Initialize dictionary with data in multiplatform compose resources

[michalgwo]

Currently, there are 2 options to initialize the dictionary, either by providing FileSystem or AssetManager, but only FileSystem is available in the common source set of the Kotlin Multiplatform project. In case when we keep our presets data in compose resources, they are not available from FileSystem, they are bundled into apk, thus right now it's not possible to get them with osmfeatures library in the common source set.

To get a raw file from compose resources we can use Res.readBytes("files/presets/preset.json") (reference).

To solve this issue, I propose to make FeatureDictionary.create() accept a Res object as a parameter and read presets from compose resources by Res.readBytes()

[westnordost]

I see. Res is compose-specific, so would add a dependency, that's a no-no.

But you can just use the regular constructor of the FeatureDictionary.

Adding a function like

fun createFeatureDictionary(
    featuresAccess: ResourceAccessAdapter,
    brandFeaturesAccess: ResourceAccessAdapter?,
) = FeatureDictionary(
    featureCollection = IDLocalizedFeatureCollection(featuresAccess),
    brandFeatureCollection = brandFeaturesAccess?.let { IDBrandPresetsFeatureCollection(it) }
)

Then, you just need to implement a ResourceAccessAdapter that uses the functions from KMP Compose Resources to access the resources.

[westnordost]

It took way too long to find this out, but you can use

val buffer = Buffer()
UnsafeBufferOperations.moveToTail(buffer, byteArray)

to wrap a ByteArray into a Buffer (without copying it). A Buffer implements Source.
Maybe one day KMP Compose Resources will also directly offer a function like Res.readSource.

[westnordost]

Is there a method like Res.exists at all, though?

[michalgwo]

Is there a method like Res.exists at all, though?

Not exactly, but it can be checked with Res.getUri() which returns MissingResourceException when the file doesn't exist.

[westnordost]

(I am curious, though, what do you need osmfeatures for? I've noticed you also posted an issue in sargunv/maplibre-compose, so you must be working on some Compose Multiplatform app that works with OSM data)

Anyway, it sounds like you can build something to initialize the data with compose resources in a few lines of code. It's such few lines of code, that I don't think it would be worth it to create a library for that (osmfeatures-compose-resources). But maybe you want to share here what code you ended up with?

[michalgwo]

Yes, I'm working on a Compose Multiplatform app that works with OSM data. I decided not to use osmfeatures and instead just read the file, parse it to json and read the values I need using kotlinx.serialization library.
Here is my code:

const val DEFAULT_PRESETS_LANGUAGE = "en"

data class IdTags(
    val presets: JsonObject,
    val fields: JsonObject
)

suspend fun getIdTagsFromFile(language: String?, logException: Boolean = false): IdTags? {
    language?.let { lang ->
        try {
            val json = getJsonFromFile("id-presets", "$lang.json", logException)

            if (json != null) {
                val basePresets = json[lang]!!.jsonObject["presets"]!!.jsonObject
                val presets = basePresets.jsonObject["presets"]!!.jsonObject
                val fields = basePresets.jsonObject["fields"]!!.jsonObject

                return IdTags(presets, fields)
            } else if (lang != DEFAULT_PRESETS_LANGUAGE) {
                return getIdTagsFromFile(DEFAULT_PRESETS_LANGUAGE, true)
            }
        } catch (e: Exception) {
            if (lang != DEFAULT_PRESETS_LANGUAGE)
                return getIdTagsFromFile(DEFAULT_PRESETS_LANGUAGE, true)
            else
                Firebase.crashlytics.recordException(e)
        }
    }
    return null
}

@OptIn(ExperimentalResourceApi::class)
private suspend fun getJsonFromFile(basepath: String, filename: String, logException: Boolean = true): JsonObject? {
    try {
        val path = Path("files/$basepath", filename)
        val string = Res.readBytes(path.toString()).decodeToString()
        return Json.parseToJsonElement(string).jsonObject
    } catch (e: Exception) {
        if (logException)
            Firebase.crashlytics.recordException(e)

        return null
    }
}

[westnordost]

okidoki, thanks