Add practice exercise secret-handshake (#697)

config.json

@@ -1251,6 +1251,20 @@
         ],
         "difficulty": 5
       },
+      {
+        "slug": "secret-handshake",
+        "name": "Secret Handshake",
+        "uuid": "6c7a96ec-0bfb-4284-bd9f-2aa6989c3bb5",
+        "practices": [],
+        "prerequisites": [
+          "custom-types",
+          "pattern-matching",
+          "maybe",
+          "lists",
+          "booleans"
+        ],
+        "difficulty": 4
+      },
       {
         "slug": "sieve",
         "name": "Sieve",

exercises/practice/secret-handshake/.docs/instructions.md

@@ -0,0 +1,48 @@
+# Instructions
+
+Your task is to convert a number between 1 and 31 to a sequence of actions in the secret handshake.
+
+The sequence of actions is chosen by looking at the rightmost five digits of the number once it's been converted to binary.
+Start at the right-most digit and move left.
+
+The actions for each number place are:
+
+```plaintext
+00001 = wink
+00010 = double blink
+00100 = close your eyes
+01000 = jump
+10000 = Reverse the order of the operations in the secret handshake.
+```
+
+Let's use the number `9` as an example:
+
+- 9 in binary is `1001`.
+- The digit that is farthest to the right is 1, so the first action is `wink`.
+- Going left, the next digit is 0, so there is no double-blink.
+- Going left again, the next digit is 0, so you leave your eyes open.
+- Going left again, the next digit is 1, so you jump.
+
+That was the last digit, so the final code is:
+
+```plaintext
+wink, jump
+```
+
+Given the number 26, which is `11010` in binary, we get the following actions:
+
+- double blink
+- jump
+- reverse actions
+
+The secret handshake for 26 is therefore:
+
+```plaintext
+jump, double blink
+```
+
+~~~~exercism/note
+If you aren't sure what binary is or how it works, check out [this binary tutorial][intro-to-binary].
+
+[intro-to-binary]: https://medium.com/basecs/bits-bytes-building-with-binary-13cb4289aafa
+~~~~

exercises/practice/secret-handshake/.docs/introduction.md

@@ -0,0 +1,7 @@
+# Introduction
+
+You are starting a secret coding club with some friends and friends-of-friends.
+Not everyone knows each other, so you and your friends have decided to create a secret handshake that you can use to recognize that someone is a member.
+You don't want anyone who isn't in the know to be able to crack the code.
+
+You've designed the code so that one person says a number between 1 and 31, and the other person turns it into a series of actions.

exercises/practice/secret-handshake/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "jiegillet"
+  ],
+  "files": {
+    "solution": [
+      "src/SecretHandshake.elm"
+    ],
+    "test": [
+      "tests/Tests.elm"
+    ],
+    "example": [
+      ".meta/src/SecretHandshake.example.elm"
+    ]
+  },
+  "blurb": "Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.",
+  "source": "Bert, in Mary Poppins",
+  "source_url": "https://www.imdb.com/title/tt0058331/quotes/?item=qt0437047"
+}

exercises/practice/secret-handshake/.meta/src/SecretHandshake.example.elm

@@ -0,0 +1,55 @@
+module SecretHandshake exposing (Command(..), commands)
+
+import Bitwise
+
+
+type Command
+    = Wink
+    | DoubleBlink
+    | CloseYourEyes
+    | Jump
+    | Reverse
+
+
+commandToCode : Command -> Int
+commandToCode command =
+    case command of
+        Wink ->
+            1
+
+        DoubleBlink ->
+            2
+
+        CloseYourEyes ->
+            4
+
+        Jump ->
+            8
+
+        Reverse ->
+            16
+
+
+commandApplies : Int -> Command -> Bool
+commandApplies number command =
+    Bitwise.and number (commandToCode command) > 0
+
+
+commands : Int -> List Command
+commands number =
+    let
+        maybeAction command =
+            if commandApplies number command then
+                Just command
+
+            else
+                Nothing
+
+        actions =
+            List.filterMap maybeAction [ Wink, DoubleBlink, CloseYourEyes, Jump ]
+    in
+    if commandApplies number Reverse then
+        List.reverse actions
+
+    else
+        actions

exercises/practice/secret-handshake/.meta/tests.toml

@@ -0,0 +1,43 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[b8496fbd-6778-468c-8054-648d03c4bb23]
+description = "wink for 1"
+
+[83ec6c58-81a9-4fd1-bfaf-0160514fc0e3]
+description = "double blink for 10"
+
+[0e20e466-3519-4134-8082-5639d85fef71]
+description = "close your eyes for 100"
+
+[b339ddbb-88b7-4b7d-9b19-4134030d9ac0]
+description = "jump for 1000"
+
+[40499fb4-e60c-43d7-8b98-0de3ca44e0eb]
+description = "combine two actions"
+
+[9730cdd5-ef27-494b-afd3-5c91ad6c3d9d]
+description = "reverse two actions"
+
+[0b828205-51ca-45cd-90d5-f2506013f25f]
+description = "reversing one action gives the same action"
+
+[9949e2ac-6c9c-4330-b685-2089ab28b05f]
+description = "reversing no actions still gives no actions"
+
+[23fdca98-676b-4848-970d-cfed7be39f81]
+description = "all possible actions"
+
+[ae8fe006-d910-4d6f-be00-54b7c3799e79]
+description = "reverse all possible actions"
+
+[3d36da37-b31f-4cdb-a396-d93a2ee1c4a5]
+description = "do nothing for zero"

exercises/practice/secret-handshake/elm.json

@@ -0,0 +1,29 @@
+{
+    "type": "application",
+    "source-directories": [
+        "src"
+    ],
+    "elm-version": "0.19.1",
+    "dependencies": {
+        "direct": {
+            "elm/core": "1.0.5",
+            "elm/json": "1.1.3",
+            "elm/parser": "1.1.0",
+            "elm/random": "1.0.0",
+            "elm/regex": "1.0.0",
+            "elm/time": "1.0.0"
+        },
+        "indirect": {}
+    },
+    "test-dependencies": {
+        "direct": {
+            "elm-explorations/test": "2.1.0",
+            "rtfeldman/elm-iso8601-date-strings": "1.1.4"
+        },
+        "indirect": {
+            "elm/bytes": "1.0.8",
+            "elm/html": "1.0.0",
+            "elm/virtual-dom": "1.0.3"
+        }
+    }
+}

exercises/practice/secret-handshake/src/SecretHandshake.elm

@@ -0,0 +1,13 @@
+module SecretHandshake exposing (Command(..), commands)
+
+
+type Command
+    = Wink
+    | DoubleBlink
+    | CloseYourEyes
+    | Jump
+
+
+commands : Int -> List Command
+commands number =
+    Debug.todo "Please implement commands"

exercises/practice/secret-handshake/tests/Tests.elm

@@ -0,0 +1,66 @@
+module Tests exposing (tests)
+
+import Expect
+import SecretHandshake exposing (Command(..))
+import Test exposing (Test, describe, skip, test)
+
+
+tests : Test
+tests =
+    describe "SecretHandshake"
+        [ -- skip <|
+          test "wink for 1" <|
+            \() ->
+                SecretHandshake.commands 1
+                    |> Expect.equal [ Wink ]
+        , skip <|
+            test "double blink for 10" <|
+                \() ->
+                    SecretHandshake.commands 2
+                        |> Expect.equal [ DoubleBlink ]
+        , skip <|
+            test "close your eyes for 100" <|
+                \() ->
+                    SecretHandshake.commands 4
+                        |> Expect.equal [ CloseYourEyes ]
+        , skip <|
+            test "jump for 1000" <|
+                \() ->
+                    SecretHandshake.commands 8
+                        |> Expect.equal [ Jump ]
+        , skip <|
+            test "combine two actions" <|
+                \() ->
+                    SecretHandshake.commands 3
+                        |> Expect.equal [ Wink, DoubleBlink ]
+        , skip <|
+            test "reverse two actions" <|
+                \() ->
+                    SecretHandshake.commands 19
+                        |> Expect.equal [ DoubleBlink, Wink ]
+        , skip <|
+            test "reversing one action gives the same action" <|
+                \() ->
+                    SecretHandshake.commands 24
+                        |> Expect.equal [ Jump ]
+        , skip <|
+            test "reversing no actions still gives no actions" <|
+                \() ->
+                    SecretHandshake.commands 16
+                        |> Expect.equal []
+        , skip <|
+            test "all possible actions" <|
+                \() ->
+                    SecretHandshake.commands 15
+                        |> Expect.equal [ Wink, DoubleBlink, CloseYourEyes, Jump ]
+        , skip <|
+            test "reverse all possible actions" <|
+                \() ->
+                    SecretHandshake.commands 31
+                        |> Expect.equal [ Jump, CloseYourEyes, DoubleBlink, Wink ]
+        , skip <|
+            test "do nothing for zero" <|
+                \() ->
+                    SecretHandshake.commands 0
+                        |> Expect.equal []
+        ]