package winkeyer

import (
	"errors"
	"sync"
	"testing"
	"time"

	"go.bug.st/serial"
)

// fakeKeyer is a serial.Port that behaves like a WinKeyer: it answers the echo
// probe and Host Open, and records everything the host sent so the handshake
// can be checked byte for byte against K1EL's documented sequence.
type fakeKeyer struct {
	mu      sync.Mutex
	written []byte
	toRead  []byte
	version byte
	// deaf drops every command — the keyer that is not there, or is not
	// listening because RTS starved it.
	deaf bool
	// mute answers the echo but never returns a version.
	mute bool
	// needsResync ignores commands until three nulls have been seen, standing
	// in for a keyer left mid-command by another program.
	needsResync bool
	nulls       int
}

func (f *fakeKeyer) Write(p []byte) (int, error) {
	f.mu.Lock()
	defer f.mu.Unlock()
	f.written = append(f.written, p...)
	if f.deaf {
		return len(p), nil
	}
	for i := 0; i < len(p); i++ {
		switch {
		case p[i] == cmdNull:
			f.nulls++
		case f.needsResync && f.nulls < 3:
			// still confused — swallow it
		case p[i] == cmdAdmin && i+1 < len(p):
			i++
			switch p[i] {
			case adminEcho:
				if i+1 < len(p) {
					i++
					f.toRead = append(f.toRead, p[i])
				}
			case adminOpen:
				if !f.mute {
					f.toRead = append(f.toRead, f.version)
				}
			}
		}
	}
	return len(p), nil
}

func (f *fakeKeyer) Read(p []byte) (int, error) {
	f.mu.Lock()
	defer f.mu.Unlock()
	if len(f.toRead) == 0 {
		return 0, nil // a timeout, not an error — what a real port does
	}
	n := copy(p, f.toRead)
	f.toRead = f.toRead[n:]
	return n, nil
}

func (f *fakeKeyer) sent() []byte {
	f.mu.Lock()
	defer f.mu.Unlock()
	return append([]byte(nil), f.written...)
}

func (f *fakeKeyer) Drain() error             { return nil }
func (f *fakeKeyer) ResetInputBuffer() error  { return nil }
func (f *fakeKeyer) ResetOutputBuffer() error { return nil }
func (f *fakeKeyer) SetDTR(bool) error        { return nil }
func (f *fakeKeyer) SetRTS(bool) error        { return nil }
func (f *fakeKeyer) GetModemStatusBits() (*serial.ModemStatusBits, error) {
	return &serial.ModemStatusBits{}, nil
}
func (f *fakeKeyer) SetReadTimeout(time.Duration) error { return nil }
func (f *fakeKeyer) Close() error                       { return nil }
func (f *fakeKeyer) Break(time.Duration) error          { return nil }
func (f *fakeKeyer) SetMode(*serial.Mode) error         { return nil }

// TestHostOpenFollowsK1ELSequence checks the handshake against the order K1EL
// publishes: three nulls to resync the parser, an echo probe to prove there is
// a keyer, then Host Open. OpsLog used to send Host Open alone, which a keyer
// left mid-command simply absorbed.
func TestHostOpenFollowsK1ELSequence(t *testing.T) {
	f := &fakeKeyer{version: 23}
	ver, err := hostOpen(f, false)
	if err != nil {
		t.Fatalf("hostOpen: %v", err)
	}
	if ver != 23 {
		t.Errorf("version = %d, want 23", ver)
	}
	want := []byte{
		cmdNull, cmdNull, cmdNull,
		cmdAdmin, adminEcho, echoProbe,
		cmdAdmin, adminOpen,
	}
	got := f.sent()
	if len(got) != len(want) {
		t.Fatalf("sent % X, want % X", got, want)
	}
	for i := range want {
		if got[i] != want[i] {
			t.Fatalf("sent % X, want % X", got, want)
		}
	}
}

// A keyer left part-way through a command by another program is the everyday
// cause of a silent WinKeyer. The nulls must recover it without the operator
// having to unplug anything.
func TestHostOpenRecoversAConfusedParser(t *testing.T) {
	f := &fakeKeyer{version: 30, needsResync: true}
	ver, err := hostOpen(f, false)
	if err != nil {
		t.Fatalf("hostOpen: %v", err)
	}
	if ver != 30 {
		t.Errorf("version = %d, want 30", ver)
	}
}

// Nothing on the port must FAIL the connection. Reporting success and then
// writing settings and text into the void is what produced a log full of
// commands and a keyer that never made a sound.
func TestHostOpenFailsWhenNothingAnswers(t *testing.T) {
	f := &fakeKeyer{deaf: true}
	if _, err := hostOpen(f, false); !errors.Is(err, errNoKeyer) {
		t.Fatalf("want errNoKeyer, got %v", err)
	}
}

// Echoing but not returning a version is a different fault and must not be
// reported as "no keyer".
func TestHostOpenReportsMissingVersion(t *testing.T) {
	f := &fakeKeyer{mute: true}
	_, err := hostOpen(f, false)
	if err == nil {
		t.Fatal("want an error")
	}
	if errors.Is(err, errNoKeyer) {
		t.Fatalf("a keyer that echoed was reported as absent: %v", err)
	}
}

// slowKeyer answers nothing until it has been "powered up" for d — a K3NG on an
// Arduino, which the DTR edge from opening the port drops into its bootloader.
type slowKeyer struct {
	fakeKeyer
	ready time.Time
}

func (s *slowKeyer) Write(p []byte) (int, error) {
	if time.Now().Before(s.ready) {
		return len(p), nil // still in the bootloader — the bytes are lost
	}
	return s.fakeKeyer.Write(p)
}

// TestHostOpenWaitsOutAnArduinoReboot is the case that started this: a K3NG
// keyer reboots when the port opens, so it misses a handshake sent 400 ms
// later. The retry has to wait long enough, and must not need the operator to
// press connect twice.
func TestHostOpenWaitsOutAnArduinoReboot(t *testing.T) {
	f := &slowKeyer{ready: time.Now().Add(1500 * time.Millisecond)}
	f.version = 23
	ver, err := hostOpen(f, false)
	if err != nil {
		t.Fatalf("hostOpen: %v", err)
	}
	if ver != 23 {
		t.Errorf("version = %d, want 23", ver)
	}
}

// Telling OpsLog the keyer is a K3NG must skip the doomed fast attempt, so the
// first try already allows for the reboot.
func TestHostOpenSlowBootSucceedsFirstTry(t *testing.T) {
	f := &slowKeyer{ready: time.Now().Add(1500 * time.Millisecond)}
	f.version = 23
	if _, err := hostOpen(f, true); err != nil {
		t.Fatalf("hostOpen: %v", err)
	}
	// One attempt: exactly one handshake on the wire, not two.
	want := len([]byte{cmdNull, cmdNull, cmdNull, cmdAdmin, adminEcho, echoProbe, cmdAdmin, adminOpen})
	if got := len(f.sent()); got != want {
		t.Errorf("sent %d bytes, want %d — the fast attempt was not skipped", got, want)
	}
}