// Package npcs normalizes merged D&D non-player character records.
package npcs

import (
	"context"
	"fmt"
	"reflect"
	"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"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/shared/diagnostics"
)

const (
	Key                 = "dnd/npcs"
	normalizationPolicy = "dnd.npcs.normalize.v1"
	NormalizationPolicy = normalizationPolicy

	ReasonCodeNPCFieldsNormalized        = "npc_fields_normalized"
	ReasonCodeNPCIDRecomputed            = "npc_id_recomputed"
	ReasonCodeSourceReferencesNormalized = "source_references_normalized"
	ReasonCodeDuplicateNPCCollapsed      = "duplicate_npc_collapsed"
)

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

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

type Options struct{}
type Normalizer struct{}

func New(Options) *Normalizer                                   { return &Normalizer{} }
func (n *Normalizer) Key() string                               { return Key }
func (n *Normalizer) ReferenceSlots() []contracts.ReferenceSlot { return nil }

func (n *Normalizer) ManifestMetadata() map[string]any {
	if n == nil {
		return nil
	}
	return map[string]any{"identity_policy": identity.Policy, "normalization_policy": normalizationPolicy}
}

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

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

type normalizedRecord struct {
	npc dnd.NPC
}

func normalizeList(input dnd.NPCList) (dnd.NPCList, []contracts.Warning) {
	if input.NPCs == nil {
		return dnd.NPCList{}, nil
	}
	records := make([]normalizedRecord, len(input.NPCs))
	warnings := make([]contracts.Warning, 0)
	for index, inputNPC := range input.NPCs {
		npc, fieldsChanged, referencesChanged := normalizeRecord(inputNPC)
		records[index] = normalizedRecord{npc: npc}
		if fieldsChanged {
			warnings = append(warnings, contracts.Warning{Scope: npcScope(index), ReasonCode: ReasonCodeNPCFieldsNormalized, Message: fmt.Sprintf("input index %d: NPC name normalized for %s", index, diagnostics.Quote(inputNPC.Name))})
		}
		if referencesChanged {
			warnings = append(warnings, contracts.Warning{Scope: npcScope(index), ReasonCode: ReasonCodeSourceReferencesNormalized, Message: fmt.Sprintf("input index %d: source references normalized (original count %d, final count %d)", index, len(inputNPC.SourceRefs), len(npc.SourceRefs))})
		}
		if inputNPC.ID != npc.ID {
			warnings = append(warnings, contracts.Warning{Scope: npcScope(index), ReasonCode: ReasonCodeNPCIDRecomputed, Message: fmt.Sprintf("input index %d: NPC ID recomputed from %s", index, diagnostics.Quote(npc.Name))})
		}
	}

	groups := canonicalNameGroups(records)
	output := dnd.NPCList{NPCs: make([]dnd.NPC, 0, len(groups))}
	for _, members := range groups {
		consolidated, referencesChanged := consolidate(records, members)
		retainedIndex := members[0]
		output.NPCs = append(output.NPCs, consolidated)
		if referencesChanged {
			warnings = append(warnings, contracts.Warning{Scope: npcScope(retainedIndex), ReasonCode: ReasonCodeSourceReferencesNormalized, Message: fmt.Sprintf("input index %d: source references normalized during identity consolidation (final count %d)", retainedIndex, len(consolidated.SourceRefs))})
		}
		if len(members) > 1 {
			warnings = append(warnings, duplicateWarning(retainedIndex, members[1:]))
		}
	}
	return output, warnings
}

func normalizeRecord(input dnd.NPC) (dnd.NPC, bool, bool) {
	output := cloneNPC(input)
	output.Name = identity.NormalizeDisplay(input.Name)
	output.SourceRefs, _, _ = canonicalizeSourceRefs(input.SourceRefs)
	output.ID = identity.DeriveID(output.Name)
	return output, input.Name != output.Name, !reflect.DeepEqual(input.SourceRefs, output.SourceRefs)
}

func cloneNPC(input dnd.NPC) dnd.NPC {
	input.SourceRefs = cloneSourceRefs(input.SourceRefs)
	return input
}

func canonicalNameGroups(records []normalizedRecord) [][]int {
	groups := make([][]int, 0, len(records))
	ownerByKey := make(map[string]int, len(records))
	for index, record := range records {
		key := identity.ComparisonKey(record.npc.Name)
		if key != "" {
			if groupIndex, ok := ownerByKey[key]; ok {
				groups[groupIndex] = append(groups[groupIndex], index)
				continue
			}
			ownerByKey[key] = len(groups)
		}
		groups = append(groups, []int{index})
	}
	return groups
}

func consolidate(records []normalizedRecord, members []int) (dnd.NPC, bool) {
	output := cloneNPC(records[members[0]].npc)
	originalRefs := cloneSourceRefs(output.SourceRefs)
	for _, member := range members[1:] {
		output.SourceRefs = append(output.SourceRefs, records[member].npc.SourceRefs...)
	}
	output.SourceRefs, _, _ = canonicalizeSourceRefs(output.SourceRefs)
	output.ID = identity.DeriveID(output.Name)
	return output, !reflect.DeepEqual(originalRefs, output.SourceRefs)
}

func canonicalizeSourceRefs(input []source.SourceRef) ([]source.SourceRef, bool, int) {
	if input == nil {
		return nil, false, 0
	}
	canonical := cloneSourceRefs(input)
	sort.SliceStable(canonical, func(left, right int) bool {
		if canonical[left].SourceID != canonical[right].SourceID {
			return canonical[left].SourceID < canonical[right].SourceID
		}
		if canonical[left].StartUnitID != canonical[right].StartUnitID {
			return canonical[left].StartUnitID < canonical[right].StartUnitID
		}
		return canonical[left].EndUnitID < canonical[right].EndUnitID
	})
	orderChanged := !reflect.DeepEqual(input, canonical)
	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, orderChanged, len(input) - len(unique)
}

func cloneSourceRefs(input []source.SourceRef) []source.SourceRef {
	if input == nil {
		return nil
	}
	return append([]source.SourceRef(nil), input...)
}

func duplicateWarning(retainedIndex int, removed []int) contracts.Warning {
	const maxDisplayedIndices = 20
	displayed := removed
	if len(displayed) > maxDisplayedIndices {
		displayed = displayed[:maxDisplayedIndices]
	}
	indices := make([]string, len(displayed))
	for index, removedIndex := range displayed {
		indices[index] = strconv.Itoa(removedIndex)
	}
	message := fmt.Sprintf("retained input index %d; removed input indices [%s]", retainedIndex, strings.Join(indices, ", "))
	if omitted := len(removed) - len(displayed); omitted > 0 {
		message += fmt.Sprintf("; %d additional removed input indices omitted", omitted)
	}
	return contracts.Warning{Scope: npcScope(retainedIndex), ReasonCode: ReasonCodeDuplicateNPCCollapsed, Message: message}
}

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

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

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

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

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

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