package app

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"os/exec"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

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

// portRegex matches dev-server URLs of the form `http(s)://host:NNNN[/path]`
// and reports the port. SPEC §7 get_process_ports is best-effort; we
// stick to URL-form sightings because bare `:NNNN` produces too many
// false positives (timestamps, exit codes, etc.).
var portRegex = regexp.MustCompile(`https?://[^\s:/]+:(\d{2,5})(?:/[^\s]*)?`)

type ChildStatus string

const (
	StatusStarting ChildStatus = "starting"
	StatusRunning  ChildStatus = "running"
	StatusStopped  ChildStatus = "stopped"
	StatusExited   ChildStatus = "exited"
	StatusErrored  ChildStatus = "errored"
)

// ChildKind matches the three process kinds in SPEC §7.
//   - agent: vendor LLM CLI launched from an agent preset (MCP-wired,
//     ephemeral — lost when the PTY exits).
//   - terminal: a bare interactive shell (ephemeral).
//   - command: a process preset or freeform argv (session-persistent —
//     survives PTY exit so it can be restart_process'd).
type ChildKind string

const (
	KindAgent    ChildKind = "agent"
	KindTerminal ChildKind = "terminal"
	KindCommand  ChildKind = "command"
)

// Owner reflects the SPEC §6 input-ownership flag.
type Owner string

const (
	OwnerUser         Owner = "user"
	OwnerOrchestrator Owner = "orchestrator"
)

// Child is one entry in the session — a PTY-backed process plus its
// emulator. Covers all three kinds (agent / terminal / command).
//
// For KindCommand the entry is session-persistent: argv/env/workingDir
// stay populated across stop/restart so Restart() can rebuild the PTY
// against the same spec.
type Child struct {
	ID       string
	Name     string
	Argv     []string
	Env      []string
	WorkDir  string
	Kind     ChildKind
	ParentID string // empty for top-level sessions

	// PresetRef names the source preset (when known). Used by trust
	// gating to re-check on restart_process. Empty for freeform-argv
	// command entries and for ephemeral terminals.
	PresetRef string

	// Identity is the per-spawn token the mcp-stdio proxy uses to
	// identify itself when calling tools. Empty for non-agent entries.
	Identity string

	// nameMu guards Name (rename_process).
	nameMu sync.RWMutex

	// ptyMu guards pty + em so Restart can swap them while pumpChild /
	// reapChild loops detect the swap by observing nil/closed PTY.
	ptyMu sync.RWMutex
	pty   *pkgpty.PTY
	em    *vt.GhosttyEmulator

	status   atomic.Pointer[ChildStatus]
	exitCode atomic.Int32

	owner atomic.Pointer[Owner]

	// lastWriteNS is the wall time of the most recent PTY-master write.
	// SPEC §11 idle heuristic: a pane is idle once nothing has been
	// written for the preset's threshold (default 1s).
	lastWriteNS atomic.Int64

	// screenVersion increments on every PTY-out chunk. SPEC §7
	// get_process_output exposes it so orchestrators can detect changes
	// without diffing content.
	screenVersion atomic.Int64

	// ringMu guards ring. The ring buffer carries the last `ringCap`
	// bytes the PTY produced, used by SPEC §7 get_process_output stream
	// mode and search_output scrollback.
	ringMu     sync.Mutex
	ring       []byte
	ringStart  int64 // absolute offset of ring[0]
	ringWrites int64 // cumulative bytes written

	// portsMu guards ports. Best-effort port detection: regex on stream.
	portsMu sync.Mutex
	ports   []PortSighting
}

// PortSighting is one entry returned by get_process_ports.
type PortSighting struct {
	Port        int    `json:"port"`
	URL         string `json:"url,omitempty"`
	FirstSeenAt string `json:"first_seen_at"`
}

const ringCap = 1 << 20 // 1 MiB per SPEC §5

// newChildEntry builds the in-memory Child record but does NOT start a
// PTY. Used so command entries can exist in the `stopped` state from the
// moment they're created. Agents and terminals call newChild() which
// chains newChildEntry + startPTY for the initial run.
func newChildEntry(id, name string, kind ChildKind, argv, env []string, parentID, workDir, presetRef string) *Child {
	c := &Child{
		ID:        id,
		Name:      name,
		Argv:      argv,
		Env:       env,
		WorkDir:   workDir,
		Kind:      kind,
		ParentID:  parentID,
		PresetRef: presetRef,
		ring:      make([]byte, 0, ringCap),
	}
	st := StatusStopped
	c.status.Store(&st)
	c.exitCode.Store(-1)
	def := OwnerUser
	if kind == KindAgent && parentID != "" {
		def = OwnerOrchestrator
	}
	c.owner.Store(&def)
	if kind == KindAgent {
		c.Identity = mintIdentity()
	}
	return c
}

func newChild(id, name string, kind ChildKind, argv, env []string, cols, rows uint16, parentID, workDir, presetRef string) (*Child, error) {
	if len(argv) == 0 {
		return nil, errors.New("child: empty argv")
	}
	c := newChildEntry(id, name, kind, argv, env, parentID, workDir, presetRef)
	if err := c.startPTY(cols, rows); err != nil {
		return nil, err
	}
	return c, nil
}

// startPTY (re)builds the emulator + PTY for this entry. Called by
// newChild on initial spawn and by Restart on subsequent runs. The
// status transitions stopped/exited → starting → running. On error the
// entry returns to errored.
func (c *Child) startPTY(cols, rows uint16) error {
	em, err := vt.NewGhosttyEmulator(cols, rows)
	if err != nil {
		return fmt.Errorf("child %s emulator: %w", c.ID, err)
	}
	starting := StatusStarting
	c.status.Store(&starting)
	p, err := pkgpty.Start(c.Argv, c.Env, cols, rows)
	if err != nil {
		em.Close()
		errored := StatusErrored
		c.status.Store(&errored)
		return fmt.Errorf("child %s pty: %w", c.ID, err)
	}
	em.OnWritePTY(func(b []byte) {
		_, _ = p.Write(b)
	})
	c.ptyMu.Lock()
	c.pty = p
	c.em = em
	c.ptyMu.Unlock()
	running := StatusRunning
	c.status.Store(&running)
	c.exitCode.Store(-1)
	c.lastWriteNS.Store(0)
	return nil
}

// IsLive reports whether the PTY is currently attached and running.
// Used by callers that need to gate input on a live PTY (vs. a stopped
// command entry).
func (c *Child) IsLive() bool {
	st := c.Status()
	return st == StatusStarting || st == StatusRunning
}

// PTY returns the current PTY pointer under read-lock. May be nil for a
// stopped command entry.
func (c *Child) PTY() *pkgpty.PTY {
	c.ptyMu.RLock()
	defer c.ptyMu.RUnlock()
	return c.pty
}

// Emulator returns the current emulator pointer under read-lock.
func (c *Child) Emulator() *vt.GhosttyEmulator {
	c.ptyMu.RLock()
	defer c.ptyMu.RUnlock()
	return c.em
}

// DisplayName is the rename_process-aware accessor for Name. Callers
// that read Name directly skip the lock; the field is still safe to
// read because Go strings are immutable, but DisplayName signals intent.
func (c *Child) DisplayName() string {
	c.nameMu.RLock()
	defer c.nameMu.RUnlock()
	return c.Name
}

// SetName updates the display name (rename_process).
func (c *Child) SetName(name string) {
	c.nameMu.Lock()
	c.Name = name
	c.nameMu.Unlock()
}

// ScreenVersion returns the current emulator snapshot version, bumped
// on every PTY-out chunk.
func (c *Child) ScreenVersion() int64 { return c.screenVersion.Load() }

func (c *Child) Status() ChildStatus {
	st := c.status.Load()
	if st == nil {
		return StatusRunning
	}
	return *st
}

func (c *Child) ExitCode() int { return int(c.exitCode.Load()) }

func (c *Child) PID() int {
	pty := c.PTY()
	if pty == nil {
		return 0
	}
	return pty.Pid()
}

func (c *Child) Owner() Owner {
	o := c.owner.Load()
	if o == nil {
		return OwnerUser
	}
	return *o
}

func (c *Child) SetOwner(o Owner) { c.owner.Store(&o) }

// IdleMS returns how many milliseconds since the last PTY write.
// 0 means "no writes yet". SPEC §11.
func (c *Child) IdleMS() int64 {
	last := c.lastWriteNS.Load()
	if last == 0 {
		return 0
	}
	return (time.Now().UnixNano() - last) / int64(time.Millisecond)
}

func (c *Child) recordWrite(chunk []byte) {
	c.lastWriteNS.Store(time.Now().UnixNano())
	c.screenVersion.Add(1)
	c.ringMu.Lock()
	c.ring = append(c.ring, chunk...)
	c.ringWrites += int64(len(chunk))
	if len(c.ring) > ringCap {
		drop := len(c.ring) - ringCap
		c.ring = c.ring[drop:]
		c.ringStart += int64(drop)
	}
	c.ringMu.Unlock()
	c.scanPortsFromChunk(chunk)
}

// scanPortsFromChunk does best-effort port detection on a PTY chunk.
// SPEC §7 get_process_ports — no probing, just stream scanning.
func (c *Child) scanPortsFromChunk(chunk []byte) {
	matches := portRegex.FindAllSubmatch(chunk, -1)
	if len(matches) == 0 {
		return
	}
	now := time.Now().UTC().Format(time.RFC3339)
	c.portsMu.Lock()
	defer c.portsMu.Unlock()
	for _, m := range matches {
		urlForm := string(m[0])
		portStr := string(m[1])
		port, err := strconv.Atoi(portStr)
		if err != nil || port < 1 || port > 65535 {
			continue
		}
		seen := false
		for _, p := range c.ports {
			if p.Port == port {
				seen = true
				break
			}
		}
		if seen {
			continue
		}
		ent := PortSighting{Port: port, FirstSeenAt: now}
		if strings.HasPrefix(urlForm, "http") {
			ent.URL = urlForm
		}
		c.ports = append(c.ports, ent)
	}
}

// Ports returns a snapshot of detected port sightings.
func (c *Child) Ports() []PortSighting {
	c.portsMu.Lock()
	defer c.portsMu.Unlock()
	out := make([]PortSighting, len(c.ports))
	copy(out, c.ports)
	return out
}

// StreamRead returns ring bytes from `since` to the current write head,
// plus the new offset. Offsets are absolute (cumulative bytes ever
// written). If `since` is before the ring start, the caller missed
// data; we return what we have and the new offset.
func (c *Child) StreamRead(since int64) ([]byte, int64) {
	c.ringMu.Lock()
	defer c.ringMu.Unlock()
	if since < c.ringStart {
		since = c.ringStart
	}
	end := c.ringStart + int64(len(c.ring))
	if since >= end {
		return nil, end
	}
	start := int(since - c.ringStart)
	out := make([]byte, end-since)
	copy(out, c.ring[start:])
	return out, end
}

func (c *Child) signal(sig syscall.Signal) error {
	pty := c.PTY()
	if pty == nil {
		return errors.New("child has no pty")
	}
	pid := pty.Pid()
	if pid <= 0 {
		return errors.New("child has no pid")
	}
	if err := syscall.Kill(-pid, sig); err == nil {
		return nil
	}
	return syscall.Kill(pid, sig)
}

// NudgeRedraw asks the child to throw away any diff-based render state
// and emit a full frame on the next tick. Used after a focus switch so
// ratatui/ink TUIs re-render coherently against the snapshot we just
// replayed. We toggle the PTY size by one row so the kernel reliably
// emits SIGWINCH (TIOCSWINSZ skips the signal if the size didn't
// change), then send SIGWINCH explicitly for TUIs that miss or coalesce
// the size-toggled signal. The emulator is left alone — it already
// matches our intended size and the brief mismatch only affects what the
// child writes during the second redraw.
func (c *Child) NudgeRedraw(cols, rows uint16) {
	pty := c.PTY()
	if pty == nil || rows < 2 {
		return
	}
	_ = pty.Resize(cols, rows-1)
	_ = pty.Resize(cols, rows)
	_ = c.signal(syscall.SIGWINCH)
}

func (c *Child) markExited(err error) {
	exitCode := int32(0)
	st := StatusExited
	if err != nil {
		var ee *exec.ExitError
		if errors.As(err, &ee) {
			exitCode = int32(ee.ExitCode())
		} else {
			exitCode = -1
			st = StatusErrored
		}
	}
	c.exitCode.Store(exitCode)
	c.status.Store(&st)
}

// teardownPTY closes the current PTY/emulator and nils them out. Used
// by Restart so the new PTY can take their place. Safe to call when
// they're already nil.
func (c *Child) teardownPTY() {
	c.ptyMu.Lock()
	p, em := c.pty, c.em
	c.pty, c.em = nil, nil
	c.ptyMu.Unlock()
	if p != nil {
		_ = p.Close()
	}
	if em != nil {
		_ = em.Close()
	}
}

// InjectAsUser is the path the human takes when typing in the focused
// pane. SPEC §6: the user's first keystroke flips ownership.
func (c *Child) InjectAsUser(b []byte) error {
	c.SetOwner(OwnerUser)
	return c.writeInput(b)
}

// InjectAsOrchestrator is the path send_message / initial_prompt /
// timer_wait writes take. Ownership flips back to orchestrator. SPEC §6.
func (c *Child) InjectAsOrchestrator(b []byte) error {
	c.SetOwner(OwnerOrchestrator)
	return c.writeInput(b)
}

// writeInput is the shared PTY write path used by both injection
// flavours. Each Enter byte (CR or LF) is split onto its own write
// with a brief delay so TUI agents with paste-detection (claude,
// codex, opencode) don't coalesce a trailing CR into the text that
// preceded it. Without the split, `pty.Write([]byte("hello\r"))`
// arrives at the agent as one read() and gets treated as multi-line
// pasted content rather than "key Enter".
func (c *Child) writeInput(b []byte) error {
	pty := c.PTY()
	if pty == nil {
		return errors.New("child has no pty")
	}
	pieces := splitOnEnter(b)
	if len(pieces) <= 1 {
		_, err := pty.Write(b)
		return err
	}
	for i, piece := range pieces {
		if i > 0 {
			time.Sleep(15 * time.Millisecond)
		}
		if _, err := pty.Write(piece); err != nil {
			return err
		}
	}
	return nil
}

func mintIdentity() string {
	var buf [12]byte
	_, _ = rand.Read(buf[:])
	return hex.EncodeToString(buf[:])
}

// mintProcessID generates the opaque short token SPEC §7 calls a
// process_id: lowercase `p_` followed by 6 hex chars. Collisions inside
// one session are checked by the caller (session.go).
func mintProcessID() string {
	var buf [3]byte
	_, _ = rand.Read(buf[:])
	return "p_" + hex.EncodeToString(buf[:])
}