// Package process manages the agent subprocess lifecycle
package process

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"log/slog"
	"os/exec"
	"sync"
	"sync/atomic"
	"time"

	"github.com/coder/acp-go-sdk"
	acpclient "github.com/kandev/kandev/internal/agentctl/acp"
	"github.com/kandev/kandev/internal/agentctl/config"
	"github.com/kandev/kandev/internal/common/logger"
	"go.uber.org/zap"
)

// Compile-time check that we export our client
var _ acp.Client = (*acpclient.Client)(nil)

// Status represents the agent process status
type Status string

const (
	StatusStopped  Status = "stopped"
	StatusStarting Status = "starting"
	StatusRunning  Status = "running"
	StatusPaused   Status = "paused"
	StatusStopping Status = "stopping"
	StatusError    Status = "error"
)

// errorWrapper wraps an error so it can be stored in atomic.Value (which cannot store nil)
type errorWrapper struct {
	err error
}

// Manager manages the agent subprocess
type Manager struct {
	cfg    *config.Config
	logger *logger.Logger

	// Process state
	cmd      *exec.Cmd
	stdin    io.WriteCloser
	stdout   io.ReadCloser
	stderr   io.ReadCloser
	status   atomic.Value // Status
	exitCode atomic.Int32
	exitErr  atomic.Value // error

	// Output buffer for streaming
	outputBuffer *OutputBuffer

	// ACP SDK connection
	acpClient *acpclient.Client
	acpConn   *acp.ClientSideConnection
	sessionID acp.SessionId

	// Session update notifications
	updatesCh chan acp.SessionNotification

	// Synchronization
	mu       sync.RWMutex
	wg       sync.WaitGroup
	stopCh   chan struct{}
	doneCh   chan struct{}
	startMu  sync.Mutex
}

// NewManager creates a new process manager
func NewManager(cfg *config.Config, log *logger.Logger) *Manager {
	m := &Manager{
		cfg:          cfg,
		logger:       log.WithFields(zap.String("component", "process-manager")),
		outputBuffer: NewOutputBuffer(cfg.OutputBufferSize),
		updatesCh:    make(chan acp.SessionNotification, 100),
	}
	m.status.Store(StatusStopped)
	m.exitCode.Store(-1)
	return m
}

// Status returns the current process status
func (m *Manager) Status() Status {
	return m.status.Load().(Status)
}

// ExitCode returns the exit code (-1 if not exited)
func (m *Manager) ExitCode() int {
	return int(m.exitCode.Load())
}

// ExitError returns the exit error if any
func (m *Manager) ExitError() error {
	if v := m.exitErr.Load(); v != nil {
		if w, ok := v.(errorWrapper); ok {
			return w.err
		}
	}
	return nil
}

// GetOutputBuffer returns the output buffer for streaming
func (m *Manager) GetOutputBuffer() *OutputBuffer {
	return m.outputBuffer
}

// Start starts the agent process
func (m *Manager) Start(ctx context.Context) error {
	m.startMu.Lock()
	defer m.startMu.Unlock()

	if m.Status() == StatusRunning || m.Status() == StatusStarting {
		return fmt.Errorf("agent is already running")
	}

	m.logger.Info("starting agent process",
		zap.Strings("args", m.cfg.AgentArgs),
		zap.String("workdir", m.cfg.WorkDir))

	m.status.Store(StatusStarting)
	m.exitCode.Store(-1)
	m.exitErr.Store(errorWrapper{err: nil})

	// Create command
	if len(m.cfg.AgentArgs) == 0 {
		m.status.Store(StatusError)
		return fmt.Errorf("no agent command configured")
	}

	// NOTE: We intentionally don't use exec.CommandContext here because we don't want
	// the HTTP request context to kill the agent process when the request completes.
	m.cmd = exec.Command(m.cfg.AgentArgs[0], m.cfg.AgentArgs[1:]...)
	m.cmd.Dir = m.cfg.WorkDir
	m.cmd.Env = m.cfg.AgentEnv

	// Set up pipes
	var err error
	m.stdin, err = m.cmd.StdinPipe()
	if err != nil {
		m.status.Store(StatusError)
		return fmt.Errorf("failed to create stdin pipe: %w", err)
	}

	m.stdout, err = m.cmd.StdoutPipe()
	if err != nil {
		m.status.Store(StatusError)
		return fmt.Errorf("failed to create stdout pipe: %w", err)
	}

	m.stderr, err = m.cmd.StderrPipe()
	if err != nil {
		m.status.Store(StatusError)
		return fmt.Errorf("failed to create stderr pipe: %w", err)
	}

	// Start the process
	if err := m.cmd.Start(); err != nil {
		m.status.Store(StatusError)
		return fmt.Errorf("failed to start agent: %w", err)
	}

	m.stopCh = make(chan struct{})
	m.doneCh = make(chan struct{})

	// Create ACP client that will handle agent requests
	m.acpClient = acpclient.NewClient(
		acpclient.WithLogger(m.logger.Zap()),
		acpclient.WithWorkspaceRoot(m.cfg.WorkDir),
		acpclient.WithUpdateHandler(func(n acp.SessionNotification) {
			select {
			case m.updatesCh <- n:
			default:
				m.logger.Warn("updates channel full, dropping notification")
			}
		}),
	)

	// Create ACP SDK connection - it handles JSON-RPC communication
	m.acpConn = acp.NewClientSideConnection(m.acpClient, m.stdin, m.stdout)
	m.acpConn.SetLogger(slog.Default().With("component", "acp-conn"))

	// Start stderr reader and exit waiter
	m.wg.Add(2)
	go m.readStderr()
	go m.waitForExit()

	m.status.Store(StatusRunning)
	m.logger.Info("agent process started", zap.Int("pid", m.cmd.Process.Pid))

	return nil
}

// GetUpdates returns the channel for session update notifications
func (m *Manager) GetUpdates() <-chan acp.SessionNotification {
	return m.updatesCh
}

// GetConnection returns the ACP connection (for advanced usage)
func (m *Manager) GetConnection() *acp.ClientSideConnection {
	m.mu.RLock()
	defer m.mu.RUnlock()
	return m.acpConn
}

// GetSessionID returns the current session ID
func (m *Manager) GetSessionID() acp.SessionId {
	m.mu.RLock()
	defer m.mu.RUnlock()
	return m.sessionID
}

// SetSessionID sets the current session ID
func (m *Manager) SetSessionID(id acp.SessionId) {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.sessionID = id
}

// Stop stops the agent process
func (m *Manager) Stop(ctx context.Context) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	status := m.Status()
	if status == StatusStopped || status == StatusStopping {
		return nil
	}

	m.logger.Info("stopping agent process")
	m.status.Store(StatusStopping)

	// Close stop channel to signal readers
	if m.stopCh != nil {
		close(m.stopCh)
	}

	// Close stdin to signal EOF to agent
	if m.stdin != nil {
		m.stdin.Close()
	}

	// Wait for process to exit with timeout
	done := make(chan struct{})
	go func() {
		m.wg.Wait()
		close(done)
	}()

	select {
	case <-done:
		m.logger.Info("agent process stopped gracefully")
	case <-ctx.Done():
		// Force kill
		if m.cmd != nil && m.cmd.Process != nil {
			m.logger.Warn("force killing agent process")
			m.cmd.Process.Kill()
		}
	}

	m.status.Store(StatusStopped)
	return nil
}



// readStderr reads stderr from the agent
func (m *Manager) readStderr() {
	defer m.wg.Done()

	scanner := bufio.NewScanner(m.stderr)
	for scanner.Scan() {
		line := scanner.Text()
		m.outputBuffer.Add(OutputLine{
			Timestamp: time.Now(),
			Stream:    "stderr",
			Content:   line,
		})
	}

	if err := scanner.Err(); err != nil {
		m.logger.Debug("stderr reader error", zap.Error(err))
	}
}

// waitForExit waits for the process to exit
func (m *Manager) waitForExit() {
	defer m.wg.Done()
	defer close(m.doneCh)

	err := m.cmd.Wait()

	if err != nil {
		m.exitErr.Store(errorWrapper{err: err})
		if exitErr, ok := err.(*exec.ExitError); ok {
			m.exitCode.Store(int32(exitErr.ExitCode()))
		}
		m.logger.Info("agent process exited with error", zap.Error(err))
	} else {
		m.exitCode.Store(0)
		m.logger.Info("agent process exited successfully")
	}

	m.status.Store(StatusStopped)
}



// GetProcessInfo returns information about the process
func (m *Manager) GetProcessInfo() map[string]interface{} {
	info := map[string]interface{}{
		"status":    string(m.Status()),
		"exit_code": m.ExitCode(),
	}

	if m.cmd != nil && m.cmd.Process != nil {
		info["pid"] = m.cmd.Process.Pid
	}

	if err := m.ExitError(); err != nil {
		info["exit_error"] = err.Error()
	}

	return info
}