Add log-levels concept exercise

concepts/strings/about.md

@@ -16,18 +16,54 @@ val s = "Escape backslash \\."
 // Escape backslash \.
 ```
 
-Raw strings use 3 double-quotes, and can contain arbitrary text (no need for escaping).
-Multiline strings are also supported, including flexible handling of indents.
+Multi-line strings are surrounded by 3 double-quotes, and can contain arbitrary text (no need for escaping).
 
 ```kotlin
 val multi = """I'm a
-    |multi-line
-    |string with special characters \ \t """
+    multi-line
+    string with special characters \ \t """
+//I'm a
+//    multi-line
+//    string with special characters  \ \t 
+```
+
+Use [trimIndent][trimIndent-doc] to remove the common indenting from the lines.
+This is useful for formatting the string:
+
+```kotlin
+val multi = """
+    I'm a
+      multi-line
+    string""".trimIndent()
 
-multi.trimMargin()  // delimiter defaults to | but can be specified
 //I'm a
-//multi-line
-//string with special characters  \ \t 
+//  multi-line
+//string
+```
+
+Alternatively, [trimMargin][trimMargin-doc] lets you specify a delimiter.
+Each line in the `String` then begins after the delimiter.
+The delimiter defaults to `|`, but you can specify a different delimiter as a parameter.
+For example:
+
+```kotlin
+val multi = """
+    |I'm a
+    |  multi-line
+    |string""".trimMargin()
+
+//I'm a
+//  multi-line
+//string
+
+val multi2 = """
+    start>I'm a
+    start>  multi-line
+    start>string""".trimMargin("start>")
+
+//I'm a
+//  multi-line
+//string
 ```
 
 Strings can be concatenated with `+`, but this is best limited to short and simple cases.
@@ -70,7 +106,7 @@ Mostly, these are [`extensions functions`][ref-extensions] rather than members o
 
 ~~~~exercism/note
 Kotlin's rather complex [documentation][ref-string-functions] pages hide extension functions in the default view.
-At moment of writing this, the most valuable content is hidden in a tab named `Members and Extensions`.
+At moment of writing this, the most valuable content is hidden in a tab named `Members & Extensions`.
 Click it to expand this section and see all the members and extensions available on the `String` class.
 
 [ref-string-functions]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-string/
@@ -85,15 +121,19 @@ str.length              // => 12 (a property, not a function)
 str.elementAt(6)        // => W
 str.elementAtOrNull(20) // => null (index out of range)
 str.substring(6, 11)    // => "World"
+str.substringAfter(" ") // => "World!"
+
+str.lowercase()         // => "hello world!"
+str.uppercase()         // => "HELLO WORLD!"
 
-str.lowercase()        // => "hello world!"
-str.uppercase()        // => "HELLO WORLD!"
+str.startsWith("Hel")   // => true
+str.endsWith("xyz")     // => false
+str.indexOf("0")        // => 4
 
-str.startsWith("Hel")  // => true
-str.endsWith("xyz")    // => false
+str.toCharArray()       // => [H, e, l, l, o,  , W, o, r, l, d, !]
+"42".toInt() + 1        // => 43  (parsing; see also toFloat)
 
-str.toCharArray()      // => [H, e, l, l, o,  , W, o, r, l, d, !]
-"42".toInt() + 1       // => 43  (parsing; see also toFloat)
+"Howdy!  ".trim()       // => "Howdy"
 ```
 
 ## Building a string
@@ -157,3 +197,5 @@ val countDown = buildString {
 [ref-sb-deleterange]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.text/-string-builder/#-1622040372%2FFunctions%2F-956074838
 [ref-buildstring]: https://kotlinlang.org/docs/java-to-kotlin-idioms-strings.html#build-a-string
 [ref-jointostring]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.collections/join-to-string.html
+[trimIndent-doc]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.text/trim-indent.html
+[trimMargin-doc]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.text/trim-margin.html

concepts/strings/introduction.md

@@ -6,27 +6,63 @@ A [`string`][ref-string] in Kotlin is an immutable sequence of Unicode character
 
 [`Unicode`][wiki-unicode] means that most of the world's writing systems can be represented, but (in contrast to older languages such as C) there is no 1:1 mapping between characters and bytes.
 
-A string is usually surrounded by double-quotes `" "`.
+A string is surrounded by double-quotes `" "`.
 
-Some characters need escaping: `\'`, `\\`, plus the usual non-printing characters such as `\t` (tab) and `\n` (newline).
+Some characters need escaping: `\\`, plus the usual non-printing characters such as `\t` (tab) and `\n` (newline).
 
 ```kotlin
-val s = "Escape apostrophe \' and backslash \\."
-// Escape apostrophe ' and backslash \.
+val s = "Escape backslash \\."
+// Escape backslash \.
 ```
 
-Raw strings use 3 double-quotes, and can contain arbitrary text (no need for escaping).
-Multiline strings are also supported, including flexible handling of indents.
+Multi-line strings are surrounded by 3 double-quotes, and can contain arbitrary text (no need for escaping).
 
 ```kotlin
 val multi = """I'm a
-    |multi-line
-    |string with special characters \ \t """
+    multi-line
+    string with special characters \ \t """
+//I'm a
+//    multi-line
+//    string with special characters  \ \t 
+```
+
+Use [trimIndent][trimIndent-doc] to remove the common indenting from the lines.
+This is useful for formatting the string:
+
+```kotlin
+val multi = """
+    I'm a
+      multi-line
+    string""".trimIndent()
 
-multi.trimMargin()  // delimiter defaults to | but can be specified
 //I'm a
-//multi-line
-//string with special characters  \ \t 
+//  multi-line
+//string
+```
+
+Alternatively, [trimMargin][trimMargin-doc] lets you specify a delimiter.
+Each line in the `String` then begins after the delimiter.
+The delimiter defaults to `|`, but you can specify a different delimiter as a parameter.
+For example:
+
+```kotlin
+val multi = """
+    |I'm a
+    |  multi-line
+    |string""".trimMargin()
+
+//I'm a
+//  multi-line
+//string
+
+val multi2 = """
+    start>I'm a
+    start>  multi-line
+    start>string""".trimMargin("start>")
+
+//I'm a
+//  multi-line
+//string
 ```
 
 Strings can be concatenated with `+`, but this is best limited to short and simple cases.
@@ -56,12 +92,12 @@ Mostly, these are [`extensions functions`][ref-extensions] rather than members o
 
 ~~~~exercism/note
 Kotlin's rather complex [documentation][ref-string-functions] pages hide extension functions in the default view.
-Be sure to click `Members and Extensions` to expand this section.
+Be sure to click `Members & Extensions` to expand this section.
 
 [ref-string-functions]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-string/
 ~~~~
 
-The following example shows just a small selection of what is available:
+The following examples show just a small selection of what is available:
 
 ```kotlin
 val str = "Hello World!"
@@ -70,15 +106,19 @@ str.length              // => 12 (a property, not a function)
 str.elementAt(6)        // => W
 str.elementAtOrNull(20) // => null (index out of range)
 str.substring(6, 11)    // => "World"
+str.substringAfter(" ") // => "World!"
+
+str.lowercase()         // => "hello world!"
+str.uppercase()         // => "HELLO WORLD!"
 
-str.lowercase()        // => "hello world!"
-str.uppercase()        // => "HELLO WORLD!"
+str.startsWith("Hel")   // => true
+str.endsWith("xyz")     // => false
+str.indexOf("0")        // => 4
 
-str.startsWith("Hel")  // => true
-str.endsWith("xyz")    // => false
+str.toCharArray()       // => [H, e, l, l, o,  , W, o, r, l, d, !]
+"42".toInt() + 1        // => 43  (parsing; see also toFloat)
 
-str.toCharArray()      // => [H, e, l, l, o,  , W, o, r, l, d, !]
-"42".toInt() + 1       // => 43  (parsing; see also toFloat)
+"Howdy!  ".trim()       // => "Howdy"
 ```
 
 
@@ -88,3 +128,5 @@ str.toCharArray()      // => [H, e, l, l, o,  , W, o, r, l, d, !]
 [ref-stringbuilder]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.text/-string-builder/
 [ref-extensions]: https://kotlinlang.org/docs/extensions.html#extensions.md
 [ref-string-functions]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-string/
+[trimIndent-doc]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.text/trim-indent.html
+[trimMargin-doc]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.text/trim-margin.html

config.json

@@ -55,6 +55,18 @@
           "basics"
         ],
         "status": "wip"
+      },
+      {
+        "slug": "log-levels",
+        "name": "log-levels",
+        "uuid": "ef54c5e6-7d31-42d1-a300-e405169dbd7f",
+        "concepts": [
+          "strings"
+        ],
+        "prerequisites": [
+          "basics"
+        ],
+        "status": "wip"
       }
     ],
     "practice": [

exercises/concept/log-levels/.docs/hints.md

@@ -0,0 +1,28 @@
+# Hints
+
+## General
+
+- Kotlin provides many [functions][ref-strings] for working with Strings. Be sure to check out the `Members & Extensions` tab! 
+
+## 1. Get message from a log line
+
+- There is a [function][ref-string-substringAfter] to extract the part of a `String` after a given delimiter.
+- Removing whitespace from a `String` is explored in [Remove All Whitespaces from a String in Kotlin][tutorial-trim-white-space].
+
+## 2. Get log level from a log line
+
+- There is also a [function][ref-string-substringBefore] to extract part of a `String` _before_ a given delimiter.
+- There is a [way][ref-string-lowercase] to change a `String` to lowercase.
+
+## 3. Reformat a log line
+
+- [String templates][docs-string-template] can be done with a [multiline string][docs-string-multiline].
+
+[docs-string-multiline]: https://kotlinlang.org/docs/strings.html#multiline-strings
+[docs-string-template]: https://kotlinlang.org/docs/strings.html#string-templates
+[ref-strings]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-string/
+[ref-string-indexOf]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-string/#-537588047%2FFunctions%2F-1430298843
+[ref-string-lowercase]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-string/#-648004414%2FFunctions%2F-956074838
+[ref-string-substringAfter]: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-string/#1564391517%2FFunctions%2F-1430298843
+[tutorial-search-text-in-string]: https://javarevisited.blogspot.com/2016/10/how-to-check-if-string-contains-another-substring-in-java-indexof-example.html
+[tutorial-trim-white-space]: https://www.baeldung.com/kotlin/string-remove-whitespace

exercises/concept/log-levels/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+In this exercise you'll be processing log-liners.
+
+Each log line is a string formatted as follows: "[<LEVEL>]: <MESSAGE>*".
+
+## 1. Get the message from a log line
+
+Implement the `LogLevels.message()` function to return the message from a log line, with the leading and trailing whitespaces removed.
+
+## 2. Get the log level from a log line
+
+Implement the `LogLevels.logLevel()` function to return the log level from a log line in lower case.
+
+## 3. Reformat a log line
+
+Implement the `LogLevels.reformat()` method that takes a log line and a location string and reformats into a message containing two lines.
+The first line is formatted as `<LEVEL>@<LOCATIOON>:`, where:
+
+* `<LEVEL>` is the log level in lower case (as from 2. Get the log level from a log line).
+* `<LOCATION>` is the location given as the second parameter.
+
+The second line contains exactly two spaces, followed by the log message (as from 1. Get the message from a log line):
+
+```kotlin
+reformat("[TRACE]: Start of function", 2, 8)
+// => "trace@208:
+  Start of function"
+```