polybar/include/utils/color.hpp

#pragma once

#include <iomanip>

#include "common.hpp"
#include "utils/string.hpp"
#include "x11/xlib.hpp"

POLYBAR_NS

namespace color_util {
  template <typename T = uint8_t>
  T alpha_channel(const uint32_t value) {
    uint8_t a = value >> 24;
    if (std::is_same<T, uint8_t>::value)
      return a << 8 / 0xff;
    else if (std::is_same<T, uint16_t>::value)
      return a << 8 | a << 8 / 0xff;
  }

  template <typename T = uint8_t>
  T red_channel(const uint32_t value) {
    uint8_t r = value >> 16;
    if (std::is_same<T, uint8_t>::value)
      return r << 8 / 0xff;
    else if (std::is_same<T, uint16_t>::value)
      return r << 8 | r << 8 / 0xff;
  }

  template <typename T = uint8_t>
  T green_channel(const uint32_t value) {
    uint8_t g = value >> 8;
    if (std::is_same<T, uint8_t>::value)
      return g << 8 / 0xff;
    else if (std::is_same<T, uint16_t>::value)
      return g << 8 | g << 8 / 0xff;
  }

  template <typename T = uint8_t>
  T blue_channel(const uint32_t value) {
    uint8_t b = value;
    if (std::is_same<T, uint8_t>::value)
      return b << 8 / 0xff;
    else if (std::is_same<T, uint16_t>::value)
      return b << 8 | b << 8 / 0xff;
  }

  template <typename T = uint32_t>
  uint32_t premultiply_alpha(const T value) {
    auto a = color_util::alpha_channel(value);
    auto r = color_util::red_channel(value) * a / 255;
    auto g = color_util::green_channel(value) * a / 255;
    auto b = color_util::blue_channel(value) * a / 255;
    return (a << 24) | (r << 16) | (g << 8) | b;
  }

  template <typename T>
  string hex(uint32_t color) {
    char s[12];
    size_t len = 0;

    uint8_t a = alpha_channel<T>(color);
    uint8_t r = red_channel<T>(color);
    uint8_t g = green_channel<T>(color);
    uint8_t b = blue_channel<T>(color);

    if (std::is_same<T, uint16_t>::value) {
      len = snprintf(s, sizeof(s), "#%02x%02x%02x%02x", a, r, g, b);
    } else if (std::is_same<T, uint8_t>::value) {
      len = snprintf(s, sizeof(s), "#%02x%02x%02x", r, g, b);
    }

    return string{s, 0, len};
  }

  inline string parse_hex(string hex) {
    if (hex.substr(0, 1) != "#")
      hex = "#" + hex;
    if (hex.length() == 4)
      hex = {'#', hex[1], hex[1], hex[2], hex[2], hex[3], hex[3]};
    if (hex.length() == 7)
      hex = "#ff" + hex.substr(1);
    if (hex.length() != 9)
      return "";
    return hex;
  }

  inline uint32_t parse(string hex, uint32_t fallback = 0) {
    if ((hex = parse_hex(hex)).empty())
      return fallback;
    return std::strtoul(&hex[1], nullptr, 16);
  }
}

POLYBAR_NS_END