Add meetup (#118)

* Add meetup

* instructions append

* remove unused code from example

Author: glennj

config.json

@@ -618,6 +618,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "meetup",
+        "name": "Meetup",
+        "uuid": "cd3c3db9-a654-4137-9135-8971b07770b7",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "pig-latin",
         "name": "Pig Latin",

exercises/practice/meetup/.busted

@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}

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

@@ -0,0 +1,15 @@
+# dummy
+
+## MoonScript-specific instructions
+
+You'll need to use Lua's builtin [`os.date`][lua-os-date] and [`os.time`][lua-os-time] functions in this exercise.
+
+- `os.time(tbl)` converts a table containing a "date time specification" into an integer value.
+  The argument is a table containing keys "year", "month", and "day"; and optionally "hour", "min", "sec", and "isdst".
+
+- `os.date(format, time)` converts an integer time value into a formatted string.
+  The format string is described in your [`strftime(3)`][strftime] man page.
+
+[lua-os-date]: https://www.lua.org/manual/5.4/manual.html#pdf-os.date
+[lua-os-time]: https://www.lua.org/manual/5.4/manual.html#pdf-os.time
+[strftime]: https://manpage.me/index.cgi?apropos=0&q=strftime&sektion=3&manpath=Debian+8.1.0&arch=default&format=html

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 six 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/config.json

@@ -0,0 +1,18 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "meetup.moon"
+    ],
+    "test": [
+      "meetup_spec.moon"
+    ],
+    "example": [
+      ".meta/example.moon"
+    ]
+  },
+  "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/example.moon

@@ -0,0 +1,28 @@
+is_teenth = (time) ->
+  day = tonumber os.date '%d', time
+  13 <= day and day <= 19
+
+{
+  meetup: (input) ->
+    {:year, :month, :week, :dayofweek} = input
+
+    days = {}
+    t = {:year, :month, day: 0}
+    while true
+      t.day += 1
+      time = os.time t
+      if month != tonumber os.date '%m', time
+        break
+      if dayofweek == os.date '%A', time
+        table.insert days, time
+
+    idx = switch week
+      when 'first'  then 1
+      when 'second' then 2
+      when 'third'  then 3
+      when 'fourth' then 4
+      when 'last'   then #days
+      when 'teenth' then is_teenth(days[2]) and 2 or 3
+
+    os.date '%Y-%m-%d', days[idx]
+}

exercises/practice/meetup/.meta/spec_generator.moon

@@ -0,0 +1,15 @@
+table.tostring = (t) ->
+  s = [string.format '%s: %q', k, v for k, v in pairs t]
+  "{#{table.concat s, ', '}}"
+
+{
+  module_imports: {'meetup'},
+
+  generate_test: (case, level) ->
+    lines = {
+      "result = meetup #{table.tostring case.input}"
+      "expected = #{quote case.expected}"
+      "assert.are.equal expected, result"
+    }
+    table.concat [indent line, level for line in *lines], '\n'
+}