29 lines
1.7 KiB
Markdown
29 lines
1.7 KiB
Markdown
---
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title: Interchange
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layout: project
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---
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**An iOS app for college transit, currently available for Chapman University.**
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View routes, shuttle locations, and estimated arrival times in a sleek,
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easy-to-use interface. I built this app using SwiftUI, Node.js and Apollo
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GraphQL, with Redis as a primary storage mechanism.
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[Download on the App Store](https://apps.apple.com/us/app/interchange-college-commute/id6739968742){: .primary-action }
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[Join the TestFlight](https://testflight.apple.com/join/HbuHfUgW){: .secondary-action }
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[Website](https://interchange.bchen.dev/){: .secondary-action }
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{: .horizontal-wrapper }
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## Design and implementation
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The server is built using Node.js. I designed a basic GraphQL schema and
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used [Apollo's GraphQL implementation](https://www.apollographql.com/docs/apollo-server/getting-started) to bring it to life.
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In GraphQL, data is represented using a schema, which is then fulfilled with
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resolvers defined in code. Each resolver function gets some information like the
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parent object, arguments, and a server-defined shared context. Seeing the dependency injection that you could do with this context, I decided on an object-oriented approach consisting of **loaders**, **repositories**, and **systems**. Loaders load data from an external source, repositories store data, and systems are composed from a set of both loaders and repositories.
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I then applied an event-driven pattern to implement the iOS notification sender, listening to updates on the shuttle repository. I would eventually reuse this pattern to implement an ETA prediction system that could run independently of an external data source.
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