// Package invariants validates normalized D&D NPC occurrence artifacts.
package invariants

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"
	occurrencemodel "gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/npcoccurrences"
	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"
	occurrenceshape "gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/validate/npcoccurrences/shape"
)

const (
	Key        = "normalize/dnd/npc-occurrences/invariants"
	ReasonCode = "invalid_npc_occurrence_normalization"
	policy     = "dnd.npc_occurrences.validator.normalized.v1"
)

type Options struct{}

type Validator struct {
	npcResolver *npcregistry.Resolver
}

var _ contracts.TypedValidator[dnd.NPCOccurrenceList] = (*Validator)(nil)
var _ contracts.ManifestMetadataProvider = (*Validator)(nil)
var _ pipeline.CheckpointFingerprintProvider = (*Validator)(nil)

func New(_ Options, references ...contracts.ReferenceSet) (*Validator, error) {
	if len(references) > 1 {
		return nil, fmt.Errorf("NPC occurrence invariants validator accepts at most one reference set")
	}
	var referenceSet contracts.ReferenceSet
	if len(references) == 1 {
		referenceSet = references[0]
	}
	resolver, err := npcregistry.NewResolver(referenceSet)
	if err != nil {
		return nil, fmt.Errorf("prepare NPC registry: %w", err)
	}
	return &Validator{npcResolver: resolver}, nil
}

func (v *Validator) Name() string { return Key }
func (v *Validator) ExecutionClass() contracts.ExecutionClass {
	return contracts.ExecutionClassDeterministic
}

func (v *Validator) ManifestMetadata() map[string]any {
	if v == nil || v.npcResolver == nil {
		return nil
	}
	metadata := map[string]any{"policy": policy}
	seeded := v.npcResolver.Seeded()
	if seeded.Bound() {
		metadata["npc_registry_digest"] = seeded.Digest()
		metadata["npc_count"] = seeded.Count()
	}
	return metadata
}

func (v *Validator) CheckpointFingerprints() []pipeline.CheckpointFingerprint {
	if v == nil || v.npcResolver == nil {
		return nil
	}
	return []pipeline.CheckpointFingerprint{
		{Name: "policy", Value: policy},
		{Name: "npc_registry", Value: v.npcResolver.Seeded().IdentityDigest()},
	}
}

func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationRequest[dnd.NPCOccurrenceList]) (contracts.ValidationResult, error) {
	if occurrenceshape.Validate(req.Value) != nil {
		return contracts.ValidationResult{Approved: true}, nil
	}
	index := source.NewDocumentIndex(req.Source)
	if !allSourceRefsValid(index, req.Value) {
		return contracts.ValidationResult{Approved: true}, nil
	}
	if v == nil || v.npcResolver == nil {
		return contracts.ValidationResult{}, fmt.Errorf("NPC occurrence invariants validator must not be nil")
	}
	npcRegistry, err := v.npcResolver.Resolve(req.References)
	if err != nil {
		return contracts.ValidationResult{}, fmt.Errorf("resolve NPC registry: %w", err)
	}
	if !npcRegistry.Bound() {
		return contracts.ValidationResult{Approved: false, ReasonCode: ReasonCode, Message: "invalid NPC occurrence normalization: NPC registry reference is required"}, nil
	}
	issues := issuesFor(shared.NewSourceRefOrderFromIndex(index), req.Value, npcRegistry)
	if len(issues) == 0 {
		return contracts.ValidationResult{Approved: true}, nil
	}
	return contracts.ValidationResult{
		Approved:   false,
		ReasonCode: ReasonCode,
		Message:    diagnostics.Aggregate("invalid NPC occurrence normalization", issues),
	}, nil
}

func allSourceRefsValid(index source.DocumentIndex, value dnd.NPCOccurrenceList) bool {
	for _, occurrence := range value.Occurrences {
		if !occurrencemodel.ValidSourceRefs(index, occurrence.SourceRefs) {
			return false
		}
	}
	return true
}

func issuesFor(order shared.SourceRefOrder, value dnd.NPCOccurrenceList, npcRegistry *npcregistry.Registry) []string {
	issues := make([]string, 0)
	for index, occurrence := range value.Occurrences {
		prefix := fmt.Sprintf("occurrences[%d]", index)
		canonical, ok := npcRegistry.LookupID(occurrence.NPCID)
		if !ok {
			issues = append(issues, prefix+".npc_id is not in the NPC registry: "+diagnostics.Quote(occurrence.NPCID))
		} else if occurrence.Name != canonical.Name {
			issues = append(issues, prefix+".name does not match npc_id: "+diagnostics.Quote(occurrence.Name))
		}
		for refIndex := 1; refIndex < len(occurrence.SourceRefs); refIndex++ {
			previous := occurrence.SourceRefs[refIndex-1]
			current := occurrence.SourceRefs[refIndex]
			if order.Less(current, previous) {
				issues = append(issues, fmt.Sprintf("%s.source_refs are not in canonical order at index %d", prefix, refIndex))
			} else if current == previous {
				issues = append(issues, fmt.Sprintf("%s.source_refs[%d] duplicates the previous reference", prefix, refIndex))
			}
		}
	}

	if !sort.SliceIsSorted(value.Occurrences, func(left, right int) bool {
		return occurrencemodel.Less(order, value.Occurrences[left], value.Occurrences[right])
	}) {
		issues = append(issues, "occurrences are not in canonical order")
	}
	seen := make(map[string]int)
	for index, occurrence := range value.Occurrences {
		key := occurrencemodel.ExactIdentity(occurrence)
		if previous, ok := seen[key]; ok {
			issues = append(issues, fmt.Sprintf("occurrences[%d] duplicates occurrence %d", index, previous))
			continue
		}
		seen[key] = index
	}
	return issues
}

func Spec() pipeline.ValidatorSpec {
	return pipeline.ValidatorSpec{Key: Key, ExecutionClass: contracts.ExecutionClassDeterministic}
}

func Register(registry *pipeline.ValidatorRegistry) error {
	return pipeline.RegisterTypedValidatorBuilder(registry, dnd.NPCOccurrenceListKind, Spec(), validateOptions, func(request pipeline.BuildRequest) (contracts.TypedValidator[dnd.NPCOccurrenceList], 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{}, err
	}
	return Options{}, nil
}

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