MainActivity: show user-friendly error messages

Also add going back support.

app/build.gradle

@@ -1,6 +1,7 @@
 plugins {
     id 'com.android.application'
     id 'kotlin-android'
+    id 'kotlin-kapt'
 }
 
 android {
@@ -40,10 +41,12 @@ android {
 dependencies {
     implementation 'androidx.core:core-ktx:1.7.0'
     implementation 'androidx.appcompat:appcompat:1.4.0'
-    implementation 'com.google.android.material:material:1.4.0'
     implementation 'androidx.constraintlayout:constraintlayout:2.1.2'
     implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.4.0"
     implementation 'androidx.legacy:legacy-support-v4:1.0.0'
+    implementation "androidx.room:room-runtime:2.3.0"
+    implementation 'com.google.android.material:material:1.4.0'
+    kapt "androidx.room:room-compiler:2.3.0"
     testImplementation 'junit:junit:4.13.2'
     androidTestImplementation 'androidx.test.ext:junit:1.1.3'
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'

app/src/main/java/dev/lowrespalmtree/comet/Database.kt

@@ -0,0 +1,21 @@
+package dev.lowrespalmtree.comet
+
+import android.content.Context
+import androidx.room.Database
+import androidx.room.Room
+import androidx.room.RoomDatabase
+
+@Database(entities = [History.HistoryEntry::class], version = 1)
+abstract class AppDatabase : RoomDatabase() {
+    abstract fun historyEntryDao(): History.HistoryEntryDao
+}
+
+object Database {
+    lateinit var INSTANCE: AppDatabase
+
+    fun init(context: Context) {
+        if (::INSTANCE.isInitialized)
+            return
+        INSTANCE = Room.databaseBuilder(context, AppDatabase::class.java, "comet").build()
+    }
+}

app/src/main/java/dev/lowrespalmtree/comet/Gemtext.kt

@@ -55,9 +55,10 @@ private fun parseLine(line: CharBuffer, isPreformatted: Boolean): Line =
         line.startsWith(">") -> BlockquoteLine(getCharsFrom(line, 1))
         line.startsWith("```") -> PreFenceLine(getCharsFrom(line, 3))
         line.startsWith("* ") -> ListItemLine(getCharsFrom(line, 2))
-        line.startsWith("=>") -> getCharsFrom(line, 2).split(" ", limit = 2)
-            .run { LinkLine(get(0), if (size == 2) get(1) else "") }
+        line.startsWith("=>") -> getCharsFrom(line, 2)
+            .split(" ", limit = 2)
+            .run { LinkLine(get(0), if (size == 2) get(1).trimStart() else "") }
         else -> if (isPreformatted) PreTextLine(line.toString()) else ParagraphLine(line.toString())
     }
 
-private fun getCharsFrom(line: CharBuffer, index: Int) = line.substring(index).removePrefix(" ")
+private fun getCharsFrom(line: CharBuffer, index: Int) = line.substring(index).trim()

app/src/main/java/dev/lowrespalmtree/comet/History.kt

@@ -0,0 +1,37 @@
+package dev.lowrespalmtree.comet
+
+import androidx.room.*
+
+object History {
+    @Entity
+    data class HistoryEntry(
+        @PrimaryKey @ColumnInfo(name = "uri") val uri: String,
+        @ColumnInfo(name = "title") var title: String?,
+        @ColumnInfo(name = "lastVisit") var lastVisit: Long,
+    )
+
+    @Dao
+    interface HistoryEntryDao {
+        @Query("SELECT * FROM HistoryEntry WHERE :uri = uri LIMIT 1")
+        fun get(uri: String): HistoryEntry?
+
+        @Query("SELECT * FROM HistoryEntry ORDER BY lastVisit DESC")
+        fun getAll(): List<HistoryEntry>
+
+        @Insert(onConflict = OnConflictStrategy.IGNORE)
+        fun insert(vararg entries: HistoryEntry)
+
+        @Update
+        fun update(vararg entries: HistoryEntry)
+    }
+
+    fun record(uri: String, title: String?) {
+        val now = System.currentTimeMillis()
+        val dao = Database.INSTANCE.historyEntryDao()
+        val entry = dao.get(uri)
+        if (entry == null)
+            dao.insert(HistoryEntry(uri, title, now))
+        else
+            dao.update(entry.also { it.title = title; it.lastVisit = now })
+    }
+}

app/src/main/java/dev/lowrespalmtree/comet/MainActivity.kt

@@ -1,6 +1,5 @@
 package dev.lowrespalmtree.comet
 
-import android.annotation.SuppressLint
 import android.app.Activity
 import android.content.ActivityNotFoundException
 import android.content.Intent
@@ -18,9 +17,8 @@ import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.viewModelScope
 import androidx.recyclerview.widget.LinearLayoutManager
 import dev.lowrespalmtree.comet.databinding.ActivityMainBinding
-import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.Job
-import kotlinx.coroutines.launch
+import kotlinx.coroutines.*
+import java.net.ConnectException
 import java.net.UnknownHostException
 import java.nio.charset.Charset
 
@@ -29,11 +27,19 @@ class MainActivity : AppCompatActivity(), ContentAdapter.ContentAdapterListen {
     private lateinit var pageViewModel: PageViewModel
     private lateinit var adapter: ContentAdapter
 
-    private val currentUrl get() = binding.addressBar.text
+    /** Property to access and set the current address bar URL value. */
+    private var currentUrl
+        get() = binding.addressBar.text.toString()
+        set(value) = binding.addressBar.setText(value)
+
+    /** A non-saved list of visited URLs. Not an history, just used for going back. */
+    private val visitedUrls = mutableListOf<String>()
 
-    @SuppressLint("SetTextI18n")
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
+
+        Database.init(applicationContext)
+
         binding = ActivityMainBinding.inflate(layoutInflater)
         setContentView(binding.root)
 
@@ -54,19 +60,32 @@ class MainActivity : AppCompatActivity(), ContentAdapter.ContentAdapterListen {
             }
         }
 
-        binding.contentSwipeLayout.setOnRefreshListener { openUrl(currentUrl.toString()) }
+        binding.contentSwipeLayout.setOnRefreshListener { openUrl(currentUrl) }
 
         pageViewModel.state.observe(this, { updateState(it) })
         pageViewModel.lines.observe(this, { updateLines(it) })
-        pageViewModel.alert.observe(this, { alert(it) })
+        pageViewModel.event.observe(this, { handleEvent(it) })
+    }
+
+    override fun onBackPressed() {
+        visitedUrls.removeLastOrNull()  // Always remove current page first.
+        val previousUrl = visitedUrls.removeLastOrNull()
+        if (previousUrl != null)
+            openUrl(previousUrl)
+        else
+            super.onBackPressed()
     }
 
     override fun onLinkClick(url: String) {
-        val base = binding.addressBar.text.toString()
-        openUrl(url, base = if (base.isNotEmpty()) base else null)
+        openUrl(url, base = if (currentUrl.isNotEmpty()) currentUrl else null)
     }
 
-    private fun openUrl(url: String, base: String? = null) {
+    private fun openUrl(url: String, base: String? = null, redirections: Int = 0) {
+        if (redirections >= 5) {
+            alert("Too many redirections.")
+            return
+        }
+
         var uri = Uri.parse(url)
         if (!uri.isAbsolute) {
             uri = if (!base.isNullOrEmpty()) joinUrls(base, url) else toGeminiUri(uri)
@@ -74,7 +93,7 @@ class MainActivity : AppCompatActivity(), ContentAdapter.ContentAdapterListen {
 
         when (uri.scheme) {
             "gemini" -> {
-                binding.addressBar.setText(uri.toString())
+                currentUrl = uri.toString()
                 pageViewModel.sendGeminiRequest(uri)
             }
             else -> openUnknownScheme(uri)
@@ -102,13 +121,21 @@ class MainActivity : AppCompatActivity(), ContentAdapter.ContentAdapterListen {
         adapter.setContent(lines)
     }
 
-    private fun alert(message: String, title: String? = null) {
-        val builder = AlertDialog.Builder(this)
-        if (title != null)
-            builder.setTitle(title)
-        else
-            builder.setTitle(title ?: R.string.alert_title)
-        builder
+    private fun handleEvent(event: PageViewModel.Event) {
+        Log.d(TAG, "handleEvent: $event")
+        if (!event.handled) {
+            when (event) {
+                is PageViewModel.SuccessEvent -> visitedUrls.add(event.uri)
+                is PageViewModel.RedirectEvent -> openUrl(event.uri, redirections = event.redirects)
+                is PageViewModel.FailureEvent -> alert(event.message)
+            }
+            event.handled = true
+        }
+    }
+
+    private fun alert(message: String) {
+        AlertDialog.Builder(this)
+            .setTitle(R.string.error_alert_title)
             .setMessage(message)
             .create()
             .show()
@@ -127,18 +154,23 @@ class MainActivity : AppCompatActivity(), ContentAdapter.ContentAdapterListen {
         val state: MutableLiveData<State> by lazy { MutableLiveData<State>(State.IDLE) }
         private var linesList = ArrayList<Line>()
         val lines: MutableLiveData<List<Line>> by lazy { MutableLiveData<List<Line>>() }
-        val alert: MutableLiveData<String> by lazy { MutableLiveData<String>() }
+        val event: MutableLiveData<Event> by lazy { MutableLiveData<Event>() }
 
         enum class State {
             IDLE, CONNECTING, RECEIVING
         }
 
+        abstract class Event(var handled: Boolean = false)
+        data class SuccessEvent(val uri: String) : Event()
+        data class RedirectEvent(val uri: String, val redirects: Int) : Event()
+        data class FailureEvent(val message: String) : Event()
+
         /**
          * Perform a request against this URI.
          *
          * The URI must be valid, absolute and with a gemini scheme.
          */
-        fun sendGeminiRequest(uri: Uri) {
+        fun sendGeminiRequest(uri: Uri, redirects: Int = 0) {
             Log.d(TAG, "sendRequest: URI \"$uri\"")
             state.postValue(State.CONNECTING)
             requestJob?.apply { if (isActive) cancel() }
@@ -148,40 +180,54 @@ class MainActivity : AppCompatActivity(), ContentAdapter.ContentAdapterListen {
                     val socket = request.connect()
                     val channel = request.proceed(socket, this)
                     Response.from(channel, viewModelScope)
-                } catch (e: UnknownHostException) {
-                    signalError("Unknown host \"${uri.authority}\".")
-                    return@launch
                 } catch (e: Exception) {
                     Log.e(TAG, "sendGeminiRequest coroutine: ${e.stackTraceToString()}")
-                    signalError("Oops! Whatever we tried to do failed!")
+                    // If we got cancelled, die silently.
+                    if (!isActive)
+                        return@launch
+                    signalError(
+                        when (e) {
+                            is UnknownHostException -> "Unknown host \"${uri.authority}\"."
+                            is ConnectException -> "Can't connect to this server: ${e.message}."
+                            else -> "Oops, something failed!"
+                        }
+                    )
                     return@launch
                 }
+                if (!isActive)
+                    return@launch
                 if (response == null) {
                     signalError("Can't parse server response.")
                     return@launch
                 }
 
                 Log.i(TAG, "sendRequest: got ${response.code} with meta \"${response.meta}\"")
-                when (response.code) {
-                    Response.Code.SUCCESS -> handleRequestSuccess(response)
+                when (response.code.getCategory()) {
+                    Response.Code.Category.SUCCESS -> handleRequestSuccess(response, uri)
+                    Response.Code.Category.REDIRECT -> handleRedirect(response, redirects = redirects + 1)
+                    Response.Code.Category.SERVER_ERROR -> handleError(response)
                     else -> signalError("Can't handle code ${response.code}.")
                 }
             }
         }
 
         private fun signalError(message: String) {
-            alert.postValue(message)
+            event.postValue(FailureEvent(message))
             state.postValue(State.IDLE)
         }
 
-        private suspend fun handleRequestSuccess(response: Response) {
+        private suspend fun handleRequestSuccess(response: Response, uri: Uri) {
             state.postValue(State.RECEIVING)
+
             linesList.clear()
             lines.postValue(linesList)
             val charset = Charset.defaultCharset()
+            var mainTitle: String? = null
             var lastUpdate = System.currentTimeMillis()
             for (line in parseData(response.data, charset, viewModelScope)) {
                 linesList.add(line)
+                if (mainTitle == null && line is TitleLine && line.level == 1)
+                    mainTitle = line.text
                 val time = System.currentTimeMillis()
                 if (time - lastUpdate >= 100) {  // Throttle to 100ms the recycler view updates…
                     lines.postValue(linesList)
@@ -189,8 +235,33 @@ class MainActivity : AppCompatActivity(), ContentAdapter.ContentAdapterListen {
                 }
             }
             lines.postValue(linesList)
+
+            // We record the history entry here: it's nice because we have the main title available
+            // and we're already in a coroutine for database access.
+            History.record(uri.toString(), mainTitle)
+            event.postValue(SuccessEvent(uri.toString()))
             state.postValue(State.IDLE)
         }
+
+        private fun handleRedirect(response: Response, redirects: Int) {
+            event.postValue(RedirectEvent(response.meta, redirects))
+        }
+
+        private fun handleError(response: Response) {
+            event.postValue(FailureEvent(when (response.code) {
+                Response.Code.TEMPORARY_FAILURE -> "40: the server encountered a temporary failure."
+                Response.Code.SERVER_UNAVAILABLE -> "41: the server is currently unavailable."
+                Response.Code.CGI_ERROR -> "42: a CGI script encountered an error."
+                Response.Code.PROXY_ERROR -> "43: the server failed to proxy the request."
+                Response.Code.SLOW_DOWN -> "44: slow down!"
+                Response.Code.PERMANENT_FAILURE -> "50: this request failed and similar requests will likely fail as well."
+                Response.Code.NOT_FOUND -> "51: this page can't be found."
+                Response.Code.GONE -> "52: this page is gone."
+                Response.Code.PROXY_REQUEST_REFUSED -> "53: the server refused to proxy the request."
+                Response.Code.BAD_REQUEST -> "59: bad request."
+                else -> "${response.code}: unknown error code."
+            }))
+        }
     }
 
     companion object {

app/src/main/java/dev/lowrespalmtree/comet/Response.kt

@@ -31,6 +31,18 @@ class Response(val code: Code, val meta: String, val data: Channel<ByteArray>) {
         CERTIFICATE_NOT_AUTHORISED(61),
         CERTIFICATE_NOT_VALID(62);
 
+        enum class Category(val value: Int) {
+            UNKNOWN(0),
+            INPUT(1),
+            SUCCESS(2),
+            REDIRECT(3),
+            SERVER_ERROR(4),
+            CLIENT_ERROR(5),
+            CERTIFICATE(6);
+        }
+
+        fun getCategory(): Category? = Category.values().associateBy(Category::value)[value / 10]
+
         companion object {
             private val MAP = values().associateBy(Code::value)
             fun fromInt(type: Int) = MAP[type]

app/src/main/res/layout/gemtext_blockquote.xml

@@ -8,5 +8,5 @@
     android:layout_height="wrap_content"
     android:paddingStart="32dp"
     android:paddingEnd="16dp"
-    android:paddingTop="4dp"
+    android:paddingTop="2dp"
     android:paddingBottom="4dp" />

app/src/main/res/layout/gemtext_link.xml

@@ -7,6 +7,6 @@
     android:layout_height="wrap_content"
     android:paddingStart="16dp"
     android:paddingEnd="16dp"
-    android:paddingTop="4dp"
+    android:paddingTop="2dp"
     android:paddingBottom="4dp"
     android:textIsSelectable="false" />

app/src/main/res/layout/gemtext_list_item.xml

@@ -8,4 +8,4 @@
     android:paddingStart="32dp"
     android:paddingEnd="16dp"
     android:paddingTop="2dp"
-    android:paddingBottom="2dp" />
+    android:paddingBottom="4dp" />

app/src/main/res/layout/gemtext_paragraph.xml

@@ -7,5 +7,5 @@
     android:layout_height="wrap_content"
     android:paddingStart="16dp"
     android:paddingEnd="16dp"
-    android:paddingTop="4dp"
+    android:paddingTop="2dp"
     android:paddingBottom="4dp" />

app/src/main/res/values/strings.xml

@@ -1,6 +1,6 @@
 <resources>
     <string name="app_name">Comet</string>
-    <string name="alert_title">Alert</string>
+    <string name="error_alert_title">Error</string>
     <string name="action_settings">Settings</string>
     <string name="url">URL</string>
 </resources>