// Package app is patterm's single foreground process. It owns the TUI,
// every PTY, every emulator, the in-process MCP server, and the
// scratchpad/preset state.
//
// There is no daemon, no detach, no socket-based client/daemon split
// (SPEC §2). One process owns everything; closing the terminal window
// ends the session and tears down every child.
package app

import (
	"errors"
	"fmt"
	"os"
	"sync"
	"syscall"
	"time"

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

// Session is the in-memory state for the running patterm process.
// In SPEC §4 terms each top-level tab is a session; v1 ships with a
// single implicit session and reserves room to grow.
type Session struct {
	projectDir string
	projectKey string

	mu       sync.Mutex
	children map[string]*Child
	order    []string

	// nameSeq tracks the default-name counter per kind (agent-1,
	// command-2, terminal-3, …). Reset is a non-goal: counters are
	// monotonic across the session lifetime.
	nameSeq map[ChildKind]int

	// listeners is the set of UI listeners that want to hear about child
	// lifecycle events (spawn/exit) — exactly one (the TUI) in v1.
	listenersMu sync.Mutex
	listeners   []ChildEventListener
}

// ChildEventListener is implemented by the TUI to react to lifecycle
// events without polling.
type ChildEventListener interface {
	OnChildSpawned(*Child)
	OnChildExited(*Child)
	// OnPTYOut is called for every chunk the child writes to its PTY.
	// Only the focused-child chunk should reach the screen — the TUI
	// filters by id.
	OnPTYOut(childID string, chunk []byte)
}

func NewSession(projectDir, projectKey string) *Session {
	return &Session{
		projectDir: projectDir,
		projectKey: projectKey,
		children:   make(map[string]*Child),
		nameSeq:    make(map[ChildKind]int),
	}
}

func (s *Session) Subscribe(l ChildEventListener) {
	s.listenersMu.Lock()
	defer s.listenersMu.Unlock()
	s.listeners = append(s.listeners, l)
}

func (s *Session) emitSpawn(c *Child) {
	s.listenersMu.Lock()
	ls := append([]ChildEventListener(nil), s.listeners...)
	s.listenersMu.Unlock()
	for _, l := range ls {
		l.OnChildSpawned(c)
	}
}

func (s *Session) emitExit(c *Child) {
	s.listenersMu.Lock()
	ls := append([]ChildEventListener(nil), s.listeners...)
	s.listenersMu.Unlock()
	for _, l := range ls {
		l.OnChildExited(c)
	}
}

func (s *Session) emitPTYOut(id string, chunk []byte) {
	s.listenersMu.Lock()
	ls := append([]ChildEventListener(nil), s.listeners...)
	s.listenersMu.Unlock()
	for _, l := range ls {
		l.OnPTYOut(id, chunk)
	}
}

func (s *Session) ChildEnv() []string {
	env := os.Environ()
	// Mark patterm-owned PTYs so a recursive `patterm` invocation can
	// detect it and degrade. The MCP socket is per-PID and lives under
	// $XDG_RUNTIME_DIR — see internal/mcp.
	env = append(env,
		"PATTERM=1",
		"PATTERM_PROJECT_KEY="+s.projectKey,
		"PATTERM_PROJECT_DIR="+s.projectDir,
	)
	return env
}

// SpawnSpec is the argument record for Session.Spawn — the new
// argv-shaped spawn API matching SPEC §7 spawn_process.
type SpawnSpec struct {
	Kind      ChildKind
	Argv      []string
	Env       []string
	WorkDir   string
	Name      string
	ParentID  string
	PresetRef string
	Identity  string // pre-minted; otherwise the constructor mints one for agents
}

// Spawn creates a new entry and starts its PTY. For Kind = command the
// entry remains in the session after PTY exit (it can be Restart'd).
// For agent/terminal the entry's lifetime equals the PTY's: reapChild
// fires emitExit and the entry stays in `exited` status until the
// caller `close_process`'s it.
func (s *Session) Spawn(spec SpawnSpec, cols, rows uint16) (*Child, error) {
	if len(spec.Argv) == 0 {
		return nil, errors.New("session.Spawn: empty argv")
	}
	if spec.Env == nil {
		spec.Env = s.ChildEnv()
	}

	s.mu.Lock()
	id := s.mintUniqueIDLocked()
	s.nameSeq[spec.Kind]++
	if spec.Name == "" {
		spec.Name = fmt.Sprintf("%s-%d", spec.Kind, s.nameSeq[spec.Kind])
	}
	s.mu.Unlock()

	c := newChildEntry(id, spec.Name, spec.Kind, spec.Argv, spec.Env, spec.ParentID, spec.WorkDir, spec.PresetRef)
	if spec.Identity != "" {
		c.Identity = spec.Identity
	}
	if err := c.startPTY(cols, rows); err != nil {
		return nil, err
	}

	s.mu.Lock()
	s.children[id] = c
	s.order = append(s.order, id)
	s.mu.Unlock()

	s.emitSpawn(c)
	go s.pumpChild(c)
	go s.reapChild(c)
	return c, nil
}

// AddCommandEntry registers a command entry without starting it. Used
// by spawn_process(kind: command) when SPEC §7 needs the entry to exist
// in `stopped` state first (we always start it after; the indirection
// is here so future versions can support deferred starts).
func (s *Session) AddCommandEntry(spec SpawnSpec) *Child {
	s.mu.Lock()
	id := s.mintUniqueIDLocked()
	s.nameSeq[spec.Kind]++
	if spec.Name == "" {
		spec.Name = fmt.Sprintf("%s-%d", spec.Kind, s.nameSeq[spec.Kind])
	}
	if spec.Env == nil {
		spec.Env = s.ChildEnv()
	}
	c := newChildEntry(id, spec.Name, spec.Kind, spec.Argv, spec.Env, spec.ParentID, spec.WorkDir, spec.PresetRef)
	s.children[id] = c
	s.order = append(s.order, id)
	s.mu.Unlock()
	s.emitSpawn(c)
	return c
}

// Start (re)attaches a PTY to an entry that is currently stopped or
// exited. Errors if the entry is already live.
func (s *Session) Start(id string, cols, rows uint16) error {
	c := s.FindChild(id)
	if c == nil {
		return fmt.Errorf("no such process %q", id)
	}
	if c.IsLive() {
		return nil // SPEC §7 start_process is a no-op on a running entry
	}
	if err := c.startPTY(cols, rows); err != nil {
		return err
	}
	go s.pumpChild(c)
	go s.reapChild(c)
	return nil
}

// Restart stops the entry (if live) then starts it again with the same
// argv/env/workdir. Per SPEC §7: valid for command entries; valid for
// agent/terminal only while their PTY is still live.
func (s *Session) Restart(id string, sig syscall.Signal, cols, rows uint16) error {
	c := s.FindChild(id)
	if c == nil {
		return fmt.Errorf("no such process %q", id)
	}
	if c.Kind != KindCommand && !c.IsLive() {
		return fmt.Errorf("restart: %s entries can only be restarted while live", c.Kind)
	}
	if c.IsLive() {
		if sig == 0 {
			sig = syscall.SIGTERM
		}
		_ = c.signal(sig)
		// Wait briefly for the reaper to mark exited. We don't need
		// strict synchronization — the reaper will run regardless; we
		// just want startPTY to land after teardown.
		deadline := time.Now().Add(2 * time.Second)
		for c.IsLive() && time.Now().Before(deadline) {
			time.Sleep(20 * time.Millisecond)
		}
		if c.IsLive() {
			// Force.
			_ = c.signal(syscall.SIGKILL)
			for c.IsLive() {
				time.Sleep(20 * time.Millisecond)
			}
		}
	}
	c.teardownPTY()
	if err := c.startPTY(cols, rows); err != nil {
		return err
	}
	go s.pumpChild(c)
	go s.reapChild(c)
	return nil
}

// Close removes an entry from the session entirely. If still live,
// stops it first. SPEC §7 close_process.
func (s *Session) Close(id string, sig syscall.Signal) error {
	c := s.FindChild(id)
	if c == nil {
		return fmt.Errorf("no such process %q", id)
	}
	if c.IsLive() {
		if sig == 0 {
			sig = syscall.SIGTERM
		}
		_ = c.signal(sig)
		deadline := time.Now().Add(2 * time.Second)
		for c.IsLive() && time.Now().Before(deadline) {
			time.Sleep(20 * time.Millisecond)
		}
		if c.IsLive() {
			_ = c.signal(syscall.SIGKILL)
			for c.IsLive() {
				time.Sleep(20 * time.Millisecond)
			}
		}
	}
	c.teardownPTY()
	s.mu.Lock()
	delete(s.children, id)
	for i, oid := range s.order {
		if oid == id {
			s.order = append(s.order[:i], s.order[i+1:]...)
			break
		}
	}
	s.mu.Unlock()
	return nil
}

// mintUniqueIDLocked mints an opaque process_id (SPEC §7) and retries
// if it collides with an existing entry. Caller holds s.mu.
func (s *Session) mintUniqueIDLocked() string {
	for {
		id := mintProcessID()
		if _, exists := s.children[id]; !exists {
			return id
		}
	}
}

func (s *Session) pumpChild(c *Child) {
	buf := make([]byte, 64*1024)
	for {
		pty := c.PTY()
		if pty == nil {
			return
		}
		n, err := pty.Read(buf)
		if n > 0 {
			chunk := make([]byte, n)
			copy(chunk, buf[:n])
			if em := c.Emulator(); em != nil {
				if _, werr := em.Write(chunk); werr != nil {
					logf("emulator.Write(child %s): %v", c.ID, werr)
				}
			}
			c.recordWrite(chunk)
			s.emitPTYOut(c.ID, chunk)
		}
		if err != nil {
			if !errors.Is(err, syscall.EIO) && !errors.Is(err, os.ErrClosed) {
				logf("pty read (child %s): %v", c.ID, err)
			}
			return
		}
	}
}

func (s *Session) reapChild(c *Child) {
	pty := c.PTY()
	if pty == nil {
		return
	}
	err := pty.Wait()
	c.markExited(err)
	logf("child %s exited (err=%v)", c.ID, err)
	s.emitExit(c)
}

// Children returns a snapshot of children in spawn order.
func (s *Session) Children() []*Child {
	s.mu.Lock()
	defer s.mu.Unlock()
	out := make([]*Child, 0, len(s.order))
	for _, id := range s.order {
		if c, ok := s.children[id]; ok {
			out = append(out, c)
		}
	}
	return out
}

// FindChild looks up a child by id; returns nil if not present.
func (s *Session) FindChild(id string) *Child {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.children[id]
}

// FindChildByIdentity finds the child whose Identity matches token.
// Used by MCP to bind a mcp-stdio greeting to its caller. Returns nil
// if no match.
func (s *Session) FindChildByIdentity(token string) *Child {
	if token == "" {
		return nil
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	for _, c := range s.children {
		if c.Identity == token {
			return c
		}
	}
	return nil
}

// Kill sends a signal (default SIGTERM) to a child by id.
func (s *Session) Kill(id string, sig syscall.Signal) error {
	c := s.FindChild(id)
	if c == nil {
		return fmt.Errorf("no such child %q", id)
	}
	if sig == 0 {
		sig = syscall.SIGTERM
	}
	return c.signal(sig)
}

// WriteInput pipes bytes to a child's PTY stdin.
func (s *Session) WriteInput(id string, b []byte) error {
	c := s.FindChild(id)
	if c == nil {
		return fmt.Errorf("no such child %q", id)
	}
	if c.Status() != StatusRunning {
		return fmt.Errorf("child %q is %s", id, c.Status())
	}
	pty := c.PTY()
	if pty == nil {
		return fmt.Errorf("child %q has no pty", id)
	}
	_, err := pty.Write(b)
	return err
}

// ResizeAll updates every child's PTY + emulator to the same cell grid.
// SPEC §5 says one viewport, no multi-client resize negotiation.
func (s *Session) ResizeAll(cols, rows uint16) {
	if cols == 0 || rows == 0 {
		return
	}
	s.mu.Lock()
	cs := make([]*Child, 0, len(s.children))
	for _, c := range s.children {
		cs = append(cs, c)
	}
	s.mu.Unlock()
	for _, c := range cs {
		if pty := c.PTY(); pty != nil {
			_ = pty.Resize(cols, rows)
		}
		if em := c.Emulator(); em != nil {
			_ = em.Resize(cols, rows)
		}
	}
}

// SerializeChild returns the VT bytes that reproduce the child's
// current screen state. Used to repaint a child after the user switches
// focus or closes the palette.
func (s *Session) SerializeChild(id string) ([]byte, error) {
	c := s.FindChild(id)
	if c == nil {
		return nil, fmt.Errorf("no such child %q", id)
	}
	em := c.Emulator()
	if em == nil {
		return nil, fmt.Errorf("child %q has no emulator", id)
	}
	return em.SerializeVT()
}

func (s *Session) SnapshotChild(id string) (string, vt.CursorState, error) {
	c := s.FindChild(id)
	if c == nil {
		return "", vt.CursorState{}, fmt.Errorf("no such child %q", id)
	}
	em := c.Emulator()
	if em == nil {
		return "", vt.CursorState{}, fmt.Errorf("child %q has no emulator", id)
	}
	text, err := em.ScreenText()
	if err != nil {
		return "", vt.CursorState{}, err
	}
	cursor, err := em.Cursor()
	if err != nil {
		return "", vt.CursorState{}, err
	}
	return text, cursor, nil
}

// Shutdown kills every child and waits briefly for them to drain.
// Called on Ctrl-D / SIGTERM / SIGHUP. SPEC §2 step 4.
func (s *Session) Shutdown() {
	s.mu.Lock()
	cs := make([]*Child, 0, len(s.children))
	for _, c := range s.children {
		cs = append(cs, c)
	}
	s.mu.Unlock()
	for _, c := range cs {
		_ = c.signal(syscall.SIGTERM)
	}
	// Close emulators and PTY masters. The reaper goroutines will fire
	// emitExit as Wait() returns.
	for _, c := range cs {
		c.teardownPTY()
	}
}

func logf(format string, args ...any) {
	if os.Getenv("PATTERM_DEBUG_LOG") == "" {
		return
	}
	f, err := os.OpenFile(os.Getenv("PATTERM_DEBUG_LOG"), os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600)
	if err != nil {
		return
	}
	defer f.Close()
	fmt.Fprintf(f, "patterm: "+format+"\n", args...)
}