package server

import (
	"fmt"
	"log"
	"os"
	"os/exec"
	"strings"
	"sync"
	"time"

	"github.com/creack/pty"
)

const (
	outputBufferSize = 1024 * 1024 // 1MB ring buffer for replay
)

// RingBuffer is a fixed-size circular buffer for terminal output.
type RingBuffer struct {
	data []byte
	size int
	pos  int
	full bool
	mu   sync.Mutex
}

// NewRingBuffer creates a new ring buffer with the given size.
func NewRingBuffer(size int) *RingBuffer {
	return &RingBuffer{data: make([]byte, size), size: size}
}

// Write appends data to the ring buffer.
func (rb *RingBuffer) Write(p []byte) {
	rb.mu.Lock()
	defer rb.mu.Unlock()
	for _, b := range p {
		rb.data[rb.pos] = b
		rb.pos++
		if rb.pos >= rb.size {
			rb.pos = 0
			rb.full = true
		}
	}
}

// Bytes returns the buffer contents in correct order.
func (rb *RingBuffer) Bytes() []byte {
	rb.mu.Lock()
	defer rb.mu.Unlock()
	if !rb.full {
		result := make([]byte, rb.pos)
		copy(result, rb.data[:rb.pos])
		return result
	}
	result := make([]byte, rb.size)
	n := copy(result, rb.data[rb.pos:])
	copy(result[n:], rb.data[:rb.pos])
	return result
}

// Reset clears the buffer.
func (rb *RingBuffer) Reset() {
	rb.mu.Lock()
	defer rb.mu.Unlock()
	rb.pos = 0
	rb.full = false
}

// consolePTYSession manages a single claude CLI running in a pseudo-terminal.
type consolePTYSession struct {
	ID          string
	Ptmx        *os.File
	Cmd         *exec.Cmd
	buffer      *RingBuffer
	subscribers map[string]chan []byte
	mu          sync.Mutex
	done        chan struct{}
	lastActive  time.Time
}

// spawnConsolePTY starts a new claude CLI in a PTY for the console.
func spawnConsolePTY(projectDir, prompt string) (*consolePTYSession, error) {
	cmd := exec.Command("claude", "--permission-mode", "dontAsk", "-p", prompt)
	cmd.Dir = projectDir
	cmd.Env = cleanEnvForPTY()

	ptmx, err := pty.StartWithSize(cmd, &pty.Winsize{Rows: 24, Cols: 120})
	if err != nil {
		return nil, fmt.Errorf("start pty: %w", err)
	}

	sess := &consolePTYSession{
		ID:          fmt.Sprintf("pty-%d", time.Now().UnixNano()),
		Ptmx:        ptmx,
		Cmd:         cmd,
		buffer:      NewRingBuffer(outputBufferSize),
		subscribers: make(map[string]chan []byte),
		done:        make(chan struct{}),
		lastActive:  time.Now(),
	}

	go sess.readLoop()
	go sess.waitExit()

	return sess, nil
}

// spawnShellPTY starts an interactive claude CLI in a PTY for the console.
func spawnShellPTY(projectDir string) (*consolePTYSession, error) {
	cmd := exec.Command("claude")
	cmd.Dir = projectDir
	cmd.Env = cleanEnvForPTY()

	ptmx, err := pty.StartWithSize(cmd, &pty.Winsize{Rows: 24, Cols: 120})
	if err != nil {
		return nil, fmt.Errorf("start pty: %w", err)
	}

	sess := &consolePTYSession{
		ID:          fmt.Sprintf("shell-%d", time.Now().UnixNano()),
		Ptmx:        ptmx,
		Cmd:         cmd,
		buffer:      NewRingBuffer(outputBufferSize),
		subscribers: make(map[string]chan []byte),
		done:        make(chan struct{}),
		lastActive:  time.Now(),
	}

	go sess.readLoop()
	go sess.waitExit()

	return sess, nil
}

// readLoop reads PTY output, writes to ring buffer, and forwards to subscribers.
func (s *consolePTYSession) readLoop() {
	buf := make([]byte, 4096)
	totalBytes := 0
	for {
		n, err := s.Ptmx.Read(buf)
		if err != nil {
			log.Printf("PTY[%s]: readLoop ended (read %d bytes total, err: %v)", s.ID, totalBytes, err)
			return
		}
		if n == 0 {
			continue
		}
		totalBytes += n
		data := make([]byte, n)
		copy(data, buf[:n])

		s.buffer.Write(data)

		s.mu.Lock()
		s.lastActive = time.Now()
		subs := len(s.subscribers)
		for _, ch := range s.subscribers {
			select {
			case ch <- data:
			default:
			}
		}
		s.mu.Unlock()

		if totalBytes == n {
			// First chunk — log it
			log.Printf("PTY[%s]: first output (%d bytes, %d subscribers)", s.ID, n, subs)
		}
	}
}

// waitExit waits for the CLI process to exit and signals done.
func (s *consolePTYSession) waitExit() {
	if s.Cmd.Process != nil {
		s.Cmd.Wait()
	}
	close(s.done)
}

// Subscribe adds a subscriber for PTY output.
func (s *consolePTYSession) Subscribe(id string) chan []byte {
	s.mu.Lock()
	defer s.mu.Unlock()
	ch := make(chan []byte, 256)
	s.subscribers[id] = ch
	return ch
}

// Unsubscribe removes a subscriber.
func (s *consolePTYSession) Unsubscribe(id string) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if ch, ok := s.subscribers[id]; ok {
		close(ch)
		delete(s.subscribers, id)
	}
}

// Resize changes the PTY terminal size.
func (s *consolePTYSession) Resize(rows, cols uint16) error {
	return pty.Setsize(s.Ptmx, &pty.Winsize{Rows: rows, Cols: cols})
}

// WriteInput sends keyboard input to the PTY.
func (s *consolePTYSession) WriteInput(data []byte) (int, error) {
	s.mu.Lock()
	s.lastActive = time.Now()
	s.mu.Unlock()
	return s.Ptmx.Write(data)
}

// GetBuffer returns the ring buffer contents for replay.
func (s *consolePTYSession) GetBuffer() []byte {
	return s.buffer.Bytes()
}

// Done returns a channel that closes when the process exits.
func (s *consolePTYSession) Done() <-chan struct{} {
	return s.done
}

// Close terminates the PTY session.
func (s *consolePTYSession) Close() {
	s.mu.Lock()
	for id, ch := range s.subscribers {
		close(ch)
		delete(s.subscribers, id)
	}
	s.mu.Unlock()

	s.Ptmx.Close()
	if s.Cmd.Process != nil {
		s.Cmd.Process.Kill()
	}
}

// cleanEnvForPTY returns environment with proper terminal settings.
func cleanEnvForPTY() []string {
	var env []string
	for _, e := range os.Environ() {
		if strings.HasPrefix(e, "CLAUDECODE=") ||
			strings.HasPrefix(e, "CLAUDE_CODE_ENTRYPOINT=") ||
			strings.HasPrefix(e, "TERM=") ||
			strings.HasPrefix(e, "COLORTERM=") {
			continue
		}
		env = append(env, e)
	}
	env = append(env, "TERM=xterm-256color", "COLORTERM=truecolor")
	return env
}