#include "fesa/fem/dof_manager.hpp"

#include <algorithm>
#include <charconv>
#include <stdexcept>
#include <string>
#include <system_error>
#include <utility>

namespace fesa {
namespace {

constexpr std::size_t dofsPerNode = 6U;

char asciiLower(char value) {
    if (value >= 'A' && value <= 'Z') {
        return static_cast<char>(value + ('a' - 'A'));
    }
    return value;
}

bool equalName(const std::string& left, const std::string& right) {
    return left.size() == right.size() &&
           std::equal(
               left.begin(), left.end(), right.begin(),
               [](char leftValue, char rightValue) {
                   return asciiLower(leftValue) == asciiLower(rightValue);
               });
}

bool tryPositiveInteger(const std::string& text, std::int64_t& value) {
    const char* const first = text.data();
    const char* const last = first + text.size();
    const auto parsed = std::from_chars(first, last, value);
    return parsed.ec == std::errc{} && parsed.ptr == last && value > 0;
}

std::vector<EntityIndex> expandBoundaryTarget(
    const Domain& domain, const BoundaryCondition& boundary) {
    for (const auto& set : domain.nodeSets()) {
        if (equalName(set.name, boundary.target)) {
            return set.nodeIndices;
        }
    }

    std::int64_t sourceLabel = 0;
    if (tryPositiveInteger(boundary.target, sourceLabel)) {
        for (std::size_t node = 0U; node < domain.nodes().size(); ++node) {
            if (domain.nodes()[node].sourceId.sourceLabel == sourceLabel) {
                return {static_cast<EntityIndex>(node)};
            }
        }
    }
    return {};
}

SparsePattern buildSparsePattern(
    std::size_t fullDofCount,
    const std::vector<EntityIndex>& activeElements,
    const std::vector<std::array<std::size_t, 12>>& elementScatters) {
    std::vector<std::vector<std::size_t>> columnsByRow(fullDofCount);
    for (const EntityIndex element : activeElements) {
        const auto& scatter = elementScatters.at(element);
        for (const std::size_t row : scatter) {
            auto& columns = columnsByRow[row];
            columns.insert(columns.end(), scatter.begin(), scatter.end());
        }
    }

    SparsePattern pattern;
    pattern.rowOffsets.reserve(fullDofCount + 1U);
    pattern.rowOffsets.push_back(0U);
    for (auto& columns : columnsByRow) {
        // Stable CSR structure is independent of element traversal duplicates.
        std::sort(columns.begin(), columns.end());
        columns.erase(std::unique(columns.begin(), columns.end()), columns.end());
        pattern.columnIndices.insert(
            pattern.columnIndices.end(), columns.begin(), columns.end());
        pattern.rowOffsets.push_back(pattern.columnIndices.size());
    }
    return pattern;
}

} // namespace

Result<DofManager> DofManager::create(const AnalysisModel& model) {
    const Domain& domain = model.domain();
    const std::size_t fullCount = domain.nodes().size() * dofsPerNode;

    std::vector<std::optional<double>> prescribedByFullDof(fullCount);
    for (const EntityIndex boundaryIndex : model.activeBoundaryConditions()) {
        const auto& boundary = model.step().boundaries.at(boundaryIndex);
        const auto target = expandBoundaryTarget(domain, boundary);
        for (const EntityIndex node : target) {
            for (int component = boundary.firstDof;
                 component <= boundary.lastDof;
                 ++component) {
                const std::size_t fullDof =
                    static_cast<std::size_t>(node) * dofsPerNode +
                    static_cast<std::size_t>(component - 1);
                auto& prescribed = prescribedByFullDof[fullDof];
                if (prescribed && *prescribed != boundary.value) {
                    return Result<DofManager>::failure(Status::failure(
                        FailureCategory::input,
                        {{Severity::error,
                          "conflicting-boundary-condition",
                          boundary.location,
                          "BOUNDARY",
                          boundary.target,
                          "Expanded boundary rows prescribe different values to one node/DOF."}}));
                }
                prescribed = boundary.value;
            }
        }
    }

    std::vector<std::size_t> freeDofs;
    std::vector<std::size_t> constrainedDofs;
    std::vector<double> constrainedValues;
    std::vector<std::optional<std::size_t>> freeEquations(fullCount);
    freeDofs.reserve(fullCount);
    constrainedDofs.reserve(fullCount);
    constrainedValues.reserve(fullCount);
    // A full-DOF scan fixes free equations, constrained DOFs, and dc in the
    // same stable order regardless of boundary declaration overlap.
    for (std::size_t fullDof = 0U; fullDof < fullCount; ++fullDof) {
        if (prescribedByFullDof[fullDof]) {
            constrainedDofs.push_back(fullDof);
            constrainedValues.push_back(*prescribedByFullDof[fullDof]);
        } else {
            freeEquations[fullDof] = freeDofs.size();
            freeDofs.push_back(fullDof);
        }
    }

    Vector prescribedValues{constrainedValues.size()};
    for (std::size_t index = 0U; index < constrainedValues.size(); ++index) {
        prescribedValues[index] = constrainedValues[index];
    }

    std::vector<std::array<std::size_t, 12>> elementScatters(
        domain.elements().size());
    for (const EntityIndex elementIndex : model.activeElements()) {
        const auto& element = domain.elements().at(elementIndex);
        auto& scatter = elementScatters.at(elementIndex);
        for (std::size_t endpoint = 0U; endpoint < element.nodeIndices.size(); ++endpoint) {
            const std::size_t node = element.nodeIndices[endpoint];
            for (std::size_t component = 0U; component < dofsPerNode; ++component) {
                scatter[endpoint * dofsPerNode + component] =
                    node * dofsPerNode + component;
            }
        }
    }

    auto pattern = buildSparsePattern(
        fullCount, model.activeElements(), elementScatters);
    return Result<DofManager>::success(DofManager{
        fullCount,
        std::move(freeEquations),
        std::move(elementScatters),
        std::move(freeDofs),
        std::move(constrainedDofs),
        std::move(prescribedValues),
        std::move(pattern)});
}

std::size_t DofManager::fullDofCount() const noexcept {
    return fullDofCount_;
}

std::size_t DofManager::freeDofCount() const noexcept {
    return freeDofs_.size();
}

std::size_t DofManager::constrainedDofCount() const noexcept {
    return constrainedDofs_.size();
}

std::size_t DofManager::fullDof(
    EntityIndex node, DofComponent component) const {
    const std::size_t componentIndex = static_cast<std::size_t>(component);
    if (node >= fullDofCount_ / dofsPerNode || componentIndex >= dofsPerNode) {
        throw std::out_of_range{"Node or DOF component is out of range."};
    }
    return static_cast<std::size_t>(node) * dofsPerNode + componentIndex;
}

std::optional<std::size_t> DofManager::freeEquation(
    std::size_t fullDof) const {
    return freeEquations_.at(fullDof);
}

const std::array<std::size_t, 12>& DofManager::elementScatter(
    EntityIndex element) const {
    return elementScatters_.at(element);
}

const std::vector<std::size_t>& DofManager::freeDofs() const noexcept {
    return freeDofs_;
}

const std::vector<std::size_t>& DofManager::constrainedDofs() const noexcept {
    return constrainedDofs_;
}

const Vector& DofManager::prescribedValues() const noexcept {
    return prescribedValues_;
}

const SparsePattern& DofManager::sparsePattern() const noexcept {
    return sparsePattern_;
}

DofManager::DofManager(
    std::size_t fullDofCount,
    std::vector<std::optional<std::size_t>> freeEquations,
    std::vector<std::array<std::size_t, 12>> elementScatters,
    std::vector<std::size_t> freeDofs,
    std::vector<std::size_t> constrainedDofs,
    Vector prescribedValues,
    SparsePattern sparsePattern)
    : fullDofCount_{fullDofCount},
      freeEquations_{std::move(freeEquations)},
      elementScatters_{std::move(elementScatters)},
      freeDofs_{std::move(freeDofs)},
      constrainedDofs_{std::move(constrainedDofs)},
      prescribedValues_{std::move(prescribedValues)},
      sparsePattern_{std::move(sparsePattern)} {}

} // namespace fesa