gitech

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// Copyright 2023 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package util
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import (
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	"fmt"
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	"strconv"
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	"strings"
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)
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// Get color as RGB values in 0..255 range from the hex color string (with or without #)
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func HexToRBGColor(colorString string) (float64, float64, float64) {
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	hexString := colorString
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	if strings.HasPrefix(colorString, "#") {
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		hexString = colorString[1:]
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	}
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	// only support transfer of rgb, rgba, rrggbb and rrggbbaa
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	// if not in these formats, use default values 0, 0, 0
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	if len(hexString) != 3 && len(hexString) != 4 && len(hexString) != 6 && len(hexString) != 8 {
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		return 0, 0, 0
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	}
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	if len(hexString) == 3 || len(hexString) == 4 {
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		hexString = fmt.Sprintf("%c%c%c%c%c%c", hexString[0], hexString[0], hexString[1], hexString[1], hexString[2], hexString[2])
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	}
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	if len(hexString) == 8 {
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		hexString = hexString[0:6]
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	}
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	color, err := strconv.ParseUint(hexString, 16, 64)
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	if err != nil {
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		return 0, 0, 0
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	}
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	r := float64(uint8(0xFF & (uint32(color) >> 16)))
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	g := float64(uint8(0xFF & (uint32(color) >> 8)))
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	b := float64(uint8(0xFF & uint32(color)))
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	return r, g, b
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}
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// Returns relative luminance for a SRGB color - https://en.wikipedia.org/wiki/Relative_luminance
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// Keep this in sync with web_src/js/utils/color.js
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func GetRelativeLuminance(color string) float64 {
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	r, g, b := HexToRBGColor(color)
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	return (0.2126729*r + 0.7151522*g + 0.0721750*b) / 255
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}
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func UseLightText(backgroundColor string) bool {
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	return GetRelativeLuminance(backgroundColor) < 0.453
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}
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// Given a background color, returns a black or white foreground color that the highest
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// contrast ratio. In the future, the APCA contrast function, or CSS `contrast-color` will be better.
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// https://github.com/color-js/color.js/blob/eb7b53f7a13bb716ec8b28c7a56f052cd599acd9/src/contrast/APCA.js#L42
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func ContrastColor(backgroundColor string) string {
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	if UseLightText(backgroundColor) {
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		return "#fff"
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	}
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	return "#000"
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}
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