book-reader/app/src/main/java/com/aryan/reader/opds/OpdsViewModel.kt

package com.aryan.reader.opds

import android.app.Application
import android.content.Context
import android.net.Uri
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.viewModelScope
import com.aryan.reader.R
import com.aryan.reader.shared.opds.SharedOpdsController
import com.aryan.reader.shared.opds.SharedOpdsDownloadNamer
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext
import okhttp3.Request
import okhttp3.Response
import timber.log.Timber
import java.io.File
import java.util.UUID

class OpdsViewModel(application: Application) : AndroidViewModel(application) {
    private val repository = OpdsRepository(application)
    private val controller = SharedOpdsController(
        repository = repository,
        feedLoadErrorMessage = { error ->
            application.getString(R.string.opds_error_load_feed, error.message.orEmpty())
        },
        idFactory = { UUID.randomUUID().toString() }
    )

    private val _uiState = MutableStateFlow(controller.state)
    val uiState: StateFlow<OpdsScreenState> = _uiState.asStateFlow()

    fun loadNextPage() {
        viewModelScope.launch {
            controller.loadNextPage(::emitState)
        }
    }

    fun downloadBook(entry: OpdsEntry, acquisition: OpdsAcquisition, context: Context, onDownloaded: (Uri) -> Unit) {
        val downloadUrl = acquisition.url
        val catalog = _uiState.value.currentCatalog
        viewModelScope.launch {
            updateDownloadState(entry.id, OpdsDownloadState(isDownloading = true, progress = 0f))
            try {
                val tempFile = withContext(Dispatchers.IO) {
                    val client = repository.getAuthenticatedClient(catalog?.username, catalog?.password)
                    val request = Request.Builder().url(downloadUrl).build()

                    client.newCall(request).execute().use { response ->
                        if (!response.isSuccessful) {
                            throw OpdsDownloadFailedException(
                                context.getString(R.string.opds_error_download_failed, response.message)
                            )
                        }

                        val body = response.body
                            ?: throw IllegalStateException(context.getString(R.string.opds_error_empty_response))
                        val contentLength = body.contentLength()
                        val ext = resolveOpdsDownloadExtension(acquisition, response)
                        val safeTitle = SharedOpdsDownloadNamer.safeFileStem(entry.title).take(50)
                        val tempFile = File(context.cacheDir, "opds_dl_${safeTitle}$ext")

                        body.byteStream().use { input ->
                            tempFile.outputStream().use { output ->
                                val buffer = ByteArray(8 * 1024)
                                var totalRead = 0L
                                var lastProgressUpdate = System.currentTimeMillis()

                                while (true) {
                                    val bytesRead = input.read(buffer)
                                    if (bytesRead == -1) break
                                    output.write(buffer, 0, bytesRead)
                                    totalRead += bytesRead

                                    if (contentLength > 0) {
                                        val now = System.currentTimeMillis()
                                        if (now - lastProgressUpdate > 200) {
                                            val progress = (totalRead.toFloat() / contentLength.toFloat()).coerceIn(0f, 1f)
                                            withContext(Dispatchers.Main) {
                                                updateDownloadState(
                                                    entry.id,
                                                    OpdsDownloadState(isDownloading = true, progress = progress)
                                                )
                                            }
                                            lastProgressUpdate = now
                                        }
                                    }
                                }
                            }
                        }
                        tempFile
                    }
                }

                onDownloaded(Uri.fromFile(tempFile))
            } catch (e: Exception) {
                Timber.e(e, "Download error")
                val message = if (e is OpdsDownloadFailedException) {
                    e.message.orEmpty()
                } else {
                    context.getString(R.string.opds_error_download_error, e.message.orEmpty())
                }
                emitState(controller.setErrorMessage(message))
            } finally {
                updateDownloadState(entry.id, null)
            }
        }
    }

    private fun resolveOpdsDownloadExtension(acquisition: OpdsAcquisition, response: Response): String {
        return SharedOpdsDownloadNamer.resolveExtension(
            acquisition = acquisition,
            contentDisposition = response.header("Content-Disposition"),
            urlPathSegment = Uri.parse(acquisition.url).lastPathSegment
        )
    }

    fun addCatalog(title: String, url: String, username: String?, password: String?) {
        emitState(controller.addCatalog(title, url, username, password))
    }

    fun removeCatalog(id: String) {
        emitState(controller.removeCatalog(id))
    }

    fun openCatalog(catalog: OpdsCatalog) {
        viewModelScope.launch {
            controller.openCatalog(catalog, ::emitState)
        }
    }

    fun openFeedUrl(url: String) {
        viewModelScope.launch {
            controller.openFeedUrl(url, ::emitState)
        }
    }

    fun navigateBack(): Boolean {
        val returnsToPreviousFeed = controller.hasFeedHistory()
        viewModelScope.launch {
            controller.navigateBack(::emitState)
        }
        return returnsToPreviousFeed
    }

    fun updateCatalog(id: String, title: String, url: String, username: String?, password: String?) {
        emitState(controller.updateCatalog(id, title, url, username, password))
    }

    fun search(query: String) {
        viewModelScope.launch {
            controller.search(query, ::emitState)
        }
    }

    fun clearError() {
        emitState(controller.clearError())
    }

    private fun updateDownloadState(entryId: String, downloadState: OpdsDownloadState?) {
        emitState(controller.updateDownloadState(entryId, downloadState))
    }

    private fun emitState(state: OpdsScreenState) {
        _uiState.value = state
    }

    private class OpdsDownloadFailedException(message: String) : Exception(message)
}