package main

import (
	"fmt"
	"log"
	"sync"
	"time"

	"tinygo.org/x/bluetooth"

	pb "powerpod/gotool/pb"
	uartframe "powerpod/gotool/uart"
)

const (
	bleServiceUUID = "6e400001-b5a3-f393-e0a9-e50e24dcca9e"
	bleCharUUID    = "6e400002-b5a3-f393-e0a9-e50e24dcca9e"
	bleDefaultName = "Powerpod"
)

type bleLink struct {
	device   bluetooth.Device
	char     bluetooth.DeviceCharacteristic
	mu       sync.Mutex
	parserMu sync.Mutex
	parser   *uartframe.Parser
	respCh   chan []byte
	streamCh chan []byte
	quiet    bool
	attMTU   int // negotiated ATT MTU (0 if unknown)
}

func openBLE(name string, settle time.Duration) (*bleLink, error) {
	if name == "" {
		name = bleDefaultName
	}
	adapter := bluetooth.DefaultAdapter
	if err := adapter.Enable(); err != nil {
		return nil, fmt.Errorf("enable bluetooth adapter: %w (check BlueZ / permissions)", err)
	}

	log.Printf("BLE scanning for %q…", name)
	var foundAddr bluetooth.Address
	var found bool
	go func() {
		time.Sleep(15 * time.Second)
		_ = adapter.StopScan()
	}()
	err := adapter.Scan(func(a *bluetooth.Adapter, result bluetooth.ScanResult) {
		if result.LocalName() != name {
			return
		}
		foundAddr = result.Address
		found = true
		_ = a.StopScan()
	})
	if err != nil {
		return nil, fmt.Errorf("scan: %w", err)
	}
	if !found {
		return nil, fmt.Errorf("device %q not found (check DIP8=BLE and advertising)", name)
	}
	return connectBLEDevice(foundAddr, settle)
}

func openBLEAddress(addrStr string, settle time.Duration) (*bleLink, error) {
	adapter := bluetooth.DefaultAdapter
	if err := adapter.Enable(); err != nil {
		return nil, fmt.Errorf("enable bluetooth adapter: %w (check BlueZ / permissions)", err)
	}
	if mac, err := bluetooth.ParseMAC(addrStr); err == nil {
		var addr bluetooth.Address
		addr.Set(mac.String())
		return connectBLEDevice(addr, settle)
	}
	// Fallback: scan until address string matches
	log.Printf("BLE resolving address %s via scan…", addrStr)
	var foundAddr bluetooth.Address
	var found bool
	go func() {
		time.Sleep(15 * time.Second)
		_ = adapter.StopScan()
	}()
	err := adapter.Scan(func(a *bluetooth.Adapter, result bluetooth.ScanResult) {
		if result.Address.String() != addrStr {
			return
		}
		foundAddr = result.Address
		found = true
		_ = a.StopScan()
	})
	if err != nil {
		return nil, fmt.Errorf("scan for address: %w", err)
	}
	if !found {
		return nil, fmt.Errorf("BLE address %s not found", addrStr)
	}
	return connectBLEDevice(foundAddr, settle)
}

func connectBLEDevice(addr bluetooth.Address, settle time.Duration) (*bleLink, error) {
	svcUUID, err := bluetooth.ParseUUID(bleServiceUUID)
	if err != nil {
		return nil, err
	}
	chrUUID, err := bluetooth.ParseUUID(bleCharUUID)
	if err != nil {
		return nil, err
	}

	adapter := bluetooth.DefaultAdapter
	log.Printf("BLE connecting to %s…", addr.String())
	device, err := adapter.Connect(addr, bluetooth.ConnectionParams{})
	if err != nil {
		return nil, fmt.Errorf("connect: %w", err)
	}

	services, err := device.DiscoverServices([]bluetooth.UUID{svcUUID})
	if err != nil || len(services) == 0 {
		_ = device.Disconnect()
		return nil, fmt.Errorf("discover service: %v", err)
	}
	chars, err := services[0].DiscoverCharacteristics([]bluetooth.UUID{chrUUID})
	if err != nil || len(chars) == 0 {
		_ = device.Disconnect()
		return nil, fmt.Errorf("discover characteristic: %v", err)
	}
	char := chars[0]

	attMTU := 0
	if mtu, err := char.GetMTU(); err == nil {
		attMTU = int(mtu)
		log.Printf("BLE ATT MTU=%d", attMTU)
		if attMTU < otaMinATTMTU {
			log.Printf("warning: MTU %d < %d — OTA (200 B chunks) and large stream ticks may fail",
				attMTU, otaMinATTMTU)
		}
	}

	link := &bleLink{
		device:   device,
		char:     char,
		parser:   uartframe.NewParser(),
		respCh:   make(chan []byte, 8),
		streamCh: make(chan []byte, 64),
		attMTU:   attMTU,
	}

	if err := char.EnableNotifications(func(buf []byte) {
		link.onNotify(buf)
	}); err != nil {
		_ = device.Disconnect()
		return nil, fmt.Errorf("enable notifications: %w (CCCD required before commands)", err)
	}

	if settle <= 0 {
		settle = time.Second
	}
	log.Printf("BLE connected; settling %v…", settle)
	time.Sleep(settle)

	return link, nil
}

func (b *bleLink) onNotify(buf []byte) {
	b.parserMu.Lock()
	defer b.parserMu.Unlock()
	for _, by := range buf {
		payload, ok, err := b.parser.Feed(by)
		if err != nil || !ok {
			continue
		}
		if len(payload) == 0 {
			continue
		}
		if payload[0] == byte(pb.MessageType_BLE_STREAM_TICK) {
			select {
			case b.streamCh <- payload:
			default:
			}
			continue
		}
		select {
		case b.respCh <- payload:
		default:
			// Prefer dropping the oldest queued frame so a late/stale reply
			// does not block the matching response for the in-flight command.
			select {
			case <-b.respCh:
			default:
			}
			select {
			case b.respCh <- payload:
			default:
				log.Printf("BLE: response channel full, dropping frame type=0x%02x", payload[0])
			}
		}
	}
}

func (b *bleLink) resetParser() {
	b.parserMu.Lock()
	b.parser = uartframe.NewParser()
	b.parserMu.Unlock()
}

func (b *bleLink) Close() error {
	return b.device.Disconnect()
}

func (b *bleLink) exchange(cmdID byte, cmdName string) ([]byte, error) {
	return b.exchangePayload([]byte{cmdID}, cmdName)
}

func (b *bleLink) exchangePayload(payload []byte, cmdName string) ([]byte, error) {
	return b.exchangePayloadTimeout(payload, cmdName, readTimeout)
}

func (b *bleLink) exchangePayloadTimeout(payload []byte, cmdName string, timeout time.Duration) ([]byte, error) {
	b.mu.Lock()
	defer b.mu.Unlock()

	if len(payload) == 0 {
		return nil, fmt.Errorf("empty payload")
	}
	expect := payload[0]
	if timeout <= 0 {
		timeout = readTimeout
	}

	frame, err := uartframe.EncodeFrame(payload)
	if err != nil {
		return nil, fmt.Errorf("encode frame: %w", err)
	}
	if !b.quiet {
		log.Printf("BLE sending %s (%d bytes)", cmdName, len(frame))
	}

	for {
		select {
		case <-b.respCh:
		default:
			goto sent
		}
	}
sent:
	if _, err := b.char.WriteWithoutResponse(frame); err != nil {
		return nil, fmt.Errorf("BLE write: %w (check DIP8=BLE)", err)
	}

	deadline := time.Now().Add(timeout)
	for {
		remain := time.Until(deadline)
		if remain <= 0 {
			// Drop a half-parsed frame (e.g. aborted multi-notify) so the next
			// exchange does not treat a new 0xAA as payload data.
			b.resetParser()
			return nil, fmt.Errorf("BLE read timeout for %s (check DIP8=BLE / -ble)", cmdName)
		}
		timer := time.NewTimer(remain)
		select {
		case resp := <-b.respCh:
			timer.Stop()
			if len(resp) == 0 {
				continue
			}
			if resp[0] != expect {
				// Stale reply (e.g. late BATTERY_STATUS after a short timeout).
				if !b.quiet {
					log.Printf("BLE: discard type=0x%02x while waiting for 0x%02x (%s)", resp[0], expect, cmdName)
				}
				continue
			}
			if !b.quiet {
				log.Printf("BLE response (%d bytes)", len(resp))
			}
			return resp, nil
		case <-timer.C:
			b.resetParser()
			return nil, fmt.Errorf("BLE read timeout for %s (check DIP8=BLE / -ble)", cmdName)
		}
	}
}

func (b *bleLink) NextStreamTick(timeout time.Duration) ([]byte, error) {
	if timeout <= 0 {
		timeout = 5 * time.Second
	}
	timer := time.NewTimer(timeout)
	defer timer.Stop()
	select {
	case p := <-b.streamCh:
		return p, nil
	case <-timer.C:
		return nil, fmt.Errorf("BLE stream tick timeout")
	}
}

// ensureOTAMTU rejects OTA when the negotiated ATT MTU cannot carry 200 B chunks.
func (b *bleLink) ensureOTAMTU() error {
	mtu := b.attMTU
	if mtu <= 0 {
		if v, err := b.char.GetMTU(); err == nil {
			mtu = int(v)
			b.attMTU = mtu
		}
	}
	if mtu < otaMinATTMTU {
		return fmt.Errorf("BLE ATT MTU %d < %d required for OTA (negotiate larger MTU)", mtu, otaMinATTMTU)
	}
	maxWrite := mtu - 3
	if maxWrite < 216 {
		return fmt.Errorf("BLE max write %d < 216 needed for 200 B OTA frames", maxWrite)
	}
	return nil
}

func (b *bleLink) writeMsg(msg *pb.UartMessage) error {
	b.mu.Lock()
	defer b.mu.Unlock()
	frame, err := encodeUartMessage(msg)
	if err != nil {
		return err
	}
	if b.attMTU > 0 && len(frame) > b.attMTU-3 {
		return fmt.Errorf("OTA frame %d exceeds BLE max write %d (MTU=%d)",
			len(frame), b.attMTU-3, b.attMTU)
	}
	if _, err := b.char.WriteWithoutResponse(frame); err != nil {
		return fmt.Errorf("BLE write: %w", err)
	}
	return nil
}

func (b *bleLink) readFrame(timeout time.Duration) ([]byte, error) {
	if timeout <= 0 {
		timeout = readTimeout
	}
	timer := time.NewTimer(timeout)
	defer timer.Stop()
	select {
	case p := <-b.respCh:
		return p, nil
	case <-timer.C:
		return nil, fmt.Errorf("BLE read timeout")
	}
}

func (b *bleLink) flushInput() {
	for {
		select {
		case <-b.respCh:
		default:
			goto streams
		}
	}
streams:
	for {
		select {
		case <-b.streamCh:
		default:
			return
		}
	}
}

func (b *bleLink) chunkPace() time.Duration { return otaHostChunkPaceBLE }