// cmd/spike is the milestone-1 throwaway: spawn a child in a PTY, pump bytes
// through a libghostty-vt-backed emulator, and dump the rendered grid as
// plain text on idle or hotkey.
//
// Stdin from the host terminal is forwarded raw to the child PTY, so vim,
// htop, claude, codex and friends behave as if you ran them directly. We are
// explicitly NOT encoding keys ourselves yet — that's a daemon-era concern.
package main

import (
	"errors"
	"flag"
	"fmt"
	"io"
	"os"
	"os/signal"
	"strings"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

	"github.com/hjbdev/patterm/internal/pty"
	"github.com/hjbdev/patterm/internal/vt"

	cpty "github.com/creack/pty"
	"golang.org/x/term"
)

const (
	defaultCols     = 120
	defaultRows     = 40
	defaultIdleMS   = 1000
	readBufferBytes = 64 * 1024
)

// Known hotkey aliases mapped to their raw control bytes.
var hotkeyAliases = map[string]byte{
	"ctrl-]":     0x1d, // GS — default, but some layouts/terminals swallow it
	"ctrl-\\":    0x1c, // FS — sends SIGQUIT in cooked mode but raw passes through
	"ctrl-^":     0x1e, // RS
	"ctrl-_":     0x1f, // US
	"ctrl-t":     0x14,
	"ctrl-o":     0x0f,
	"ctrl-space": 0x00, // NUL
}

type spikeFlags struct {
	cols, rows    int
	idleMS        int
	followHost    bool
	noPassthrough bool
	bytesPath     string
	gridPath      string
	gridToStderr  bool
	hotkey        string
	debugStdin    bool
}

func main() {
	var f spikeFlags
	flag.IntVar(&f.cols, "cols", defaultCols, "PTY columns (overridden by host size if -follow-host)")
	flag.IntVar(&f.rows, "rows", defaultRows, "PTY rows (overridden by host size if -follow-host)")
	flag.IntVar(&f.idleMS, "dump-after-idle", defaultIdleMS, "dump grid to stderr after this many ms of PTY silence (0 disables)")
	flag.BoolVar(&f.followHost, "follow-host", true, "use the host terminal's size and follow SIGWINCH")
	flag.BoolVar(&f.noPassthrough, "no-stdin", false, "don't forward host stdin to the child PTY")
	flag.StringVar(&f.bytesPath, "bytes-out", "", "tee raw PTY bytes to this file (default: spike-<pid>.bytes when child starts)")
	flag.StringVar(&f.gridPath, "grid-out", "", "write grid dumps to this file (default: spike-<pid>.grid.log). Use - for stderr (will visually corrupt alt-screen TUIs).")
	flag.BoolVar(&f.gridToStderr, "grid-stderr", false, "also echo each grid dump to stderr. Convenient for non-TUI children (echo, bash); avoid with vim/htop/agent CLIs.")
	flag.StringVar(&f.hotkey, "hotkey", "ctrl-]", "key chord that triggers a grid dump: ctrl-], ctrl-\\, ctrl-^, ctrl-_, ctrl-t, ctrl-o, ctrl-space")
	flag.BoolVar(&f.debugStdin, "debug-stdin", false, "log every stdin byte to stderr as we read it (for working out what your terminal sends)")
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "usage: spike [flags] -- <argv>\n\nflags:\n")
		flag.PrintDefaults()
		fmt.Fprintf(os.Stderr, "\nWhile running, press the configured -hotkey to dump the grid.\nDefault sink is spike-<pid>.grid.log; tail -f it in another terminal.\n")
	}
	flag.Parse()

	argv := flag.Args()
	if len(argv) == 0 {
		flag.Usage()
		os.Exit(2)
	}

	hotkey, ok := hotkeyAliases[strings.ToLower(f.hotkey)]
	if !ok {
		fmt.Fprintf(os.Stderr, "spike: unknown -hotkey %q (see -h for options)\n", f.hotkey)
		os.Exit(2)
	}

	startCols, startRows := uint16(f.cols), uint16(f.rows)
	if f.followHost {
		if c, r, ok := hostSize(); ok {
			startCols, startRows = c, r
		}
	}

	if err := run(argv, startCols, startRows, f.idleMS, f.followHost, !f.noPassthrough, f.bytesPath, f.gridPath, f.gridToStderr, hotkey, f.debugStdin); err != nil {
		fmt.Fprintf(os.Stderr, "spike: %v\n", err)
		os.Exit(1)
	}
}

func run(argv []string, cols, rows uint16, idleMS int, followHost, stdinPassthrough bool, bytesPath, gridPath string, gridToStderr bool, hotkey byte, debugStdin bool) error {
	em, err := vt.NewGhosttyEmulator(cols, rows)
	if err != nil {
		return fmt.Errorf("emulator: %w", err)
	}
	defer em.Close()

	child, err := pty.Start(argv, nil, "", cols, rows)
	if err != nil {
		return fmt.Errorf("pty: %w", err)
	}
	defer child.Close()

	// Wire WRITE_PTY back to the child's stdin so DA/DSR query responses
	// reach the program asking.
	em.OnWritePTY(func(b []byte) {
		if _, werr := child.Write(b); werr != nil {
			fmt.Fprintf(os.Stderr, "\r\nspike: write_pty back to child failed: %v\r\n", werr)
		}
	})

	// Set up the bytes tee.
	if bytesPath == "" {
		bytesPath = fmt.Sprintf("spike-%d.bytes", child.Pid())
	}
	bytesFile, err := os.Create(bytesPath)
	if err != nil {
		return fmt.Errorf("bytes tee: %w", err)
	}
	defer bytesFile.Close()

	// Set up the grid sink. By default this is a file, not stderr, because
	// writing a multi-line dump to the host terminal while an alt-screen TUI
	// owns it visually corrupts the host display (the TUI inside the PTY is
	// fine; libghostty-vt's grid is fine; only the host's render breaks).
	var gridSink *os.File
	gridIsStderr := false
	switch gridPath {
	case "-":
		gridSink = os.Stderr
		gridIsStderr = true
	case "":
		gridPath = fmt.Sprintf("spike-%d.grid.log", child.Pid())
		fallthrough
	default:
		gridSink, err = os.Create(gridPath)
		if err != nil {
			return fmt.Errorf("grid log: %w", err)
		}
		defer gridSink.Close()
	}

	fmt.Fprintf(os.Stderr, "spike: child pid=%d, bytes=%s, grid=%s (%dx%d)\r\n",
		child.Pid(), bytesPath, gridPath, cols, rows)
	if !gridIsStderr {
		fmt.Fprintf(os.Stderr, "spike: tail -f %s in another terminal to watch dumps live\r\n", gridPath)
	}

	// Set host stdin to raw mode so key sequences (arrows, Ctrl-C, etc.)
	// reach the child intact. Save the state for restore.
	var restoreState *term.State
	if stdinPassthrough && term.IsTerminal(int(os.Stdin.Fd())) {
		st, err := term.MakeRaw(int(os.Stdin.Fd()))
		if err != nil {
			return fmt.Errorf("stdin raw: %w", err)
		}
		restoreState = st
		defer term.Restore(int(os.Stdin.Fd()), restoreState)
	}

	// Idle detection: PTY reader updates lastWrite; ticker checks if we
	// crossed the threshold without writes and prints a grid dump.
	var lastWriteNS atomic.Int64
	lastWriteNS.Store(time.Now().UnixNano())
	var lastDumpNS atomic.Int64
	var dumpRequest = make(chan string, 4)

	// Coordinated shutdown.
	var wg sync.WaitGroup
	done := make(chan struct{})
	closeDone := sync.OnceFunc(func() { close(done) })

	// Reader: PTY -> stdout passthrough + emulator + bytes tee.
	wg.Add(1)
	go func() {
		defer wg.Done()
		defer closeDone()
		buf := make([]byte, readBufferBytes)
		for {
			n, rerr := child.Read(buf)
			if n > 0 {
				chunk := buf[:n]
				// Tee to host stdout so the user can see the TUI normally.
				_, _ = os.Stdout.Write(chunk)
				// Tee to bytes file for golden replay.
				_, _ = bytesFile.Write(chunk)
				// Feed the emulator.
				if _, werr := em.Write(chunk); werr != nil {
					fmt.Fprintf(os.Stderr, "\r\nspike: emulator.Write error: %v\r\n", werr)
				}
				lastWriteNS.Store(time.Now().UnixNano())
			}
			if rerr != nil {
				// EIO from the PTY master is the normal "child closed its
				// side" signal on Linux; treat it like EOF.
				if rerr != io.EOF && !errors.Is(rerr, syscall.EIO) {
					fmt.Fprintf(os.Stderr, "\r\nspike: pty read: %v\r\n", rerr)
				}
				return
			}
		}
	}()

	// Writer: stdin -> PTY, watching for the dump hotkey.
	if stdinPassthrough {
		wg.Add(1)
		go func() {
			defer wg.Done()
			buf := make([]byte, 1024)
			for {
				select {
				case <-done:
					return
				default:
				}
				n, rerr := os.Stdin.Read(buf)
				if n > 0 {
					chunk := buf[:n]
					if debugStdin {
						fmt.Fprintf(os.Stderr, "\r\nspike[debug-stdin]: %d bytes:", n)
						for _, b := range chunk {
							fmt.Fprintf(os.Stderr, " %02x", b)
						}
						fmt.Fprintf(os.Stderr, "\r\n")
					}
					out := make([]byte, 0, len(chunk))
					for _, b := range chunk {
						if b == hotkey {
							select {
							case dumpRequest <- "hotkey":
							default:
								// channel full; user is mashing the hotkey,
								// dumps are still coming
							}
							continue
						}
						out = append(out, b)
					}
					if len(out) > 0 {
						if _, werr := child.Write(out); werr != nil {
							return
						}
					}
				}
				if rerr != nil {
					return
				}
			}
		}()
	}

	// SIGWINCH propagation.
	if followHost {
		winch := make(chan os.Signal, 1)
		signal.Notify(winch, syscall.SIGWINCH)
		wg.Add(1)
		go func() {
			defer wg.Done()
			defer signal.Stop(winch)
			for {
				select {
				case <-done:
					return
				case <-winch:
					if c, r, ok := hostSize(); ok {
						_ = child.Resize(c, r)
						_ = em.Resize(c, r)
					}
				}
			}
		}()
	}

	// Idle ticker: enqueue an "idle" dump request when crossing the threshold.
	if idleMS > 0 {
		wg.Add(1)
		go func() {
			defer wg.Done()
			tick := time.NewTicker(time.Duration(idleMS) * time.Millisecond / 4)
			defer tick.Stop()
			for {
				select {
				case <-done:
					return
				case <-tick.C:
					now := time.Now().UnixNano()
					lw := lastWriteNS.Load()
					ld := lastDumpNS.Load()
					if now-lw >= int64(idleMS)*int64(time.Millisecond) && lw > ld {
						lastDumpNS.Store(now)
						dumpRequest <- "idle"
					}
				}
			}
		}()
	}

	// Dump worker: serialises grid reads. PlainText is not cheap and we
	// don't want overlapping calls.
	wg.Add(1)
	go func() {
		defer wg.Done()
		for {
			select {
			case <-done:
				return
			case reason := <-dumpRequest:
				dumpGrid(em, reason, gridSink, gridIsStderr || gridToStderr)
			}
		}
	}()

	// Wait for the child to exit, then close everything down.
	exitErr := child.Wait()
	closeDone()
	wg.Wait()

	// Final dump for the record.
	dumpGrid(em, "final", gridSink, gridIsStderr || gridToStderr)

	if restoreState != nil {
		_ = term.Restore(int(os.Stdin.Fd()), restoreState)
	}
	fmt.Fprintf(os.Stderr, "spike: child exited (%v); bytes=%s grid=%s\r\n", exitErr, bytesPath, gridPath)
	return nil
}

// dumpGrid renders the emulator's active screen and writes it to sink.
//
// When sinkIsTTY is true the lines are terminated with CRLF so they render
// correctly even when stdin is in raw mode. Otherwise we use plain LF —
// log files don't want CRs.
func dumpGrid(em *vt.GhosttyEmulator, reason string, sink *os.File, sinkIsTTY bool) {
	txt, err := em.PlainText()
	if err != nil {
		fmt.Fprintf(os.Stderr, "\r\nspike: PlainText (%s): %v\r\n", reason, err)
		return
	}
	cur, _ := em.Cursor()
	scr, _ := em.ActiveScreen()
	screenName := "primary"
	if scr == vt.ScreenAlternate {
		screenName = "alternate"
	}
	eol := "\n"
	if sinkIsTTY {
		eol = "\r\n"
	}
	sep := strings.Repeat("-", 78)
	header := fmt.Sprintf("[grid dump: %s @ %s | screen=%s cursor=(%d,%d) visible=%v]",
		reason, time.Now().Format(time.RFC3339Nano), screenName, cur.Col, cur.Row, cur.Visible)
	fmt.Fprintf(sink, "%s%s%s%s%s%s", eol, sep, eol, header, eol, sep+eol)
	for _, line := range strings.Split(txt, "\n") {
		fmt.Fprintf(sink, "%s%s", line, eol)
	}
	fmt.Fprintf(sink, "%s%s", sep, eol)

	// If the sink is a file (not the host TTY), print a one-line breadcrumb
	// to stderr so the user knows the hotkey fired — but only for explicit
	// user-triggered dumps (hotkey), and only when the child is on the
	// primary screen. Skipping idle/final dumps keeps the host terminal
	// quiet during normal interactive use.
	if !sinkIsTTY && reason == "hotkey" && scr != vt.ScreenAlternate {
		fmt.Fprintf(os.Stderr, "\r\nspike: dumped grid -> %s\r\n", sink.Name())
	}
}

func hostSize() (cols, rows uint16, ok bool) {
	ws, err := cpty.GetsizeFull(os.Stdin)
	if err != nil {
		return 0, 0, false
	}
	if ws.Cols == 0 || ws.Rows == 0 {
		return 0, 0, false
	}
	return ws.Cols, ws.Rows, true
}