//
//  CryptoSwift
//
//  Copyright (C) 2014-2017 Marcin Krzyżanowski <marcin@krzyzanowskim.com>
//  This software is provided 'as-is', without any express or implied warranty.
//
//  In no event will the authors be held liable for any damages arising from the use of this software.
//
//  Permission is granted to anyone to use this software for any purpose,including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
//
//  - The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation is required.
//  - Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
//  - This notice may not be removed or altered from any source or binary distribution.
//

extension Array {
    public init(reserveCapacity: Int) {
        self = Array<Element>()
        self.reserveCapacity(reserveCapacity)
    }

    var slice: ArraySlice<Element> {
        return self[self.startIndex ..< self.endIndex]
    }
}

extension Array where Element == UInt8 {
    public init(hex: String) {
        self.init(reserveCapacity: hex.unicodeScalars.lazy.underestimatedCount)
        var buffer: UInt8?
        var skip = hex.hasPrefix("0x") ? 2 : 0
        for char in hex.unicodeScalars.lazy {
            guard skip == 0 else {
                skip -= 1
                continue
            }
            guard char.value >= 48 && char.value <= 102 else {
                removeAll()
                return
            }
            let v: UInt8
            let c: UInt8 = UInt8(char.value)
            switch c {
            case let c where c <= 57:
                v = c - 48
            case let c where c >= 65 && c <= 70:
                v = c - 55
            case let c where c >= 97:
                v = c - 87
            default:
                removeAll()
                return
            }
            if let b = buffer {
                append(b << 4 | v)
                buffer = nil
            } else {
                buffer = v
            }
        }
        if let b = buffer {
            append(b)
        }
    }

    public func toHexString() -> String {
        return `lazy`.reduce("") {
            var s = String($1, radix: 16)
            if s.count == 1 {
                s = "0" + s
            }
            return $0 + s
        }
    }
}
