QrCode.hpp

#pragma once

#include <cstdint>
#include <deque>
#include <stdexcept>
#include <string>
#include <vector>
#include "QrSegment.hpp"


namespace qrcodegen {

	/*
	 * A QR Code symbol, which is a type of two-dimension barcode.
	 * Invented by Denso Wave and described in the ISO/IEC 18004 standard.
	 * Instances of this class represent an immutable square grid of black and white cells.
	 * The class provides static factory functions to create a QR Code from text or binary data.
	 * The class covers the QR Code Model 2 specification, supporting all versions (sizes)
	 * from 1 to 40, all 4 error correction levels, and 4 character encoding modes.
	 *
	 * Ways to create a QR Code object:
	 * - High level: Take the payload data and call QrCode::encodeText() or QrCode::encodeBinary().
	 * - Mid level: Custom-make the list of segments and call QrCode::encodeSegments().
	 * - Low level: Custom-make the array of data codeword bytes (including
	 *   segment headers and final padding, excluding error correction codewords),
	 *   supply the appropriate version number, and call the QrCode() constructor.
	 * (Note that all ways require supplying the desired error correction level.)
	 */
	class QrCode final {

		/*---- Public helper enumeration ----*/

		/* The error correction level in a QR Code symbol. */
	public: enum class Ecc {
		LOW = 0,  // The QR Code can tolerate about  7% erroneous codewords
		MEDIUM,  // The QR Code can tolerate about 15% erroneous codewords
		QUARTILE,  // The QR Code can tolerate about 25% erroneous codewords
		HIGH,  // The QR Code can tolerate about 30% erroneous codewords
	};


			// Returns a value in the range 0 to 3 (unsigned 2-bit integer).
	private: static int getFormatBits(Ecc ecl);



			 /*---- Static factory functions (high level) ----*/

			 /*
			  * Returns a QR Code representing the given Unicode text string at the given error correction level.
			  * As a conservative upper bound, this function is guaranteed to succeed for strings that have 2953 or fewer
			  * UTF-8 code units (not Unicode code points) if the low error correction level is used. The smallest possible
			  * QR Code version is automatically chosen for the output. The ECC level of the result may be higher than
			  * the ecl argument if it can be done without increasing the version.
			  */
	public: static QrCode encodeText(const char *text, Ecc ecl);


			/*
			 * Returns a QR Code representing the given binary data at the given error correction level.
			 * This function always encodes using the binary segment mode, not any text mode. The maximum number of
			 * bytes allowed is 2953. The smallest possible QR Code version is automatically chosen for the output.
			 * The ECC level of the result may be higher than the ecl argument if it can be done without increasing the version.
			 */
	public: static QrCode encodeBinary(const std::vector<std::uint8_t> &data, Ecc ecl);


			/*---- Static factory functions (mid level) ----*/

			/*
			 * Returns a QR Code representing the given segments with the given encoding parameters.
			 * The smallest possible QR Code version within the given range is automatically
			 * chosen for the output. Iff boostEcl is true, then the ECC level of the result
			 * may be higher than the ecl argument if it can be done without increasing the
			 * version. The mask number is either between 0 to 7 (inclusive) to force that
			 * mask, or -1 to automatically choose an appropriate mask (which may be slow).
			 * This function allows the user to create a custom sequence of segments that switches
			 * between modes (such as alphanumeric and byte) to encode text in less space.
			 * This is a mid-level API; the high-level API is encodeText() and encodeBinary().
			 */
	public: static QrCode encodeSegments(const std::vector<QrSegment> &segs, Ecc ecl,
		int minVersion = 1, int maxVersion = 40, int mask = -1, bool boostEcl = true);  // All optional parameters



	/*---- Instance fields ----*/

	// Immutable scalar parameters:

	/* The version number of this QR Code, which is between 1 and 40 (inclusive).
	 * This determines the size of this barcode. */
	private: int version;

			 /* The width and height of this QR Code, measured in modules, between
			  * 21 and 177 (inclusive). This is equal to version * 4 + 17. */
	private: int size;

			 /* The error correction level used in this QR Code. */
	private: Ecc errorCorrectionLevel;

			 /* The index of the mask pattern used in this QR Code, which is between 0 and 7 (inclusive).
			  * Even if a QR Code is created with automatic masking requested (mask = -1),
			  * the resulting object still has a mask value between 0 and 7. */
	private: int mask;

			 // Private grids of modules/pixels, with dimensions of size*size:

			 // The modules of this QR Code (false = white, true = black).
			 // Immutable after constructor finishes. Accessed through getModule().
	private: std::vector<std::vector<bool> > modules;

			 // Indicates function modules that are not subjected to masking. Discarded when constructor finishes.
	private: std::vector<std::vector<bool> > isFunction;



			 /*---- Constructor (low level) ----*/

			 /*
			  * Creates a new QR Code with the given version number,
			  * error correction level, data codeword bytes, and mask number.
			  * This is a low-level API that most users should not use directly.
			  * A mid-level API is the encodeSegments() function.
			  */
	public: QrCode(int ver, Ecc ecl, const std::vector<std::uint8_t> &dataCodewords, int mask);



			/*---- Public instance methods ----*/

			/* Returns this QR Code's version, in the range [1, 40]. */
	public: int getVersion() const;


			/* Returns this QR Code's size, in the range [21, 177].*/
	public: int getSize() const;


			/* Returns this QR Code's error correction level.*/
	public: Ecc getErrorCorrectionLevel() const;


			/* Returns this QR Code's mask, in the range [0, 7]. */
	public: int getMask() const;


			/*
			 * Returns the color of the module (pixel) at the given coordinates, which is false
			 * for white or true for black. The top left corner has the coordinates (x=0, y=0).
			 * If the given coordinates are out of bounds, then false (white) is returned.
			 */
	public: bool getModule(int x, int y) const;


			/*
			 * Returns a string of SVG code for an image depicting this QR Code, with the given number
			 * of border modules. The string always uses Unix newlines (\n), regardless of the platform.
			 */
	public: std::string toSvgString(int border) const;



			/*---- Private helper methods for constructor: Drawing function modules ----*/

			// Reads this object's version field, and draws and marks all function modules.
	private: void drawFunctionPatterns();


			 // Draws two copies of the format bits (with its own error correction code)
			 // based on the given mask and this object's error correction level field.
	private: void drawFormatBits(int mask);


			 // Draws two copies of the version bits (with its own error correction code),
			 // based on this object's version field, iff 7 <= version <= 40.
	private: void drawVersion();


			 // Draws a 9*9 finder pattern including the border separator,
			 // with the center module at (x, y). Modules can be out of bounds.
	private: void drawFinderPattern(int x, int y);


			 // Draws a 5*5 alignment pattern, with the center module
			 // at (x, y). All modules must be in bounds.
	private: void drawAlignmentPattern(int x, int y);


			 // Sets the color of a module and marks it as a function module.
			 // Only used by the constructor. Coordinates must be in bounds.
	private: void setFunctionModule(int x, int y, bool isBlack);


			 // Returns the color of the module at the given coordinates, which must be in range.
	private: bool module(int x, int y) const;


			 /*---- Private helper methods for constructor: Codewords and masking ----*/

			 // Returns a new byte string representing the given data with the appropriate error correction
			 // codewords appended to it, based on this object's version and error correction level.
	private: std::vector<std::uint8_t> addEccAndInterleave(const std::vector<std::uint8_t> &data) const;


			 // Draws the given sequence of 8-bit codewords (data and error correction) onto the entire
			 // data area of this QR Code. Function modules need to be marked off before this is called.
	private: void drawCodewords(const std::vector<std::uint8_t> &data);


			 // XORs the codeword modules in this QR Code with the given mask pattern.
			 // The function modules must be marked and the codeword bits must be drawn
			 // before masking. Due to the arithmetic of XOR, calling applyMask() with
			 // the same mask value a second time will undo the mask. A final well-formed
			 // QR Code needs exactly one (not zero, two, etc.) mask applied.
	private: void applyMask(int mask);


			 // Calculates and returns the penalty score based on state of this QR Code's current modules.
			 // This is used by the automatic mask choice algorithm to find the mask pattern that yields the lowest score.
	private: long getPenaltyScore() const;



			 /*---- Private helper functions ----*/

			 // Returns an ascending list of positions of alignment patterns for this version number.
			 // Each position is in the range [0,177), and are used on both the x and y axes.
			 // This could be implemented as lookup table of 40 variable-length lists of unsigned bytes.
	private: std::vector<int> getAlignmentPatternPositions() const;


			 // Returns the number of data bits that can be stored in a QR Code of the given version number, after
			 // all function modules are excluded. This includes remainder bits, so it might not be a multiple of 8.
			 // The result is in the range [208, 29648]. This could be implemented as a 40-entry lookup table.
	private: static int getNumRawDataModules(int ver);


			 // Returns the number of 8-bit data (i.e. not error correction) codewords contained in any
			 // QR Code of the given version number and error correction level, with remainder bits discarded.
			 // This stateless pure function could be implemented as a (40*4)-cell lookup table.
	private: static int getNumDataCodewords(int ver, Ecc ecl);


			 // Inserts the given value to the front of the given array, which shifts over the
			 // existing values and deletes the last value. A helper function for getPenaltyScore().
	private: static void addRunToHistory(int run, std::deque<int> &history);


			 // Tests whether the given run history has the pattern of ratio 1:1:3:1:1 in the middle, and
			 // surrounded by at least 4 on either or both ends. A helper function for getPenaltyScore().
			 // Must only be called immediately after a run of white modules has ended.
	private: static bool hasFinderLikePattern(const std::deque<int> &runHistory);


			 // Returns true iff the i'th bit of x is set to 1.
	private: static bool getBit(long x, int i);


			 /*---- Constants and tables ----*/

			 // The minimum version number supported in the QR Code Model 2 standard.
	public: static constexpr int MIN_VERSION = 1;

			// The maximum version number supported in the QR Code Model 2 standard.
	public: static constexpr int MAX_VERSION = 40;


			// For use in getPenaltyScore(), when evaluating which mask is best.
	private: static const int PENALTY_N1;
	private: static const int PENALTY_N2;
	private: static const int PENALTY_N3;
	private: static const int PENALTY_N4;


	private: static const std::int8_t ECC_CODEWORDS_PER_BLOCK[4][41];
	private: static const std::int8_t NUM_ERROR_CORRECTION_BLOCKS[4][41];



			 /*---- Private helper class ----*/

			 /*
			  * Computes the Reed-Solomon error correction codewords for a sequence of data codewords
			  * at a given degree. Objects are immutable, and the state only depends on the degree.
			  * This class exists because each data block in a QR Code shares the same the divisor polynomial.
			  */
	private: class ReedSolomonGenerator final {

		/*-- Immutable field --*/

		// Coefficients of the divisor polynomial, stored from highest to lowest power, excluding the leading term which
		// is always 1. For example the polynomial x^3 + 255x^2 + 8x + 93 is stored as the uint8 array {255, 8, 93}.
	private: std::vector<std::uint8_t> coefficients;


			 /*-- Constructor --*/

			 /*
			  * Creates a Reed-Solomon ECC generator for the given degree. This could be implemented
			  * as a lookup table over all possible parameter values, instead of as an algorithm.
			  */
	public: explicit ReedSolomonGenerator(int degree);


			/*-- Method --*/

			/*
			 * Computes and returns the Reed-Solomon error correction codewords for the given
			 * sequence of data codewords. The returned object is always a new byte array.
			 * This method does not alter this object's state (because it is immutable).
			 */
	public: std::vector<std::uint8_t> getRemainder(const std::vector<std::uint8_t> &data) const;


			/*-- Static function --*/

			// Returns the product of the two given field elements modulo GF(2^8/0x11D).
			// All inputs are valid. This could be implemented as a 256*256 lookup table.
	private: static std::uint8_t multiply(std::uint8_t x, std::uint8_t y);

	};

	};



	/*---- Public exception class ----*/

	/*
	 * Thrown when the supplied data does not fit any QR Code version. Ways to handle this exception include:
	 * - Decrease the error correction level if it was greater than Ecc::LOW.
	 * - If the encodeSegments() function was called with a maxVersion argument, then increase
	 *   it if it was less than QrCode::MAX_VERSION. (This advice does not apply to the other
	 *   factory functions because they search all versions up to QrCode::MAX_VERSION.)
	 * - Split the text data into better or optimal segments in order to reduce the number of bits required.
	 * - Change the text or binary data to be shorter.
	 * - Change the text to fit the character set of a particular segment mode (e.g. alphanumeric).
	 * - Propagate the error upward to the caller/user.
	 */
	class data_too_long : public std::length_error {

	public: explicit data_too_long(const std::string &msg);

	};

}