// Copyright 2024 Google LLC

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

// http://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

package com.example.mountainmarkers.data.local

import android.content.Context

import android.util.Xml

import com.example.mountainmarkers.R

import com.example.mountainmarkers.data.utils.meters

import com.google.android.gms.maps.model.LatLng

import dagger.hilt.android.qualifiers.ApplicationContext

import java.io.IOException

import java.io.InputStream

import kotlinx.coroutines.Dispatchers

import kotlinx.coroutines.flow.MutableStateFlow

import kotlinx.coroutines.flow.StateFlow

import kotlinx.coroutines.withContext

import org.xmlpull.v1.XmlPullParser

import org.xmlpull.v1.XmlPullParserException

/**

* Repository for loading the list of mountain peaks.

*/

class MountainsRepository(@ApplicationContext val context: Context) {

private val _mountains = MutableStateFlow(emptyList<Mountain>())

val mountains: StateFlow<List<Mountain>> = _mountains

private var loaded = false

/**

* Loads the list of mountains from the list of mountains from the raw resource.

*/

suspend fun loadMountains(): StateFlow<List<Mountain>> {

if (!loaded) {

loaded = true

_mountains.value = withContext(Dispatchers.IO) {

context.resources.openRawResource(R.raw.top_peaks).use { inputStream ->

readMountains(inputStream)

}

}

}

return mountains

}

/**

* Reads the [Waypoint]s from the given [inputStream] and returns a list of [Mountain]s.

*/

private fun readMountains(inputStream: InputStream) =

readWaypoints(inputStream).mapIndexed { index, waypoint ->

waypoint.toMountain(index)

}.toList()

/**

* Class for collecting data fields and creating a valid [Waypoint] or null if any required data

* is invalid or missing.

*/

private data class WaypointBuilder(

var latitude: Double? = null,

var longitude: Double? = null,

var name: String? = null,

var elevation: Double? = null,

) {

fun build(): Waypoint? {

val latitude = latitude ?: return null

val longitude = longitude ?: return null

val elevation = elevation ?: return null

val name = name ?: return null

return Waypoint(

name = name,

location = LatLng(latitude, longitude),

elevationMeters = elevation,

)

}

}

/**

* Read all of the waypoints from a GPX file.

*/

private fun readWaypoints(inputStream: InputStream): Sequence<Waypoint> = sequence {

// We don't use namespaces

val ns: String? = null

val parser = Xml.newPullParser()

parser.setInput(inputStream, null)

try {

var eventType = parser.eventType

var builder: WaypointBuilder? = null

while (eventType != XmlPullParser.END_DOCUMENT) {

when (eventType) {

XmlPullParser.START_TAG -> {

if (parser.name == "wpt") {

builder = WaypointBuilder(

latitude = parser.getAttributeValue(ns, "lat").toDouble(),

longitude = parser.getAttributeValue(ns, "lon").toDouble(),

)

} else if (builder != null) {

when (parser.name) {

"name" -> builder.name = parser.nextText()

"ele" -> builder.elevation = parser.nextText().toDouble()

}

}

}

XmlPullParser.END_TAG -> {

if (parser.name == "wpt" && builder != null) {

builder.build()?.let { waypoint -> yield(waypoint) }

builder = null

}

}

}

eventType = parser.next()

}

} catch (e: XmlPullParserException) {

// Handle parsing errors

} catch (e: IOException) {

// Handle IO errors

}

}

}

private data class Waypoint(

val name: String,

val location: LatLng,

val elevationMeters: Double,

)

private fun Waypoint.toMountain(id: Int): Mountain {

return Mountain(

id = id,

name = name,

location = location,

elevation = elevationMeters.meters

)

}