dbc/core/decode_database.cpp

// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Dim Himro

#include "decode_database.h"
#include "signal_layout.h"
#include <bitset>
#include <cmath>
#include <limits>
#include <stdexcept>
#include <unordered_set>

namespace {
    constexpr std::size_t MaximumPayloadBits = std::numeric_limits<std::uint8_t>::max() * 8U;
    using SignalBits = std::bitset<MaximumPayloadBits>;

    void ValidateSignal(const DecodeSignal &signal, std::uint8_t dlc) {
        if (signal.byteOrder != ByteOrder::Intel && signal.byteOrder != ByteOrder::Motorola)
            throw std::invalid_argument("Invalid signal byte order: " + signal.name);
        if (signal.valueType != ValueType::Unsigned && signal.valueType != ValueType::Signed)
            throw std::invalid_argument("Invalid signal value type: " + signal.name);
        if (signal.multiplexing.role != MultiplexRole::Unconditional &&
            signal.multiplexing.role != MultiplexRole::Selector &&
            signal.multiplexing.role != MultiplexRole::Branch)
            throw std::invalid_argument("Invalid multiplexing role: " + signal.name);
        if (!IsValidSignalLayout(signal.startBit, signal.length,
                                 signal.byteOrder == ByteOrder::Intel, dlc))
            throw std::invalid_argument("Invalid signal length or payload position: " + signal.name);
        if (!std::isfinite(signal.factor) || !std::isfinite(signal.offset) ||
            !std::isfinite(signal.minimum) || !std::isfinite(signal.maximum) ||
            signal.minimum > signal.maximum)
            throw std::invalid_argument("Invalid signal numeric parameters: " + signal.name);
    }

    SignalBits GetSignalBits(const DecodeSignal &signal) {
        SignalBits bits;
        const bool littleEndian = signal.byteOrder == ByteOrder::Intel;
        const std::uint64_t start = SignalStartCoordinate(signal.startBit, littleEndian);
        for (std::uint32_t index = 0U; index < signal.length; ++index) {
            const std::uint64_t coordinate = start + index;
            const std::uint64_t bit = littleEndian ? coordinate
                                                   : coordinate / 8U * 8U + 7U - coordinate % 8U;
            bits.set(static_cast<std::size_t>(bit));
        }
        return bits;
    }

    bool AreMutuallyExclusive(const DecodeSignal &first, const DecodeSignal &second) {
        return first.multiplexing.role == MultiplexRole::Branch &&
               second.multiplexing.role == MultiplexRole::Branch &&
               first.multiplexing.value != second.multiplexing.value;
    }

    void ValidateFrame(const DecodeFrame &frame) {
        const std::uint32_t maximumId = frame.isExtended ? 0x1FFFFFFFU : 0x7FFU;
        if (frame.canId > maximumId)
            throw std::invalid_argument("Invalid normalized CAN ID: " + std::to_string(frame.canId));

        std::unordered_set<std::string> names;
        const DecodeSignal *selector = nullptr;
        for (const DecodeSignal &signal: frame.signals) {
            if (!names.insert(signal.name).second)
                throw std::invalid_argument("Duplicate runtime signal key: " + signal.name);
            ValidateSignal(signal, frame.dlc);
            if (signal.multiplexing.role == MultiplexRole::Selector) {
                if (selector != nullptr || signal.valueType != ValueType::Unsigned)
                    throw std::invalid_argument("Multiplexing requires one unsigned selector per frame");
                selector = &signal;
            }
        }

        std::vector<SignalBits> layouts;
        layouts.reserve(frame.signals.size());
        for (std::size_t index = 0U; index < frame.signals.size(); ++index) {
            const DecodeSignal &signal = frame.signals[index];
            if (signal.multiplexing.role == MultiplexRole::Branch &&
                (selector == nullptr ||
                 (selector->length < 64U && signal.multiplexing.value >= (std::uint64_t(1U) << selector->length))))
                throw std::invalid_argument("Missing selector or branch value outside selector range: " + signal.name);
            const SignalBits bits = GetSignalBits(signal);
            for (std::size_t previous = 0U; previous < index; ++previous) {
                if (!AreMutuallyExclusive(signal, frame.signals[previous]) && (bits & layouts[previous]).any())
                    throw std::invalid_argument("Overlapping signals: " + signal.name);
            }
            layouts.push_back(bits);
        }
    }
}// namespace

DecodeDatabase::Storage::Storage(const std::vector<DecodeFrame> &definitions)
    : frames(definitions) {
    // Validate the complete snapshot before creating its lookup index.
    for (const DecodeFrame &frame: frames)
        ValidateFrame(frame);
    frameIndexByKey.reserve(frames.size());
    for (std::size_t index = 0U; index < frames.size(); ++index) {
        if (!frameIndexByKey.emplace(frames[index].GetKey(), index).second)
            throw std::invalid_argument("Duplicate runtime frame key");
    }
}

DecodeDatabase::DecodeDatabase(const std::vector<DecodeFrame> &frames)
    : storage(std::make_shared<const Storage>(frames)) {
}

const std::vector<DecodeFrame> &DecodeDatabase::GetFrames() const {
    static const std::vector<DecodeFrame> empty;
    return storage ? storage->frames : empty;
}

std::shared_ptr<const DecodeFrame> DecodeDatabase::FindFrame(const FrameKey &key) const {
    if (!storage)
        return nullptr;
    const std::unordered_map<FrameKey, std::size_t, FrameKeyHasher>::const_iterator it =
            storage->frameIndexByKey.find(key);
    if (it == storage->frameIndexByKey.end())
        return nullptr;
    return std::shared_ptr<const DecodeFrame>(storage, &storage->frames[it->second]);
}

std::shared_ptr<const DecodeSignal> DecodeDatabase::FindSignal(const SignalKey &key) const {
    const std::shared_ptr<const DecodeFrame> frame = FindFrame(key.frame);
    if (!frame)
        return nullptr;
    for (const DecodeSignal &signal: frame->signals) {
        if (signal.name == key.name)
            return std::shared_ptr<const DecodeSignal>(frame, &signal);
    }
    return nullptr;
}