//
//  MD5.swift
//  CryptoSwift
//
//  Created by Marcin Krzyzanowski on 06/08/14.
//  Copyright (c) 2014 Marcin Krzyzanowski. All rights reserved.
//

public final class MD5: DigestType  {
    static let blockSize:Int = 64
    static let digestLength:Int = 16 // 128 / 8
    fileprivate static let hashInitialValue:Array<UInt32> = [0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476]

    fileprivate var accumulated = Array<UInt8>()
    fileprivate var processedBytesTotalCount: Int = 0
    fileprivate var accumulatedHash:Array<UInt32> = MD5.hashInitialValue

    /** specifies the per-round shift amounts */
    private let s: Array<UInt32> = [7, 12, 17, 22,  7, 12, 17, 22,  7, 12, 17, 22,  7, 12, 17, 22,
                       5,  9, 14, 20,  5,  9, 14, 20,  5,  9, 14, 20,  5,  9, 14, 20,
                       4, 11, 16, 23,  4, 11, 16, 23,  4, 11, 16, 23,  4, 11, 16, 23,
                       6, 10, 15, 21,  6, 10, 15, 21,  6, 10, 15, 21,  6, 10, 15, 21]
    
    /** binary integer part of the sines of integers (Radians) */
    private let k: Array<UInt32> = [0xd76aa478,0xe8c7b756,0x242070db,0xc1bdceee,
                       0xf57c0faf,0x4787c62a,0xa8304613,0xfd469501,
                       0x698098d8,0x8b44f7af,0xffff5bb1,0x895cd7be,
                       0x6b901122,0xfd987193,0xa679438e,0x49b40821,
                       0xf61e2562,0xc040b340,0x265e5a51,0xe9b6c7aa,
                       0xd62f105d,0x2441453,0xd8a1e681,0xe7d3fbc8,
                       0x21e1cde6,0xc33707d6,0xf4d50d87,0x455a14ed,
                       0xa9e3e905,0xfcefa3f8,0x676f02d9,0x8d2a4c8a,
                       0xfffa3942,0x8771f681,0x6d9d6122,0xfde5380c,
                       0xa4beea44,0x4bdecfa9,0xf6bb4b60,0xbebfbc70,
                       0x289b7ec6,0xeaa127fa,0xd4ef3085,0x4881d05,
                       0xd9d4d039,0xe6db99e5,0x1fa27cf8,0xc4ac5665,
                       0xf4292244,0x432aff97,0xab9423a7,0xfc93a039,
                       0x655b59c3,0x8f0ccc92,0xffeff47d,0x85845dd1,
                       0x6fa87e4f,0xfe2ce6e0,0xa3014314,0x4e0811a1,
                       0xf7537e82,0xbd3af235,0x2ad7d2bb,0xeb86d391]

    public init() {
        
    }

    public func calculate(for bytes: Array<UInt8>) -> Array<UInt8> {
        do {
            return try self.update(withBytes: bytes, isLast: true)
        } catch {
            fatalError()
        }
    }

    // mutating currentHash in place is way faster than returning new result
    fileprivate func process<C: Collection>(block chunk: C, currentHash: inout Array<UInt32>) where C.Iterator.Element == UInt8, C.Index == Int {

        // break chunk into sixteen 32-bit words M[j], 0 ≤ j ≤ 15
        var M = chunk.toUInt32Array()
        assert(M.count == 16, "Invalid array")

        // Initialize hash value for this chunk:
        var A:UInt32 = currentHash[0]
        var B:UInt32 = currentHash[1]
        var C:UInt32 = currentHash[2]
        var D:UInt32 = currentHash[3]

        var dTemp:UInt32 = 0

        // Main loop
        for j in 0..<k.count {
            var g = 0
            var F:UInt32 = 0

            switch (j) {
            case 0...15:
                F = (B & C) | ((~B) & D)
                g = j
                break
            case 16...31:
                F = (D & B) | (~D & C)
                g = (5 * j + 1) % 16
                break
            case 32...47:
                F = B ^ C ^ D
                g = (3 * j + 5) % 16
                break
            case 48...63:
                F = C ^ (B | (~D))
                g = (7 * j) % 16
                break
            default:
                break
            }
            dTemp = D
            D = C
            C = B
            B = B &+ rotateLeft(A &+ F &+ k[j] &+ M[g], by: s[j])
            A = dTemp
        }

        currentHash[0] = currentHash[0] &+ A
        currentHash[1] = currentHash[1] &+ B
        currentHash[2] = currentHash[2] &+ C
        currentHash[3] = currentHash[3] &+ D
    }
}

extension MD5: Updatable {
    public func update<T: Sequence>(withBytes bytes: T, isLast: Bool = false) throws -> Array<UInt8> where T.Iterator.Element == UInt8 {
        self.accumulated += bytes

        if isLast {
            let lengthInBits = (self.processedBytesTotalCount + self.accumulated.count) * 8
            let lengthBytes = lengthInBits.bytes(totalBytes: 64 / 8) // A 64-bit representation of b

            // Step 1. Append padding
            bitPadding(to: &self.accumulated, blockSize: MD5.blockSize, allowance: 64 / 8)

            // Step 2. Append Length a 64-bit representation of lengthInBits
            self.accumulated += lengthBytes.reversed()
        }

        var processedBytes = 0
        for chunk in BytesSequence(chunkSize: MD5.blockSize, data: self.accumulated) {
            if (isLast || (self.accumulated.count - processedBytes) >= MD5.blockSize) {
                self.process(block: chunk, currentHash: &self.accumulatedHash)
                processedBytes += chunk.count
            }
        }
        self.accumulated.removeFirst(processedBytes)
        self.processedBytesTotalCount += processedBytes

        // output current hash
        var result = Array<UInt8>()
        result.reserveCapacity(MD5.digestLength)

        for hElement in self.accumulatedHash {
            let hLE = hElement.littleEndian
            result += [UInt8(hLE & 0xff), UInt8((hLE >> 8) & 0xff), UInt8((hLE >> 16) & 0xff), UInt8((hLE >> 24) & 0xff)]
        }

        // reset hash value for instance
        if isLast {
            self.accumulatedHash = MD5.hashInitialValue
        }

        return result
    }
}