feat: support serving static maps

[achou11]

Closes #437

Towards #439

Stacked on #440

Combines changes extracted from digidem/mapeo-map-server#101 and digidem/comapeo-mobile#155

Notes:

• Implements a generalized Fastify plugin for handling more general maps-related functionality.
  • declares a dependency on a plugin that implements functionality related to serving the static maps, which is functionally similar to https://github.com/digidem/mapeo-server
  • implements a portion of Implement style.json resolution strategy a when handling the stable style url #439

[achou11]

highlighting this. are we able to assume that the tile urls use z/x/y format and the directories that are stored on the filesystem follow that convention? basically, how much control do we usually have over the style.json files that are used?

[EvanHahn]

Not my most helpful comment, but want to explicitly say: I don't know. My hunch is that we should get an answer to this before the MVP, but not before merging this.

[achou11]

will enable this test when working on #439

[EvanHahn]

Had the following thought while I was reviewing: you've split this into multiple Fastify plugins. Why not just have one big plugin? I worry this is a premature abstraction...are there ever cases where you wouldn't include all the plugins?

[achou11]

Had the following thought while I was reviewing: you've split this into multiple Fastify plugins. Why not just have one big plugin? I worry this is a premature abstraction...are there ever cases where you wouldn't include all the plugins?

could categorize as premature but useful (also easier to build iteratively since they're all rather distinct functionalities).

the idea was to build this in a way that could potentially be split off into its own package that contais all of these plugins. to summarize the purpose of each plugin:

• maps: mostly specific to the "new" maps serving approach for Mapeo. the initial implementation uses a decorator exposed by static maps plugin but that's to support backward compatibility for how maps are stored on a device (since the map manager isn't implemented for comapeo yet). eventually, this will primarily use the JS API for the map server dep that you've been working on, and expose the routes necessary to power the Mapeo Map Manager.

• static-maps: adding functionality for the "legacy" map serving approach that Mapeo uses i.e. an embedded directory with a specific structure and some metadata files that get served statically. this is isolated from the new approach but we need the functionality for backwards compat reasons to ease the transition.

• offline-map: very specific to how mapeo works - probably didn't need to be its own plugin but made it easier to isolate the implementation

are there ever cases where you wouldn't include all the plugins?

if we ever fully move away from the static directory approach of serving maps, then it'll be easier to remove that piece with the plugin approach implemented here. so in theory, yes - the static-maps plugin could potentially cease to exist if we ever reach that point 😄