

#include "ndef.h"
// Everything read here comes off an NFC tag that anyone can write, so every
// length taken from the buffer is bounds-checked before it is used.
#define NDEF_NEED(n)                                                                               \
    {                                                                                              \
        if ((addr + (uint16_t)(n)) > buf_len) {                                                    \
            NDEF_MSG.success = NDEF_ERR_TRUNCATED;                                                 \
            return NDEF_MSG;                                                                       \
        }                                                                                          \
    }

ndef_message readNDEFText(unsigned char *buf, uint8_t buf_len) {
    uint16_t addr = 0;
    NDEF_MSG.success = 0;
    NDEF_MSG.payload_len = 0;
    NDEF_MSG.payload[0] = '\0';

    NDEF_NEED(2);
    if (buf[0] != NDEF_TLV) {
        NDEF_MSG.success = 1;
        return NDEF_MSG;
    }

    if (buf[1] == 0xFF) {
        NDEF_MSG.success = 2;
        return NDEF_MSG;
    };

    // int len_field = buf[1];
    addr = 2;

    NDEF_NEED(3);
    // bool is_short_record = (buf[addr] & NDEF_SHORT_RECORD) == NDEF_SHORT_RECORD;
    bool has_id_length = (buf[addr] & NDEF_ID_LEN) == NDEF_ID_LEN;
    uint8_t tnf = buf[addr] & 0x7;
    addr += 1; // 3

    uint8_t type_length = buf[addr];
    addr += 1; // 4

    uint8_t payload_length = buf[addr];
    addr += 1; // 5

    uint8_t id_length = 0;
    if (has_id_length) {
        NDEF_NEED(1);
        id_length = buf[addr];
        addr += 1;
    }

    // Only the first type byte is ever inspected, so skip the rest rather than
    // copying them into a tag-sized VLA.
    NDEF_NEED(type_length);
    uint8_t type_value_0 = (type_length > 0) ? buf[addr] : 0;
    addr += type_length;

    if (type_value_0 != NDEF_TEXT_RECORD) {
        NDEF_MSG.success = 11;
        return NDEF_MSG;
    };
    if (tnf != TNF_KNOWN) {
        NDEF_MSG.success = 12;
        return NDEF_MSG;
    };

    if (has_id_length && (id_length > 0)) {
        NDEF_NEED(id_length);
        addr += id_length;
    }

    NDEF_NEED(1);
    uint8_t lang_str_len = buf[addr];

    // payload_length covers the language-length byte plus the language code
    // plus the text. Subtracting without this check wraps a uint8_t to ~250.
    if (payload_length < ((uint16_t)lang_str_len + 1)) {
        NDEF_MSG.success = NDEF_ERR_BAD_LENGTH;
        return NDEF_MSG;
    }
    payload_length -= lang_str_len; // Language string
    payload_length -= 1;            // The byte that says how long the language string is

    NDEF_NEED((uint16_t)lang_str_len + 1);
    addr += lang_str_len;
    addr += 1;

    // Leave room for the terminator the UART print and strchr() both rely on.
    if (payload_length > (sizeof(NDEF_MSG.payload) - 1)) {
        payload_length = sizeof(NDEF_MSG.payload) - 1;
    }
    NDEF_NEED(payload_length);

    for (uint8_t i = 0; i < (payload_length); i++) {
        NDEF_MSG.payload[i] = buf[addr];
        addr += 1;
    }
    NDEF_MSG.payload[payload_length] = '\0';
    NDEF_MSG.payload_len = payload_length;

    #if DO_UART
    uart_sendString(NDEF_MSG.payload);
    uart_sendString("\n");
    #endif

    return NDEF_MSG;
};