ctx, "init (power on)")
}

// waitIdle waits for the BUSY pin to read HIGH, applying the busy
// timeout on top of the caller's context.
func (d *Dev) waitIdle(ctx context.Context, what string) error {
	ctx, cancel := context.WithTimeout(ctx, d.o.BusyTimeout)
	defer cancel()
	if err := d.b.WaitIdle(ctx); err != nil {
		return fmt.Errorf("epd7in3e: %s: %w", what, err)
	}
	return nil
}

// Display packs img and refreshes the panel with it. img must be
// 800x480, or 480x800, which is rotated 90 degrees clockwise. By
// default img is Floyd-Steinberg dithered to the panel palette.
func (d *Dev) Display(ctx context.Context, img image.Image) error {
	d.mu.Lock()
	defer d.mu.Unlock()
	if d.asleep {
		return ErrAsleep
	}
	if d.o.Dither {
		img = Quantise(img, true)
	}
	buf := make([]byte, FrameBytes)
	if err := Pack(buf, img); err != nil {
		return fmt.Errorf("epd7in3e: display: %w", err)
	}
	return d.refreshLocked(ctx, buf)
}

// DisplayRaw refreshes the panel with a pre-packed frame buffer. buf
// must be exactly FrameBytes long.
func (d *Dev) DisplayRaw(ctx context.Context, buf []byte) error {
	d.mu.Lock()
	defer d.mu.Unlock()
	if d.asleep {
		return ErrAsleep
	}
	if len(buf) != FrameBytes {
		return fmt.Errorf("epd7in3e: display raw: buffer is %d bytes, want %d", len(buf), FrameBytes)
	}
	return d.refreshLocked(ctx, buf)
}

// Clear fills the panel with one solid colour.
func (d *Dev) Clear(ctx context.Context, c Color) error {
	if !c.isPanelColour() {
		return fmt.Errorf("epd7in3e: clear: colour 0x%X: %w", c, ErrBadColor)
	}
	d.mu.Lock()
	defer d.mu.Unlock()
	if d.asleep {
		return ErrAsleep
	}
	buf := make([]byte, FrameBytes)
	v := byte(c)<<4 | byte(c)
	for i := range buf {
		buf[i] = v
	}
	return d.refreshLocked(ctx, buf)
}

// refreshLocked sends buf as the 0x10 frame data and runs the refresh
// sequence: power on, the second 0x06 booster setting, refresh, power
// off. The panel is left powered off.
func (d *Dev) refreshLocked(ctx context.Context, buf []byte) error {
	if err := d.b.Cmd(0x10); err != nil {
		return fmt.Errorf("epd7in3e: refresh: command 0x10: %w", err)
	}
	if err := d.b.Data(buf); err != nil {
		return fmt.Errorf("epd7in3e: refresh: frame data: %w", err)
	}
	if err := d.b.Cmd(0x04); err != nil {
		return fmt.Errorf("epd7in3e: refresh: power on: %w", err)
	}
	if err := d.waitIdle(ctx, "refresh (power on)"); err != nil {
		return err
	}
	if err := d.b.Cmd(0x06); err != nil {
		return fmt.Errorf("epd7in3e: refresh: second booster: %w", err)
	}
	if err := d.b.Data(secondBoost); err != nil {
		return fmt.Errorf("epd7in3e: refresh: second booster data: %w", err)
	}
	if err := d.b.Cmd(0x12); err != nil {
		return fmt.Errorf("epd7in3e: refresh: refresh command: %w", err)
	}
	if err := d.b.Data([]byte{0x00}); err != nil {
		return fmt.Errorf("epd7in3e: refresh: refresh data: %w", err)
	}
	if err := d.waitIdle(ctx, "refresh"); err != nil {
		return err
	}
	if err := d.b.Cmd(0x02); err != nil {
		return fmt.Errorf("epd7in3e: refresh: power off: %w", err)
	}
	if err := d.b.Data([]byte{0x00}); err != nil {
		return fmt.Errorf("epd7in3e: refresh: power off data: %w", err)
	}
	return d.waitIdle(ctx, "refresh (power off)")
}

// Sleep puts the panel into deep sleep. The panel ignores commands
// until the next Init.
func (d *Dev) Sleep(ctx context.Context) error {
	d.mu.Lock()
	defer d.mu.Unlock()
	return d.sleepLocked(ctx)
}

// Bounds is the panel's logical frame: 800x480 at the origin.
func (d *Dev) Bounds() image.Rectangle {
	return image.Rect(0, 0, Width, Height)
}

// Halt powers the panel off. If it is not already asleep, it first
// enters deep sleep. A later Init brings the panel back.
func (d *Dev) Halt() error {
	d.mu.Lock()
	defer d.mu.Unlock()
	if !d.asleep {
		if err := d.sleepLocked(context.Background()); err != nil {
			return fmt.Errorf("epd7in3e: halt: %w", err)
		}
	}
	if err := d.b.Power(false); err != nil {
		return fmt.Errorf("epd7in3e: halt: power off: %w", err)
	}
	return nil
}

func (d *Dev) sleepLocked(ctx context.Context) error {
	if err := d.b.Cmd(0x02); err != nil {
		return fmt.Errorf("sleep: power off: %w", err)
	}
	if err := d.b.Data([]byte{0x00}); err != nil {
		return fmt.Errorf("sleep: power off data: %w", err)
	}
	if err := d.waitIdle(ctx, "sleep (power off)"); err != nil {
		return err
	}
	if err := d.b.Cmd(0x07); err != nil {
		return fmt.Errorf("sleep: deep sleep: %w", err)
	}
	if err := d.b.Data([]byte{0xA5}); err != nil {
		return fmt.Errorf("sleep: deep sleep data: %w", err)
	}
	d.asleep = true
	return nil
}