/**
 * @file dbc_decoder.h
 * @brief
 *
 * Created: 2026-03-13
 * Author: Deeaitch (Dim. Himro)
 *
 * Licensed under the MIT License.
 * See LICENSE file in the project root for full license text.
 */

#ifndef DBC_DECODER_H
#define DBC_DECODER_H

#include <cstdint>
#include <variant>
#include <vector>

#include "decode_database.h"

/**
 * @brief Raw CAN frame used for runtime or trace decoding.
 */
struct RawCanFrame {
    std::uint32_t canId = 0U;       /**< Normalized CAN ID. */
    bool isExtended = false;        /**< true for extended frame. */
    std::vector<std::uint8_t> data; /**< Payload bytes. */

    RawCanFrame() = default;
};

enum class SignalDecodeStatus {
    InvalidDefinition,
    InsufficientPayload,
    SelectorUnavailable,
    Inactive,
    Valid,
    PhysicalConversionFailed
};

/** Frame summary: short payload takes precedence over individual signal errors. */
enum class FrameDecodeStatus {
    UnknownFrame,
    InsufficientPayload,
    SignalErrors,
    Valid
};

/**
 * @brief One decoded signal value.
 */
struct DecodedSignalValue {
    std::shared_ptr<const DecodeSignal> definition; /**< Owning immutable definition. */
    SignalKey key;                                  /**< Stable application identifier. */
    RawSignalValue rawValue = std::uint64_t(0U);    /**< Exact raw value for Valid or PhysicalConversionFailed. */
    double physicalValue = 0.0;                     /**< Conversion result, possibly NaN/Inf on failure. */
    bool valid = false;                             /**< true if decoding succeeded. */
    SignalDecodeStatus status = SignalDecodeStatus::InvalidDefinition;

    /** Lookup using the raw integer; nullptr for invalid or unmapped values. */
    const std::string *GetValueDescription() const {
        return valid && definition ? FindValueDescription(definition->valueDescriptions, rawValue) : nullptr;
    }

    DecodedSignalValue() = default;
};

/**
 * @brief Fully decoded frame.
 */
struct DecodedFrameValue {
    std::shared_ptr<const DecodeFrame> definition; /**< Owning immutable definition. */
    FrameKey key;                                  /**< Stable application identifier. */
    std::vector<DecodedSignalValue> signals;       /**< Decoded signal values. */
    bool valid = false;                            /**< true if frame was matched. */
    FrameDecodeStatus status = FrameDecodeStatus::UnknownFrame; /**< Inspect signals for individual failures. */

    DecodedFrameValue() = default;
};

/**
 * @brief Runtime CAN decoder using prebuilt decode database.
 */
class DbcDecoder {
public:
    /**
     * @brief Find frame definition by CAN ID.
     * @param database Runtime decode database.
     * @param canId Normalized CAN ID.
     * @param isExtended true for extended frame.
     * @return Owning immutable frame handle or nullptr. Safe across reload.
     */
    std::shared_ptr<const DecodeFrame> FindFrame(const DecodeDatabase &database,
                                                 std::uint32_t canId,
                                                 bool isExtended) const;

    /**
     * @brief Decode one raw CAN frame.
     * @param database Runtime decode database.
     * @param frame Raw CAN frame.
     * Short payloads decode available signals; bytes beyond declared DLC are ignored.
     * @return Decoded frame value.
     */
    DecodedFrameValue Decode(const DecodeDatabase &database,
                             const RawCanFrame &frame) const;

private:
    static bool IsValidDefinition(const DecodeSignal &signal, std::uint8_t dlc);

    struct SelectorState {
        const DecodeSignal *definition = nullptr;
        bool valid = false;
        bool available = false;
        std::uint64_t value = 0U;
    };

    static SelectorState ReadSelector(const DecodeFrame &definition, const RawCanFrame &frame);
    static DecodedSignalValue DecodeOneSignal(const DecodeSignal &signal,
                                              std::uint8_t dlc,
                                              const RawCanFrame &frame,
                                              const SelectorState &selector);

    static bool ExtractUnsigned(const std::vector<std::uint8_t> &data,
                                const DecodeSignal &signal,
                                std::uint64_t &value);

    static bool ExtractIntel(const std::vector<std::uint8_t> &data,
                             std::uint32_t startBit,
                             std::uint32_t length,
                             std::uint64_t &value);

    static bool ExtractMotorola(const std::vector<std::uint8_t> &data,
                                std::uint32_t startBit,
                                std::uint32_t length,
                                std::uint64_t &value);

    static std::int64_t SignExtend(std::uint64_t value, std::uint32_t bitLength);
};

#endif /* DBC_DECODER_H */