package main

import (
	"errors"
	"fmt"
	"log"
	"sync"
	"time"
)

// errUARTBusy is returned when the port is held for OTA (poller should not treat as unplug).
var errUARTBusy = errors.New("uart busy (OTA in progress)")

// errOTAInProgress is returned when a second OTA upload is attempted while one is running.
var errOTAInProgress = errors.New("OTA upload already in progress")

// managedSerial keeps the UART open and reconnects after I/O failures or unplug.
type managedSerial struct {
	portName string
	baud     int
	quiet    bool

	mu        sync.Mutex
	sp        *serialPort
	otaActive bool // UART held for firmware upload; poll/API must not interleave
}

func newManagedSerial(portName string, baud int) *managedSerial {
	return &managedSerial{
		portName: portName,
		baud:     baud,
	}
}

func (m *managedSerial) Close() error {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.closeLocked()
}

func (m *managedSerial) IsConnected() bool {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.sp != nil
}

func (m *managedSerial) openLocked() error {
	sp, err := openSerial(m.portName, m.baud)
	if err != nil {
		return err
	}
	sp.quiet = m.quiet
	m.sp = sp
	if !m.quiet {
		log.Printf("UART %s connected (%d baud)", m.portName, m.baud)
	}
	return nil
}

func (m *managedSerial) closeLocked() error {
	if m.sp == nil {
		return nil
	}
	err := m.sp.port.Close()
	m.sp = nil
	return err
}

func (m *managedSerial) invalidateLocked(reason error) {
	if m.sp == nil {
		return
	}
	if !m.quiet {
		log.Printf("UART %s disconnected: %v", m.portName, reason)
	}
	_ = m.closeLocked()
}

func (m *managedSerial) withPort(fn func(*serialPort) error) error {
	return m.withPortLocked(false, fn)
}

// withPortPoll is like withPort but returns errUARTBusy during OTA (no TryLock race).
func (m *managedSerial) withPortPoll(fn func(*serialPort) error) error {
	return m.withPortLocked(true, fn)
}

func (m *managedSerial) withPortLocked(poll bool, fn func(*serialPort) error) error {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.otaActive {
		return errUARTBusy
	}

	if m.sp == nil {
		if err := m.openLocked(); err != nil {
			return fmt.Errorf("%s: %w", m.portName, err)
		}
	}

	err := fn(m.sp)
	if err != nil {
		m.invalidateLocked(err)
	}
	return err
}

func (m *managedSerial) recoverAfterMasterRestart() {
	const bootWait = 6 * time.Second

	m.mu.Lock()
	m.closeLocked()
	m.mu.Unlock()

	log.Printf("UART: master restart — waiting %s for boot", bootWait)
	time.Sleep(bootWait)

	m.mu.Lock()
	defer m.mu.Unlock()
	if err := m.openLocked(); err != nil {
		log.Printf("UART reconnect after master restart: %v", err)
		return
	}
	flushSerialInput(m.sp)
	log.Printf("UART %s ready after master restart", m.portName)
}

func (m *managedSerial) exchangePayload(payload []byte, cmdName string) ([]byte, error) {
	return m.exchangePayloadVia(m.withPort, payload, cmdName)
}

func (m *managedSerial) exchangePayloadPoll(payload []byte, cmdName string) ([]byte, error) {
	return m.exchangePayloadVia(m.withPortPoll, payload, cmdName)
}

func (m *managedSerial) exchangePayloadVia(
	portFn func(func(*serialPort) error) error,
	payload []byte, cmdName string,
) ([]byte, error) {
	var resp []byte
	err := portFn(func(sp *serialPort) error {
		var e error
		resp, e = sp.exchangePayloadLocked(payload, cmdName, readTimeout)
		return e
	})
	return resp, err
}

func (m *managedSerial) exchange(cmdID byte, cmdName string) ([]byte, error) {
	return m.exchangeVia(m.withPort, cmdID, cmdName)
}

func (m *managedSerial) exchangePoll(cmdID byte, cmdName string) ([]byte, error) {
	return m.exchangeVia(m.withPortPoll, cmdID, cmdName)
}

func (m *managedSerial) exchangeVia(
	portFn func(func(*serialPort) error) error,
	cmdID byte, cmdName string,
) ([]byte, error) {
	var resp []byte
	err := portFn(func(sp *serialPort) error {
		var e error
		resp, e = sp.exchangeLocked(cmdID, cmdName)
		return e
	})
	return resp, err
}

func disconnectedState(portName string, err error) DashboardState {
	msg := "UART disconnected"
	if err != nil {
		msg = err.Error()
	}
	return DashboardState{
		UpdatedAt:     time.Now().Format(time.RFC3339),
		SerialPort:    portName,
		UARTConnected: false,
		SerialOK:      false,
		SerialError:   msg,
		Master:        MasterView{OK: false, Error: msg},
		Clients:       []ClientView{},
	}
}