Nicer descriptions for DecodingErrors

YouDeserveNiceErrors.swift

extension DecodingError.Context {
    var pathDescription: String {
        pathDescription(for: codingPath)
    }

    func path(including final: CodingKey) -> String {
        pathDescription(for: codingPath + [final])
    }

    private func pathDescription(for path: [CodingKey]) -> String {
        guard !path.isEmpty else {
            return "root"
        }
        return path
            .enumerated()
            .map { (offset, key) -> String in
                if let idx = key.intValue {
                    return "[\(idx)]"
                } else {
                    return offset > 0 ? ".\(key.stringValue)" : key.stringValue
                }
            }
            .joined()
    }
}

public struct JSONBodyDecodingError: ReportableError {
    let statusCode: StatusCode = .badRequest

    let message: String

    init<Type>(type: Type.Type, underlyingError: DecodingError?) {
        switch underlyingError {
        case .dataCorrupted:
            self.message = "The endpoint expects a JSON body, which was not valid JSON."
        case let .keyNotFound(key, context):
            self.message = "The endpoint expects JSON with a value at the \(context.path(including: key)), but it was missing."
        case let .typeMismatch(type, context):
            var typeName = "\(type)"
            if typeName.contains("UnkeyedDecodingContainer") {
                typeName = "Array"
            } else if typeName.contains("KeyedDecodingContainer") {
                typeName = "Object"
            }
            self.message = "The endpoint expects JSON with a value of type \"\(typeName)\" at the \(context.pathDescription), but a different type was found."
        case let .valueNotFound(type, context):
            var typeName = "\(type)"
            if typeName.contains("UnkeyedDecodingContainer") {
                typeName = "Array"
            } else if typeName.contains("KeyedDecodingContainer") {
                typeName = "Object"
            }
            self.message = "The endpoint expects JSON with a value of type \"\(typeName)\" at the \(context.pathDescription), but null was found."
        default:
            self.message = "The endpoint expects JSON, which could not be decoded."
        }
    }
}