EncoderConfiguration.swift

import Foundation

extension CSVEncoder {
  /// Configuration for how to write CSV data.
  @dynamicMemberLookup public struct Configuration {
    /// The underlying `CSVWriter` configurations.
    @usableFromInline private(set) var writerConfiguration: CSVWriter.Configuration
    /// The strategy to use when encoding `nil`.
    public var nilStrategy: Strategy.NilEncoding
    /// The strategy to use when encoding Boolean values.
    public var boolStrategy: Strategy.BoolEncoding
    /// The strategy to use when dealing with non-conforming numbers (e.g. `NaN`, `+Infinity`, or `-Infinity`).
    public var nonConformingFloatStrategy: Strategy.NonConformingFloat
    /// The strategy to use when encoding decimal values.
    public var decimalStrategy: Strategy.DecimalEncoding
    /// The strategy to use when encoding dates.
    public var dateStrategy: Strategy.DateEncoding
    /// The strategy to use when encoding binary data.
    public var dataStrategy: Strategy.DataEncoding
    /// Indication on how encoded CSV rows are cached and actually written to the output target.
    public var bufferingStrategy: Strategy.EncodingBuffer

    /// Designated initializer setting the default values.
    public init() {
      self.nilStrategy = .empty
      self.boolStrategy = .deferredToString
      self.writerConfiguration = CSVWriter.Configuration()
      self.nonConformingFloatStrategy = .throw
      self.decimalStrategy = .locale(nil)
      self.dateStrategy = .deferredToDate
      self.dataStrategy = .base64
      self.bufferingStrategy = .keepAll
    }
    
    /// Gives direct access to all CSV writer's configuration values.
    /// - parameter member: Writable key path for the writer's configuration values.
    public subscript<V>(dynamicMember member: WritableKeyPath<CSVWriter.Configuration,V>) -> V {
      @inlinable get { self.writerConfiguration[keyPath: member] }
      set { self.writerConfiguration[keyPath: member] = newValue }
    }
  }
}

extension Strategy {
  /// The strategy to use for encoding `nil`.
  public enum NilEncoding {
    /// `nil` is encoded as an empty string.
    case empty
    /// Encode `nil` as a custom value encoded by the given closure. If the closure fails to encode a value into the given encoder, the error will be bubled up.
    ///
    /// Custom `nil` encoding adheres to the same behavior as a custom `Encodable` type. For example:
    ///
    ///     let encoder = CSVEncoder()
    ///     encoder.nilStrategy = .custom({
    ///         var container = try $0.singleValueContainer()
    ///         try container.encode("-")
    ///     })
    ///
    /// - parameter encoding: Function receiving the encoder instance to encode `nil`.
    /// - parameter encoder: The encoder on which to encode a custom `nil` representation.
    case custom(_ encoding: (_ encoder: Encoder) throws -> Void)
  }

  ///
  public enum BoolEncoding {
    /// Defers to `String`'s initializer.
    case deferredToString
    /// Encode the `Bool` as `0` or `1`
    case numeric
    /// Encode the `Bool` as a custom value encoded by the given closure. If the closure fails to encode a value into the given encoder, the error will be bubled up.
    ///
    /// Custom `Bool` encoding adheres to the same behavior as a custom `Encodable` type. For example:
    ///
    ///     let encoder = CSVEncoder()
    ///     encoder.boolStrategy = .custom({
    ///         var container = try $1.singleValueContainer()
    ///         try container.encode($0 ? "si" : "no")
    ///     })
    ///
    /// - parameter encoding: Function receiving the necessary instances to encode a custom `Decimal` value.
    /// - parameter value: The value to be encoded.
    /// - parameter encoder: The encoder on which to generate a single value container.
    case custom(_ encoding: (_ value: Bool, _ encoder: Encoder) throws -> Void)
  }

  /// The strategy to use for encoding `Decimal` values.
  public enum DecimalEncoding {
    /// The locale used to write the number (specifically the `decimalSeparator` property).
    /// - parameter locale: The locale used to encode a `Decimal` value into a `String` value. If `nil`, the current user's locale will be used.
    case locale(_ locale: Locale? = nil)
    /// Encode the `Decimal` as a custom value encoded by the given closure. If the closure fails to encode a value into the given encoder, the error will be bubled up.
    ///
    /// Custom `Decimal` encoding adheres to the same behavior as a custom `Encodable` type. For example:
    ///
    ///     let encoder = CSVEncoder()
    ///     encoder.decimalStrategy = .custom({
    ///         var container = try $1.singleValueContainer()
    ///         try container.encode($0.description)
    ///     })
    ///
    /// - parameter encoding: Function receiving the necessary instances to encode a custom `Decimal` value.
    /// - parameter value: The value to be encoded.
    /// - parameter encoder: The encoder on which to generate a single value container.
    case custom(_ encoding: (_ value: Decimal, _ encoder: Encoder) throws -> Void)
  }

  /// The strategy to use for encoding `Date` values.
  public enum DateEncoding {
    /// Defer to `Date` for choosing an encoding.
    case deferredToDate
    /// Encode the `Date` as a UNIX timestamp (as a number).
    case secondsSince1970
    /// Encode the `Date` as UNIX millisecond timestamp (as a number).
    case millisecondsSince1970
    /// Encode the `Date` as an ISO-8601-formatted string (in RFC 3339 format).
    case iso8601
    /// Encode the `Date` as a string formatted by the given formatter.
    /// - parameter formatter: The date formatter used to encode a `Date` value into a `String`.
    case formatted(_ formatter: DateFormatter)
    /// Formats dates by calling a user-defined function. If the closure fails to encode a value into the given encoder, the error will be bubled up.
    ///
    /// Custom `Date` encoding adheres to the same behavior as a custom `Encodable` type. For example:
    ///
    ///     let encoder = CSVEncoder()
    ///     encoder.dateStrategy = .custom({
    ///         var container = try $1.singleValueContainer()
    ///         let customRepresentation: String = // transform Date $0 into a String or throw if the date cannot be converted.
    ///         try container.encode(customRepresentation)
    ///     })
    ///
    /// - parameter encoding: Function receiving the necessary instances to encode a custom `Date` value.
    /// - parameter value: The value to be encoded.
    /// - parameter encoder: The encoder on which to generate a single value container.
    case custom(_ encoding: (_ value: Date, _ encoder: Encoder) throws -> Void)
  }

  /// The strategy to use for encoding `Data` values.
  public enum DataEncoding {
    /// Defer to `Data` for choosing an encoding.
    case deferredToData
    /// Encoded the `Data` as a Base64-encoded string.
    case base64
    /// Formats data blobs by calling a user defined function. If the closure fails to encode a value into the given encoder, the encoder will encode an empty automatic container in its place.
    ///
    /// Custom `Data` encoding adheres to the same behavior as a custom `Encodable` type. For example:
    ///
    ///     let encoder = CSVEncoder()
    ///     encoder.dataStrategy = .custom({
    ///         var container = try $1.singleValueContainer()
    ///         let customRepresentation: String = // transform Data $0 into a String or throw if the data cannot be converted.
    ///         try container.encode(customRepresentation)
    ///     })
    ///
    /// - parameter encoding: Function receiving the necessary instances to encode a custom `Data` value.
    /// - parameter value: The value to be encoded.
    /// - parameter encoder: The encoder on which to generate a single value container.
    case custom(_ encoding: (_ value: Data, _ encoder: Encoder) throws -> Void)
  }

  /// Indication on how encoded CSV rows are cached and written to the output target (file, data blocb, or string).
  ///
  /// CSV encoding is an inherently sequential operation, i.e. row 2 must be encoded after row 1. On the other hand, the `Encodable` protocol allows CSV rows to be encoded in a random-order through _keyed container_.
  ///
  /// Selecting the appropriate buffering strategy lets you pick your encoding style and minimize memory usage.
  public enum EncodingBuffer {
    /// All encoded rows/fields are cached and the _writing_ only occurs at the end of the encodable process.
    ///
    /// _Keyed containers_ can be used to encode rows/fields unordered. That means, a row at position 5 may be encoded before the row at position 3. Similar behavior is supported for fields within a row.
    /// - remark: This strategy consumes the largest amount of memory from all the supported options.
    case keepAll
    /// Encoded rows may be cached, but the encoder will keep the buffer as small as possible by writing completed ordered rows.
    ///
    /// _Keyed containers_ can be used to encode rows/fields unordered. The writer will however consume rows in order.
    ///
    /// For example, an encoder starts encoding row 1 and gets all its fields. The row will get written and no cache for the row is kept anymore. Same situation occurs when the row 2 is encoded.
    /// However, the user may decide to jump to row 5 and encode it. This row will be kept in the cache till row 3 and 4 are encoded, at which time row 3, 4, 5, and any subsequent rows will be writen.
    /// - attention: If no headers are passed during configuration the encoder has no way to know when a row is completed. That is why, the `.keepAll` buffering strategy will be used instead for such a case.
    /// - remark: This strategy tries to keep the cache to a minimum, but memory usage may be big if there are holes while encoding rows/fields. Those holes are filled with empty rows/fields at the end of the encoding process.
    case assembled
    /// Only the last row (the one being written) is kept in memory. Writes are performed sequentially.
    ///
    /// _Keyed containers_ can be used, but at file-level any forward jump will imply writing empty-rows. At row-level _keyed containers_ may still be used for random-order writing.
    /// - remark: This strategy provides the smallest usage of memory from them all.
    case sequential
  }
}

// MARK: -

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

  public static var errorDomain: String {
    "Encoder"
  }

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