#include "hdlc_frame.h"

#include <string.h>

#define START_FLAG 0x7E
#define END_FLAG 0x7E
#define ESCAPE_FLAG 0x7D
#define ESCAPE_XOR 0x20

void init_HDLCFrame(HDLCFrame* frame, uint8_t address, uint8_t control, uint8_t* data, size_t data_length) {
    frame->address = address;
    frame->control = control;
    frame->data = data;
    frame->data_length = data_length;
}

uint16_t calculate_fcs(const HDLCFrame *frame, size_t i) {
    uint16_t fcs = 0xFFFF;

    uint8_t data_bytes[2 + frame->data_length];
    data_bytes[0] = frame->address;
    data_bytes[1] = frame->control;
    memcpy(data_bytes + 2, frame->data, frame->data_length);

    for (size_t i = 0; i < frame->data_length + 2; i++) {
        uint8_t byte = data_bytes[i];
        fcs = (fcs >> 8) ^ (fcs << 8) ^ byte;
        fcs &= 0xFFFF;
    }

    return fcs;
}

void create_frame(const HDLCFrame* frame, uint8_t* result) {
    size_t index = 0;

    result[index++] = START_FLAG;
    result[index++] = frame->address;
    result[index++] = frame->control;

    if (frame->data != NULL) {
        for (size_t i = 0; i < frame->data_length; i++) {
            uint8_t byte = frame->data[i];
            if (byte == START_FLAG || byte == END_FLAG || byte == ESCAPE_FLAG) {
                result[index++] = ESCAPE_FLAG;
                result[index++] = byte ^ ESCAPE_XOR;
            } else {
                result[index++] = byte;
            }
        }
    }

    uint16_t fcs = calculate_fcs(frame, 0);
    result[index++] = fcs & 0xFF;
    result[index++] = (fcs >> 8) & 0xFF;
    result[index++] = END_FLAG;
}

void init_IFrame(IFrame* frame, uint8_t address, uint8_t receive_sequence_number, uint8_t poll_final,
                 uint8_t send_sequence_number, uint8_t* data, size_t data_length) {
    init_HDLCFrame(&frame->base, address,
                   ((receive_sequence_number & 0b111) << 6) | ((poll_final & 0b1) << 4) |
                   ((send_sequence_number & 0b111) << 1) | 0,
                   data, data_length);
    frame->receive_sequence_number = receive_sequence_number;
    frame->poll_final = poll_final;
    frame->send_sequence_number = send_sequence_number;
}

void init_SFrame(SFrame* frame, uint8_t address, uint8_t receive_sequence_number, uint8_t poll_final,
                 const char* frame_type) {
    uint8_t frame_type_value;
    if (strcmp(frame_type, "RR") == 0) {
        frame_type_value = 0;
    } else if (strcmp(frame_type, "RNR") == 0) {
        frame_type_value = 1;
    } else if (strcmp(frame_type, "REJ") == 0) {
        frame_type_value = 2;
    } else if (strcmp(frame_type, "SREJ") == 0) {
        frame_type_value = 3;
    } else {
        // Handle error
        return;
    }

    init_HDLCFrame(&frame->base, address,
                   ((receive_sequence_number & 0b111) << 6) | ((poll_final & 0b1) << 5) |
                   ((frame_type_value & 0b111) << 2) | 1,
                   NULL, 0);
    frame->receive_sequence_number = receive_sequence_number;
    frame->poll_final = poll_final;
    frame->frame_type = frame_type;
}

void init_UFrame(UFrame* frame, uint8_t address, uint8_t poll_final, const char* frame_type,
                 uint8_t* data, size_t data_length) {
    uint8_t frame_type_value;
    if (strcmp(frame_type, "BP") == 0) {
        frame_type_value = 63;
    } else {
        // Handle error
        return;
    }

    init_HDLCFrame(&frame->base, address, (frame_type_value << 2) | 3, data, data_length);
    frame->poll_final = poll_final;
    frame->frame_type = frame_type;
}