Haik Aslanyan
91 lines
4.2 KiB
Swift
91 lines
4.2 KiB
Swift
// MIT License
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// Copyright (c) 2020 Haik Aslanyan
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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import Foundation
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final class RCBitCoder {
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private let configuration: RCCoderConfiguration
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init(configuration: RCCoderConfiguration) {
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self.configuration = configuration
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}
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}
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extension RCBitCoder {
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func encode(message: String) throws -> RCData {
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var specialCharacters = RCConstants.emptyCharacters
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specialCharacters.append(RCConstants.startingCharacter)
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guard message.map({$0}).allSatisfy({configuration.characters.contains($0) && !specialCharacters.contains($0)}) else {
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throw RCError.invalidCharacter
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}
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guard message.count <= configuration.maxMessageCount else {
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throw RCError.longText
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}
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var dataBytes = message.map({configuration.characters.firstIndex(of: $0)!})
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dataBytes.insert(configuration.characters.firstIndex(of: RCConstants.startingCharacter)!, at: 0)
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let emptyIndexes = RCConstants.emptyCharacters.map({configuration.characters.firstIndex(of: $0)!})
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let randomBytes = (0..<configuration.maxMessageCount).map({_ in emptyIndexes[Int.random(in: 0..<emptyIndexes.count)]})
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dataBytes.append(contentsOf: randomBytes)
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dataBytes = Array(dataBytes.prefix(configuration.maxMessageCount))
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let encodedBits = dataBytes.map { byte -> [RCBit] in
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var stringValue = String(repeating: "0", count: configuration.bitesPerSymbol)
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stringValue += String(byte, radix: 2)
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return stringValue.suffix(configuration.bitesPerSymbol).compactMap({RCBit($0)})
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}.flatMap({$0})
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var totalBits = [RCBit](repeating: .zero, count: RCConstants.maxBitesPerSection * 3)
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totalBits.insert(contentsOf: encodedBits, at: 0)
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totalBits = Array(totalBits.prefix(RCConstants.maxBitesPerSection * 3))
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//reed solomon
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return RCData(totalBits)
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}
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func decode(_ bits: [RCBit]) throws -> String {
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guard bits.contains(.one) else { return "" }
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//decode bits to indexes
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let bytes = stride(from: 0, to: bits.count, by: configuration.bitesPerSymbol).map {
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Array(bits[$0 ..< min($0 + configuration.bitesPerSymbol, bits.count)])
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}
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var indexes = bytes.map({ bits in
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return bits.reduce(0) { accumulated, current in
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accumulated << 1 | current.rawValue
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}
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})
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var sectionIndexes = indexes.chunked(into: 4)
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let startingIndex = configuration.characters.firstIndex(of: RCConstants.startingCharacter)!
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guard let firstSectionIndex = sectionIndexes.firstIndex(where: {$0.first == startingIndex}) else {
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throw RCError.decoding
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}
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let previousSections = Array(sectionIndexes.prefix(firstSectionIndex))
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sectionIndexes = Array(sectionIndexes.dropFirst(firstSectionIndex))
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sectionIndexes.append(contentsOf: previousSections)
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//reed solomon check
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let emptyIndexes = RCConstants.emptyCharacters.map({configuration.characters.firstIndex(of: $0)!})
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indexes = Array(sectionIndexes.flatMap({$0}).prefix(configuration.maxMessageCount)).filter({!emptyIndexes.contains($0)})
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guard (indexes.max() ?? 0) <= configuration.characters.count else {
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throw RCError.wrongConfiguration
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}
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return String(indexes.compactMap({configuration.characters[$0]}))
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}
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}
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