Implement phone-number in Dart

dart/phone-number/HELP.md

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+# Help
+
+## Running the tests
+
+To run the tests:
+
+```sh
+$ dart test
+```
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit lib/phone_number.dart` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Dart track's documentation](https://exercism.org/docs/tracks/dart)
+- The [Dart track's programming category on the forum](https://forum.exercism.org/c/programming/dart)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+To get help if you're having trouble, you can use one of the following resources:
+
+- [Dart API Documentation](https://api.dart.dev/)
+- [Dart Gitter Chat](https://gitter.im/dart-lang/home)
+- [Community Information](https://www.dart.dev/community)
+- [/r/dartlang](https://www.reddit.com/r/dartlang) is the Dart subreddit.
+- [StackOverflow](https://stackoverflow.com/questions/tagged/dart) can be used to search for your problem and see if it has been answered already. You can also ask and answer questions.

dart/phone-number/README.md

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+# Phone Number
+
+Welcome to Phone Number on Exercism's Dart Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Clean up user-entered phone numbers so that they can be sent SMS messages.
+
+The **North American Numbering Plan (NANP)** is a telephone numbering system used by many countries in North America like the United States, Canada or Bermuda.
+All NANP-countries share the same international country code: `1`.
+
+NANP numbers are ten-digit numbers consisting of a three-digit Numbering Plan Area code, commonly known as *area code*, followed by a seven-digit local number.
+The first three digits of the local number represent the *exchange code*, followed by the unique four-digit number which is the *subscriber number*.
+
+The format is usually represented as
+
+```text
+(NXX)-NXX-XXXX
+```
+
+where `N` is any digit from 2 through 9 and `X` is any digit from 0 through 9.
+
+Your task is to clean up differently formatted telephone numbers by removing punctuation and the country code (1) if present.
+
+For example, the inputs
+
+- `+1 (613)-995-0253`
+- `613-995-0253`
+- `1 613 995 0253`
+- `613.995.0253`
+
+should all produce the output
+
+`6139950253`
+
+**Note:** As this exercise only deals with telephone numbers used in NANP-countries, only 1 is considered a valid country code.
+
+A function with a *return type* can only return data of that *type* and `null`.
+However the function caller is only expecting one data type.
+
+Example:
+```dart
+String hello(int a){
+    if ( a == 0){
+        return "a";
+    } else {
+        return null;
+    }
+}
+```
+To make it more clear that this function can also return `null` or more data types, use `dynamic`.
+```dart
+dynamic hello(int a){
+    if ( a == 0){
+        return "a";
+    } else {
+        return null;
+    }
+}
+
+## Source
+
+### Created by
+
+- @devkabiir
+
+### Contributed to by
+
+- @kytrinyx
+- @Stargator
+
+### Based on
+
+Exercise by the JumpstartLab team for students at The Turing School of Software and Design. - https://turing.edu

dart/phone-number/analysis_options.yaml

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+analyzer:
+  strong-mode:
+    implicit-casts: false
+    implicit-dynamic: false
+  errors:
+    unused_element:        error
+    unused_import:         error
+    unused_local_variable: error
+    dead_code:             error
+
+linter:
+  rules:
+    # Error Rules
+    - avoid_relative_lib_imports
+    - avoid_types_as_parameter_names
+    - literal_only_boolean_expressions
+    - no_adjacent_strings_in_list
+    - valid_regexps

dart/phone-number/lib/phone_number.dart

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+class PhoneNumber {
+  String clean(String number) {
+    String cleaned = number.replaceAll(RegExp('[ \-\.]'), '');
+
+    if (cleaned.contains(RegExp('[A-Za-z]'))) {
+      throw FormatException('letters not permitted');
+    }
+    if (cleaned.contains(RegExp('[^0-9]'))) {
+      throw FormatException('punctuations not permitted');
+    }
+    if (cleaned.length < 10) {
+      throw FormatException('must not be fewer than 10 digits');
+    }
+    if (cleaned.length > 11) {
+      throw FormatException('must not be greater than 11 digits');
+    }
+    if (cleaned.length == 11 && cleaned[0] != '1') {
+      throw FormatException('11 digits must start with 1');
+    }
+    if (cleaned.length == 11) {
+      cleaned = cleaned.substring(1);
+    }
+    if(cleaned[0] == '0') {
+      throw FormatException('area code cannot start with zero');
+    }
+    if(cleaned[0] == '1') {
+      throw FormatException('area code cannot start with one');
+    }
+    if(cleaned[3] == '0') {
+      throw FormatException('exchange code cannot start with zero');
+    }
+    if(cleaned[3] == '1') {
+      throw FormatException('exchange code cannot start with one');
+    }
+    return cleaned;
+  }
+}