#pragma once

#include <optional>

#include "serif/discretization/domain/concepts.hpp"
#include "serif/discretization/domain/mesh/topology.hpp"
#include "serif/discretization/domain/relation/relations.hpp"
#include "serif/discretization/domain/relation/validation/runtime.hpp"
#include "serif/discretization/domain/schema/concepts.hpp"
#include "serif/discretization/domain/schema/validation/validator.hpp"

// Inscribed<InnerT, OuterT>: every face where the inner domain stops must have
// the outer domain on the far side.
namespace serif::discretization::domain::schema::validation {
    using relation::Inscribed;

    using relation::validation::RelationValidationResult;
    using relation::validation::RelationValidationFailure;

    template <IsDomainOrSet InnerT, IsDomainOrSet OuterT>
    struct RelationValidator<Inscribed<InnerT, OuterT>> {
        template <IsSchema SchemaT>
        [[nodiscard]] static RelationValidationResult validate(const mesh::MeshTopology &topology) {
            static_assert(
                SchemaT::template contains_domain<InnerT>(), "The inner domain of an Inscribed relation is not present in the supplied schema. Inscribed cannot be enforced"
            );

            static_assert(
                SchemaT::template contains_domain<OuterT>(), "The outer domain of an Inscribed relation is not present in the supplied schema. Inscribed cannot be enforced"
            );

            bool foundInnerElement  = false;
            bool foundOuterElement  = false;
            bool foundInnerBoundary = false;

            for (int elementID = 0; elementID < topology.element_count(); ++elementID) {
                const int domainID = topology.element_domain_id(elementID);

                foundInnerElement = foundInnerElement || SchemaT::template domain_id_belongs_to<InnerT>(domainID);
                foundOuterElement = foundOuterElement || SchemaT::template domain_id_belongs_to<OuterT>(domainID);
            }

            if (!foundInnerElement) {
                return {.failure = RelationValidationFailure::InnerDomainAbsent};
            }

            if (!foundOuterElement) {
                return {.failure = RelationValidationFailure::OuterDomainAbsent};
            }

            for (int faceID = 0; faceID < topology.face_count(); ++faceID) {
                const mesh::FaceElements faceElements = topology.face_elements(faceID);

                const int firstElementID  = faceElements.firstElementID;
                const int secondElementID = faceElements.secondElementID;

                const bool firstIsInner  = firstElementID >= 0 &&
                    SchemaT::template domain_id_belongs_to<InnerT>(topology.element_domain_id(firstElementID));
                const bool secondIsInner = secondElementID >= 0 &&
                    SchemaT::template domain_id_belongs_to<InnerT>(topology.element_domain_id(secondElementID));

                if (firstIsInner == secondIsInner) {
                    continue;
                }

                foundInnerBoundary = true;

                const int innerElementID    = firstIsInner ? firstElementID : secondElementID;
                const int adjacentElementID = firstIsInner ? secondElementID : firstElementID;

                if (adjacentElementID < 0) {
                    return {
                        .failure = RelationValidationFailure::InnerDomainTouchesMeshBoundary,
                        .inscribedDiagnostics = std::make_optional<RelationValidationResult::InscribedDiagnostics>({
                            .faceID         = faceID,
                            .innerElementID = innerElementID,
                        })};
                }

                const int adjacentDomainID = topology.element_domain_id(adjacentElementID);

                if (!SchemaT::template domain_id_belongs_to<OuterT>(adjacentDomainID)) {
                    return {
                        .failure = RelationValidationFailure::InnerDomainTouchesUnexpectedDomain,
                        .inscribedDiagnostics = std::make_optional<RelationValidationResult::InscribedDiagnostics>({
                            .faceID            = faceID,
                            .innerElementID    = innerElementID,
                            .adjacentElementID = adjacentElementID,
                            .adjacentDomainID  = adjacentDomainID
                        })};
                }
            }

            if (!foundInnerBoundary) {
                return {.failure = RelationValidationFailure::InnerDomainHasNoBoundary};
            }

            return {};
        }
    };
}