// Package lifecycle provides service job lifecycle management for long-running services.
package lifecycle

import (
	"context"
	"fmt"
	"net/http"
	"os/exec"
	"syscall"
	"time"

	"github.com/jfraeys/fetch_ml/internal/domain"
	"github.com/jfraeys/fetch_ml/internal/scheduler"
)

// ServiceManager handles the lifecycle of long-running service jobs (Jupyter, vLLM)
type ServiceManager struct {
	task        *domain.Task
	spec        ServiceSpec
	cmd         *exec.Cmd
	port        int
	stateMgr    *StateManager
	logger      Logger
	healthCheck *scheduler.HealthCheck
	httpClient  *http.Client // Reusable HTTP client for health checks
}

// ServiceSpec defines the specification for a service job
type ServiceSpec struct {
	Command     []string
	Env         map[string]string
	Port        int
	HealthCheck *scheduler.HealthCheck
}

// NewServiceManager creates a new service manager
func NewServiceManager(task *domain.Task, spec ServiceSpec, port int, stateMgr *StateManager, logger Logger) *ServiceManager {
	return &ServiceManager{
		task:        task,
		spec:        spec,
		port:        port,
		stateMgr:    stateMgr,
		logger:      logger,
		healthCheck: spec.HealthCheck,
		httpClient:  &http.Client{Timeout: 5 * time.Second}, // Shared client with connection reuse
	}
}

// Run executes the service lifecycle: start, wait for ready, health loop
func (sm *ServiceManager) Run(ctx context.Context) error {
	if err := sm.start(); err != nil {
		sm.logger.Error("service start failed", "task_id", sm.task.ID, "error", err)
		if sm.stateMgr != nil {
			if err := sm.stateMgr.Transition(sm.task, StateFailed); err != nil {
				sm.logger.Error("failed to transition to failed", "task_id", sm.task.ID, "error", err)
			}
		}
		return fmt.Errorf("start service: %w", err)
	}

	// Wait for readiness
	readyCtx, cancel := context.WithTimeout(ctx, 120*time.Second)
	defer cancel()
	if err := sm.waitReady(readyCtx); err != nil {
		sm.logger.Error("service readiness check failed", "task_id", sm.task.ID, "error", err)
		if sm.stateMgr != nil {
			if err := sm.stateMgr.Transition(sm.task, StateFailed); err != nil {
				sm.logger.Error("failed to transition to failed", "task_id", sm.task.ID, "error", err)
			}
		}
		_ = sm.stop()
		return fmt.Errorf("wait ready: %w", err)
	}

	// Transition to serving state
	if sm.stateMgr != nil {
		if err := sm.stateMgr.Transition(sm.task, StateServing); err != nil {
			sm.logger.Error("failed to transition to serving", "task_id", sm.task.ID, "error", err)
		}
	}

	sm.logger.Info("service is serving", "task_id", sm.task.ID, "port", sm.port)

	// Run health loop
	return sm.healthLoop(ctx)
}

// start launches the service process
func (sm *ServiceManager) start() error {
	if len(sm.spec.Command) == 0 {
		return fmt.Errorf("no command specified")
	}

	sm.cmd = exec.Command(sm.spec.Command[0], sm.spec.Command[1:]...)

	// Set environment
	for k, v := range sm.spec.Env {
		sm.cmd.Env = append(sm.cmd.Env, fmt.Sprintf("%s=%s", k, v))
	}

	// Start process
	if err := sm.cmd.Start(); err != nil {
		return fmt.Errorf("start process: %w", err)
	}

	return nil
}

// waitReady blocks until the service passes readiness check or timeout
func (sm *ServiceManager) waitReady(ctx context.Context) error {
	if sm.healthCheck == nil || sm.healthCheck.ReadinessEndpoint == "" {
		// No readiness check - assume ready immediately
		return nil
	}

	ticker := time.NewTicker(1 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
			if sm.checkReadiness() {
				return nil
			}
		}
	}
}

// healthLoop monitors service health until context cancellation
func (sm *ServiceManager) healthLoop(ctx context.Context) error {
	if sm.healthCheck == nil {
		// No health check - just wait for context cancellation
		<-ctx.Done()
		return sm.gracefulStop()
	}

	interval := time.Duration(sm.healthCheck.IntervalSecs) * time.Second
	if interval == 0 {
		interval = 15 * time.Second
	}

	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return sm.gracefulStop()
		case <-ticker.C:
			if !sm.checkLiveness() {
				sm.logger.Error("service liveness check failed", "task_id", sm.task.ID)
				if sm.stateMgr != nil {
					if err := sm.stateMgr.Transition(sm.task, StateFailed); err != nil {
						sm.logger.Error("failed to transition to failed", "task_id", sm.task.ID, "error", err)
						return fmt.Errorf("transition to failed: %w", err)
					}
				}
				return fmt.Errorf("liveness check failed")
			}
		}
	}
}

// checkLiveness returns true if the service process is alive
func (sm *ServiceManager) checkLiveness() bool {
	if sm.cmd == nil || sm.cmd.Process == nil {
		return false
	}

	// Check process state
	if sm.healthCheck != nil && sm.healthCheck.LivenessEndpoint != "" {
		// HTTP liveness check using shared client
		resp, err := sm.httpClient.Get(sm.healthCheck.LivenessEndpoint)
		if err != nil {
			return false
		}
		defer resp.Body.Close()
		return resp.StatusCode == 200
	}

	// Process existence check
	return sm.cmd.Process.Signal(syscall.Signal(0)) == nil
}

// checkReadiness returns true if the service is ready to accept traffic
func (sm *ServiceManager) checkReadiness() bool {
	if sm.healthCheck == nil || sm.healthCheck.ReadinessEndpoint == "" {
		return true
	}

	// Use shared HTTP client for connection reuse
	resp, err := sm.httpClient.Get(sm.healthCheck.ReadinessEndpoint)
	if err != nil {
		return false
	}
	defer resp.Body.Close()
	return resp.StatusCode == 200
}

// gracefulStop stops the service gracefully with a timeout
func (sm *ServiceManager) gracefulStop() error {
	sm.logger.Info("gracefully stopping service", "task_id", sm.task.ID)

	if sm.stateMgr != nil {
		if err := sm.stateMgr.Transition(sm.task, StateStopping); err != nil {
			sm.logger.Error("failed to transition to stopping", "task_id", sm.task.ID, "error", err)
		}
	}

	if sm.cmd == nil || sm.cmd.Process == nil {
		if sm.stateMgr != nil {
			if err := sm.stateMgr.Transition(sm.task, StateCompleted); err != nil {
				sm.logger.Error("failed to transition to completed", "task_id", sm.task.ID, "error", err)
			}
		}
		return nil
	}

	// Send SIGTERM for graceful shutdown
	if err := sm.cmd.Process.Signal(syscall.SIGTERM); err != nil {
		sm.logger.Warn("SIGTERM failed, using SIGKILL", "task_id", sm.task.ID, "error", err)
		if err := sm.cmd.Process.Kill(); err != nil {
			sm.logger.Error("failed to kill process", "task_id", sm.task.ID, "error", err)
		}
	} else {
		// Wait for graceful shutdown
		done := make(chan error, 1)
		go func() {
			done <- sm.cmd.Wait()
		}()

		select {
		case <-done:
			// Graceful shutdown completed
		case <-time.After(30 * time.Second):
			// Timeout - force kill
			sm.logger.Warn("graceful shutdown timeout, forcing kill", "task_id", sm.task.ID)
			if err := sm.cmd.Process.Kill(); err != nil {
				sm.logger.Error("failed to kill process", "task_id", sm.task.ID, "error", err)
			}
		}
	}

	if sm.stateMgr != nil {
		if err := sm.stateMgr.Transition(sm.task, StateCompleted); err != nil {
			sm.logger.Error("failed to transition to completed", "task_id", sm.task.ID, "error", err)
		}
	}

	return nil
}

// stop forcefully stops the service
func (sm *ServiceManager) stop() error {
	if sm.cmd == nil || sm.cmd.Process == nil {
		return nil
	}
	return sm.cmd.Process.Kill()
}

// GetPort returns the assigned port for the service
func (sm *ServiceManager) GetPort() int {
	return sm.port
}