// Filename: internal/task/task.go
package task

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"gemini-balancer/internal/store"
	"time"

	"github.com/sirupsen/logrus"
)

const (
	ResultTTL = 60 * time.Minute
)

type Reporter interface {
	StartTask(ctx context.Context, keyGroupID uint, taskType, resourceID string, total int, timeout time.Duration) (*Status, error)
	EndTaskByID(ctx context.Context, taskID, resourceID string, result any, taskErr error)
	UpdateProgressByID(ctx context.Context, taskID string, processed int) error
	UpdateTotalByID(ctx context.Context, taskID string, total int) error
}

type Status struct {
	ID              string     `json:"id"`
	TaskType        string     `json:"task_type"`
	IsRunning       bool       `json:"is_running"`
	ResourceID      string     `json:"resource_id,omitempty"`
	Processed       int        `json:"processed"`
	Total           int        `json:"total"`
	Result          any        `json:"result,omitempty"`
	Error           string     `json:"error,omitempty"`
	StartedAt       time.Time  `json:"started_at"`
	FinishedAt      *time.Time `json:"finished_at,omitempty"`
	DurationSeconds float64    `json:"duration_seconds,omitempty"`
}

type Task struct {
	store  store.Store
	logger *logrus.Entry
}

func NewTask(store store.Store, logger *logrus.Logger) *Task {
	return &Task{
		store:  store,
		logger: logger.WithField("component", "TaskService📋"),
	}
}

var _ Reporter = (*Task)(nil)

func (s *Task) getResourceLockKey(resourceID string) string {
	return fmt.Sprintf("task:lock:%s", resourceID)
}

func (s *Task) getTaskDataKey(taskID string) string {
	return fmt.Sprintf("task:data:%s", taskID)
}

func (s *Task) getIsRunningFlagKey(taskID string) string {
	return fmt.Sprintf("task:running:%s", taskID)
}

func (s *Task) StartTask(ctx context.Context, keyGroupID uint, taskType, resourceID string, total int, timeout time.Duration) (*Status, error) {
	lockKey := s.getResourceLockKey(resourceID)

	if existingTaskID, err := s.store.Get(ctx, lockKey); err == nil && len(existingTaskID) > 0 {
		return nil, fmt.Errorf("a task is already running for this resource (ID: %s)", string(existingTaskID))
	}

	taskID := fmt.Sprintf("%d-%d", time.Now().UnixNano(), keyGroupID)
	taskKey := s.getTaskDataKey(taskID)
	runningFlagKey := s.getIsRunningFlagKey(taskID)
	status := &Status{
		ID:         taskID,
		TaskType:   taskType,
		IsRunning:  true,
		ResourceID: resourceID,
		Total:      total,
		StartedAt:  time.Now(),
	}
	statusBytes, err := json.Marshal(status)
	if err != nil {
		return nil, fmt.Errorf("failed to serialize new task status: %w", err)
	}

	if timeout == 0 {
		timeout = ResultTTL * 24
	}

	if err := s.store.Set(ctx, lockKey, []byte(taskID), timeout); err != nil {
		return nil, fmt.Errorf("failed to acquire task resource lock: %w", err)
	}
	if err := s.store.Set(ctx, taskKey, statusBytes, timeout); err != nil {
		_ = s.store.Del(ctx, lockKey)
		return nil, fmt.Errorf("failed to set new task data in store: %w", err)
	}

	if err := s.store.Set(ctx, runningFlagKey, []byte("1"), timeout); err != nil {
		_ = s.store.Del(ctx, lockKey)
		_ = s.store.Del(ctx, taskKey)
		return nil, fmt.Errorf("failed to set task running flag: %w", err)
	}
	return status, nil
}

func (s *Task) EndTaskByID(ctx context.Context, taskID, resourceID string, resultData any, taskErr error) {
	lockKey := s.getResourceLockKey(resourceID)
	defer func() {
		if err := s.store.Del(ctx, lockKey); err != nil {
			s.logger.WithError(err).Warnf("Failed to release resource lock '%s' for task %s.", lockKey, taskID)
		}
	}()
	runningFlagKey := s.getIsRunningFlagKey(taskID)
	_ = s.store.Del(ctx, runningFlagKey)

	status, err := s.GetStatus(ctx, taskID)
	if err != nil {
		s.logger.WithError(err).Errorf("Could not get task status for task ID %s during EndTask. Lock has been released, but task data may be stale.", taskID)
		return
	}
	if !status.IsRunning {
		s.logger.Warnf("EndTaskByID called for an already finished task: %s", taskID)
		return
	}
	now := time.Now()
	status.IsRunning = false
	status.FinishedAt = &now
	status.DurationSeconds = now.Sub(status.StartedAt).Seconds()
	if taskErr != nil {
		status.Error = taskErr.Error()
	} else {
		status.Result = resultData
	}
	updatedTaskBytes, _ := json.Marshal(status)
	taskKey := s.getTaskDataKey(taskID)
	if err := s.store.Set(ctx, taskKey, updatedTaskBytes, ResultTTL); err != nil {
		s.logger.WithError(err).Errorf("Failed to save final status for task %s.", taskID)
	}
}

func (s *Task) GetStatus(ctx context.Context, taskID string) (*Status, error) {
	taskKey := s.getTaskDataKey(taskID)
	statusBytes, err := s.store.Get(ctx, taskKey)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			return nil, errors.New("task not found")
		}
		return nil, fmt.Errorf("failed to get task status from store: %w", err)
	}

	var status Status
	if err := json.Unmarshal(statusBytes, &status); err != nil {
		return nil, fmt.Errorf("corrupted task data in store for ID %s", taskID)
	}
	if !status.IsRunning && status.FinishedAt != nil {
		status.DurationSeconds = status.FinishedAt.Sub(status.StartedAt).Seconds()
	}
	return &status, nil
}

func (s *Task) updateTask(ctx context.Context, taskID string, updater func(status *Status)) error {
	runningFlagKey := s.getIsRunningFlagKey(taskID)
	if _, err := s.store.Get(ctx, runningFlagKey); err != nil {
		return nil
	}
	status, err := s.GetStatus(ctx, taskID)
	if err != nil {
		s.logger.WithError(err).Warnf("Failed to get task status for update on task %s. Update will not be saved.", taskID)
		return nil
	}
	if !status.IsRunning {
		return nil
	}
	updater(status)
	statusBytes, marshalErr := json.Marshal(status)
	if marshalErr != nil {
		s.logger.WithError(marshalErr).Errorf("Failed to serialize status for update on task %s.", taskID)
		return nil
	}
	taskKey := s.getTaskDataKey(taskID)
	if err := s.store.Set(ctx, taskKey, statusBytes, ResultTTL*24); err != nil {
		s.logger.WithError(err).Warnf("Failed to save update for task %s.", taskID)
	}
	return nil
}

func (s *Task) UpdateProgressByID(ctx context.Context, taskID string, processed int) error {
	return s.updateTask(ctx, taskID, func(status *Status) {
		status.Processed = processed
	})
}

func (s *Task) UpdateTotalByID(ctx context.Context, taskID string, total int) error {
	return s.updateTask(ctx, taskID, func(status *Status) {
		status.Total = total
	})
}