// Package npcinteractions normalizes merged D&D NPC interaction candidates.
package npcinteractions

import (
	"context"
	"fmt"
	"sort"
	"strconv"
	"strings"

	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
	"gitea.maximumdirect.net/eric/notarius/internal/framework/contracts"
	"gitea.maximumdirect.net/eric/notarius/internal/framework/pipeline"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/npcs/identity"
	npcregistry "gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/npcs/registry"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/shared"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/shared/diagnostics"
)

const (
	Key                 = "dnd/npc-interactions"
	normalizationPolicy = "dnd.npc_interactions.normalize.v1"
	NormalizationPolicy = normalizationPolicy

	ReasonCodeNameCanonicalized     = "npc_interaction_name_canonicalized"
	ReasonCodeSourceRefsNormalized  = "source_references_normalized"
	ReasonCodeInteractionsReordered = "npc_interactions_reordered"
	ReasonCodeDuplicateCollapsed    = "duplicate_npc_interaction_collapsed"
)

const (
	NPCRegistryReferenceSlot = npcregistry.ReferenceSlot
	NPCRegistryMaxBytes      = npcregistry.MaxBytes
)

var requiredCapabilities = []string{"merged"}
var providedCapabilities = []string{"normalized"}

var referenceSlotDescriptions = shared.ReferenceSlotDescriptions{
	Glossary: "Optional campaign glossary reference material used only for interaction disambiguation.",
	Party:    "Optional party roster reference material used only for interaction disambiguation.",
	Players:  "Optional player list reference material used only for interaction disambiguation.",
	Roster:   "Deprecated alias for party roster reference material used only for interaction disambiguation.",
}

var _ contracts.Normalizer[dnd.NPCInteractionList] = (*Normalizer)(nil)
var _ contracts.ManifestMetadataProvider = (*Normalizer)(nil)
var _ pipeline.CheckpointFingerprintProvider = (*Normalizer)(nil)

type Options struct{}

type Normalizer struct {
	npcResolver *npcregistry.Resolver
}

func New(_ Options, references ...contracts.ReferenceSet) (*Normalizer, error) {
	if len(references) > 1 {
		return nil, normalizerErrorf("at most one reference set may be supplied")
	}
	var referenceSet contracts.ReferenceSet
	if len(references) == 1 {
		referenceSet = references[0]
	}
	resolver, err := npcregistry.NewResolver(referenceSet)
	if err != nil {
		return nil, normalizerErrorf("prepare NPC registry: %w", err)
	}
	return &Normalizer{npcResolver: resolver}, nil
}

func (n *Normalizer) Key() string { return Key }

func (n *Normalizer) ReferenceSlots() []contracts.ReferenceSlot { return referenceSlots() }

func (n *Normalizer) ManifestMetadata() map[string]any {
	if n == nil || n.npcResolver == nil {
		return nil
	}
	metadata := map[string]any{
		"normalization_policy": normalizationPolicy,
		"identity_policy":      identity.Policy,
	}
	seeded := n.npcResolver.Seeded()
	if seeded.Bound() {
		metadata["npc_registry_digest"] = seeded.Digest()
		metadata["npc_count"] = seeded.Count()
	}
	return metadata
}

func (n *Normalizer) CheckpointFingerprints() []pipeline.CheckpointFingerprint {
	if n == nil || n.npcResolver == nil {
		return nil
	}
	return []pipeline.CheckpointFingerprint{
		{Name: "normalization_policy", Value: normalizationPolicy},
		{Name: "identity_policy", Value: identity.Policy},
		{Name: "npc_registry", Value: n.npcResolver.Seeded().ProjectionDigest()},
	}
}

func (n *Normalizer) Normalize(ctx context.Context, req contracts.TypedNormalizeRequest[dnd.NPCInteractionList]) (contracts.TypedNormalizeResult[dnd.NPCInteractionList], error) {
	if n == nil || n.npcResolver == nil {
		return contracts.TypedNormalizeResult[dnd.NPCInteractionList]{}, normalizerErrorf("normalizer must not be nil")
	}
	if ctx == nil {
		return contracts.TypedNormalizeResult[dnd.NPCInteractionList]{}, normalizerErrorf("context must not be nil")
	}
	if err := ctx.Err(); err != nil {
		return contracts.TypedNormalizeResult[dnd.NPCInteractionList]{}, normalizerErrorf("context error before normalize: %w", err)
	}

	registry, err := n.npcResolver.Resolve(req.References)
	if err != nil {
		return contracts.TypedNormalizeResult[dnd.NPCInteractionList]{}, normalizerErrorf("resolve NPC registry: %w", err)
	}
	if !registry.Bound() {
		return contracts.TypedNormalizeResult[dnd.NPCInteractionList]{}, normalizerErrorf("NPC registry reference is required")
	}
	value, warnings := normalizeList(req.MergeOutput.Value, req.Source, registry)
	return contracts.TypedNormalizeResult[dnd.NPCInteractionList]{Value: value, Warnings: warnings}, nil
}

type normalizedRecord struct {
	interaction dnd.NPCInteraction
	inputIndex  int
	earliest    int
	hasEvidence bool
}

type nameCanonicalization struct {
	from string
	to   string
}

func normalizeList(input dnd.NPCInteractionList, doc *source.SourceDocument, registry *npcregistry.Registry) (dnd.NPCInteractionList, []contracts.Warning) {
	if input.Interactions == nil {
		return dnd.NPCInteractionList{}, nil
	}

	records := make([]normalizedRecord, len(input.Interactions))
	warnings := make([]contracts.Warning, 0)
	for index, inputInteraction := range input.Interactions {
		interaction, nameChange, refsChanged := normalizeInteraction(inputInteraction, doc, registry)
		earliest, hasEvidence := earliestSourcePosition(doc, interaction)
		records[index] = normalizedRecord{interaction: interaction, inputIndex: index, earliest: earliest, hasEvidence: hasEvidence}
		if nameChange != nil {
			warnings = append(warnings, contracts.Warning{
				Scope:      interactionScope(index),
				ReasonCode: ReasonCodeNameCanonicalized,
				Message: fmt.Sprintf("input index %d: NPC name canonicalized from %s to %s",
					index, diagnostics.Quote(nameChange.from), diagnostics.Quote(nameChange.to)),
			})
		}
		if refsChanged {
			warnings = append(warnings, contracts.Warning{
				Scope:      interactionScope(index),
				ReasonCode: ReasonCodeSourceRefsNormalized,
				Message: fmt.Sprintf("input index %d: source references normalized (original count %d, final count %d)",
					index, len(inputInteraction.SourceRefs), len(interaction.SourceRefs)),
			})
		}
	}

	sort.SliceStable(records, func(left, right int) bool { return recordLess(doc, records[left], records[right]) })
	for position, record := range records {
		if position == record.inputIndex {
			continue
		}
		warnings = append(warnings, contracts.Warning{
			Scope:      interactionScope(record.inputIndex),
			ReasonCode: ReasonCodeInteractionsReordered,
			Message:    fmt.Sprintf("input index %d moved to normalized position %d by source chronology", record.inputIndex, position),
		})
	}

	output, duplicateWarnings := collapseDuplicates(records, doc)
	warnings = append(warnings, duplicateWarnings...)
	return dnd.NPCInteractionList{Interactions: output}, warnings
}

func normalizeInteraction(input dnd.NPCInteraction, doc *source.SourceDocument, registry *npcregistry.Registry) (dnd.NPCInteraction, *nameCanonicalization, bool) {
	output := cloneInteraction(input)
	if canonical, ok := registry.Lookup(identity.NormalizeDisplay(input.Name)); ok {
		output.Name = canonical.Name
	}
	var nameChange *nameCanonicalization
	if input.Name != output.Name {
		nameChange = &nameCanonicalization{from: input.Name, to: output.Name}
	}
	output.SourceRefs = canonicalizeSourceRefs(doc, input.SourceRefs)
	return output, nameChange, !sourceRefsEqual(input.SourceRefs, output.SourceRefs)
}

func cloneInteraction(input dnd.NPCInteraction) dnd.NPCInteraction {
	output := input
	if input.SourceRefs != nil {
		output.SourceRefs = append([]source.SourceRef(nil), input.SourceRefs...)
	}
	return output
}

func canonicalizeSourceRefs(doc *source.SourceDocument, input []source.SourceRef) []source.SourceRef {
	if input == nil {
		return nil
	}
	canonical := append([]source.SourceRef(nil), input...)
	sort.SliceStable(canonical, func(left, right int) bool { return sourceRefLess(doc, canonical[left], canonical[right]) })
	unique := make([]source.SourceRef, 0, len(canonical))
	for _, ref := range canonical {
		if len(unique) == 0 || unique[len(unique)-1] != ref {
			unique = append(unique, ref)
		}
	}
	return unique
}

func sourceRefsEqual(left, right []source.SourceRef) bool {
	if (left == nil) != (right == nil) || len(left) != len(right) {
		return false
	}
	for index := range left {
		if left[index] != right[index] {
			return false
		}
	}
	return true
}

func sourceRefLess(doc *source.SourceDocument, left, right source.SourceRef) bool {
	if left.SourceID != right.SourceID {
		return left.SourceID < right.SourceID
	}
	leftStart, leftStartOK := source.UnitIndex(doc, left.StartUnitID)
	rightStart, rightStartOK := source.UnitIndex(doc, right.StartUnitID)
	if leftStartOK != rightStartOK {
		return leftStartOK
	}
	if leftStartOK && leftStart != rightStart {
		return leftStart < rightStart
	}
	if left.StartUnitID != right.StartUnitID {
		return left.StartUnitID < right.StartUnitID
	}
	leftEnd, leftEndOK := source.UnitIndex(doc, left.EndUnitID)
	rightEnd, rightEndOK := source.UnitIndex(doc, right.EndUnitID)
	if leftEndOK != rightEndOK {
		return leftEndOK
	}
	if leftEndOK && leftEnd != rightEnd {
		return leftEnd < rightEnd
	}
	return left.EndUnitID < right.EndUnitID
}

func earliestSourcePosition(doc *source.SourceDocument, interaction dnd.NPCInteraction) (int, bool) {
	found := false
	earliest := 0
	for _, ref := range interaction.SourceRefs {
		if source.ValidateRef(doc, ref) != nil {
			continue
		}
		position, ok := source.UnitIndex(doc, ref.StartUnitID)
		if !ok || (found && position >= earliest) {
			continue
		}
		earliest = position
		found = true
	}
	return earliest, found
}

func recordLess(doc *source.SourceDocument, left, right normalizedRecord) bool {
	if left.hasEvidence != right.hasEvidence {
		return left.hasEvidence
	}
	if left.hasEvidence && left.earliest != right.earliest {
		return left.earliest < right.earliest
	}
	leftKey := identity.ComparisonKey(left.interaction.Name)
	rightKey := identity.ComparisonKey(right.interaction.Name)
	if leftKey != rightKey {
		return leftKey < rightKey
	}
	if left.interaction.Name != right.interaction.Name {
		return left.interaction.Name < right.interaction.Name
	}
	if left.interaction.Kind != right.interaction.Kind {
		return left.interaction.Kind < right.interaction.Kind
	}
	return sourceRefsLess(doc, left.interaction.SourceRefs, right.interaction.SourceRefs)
}

func sourceRefsLess(doc *source.SourceDocument, left, right []source.SourceRef) bool {
	for index := 0; index < len(left) && index < len(right); index++ {
		if left[index] == right[index] {
			continue
		}
		return sourceRefLess(doc, left[index], right[index])
	}
	return len(left) < len(right)
}

type duplicateGroup struct {
	retainedIndex int
	removed       []int
}

func collapseDuplicates(records []normalizedRecord, doc *source.SourceDocument) ([]dnd.NPCInteraction, []contracts.Warning) {
	if len(records) == 0 {
		return make([]dnd.NPCInteraction, 0), nil
	}
	keep := make([]bool, len(records))
	groups := make([]duplicateGroup, 0)
	groupByKey := make(map[string]int)
	for index, record := range records {
		key, eligible := duplicateKey(record.interaction, doc)
		if !eligible {
			keep[index] = true
			continue
		}
		groupIndex, exists := groupByKey[key]
		if !exists {
			groupByKey[key] = len(groups)
			groups = append(groups, duplicateGroup{retainedIndex: record.inputIndex})
			keep[index] = true
			continue
		}
		groups[groupIndex].removed = append(groups[groupIndex].removed, record.inputIndex)
	}
	output := make([]dnd.NPCInteraction, 0, len(records))
	for index, record := range records {
		if keep[index] {
			output = append(output, cloneInteraction(record.interaction))
		}
	}
	warnings := make([]contracts.Warning, 0)
	for _, group := range groups {
		if len(group.removed) != 0 {
			warnings = append(warnings, duplicateWarning(group.retainedIndex, group.removed))
		}
	}
	return output, warnings
}

func duplicateKey(interaction dnd.NPCInteraction, doc *source.SourceDocument) (string, bool) {
	if len(interaction.SourceRefs) == 0 {
		return "", false
	}
	for _, ref := range interaction.SourceRefs {
		if source.ValidateRef(doc, ref) != nil {
			return "", false
		}
	}
	var key strings.Builder
	writeKeyString(&key, interaction.Name)
	writeKeyString(&key, string(interaction.Kind))
	for _, ref := range interaction.SourceRefs {
		writeKeyString(&key, ref.SourceID)
		writeKeyInt(&key, ref.StartUnitID)
		writeKeyInt(&key, ref.EndUnitID)
	}
	return key.String(), true
}

func writeKeyString(builder *strings.Builder, value string) {
	builder.WriteString(strconv.Itoa(len(value)))
	builder.WriteByte(':')
	builder.WriteString(value)
}

func writeKeyInt(builder *strings.Builder, value int) {
	builder.WriteString(strconv.Itoa(value))
	builder.WriteByte(';')
}

func duplicateWarning(retainedIndex int, removed []int) contracts.Warning {
	issues := make([]string, len(removed))
	for index, removedIndex := range removed {
		issues[index] = fmt.Sprintf("removed input index %d", removedIndex)
	}
	return contracts.Warning{
		Scope:      interactionScope(retainedIndex),
		ReasonCode: ReasonCodeDuplicateCollapsed,
		Message: diagnostics.Aggregate(
			fmt.Sprintf("duplicate NPC interaction collapsed; retained input index %d", retainedIndex), issues),
	}
}

func interactionScope(index int) string { return fmt.Sprintf("interactions[%d]", index) }

func referenceSlots() []contracts.ReferenceSlot {
	slots := shared.ReferenceSlots(referenceSlotDescriptions)
	slots = append(slots, contracts.ReferenceSlot{
		Name:                  NPCRegistryReferenceSlot,
		Description:           "Required normalized NPC registry used only for interaction identity grounding, never as interaction evidence.",
		Required:              true,
		AcceptedMediaTypes:    []string{"application/json"},
		AcceptedArtifactKinds: []contracts.ArtifactKind{dnd.NPCListKind},
		MaxBytes:              NPCRegistryMaxBytes,
	})
	sort.Slice(slots, func(left, right int) bool { return slots[left].Name < slots[right].Name })
	return slots
}

func ModuleSpec() pipeline.ModuleSpec {
	return pipeline.ModuleSpec{
		Key:            Key,
		Stage:          pipeline.StageNormalize,
		Requires:       append([]string(nil), requiredCapabilities...),
		Provides:       append([]string(nil), providedCapabilities...),
		ArtifactKind:   dnd.NPCInteractionListKind,
		ReferenceSlots: referenceSlots(),
	}
}

func Register(registry *pipeline.NormalizerRegistry) error {
	return pipeline.RegisterNormalizerBuilder(registry, ModuleSpec(), validateOptions, func(request pipeline.BuildRequest) (contracts.Normalizer[dnd.NPCInteractionList], error) {
		options, err := DecodeOptions(request.Options)
		if err != nil {
			return nil, err
		}
		return New(options, request.References)
	})
}

func DecodeOptions(options map[string]any) (Options, error) {
	if err := pipeline.RejectUnknownOptions(options); err != nil {
		return Options{}, normalizerErrorf("%w", err)
	}
	return Options{}, nil
}

func validateOptions(options map[string]any) error { _, err := DecodeOptions(options); return err }

func normalizerErrorf(format string, args ...any) error {
	return fmt.Errorf("dnd NPC interactions normalizer: "+format, args...)
}