Add Vehicle Purchase exercise for Patterns concept (#326)

* Add Vehicle Purchase exercise for Patterns concept

Co-authored-by: Isaac Good <[email protected]>

Author: glennj

config.json

@@ -55,6 +55,18 @@
           "fundamentals"
         ],
         "status": "wip"
+      },
+      {
+        "slug": "vehicle-purchase",
+        "name": "vehicle-purchase",
+        "uuid": "9e4e4ec3-ee4e-4f66-8fe2-fd10ede24df7",
+        "concepts": [
+          "patterns"
+        ],
+        "prerequisites": [
+          "fundamentals"
+        ],
+        "status": "wip"
       }
     ],
     "practice": [
@@ -521,7 +533,7 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 4,
-	"status": "deprecated"
+        "status": "deprecated"
       },
       {
         "slug": "pig-latin",

exercises/concept/vehicle-purchase/.docs/hints.md

@@ -0,0 +1,18 @@
+# Hints
+
+## General
+
+- You can accomplish all of these tasks without using an `if` statement.
+
+## 1. Determine if you will need a drivers license
+
+- Use the [equality operator][cmp] to check whether the first field equals a certain string.
+- Use a a regular expression to check if the second field contains the required substrings.
+- Use one of the two [boolean operators][bool] to combine the two requirements.
+
+## 2.Calculate an estimation for the price of a used vehicle
+
+- Use the [comparison operators][cmp] to determine which discount to use.
+
+[cmp]: https://www.gnu.org/software/gawk/manual/html_node/Comparison-Operators.html
+[bool]: https://www.gnu.org/software/gawk/manual/html_node/Boolean-Ops.html

exercises/concept/vehicle-purchase/.docs/instructions.md

@@ -0,0 +1,45 @@
+# Instructions
+
+In this exercise, you will write a program to help you prepare to buy a vehicle.
+
+You have two tasks: determine if you will need to get a license, and estimate the acceptable price for a used vehicle.
+
+## 1. Determine if you will need a drivers license
+
+Some kinds of vehicles require a drivers license to operate them.
+Assume only vehicles containing `car` or `truck` require a license; everything else can be operated without a license.
+
+Implement a `pattern {action}` pair that matches when the first field is `needs_license`.
+It should get the kind of vehicle from the second field, and print "true" if you need a license for that kind of vehicle.
+If you don't need a license, you don't need to print anything.
+
+```sh
+echo "needs_license,dumptruck" | gawk -f vehicle-purchase.awk
+# => true
+
+echo "needs_license,bike" | gawk -f vehicle-purchase.awk
+# => (empty output)
+```
+
+## 2. Calculate an estimation for the price of a used vehicle
+
+Now that you have made your decision, you want to make sure you get a fair price at the dealership.
+Since you are interested in buying a used vehicle, the price depends on how old the vehicle is.
+For a rough estimate, assume if the vehicle is less than 3 years old, it costs 80% of the original price it had when new.
+If it is more than 10 years old, it costs 50%.
+If the vehicle is at least 3 years old but not older than 10 years, it costs 70% of the original price.
+
+Implement a `pattern {action}` pair that matches when the first field is `resell_price`.
+It should get the original price of the vehicle from the second field, and the age from the third field.
+The action should print the estimated price.
+
+```sh
+echo "resell_price,1000,1" | gawk -f vehicle-purchase.awk
+# => 800
+
+echo "resell_price,1000,5" | gawk -f vehicle-purchase.awk
+# => 700
+
+echo "resell_price,1000,15" | gawk -f vehicle-purchase.awk
+# => 500
+```

exercises/concept/vehicle-purchase/.docs/introduction.md

@@ -0,0 +1,104 @@
+# Introduction
+
+## More about Patterns
+
+Recall from the Fundamentals concept, an AWK program is composed of **pattern-action pairs**.
+
+```awk
+pattern1 { action1 }
+pattern2 { action2 }
+...
+```
+
+### What do we mean by "pattern"?
+
+The "pattern" is any AWK expression.
+The truthiness of the expression's result determines if the action is executed.
+
+### The Empty Pattern
+
+The pattern can be omitted.
+In this case, the action is performed for every record.
+
+We can print all the usernames in the passwd file.
+
+```sh
+awk -F: '{print $1}' /etc/passwd
+```
+
+### Regular Expressions
+
+AWK can compare strings against regular expressions to obtain a boolean result.
+
+Use the `~` regex-matching operator to match a particular field. 
+This operator takes a string as the left-hand operand and a regular expression as the right-hand operand.
+A regular expression literal is enclosed in `/` slashes.
+
+To find the users in the passwd file who log in with bash:
+
+```sh
+awk -F: '$7 ~ /bash/ {print $1}' /etc/passwd
+```
+
+`!~` is the "regex does **not** match" operator.
+
+To match a regex against the current record, you can do `$0 ~ /regex/`.
+This is so common there is a shorthand: you can drop the `$0` and `~` and simply write `/regex/`
+
+```sh
+awk '/regex/' data.txt
+```
+
+~~~~exercism/note
+Compare that AWK one-liner with the equivalent grep command
+
+```sh
+grep 'regex' data.txt
+```
+
+AWK gives you a whole programming language without sacrificing succinctness.
+~~~~
+
+We'll get more into GNU AWK's regular expression flavor in a further concept.
+
+### Expressions
+
+AWK expressions (arithmetic, logical, or otherwise) can be used as patterns.
+
+To extract all users with UID 1000 or above:
+
+```sh
+awk -F: '$3 >= 1000' /etc/passwd
+```
+
+Recall that AWK's false values are the number zero and the empty string, and all other numbers or strings are true.
+Any expression that evaluates to a number or a string can be used as a pattern.
+
+### Functions
+
+Any [builtin][builtins] or [user-defined][] function can be used in an expression, and hence in the pattern.
+A couple of examples:
+
+```awk
+length($1) {print "first field is not empty"}
+```
+```awk
+toupper(substr($1, 1, 1)) ~ /[AEIOU]/ {print "starts with a vowel"}
+```
+
+### Constant Patterns
+
+A common AWK idiom is:
+
+```sh
+{
+    xyz()   # some code that transforms each record
+}
+1
+```
+
+`1` is a truthy pattern with no associated action.
+This means "print the current record."
+
+[builtins]: https://www.gnu.org/software/gawk/manual/html_node/Built_002din.html
+[user-defined]: https://www.gnu.org/software/gawk/manual/html_node/User_002ddefined.html

exercises/concept/vehicle-purchase/.docs/introduction.md.tpl

@@ -0,0 +1,3 @@
+# Introduction
+
+%{concept:patterns}

exercises/concept/vehicle-purchase/.meta/config.json

@@ -0,0 +1,20 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "vehicle-purchase.awk"
+    ],
+    "test": [
+      "test-vehicle-purchase.bats"
+    ],
+    "exemplar": [
+      ".meta/exemplar.awk"
+    ]
+  },
+  "forked_from": [
+    "javascript/vehicle-purchase"
+  ],
+  "blurb": "Learn about AWK patterns while preparing for your next vehicle purchase."
+}

exercises/concept/vehicle-purchase/.meta/exemplar.awk

@@ -0,0 +1,7 @@
+BEGIN {FS = ","}
+
+$1 == "needs_license" && $2 ~ /car|truck/ {print "true"}
+
+$1 == "resell_price" && $3 < 3              {print $2 * 0.8}
+$1 == "resell_price" && 3 <= $3 && $3 <= 10 {print $2 * 0.7}
+$1 == "resell_price" && $3 > 10             {print $2 * 0.5}