A matcher to spy

CallRecordMatcher.swift

//
//  CallRecordMatcher.swift
//  Verse
//
//  Created by Alex Manzella on 13/01/17.
//  Copyright © 2017 Verse Technologies, Inc. All rights reserved.
//

import Foundation
import Nimble

protocol Spy: class {
    var recordedFunctions: [String] { get set }
}

extension Spy {
    func record(function: String = #function) {
        recordedFunctions.append(function)
    }
}

func call(_ function: String) -> CallRecordMatcher {
    return CallRecordMatcher(function: function)
}

struct CallRecordMatcher: Matcher {

    enum Failure: Error {
        case invalidSpy
    }

    typealias ValueType = Spy

    let function: String

    private func composeFailureMessage(_ message: FailureMessage, negated: Bool) {
        message.expected = "Expected \(function)"
        let negation = negated ? "not" : ""
        message.to = "to \(negation) be called"
        message.postfixMessage = ""
        message.actualValue = nil
    }

    private func didCallFunction(_ actualExpression: Expression<Spy>) throws -> Bool {
        guard let spy = try actualExpression.evaluate() else {
            throw Failure.invalidSpy
        }

        return spy.recordedFunctions.contains(function)
    }

    func matches(_ actualExpression: Expression<Spy>,
                 failureMessage: FailureMessage) throws -> Bool {
        composeFailureMessage(failureMessage, negated: false)
        return try didCallFunction(actualExpression)
    }

    func doesNotMatch(_ actualExpression: Expression<Spy>,
                      failureMessage: FailureMessage) throws -> Bool {
        composeFailureMessage(failureMessage, negated: true)
        return try !didCallFunction(actualExpression)
    }
}