parseCSSColor.swift

// Swift port by Devin Abbott <[email protected]>, 2017.

// (c) Dean McNamee <[email protected]>, 2012.
//
// https://github.com/deanm/css-color-parser-js

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.

import Foundation

typealias CSSColor = (r: Int, g: Int, b: Int, a: Double)

// http://www.w3.org/TR/css3-color/
fileprivate let kCSSColorTable: [String: CSSColor] = [
    "transparent": (0,0,0,0), "aliceblue": (240,248,255,1),
    "antiquewhite": (250,235,215,1), "aqua": (0,255,255,1),
    "aquamarine": (127,255,212,1), "azure": (240,255,255,1),
    "beige": (245,245,220,1), "bisque": (255,228,196,1),
    "black": (0,0,0,1), "blanchedalmond": (255,235,205,1),
    "blue": (0,0,255,1), "blueviolet": (138,43,226,1),
    "brown": (165,42,42,1), "burlywood": (222,184,135,1),
    "cadetblue": (95,158,160,1), "chartreuse": (127,255,0,1),
    "chocolate": (210,105,30,1), "coral": (255,127,80,1),
    "cornflowerblue": (100,149,237,1), "cornsilk": (255,248,220,1),
    "crimson": (220,20,60,1), "cyan": (0,255,255,1),
    "darkblue": (0,0,139,1), "darkcyan": (0,139,139,1),
    "darkgoldenrod": (184,134,11,1), "darkgray": (169,169,169,1),
    "darkgreen": (0,100,0,1), "darkgrey": (169,169,169,1),
    "darkkhaki": (189,183,107,1), "darkmagenta": (139,0,139,1),
    "darkolivegreen": (85,107,47,1), "darkorange": (255,140,0,1),
    "darkorchid": (153,50,204,1), "darkred": (139,0,0,1),
    "darksalmon": (233,150,122,1), "darkseagreen": (143,188,143,1),
    "darkslateblue": (72,61,139,1), "darkslategray": (47,79,79,1),
    "darkslategrey": (47,79,79,1), "darkturquoise": (0,206,209,1),
    "darkviolet": (148,0,211,1), "deeppink": (255,20,147,1),
    "deepskyblue": (0,191,255,1), "dimgray": (105,105,105,1),
    "dimgrey": (105,105,105,1), "dodgerblue": (30,144,255,1),
    "firebrick": (178,34,34,1), "floralwhite": (255,250,240,1),
    "forestgreen": (34,139,34,1), "fuchsia": (255,0,255,1),
    "gainsboro": (220,220,220,1), "ghostwhite": (248,248,255,1),
    "gold": (255,215,0,1), "goldenrod": (218,165,32,1),
    "gray": (128,128,128,1), "green": (0,128,0,1),
    "greenyellow": (173,255,47,1), "grey": (128,128,128,1),
    "honeydew": (240,255,240,1), "hotpink": (255,105,180,1),
    "indianred": (205,92,92,1), "indigo": (75,0,130,1),
    "ivory": (255,255,240,1), "khaki": (240,230,140,1),
    "lavender": (230,230,250,1), "lavenderblush": (255,240,245,1),
    "lawngreen": (124,252,0,1), "lemonchiffon": (255,250,205,1),
    "lightblue": (173,216,230,1), "lightcoral": (240,128,128,1),
    "lightcyan": (224,255,255,1), "lightgoldenrodyellow": (250,250,210,1),
    "lightgray": (211,211,211,1), "lightgreen": (144,238,144,1),
    "lightgrey": (211,211,211,1), "lightpink": (255,182,193,1),
    "lightsalmon": (255,160,122,1), "lightseagreen": (32,178,170,1),
    "lightskyblue": (135,206,250,1), "lightslategray": (119,136,153,1),
    "lightslategrey": (119,136,153,1), "lightsteelblue": (176,196,222,1),
    "lightyellow": (255,255,224,1), "lime": (0,255,0,1),
    "limegreen": (50,205,50,1), "linen": (250,240,230,1),
    "magenta": (255,0,255,1), "maroon": (128,0,0,1),
    "mediumaquamarine": (102,205,170,1), "mediumblue": (0,0,205,1),
    "mediumorchid": (186,85,211,1), "mediumpurple": (147,112,219,1),
    "mediumseagreen": (60,179,113,1), "mediumslateblue": (123,104,238,1),
    "mediumspringgreen": (0,250,154,1), "mediumturquoise": (72,209,204,1),
    "mediumvioletred": (199,21,133,1), "midnightblue": (25,25,112,1),
    "mintcream": (245,255,250,1), "mistyrose": (255,228,225,1),
    "moccasin": (255,228,181,1), "navajowhite": (255,222,173,1),
    "navy": (0,0,128,1), "oldlace": (253,245,230,1),
    "olive": (128,128,0,1), "olivedrab": (107,142,35,1),
    "orange": (255,165,0,1), "orangered": (255,69,0,1),
    "orchid": (218,112,214,1), "palegoldenrod": (238,232,170,1),
    "palegreen": (152,251,152,1), "paleturquoise": (175,238,238,1),
    "palevioletred": (219,112,147,1), "papayawhip": (255,239,213,1),
    "peachpuff": (255,218,185,1), "peru": (205,133,63,1),
    "pink": (255,192,203,1), "plum": (221,160,221,1),
    "powderblue": (176,224,230,1), "purple": (128,0,128,1),
    "rebeccapurple": (102,51,153,1),
    "red": (255,0,0,1), "rosybrown": (188,143,143,1),
    "royalblue": (65,105,225,1), "saddlebrown": (139,69,19,1),
    "salmon": (250,128,114,1), "sandybrown": (244,164,96,1),
    "seagreen": (46,139,87,1), "seashell": (255,245,238,1),
    "sienna": (160,82,45,1), "silver": (192,192,192,1),
    "skyblue": (135,206,235,1), "slateblue": (106,90,205,1),
    "slategray": (112,128,144,1), "slategrey": (112,128,144,1),
    "snow": (255,250,250,1), "springgreen": (0,255,127,1),
    "steelblue": (70,130,180,1), "tan": (210,180,140,1),
    "teal": (0,128,128,1), "thistle": (216,191,216,1),
    "tomato": (255,99,71,1), "turquoise": (64,224,208,1),
    "violet": (238,130,238,1), "wheat": (245,222,179,1),
    "white": (255,255,255,1), "whitesmoke": (245,245,245,1),
    "yellow": (255,255,0,1), "yellowgreen": (154,205,50,1)]

// Clamp to integer 0 .. 255.
fileprivate func clamp_css_byte(_ i: Int) -> Int {
    return i < 0 ? 0 : i > 255 ? 255 : i
}

// Clamp to float 0.0 .. 1.0.
fileprivate func clamp_css_float(_ f: Double) -> Double {
    return f < 0 ? 0 : f > 1 ? 1 : f
}

// int or percentage.
fileprivate func parse_css_int(_ str: String) -> Int {
    if str.hasSuffix("%") {
        let digits = str.replacingOccurrences(of: "%", with: "")
        let value = (Double(digits) ?? 0) / 100 * 255
        return clamp_css_byte(Int(value))
    }
    
    return clamp_css_byte(Int(str) ?? 0)
}

// float or percentage.
fileprivate func parse_css_float(_ str: String) -> Double {
    if str.hasSuffix("%") {
        let digits = str.replacingOccurrences(of: "%", with: "")
        return clamp_css_float((Double(digits) ?? 0) / 100);
    }
    
    return clamp_css_float(Double(str) ?? 0);
}

fileprivate func css_hue_to_rgb(_ m1: Double, _ m2: Double, _ h: Double) -> Double {
    var h = h
    
    if h < 0 { h += 1 }
    else if h > 1 { h -= 1 }
    
    if h * 6 < 1 { return m1 + (m2 - m1) * h * 6 }
    if h * 2 < 1 { return m2 }
    if h * 3 < 2 { return m1 + (m2 - m1) * (2/3 - h) * 6 }
    return m1
}

func parseCSSColor(_ css_str: String) -> CSSColor? {
    // Remove all whitespace, not compliant, but should just be more accepting.
    var str = css_str.replacingOccurrences(of: " ", with: "").lowercased()
    
    // Color keywords (and transparent) lookup.
    if let match = kCSSColorTable[str] {
        return match;  // dup.
    }
    
    // #abc and #abc123 syntax.
    if (str.first == "#") {
        if (str.count == 4) {
            str.remove(at: str.startIndex) // TODO(deanm): Stricter parsing.
            guard let iv = Int(str, radix: 16) else { return nil }
            if !(iv >= 0 && iv <= 0xfff) { return nil } // Covers NaN.
            return (
                ((iv & 0xf00) >> 4) | ((iv & 0xf00) >> 8),
                (iv & 0xf0) | ((iv & 0xf0) >> 4),
                (iv & 0xf) | ((iv & 0xf) << 4),
                1
            )
        } else if (str.count == 7) {
            str.remove(at: str.startIndex) // TODO(deanm): Stricter parsing.
            guard let iv = Int(str, radix: 16) else { return nil }
            if (!(iv >= 0 && iv <= 0xffffff)) { return nil } // Covers NaN.
            return (
                (iv & 0xff0000) >> 16,
                (iv & 0xff00) >> 8,
                iv & 0xff,
                1
            )
        }
        
        return nil
    }
    
    let op = str.index(of: "(")
    let ep = str.index(of: ")")
    
    if let op = op, ep == str.index(before: str.endIndex), let ep = ep {
        let fname = str.substring(to: op)
        let range: Range<String.Index> = str.index(after: op)..<ep
        var params: [String] = str.substring(with: range).components(separatedBy: ",")
        
        var alpha: Double = 1;  // To allow case fallthrough.
        
        switch (fname) {
        case "rgba":
            if params.count != 4 { return nil }
            alpha = parse_css_float(params.popLast()!)
            fallthrough
        case "rgb":
            if (params.count != 3) { return nil }
            return (
                parse_css_int(params[0]),
                parse_css_int(params[1]),
                parse_css_int(params[2]),
                alpha
            )
        case "hsla":
            if (params.count != 4) { return nil }
            alpha = parse_css_float(params.popLast()!)
            fallthrough
        case "hsl":
            if (params.count != 3) { return nil }
            let hue = Double(params[0]) ?? 0
            let h = (hue.remainder(dividingBy: 360) + 360).remainder(dividingBy: 360) / 360 // 0 .. 1
            // NOTE(deanm): According to the CSS spec s/l should only be
            // percentages, but we don't bother and let float or percentage.
            let s = parse_css_float(params[1])
            let l = parse_css_float(params[2])
            let m2 = l <= 0.5 ? l * (s + 1) : l + s - l * s
            let m1 = l * 2 - m2
            return (
                clamp_css_byte(Int(css_hue_to_rgb(m1, m2, h+1/3) * 255.0)),
                clamp_css_byte(Int(css_hue_to_rgb(m1, m2, h) * 255.0)),
                clamp_css_byte(Int(css_hue_to_rgb(m1, m2, h-1/3) * 255.0)),
                alpha
            )
        default:
            return nil;
        }
    }
    
    return nil;
}

fileprivate func colorComponent(for int: Int) -> CGFloat {
    return CGFloat(int) / 255.0
}

#if os(iOS)
    import UIKit
    
    extension UIColor {
        static func parse(css: String) -> UIColor? {
            guard let color = parseCSSColor(css) else { return nil }
            
            return UIColor(
                red: colorComponent(for: color.r),
                green: colorComponent(for: color.g),
                blue: colorComponent(for: color.b),
                alpha: CGFloat(color.a)
            )
        }
    }
#elseif os(OSX)
    import AppKit
    
    extension NSColor {
        static func parse(css: String) -> NSColor? {
            guard let color = parseCSSColor(css) else { return nil }
            
            return NSColor(
                red: colorComponent(for: color.r),
                green: colorComponent(for: color.g),
                blue: colorComponent(for: color.b),
                alpha: CGFloat(color.a)
            )
        }
    }
#endif