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assign1.md

+# Assignment 1: Swift and Extensions   
+**Due: Feb 16, 2020, 11:59:59 pm, v0.3**
+
+
+## Goals
+The primary goal of this project is to to familiarize yourself with the environment and
+the language. All in this class will be written in Swift 5.1, using XCode 11 as your
+friendly development environment. *Errors resulting from development in different
+environments still result in loss of points.*  More importantly, `SwiftUI` will not work
+on anything before Mojave.
+
+Specifically, you will do the following:
+1. create a standard single-view app, "*assign1*" that does nothing (other than
+compile and show a blank screen), but does include a model of our app: "Triples".
+
+In the process you will obviously learn quite a bit about the `XCode` environment, about
+unit tests in the context of Swift applications, and about defining type extensions.
+
+## Using git
+We will use [*git*](https://git-scm.com/doc) ([cheat sheet](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=2ahUKEwi_uaemsqXgAhVmzlkKHc-HCUkQFjABegQIAhAC&url=https%3A%2F%2Feducation.github.com%2Fgit-cheat-sheet-education.pdf&usg=AOvVaw2D3W2R0fwoOBi8YrhZYLFJ)) both to distribute starting files, for those projects that
+have them (not `assign1`), and to submit the work that you create. Each of you will have had a single
+gitlab repository create, e.g. `ios436spring2020/cmsc436-<dirid>` (but use your
+directoryid, which is NOT a number). Clone this repository as follows:
+1. log into gitlab and verify that you have the above repository
+1. create and upload a public key as described below in "Upload Public Key". This will allow you to
+   access gitlab via `ssh`, which is much less kludgy/buggy than https.
+1. In your terminal window, clone via `git clone git@gitlab.cs.umd.edu:ios436spring2020/cmsc436-<dirid>` (again, use *your*
+dirid). **cd** into this directory.
+    - **Note** that if your repository is not found, or you don't have
+        permissions, it's because our script could not finish setting the
+        repository up until you had logged into gitlab.cs.umd.edu at least
+        once. Please do this at once, and then try again the next day. If it
+        still fail, email me directly w/ subject "436 repository".
+2. Establish a new *upstream remote*:  `git remote add upstream
+   git@gitlab.cs.umd.edu:keleher/cmsc436spring2020-starter.git` This remote
+   will be where you *pull* startup files from when each new project, or iteration of a
+   project, is made available (`git pull upstream master'). **You will not
+   need the upstream remote for this project, but set it up anyway.**
+3. Verify your setup by executing `git remote -v`. You should see something
+like:
+```
+origin  git@gitlab.cs.umd.edu:ios436spring2020/cmsc436-<dirid>.git (fetch)
+origin  git@gitlab.cs.umd.edu:ios436spring2020/cmsc436-<dirid>.git (push)
+upstream    git@gitlab.cs.umd.edu:keleher/cmsc436spring2020-starter.git (fetch)
+upstream    git@gitlab.cs.umd.edu:keleher/cmsc436spring2020-starter.git (push)
+```
+
+Uploading your completed work is a two-step process: `git commit -m "a
+label"`, followed by `git push origin master`. Verify by logging into the
+gitlab website and making sure your new changes are there.
+
+It's a good idea to
+commit intermediate versions of your code many times during the development process.
+
+
+### Upload Public Key
+If you don't already have an RSA public key-pair, do the following:
+```
+    > cd
+    > ssh-keygen -t rsa
+      (hit return in response to all prompts)
+```
+Upload the contents of `~/.ssh/id_rsa.pub` to gitlab by logging in,
+selecting 'Settings' from the menu in the upper right, and then selecting 'ssh
+keys' from the left of the page. Add your key by pasting into the textbox,
+giving your machine's name as a title, and clicking 'Add Key'.
+
+    
+# Building An App
+We are going to build an apple called `Triples` in two or three stages. In the first
+stage, we are just going to design and implement the model, and unit-test it.
+
+As we did in class, you will create a new single-view iOS app:
+- Create a new project in XCode and save to your `cmsc436-<dirid>` directory. 
+- When creating the project:
+  - also call it `assign1`
+  - **check "unit tests"**, uncheck `git`, uncheck UI tests
+  - select a "single-view" iOS app even though we will not have any graphical characteristics
+- Note that new files must be explicitly added to git via `git add <file>...`.
+
+Create a new file `model.swift` in the app by selecting "New File" from the, and then
+selecting the Swift file icon in the dialog, and name it `model.swift`. 
+`model.swift` will contain the "model" known from the model-view-controller (MVC) paradigm.
+
+## App Logic
+Our game action will be similar to the app `Threes` app on the apple and android app
+stores. A portion of the game play is shown here:
+
+![Similar gameplay](https://sedna.cs.umd.edu/clips/assign1DemoThrees.mp4)
+
+
+## Your Tasks
+Your tasks are to implement the *model* behind the gameplay shown in the clip. Specifically, you will
+implement the "collapse", which given a swipe in a direction collapses each row or column
+parallel to the swipe by eliminating a blank, combining a 1 and a 2, or combining two
+consecutive tiles w/ the same value, 3 or higher.  For more specifics, see the tests
+described below.
+
+## The `Triples` Class
+
+In the file `model.swift` you need to define a new class `Triples`,
+which implements the methods discussed below. Most importantly,
+`Triples` will need the following definitions:
+```
+     var board: [[Int]]
+
+     func newgame() {}                   // re-inits 'board', and any other state you define
+     func rotate() {}                    // rotate a square 2D Int array clockwise
+     func shift() {}                     // collapse to the left
+     func collapse(dir: Direction))      // collapse in specified direction using shift() and rotate()
+```
+Note that methods merely modify the `board` property. We are not taking any
+actions based on the board, or doing any GUI work at all.
+`Direction` is an `enum` that you will define for the four directions referenced below.
+     
+Outside `Triples`, you will need to build two other functions, one of which
+should be called in your `rotate()` method (ideally the generic, but the
+explicit `Int` version is fine if you don't get the generic working).
+The first is:    
+```
+     // class-less function that will return of any square 2D Int array rotated clockwise
+     public func rotate2Dints(input: [[Int]]) -> [[Int]] {}  
+```
+You should also build `rotate2D`, which is a *generic* version of the above.
+
+### Unit Tests
+Copy the following unit tests verbatim into your file
+`assign1Ttests.swift`. Do no change anything, as we will use the exact tests
+below to test your definitions in `model.swift`. 
+```
+    func testSetup() {
+        let game = Triples()
+        game.newgame()
+        
+        XCTAssertTrue((game.board.count == 4) && (game.board[3].count == 4))
+    }
+```
+Tests to ensure your app defines a 4x4 2D array of `Int`s.
+
+### Rotate
+Build a func `rotate2DInts` that will take any 2D Int array and rotate it once
+clockwise. Your func may assume that the array is square.
+```
+    func testRotate1() {
+        var board = [[0,3,3,3],[1,2,3,3],[0,2,1,3],[3,3,6,6]]
+        board = rotate2DInts(input: board)
+        XCTAssertTrue(board == [[3,0,1,0],[3,2,2,3],[6,1,3,3],[6,3,3,3]])
+    }
+```
+
+### Generic Rotate
+Same test using a generic func you must write called `rotate2D`, and which will work on
+any type of array.
+```
+    func testRotate1() {
+        var board = [[0,3,3,3],[1,2,3,3],[0,2,1,3],[3,3,6,6]]
+        board = rotate2D(input: board)
+        XCTAssertTrue(board == [[3,0,1,0],[3,2,2,3],[6,1,3,3],[6,3,3,3]])
+    }
+```
+
+Try again with strings.
+```
+    func testRotate3() {
+        var board = [["0","3","3","3"],["1","2","3","3"],["0","2","1","3"],["3","3","6","6"]]
+        board = rotate2D(input: board)
+        XCTAssertTrue(board == [["3","0","1","0"],["3","2","2","3"],["6","1","3","3"],["6","3","3","3"]])
+    }
+```
+
+### Collapsing
+Write a `shift()` method that collapses each row to the left (as if w/ a left swipe in the
+clip). 
+```
+    func testShift() {
+        let game = Triples()
+        game.board = [[0,3,3,3],[1,2,3,3],[0,2,1,3],[3,3,6,6]]
+        game.shift()
+        XCTAssertTrue(game.board == [[3,3,3,0],[3,3,3,0],[2,1,3,0],[6,6,6,0]])
+    }
+```
+
+Write and test a `collapse()` method will take a `Direction` enumeration collapse in the
+direction specified. Internally, you should build `collapse` using `shift()` and `rotate()`.
+```
+    func testLeft() {
+        let game = Triples()
+        game.board = [[0,3,3,3],[1,2,3,3],[0,2,1,3],[3,3,6,6]]
+        game.collapse(dir: .left)
+        XCTAssertTrue(game.board == [[3,3,3,0],[3,3,3,0],[2,1,3,0],[6,6,6,0]])
+    }
+
+    func testRight() {
+        let game = Triples()
+        game.board = [[0,3,3,3],[1,2,3,3],[0,2,1,3],[3,3,6,6]]
+        game.collapse(dir: .right)
+        XCTAssertTrue(game.board == [[0,0,3,6],[0,1,2,6],[0,0,3,3],[0,3,3,12]])
+
+    }
+
+    func testDown() {
+        let game = Triples()
+        game.board = [[0,3,3,3],[1,2,3,3],[0,2,1,3],[3,3,6,6]]
+        game.collapse(dir: .down)
+        XCTAssertTrue(game.board == [[0,3,0,0],[0,2,6,3],[1,2,1,6],[3,3,6,6]])
+    }
+
+    func testUp() {
+        let game = Triples()
+        game.board = [[0,3,3,3],[1,2,3,3],[0,2,1,3],[3,3,6,6]]
+        game.collapse(dir: .up)
+        XCTAssertTrue(game.board == [[1,3,6,6],[0,2,1,3],[3,2,6,6],[0,3,0,0]])
+    }
+```
+
+# Submit, and Grading
+Submit by pushing your project to your 436 repository. **Check this** by visiting your
+repository in a web browser at `https://gitlab.cs.umd.edu/ios436spring2020/cmsc436-<dirid>`
+
+Each of the nine tests is worth 1 point. There is no partial credit.
+
+
+# Notes
+- Remember, frequently save your work on gitlab through the folloing. This is exactly the same sequence you will use with the final submit. We will download
+  your repository from gitlab directly.
+```
+    git add assign1
+    git commit -m "a message"
+    git push origin master
+```
+