Add space-age exercise (#380)

config.json

@@ -393,6 +393,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "space-age",
+        "name": "Space Age",
+        "uuid": "183eb493-2141-4823-8fe6-0f01ecbcb27a",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "square-root",
         "name": "Square Root",

exercises/practice/space-age/.docs/instructions.md

@@ -0,0 +1,28 @@
+# Instructions
+
+Given an age in seconds, calculate how old someone would be on a planet in our Solar System.
+
+One Earth year equals 365.25 Earth days, or 31,557,600 seconds.
+If you were told someone was 1,000,000,000 seconds old, their age would be 31.69 Earth-years.
+
+For the other planets, you have to account for their orbital period in Earth Years:
+
+| Planet  | Orbital period in Earth Years |
+| ------- | ----------------------------- |
+| Mercury | 0.2408467                     |
+| Venus   | 0.61519726                    |
+| Earth   | 1.0                           |
+| Mars    | 1.8808158                     |
+| Jupiter | 11.862615                     |
+| Saturn  | 29.447498                     |
+| Uranus  | 84.016846                     |
+| Neptune | 164.79132                     |
+
+~~~~exercism/note
+The actual length of one complete orbit of the Earth around the sun is closer to 365.256 days (1 sidereal year).
+The Gregorian calendar has, on average, 365.2425 days.
+While not entirely accurate, 365.25 is the value used in this exercise.
+See [Year on Wikipedia][year] for more ways to measure a year.
+
+[year]: https://en.wikipedia.org/wiki/Year#Summary
+~~~~

exercises/practice/space-age/.docs/introduction.md

@@ -0,0 +1,20 @@
+# Introduction
+
+The year is 2525 and you've just embarked on a journey to visit all planets in the Solar System (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune).
+The first stop is Mercury, where customs require you to fill out a form (bureaucracy is apparently _not_ Earth-specific).
+As you hand over the form to the customs officer, they scrutinize it and frown.
+"Do you _really_ expect me to believe you're just 50 years old?
+You must be closer to 200 years old!"
+
+Amused, you wait for the customs officer to start laughing, but they appear to be dead serious.
+You realize that you've entered your age in _Earth years_, but the officer expected it in _Mercury years_!
+As Mercury's orbital period around the sun is significantly shorter than Earth, you're actually a lot older in Mercury years.
+After some quick calculations, you're able to provide your age in Mercury Years.
+The customs officer smiles, satisfied, and waves you through.
+You make a mental note to pre-calculate your planet-specific age _before_ future customs checks, to avoid such mix-ups.
+
+~~~~exercism/note
+If you're wondering why Pluto didn't make the cut, go watch [this YouTube video][pluto-video].
+
+[pluto-video]: https://www.youtube.com/watch?v=Z_2gbGXzFbs
+~~~~

exercises/practice/space-age/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "space-age.el"
+    ],
+    "test": [
+      "space-age-test.el"
+    ],
+    "example": [
+      ".meta/example.el"
+    ]
+  },
+  "blurb": "Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.",
+  "source": "Partially inspired by Chapter 1 in Chris Pine's online Learn to Program tutorial.",
+  "source_url": "https://pine.fm/LearnToProgram/?Chapter=01"
+}

exercises/practice/space-age/.meta/example.el

@@ -0,0 +1,26 @@
+;;; space-age.el --- Space Age (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(defun orbital-period (planet)
+  (pcase planet
+    (:mercury 0.2408467)
+    (:venus 0.61519726)
+    (:earth 1.0)
+    (:mars 1.8808158)
+    (:jupiter 11.862615)
+    (:saturn 29.447498)
+    (:uranus 84.016846)
+    (:neptune 164.79132)
+    (_ (error "not a planet"))))
+
+(defun age (planet seconds)
+  (/ seconds (* (orbital-period planet) 31557600)))
+
+
+(provide 'space-age)
+;;; space-age.el ends here
+

exercises/practice/space-age/.meta/tests.toml

@@ -0,0 +1,37 @@
+# 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.
+
+[84f609af-5a91-4d68-90a3-9e32d8a5cd34]
+description = "age on Earth"
+
+[ca20c4e9-6054-458c-9312-79679ffab40b]
+description = "age on Mercury"
+
+[502c6529-fd1b-41d3-8fab-65e03082b024]
+description = "age on Venus"
+
+[9ceadf5e-a0d5-4388-9d40-2c459227ceb8]
+description = "age on Mars"
+
+[42927dc3-fe5e-4f76-a5b5-f737fc19bcde]
+description = "age on Jupiter"
+
+[8469b332-7837-4ada-b27c-00ee043ebcad]
+description = "age on Saturn"
+
+[999354c1-76f8-4bb5-a672-f317b6436743]
+description = "age on Uranus"
+
+[80096d30-a0d4-4449-903e-a381178355d8]
+description = "age on Neptune"
+
+[57b96e2a-1178-40b7-b34d-f3c9c34e4bf4]
+description = "invalid planet causes error"

exercises/practice/space-age/space-age-test.el

@@ -0,0 +1,53 @@
+;;; space-age-test.el --- Tests for Space Age (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(load-file "space-age.el")
+(declare-function age "space-age.el" (planet seconds))
+
+
+(defmacro should-approximate (expected actual)
+    (list 'should (list '< (- expected 0.01) actual (+ expected 0.01))))
+
+
+(ert-deftest age-on-earth ()
+  (should-approximate 31.69 (age :earth 1000000000)))
+
+
+(ert-deftest age-on-mercury ()
+  (should-approximate 280.88 (age :mercury 2134835688)))
+
+
+(ert-deftest age-on-venus ()
+  (should-approximate 9.78 (age :venus 189839836)))
+
+
+(ert-deftest age-on-mars ()
+  (should-approximate 35.88 (age :mars 2129871239)))
+
+
+(ert-deftest age-on-jupiter ()
+  (should-approximate 2.41 (age :jupiter 901876382)))
+
+
+(ert-deftest age-on-saturn ()
+  (should-approximate 2.15 (age :saturn 2000000000)))
+
+
+(ert-deftest age-on-uranus ()
+  (should-approximate 0.46 (age :uranus 1210123456)))
+
+
+(ert-deftest age-on-neptune ()
+  (should-approximate 0.35 (age :neptune 1821023456)))
+
+
+(ert-deftest invalid-planet-causes-error ()
+  (should-error (age :sun 680804807)))
+
+
+(provide 'space-age-test)
+;;; space-age-test.el ends here

exercises/practice/space-age/space-age.el

@@ -0,0 +1,14 @@
+;;; space-age.el --- Space Age (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(defun age (planet seconds)
+  (error "Delete this S-Expression and write your own implementation"))
+
+
+(provide 'space-age)
+;;; space-age.el ends here
+