// Package worker provides background workers for async task processing.
package worker

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

	"github.com/orchard9/rdev/internal/domain"
	"github.com/orchard9/rdev/internal/metrics"
	"github.com/orchard9/rdev/internal/service"
)

// WorkExecutor is a background daemon that polls the work queue for tasks
// and executes them via task-type-specific handlers. It self-registers as
// a worker, sends heartbeats, and reports results.
type WorkExecutor struct {
	workerSvc  *service.WorkerService
	workSvc    *service.WorkService
	buildExec  *BuildExecutor
	verifyExec *VerifyExecutor
	sdlcExec   *SDLCTaskExecutor
	logger     *slog.Logger

	workerID     string
	hostname     string
	version      string
	capabilities []string
	pollPeriod   time.Duration
	hbPeriod     time.Duration
	taskTimeout  time.Duration

	started int32 // atomic flag to prevent double-start
	ctx     context.Context
	cancel  context.CancelFunc
	wg      sync.WaitGroup
}

// WorkExecutorConfig holds configuration for the work executor.
type WorkExecutorConfig struct {
	// WorkerID uniquely identifies this executor instance.
	// Defaults to HOSTNAME env var or "rdev-worker-0".
	WorkerID string

	// Version reported to the worker registry.
	Version string

	// Capabilities reported to the worker registry.
	Capabilities []string

	// PollPeriod is how often to check for new tasks.
	PollPeriod time.Duration

	// HeartbeatPeriod is how often to send heartbeats.
	HeartbeatPeriod time.Duration

	// TaskTimeout is the maximum time a single task may run.
	// Default: 15 minutes.
	TaskTimeout time.Duration

	Logger *slog.Logger
}

// DefaultWorkExecutorConfig returns sensible defaults.
func DefaultWorkExecutorConfig() *WorkExecutorConfig {
	workerID := os.Getenv("HOSTNAME")
	if workerID == "" {
		workerID = "rdev-worker-0"
	}
	return &WorkExecutorConfig{
		WorkerID:        workerID,
		Capabilities:    []string{"build"},
		PollPeriod:      5 * time.Second,
		HeartbeatPeriod: 30 * time.Second,
		TaskTimeout:     15 * time.Minute,
		Logger:          slog.Default(),
	}
}

// NewWorkExecutor creates a new work executor daemon.
func NewWorkExecutor(
	workerSvc *service.WorkerService,
	workSvc *service.WorkService,
	buildExec *BuildExecutor,
	verifyExec *VerifyExecutor,
	sdlcExec *SDLCTaskExecutor,
	cfg *WorkExecutorConfig,
) *WorkExecutor {
	if cfg == nil {
		cfg = DefaultWorkExecutorConfig()
	}

	hostname, _ := os.Hostname()
	if hostname == "" {
		hostname = cfg.WorkerID
	}

	ctx, cancel := context.WithCancel(context.Background())

	capabilities := cfg.Capabilities
	if len(capabilities) == 0 {
		capabilities = []string{"build"}
	}

	taskTimeout := cfg.TaskTimeout
	if taskTimeout == 0 {
		taskTimeout = 15 * time.Minute
	}

	return &WorkExecutor{
		workerSvc:    workerSvc,
		workSvc:      workSvc,
		buildExec:    buildExec,
		verifyExec:   verifyExec,
		sdlcExec:     sdlcExec,
		logger:       cfg.Logger.With("component", "work-executor"),
		workerID:     cfg.WorkerID,
		hostname:     hostname,
		version:      cfg.Version,
		capabilities: capabilities,
		pollPeriod:   cfg.PollPeriod,
		hbPeriod:     cfg.HeartbeatPeriod,
		taskTimeout:  taskTimeout,
		ctx:          ctx,
		cancel:       cancel,
	}
}

// Start registers the worker and begins the poll and heartbeat loops.
func (e *WorkExecutor) Start() error {
	if !atomic.CompareAndSwapInt32(&e.started, 0, 1) {
		return fmt.Errorf("executor already started")
	}

	// Register this worker in the pool
	worker := &domain.Worker{
		ID:           e.workerID,
		Hostname:     e.hostname,
		Capabilities: e.capabilities,
		Version:      e.version,
	}
	if err := e.workerSvc.Register(e.ctx, worker); err != nil {
		return err
	}

	e.logger.Info("work executor started",
		"worker_id", e.workerID,
		"poll_period", e.pollPeriod,
		"heartbeat_period", e.hbPeriod,
	)

	// Start heartbeat loop
	e.wg.Add(1)
	go e.heartbeatLoop()

	// Start poll loop
	e.wg.Add(1)
	go e.pollLoop()

	return nil
}

// Stop gracefully shuts down the executor.
func (e *WorkExecutor) Stop() {
	e.logger.Info("work executor stopping", "worker_id", e.workerID)
	e.cancel()
	e.wg.Wait()

	// Deregister (best-effort, context is cancelled so use a fresh one)
	ctx, cancel := context.WithTimeout(context.Background(), TimeoutQuickOp)
	defer cancel()
	if err := e.workerSvc.Deregister(ctx, e.workerID); err != nil {
		e.logger.Warn("failed to deregister worker", "error", err)
	}

	e.logger.Info("work executor stopped", "worker_id", e.workerID)
}

// WorkerID returns the executor's worker ID.
func (e *WorkExecutor) WorkerID() string {
	return e.workerID
}

// Running returns true if the executor context has not been cancelled.
func (e *WorkExecutor) Running() bool {
	return e.ctx.Err() == nil
}

// heartbeatLoop sends periodic heartbeats to the worker registry.
func (e *WorkExecutor) heartbeatLoop() {
	defer e.wg.Done()

	ticker := time.NewTicker(e.hbPeriod)
	defer ticker.Stop()

	for {
		select {
		case <-e.ctx.Done():
			return
		case <-ticker.C:
			if err := e.workerSvc.Heartbeat(e.ctx, e.workerID); err != nil {
				e.logger.Warn("heartbeat failed", "error", err)
			}
		}
	}
}

// pollLoop checks for available tasks on a ticker.
func (e *WorkExecutor) pollLoop() {
	defer e.wg.Done()

	ticker := time.NewTicker(e.pollPeriod)
	defer ticker.Stop()

	for {
		select {
		case <-e.ctx.Done():
			return
		case <-ticker.C:
			e.tryClaimAndExecute()
		}
	}
}

// tryClaimAndExecute attempts to claim a task and execute it.
func (e *WorkExecutor) tryClaimAndExecute() {
	task, err := e.workerSvc.ClaimTask(e.ctx, e.workerID)
	if err != nil {
		e.logger.Warn("failed to claim task", "error", err)
		return
	}
	if task == nil {
		return // No tasks available
	}

	e.logger.Info("executing task",
		"task_id", task.ID,
		"project_id", task.ProjectID,
		"type", task.Type,
	)

	taskCtx, taskCancel := context.WithTimeout(e.ctx, e.taskTimeout)
	defer taskCancel()

	result := e.executeTask(taskCtx, task)

	// Record build metrics
	status := "success"
	if !result.Success {
		status = "failed"
	}
	metrics.RecordBuild(task.ProjectID, status, result.DurationMs)

	if result.Success {
		if err := e.workerSvc.CompleteTask(e.ctx, e.workerID, task.ID, result); err != nil {
			e.logger.Error("failed to complete task",
				"task_id", task.ID,
				"error", err,
			)
		}
	} else {
		// Fail the task through worker service (updates audit + handles retry logic)
		if result.Error == "" {
			result.Error = "execution failed"
		}

		if err := e.workerSvc.FailTask(e.ctx, e.workerID, task.ID, result, e.workSvc); err != nil {
			e.logger.Error("failed to record task failure",
				"task_id", task.ID,
				"error", err,
			)
		}
	}
}

// executeTask routes a task to the appropriate handler based on its type.
func (e *WorkExecutor) executeTask(ctx context.Context, task *domain.WorkTask) *domain.BuildResult {
	switch task.Type {
	case domain.WorkTaskTypeBuild:
		return e.buildExec.Execute(ctx, task)
	case domain.WorkTaskTypeVerify:
		if e.verifyExec == nil {
			return &domain.BuildResult{
				Success: false,
				Error:   "verify executor not configured",
			}
		}
		return e.verifyExec.Execute(ctx, task)
	case domain.WorkTaskTypeSDLC:
		if e.sdlcExec == nil {
			return &domain.BuildResult{
				Success: false,
				Error:   "sdlc executor not configured",
			}
		}
		return e.sdlcExec.Execute(ctx, task)
	default:
		return &domain.BuildResult{
			Success: false,
			Error:   "unsupported task type: " + string(task.Type),
		}
	}
}