unit_si.hh

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/*!
 *
 * Copyright (C) 2015 Technical University of Liberec.  All rights reserved.
 * 
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License version 3 as published by the
 * Free Software Foundation. (http://www.gnu.org/licenses/gpl-3.0.en.html)
 * 
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
 *
 * 
 * @file    unit_si.hh
 * @brief   
 */

#ifndef UNIT_SI_HH_
#define UNIT_SI_HH_

#include <vector>
#include <string>


/**
 * @brief Class for representation SI units of Fields.
 *
 * Units are set through exponents of basic SI units. These exponents are set in methods with same
 * name as unit symbols (e.g. kg(), K() etc).
 *
 * Class contains method that provides formated string representing full unit symbol (usable in
 * LaTeX output).
 *
 * UnitSI object contains flag that says if it is defined
 * - undefined object can't be formated
 * - if any exponent is set, flag is set to defined
 *
 * Class contains static methods that return frequently used derived units (Watt, Pascal etc).
 */
class UnitSI {
public:
    /// Constructor
    UnitSI();

    /// Methods return frequently used derived units
    /// Returns Newton
    static UnitSI & N();
    /// Returns Joule
    static UnitSI & J();
    /// Returns Watt
    static UnitSI & W();
    /// Returns Pascal
    static UnitSI & Pa();
    /// Returns dimensionless unit
    static UnitSI & dimensionless();

    /// Methods set values of exponents for SI units with similar name
    UnitSI & m(int exp = 1);
    UnitSI & kg(int exp = 1);
    UnitSI & s(int exp = 1);
    UnitSI & A(int exp = 1);
    UnitSI & K(int exp = 1);
    UnitSI & mol(int exp = 1);
    UnitSI & cd(int exp = 1);
    /// The dimension dependent meter: md^y = m^(yd), where 'd' is dimension.
    UnitSI & md(int exp = -1);

    /**
     * Makes unit description string in Latex format, e.g. "$[m.kg^{2}.s^{-2}]$"
     *
     * Have assert for undefined units.
     */
    std::string format_latex() const;

    std::string format_text() const;

    /**
     * Machine readable JSON format. Units are stored as a record with keys given by
     * SI units strings (corresponding to setters). Values of the keys are integer.
     */
    std::string json() const;

    /**
     * Set flag that unit is undefined.
     *
     * Default value is true (set in constructor).
     * If any exponent is set, @p undef_ flag is unset.
     * In all fields unit must be defined by user.
     */
    void undef(bool val = true);

    /// Return true if the unit is defined.
    bool is_def() const;

private:
    /// Values determine positions of exponents in exponents_ vector
    enum UnitOrder {
        order_m=0,
        order_md=1,
        order_kg=2,
        order_s=3,
        order_A=4,
        order_K=5,
        order_mol=6,
        order_cd=7,
        n_base_units=8
    };

    /// Variable parts of output format. Used in the @p format method.
    struct OutputFormat {
        std::string exp_open, exp_close, delimiter;
    };

    /**
     * Symbols for individual units. Can not use static variable due to usage in static initialization.
     */
    static const std::string &unit_symbol(unsigned int idx);

    /// Generic output formating method.
    std::string format(OutputFormat form) const;


    /**
     * Stores exponents of base SI units in the order given by the
     * UnitOrder enum
     *
     * where md represents value of exponent depended on dimension (m^{-d})
     */
    std::vector<int> exponents_;


    /**
     * Flag if object is undefined.
     *
     * Value is set on true in constructor, when any exponent is changed, false value is set.
     */
    bool undef_;

    /// Product of two units.
    friend UnitSI operator *(const UnitSI &a, const UnitSI &b);
    /// Proportion of two units.
    friend UnitSI operator /(const UnitSI &a, const UnitSI &b);
};


/// Product of two units.
UnitSI operator *(const UnitSI &a, const UnitSI &b);

/// Proportion of two units.
UnitSI operator /(const UnitSI &a, const UnitSI &b);


#endif /* UNIT_SI_HH_ */