package automations

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"sync"
)

// Service composes the Scheduler (cron), the Engine (event rules) and the
// ReminderStore into a single automation engine with one lifecycle. It routes
// event rules to the Engine and cron rules to the Scheduler by Trigger kind.
type Service struct {
	cfg  Config
	deps Deps
	log  *slog.Logger

	sched  *Scheduler
	engine *Engine
	remind *ReminderStore

	mu        sync.RWMutex
	cronRules map[string]ScheduleID // rule id -> schedule id
}

// NewService builds an automation engine from cfg and deps. The bus in deps is
// required. It also resolves the AI pipeline used by AIAction construction.
func NewService(cfg Config, deps Deps) (*Service, error) {
	if deps.Bus == nil {
		return nil, fmt.Errorf("automations: new service: %w", ErrNilBus)
	}
	sched, err := New(cfg, deps)
	if err != nil {
		return nil, err
	}
	engine, err := NewEngine(cfg, deps)
	if err != nil {
		return nil, err
	}
	remind, err := NewReminder(cfg, deps)
	if err != nil {
		return nil, err
	}
	return &Service{
		cfg:       cfg,
		deps:      deps,
		log:       sourcedLog(deps.Log),
		sched:     sched,
		engine:    engine,
		remind:    remind,
		cronRules: make(map[string]ScheduleID),
	}, nil
}

// Pipeline returns the service's resolved AI pipeline, or nil when neither a loop
// nor an agent is configured.
func (s *Service) Pipeline() Pipeline { return s.deps.pipeline() }

// Scheduler returns the underlying cron scheduler.
func (s *Service) Scheduler() *Scheduler { return s.sched }

// Engine returns the underlying event rule engine.
func (s *Service) Engine() *Engine { return s.engine }

// ReminderStore returns the underlying reminder store.
func (s *Service) ReminderStore() *ReminderStore { return s.remind }

// AddSchedule delegates to the Scheduler.
func (s *Service) AddSchedule(ctx context.Context, cronExpr string, action Action) (ScheduleID, error) {
	return s.sched.AddSchedule(ctx, cronExpr, action)
}

// AddRule routes an event rule to the Engine and a cron rule to the Scheduler. A
// malformed rule returns an error wrapping ErrInvalidRule.
func (s *Service) AddRule(ctx context.Context, r Rule) error {
	if !r.valid() {
		return fmt.Errorf("automations: add rule %q: %w", r.ID, ErrInvalidRule)
	}
	switch r.Trigger {
	case TriggerEvent:
		return s.engine.AddEvent(ctx, r)
	case TriggerCron:
		id, err := s.sched.AddSchedule(ctx, r.Expression, r.Action)
		if err != nil {
			return err
		}
		s.mu.Lock()
		s.cronRules[r.ID] = id
		s.mu.Unlock()
		return nil
	default:
		return fmt.Errorf("automations: add rule %q: %w", r.ID, ErrInvalidRule)
	}
}

// RemoveRule removes an event or cron rule by id. It returns an error wrapping
// ErrNotFound when no such rule exists.
func (s *Service) RemoveRule(ctx context.Context, id string) error {
	s.mu.Lock()
	if schedID, ok := s.cronRules[id]; ok {
		delete(s.cronRules, id)
		s.mu.Unlock()
		s.sched.RemoveSchedule(schedID)
		return nil
	}
	s.mu.Unlock()
	return s.engine.RemoveRule(ctx, id)
}

// AddReminder delegates to the ReminderStore.
func (s *Service) AddReminder(ctx context.Context, r Reminder) error {
	return s.remind.Add(ctx, r)
}

// Reminders returns a sorted snapshot of registered reminders.
func (s *Service) Reminders() []Reminder { return s.remind.List() }

// CancelReminder delegates to the ReminderStore.
func (s *Service) CancelReminder(ctx context.Context, id string) error {
	return s.remind.Cancel(ctx, id)
}

// Start starts the scheduler, the event engine and the reminder loop.
func (s *Service) Start(ctx context.Context) error {
	if err := s.sched.Start(ctx); err != nil {
		return err
	}
	if err := s.engine.Start(ctx); err != nil {
		return err
	}
	return s.remind.Start(ctx)
}

// Stop stops the reminder loop, the event engine and the scheduler, collecting
// errors from each.
func (s *Service) Stop(ctx context.Context) error {
	var errs []error
	if err := s.remind.Stop(ctx); err != nil {
		errs = append(errs, err)
	}
	if err := s.engine.Stop(ctx); err != nil {
		errs = append(errs, err)
	}
	if err := s.sched.Stop(ctx); err != nil {
		errs = append(errs, err)
	}
	return errors.Join(errs...)
}