Add meetup exercise

config.json

@@ -571,6 +571,14 @@
         "prerequisites": [],
         "difficulty": 4
       },
+      {
+        "slug": "meetup",
+        "name": "Meetup",
+        "uuid": "0ef0cb6e-fe81-4988-bc13-26caac30c4d8",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
       {
         "slug": "perfect-numbers",
         "name": "Perfect Numbers",

exercises/practice/meetup/.docs/instructions.md

@@ -0,0 +1,34 @@
+# Instructions
+
+Your task is to find the exact date of a meetup, given a month, year, weekday and week.
+
+There are five week values to consider: `first`, `second`, `third`, `fourth`, `last`, `teenth`.
+
+For example, you might be asked to find the date for the meetup on the first Monday in January 2018 (January 1, 2018).
+
+Similarly, you might be asked to find:
+
+- the third Tuesday of August 2019 (August 20, 2019)
+- the teenth Wednesday of May 2020 (May 13, 2020)
+- the fourth Sunday of July 2021 (July 25, 2021)
+- the last Thursday of November 2022 (November 24, 2022)
+- the teenth Saturday of August 1953 (August 15, 1953)
+
+## Teenth
+
+The teenth week refers to the seven days in a month that end in '-teenth' (13th, 14th, 15th, 16th, 17th, 18th and 19th).
+
+If asked to find the teenth Saturday of August, 1953, we check its calendar:
+
+```plaintext
+    August 1953
+Su Mo Tu We Th Fr Sa
+                   1
+ 2  3  4  5  6  7  8
+ 9 10 11 12 13 14 15
+16 17 18 19 20 21 22
+23 24 25 26 27 28 29
+30 31
+```
+
+From this we find that the teenth Saturday is August 15, 1953.

exercises/practice/meetup/.docs/introduction.md

@@ -0,0 +1,29 @@
+# Introduction
+
+Every month, your partner meets up with their best friend.
+Both of them have very busy schedules, making it challenging to find a suitable date!
+Given your own busy schedule, your partner always double-checks potential meetup dates with you:
+
+- "Can I meet up on the first Friday of next month?"
+- "What about the third Wednesday?"
+- "Maybe the last Sunday?"
+
+In this month's call, your partner asked you this question:
+
+- "I'd like to meet up on the teenth Thursday; is that okay?"
+
+Confused, you ask what a "teenth" day is.
+Your partner explains that a teenth day, a concept they made up, refers to the days in a month that end in '-teenth':
+
+- 13th (thirteenth)
+- 14th (fourteenth)
+- 15th (fifteenth)
+- 16th (sixteenth)
+- 17th (seventeenth)
+- 18th (eighteenth)
+- 19th (nineteenth)
+
+As there are also seven weekdays, it is guaranteed that each day of the week has _exactly one_ teenth day each month.
+
+Now that you understand the concept of a teenth day, you check your calendar.
+You don't have anything planned on the teenth Thursday, so you happily confirm the date with your partner.

exercises/practice/meetup/.meta/Example.roc

@@ -0,0 +1,48 @@
+module [meetup]
+
+import isodate.Date
+
+Week : [First, Second, Third, Fourth, Last, Teenth]
+DayOfWeek : [Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday]
+
+meetup : { year : I64, month : U8, week : Week, dayOfWeek : DayOfWeek } -> Result Str [InvalidMonth, InvalidYear]
+meetup = \{ year, month, week, dayOfWeek } ->
+    if month == 0 || month > 12 then
+        Err InvalidMonth
+        else
+
+    firstDay = Date.fromYmd year month 1
+    firstWeekday = Date.weekday firstDay.year firstDay.month firstDay.dayOfMonth
+    firstTime = (7 + dayOfWeekNumber dayOfWeek - firstWeekday) % 7 + 1
+    dayOfMonth =
+        when week is
+            First -> firstTime
+            Second -> firstTime + 7
+            Third -> firstTime + 14
+            Fourth -> firstTime + 21
+            Last ->
+                if firstTime + 28 > Date.daysInMonth year month then
+                    firstTime + 21
+                else
+                    firstTime + 28
+
+            Teenth ->
+                if firstTime == 6 then 13 else firstTime + 14
+    Ok "$(year |> padNumber 4)-$(month |> padNumber 2)-$(dayOfMonth |> padNumber 2)"
+
+padNumber : Num *, U64 -> Str
+padNumber = \number, pad ->
+    numberStr = number |> Num.toStr
+    numZeros = pad |> Num.subSaturated (numberStr |> Str.toUtf8 |> List.len)
+    "$(Str.repeat "0" numZeros)$(numberStr)"
+
+dayOfWeekNumber : DayOfWeek -> U8
+dayOfWeekNumber = \dayOfWeek ->
+    when dayOfWeek is
+        Sunday -> 0
+        Monday -> 1
+        Tuesday -> 2
+        Wednesday -> 3
+        Thursday -> 4
+        Friday -> 5
+        Saturday -> 6

exercises/practice/meetup/.meta/config.json

@@ -0,0 +1,18 @@
+{
+  "authors": [
+    "ageron"
+  ],
+  "files": {
+    "solution": [
+      "Meetup.roc"
+    ],
+    "test": [
+      "meetup-test.roc"
+    ],
+    "example": [
+      ".meta/Example.roc"
+    ]
+  },
+  "blurb": "Calculate the date of meetups.",
+  "source": "Jeremy Hinegardner mentioned a Boulder meetup that happens on the Wednesteenth of every month"
+}

exercises/practice/meetup/.meta/template.j2

@@ -0,0 +1,19 @@
+{%- import "generator_macros.j2" as macros with context -%}
+{{ macros.canonical_ref() }}
+{{ macros.header(imports=["isodate"]) }}
+
+import {{ exercise | to_pascal }} exposing [{{ cases[0]["property"] | to_camel }}]
+
+{% for case in cases -%}
+# {{ case["description"] }}
+expect
+    result = {{ case["property"] | to_camel }} {
+        year: {{ case["input"]["year"] | to_roc }},
+        month: {{ case["input"]["month"] | to_roc }},
+        week: {{ case["input"]["week"] | to_pascal }},
+        dayOfWeek: {{ case["input"]["dayofweek"] | to_pascal }},
+    }
+    expected = Ok {{ case["expected"] | to_roc }}
+    result == expected
+
+{% endfor %}