// Package itemevents normalizes merged D&D item-event candidates.
package itemevents

import (
	"context"
	"fmt"
	"sort"

	"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"
	itemeventmodel "gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/itemevents"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/shared"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/shared/diagnostics"
)

const (
	Key                 = "dnd/item-events"
	normalizationPolicy = "dnd.item_events.normalize.v1"
	NormalizationPolicy = normalizationPolicy

	ReasonCodeDisplayNormalized    = "item_event_display_normalized"
	ReasonCodeSourceRefsNormalized = "source_references_normalized"
	ReasonCodeEventsReordered      = "item_events_reordered"
	ReasonCodeDuplicateCollapsed   = "duplicate_item_event_collapsed"
	ReasonCodeWarningsOmitted      = "item_event_normalization_warnings_omitted"
)

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

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

// Options deliberately has no fields: item-event normalization has no
// generated-reference dependency or configurable semantic behavior.
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{"normalization_policy": normalizationPolicy}
}

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

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

	index := source.NewDocumentIndex(req.Source)
	value, warnings := normalizeList(req.MergeOutput.Value, index, shared.NewSourceRefOrderFromIndex(index))
	return contracts.TypedNormalizeResult[dnd.ItemEventList]{Value: value, Warnings: warnings}, nil
}

type normalizedRecord struct {
	event      dnd.ItemEvent
	inputIndex int
}

func normalizeList(input dnd.ItemEventList, index source.DocumentIndex, order shared.SourceRefOrder) (dnd.ItemEventList, []contracts.Warning) {
	if input.Events == nil {
		return dnd.ItemEventList{}, nil
	}

	records := make([]normalizedRecord, len(input.Events))
	warnings := make([]contracts.Warning, 0)
	for index, inputEvent := range input.Events {
		event, changedFields, refsChanged := normalizeEvent(inputEvent, order)
		records[index] = normalizedRecord{event: event, inputIndex: index}
		if len(changedFields) != 0 {
			warnings = append(warnings, contracts.Warning{
				Scope:      eventScope(index),
				ReasonCode: ReasonCodeDisplayNormalized,
				Message: fmt.Sprintf("input index %d: normalized display whitespace in %s", index,
					diagnostics.Aggregate("fields", changedFields)),
			})
		}
		if refsChanged {
			warnings = append(warnings, contracts.Warning{
				Scope:      eventScope(index),
				ReasonCode: ReasonCodeSourceRefsNormalized,
				Message: fmt.Sprintf("input index %d: source references normalized (original count %d, final count %d)",
					index, len(inputEvent.SourceRefs), len(event.SourceRefs)),
			})
		}
	}

	sort.SliceStable(records, func(left, right int) bool {
		return itemeventmodel.Less(order, records[left].event, records[right].event)
	})
	for position, record := range records {
		if position == record.inputIndex {
			continue
		}
		warnings = append(warnings, contracts.Warning{
			Scope:      eventScope(record.inputIndex),
			ReasonCode: ReasonCodeEventsReordered,
			Message:    fmt.Sprintf("input index %d moved to normalized position %d", record.inputIndex, position),
		})
	}

	output, duplicateWarnings := collapseDuplicates(records, index, order)
	warnings = append(warnings, duplicateWarnings...)
	return dnd.ItemEventList{Events: output}, diagnostics.LimitWarnings(warnings, "item_events", ReasonCodeWarningsOmitted)
}

func normalizeEvent(input dnd.ItemEvent, order shared.SourceRefOrder) (dnd.ItemEvent, []string, bool) {
	output := cloneEvent(input)
	changedFields := make([]string, 0, 3)
	for _, field := range []struct {
		name  string
		value *string
	}{
		{name: "name", value: &output.Name},
		{name: "from", value: &output.From},
		{name: "to", value: &output.To},
	} {
		trimmed := itemeventmodel.DisplayValue(*field.value)
		if *field.value != trimmed {
			*field.value = trimmed
			changedFields = append(changedFields, field.name)
		}
	}
	output.SourceRefs = order.Canonicalize(input.SourceRefs)
	return output, changedFields, !itemeventmodel.SourceRefsEqual(input.SourceRefs, output.SourceRefs)
}

func cloneEvent(input dnd.ItemEvent) dnd.ItemEvent {
	output := input
	if input.Quantity != nil {
		quantity := *input.Quantity
		output.Quantity = &quantity
	}
	if input.SourceRefs != nil {
		output.SourceRefs = append([]source.SourceRef(nil), input.SourceRefs...)
	}
	return output
}

type duplicateGroup struct {
	retainedIndex int
	removed       []int
}

func collapseDuplicates(records []normalizedRecord, index source.DocumentIndex, order shared.SourceRefOrder) ([]dnd.ItemEvent, []contracts.Warning) {
	if len(records) == 0 {
		return make([]dnd.ItemEvent, 0), nil
	}

	keep := make([]bool, len(records))
	groups := make([]duplicateGroup, 0)
	groupByKey := make(map[string]int)
	for recordIndex, record := range records {
		if !itemeventmodel.ValidSourceRefs(index, record.event.SourceRefs) {
			keep[recordIndex] = true
			continue
		}
		key := itemeventmodel.ExactIdentity(order, record.event)
		groupIndex, exists := groupByKey[key]
		if !exists {
			groupByKey[key] = len(groups)
			groups = append(groups, duplicateGroup{retainedIndex: record.inputIndex})
			keep[recordIndex] = true
			continue
		}
		groups[groupIndex].removed = append(groups[groupIndex].removed, record.inputIndex)
	}

	output := make([]dnd.ItemEvent, 0, len(records))
	for recordIndex, record := range records {
		if keep[recordIndex] {
			output = append(output, cloneEvent(record.event))
		}
	}
	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 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:      eventScope(retainedIndex),
		ReasonCode: ReasonCodeDuplicateCollapsed,
		Message: diagnostics.Aggregate(
			fmt.Sprintf("duplicate item event collapsed; retained input index %d", retainedIndex), issues),
	}
}

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

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

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

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 item events normalizer: "+format, args...)
}