SinatraPostCodeChecker

A simple web application to work out if a given postcode is within a service area

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• Postcodes are grouped into larger blocks called LSOAs, a postcodes LSOA can be found via the postcodes.io API. This can be leveraged using a PostcodesAPI::Client wrapper class instance and invoking the lookup_postcode method.

• Configured LSOAs are stored in the local database, only postcodes with a matching LSOA whos allowed column is set to true are servicable. This can be checked by invoking the LSOA.allowed? model method.

• Some postcodes are unknown by the API or may be servicable despite being outside of the allowed LSOAs. These are stored in the database and are servicable if their allowed column is set to true. This can be checked by invoking the Postcode.allowed? model method.

• Any postcode not in the LSOA allowed list or the Postcode allowed list is not servicable, this can be checked by leveraging the PostcodesChecker::Service class instance and invoking the servicable? method. This core functionality is exposed publically via the PostcodesController using a html form at 'GET /postcodes' to submit a request to 'GET /postcodes/check' with a postcode param

Using the application

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• Navigate to /postcodes and enter the postcode you wish to check
• If a postcode is servicable it will render a message and a: '✓'
• If a postcode is not servicable it will render a message and a: '✗'
• If the postcode is invalid it will render: 'Error: Invalid postcode:'
• If a server error occurs or the request cannot be proccessed it will render: 'Error: Internal server error'

Installation

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• Requires SQLite, Ruby 2.7.2 and Bundler gem
• Install dependancies with: bundle install

Database

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• Configure and seed the SQLite database: rake db:setup
• Seed files should be placed at: seeds/#{RACK_ENV}/#{model}s.json

Running the project

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• Run the server: bundle & rackup
• Navigate to 127.0.0.1:9292/postcodes

Tests

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• Run the tests suite: rspec

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Future development

• If or when the Postcode/LSOA allowed list grows alongside additional data, we may want to transition to Postgres. SQLite is currently used due to its simplicity and the small amounts of data stored (Using json files with a simple whitelist array is also a valid approach to use for small amounts of data).
• The PostcodesController /postcodes/check function could become an API endpoint. For example /postcodes/api/check for use with external services or frontends, whilst preserving the original sinatra render functionality.
• The sinatra application and the postcodes.io remote api could both be run as docker services on the same server. This would improve ease of deployment, reduce latency and remove the reliance on a third party service.
• A redis db could be used to cache api calls to postcodes.io. This would speed up responses and reduce the number of external api calls.