package learnermemory

import (
	"errors"
	"fmt"
	"strings"
	"sync/atomic"
	"time"

	"tutor/internal/workflows"
)

type Service struct {
	store Store
	ids   atomic.Uint64
}

func NewService(store Store) *Service {
	return &Service{store: store}
}

func (s *Service) EnsureProfile(input ProfileInput) (Profile, error) {
	if strings.TrimSpace(input.UserID) == "" {
		return Profile{}, errors.New("user_id is required")
	}
	if strings.TrimSpace(input.TargetRole) == "" {
		return Profile{}, errors.New("target_role is required")
	}

	profile := Profile{
		UserID:            input.UserID,
		TargetRole:        input.TargetRole,
		Stack:             append([]string(nil), input.Stack...),
		InterviewTimeline: input.InterviewTimeline,
		Preferences:       append([]string(nil), input.Preferences...),
		UpdatedAt:         time.Now().UTC(),
	}
	return s.store.UpsertProfile(profile)
}

func (s *Service) ApplyCandidate(candidate workflows.MemoryUpdateCandidate) error {
	if strings.TrimSpace(candidate.UserID) == "" {
		return errors.New("candidate user_id is required")
	}

	for _, update := range candidate.Updates {
		if len(update.Evidence) == 0 {
			continue
		}
		if strings.TrimSpace(update.Concept.ID) == "" {
			continue
		}
		if err := s.applyUpdate(candidate.UserID, update); err != nil {
			return err
		}
	}
	return nil
}

func (s *Service) Snapshot(userID string) (Snapshot, error) {
	if strings.TrimSpace(userID) == "" {
		return Snapshot{}, errors.New("user_id is required")
	}
	return s.store.Snapshot(userID)
}

func (s *Service) applyUpdate(userID string, update workflows.MemoryUpdate) error {
	now := time.Now().UTC()
	switch update.Kind {
	case workflows.MemoryConceptMastery:
		return s.store.UpsertMastery(ConceptMastery{
			UserID:    userID,
			Concept:   update.Concept,
			State:     update.ProposedState,
			Evidence:  append([]workflows.EvidenceRef(nil), update.Evidence...),
			UpdatedAt: now,
		})
	case workflows.MemoryMisconception:
		return s.store.AddMisconception(Misconception{
			ID:          s.nextID("misconception"),
			UserID:      userID,
			Concept:     update.Concept,
			Label:       update.Summary,
			Description: update.Summary,
			Evidence:    append([]workflows.EvidenceRef(nil), update.Evidence...),
			UpdatedAt:   now,
		})
	case workflows.MemoryIntervention:
		return s.store.AddIntervention(Intervention{
			ID:        s.nextID("intervention"),
			UserID:    userID,
			Concept:   update.Concept,
			Summary:   update.Summary,
			Evidence:  append([]workflows.EvidenceRef(nil), update.Evidence...),
			UpdatedAt: now,
		})
	case workflows.MemoryReviewSchedule:
		return s.store.AddReviewSchedule(ReviewSchedule{
			ID:        s.nextID("review"),
			UserID:    userID,
			Concept:   update.Concept,
			Reason:    update.Summary,
			Evidence:  append([]workflows.EvidenceRef(nil), update.Evidence...),
			UpdatedAt: now,
		})
	default:
		return nil
	}
}

func (s *Service) nextID(prefix string) string {
	return fmt.Sprintf("%s-%d", prefix, s.ids.Add(1))
}