#include "Frame.h"
#include "FieldCodec.h"

namespace ccu {

bool Frame::parseId(const std::vector<uint8_t>& buf, uint16_t& outId) {
    if (buf.size() < FRAME_HEADER_LEN) return false;
    if (buf[0] != FRAME_START1 || buf[1] != FRAME_START2) return false;
    outId = FieldCodec::getU16(buf, 2);
    return true;
}

bool Frame::parseHeader(const std::vector<uint8_t>& buf, FrameHeader& h) {
    if (buf.size() < FRAME_HEADER_LEN) return false;
    if (buf[0] != FRAME_START1 || buf[1] != FRAME_START2) return false;
    h.start1 = buf[0];
    h.start2 = buf[1];
    h.id     = FieldCodec::getU16(buf, 2);
    h.length = FieldCodec::getU16(buf, 4);
    return true;
}

std::vector<uint8_t> Frame::build(
    uint16_t id,
    const std::vector<uint8_t>& payload,
    const ChecksumPolicy& checksum) {

    size_t csSize = checksum.size();
    size_t total  = FRAME_HEADER_LEN + payload.size() + csSize;

    std::vector<uint8_t> frame(total, 0);
    frame[0] = FRAME_START1;
    frame[1] = FRAME_START2;
    FieldCodec::putU16(frame, 2, id);
    FieldCodec::putU16(frame, 4, static_cast<uint16_t>(total)); // 域字节数=整个包长度

    std::copy(payload.begin(), payload.end(), frame.begin() + FRAME_HEADER_LEN);

    if (csSize > 0) {
        // 校验和：对起始符到校验和之前所有字节求和
        std::vector<uint8_t> body(frame.begin(), frame.end() - csSize);
        uint32_t sum = checksum.compute(body);
        size_t off = frame.size() - csSize;
        if (csSize == 4)      FieldCodec::putU32(frame, off, sum);
        else if (csSize == 1) frame[off] = static_cast<uint8_t>(sum & 0xFF);
        else                  FieldCodec::putU16(frame, off, static_cast<uint16_t>(sum));
    }
    return frame;
}

} // namespace ccu