#include <qpdf/InputSource.hh>

#include <qpdf/QIntC.hh>

#include <qpdf/QTC.hh>

#include <cstring>

#include <stdexcept>

void

InputSource::setLastOffset(qpdf_offset_t offset)

{

    this->last_offset = offset;

}

qpdf_offset_t

InputSource::getLastOffset() const

{

    return this->last_offset;

}

std::string

InputSource::readLine(size_t max_line_length)

{

    // Return at most max_line_length characters from the next line. Lines are terminated by one or

    // more \r or \n characters. Consume the trailing newline characters but don't return them.

    // After this is called, the file will be positioned after a line terminator or at the end of

    // the file, and last_offset will point to position the file had when this method was called.

    qpdf_offset_t offset = this->tell();

    auto bp = std::make_unique<char[]>(max_line_length + 1);

    char* buf = bp.get();

    memset(buf, '\0', max_line_length + 1);

    this->read(buf, max_line_length);

    this->seek(offset, SEEK_SET);

    qpdf_offset_t eol = this->findAndSkipNextEOL();

    this->last_offset = offset;

    size_t line_length = QIntC::to_size(eol - offset);

    if (line_length < max_line_length) {

        buf[line_length] = '\0';

    }

    return {buf};

}

bool

InputSource::findFirst(char const* start_chars, qpdf_offset_t offset, size_t len, Finder& finder)

{

    // Basic approach: search for the first character of start_chars starting from offset but not

    // going past len (if len != 0). Once the first character is found, see if it is the beginning

    // of a sequence of characters matching start_chars. If so, call finder.check() to do

    // caller-specific additional checks. If not, keep searching.

    // This code is tricky and highly subject to off-by-one or other edge case logic errors. See

    // comments throughout that explain how we're not missing any edge cases. There are also tests

    // specifically constructed to make sure we caught the edge cases in testing.

    char buf[1025]; // size known to input_source.cc in libtests

    // To enable us to guarantee null-termination, save an extra byte so that buf[size] is valid

    // memory.

    size_t size = sizeof(buf) - 1;

    if ((strlen(start_chars) < 1) || (strlen(start_chars) > size)) {

        throw std::logic_error("InputSource::findSource called with"

                               " too small or too large of a character sequence");

    }

    char* p = nullptr;

    qpdf_offset_t buf_offset = offset;

    size_t bytes_read = 0;

    // Guarantee that we return from this loop. Each time through, we either return, advance p, or

    // restart the loop with a condition that will cause return on the next pass. Eventually we will

    // either be out of range or hit EOF, either of which forces us to return.

    while (true) {

        // Do we need to read more data? Pretend size = 5, buf starts at 0, and start_chars has 3

        // characters. buf[5] is valid and null. If p == 2, start_chars could be buf[2] through

        // buf[4], so p + strlen(start_chars) == buf + size is okay. If p points to buf[size], since

        // strlen(start_chars) is always >= 1, this overflow test will be correct for that case

        // regardless of start_chars.

        if ((p == nullptr) || ((p + strlen(start_chars)) > (buf + bytes_read))) {

            if (p) {

                QTC::TC(

                    "libtests", "InputSource read next block", ((p == buf + bytes_read) ? 0 : 1));

                buf_offset += (p - buf);

            }

            this->seek(buf_offset, SEEK_SET);

            // Read into buffer and zero out the rest of the buffer including buf[size]. We

            // allocated an extra byte so that we could guarantee null termination as an extra

            // protection against overrun when using string functions.

            bytes_read = this->read(buf, size);

            if (bytes_read < strlen(start_chars)) {

                QTC::TC("libtests", "InputSource find EOF", bytes_read == 0 ? 0 : 1);

                return false;

            }

            memset(buf + bytes_read, '\0', 1 + (size - bytes_read));

            p = buf;

        }

        // Search for the first character.

        if ((p = static_cast<char*>(

                 // line-break

                 memchr(p, start_chars[0], bytes_read - QIntC::to_size(p - buf)))) != nullptr) {

            if (p == buf) {

                QTC::TC("libtests", "InputSource found match at buf[0]");

            }

            // Found first letter.

            if (len != 0) {

                // Make sure it's in range.

                size_t p_relative_offset = QIntC::to_size((p - buf) + (buf_offset - offset));

                if (p_relative_offset >= len) {

                    // out of range

                    QTC::TC("libtests", "InputSource out of range");

                    return false;

                }

            }

            if ((p + strlen(start_chars)) > (buf + bytes_read)) {

                // If there are not enough bytes left in the file for start_chars, we will detect

                // this on the next pass as EOF and return.

                QTC::TC("libtests", "InputSource not enough bytes");

                continue;

            }

            // See if p points to a sequence matching start_chars. We already checked above to make

            // sure we are not going to overrun memory.

            if (strncmp(p, start_chars, strlen(start_chars)) == 0) {

                // Call finder.check() with the input source positioned to the point of the match.

                this->seek(buf_offset + (p - buf), SEEK_SET);

                if (finder.check()) {

                    return true;

                } else {

                    QTC::TC("libtests", "InputSource start_chars matched but not check");

                }

            } else {

                QTC::TC("libtests", "InputSource first char matched but not string");

            }

            // This occurrence of the first character wasn't a match. Skip over it and keep

            // searching.

            ++p;

        } else {

            // Trigger reading the next block

            p = buf + bytes_read;

        }

    }

    throw std::logic_error("InputSource after while (true)");

}

bool

InputSource::findLast(char const* start_chars, qpdf_offset_t offset, size_t len, Finder& finder)

{

    bool found = false;

    qpdf_offset_t after_found_offset = 0;

    qpdf_offset_t cur_offset = offset;

    size_t cur_len = len;

    while (this->findFirst(start_chars, cur_offset, cur_len, finder)) {

        if (found) {

            QTC::TC("libtests", "InputSource findLast found more than one");

        } else {

            found = true;

        }

        after_found_offset = this->tell();

        cur_offset = after_found_offset;

        cur_len = len - QIntC::to_size((cur_offset - offset));

    }

    if (found) {

        this->seek(after_found_offset, SEEK_SET);

    }

    return found;

}