package api

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net"
	"net/http"
	"os"
	"os/exec"
	"runtime"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/sipeed/picoclaw/pkg/channels/pico"
	"github.com/sipeed/picoclaw/pkg/config"
	"github.com/sipeed/picoclaw/pkg/health"
	"github.com/sipeed/picoclaw/pkg/logger"
	ppid "github.com/sipeed/picoclaw/pkg/pid"
	"github.com/sipeed/picoclaw/web/backend/utils"
)

// gateway holds the state for the managed gateway process.
var gateway = struct {
	mu                  sync.Mutex
	cmd                 *exec.Cmd
	owned               bool // true if we started the process, false if we attached to an existing one
	bootDefaultModel    string
	bootConfigSignature string
	runtimeStatus       string
	startupDeadline     time.Time
	logs                *LogBuffer
	pidData             *ppid.PidFileData // pid file data read from picoclaw.pid.json
	picoToken           string            // cached pico token from config (for proxy auth validation)
}{
	runtimeStatus: "stopped",
	logs:          NewLogBuffer(200),
}

// refreshPicoToken updates gateway.picoToken from cfg
func refreshPicoToken(cfg *config.Config) {
	gateway.mu.Lock()
	defer gateway.mu.Unlock()
	gateway.picoToken = cfg.Channels.Pico.Token.String()
}

// refreshPicoTokensLocked reads the pico token from config and caches it.
// Caller must hold gateway.mu (or be sole writer).
func refreshPicoTokensLocked(configPath string) {
	cfg, err := config.LoadConfig(configPath)
	if err != nil {
		return
	}
	gateway.picoToken = cfg.Channels.Pico.Token.String()
}

const (
	protocolKey = "Sec-Websocket-Protocol"
	tokenPrefix = "token."
)

// picoComposedToken returns "pico-"+pidToken+picoToken for gateway auth.
func picoComposedToken(token string) string {
	gateway.mu.Lock()
	defer gateway.mu.Unlock()
	// if not initial pico token, don't allow gateway auth
	if gateway.picoToken == "" || gateway.pidData == nil {
		return ""
	}
	if tokenPrefix+gateway.picoToken != token {
		return ""
	}
	return pico.PicoTokenPrefix + gateway.pidData.Token + gateway.picoToken
}

var (
	gatewayStartupWindow          = 15 * time.Second
	gatewayRestartGracePeriod     = 5 * time.Second
	gatewayRestartForceKillWindow = 3 * time.Second
	gatewayRestartPollInterval    = 100 * time.Millisecond
)

var gatewayHealthGet = func(url string, timeout time.Duration) (*http.Response, error) {
	client := http.Client{Timeout: timeout}
	return client.Get(url)
}

// getGatewayHealth checks the gateway health endpoint and returns the status response.
// Returns (*health.StatusResponse, statusCode, error). If error is not nil, the other values are not valid.
func (h *Handler) getGatewayHealth(cfg *config.Config, timeout time.Duration) (*health.StatusResponse, int, error) {
	// Prefer port/host from pidData when available.
	var port int
	var host string
	gateway.mu.Lock()
	if d := gateway.pidData; d != nil && d.Port > 0 {
		port = d.Port
		host = d.Host
	}
	gateway.mu.Unlock()
	if port == 0 {
		port = 18790
		if cfg != nil && cfg.Gateway.Port != 0 {
			port = cfg.Gateway.Port
		}
	}
	if host == "" {
		host = gatewayProbeHost(h.effectiveGatewayBindHost(cfg))
	}

	url := "http://" + net.JoinHostPort(host, strconv.Itoa(port)) + "/health"

	return getGatewayHealthByURL(url, timeout)
}

func getGatewayHealthByURL(url string, timeout time.Duration) (*health.StatusResponse, int, error) {
	resp, err := gatewayHealthGet(url, timeout)
	if err != nil {
		return nil, 0, err
	}
	defer resp.Body.Close()

	var healthResponse health.StatusResponse
	if decErr := json.NewDecoder(resp.Body).Decode(&healthResponse); decErr != nil {
		return nil, resp.StatusCode, decErr
	}

	return &healthResponse, resp.StatusCode, nil
}

// registerGatewayRoutes binds gateway lifecycle endpoints to the ServeMux.
func (h *Handler) registerGatewayRoutes(mux *http.ServeMux) {
	mux.HandleFunc("GET /api/gateway/status", h.handleGatewayStatus)
	mux.HandleFunc("GET /api/gateway/logs", h.handleGatewayLogs)
	mux.HandleFunc("POST /api/gateway/logs/clear", h.handleGatewayClearLogs)
	mux.HandleFunc("POST /api/gateway/start", h.handleGatewayStart)
	mux.HandleFunc("POST /api/gateway/stop", h.handleGatewayStop)
	mux.HandleFunc("POST /api/gateway/restart", h.handleGatewayRestart)
}

// TryAutoStartGateway checks whether gateway start preconditions are met and
// starts it when possible. Intended to be called by the backend at startup.
func (h *Handler) TryAutoStartGateway() {
	// Check PID file first to detect an already-running gateway.
	pidData := ppid.ReadPidFileWithCheck(globalConfigDir())
	if pidData != nil {
		gateway.mu.Lock()
		ready, reason, err := h.gatewayStartReady()
		if err != nil {
			logger.ErrorC("gateway", fmt.Sprintf("Skip auto-starting gateway: %v", err))
			gateway.mu.Unlock()
			return
		}
		logger.Infof("ready: %v, reason: %s", ready, reason)
		if !ready {
			logger.InfoC("gateway", fmt.Sprintf("Skip auto-starting gateway: %s", reason))
			gateway.mu.Unlock()
			return
		}
		pid := pidData.PID
		_, err = h.startGatewayLocked("starting", pid)
		if err != nil {
			logger.ErrorC("gateway", fmt.Sprintf("Failed to attach to running gateway (PID: %d): %v", pid, err))
		} else {
			gateway.pidData = pidData
			refreshPicoTokensLocked(h.configPath)
			logger.InfoC("gateway", fmt.Sprintf("Attached to running gateway via PID file (PID: %d)", pid))
		}
		gateway.mu.Unlock()
		return
	}

	gateway.mu.Lock()
	defer gateway.mu.Unlock()

	if gateway.cmd != nil && gateway.cmd.Process != nil {
		gateway.cmd = nil
	}

	ready, reason, err := h.gatewayStartReady()
	if err != nil {
		logger.ErrorC("gateway", fmt.Sprintf("Skip auto-starting gateway: %v", err))
		return
	}
	if !ready {
		logger.InfoC("gateway", fmt.Sprintf("Skip auto-starting gateway: %s", reason))
		return
	}

	pid, err := h.startGatewayLocked("starting", 0)
	if err != nil {
		logger.ErrorC("gateway", fmt.Sprintf("Failed to auto-start gateway: %v", err))
		return
	}
	logger.InfoC("gateway", fmt.Sprintf("Gateway auto-started (PID: %d)", pid))
}

// gatewayStartReady validates whether current config can start the gateway.
func (h *Handler) gatewayStartReady() (bool, string, error) {
	cfg, err := config.LoadConfig(h.configPath)
	if err != nil {
		return false, "", fmt.Errorf("failed to load config: %w", err)
	}

	modelName := strings.TrimSpace(cfg.Agents.Defaults.GetModelName())
	if modelName == "" {
		return false, "no default model configured", nil
	}

	modelCfg := lookupModelConfig(cfg, modelName)
	if modelCfg == nil {
		return false, fmt.Sprintf("default model %q is invalid", modelName), nil
	}

	if !hasModelConfiguration(modelCfg) {
		return false, fmt.Sprintf("default model %q has no credentials configured", modelName), nil
	}
	if requiresRuntimeProbe(modelCfg) && !probeLocalModelAvailability(modelCfg) {
		return false, fmt.Sprintf("default model %q is not reachable", modelName), nil
	}

	return true, "", nil
}

func lookupModelConfig(cfg *config.Config, modelName string) *config.ModelConfig {
	modelCfg, err := cfg.GetModelConfig(modelName)
	if err != nil {
		return nil
	}
	return modelCfg
}

func computeConfigSignature(cfg *config.Config) string {
	if cfg == nil {
		return ""
	}
	var parts []string
	defaultModel := strings.TrimSpace(cfg.Agents.Defaults.GetModelName())
	if defaultModel != "" {
		parts = append(parts, "model:"+defaultModel)
	}
	toolSignatures := []string{}
	if cfg.Tools.ReadFile.Enabled {
		toolSignatures = append(toolSignatures, "read_file")
	}
	if cfg.Tools.WriteFile.Enabled {
		toolSignatures = append(toolSignatures, "write_file")
	}
	if cfg.Tools.ListDir.Enabled {
		toolSignatures = append(toolSignatures, "list_dir")
	}
	if cfg.Tools.EditFile.Enabled {
		toolSignatures = append(toolSignatures, "edit_file")
	}
	if cfg.Tools.AppendFile.Enabled {
		toolSignatures = append(toolSignatures, "append_file")
	}
	if cfg.Tools.Exec.Enabled {
		toolSignatures = append(toolSignatures, "exec")
	}
	if cfg.Tools.Cron.Enabled {
		toolSignatures = append(toolSignatures, "cron")
	}
	if cfg.Tools.Web.Enabled {
		toolSignatures = append(toolSignatures, "web")
	}
	if cfg.Tools.WebFetch.Enabled {
		toolSignatures = append(toolSignatures, "web_fetch")
	}
	if cfg.Tools.Message.Enabled {
		toolSignatures = append(toolSignatures, "message")
	}
	if cfg.Tools.SendFile.Enabled {
		toolSignatures = append(toolSignatures, "send_file")
	}
	if cfg.Tools.FindSkills.Enabled {
		toolSignatures = append(toolSignatures, "find_skills")
	}
	if cfg.Tools.InstallSkill.Enabled {
		toolSignatures = append(toolSignatures, "install_skill")
	}
	if cfg.Tools.Spawn.Enabled {
		toolSignatures = append(toolSignatures, "spawn")
	}
	if cfg.Tools.SpawnStatus.Enabled {
		toolSignatures = append(toolSignatures, "spawn_status")
	}
	if cfg.Tools.I2C.Enabled {
		toolSignatures = append(toolSignatures, "i2c")
	}
	if cfg.Tools.SPI.Enabled {
		toolSignatures = append(toolSignatures, "spi")
	}
	if cfg.Tools.MCP.Enabled {
		toolSignatures = append(toolSignatures, "mcp")
	}
	if cfg.Tools.MCP.Discovery.Enabled {
		toolSignatures = append(toolSignatures, "mcp_discovery")
	}
	if cfg.Tools.MCP.Discovery.UseRegex {
		toolSignatures = append(toolSignatures, "mcp_discovery_regex")
	}
	if cfg.Tools.MCP.Discovery.UseBM25 {
		toolSignatures = append(toolSignatures, "mcp_discovery_bm25")
	}
	if len(toolSignatures) > 0 {
		parts = append(parts, "tools:"+strings.Join(toolSignatures, ","))
	}
	return strings.Join(parts, ";")
}

func gatewayRestartRequiredBySignature(bootSignature, currentSignature, gatewayStatus string) bool {
	if gatewayStatus != "running" {
		return false
	}
	if bootSignature == "" || currentSignature == "" {
		return false
	}
	return bootSignature != currentSignature
}

func isCmdProcessAliveLocked(cmd *exec.Cmd) bool {
	if cmd == nil || cmd.Process == nil {
		return false
	}

	// Wait() sets ProcessState when the process exits; use it when available.
	if cmd.ProcessState != nil && cmd.ProcessState.Exited() {
		return false
	}

	// Windows does not support Signal(0) probing. If we still own cmd and it
	// has not reported exit, treat it as alive.
	if runtime.GOOS == "windows" {
		return true
	}

	return cmd.Process.Signal(syscall.Signal(0)) == nil
}

func setGatewayRuntimeStatusLocked(status string) {
	gateway.runtimeStatus = status
	if status == "starting" || status == "restarting" {
		gateway.startupDeadline = time.Now().Add(gatewayStartupWindow)
		return
	}
	gateway.startupDeadline = time.Time{}
}

// attachToGatewayProcess attaches to an existing gateway process by PID
// and updates the gateway state accordingly.
// Assumes gateway.mu is held by the caller.
func attachToGatewayProcessLocked(pid int, cfg *config.Config) error {
	process, err := os.FindProcess(pid)
	if err != nil {
		return fmt.Errorf("failed to find process for PID %d: %w", pid, err)
	}

	gateway.cmd = &exec.Cmd{Process: process}
	gateway.owned = false // We didn't start this process
	setGatewayRuntimeStatusLocked("running")

	// Update bootDefaultModel and bootConfigSignature from config
	if cfg != nil {
		defaultModelName := strings.TrimSpace(cfg.Agents.Defaults.GetModelName())
		gateway.bootDefaultModel = defaultModelName
		gateway.bootConfigSignature = computeConfigSignature(cfg)
	}

	logger.InfoC("gateway", fmt.Sprintf("Attached to gateway process (PID: %d)", pid))
	return nil
}

func gatewayStatusWithoutHealthLocked() string {
	if gateway.runtimeStatus == "starting" || gateway.runtimeStatus == "restarting" {
		if gateway.startupDeadline.IsZero() || time.Now().Before(gateway.startupDeadline) {
			return gateway.runtimeStatus
		}
		return "error"
	}
	if gateway.runtimeStatus == "running" {
		return "running"
	}
	if gateway.runtimeStatus == "error" {
		return "error"
	}
	return "stopped"
}

func waitForGatewayProcessExit(cmd *exec.Cmd, timeout time.Duration) bool {
	if cmd == nil || cmd.Process == nil {
		return true
	}

	deadline := time.Now().Add(timeout)
	for {
		if !isCmdProcessAliveLocked(cmd) {
			return true
		}
		if time.Now().After(deadline) {
			return false
		}
		time.Sleep(gatewayRestartPollInterval)
	}
}

// StopGateway stops the gateway process if it was started by this handler.
// This method is called during application shutdown to ensure the gateway subprocess
// is properly terminated. It only stops processes that were started by this handler,
// not processes that were attached to from existing instances.
func (h *Handler) StopGateway() {
	gateway.mu.Lock()
	defer gateway.mu.Unlock()

	// Only stop if we own the process (started it ourselves)
	if !gateway.owned || gateway.cmd == nil || gateway.cmd.Process == nil {
		return
	}

	pid, err := stopGatewayLocked()
	if err != nil {
		logger.ErrorC("gateway", fmt.Sprintf("Failed to stop gateway (PID %d): %v", pid, err))
		return
	}

	logger.InfoC("gateway", fmt.Sprintf("Gateway stopped (PID: %d)", pid))
}

// stopGatewayLocked sends a stop signal to the gateway process.
// Assumes gateway.mu is held by the caller.
// Returns the PID of the stopped process and any error encountered.
func stopGatewayLocked() (int, error) {
	if gateway.cmd == nil || gateway.cmd.Process == nil {
		return 0, nil
	}

	pid := gateway.cmd.Process.Pid

	// Send SIGTERM for graceful shutdown (SIGKILL on Windows)
	var sigErr error
	if runtime.GOOS == "windows" {
		sigErr = gateway.cmd.Process.Kill()
	} else {
		sigErr = gateway.cmd.Process.Signal(syscall.SIGTERM)
	}

	if sigErr != nil {
		return pid, sigErr
	}

	logger.InfoC("gateway", fmt.Sprintf("Sent stop signal to gateway (PID: %d)", pid))
	gateway.cmd = nil
	gateway.owned = false
	gateway.bootDefaultModel = ""
	gateway.pidData = nil
	setGatewayRuntimeStatusLocked("stopped")

	return pid, nil
}

func stopGatewayProcessForRestart(cmd *exec.Cmd) error {
	if cmd == nil || cmd.Process == nil || !isCmdProcessAliveLocked(cmd) {
		return nil
	}

	var stopErr error
	if runtime.GOOS == "windows" {
		stopErr = cmd.Process.Kill()
	} else {
		stopErr = cmd.Process.Signal(syscall.SIGTERM)
	}
	if stopErr != nil && isCmdProcessAliveLocked(cmd) {
		return fmt.Errorf("failed to stop existing gateway: %w", stopErr)
	}

	if waitForGatewayProcessExit(cmd, gatewayRestartGracePeriod) {
		return nil
	}

	if runtime.GOOS != "windows" {
		killErr := cmd.Process.Signal(syscall.SIGKILL)
		if killErr != nil && isCmdProcessAliveLocked(cmd) {
			return fmt.Errorf("failed to force-stop existing gateway: %w", killErr)
		}
		if waitForGatewayProcessExit(cmd, gatewayRestartForceKillWindow) {
			return nil
		}
	}

	return fmt.Errorf("existing gateway did not exit before restart")
}

func (h *Handler) startGatewayLocked(initialStatus string, existingPid int) (int, error) {
	cfg, err := config.LoadConfig(h.configPath)
	if err != nil {
		return 0, fmt.Errorf("failed to load config: %w", err)
	}
	defaultModelName := strings.TrimSpace(cfg.Agents.Defaults.GetModelName())

	var cmd *exec.Cmd
	var pid int

	if existingPid > 0 {
		// Attach to existing process
		pid = existingPid
		gateway.cmd = nil // Clear first to ensure clean state
		if err = attachToGatewayProcessLocked(pid, cfg); err != nil {
			logger.ErrorC("gateway", fmt.Sprintf("Failed to attach to existing gateway (PID %d): %v", pid, err))
			return 0, err
		}

		return pid, nil
	}

	// Start new process
	// Locate the picoclaw executable
	execPath := utils.FindPicoclawBinary()
	logger.InfoC("gateway", fmt.Sprintf("Starting gateway process (%s)", execPath))

	cmd = exec.Command(execPath, "gateway", "-E")
	cmd.Env = os.Environ()
	// Forward the launcher's config path via the environment variable that
	// GetConfigPath() already reads, so the gateway sub-process uses the same
	// config file without requiring a --config flag on the gateway subcommand.
	if h.configPath != "" {
		cmd.Env = append(cmd.Env, config.EnvConfig+"="+h.configPath)
	}
	if host := h.gatewayHostOverride(); host != "" {
		cmd.Env = append(cmd.Env, config.EnvGatewayHost+"="+host)
	}

	stdoutPipe, err := cmd.StdoutPipe()
	if err != nil {
		return 0, fmt.Errorf("failed to create stdout pipe: %w", err)
	}

	stderrPipe, err := cmd.StderrPipe()
	if err != nil {
		return 0, fmt.Errorf("failed to create stderr pipe: %w", err)
	}

	// Clear old logs for this new run
	gateway.logs.Reset()

	// Ensure Pico Channel is configured before starting gateway
	changed, err := h.EnsurePicoChannel("")
	if err != nil {
		logger.ErrorC("gateway", fmt.Sprintf("Warning: failed to ensure pico channel: %v", err))
		// Non-fatal: gateway can still start without pico channel
	}
	// Refresh cached pico token in case EnsurePicoChannel generated a new one.
	// Already holding gateway.mu from caller.
	if changed {
		refreshPicoTokensLocked(h.configPath)
	}

	if err := cmd.Start(); err != nil {
		return 0, fmt.Errorf("failed to start gateway: %w", err)
	}

	gateway.cmd = cmd
	gateway.owned = true // We started this process
	gateway.bootDefaultModel = defaultModelName
	gateway.bootConfigSignature = computeConfigSignature(cfg)
	setGatewayRuntimeStatusLocked(initialStatus)
	pid = cmd.Process.Pid
	logger.InfoC("gateway", fmt.Sprintf("Started picoclaw gateway (PID: %d) from %s", pid, execPath))

	// Capture stdout/stderr in background
	go scanPipe(stdoutPipe, gateway.logs)
	go scanPipe(stderrPipe, gateway.logs)

	// Wait for exit in background and clean up
	go func() {
		if err := cmd.Wait(); err != nil {
			logger.ErrorC("gateway", fmt.Sprintf("Gateway process exited: %v", err))
		} else {
			logger.InfoC("gateway", "Gateway process exited normally")
		}

		gateway.mu.Lock()
		if gateway.cmd == cmd {
			gateway.cmd = nil
			gateway.bootDefaultModel = ""
			gateway.bootConfigSignature = ""
			if gateway.runtimeStatus != "restarting" {
				setGatewayRuntimeStatusLocked("stopped")
			}
		}
		gateway.mu.Unlock()
	}()

	// Start a goroutine to probe pidFile and health, update runtime state once ready.
	go func() {
		for i := 0; i < 30; i++ { // try for up to 15 seconds
			time.Sleep(500 * time.Millisecond)
			gateway.mu.Lock()
			stillOurs := gateway.cmd == cmd
			gateway.mu.Unlock()
			if !stillOurs {
				return
			}

			// Poll for pidFile first — once available we have port/host/token.
			if pd := ppid.ReadPidFileWithCheck(globalConfigDir()); pd != nil && pd.PID == pid {
				gateway.mu.Lock()
				if gateway.cmd == cmd {
					gateway.pidData = pd
					setGatewayRuntimeStatusLocked("running")
				}
				gateway.mu.Unlock()
				logger.InfoC("gateway", fmt.Sprintf("Gateway pidFile detected (PID: %d, port: %d)", pd.PID, pd.Port))
				return
			}

			// Fallback: probe health endpoint to confirm liveness.
			cfg, err := config.LoadConfig(h.configPath)
			if err != nil {
				continue
			}
			_, statusCode, err := h.getGatewayHealth(cfg, 1*time.Second)
			if err == nil && statusCode == http.StatusOK {
				gateway.mu.Lock()
				if gateway.cmd == cmd {
					setGatewayRuntimeStatusLocked("running")
				}
				gateway.mu.Unlock()
				return
			}
		}
	}()

	return pid, nil
}

// handleGatewayStart starts the picoclaw gateway subprocess.
//
//	POST /api/gateway/start
func (h *Handler) handleGatewayStart(w http.ResponseWriter, r *http.Request) {
	// Check PID file first to detect an already-running gateway.
	pidData := ppid.ReadPidFileWithCheck(globalConfigDir())
	if pidData != nil {
		pid := pidData.PID
		gateway.mu.Lock()
		ready, reason, err := h.gatewayStartReady()
		if err != nil {
			gateway.mu.Unlock()
			http.Error(
				w,
				fmt.Sprintf("Failed to validate gateway start conditions: %v", err),
				http.StatusInternalServerError,
			)
			return
		}
		if !ready {
			gateway.mu.Unlock()
			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)
			json.NewEncoder(w).Encode(map[string]any{
				"status":  "precondition_failed",
				"message": reason,
			})
			return
		}
		_, err = h.startGatewayLocked("starting", pid)
		if err != nil {
			gateway.mu.Unlock()
			logger.ErrorC("gateway", fmt.Sprintf("Failed to attach to running gateway (PID: %d): %v", pid, err))
			http.Error(w, fmt.Sprintf("Failed to attach to gateway: %v", err), http.StatusInternalServerError)
			return
		}
		gateway.pidData = pidData
		gateway.mu.Unlock()
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusOK)
		json.NewEncoder(w).Encode(map[string]any{
			"status": "ok",
			"pid":    pid,
		})
		return
	}

	gateway.mu.Lock()
	defer gateway.mu.Unlock()

	if gateway.cmd != nil && gateway.cmd.Process != nil {
		gateway.cmd = nil
		setGatewayRuntimeStatusLocked("stopped")
	}

	ready, reason, err := h.gatewayStartReady()
	if err != nil {
		http.Error(
			w,
			fmt.Sprintf("Failed to validate gateway start conditions: %v", err),
			http.StatusInternalServerError,
		)
		return
	}
	if !ready {
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusBadRequest)
		json.NewEncoder(w).Encode(map[string]any{
			"status":  "precondition_failed",
			"message": reason,
		})
		return
	}

	pid, err := h.startGatewayLocked("starting", 0)
	if err != nil {
		http.Error(w, fmt.Sprintf("Failed to start gateway: %v", err), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]any{
		"status": "ok",
		"pid":    pid,
	})
}

// handleGatewayStop stops the running gateway subprocess gracefully.
// Note: Unlike StopGateway (which only stops self-started processes), this API endpoint
// stops any gateway process, including attached ones. This is intentional for user control.
//
//	POST /api/gateway/stop
func (h *Handler) handleGatewayStop(w http.ResponseWriter, r *http.Request) {
	gateway.mu.Lock()
	defer gateway.mu.Unlock()

	if gateway.cmd == nil || gateway.cmd.Process == nil {
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(map[string]any{
			"status": "not_running",
		})
		return
	}

	pid, err := stopGatewayLocked()
	if err != nil {
		http.Error(w, fmt.Sprintf("Failed to stop gateway (PID %d): %v", pid, err), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]any{
		"status": "ok",
		"pid":    pid,
	})
}

// RestartGateway restarts the gateway process. This is a non-blocking operation
// that stops the current gateway (if running) and starts a new one.
// Returns the PID of the new gateway process or an error.
func (h *Handler) RestartGateway() (int, error) {
	ready, reason, err := h.gatewayStartReady()
	if err != nil {
		return 0, fmt.Errorf("failed to validate gateway start conditions: %w", err)
	}
	if !ready {
		return 0, &preconditionFailedError{reason: reason}
	}

	gateway.mu.Lock()
	previousCmd := gateway.cmd
	setGatewayRuntimeStatusLocked("restarting")
	gateway.mu.Unlock()

	if err = stopGatewayProcessForRestart(previousCmd); err != nil {
		gateway.mu.Lock()
		if gateway.cmd == previousCmd {
			if isCmdProcessAliveLocked(previousCmd) {
				setGatewayRuntimeStatusLocked("running")
			} else {
				gateway.cmd = nil
				gateway.bootDefaultModel = ""
				setGatewayRuntimeStatusLocked("error")
			}
		}
		gateway.mu.Unlock()
		return 0, fmt.Errorf("failed to stop gateway: %w", err)
	}

	gateway.mu.Lock()
	if gateway.cmd == previousCmd {
		gateway.cmd = nil
		gateway.bootDefaultModel = ""
	}
	pid, err := h.startGatewayLocked("restarting", 0)
	if err != nil {
		gateway.cmd = nil
		gateway.bootDefaultModel = ""
		setGatewayRuntimeStatusLocked("error")
	}
	gateway.mu.Unlock()
	if err != nil {
		return 0, fmt.Errorf("failed to start gateway: %w", err)
	}

	return pid, nil
}

// preconditionFailedError is returned when gateway restart preconditions are not met
type preconditionFailedError struct {
	reason string
}

func (e *preconditionFailedError) Error() string {
	return e.reason
}

// IsBadRequest returns true if the error should result in a 400 Bad Request status
func (e *preconditionFailedError) IsBadRequest() bool {
	return true
}

// handleGatewayRestart stops the gateway (if running) and starts a new instance.
//
//	POST /api/gateway/restart
func (h *Handler) handleGatewayRestart(w http.ResponseWriter, r *http.Request) {
	pid, err := h.RestartGateway()
	if err != nil {
		// Check if it's a precondition failed error
		var precondErr *preconditionFailedError
		if errors.As(err, &precondErr) {
			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)
			json.NewEncoder(w).Encode(map[string]any{
				"status":  "precondition_failed",
				"message": precondErr.reason,
			})
			return
		}
		http.Error(w, fmt.Sprintf("Failed to restart gateway: %v", err), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]any{
		"status": "ok",
		"pid":    pid,
	})
}

// handleGatewayClearLogs clears the in-memory gateway log buffer.
//
//	POST /api/gateway/logs/clear
func (h *Handler) handleGatewayClearLogs(w http.ResponseWriter, r *http.Request) {
	gateway.logs.Clear()

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]any{
		"status":     "cleared",
		"log_total":  0,
		"log_run_id": gateway.logs.RunID(),
	})
}

// handleGatewayStatus returns the gateway run status and health info.
//
//	GET /api/gateway/status
func (h *Handler) handleGatewayStatus(w http.ResponseWriter, r *http.Request) {
	data := h.gatewayStatusData()
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(data)
}

func (h *Handler) gatewayStatusData() map[string]any {
	data := map[string]any{}
	var configDefaultModel string
	cfg, cfgErr := config.LoadConfig(h.configPath)
	if cfgErr == nil && cfg != nil {
		configDefaultModel = strings.TrimSpace(cfg.Agents.Defaults.GetModelName())
		if configDefaultModel != "" {
			data["config_default_model"] = configDefaultModel
		}
	}

	// Primary detection: read PID file and check if process is alive.
	pidData := ppid.ReadPidFileWithCheck(globalConfigDir())
	if pidData != nil {
		gateway.mu.Lock()
		gateway.pidData = pidData
		if pidData.Version != "" {
			data["gateway_version"] = pidData.Version
		}
		setGatewayRuntimeStatusLocked("running")

		// Attach if we don't already track this PID.
		if gateway.cmd == nil || gateway.cmd.Process == nil || gateway.cmd.Process.Pid != pidData.PID {
			_ = attachToGatewayProcessLocked(pidData.PID, cfg)
		}

		bootDefaultModel := gateway.bootDefaultModel
		if bootDefaultModel != "" {
			data["boot_default_model"] = bootDefaultModel
		}
		data["gateway_status"] = "running"
		data["pid"] = pidData.PID
		gateway.mu.Unlock()
	} else {
		// Fallback: probe health endpoint to get pid and status
		_, statusCode, err := h.getGatewayHealth(cfg, 2*time.Second)
		if err != nil {
			gateway.mu.Lock()
			data["gateway_status"] = gatewayStatusWithoutHealthLocked()
			gateway.pidData = nil
			gateway.mu.Unlock()
			logger.ErrorC("gateway", fmt.Sprintf("Gateway health check failed: %v", err))
		} else {
			logger.InfoC("gateway", fmt.Sprintf("Gateway health status: %d", statusCode))
			if statusCode != http.StatusOK {
				gateway.mu.Lock()
				setGatewayRuntimeStatusLocked("error")
				gateway.pidData = nil
				gateway.mu.Unlock()
				data["gateway_status"] = "error"
				data["status_code"] = statusCode
			} else {
				gateway.mu.Lock()
				setGatewayRuntimeStatusLocked("running")
				bootDefaultModel := gateway.bootDefaultModel
				if bootDefaultModel != "" {
					data["boot_default_model"] = bootDefaultModel
				}
				data["gateway_status"] = "running"
				gateway.mu.Unlock()
			}
		}
	}

	gatewayStatus, _ := data["gateway_status"].(string)
	currentConfigSignature := computeConfigSignature(cfg)
	gateway.mu.Lock()
	bootConfigSignature := gateway.bootConfigSignature
	gateway.mu.Unlock()
	data["gateway_restart_required"] = gatewayRestartRequiredBySignature(
		bootConfigSignature,
		currentConfigSignature,
		gatewayStatus,
	)

	ready, reason, readyErr := h.gatewayStartReady()
	if readyErr != nil {
		data["gateway_start_allowed"] = false
		data["gateway_start_reason"] = readyErr.Error()
	} else {
		data["gateway_start_allowed"] = ready
		if !ready {
			data["gateway_start_reason"] = reason
		}
	}

	return data
}

// handleGatewayLogs returns buffered gateway logs, optionally incrementally.
//
//	GET /api/gateway/logs
func (h *Handler) handleGatewayLogs(w http.ResponseWriter, r *http.Request) {
	data := gatewayLogsData(r)
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(data)
}

// gatewayLogsData reads log_offset and log_run_id query params from the request
// and returns incremental log lines.
func gatewayLogsData(r *http.Request) map[string]any {
	data := map[string]any{}
	clientOffset := 0
	clientRunID := -1

	if v := r.URL.Query().Get("log_offset"); v != "" {
		if n, err := strconv.Atoi(v); err == nil {
			clientOffset = n
		}
	}

	if v := r.URL.Query().Get("log_run_id"); v != "" {
		if n, err := strconv.Atoi(v); err == nil {
			clientRunID = n
		}
	}

	runID := gateway.logs.RunID()

	if runID == 0 {
		data["logs"] = []string{}
		data["log_total"] = 0
		data["log_run_id"] = 0
		return data
	}

	// If runID changed, reset offset to get all logs from new run
	offset := clientOffset
	if clientRunID != runID {
		offset = 0
	}

	lines, total, runID := gateway.logs.LinesSince(offset)
	if lines == nil {
		lines = []string{}
	}

	data["logs"] = lines
	data["log_total"] = total
	data["log_run_id"] = runID
	return data
}

// scanPipe reads lines from r and appends them to buf. Returns when r reaches EOF.
func scanPipe(r io.Reader, buf *LogBuffer) {
	scanner := bufio.NewScanner(r)
	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for scanner.Scan() {
		buf.Append(scanner.Text())
	}
}