Color.h

// SPDX-License-Identifier: GPL-2.0-only
 
#pragma once
 
#include <iostream>
#include <unistd.h>
 
namespace SlHelpers {
class Color {
public:
    enum C : unsigned {
        BLACK = 30,
        RED = 31,
        GREEN = 32,
        YELLOW = 33,
        BLUE = 34,
        MAGENTA = 35,
        CYAN = 36,
        WHITE = 37,
        COL256 = 38,
        DEFAULT = 39,
    };

    enum Ctrl {
        NoNL,
        NL,
    };

    explicit Color(enum C c = DEFAULT) noexcept : Color(std::cout, c) {}

    explicit Color(std::ostream &os, enum C c = DEFAULT) noexcept : m_NL(true), m_os(os) {
        if (doColor(os))
            m_os << seqBegin << c << 'm';
    }

    Color(unsigned char r, unsigned char g, unsigned char b) noexcept
        : Color(std::cout, r, g, b) {}

    Color(std::ostream &os, unsigned char r, unsigned char g, unsigned char b) noexcept
        : m_NL(true), m_os(os) {
        if (!doColor(os))
            return;
        m_os << seqBegin << COL256 << ";2;" <<
            toUnsigned(r) << ';' <<
            toUnsigned(g) << ';' <<
            toUnsigned(b) << 'm';
    }
 
    ~Color() {
        if (doColor(m_os))
            m_os << seqEnd;
        if (m_NL)
            m_os << '\n';
    }

    static void forceColor(bool force) { m_forceColor = force; }
    static void forceColorValue(bool value) { m_forceColorValue = value; }

    std::ostream &os() { return m_os; }

    void ctrl(Ctrl ctrl) {
        switch (ctrl) {
        case NL:
        case NoNL:
            m_NL = ctrl == NL;
            break;
        }
    }
 
private:
    template<typename T>
    static unsigned toUnsigned(const T &val) { return val; }
    static unsigned outIndex(const std::ostream &os) {
        if (os.rdbuf() == std::cout.rdbuf())
            return 0U;
        if (os.rdbuf() == std::cerr.rdbuf())
            return 1U;
        return 2U;
    }
    static bool doColor(const std::ostream &os) {
        if (m_forceColor)
            return m_forceColorValue;
        auto idx = outIndex(os);
        if (m_doColor[idx] < 0)
            m_doColor[idx] = isatty(idx + 1);
        return m_doColor[idx];
    }
 
    friend void testColor();
    inline static std::string_view seqBegin = "\033[01;";
    inline static std::string_view seqEnd = "\033[0m";
    inline static signed char m_doColor[] = { -1, -1, 1 };
    inline static bool m_forceColor = false;
    inline static bool m_forceColorValue = false;
    bool m_NL;
    std::ostream &m_os;
};
 
inline Color &&operator<<(Color &&os, const Color::Ctrl &ctrl)
{
    os.ctrl(ctrl);
    return std::move(os);
}
 
template<typename T>
Color &&operator<<(Color &&os, const T &x)
{
    os.os() << x;
    return std::move(os);
}
 
}