package progression

import (
	"errors"
	"sort"
	"strings"

	"tutor/internal/learnermemory"
	"tutor/internal/workflows"
)

type Service struct {
	memory *learnermemory.Service
}

func NewService(memory *learnermemory.Service) *Service {
	return &Service{memory: memory}
}

func (s *Service) ReadinessMap(userID string) (ReadinessMap, error) {
	snapshot, err := s.snapshot(userID)
	if err != nil {
		return ReadinessMap{}, err
	}

	concepts := make([]ConceptProgress, 0, len(snapshot.Mastery))
	for _, mastery := range snapshot.Mastery {
		concepts = append(concepts, ConceptProgress{
			Concept:     mastery.Concept,
			State:       mastery.State,
			LadderLevel: ladderForState(mastery.State),
			NextAction:  actionForState(mastery.State),
			Evidence:    append([]workflows.EvidenceRef(nil), mastery.Evidence...),
		})
	}
	sort.Slice(concepts, func(i, j int) bool {
		return concepts[i].Concept.ID < concepts[j].Concept.ID
	})

	readiness := ReadinessMap{
		UserID:              snapshot.Profile.UserID,
		Track:               trackFromConcepts(concepts),
		ReadinessPercentage: readinessPercentage(concepts),
		Concepts:            concepts,
		Rewards:             rewardsFromConcepts(concepts),
		Unlocks:             unlocksFromConcepts(concepts),
	}
	return readiness, nil
}

func (s *Service) NextChallenge(userID string) (workflows.NextChallenge, error) {
	readiness, err := s.ReadinessMap(userID)
	if err != nil {
		return workflows.NextChallenge{}, err
	}
	if len(readiness.Concepts) == 0 {
		return workflows.NextChallenge{}, errors.New("no learner memory concepts available")
	}

	target := readiness.Concepts[0]
	for _, concept := range readiness.Concepts[1:] {
		if readinessScore(concept.State) < readinessScore(target.State) {
			target = concept
		}
	}

	return workflows.NextChallenge{
		UserID:           readiness.UserID,
		Track:            readiness.Track,
		Concept:          target.Concept,
		LadderLevel:      target.LadderLevel,
		Question:         challengeQuestion(target),
		Rationale:        "Selected from the weakest evidenced learner-memory concept.",
		DifficultyAction: workflowDifficulty(target.NextAction),
		Evidence:         append([]workflows.EvidenceRef(nil), target.Evidence...),
	}, nil
}

func (s *Service) snapshot(userID string) (learnermemory.Snapshot, error) {
	if s.memory == nil {
		return learnermemory.Snapshot{}, errors.New("learner memory not configured")
	}
	if strings.TrimSpace(userID) == "" {
		return learnermemory.Snapshot{}, errors.New("user_id is required")
	}
	return s.memory.Snapshot(userID)
}

func ladderForState(state workflows.ReadinessState) workflows.LadderLevel {
	switch state {
	case workflows.ReadinessFragile:
		return workflows.LadderDefine
	case workflows.ReadinessImproving:
		return workflows.LadderTradeoffs
	case workflows.ReadinessInterviewReady:
		return workflows.LadderDesignConstraints
	case workflows.ReadinessStrongSignal:
		return workflows.LadderInterviewPressure
	default:
		return workflows.LadderDefine
	}
}

func actionForState(state workflows.ReadinessState) DifficultyAction {
	switch state {
	case workflows.ReadinessFragile:
		return ActionRecover
	case workflows.ReadinessImproving:
		return ActionHold
	case workflows.ReadinessInterviewReady, workflows.ReadinessStrongSignal:
		return ActionRaise
	default:
		return ActionLower
	}
}

func workflowDifficulty(action DifficultyAction) workflows.DifficultyAction {
	switch action {
	case ActionRecover:
		return workflows.DifficultyRecover
	case ActionLower:
		return workflows.DifficultyLower
	case ActionRaise:
		return workflows.DifficultyRaise
	default:
		return workflows.DifficultyHold
	}
}

func readinessPercentage(concepts []ConceptProgress) int {
	if len(concepts) == 0 {
		return 0
	}
	total := 0
	for _, concept := range concepts {
		total += readinessScore(concept.State)
	}
	return total * 100 / (len(concepts) * 4)
}

func readinessScore(state workflows.ReadinessState) int {
	switch state {
	case workflows.ReadinessFragile:
		return 1
	case workflows.ReadinessImproving:
		return 2
	case workflows.ReadinessInterviewReady:
		return 3
	case workflows.ReadinessStrongSignal:
		return 4
	default:
		return 0
	}
}

func rewardsFromConcepts(concepts []ConceptProgress) []Reward {
	rewards := []Reward{}
	for _, concept := range concepts {
		if len(concept.Evidence) == 0 || readinessScore(concept.State) < 2 {
			continue
		}
		rewards = append(rewards, Reward{
			Kind:     RewardConceptProgress,
			Label:    "Evidence-backed progress on " + concept.Concept.Label,
			Evidence: append([]workflows.EvidenceRef(nil), concept.Evidence...),
		})
	}
	return rewards
}

func unlocksFromConcepts(concepts []ConceptProgress) []Unlock {
	stable := []workflows.EvidenceRef{}
	for _, concept := range concepts {
		if readinessScore(concept.State) < 3 || len(concept.Evidence) == 0 {
			continue
		}
		stable = append(stable, concept.Evidence...)
	}
	if len(stable) < 2 {
		return []Unlock{}
	}
	return []Unlock{{
		Kind:     UnlockBossQuestion,
		Label:    "Integrated backend interview boss question",
		Evidence: append([]workflows.EvidenceRef(nil), stable...),
	}}
}

func trackFromConcepts(concepts []ConceptProgress) string {
	if len(concepts) == 0 {
		return ""
	}
	return concepts[0].Concept.Track
}

func challengeQuestion(concept ConceptProgress) string {
	switch concept.LadderLevel {
	case workflows.LadderTradeoffs:
		return "Explain a production tradeoff for " + concept.Concept.Label + "."
	case workflows.LadderDesignConstraints:
		return "Design a constrained backend scenario that uses " + concept.Concept.Label + "."
	case workflows.LadderInterviewPressure:
		return "Answer a timed interview follow-up about " + concept.Concept.Label + "."
	default:
		return "Define " + concept.Concept.Label + " and give one concrete backend example."
	}
}