package ontology

import (
	"errors"
	"fmt"
	"sort"
	"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) Ingest(input IngestInput) (IngestResult, error) {
	if strings.TrimSpace(input.Title) == "" {
		return IngestResult{}, errors.New("title is required")
	}
	if strings.TrimSpace(input.Body) == "" {
		return IngestResult{}, errors.New("body is required")
	}

	now := time.Now().UTC()
	material := Material{
		ID:         s.nextID("material"),
		Title:      input.Title,
		SourceType: sourceTypeOrDefault(input.SourceType),
		Body:       input.Body,
		CreatedAt:  now,
	}

	concepts := s.extractConcepts(material, now)
	edges := s.extractEdges(concepts, now)
	gaps := s.detectGaps(concepts, edges, now)
	if err := s.store.Save(material, concepts, edges, gaps); err != nil {
		return IngestResult{}, err
	}

	return IngestResult{
		Material: material,
		Snapshot: s.store.Snapshot(),
	}, nil
}

func (s *Service) Snapshot() Snapshot {
	return s.store.Snapshot()
}

func (s *Service) extractConcepts(material Material, now time.Time) []ConceptCandidate {
	body := strings.ToLower(material.Body)
	concepts := []ConceptCandidate{}
	for _, known := range knownConcepts {
		quote, ok := firstKeywordQuote(body, material.Body, known.Keywords)
		if !ok {
			continue
		}
		concepts = append(concepts, ConceptCandidate{
			ID:      s.nextID("concept"),
			Concept: known.Ref,
			Summary: "Source material mentions " + known.Ref.Label + ".",
			Evidence: []workflows.EvidenceRef{{
				Kind:       workflows.EvidenceSource,
				ID:         material.ID,
				Quote:      quote,
				Confidence: 0.72,
			}},
			ReviewState: ReviewCandidate,
			CreatedAt:   now,
		})
	}
	sort.Slice(concepts, func(i, j int) bool {
		return concepts[i].Concept.ID < concepts[j].Concept.ID
	})
	return concepts
}

func (s *Service) extractEdges(concepts []ConceptCandidate, now time.Time) []EdgeCandidate {
	byID := make(map[string]ConceptCandidate, len(concepts))
	for _, concept := range concepts {
		byID[concept.Concept.ID] = concept
	}

	edges := []EdgeCandidate{}
	for _, rule := range prerequisiteRules {
		from, fromOK := byID[rule.FromID]
		to, toOK := byID[rule.ToID]
		if !fromOK || !toOK {
			continue
		}
		edges = append(edges, EdgeCandidate{
			ID:          s.nextID("edge"),
			From:        from.Concept,
			To:          to.Concept,
			Kind:        EdgePrerequisite,
			Evidence:    append([]workflows.EvidenceRef(nil), from.Evidence...),
			ReviewState: ReviewCandidate,
			CreatedAt:   now,
		})
	}
	return edges
}

func (s *Service) detectGaps(
	concepts []ConceptCandidate,
	edges []EdgeCandidate,
	now time.Time,
) []Gap {
	gaps := []Gap{}
	byID := make(map[string]ConceptCandidate, len(concepts))
	for _, concept := range concepts {
		byID[concept.Concept.ID] = concept
		if len(concept.Evidence) == 1 && len(strings.Fields(concept.Evidence[0].Quote)) < 6 {
			gaps = append(gaps, Gap{
				ID:                 s.nextID("gap"),
				Concept:            concept.Concept,
				GapType:            GapWeakEvidence,
				Reason:             "Concept is mentioned, but source support is thin.",
				SupportingEvidence: append([]workflows.EvidenceRef(nil), concept.Evidence...),
				ProposedAction:     ActionRequestSource,
				ReviewState:        ReviewCandidate,
				CreatedAt:          now,
			})
		}
	}

	for _, rule := range prerequisiteRules {
		to, toOK := byID[rule.ToID]
		if !toOK {
			continue
		}
		if _, fromOK := byID[rule.FromID]; fromOK {
			continue
		}
		gaps = append(gaps, Gap{
			ID:                 s.nextID("gap"),
			Concept:            to.Concept,
			GapType:            GapMissingPrerequisite,
			Reason:             "Prerequisite concept " + rule.FromID + " is missing from the material.",
			SupportingEvidence: append([]workflows.EvidenceRef(nil), to.Evidence...),
			ProposedAction:     ActionGenerateCandidate,
			ReviewState:        ReviewCandidate,
			CreatedAt:          now,
		})
	}

	if len(edges) == 0 && len(concepts) > 1 {
		first := concepts[0]
		gaps = append(gaps, Gap{
			ID:                 s.nextID("gap"),
			Concept:            first.Concept,
			GapType:            GapMissingPrerequisite,
			Reason:             "Concept relationship is inferred as incomplete and needs review.",
			SupportingEvidence: append([]workflows.EvidenceRef(nil), first.Evidence...),
			ProposedAction:     ActionHumanReview,
			ReviewState:        ReviewCandidate,
			CreatedAt:          now,
		})
	}
	return gaps
}

func firstKeywordQuote(lowerBody string, originalBody string, keywords []string) (string, bool) {
	for _, keyword := range keywords {
		index := strings.Index(lowerBody, strings.ToLower(keyword))
		if index < 0 {
			continue
		}
		start := max(0, index-40)
		end := min(len(originalBody), index+len(keyword)+80)
		return strings.TrimSpace(originalBody[start:end]), true
	}
	return "", false
}

func sourceTypeOrDefault(sourceType string) string {
	if strings.TrimSpace(sourceType) == "" {
		return "text"
	}
	return sourceType
}

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