// 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"
	"sync/atomic"
	"syscall"
	"time"

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

const childStopTimeout = 2 * time.Second

// 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.
	// listeners is an atomic.Pointer to a frozen slice. Subscribe
	// copy-on-writes the slice; emit* paths use a single atomic Load.
	// This drops one mutex acquisition per PTY chunk on the hot path.
	listenersMu sync.Mutex
	listeners   atomic.Pointer[[]ChildEventListener]

	// persistStore records top-level command entries to a per-project
	// JSON file so they can be re-spawned after patterm restarts.
	// Optional; nil means "no persistence" (used by unit tests).
	persistStore *persist.Store
}

// SetPersistStore attaches a process-persistence store. Future Spawn /
// Close / Rename / SetAutoRestart calls on top-level command entries
// will mirror the change into the store.
func (s *Session) SetPersistStore(p *persist.Store) {
	s.mu.Lock()
	s.persistStore = p
	s.mu.Unlock()
}

// 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)
	// OnChildStateChanged fires when the idle-detection classifier
	// updates a child's IdleState. Listeners use this to repaint the
	// sidebar badge and to evaluate idle-aware timers.
	OnChildStateChanged(childID string, state IdleState)
}

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()
	prev := s.listenersSnapshot()
	next := make([]ChildEventListener, 0, len(prev)+1)
	next = append(next, prev...)
	next = append(next, l)
	s.listeners.Store(&next)
}

// Unsubscribe removes a previously-registered listener. Safe to call
// with a listener that wasn't registered (no-op).
func (s *Session) Unsubscribe(l ChildEventListener) {
	s.listenersMu.Lock()
	defer s.listenersMu.Unlock()
	prev := s.listenersSnapshot()
	if len(prev) == 0 {
		return
	}
	next := make([]ChildEventListener, 0, len(prev))
	for _, e := range prev {
		if e != l {
			next = append(next, e)
		}
	}
	s.listeners.Store(&next)
}

// listenersSnapshot returns the frozen listener slice. Safe to call
// without the listeners mutex.
func (s *Session) listenersSnapshot() []ChildEventListener {
	p := s.listeners.Load()
	if p == nil {
		return nil
	}
	return *p
}

func (s *Session) emitSpawn(c *Child) {
	for _, l := range s.listenersSnapshot() {
		l.OnChildSpawned(c)
	}
}

func (s *Session) emitExit(c *Child) {
	for _, l := range s.listenersSnapshot() {
		l.OnChildExited(c)
	}
}

// emitPTYOut dispatches a fresh PTY chunk to every listener. Listeners
// MUST NOT retain `chunk` past return — the slice is owned by the
// pumpChild read buffer and is overwritten on the next read.
func (s *Session) emitPTYOut(id string, chunk []byte) {
	for _, l := range s.listenersSnapshot() {
		l.OnPTYOut(id, chunk)
	}
}

func (s *Session) emitStateChanged(id string, state IdleState) {
	for _, l := range s.listenersSnapshot() {
		l.OnChildStateChanged(id, state)
	}
}

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
	// CleanupPaths are owned runtime files/dirs removed when the child exits
	// or is closed. They must be attached before the PTY starts so a
	// fast-exiting child cannot outrun cleanup registration.
	CleanupPaths []string
	// IdleDetection is the resolved per-preset idle classifier config.
	// Must be installed before the child is published to s.children so
	// the classifier goroutine never observes a nil/default config for
	// a preset that overrides it.
	IdleDetection *resolvedIdleDetection
}

// 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
	}
	for _, path := range spec.CleanupPaths {
		c.AddCleanupPath(path)
	}
	// Install idle-detection BEFORE publishing to s.children — otherwise
	// the classifier goroutine could read c.idleDetection while the
	// launcher is still racing to set it.
	if spec.IdleDetection != nil {
		c.setIdleDetection(spec.IdleDetection)
	}
	runID, err := c.startPTY(cols, rows)
	if err != nil {
		c.cleanupOwnedPaths()
		return nil, err
	}

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

	// Wire persistence callback BEFORE registering so SetName /
	// SetAutoRestart calls that race the listener still hit the store.
	if store != nil {
		c.setPersistFn(func(ch *Child) {
			s.persistEntry(ch)
		})
		s.persistEntry(c)
	}

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

// persistEntry writes (or refreshes) the persist record for c if it
// qualifies — top-level command entries only. No-op when no store is
// attached.
func (s *Session) persistEntry(c *Child) {
	s.mu.Lock()
	store := s.persistStore
	s.mu.Unlock()
	if store == nil || !shouldPersist(c) {
		return
	}
	e := persist.Entry{
		ID:          c.ID,
		Name:        c.DisplayName(),
		Argv:        append([]string(nil), c.Argv...),
		WorkDir:     c.WorkDir,
		PresetRef:   c.PresetRef,
		AutoRestart: c.AutoRestart(),
	}
	if err := store.Save(e); err != nil {
		logf("persist save %s: %v", c.ID, err)
	}
}

func (s *Session) forgetPersisted(id string) {
	s.mu.Lock()
	store := s.persistStore
	s.mu.Unlock()
	if store == nil {
		return
	}
	if err := store.Remove(id); err != nil {
		logf("persist remove %s: %v", id, err)
	}
}

// shouldPersist gates which Child entries get mirrored into the
// persist store. v1 only restores top-level command entries — agents
// and terminals are ephemeral by design, and sub-agent-spawned
// commands belong to their orchestrator's lifecycle.
func shouldPersist(c *Child) bool {
	return c != nil && c.Kind == KindCommand && c.ParentID == ""
}

// 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
	}
	runID, err := c.startPTY(cols, rows)
	if err != nil {
		return err
	}
	go s.pumpChild(c, runID)
	go s.reapChild(c, runID)
	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)
	}
	// Only live entries can own runtime MCP config paths today. Keep the
	// reaper from cleaning those paths while restart swaps the PTY.
	c.restarting.Store(true)
	defer c.restarting.Store(false)
	if c.IsLive() {
		terminateAndWait(c, sig, childStopTimeout)
	}
	c.teardownPTY()
	runID, err := c.startPTY(cols, rows)
	if err != nil {
		return err
	}
	go s.pumpChild(c, runID)
	go s.reapChild(c, runID)
	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() {
		terminateAndWait(c, sig, childStopTimeout)
	}
	c.teardownPTY()
	c.cleanupOwnedPaths()
	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()
	s.forgetPersisted(id)
	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, runID uint64) {
	pty := c.ptyForRun(runID)
	if pty == nil {
		return
	}
	// One PTY read buffer per pump goroutine. Consumers downstream
	// (em.Write is synchronous through CGO; recordWrite append-copies
	// into the ring; renderer.Render copies into its pending buffer)
	// all complete or copy before returning, so the buffer can be
	// reused without aliasing live data. See ChildEventListener.OnPTYOut
	// docstring — listeners must not retain `chunk`.
	buf := make([]byte, 64*1024)
	for {
		n, err := pty.Read(buf)
		if n > 0 {
			if !c.isCurrentRun(runID) {
				return
			}
			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)
				}
				// OSC 0/2 title updates ride on the same byte stream as
				// the rest of the output. Polling the emulator after each
				// chunk is cheap on its own (one CGO call) but codex/
				// ratatui sends so many small chunks that the per-chunk
				// CGO cost becomes measurable. Skip the Title poll when
				// the chunk doesn't carry an OSC start byte at all; the
				// title can only change on chunks that include one.
				if containsOSC(chunk) {
					if t, terr := em.Title(); terr == nil {
						c.recordTitle(t)
					}
				}
			}
			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, runID uint64) {
	pty := c.ptyForRun(runID)
	if pty == nil {
		return
	}
	err := pty.Wait()
	if !c.isCurrentRun(runID) || c.restarting.Load() {
		return
	}
	c.markExited(err)
	logf("child %s exited (err=%v)", c.ID, err)
	s.emitExit(c)
	s.killDescendantsOf(c.ID)
	if !c.restarting.Load() {
		c.cleanupOwnedPaths()
	}
	// Terminals are ephemeral: unlike command entries (kept around for
	// restart_process) and agents (which the user clears via close_process
	// once they're done with the corpse), an exited terminal has nothing
	// useful left to do. Drop it from the session so it disappears from
	// the Processes sidebar / switch list immediately.
	if c.Kind == KindTerminal && !c.restarting.Load() {
		c.teardownPTY()
		s.mu.Lock()
		delete(s.children, c.ID)
		for i, oid := range s.order {
			if oid == c.ID {
				s.order = append(s.order[:i], s.order[i+1:]...)
				break
			}
		}
		s.mu.Unlock()
	}
}

// killDescendantsOf terminates every still-live direct child of
// parentID. SPEC §2: closing the patterm process tears down every
// child it spawned; the same rule applies in-session — when an
// orchestrator dies (natural exit, user Ctrl-C, MCP close, anything
// that makes its PTY EOF), the agents/commands/terminals it spawned
// must die with it. We only signal direct children here: each
// descendant's own reapChild will fire and recurse, so the cascade
// flows through arbitrary depth without us walking the tree.
func (s *Session) killDescendantsOf(parentID string) {
	if parentID == "" {
		return
	}
	s.mu.Lock()
	var live []*Child
	for _, c := range s.children {
		if c.ParentID == parentID && c.IsLive() {
			live = append(live, c)
		}
	}
	s.mu.Unlock()
	if len(live) == 0 {
		return
	}
	for _, c := range live {
		_ = c.signal(syscall.SIGTERM)
	}
	waitForAllStopped(live, childStopTimeout)
	for _, c := range live {
		if c.IsLive() {
			_ = c.signal(syscall.SIGKILL)
		}
	}
	waitForAllStopped(live, childStopTimeout)
}

func waitForAllStopped(children []*Child, timeout time.Duration) bool {
	deadline := time.Now().Add(timeout)
	for time.Now().Before(deadline) {
		anyLive := false
		for _, c := range children {
			if c.IsLive() {
				anyLive = true
				break
			}
		}
		if !anyLive {
			return true
		}
		time.Sleep(20 * time.Millisecond)
	}
	return false
}

func terminateAndWait(c *Child, sig syscall.Signal, timeout time.Duration) {
	if sig == 0 {
		sig = syscall.SIGTERM
	}
	_ = c.signal(sig)
	deadline := time.Now().Add(timeout)
	for c.IsLive() && time.Now().Before(deadline) {
		time.Sleep(20 * time.Millisecond)
	}
	if !c.IsLive() {
		return
	}
	_ = c.signal(syscall.SIGKILL)
	deadline = time.Now().Add(timeout)
	for c.IsLive() && time.Now().Before(deadline) {
		time.Sleep(20 * time.Millisecond)
	}
}

// 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) StyledSnapshotChild(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.StyledScreenVT()
}

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()
		c.cleanupOwnedPaths()
	}
}

// containsOSC reports whether chunk holds a sequence that could begin
// an OSC. OSC starts as ESC ] (0x1b 0x5d) or the bare C1 ] (0x9d),
// so a chunk without either cannot have changed the emulator's OSC
// title state. Used to short-circuit the per-chunk Title() poll from
// pumpChild, which otherwise pays a CGO call for every chunk even
// when codex/ratatui is just emitting SGR-styled output.
func containsOSC(chunk []byte) bool {
	for i, b := range chunk {
		if b == 0x9d {
			return true
		}
		if b == 0x1b && i+1 < len(chunk) && chunk[i+1] == ']' {
			return true
		}
	}
	return false
}

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...)
}