CoV-Spectrum uses two REST APIs. Genome sequence data are coming from LAPIS which is a general purpose API for querying sequencing data. LAPIS is being developed as an individual software. It is documented here. The frontend code makes requests to this API through functions in src/data/api-lapis.ts.
In addition, CoV-Spectrum has an own and dedicated API. This API provides data that are specific to CoV-Spectrum. It includes case data, operations for login, etc. The code is in the cov-spectrum-server repository. The frontend code makes requests to this API through functions in src/data/api.ts.
Note: LAPIS use the country names as they are provided by the underlying data source (GenBank, Nextstrain, or GISAID). CoV-Spectrum uses a different set of names. For example, GISAID writes "USA", but CoV-Spectrum uses "United States". The mapping of the country names is provided by the CoV-Spectrum API at endpoint /resource/country.
We distinguish between two types of data: general/shared/plot-unrelated data and plot-related data. All the code that are related to general data are in src/data. The general data are wrapped in Dataset objects. There are a few different types of Datasets: for example, DetailedSampleAggDataset, DateCountSampleDataset, CaseCountDataset. Each dataset has a Selector which is a set of filters. These are the filters that have been applied, i.e., all entries in the payload of a dataset fulfill the filters.
A Dataset can be directly fetched from the API and/or be derived from another Dataset. For example, we can derive a DateCountSampleDataset from DetailedSampleAggDataset.
Most API data is public and does not require an API key. See the API doc for info about what does require a key ("private").
The helper functions in src/data/api.ts automatically attach an API if the user is logged in. In your code you may want to hide things or show warnings if a user isn't logged in. For this you can use AccountService.isLoggedIn(). Note that you don't have to listen for updates about the login state, since the application is fully reloaded after login and logout.