DecoderConfiguration.swift

import Foundation

extension CSVDecoder {
  /// Configuration for how to read CSV data.
  @dynamicMemberLookup public struct Configuration {
    /// The underlying `CSVReader` configurations.
    @usableFromInline private(set) var readerConfiguration: CSVReader.Configuration
    /// The strategy to use when decoding a `nil` representation.
    public var nilStrategy: Strategy.NilDecoding
    /// The strategy to use when decoding Boolean values.
    public var boolStrategy: Strategy.BoolDecoding
    /// The strategy to use when dealing with non-conforming numbers.
    public var nonConformingFloatStrategy: Strategy.NonConformingFloat
    /// The strategy to use when decoding decimal values.
    public var decimalStrategy: Strategy.DecimalDecoding
    /// The strategy to use when decoding dates.
    public var dateStrategy: Strategy.DateDecoding
    /// The strategy to use when decoding binary data.
    public var dataStrategy: Strategy.DataDecoding
    /// The amount of CSV rows kept in memory after decoding to allow the random-order jumping exposed by keyed containers.
    public var bufferingStrategy: Strategy.DecodingBuffer

    /// Designated initializer setting the default values.
    public init() {
      self.readerConfiguration = CSVReader.Configuration()
      self.nilStrategy = .empty
      self.boolStrategy = .insensitive
      self.nonConformingFloatStrategy = .throw
      self.decimalStrategy = .locale(nil)
      self.dateStrategy = .deferredToDate
      self.dataStrategy = .base64
      self.bufferingStrategy = .keepAll
    }

    /// Gives direct access to all CSV reader's configuration values.
    /// - parameter member: Writable key path for the reader's configuration value.
    public subscript<V>(dynamicMember member: WritableKeyPath<CSVReader.Configuration,V>) -> V {
      @inlinable get { self.readerConfiguration[keyPath: member] }
      set { self.readerConfiguration[keyPath: member] = newValue }
    }
  }
}

extension Strategy {
  /// The strategy to use for decoding `nil` representations.
  public enum NilDecoding {
    /// An empty string is considered a `nil` value.
    ///
    /// An empty string can be both the absence of characters between field delimiters and an empty escaped field (e.g. `""`).
    case empty
    /// Decodes the `nil` as a custom value decoded by the given closure.
    ///
    /// Custom `nil` decoding adheres to the same behavior as a custom `Decodable` type. For example:
    ///
    ///     let decoder = CSVDecoder()
    ///     decoder.nilStrategy = .custom({
    ///         let container = try $0.singleValueContainer()
    ///         let string = try container.decode(String.self)
    ///         return string == "-"
    ///     })
    ///
    /// - parameter decoding: Function receiving the CSV decoder used to parse a custom `nil` value.
    /// - parameter decoder: The decoder on which to fetch a single value container to obtain the underlying `String` value.
    /// - returns: Boolean indicating whether the encountered value was a `nil` representation. If the value is not supported, return `false`.
    case custom(_ decoding: (_ decoder: Decoder) -> Bool)
  }

  /// The strategy to use for decoding `Bool` values.
  public enum BoolDecoding {
    /// Defer to `Bool`'s `LosslessStringConvertible` initializer.
    ///
    /// For a value to be considered `true` or `false`, it must be a string with the exact value of `"true"` or `"false"`.
    case deferredToBool
    /// Decodes a Boolean from an underlying string value by transforming `true`/`false` and `yes`/`no` disregarding case sensitivity.
    ///
    /// The value: `True`, `TRUE`, `TruE` or `YES`are accepted.
    case insensitive
    /// Decodes the `Bool` from an underlying `0` or `1`
    case numeric
    /// Decodes the `Bool` as a custom value decoded by the given closure. If the closure fails to decode a value from the given decoder, the error will be bubled up.
    ///
    /// Custom `Bool` decoding adheres to the same behavior as a custom `Decodable` type. For example:
    ///
    ///     let decoder = CSVDecoder()
    ///     decoder.boolStrategy = .custom({
    ///         let container = try $0.singleValueContainer()
    ///         switch try container.decode(String.self) {
    ///         case "si": return true
    ///         case "no": return false
    ///         default: throw CSVError<CSVDecoder>(...)
    ///         }
    ///     })
    ///
    /// - parameter decoding: Function receiving the CSV decoder used to parse a custom `Bool` value.
    /// - parameter decoder: The decoder on which to fetch a single value container to obtain the underlying `String` value.
    /// - returns: Boolean value decoded from the underlying storage.
    case custom(_ decoding: (_ decoder: Decoder) throws -> Bool)
  }

  /// The strategy to use for decoding `Decimal` values.
  public enum DecimalDecoding {
    /// The locale used to interpret the number (specifically `decimalSeparator`).
    case locale(Locale? = nil)
    /// Decode the `Decimal` as a custom value decoded by the given closure. If the closure fails to decode a value from the given decoder, the error will be bubled up.
    ///
    /// Custom `Decimal` decoding adheres to the same behavior as a custom `Decodable` type. For example:
    ///
    ///     let decoder = CSVDecoder()
    ///     decoder.decimalStrategy = .custom({
    ///         let value = try Float(from: decoder)
    ///         return Decimal(value)
    ///     })
    ///
    /// - parameter decoding: Function receiving the CSV decoder used to parse a custom `Decimal` value.
    /// - parameter decoder: The decoder on which to fetch a single value container to obtain the underlying `String` value.
    /// - returns: `Decimal` value decoded from the underlying storage.
    case custom(_ decoding: (_ decoder: Decoder) throws -> Decimal)
  }

  /// The strategy to use for decoding `Date` values.
  public enum DateDecoding {
    /// Defer to `Date` for decoding.
    case deferredToDate
    /// Decode the `Date` as a UNIX timestamp from a number.
    case secondsSince1970
    /// Decode the `Date` as UNIX millisecond timestamp from a number.
    case millisecondsSince1970
    /// Decode the `Date` as an ISO-8601-formatted string (in RFC 3339 format).
    case iso8601
    /// Decode the `Date` as a string parsed by the given formatter.
    case formatted(DateFormatter)
    /// Decode the `Date` as a custom value decoded by the given closure. If the closure fails to decode a value from the given decoder, the error will be bubled up.
    ///
    /// Custom `Date` decoding adheres to the same behavior as a custom `Decodable` type. For example:
    ///
    ///     let decoder = CSVDecoder()
    ///     decoder.dateStrategy = .custom({
    ///         let container = try $0.singleValueContainer()
    ///         let string = try container.decode(String.self)
    ///         // Now returns the date represented by the custom string or throw an error if the string cannot be converted to a date.
    ///     })
    ///
    /// - parameter decoding: Function receiving the CSV decoder used to parse a custom `Date` value.
    /// - parameter decoder: The decoder on which to fetch a single value container to obtain the underlying `String` value.
    /// - returns: `Date` value decoded from the underlying storage.
    case custom(_ decoding: (_ decoder: Decoder) throws -> Date)
  }

  /// The strategy to use for decoding `Data` values.
  public enum DataDecoding {
    /// Defer to `Data` for decoding.
    case deferredToData
    /// Decode the `Data` from a Base64-encoded string.
    case base64
    /// Decode the `Data` as a custom value decoded by the given closure. If the closure fails to decode a value from the given decoder, the error will be bubled up.
    ///
    /// Custom `Data` decoding adheres to the same behavior as a custom `Decodable` type. For example:
    ///
    ///     let decoder = CSVDecoder()
    ///     decoder.dataStrategy = .custom({
    ///         let container = try $0.singleValueContainer()
    ///         let string = try container.decode(String.self)
    ///         // Now returns the data represented by the custom string or throw an error if the string cannot be converted to a data.
    ///     })
    ///
    /// - parameter decoding: Function receiving the CSV decoder used to parse a custom `Data` value.
    /// - parameter decoder: The decoder on which to fetch a single value container to obtain the underlying `String` value.
    /// - returns: `Data` value decoded from the underlying storage.
    case custom(_ decoding: (_ decoder: Decoder) throws -> Data)
  }

  /// Indication of how many rows are cached for reuse by the decoder.
  ///
  /// CSV decoding is an inherently sequential operation; i.e. row 2 must be decoded after row 1. This due to the string encoding, the field/row delimiter usage, and by not setting the underlying row width.
  /// On the other hand, the `Decodable` protocol allows CSV rows to be decoded in random-order through the keyed containers. For example, a user can ask for a row at position 24 and then ask for the CSV row at index 3.
  ///
  /// A buffer is used to marry the sequential needs of the CSV decoder and `Decodable`'s _random-access_ nature. This buffer stores all decoded CSV rows (starts with none and gets filled as more rows are being decoded).
  /// The `DecodingBuffer` strategy gives you the option to control the buffer's memory usage and whether rows are being discarded after being decoded.
  public enum DecodingBuffer {
    /// All decoded CSV rows are cached.
    /// Forward/Backwards decoding jumps are allowed. A row that has been previously decoded can be decoded again.
    /// - remark: This strategy consumes the largest amount of memory from all the supported options.
    case keepAll
    //        /// Only CSV fields that have been decoded but not requested by the user are being kept in memory.
    //        ///
    //        /// _Keyed containers_ can be used to read rows/fields unordered. However, previously requested rows cannot be requested again or an error will be thrown.
    //        /// - remark: This strategy tries to keep the cache to a minimum, but memory usage may be big if the user doesn't request intermediate rows.
    //        case unrequested
    /// No rows are kept in memory (except for the CSV row being decoded at the moment)
    ///
    /// _Keyed containers_ can be used, but at a file-level any forward jump will discard the in-between rows. At a row-level _keyed containers_ may still be used for random-order reading.
    /// - remark: This strategy provides the smallest usage of memory from them all.
    case sequential
  }
}

// MARK: -

extension CSVDecoder: Failable {
  /// The type of error raised by the CSV decoder.
  public enum Error: Int {
    /// Some of the configuration values provided are invalid.
    case invalidConfiguration = 1
    /// The decoding coding path is invalid.
    case invalidPath = 2
    /// An error occurred on the encoder buffer.
    case bufferFailure = 4
  }

  public static var errorDomain: String {
    "Decoder"
  }

  public static func errorDescription(for failure: Error) -> String {
    switch failure {
    case .invalidConfiguration: return "Invalid configuration"
    case .invalidPath: return "Invalid path"
    case .bufferFailure: return "Invalid buffer state"
    }
  }
}