oldphonekeypaddecoder

OldPhoneKeypadDecoder

A .NET library that converts numeric keypad sequences into text, simulating classic mobile phone text input (T9). Implements the Chain of Responsibility pattern for processing multi-press character sequences, special characters, backspace, and spaces.

Features

• Multi-press character selection (e.g., pressing '2' three times gives 'C')
• Special characters through the '1' key
• Backspace (*) and confirmation (#) functionality
• Space character through '0' key
• Pause between characters using space
• Chain of Responsibility pattern for extensible character handling

Installation

dotnet add package OldPhoneKeypadDecoder

using OldPhoneKeypadDecoder.Services;
using OldPhoneKeypadDecoder.Strategies;
// Create the decoder service
var keyLayoutStrategy = new OldPhoneKeyLayoutStrategy();
var decoderService = new OldPhoneKeypadDecoderService(keyLayoutStrategy);
// Decode input
string result = decoderService.Decode("44433555555666#"); // Returns "HELLO"

Input Format

• Numbers (2-9): Letters (press multiple times for different letters)
• 1: Special characters (&, ', ()
• 0: Space character
• *: Backspace
• #: Confirm/End input
• Space: Pause between characters

Key Mappings

• 1 -> &, ', (
• 2 -> A, B, C
• 3 -> D, E, F
• 4 -> G, H, I
• 5 -> J, K, L
• 6 -> M, N, O
• 7 -> P, Q, R, S
• 8 -> T, U, V
• 9 -> W, X, Y, Z
• 0 -> Space

Examples

decoderService.Decode("2#") // "A"
decoderService.Decode("22#") // "B"
decoderService.Decode("222#") // "C"
decoderService.Decode("44 444#") // "HI"
decoderService.Decode("44433 555#") // "IE"
decoderService.Decode("227#") // "B" (backspace removes 'A')

Project Structure

• src/OldPhoneKeypadDecoder/: Core library
• src/OldPhoneKeypadDecoder.ConsoleApp/: Console application demo
• tests/OldPhoneKeypadDecoder.Tests/: Unit tests

Documentation

• Source Code Documentation: Detailed architecture overview, design patterns, and component descriptions
• Testing Documentation: Detailed testing overview

Development

# Clone the repository
git clone https://github.com/thromel/OldPhoneKeypadDecoder.git
# Build the solution
dotnet build
# Run tests
dotnet test
# Run console demo
dotnet run --project src/OldPhoneKeypadDecoder.ConsoleApp

Contributing

• Fork the repository
• Create your feature branch (git checkout -b feature/amazing-feature)
• Commit your changes (git commit -m 'Add some amazing feature')
• Push to the branch (git push origin feature/amazing-feature)
• Open a Pull Request

License

This project is licensed under the MIT License - see the LICENSE file for details.