import Foundation
import CoreText

extension UnicodeScalar {
    var isEmoji: Bool {
        switch value {
            case 0x1F600...0x1F64F, // Emoticons
            0x1F300...0x1F5FF, // Misc Symbols and Pictographs
            0x1F680...0x1F6FF, // Transport and Map
            0x1F1E6...0x1F1FF, // Regional country flags
            0x2600...0x26FF, // Misc symbols
            0x2700...0x27BF, // Dingbats
            0xE0020...0xE007F, // Tags
            0xFE00...0xFE0F, // Variation Selectors
            0x1F900...0x1F9FF, // Supplemental Symbols and Pictographs
            127000...127600, // Various asian characters
            65024...65039, // Variation selector
            9100...9300, // Misc items
            8400...8447: // Combining Diacritical Marks for Symbols
                return true
            default:
                return false
        }
    }
    
    var isZeroWidthJoiner: Bool {
        return value == 8205
    }
}

extension String {
    func trimmingTrailingSpaces() -> String {
        var t = self
        while t.hasSuffix(" ") {
            t = "" + t.dropLast()
        }
        return t
    }
    
    var glyphCount: Int {
        let richText = NSAttributedString(string: self)
        let line = CTLineCreateWithAttributedString(richText)
        return CTLineGetGlyphCount(line)
    }
    
    var isSingleEmoji: Bool {
        return glyphCount == 1 && containsEmoji
    }
    
    var containsEmoji: Bool {
        return unicodeScalars.contains { $0.isEmoji }
    }
    
    var containsOnlyEmoji: Bool {
        return !isEmpty && !unicodeScalars.contains(where: {
            !$0.isEmoji && !$0.isZeroWidthJoiner
        })
    }
    
    // The next tricks are mostly to demonstrate how tricky it can be to determine emoji's
    // If anyone has suggestions how to improve this, please let me know
    var emojiString: String {
        return emojiScalars.map { String($0) }.reduce("", +)
    }
    
    var firstEmoji: String {
        if let first = emojiScalars.first {
            return String(first)
        } else {
            return ""
        }
    }
    
    var emojis: [String] {
        var scalars: [[UnicodeScalar]] = []
        var currentScalarSet: [UnicodeScalar] = []
        var previousScalar: UnicodeScalar?
        
        for scalar in emojiScalars {
            if let prev = previousScalar, !prev.isZeroWidthJoiner && !scalar.isZeroWidthJoiner {
                scalars.append(currentScalarSet)
                currentScalarSet = []
            }
            currentScalarSet.append(scalar)
            
            previousScalar = scalar
        }
        
        scalars.append(currentScalarSet)
        
        return scalars.map { $0.map{ String($0) } .reduce("", +) }
    }
    
    fileprivate var emojiScalars: [UnicodeScalar] {
        var chars: [UnicodeScalar] = []
        var previous: UnicodeScalar?
        for cur in unicodeScalars {
            if let previous = previous, previous.isZeroWidthJoiner && cur.isEmoji {
                chars.append(previous)
                chars.append(cur)
            } else if cur.isEmoji {
                chars.append(cur)
            }
            
            previous = cur
        }
        
        return chars
    }
}