LeadKit/TINetworking/Sources/RequestPreprocessors/DefaultSecuritySchemesRequestPreprocessor.swift

//
//  Copyright (c) 2022 Touch Instinct
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//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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import TIFoundationUtils

open class DefaultEndpointSecurityPreprocessor: EndpointRequestPreprocessor {
    enum PreprocessError: Error {
        case missingSecurityScheme(String, [String: SecurityScheme])
        case unableToSatisfyRequirements(anyOfRequired: [[String]],
                                         registeredPreprocessors: [String: SecuritySchemePreprocessor])
    }

    private let openApi: OpenAPI

    private var schemePreprocessors: [String: SecuritySchemePreprocessor]

    public init(openApi: OpenAPI, schemePreprocessors: [String: SecuritySchemePreprocessor] = [:]) {
        self.openApi = openApi
        self.schemePreprocessors = schemePreprocessors
    }

    public func preprocess<B, S>(request: EndpointRequest<B, S>,
                                 completion: @escaping (Result<EndpointRequest<B, S>, Error>) -> Void) -> Cancellable {

        guard !request.security.compactMap({ $0 }).isEmpty else {
            completion(.success(request))
            return Cancellables.nonCancellable()
        }

        do {
            let endpointSchemes: [[KeyValueTuple<String, SecurityScheme>]] = try request.security.map {
                try $0.map {
                    guard let securityScheme = openApi.security[$0] else {
                        throw PreprocessError.missingSecurityScheme($0, openApi.security)
                    }

                    return ($0, securityScheme)
                }
            }

            return Self.preprocess(request: request,
                                   using: endpointSchemes,
                                   schemePreprocessors: schemePreprocessors) { [schemePreprocessors] in
                completion($0.mapError { _ in
                    PreprocessError.unableToSatisfyRequirements(anyOfRequired: request.security,
                                                                registeredPreprocessors: schemePreprocessors)
                })
            }
        } catch {
            completion(.failure(error))
            return Cancellables.nonCancellable()
        }
    }

    public func register(preprocessor: SecuritySchemePreprocessor, for scheme: String) {
        schemePreprocessors[scheme] = preprocessor
    }

    private static func preprocess<B, S, SC: Collection>(request: EndpointRequest<B, S>,
                                                         using schemes: SC,
                                                         schemePreprocessors: [String: SecuritySchemePreprocessor],
                                                         completion: @escaping (Result<EndpointRequest<B, S>, Error>) -> Void)
    -> Cancellable where SC.Element == [KeyValueTuple<String, SecurityScheme>] {

        guard let schemeGroup = schemes.first else {
            completion(.success(request))
            return Cancellables.nonCancellable()
        }

        let preprocessorsGroup: [KeyValueTuple<SecurityScheme, SecuritySchemePreprocessor>] = schemeGroup.compactMap {
            guard let preprocessor = schemePreprocessors[$0.key] else {
                return nil
            }

            return ($0.value, preprocessor)
        }

        guard preprocessorsGroup.count == schemeGroup.count else {
            // unable to satisfy group requirement
            // try next scheme group
            return preprocess(request: request,
                              using: schemes.dropFirst(),
                              schemePreprocessors: schemePreprocessors,
                              completion: completion)
        }

        return ScopeCancellable { scope in
            preprocess(request: request,
                       with: preprocessorsGroup) {

                switch $0 {
                case let .success(modifiedRequest):
                    completion(.success(modifiedRequest))

                case let .failure(error):
                    guard !schemes.isEmpty else {
                        completion(.failure(error))
                        return
                    }

                    preprocess(request: request,
                               using: schemes.dropFirst(),
                               schemePreprocessors: schemePreprocessors,
                               completion: completion)
                        .add(to: scope)
                }
            }
        }
    }

    private static func preprocess<B, S, G: Collection>(request: EndpointRequest<B, S>,
                                                        with groups: G,
                                                        completion: @escaping (Result<EndpointRequest<B, S>, Error>) -> Void)
    -> Cancellable where G.Element == KeyValueTuple<SecurityScheme, SecuritySchemePreprocessor> {

        guard let group = groups.first else {
            completion(.success(request))
            return Cancellables.nonCancellable()
        }

        return ScopeCancellable { scope in
            group.value.preprocess(request: request,
                                   using: group.key) {
                switch $0 {
                case let .success(modifiedRequest):
                    preprocess(request: modifiedRequest,
                               with: groups.dropFirst(),
                               completion: completion)
                        .add(to: scope)

                case let .failure(error):
                    completion(.failure(error))
                }
            }
        }
    }
}