// Package invariants validates normalized D&D combat-turn artifacts.
package invariants

import (
	"context"
	"fmt"
	"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"
	"gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/shared/diagnostics"
	combatshape "gitea.maximumdirect.net/eric/notarius/internal/modules/dnd/validate/combatturns/shape"
)

const (
	Key        = "normalize/dnd/combat-turns/invariants"
	ReasonCode = "invalid_combat_turn_normalization"
	policy     = "dnd.combat_turns.validator.normalized.v2"
)

type Options struct{}
type Validator struct{}

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

func New(Options) *Validator      { return &Validator{} }
func (v *Validator) Name() string { return Key }
func (v *Validator) ExecutionClass() contracts.ExecutionClass {
	return contracts.ExecutionClassDeterministic
}
func (v *Validator) CheckpointFingerprints() []pipeline.CheckpointFingerprint {
	return []pipeline.CheckpointFingerprint{{Name: "policy", Value: policy}}
}

func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationRequest[dnd.CombatTurnList]) (contracts.ValidationResult, error) {
	if err := Validate(req.Source, req.Value); err != nil {
		return contracts.ValidationResult{Approved: false, ReasonCode: ReasonCode, Message: err.Error()}, nil
	}
	return contracts.ValidationResult{Approved: true}, nil
}

// Validate checks only invariants owned by normalized combat-turn output. A
// shape or source-reference failure is deliberately deferred to its owner.
func Validate(doc *source.SourceDocument, value dnd.CombatTurnList) error {
	if combatshape.Validate(value) != nil {
		return nil
	}
	index := source.NewDocumentIndex(doc)
	if !sourceRefsValid(index, value) {
		return nil
	}
	issues := issuesFor(shared.NewSourceRefOrderFromIndex(index), value)
	if len(issues) == 0 {
		return nil
	}
	return fmt.Errorf("%s", diagnostics.Aggregate("invalid combat turn normalization", issues))
}

func issuesFor(order shared.SourceRefOrder, value dnd.CombatTurnList) []string {
	issues := make([]string, 0)
	seenIdentity := make(map[string]int)
	previousPosition := -1
	for turnIndex, turn := range value.CombatTurns {
		prefix := fmt.Sprintf("combat_turns[%d]", turnIndex)
		if turn.Actor != identity.NormalizeDisplay(turn.Actor) {
			issues = append(issues, prefix+".actor is not display-normalized: "+diagnostics.Quote(turn.Actor))
		}
		for refIndex := 1; refIndex < len(turn.SourceRefs); refIndex++ {
			previous := turn.SourceRefs[refIndex-1]
			current := turn.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))
			}
		}

		position, ok := order.EarliestValid(turn.SourceRefs)
		if !ok {
			continue
		}
		if previousPosition > position {
			issues = append(issues, fmt.Sprintf("%s is out of chronological order: evidence position %d follows %d", prefix, position, previousPosition))
		}
		previousPosition = position

		if key, ok := duplicateKey(turn); ok {
			if previous, exists := seenIdentity[key]; exists {
				issues = append(issues, fmt.Sprintf("%s duplicates combat turn %d under normalized identity", prefix, previous))
			} else {
				seenIdentity[key] = turnIndex
			}
		}
	}
	return issues
}

func sourceRefsValid(index source.DocumentIndex, value dnd.CombatTurnList) bool {
	for _, turn := range value.CombatTurns {
		for _, ref := range turn.SourceRefs {
			if index.ValidateRef(ref) != nil {
				return false
			}
		}
	}
	return true
}

func duplicateKey(turn dnd.CombatTurn) (string, bool) {
	if len(turn.SourceRefs) == 0 {
		return "", false
	}
	var key strings.Builder
	writeKeyString(&key, identity.ComparisonKey(turn.Actor))
	writeKeyString(&key, string(turn.TurnKind))
	for _, ref := range turn.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 Spec() pipeline.ValidatorSpec {
	return pipeline.ValidatorSpec{Key: Key, ExecutionClass: contracts.ExecutionClassDeterministic}
}

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

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