Implement database access (with migrations)

core/assets/main/migrations/009.sql

@@ -0,0 +1,5 @@
+create table Habits ( id integer primary key autoincrement, archived integer, color integer, description text, freq_den integer, freq_num integer, highlight integer, name text, position integer, reminder_hour integer, reminder_min integer )
+create table Checkmarks ( id integer primary key autoincrement, habit integer references habits(id), timestamp integer, value integer )
+create table Repetitions ( id integer primary key autoincrement, habit integer references habits(id), timestamp integer )
+create table Streak ( id integer primary key autoincrement, end integer, habit integer references habits(id), length integer, start integer )
+create table Score ( id integer primary key autoincrement, habit integer references habits(id), score integer, timestamp integer )

core/assets/main/migrations/010.sql

@@ -0,0 +1,3 @@
+delete from Score
+delete from Streak
+delete from Checkmarks

core/assets/main/migrations/011.sql

@@ -0,0 +1 @@
+alter table Habits add column reminder_days integer not null default 127

core/assets/main/migrations/012.sql

@@ -0,0 +1,3 @@
+delete from Score
+delete from Streak
+delete from Checkmarks

core/assets/main/migrations/013.sql

@@ -0,0 +1,4 @@
+create index idx_score_habit_timestamp on Score(habit, timestamp)
+create index idx_checkmark_habit_timestamp on Checkmarks(habit, timestamp)
+create index idx_repetitions_habit_timestamp on Repetitions(habit, timestamp)
+create index idx_streak_habit_end on Streak(habit, end)

core/assets/main/migrations/014.sql

@@ -0,0 +1,14 @@
+update habits set color=0 where color=-2937041
+update habits set color=1 where color=-1684967
+update habits set color=2 where color=-415707
+update habits set color=3 where color=-5262293
+update habits set color=4 where color=-13070788
+update habits set color=5 where color=-16742021
+update habits set color=6 where color=-16732991
+update habits set color=7 where color=-16540699
+update habits set color=8 where color=-10603087
+update habits set color=9 where color=-7461718
+update habits set color=10 where color=-2614432
+update habits set color=11 where color=-13619152
+update habits set color=12 where color=-5592406
+update habits set color=0 where color<0 or color>12

core/assets/main/migrations/015.sql

@@ -0,0 +1,3 @@
+delete from Score
+delete from Streak
+delete from Checkmarks

core/assets/main/migrations/016.sql

@@ -0,0 +1,2 @@
+alter table Habits add column type integer not null default 0
+alter table Repetitions add column value integer not null default 2

core/assets/main/migrations/017.sql

@@ -0,0 +1,5 @@
+drop table Score
+create table Score ( id integer primary key autoincrement, habit integer references habits(id), score real, timestamp integer)
+create index idx_score_habit_timestamp on Score(habit, timestamp)
+delete from streak
+delete from checkmarks

core/assets/main/migrations/018.sql

@@ -0,0 +1,3 @@
+alter table Habits add column target_type integer not null default 0
+alter table Habits add column target_value real not null default 0
+alter table Habits add column unit text not null default ""

core/assets/main/migrations/019.sql

@@ -0,0 +1 @@
+create table Events ( id integer primary key autoincrement, timestamp integer, message text, server_id integer )

core/assets/main/migrations/020.sql

@@ -0,0 +1,3 @@
+drop table checkmarks
+drop table streak
+drop table score

core/assets/main/migrations/021.sql

@@ -0,0 +1,12 @@
+update habits set color=19 where color=12
+update habits set color=17 where color=11
+update habits set color=15 where color=10
+update habits set color=14 where color=9
+update habits set color=13 where color=8
+update habits set color=10 where color=7
+update habits set color=9 where color=6
+update habits set color=8 where color=5
+update habits set color=7 where color=4
+update habits set color=5 where color=3
+update habits set color=4 where color=2
+update habits set color=0 where color<0 or color>19

core/assets/main/migrations/022.sql

@@ -0,0 +1,11 @@
+delete from repetitions where habit not in (select id from habits)
+delete from repetitions where timestamp is null
+delete from repetitions where habit is null
+delete from repetitions where rowid not in ( select min(rowid) from repetitions group by habit, timestamp )
+alter table Repetitions rename to RepetitionsBak
+create table Repetitions ( id integer primary key autoincrement, habit integer not null references habits(id), timestamp integer not null, value integer not null)
+drop index if exists idx_repetitions_habit_timestamp
+create unique index idx_repetitions_habit_timestamp on Repetitions( habit, timestamp)
+insert into Repetitions select * from RepetitionsBak
+drop table RepetitionsBak
+pragma foreign_keys=ON

core/assets/test/hello.txt

@@ -0,0 +1,2 @@
+Hello World!
+This is a resource.

core/build.gradle

@@ -48,8 +48,8 @@ kotlin {
             compilations.main.outputKinds('FRAMEWORK')
         }
 
-        // Replace the target above with the following to produce a framework
-        // which can be installed on a real iPhone.
+        // Replace the target above by the following one to produce a framework
+        // which can be installed on a real iPhone:
         // fromPreset(presets.iosArm64, 'iOS') {
         //     compilations.main.outputKinds('FRAMEWORK')
         // }
@@ -76,6 +76,20 @@ kotlin {
             dependencies {
                 implementation 'org.jetbrains.kotlin:kotlin-test'
                 implementation 'org.jetbrains.kotlin:kotlin-test-junit'
+                implementation 'org.xerial:sqlite-jdbc:3.25.2'
+            }
+        }
+    }
+
+    task iosTest {
+        dependsOn 'linkTestDebugExecutableIOS'
+        group = JavaBasePlugin.VERIFICATION_GROUP
+        description = "Runs tests for target 'ios' on an iOS simulator"
+
+        doLast {
+            def binary = kotlin.targets.iOS.compilations.test.getBinary('EXECUTABLE', 'DEBUG')
+            exec {
+                commandLine 'xcrun', 'simctl', 'spawn', "iPhone 8", binary.absolutePath
             }
         }
     }

core/src/commonMain/kotlin/org/isoron/uhabits/Backend.kt

@@ -19,37 +19,38 @@
 
 package org.isoron.uhabits
 
-import org.isoron.uhabits.models.Color
-import org.isoron.uhabits.models.Frequency
-import org.isoron.uhabits.models.Habit
-import org.isoron.uhabits.models.HabitType
-import kotlin.random.Random
+import org.isoron.uhabits.models.HabitList
+import org.isoron.uhabits.utils.*
 
-class Backend {
-    var nextId = 1
-    var habits = mutableListOf<Habit>()
+class Backend(var databaseOpener: DatabaseOpener,
+              var fileOpener: FileOpener,
+              var log: Log) {
 
-    fun getHabitList(): Map<Int, Map<String, *>> {
-        return habits.map { h ->
-            h.id to mapOf("name" to h.name,
-                          "color" to h.color.paletteIndex)
-        }.toMap()
+    var db: Database
+
+    var habits: HabitList
+
+    init {
+        val dbFile = fileOpener.openUserFile("uhabits.sqlite3")
+        db = databaseOpener.open(dbFile)
+        db.migrateTo(LOOP_DATABASE_VERSION, fileOpener, log)
+        habits = HabitList(db)
+    }
+
+    fun getHabitList(): List<Map<String, *>> {
+        return habits.getActive().map { h ->
+            mapOf("key" to h.id.toString(),
+                  "name" to h.name,
+                  "color" to h.color.paletteIndex)
+        }
     }
 
     fun createHabit(name: String) {
-        val c = (nextId / 4) % 5
-        habits.add(Habit(nextId, name, "", Frequency(1, 1), Color(c),
-                         false, habits.size, "", 0, HabitType.YES_NO_HABIT))
-        nextId += 1
     }
 
     fun deleteHabit(id: Int) {
-        val h = habits.find { h -> h.id == id }
-        if (h != null) habits.remove(h)
     }
 
     fun updateHabit(id: Int, name: String) {
-        val h = habits.find { h -> h.id == id }
-        h?.name = name
     }
 }

core/src/commonMain/kotlin/org/isoron/uhabits/Config.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits
+
+const val LOOP_DATABASE_VERSION = 22

core/src/commonMain/kotlin/org/isoron/uhabits/models/HabitList.kt

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.models
+
+import org.isoron.uhabits.utils.Database
+import org.isoron.uhabits.utils.StepResult
+
+class HabitList(var db: Database) {
+    var habits = mutableListOf<Habit>()
+
+    init {
+        loadHabitsFromDatabase()
+    }
+
+    fun getActive(): List<Habit> {
+        return habits.filter { h -> !h.isArchived }
+    }
+
+    private fun loadHabitsFromDatabase() {
+        val stmt = db.prepareStatement(
+                "select id, name, description, freq_num, freq_den, color, " +
+                        "archived, position, unit, target_value, type " +
+                        "from habits")
+
+        while (stmt.step() == StepResult.ROW) {
+            habits.add(Habit(id = stmt.getInt(0),
+                             name = stmt.getText(1),
+                             description = stmt.getText(2),
+                             frequency = Frequency(stmt.getInt(3),
+                                                   stmt.getInt(4)),
+                             color = Color(stmt.getInt(5)),
+                             isArchived = (stmt.getInt(6) != 0),
+                             position = stmt.getInt(7),
+                             unit = stmt.getText(8),
+                             target = 0,
+                             type = HabitType.YES_NO_HABIT))
+        }
+        stmt.finalize()
+    }
+}

core/src/commonMain/kotlin/org/isoron/uhabits/utils/Database.kt

@@ -0,0 +1,88 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+enum class StepResult {
+    ROW,
+    DONE
+}
+
+interface PreparedStatement {
+    fun step(): StepResult
+    fun finalize()
+    fun getInt(index: Int): Int
+    fun getText(index: Int): String
+    fun bindInt(index: Int, value: Int)
+    fun bindText(index: Int, value: String)
+    fun reset()
+}
+
+interface Database {
+    fun prepareStatement(sql: String): PreparedStatement
+    fun close()
+}
+
+interface DatabaseOpener {
+    fun open(file: UserFile): Database
+}
+
+fun Database.execute(sql: String) {
+    val stmt = prepareStatement(sql)
+    stmt.step()
+    stmt.finalize()
+}
+
+fun Database.queryInt(sql: String): Int {
+    val stmt = prepareStatement(sql)
+    stmt.step()
+    val result = stmt.getInt(0)
+    stmt.finalize()
+    return result
+}
+
+fun Database.begin() = execute("begin")
+fun Database.commit() = execute("commit")
+fun Database.rollback() = execute("rollback")
+fun Database.getVersion() = queryInt("pragma user_version")
+fun Database.setVersion(v: Int) = execute("pragma user_version = $v")
+
+fun Database.migrateTo(newVersion: Int, fileOpener: FileOpener, log: Log) {
+    val currentVersion = getVersion()
+    log.debug("Current database version: $currentVersion")
+
+    if (currentVersion == newVersion) return
+    log.debug("Upgrading to version: $newVersion")
+
+    if (currentVersion > newVersion)
+        throw RuntimeException("database produced by future version of the application")
+    
+    begin()
+    for (v in (currentVersion + 1)..newVersion) {
+        log.debug("Running migration $v")
+        val filename = sprintf("migrations/%03d.sql", v)
+        val migrationFile = fileOpener.openResourceFile(filename)
+        for (line in migrationFile.readLines()) {
+            if (line.isEmpty()) continue
+            execute(line)
+        }
+        setVersion(v)
+    }
+    commit()
+}

core/src/commonMain/kotlin/org/isoron/uhabits/utils/Files.kt

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+/**
+ * Represents a file that was shipped with the application, such as migration
+ * files or translations. These files cannot be deleted.
+ */
+interface ResourceFile {
+    fun readLines(): List<String>
+}
+
+/**
+ * Represents a file that was created after the application was installed, as a
+ * result of some user action, such as databases and logs. These files can be
+ * deleted.
+ */
+interface UserFile {
+    fun delete()
+    fun exists(): Boolean
+}
+
+interface FileOpener {
+    /**
+     * Opens a file which was shipped bundled with the application, such as a
+     * migration file.
+     *
+     * The path is relative to the assets folder. For example, to open
+     * assets/main/migrations/09.sql you should provide migrations/09.sql
+     * as the filename.
+     */
+    fun openResourceFile(filename: String): ResourceFile
+
+    /**
+     * Opens a file which was not shipped with the application, such as
+     * databases and logs.
+     *
+     * The path is relative to the user folder. For example, if the application
+     * stores the user data at /home/user/.loop/ and you wish to open the file
+     * /home/user/.loop/crash.log, you should provide crash.log as the filename.
+     */
+    fun openUserFile(filename: String): UserFile
+}

core/src/commonMain/kotlin/org/isoron/uhabits/utils/Log.kt

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+interface Log {
+    fun info(msg: String)
+    fun debug(msg: String)
+}

core/src/commonMain/kotlin/org/isoron/uhabits/utils/Strings.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+expect fun sprintf(format: String, vararg args: Any?): String

core/src/commonTest/kotlin/org/isoron/uhabits/utils/StringsTest.kt

@@ -17,33 +17,14 @@
  * with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-package org.isoron.uhabits
+package org.isoron.uhabits.utils
 
 import kotlin.test.Test
 import kotlin.test.assertEquals
-import kotlin.test.assertTrue
 
-class BackendTest {
+class StringsTest {
     @Test
-    fun testBackend() {
-        val backend = Backend()
-        assertEquals(backend.getHabitList().size, 0)
-
-        backend.createHabit("Brush teeth")
-        backend.createHabit("Wake up early")
-
-        var result = backend.getHabitList()
-        assertEquals(result.size, 2)
-        assertEquals(result[1]!!["name"], "Brush teeth")
-        assertEquals(result[2]!!["name"], "Wake up early")
-
-        backend.deleteHabit(1)
-        result = backend.getHabitList()
-        assertEquals(result.size, 1)
-        assertTrue(2 in result.keys)
-
-        backend.updateHabit(2, "Wake up late")
-        result = backend.getHabitList()
-        assertEquals(result[2]!!["name"], "Wake up late")
+    fun testSprintf() {
+        assertEquals("Number 004", sprintf("Number %03d", 4))
     }
 }

core/src/iosMain/kotlin/org/isoron/uhabits/utils/Strings.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+import kotlinx.cinterop.*
+
+actual fun sprintf(format: String, vararg args: Any?): String {
+    val buffer = ByteArray(1000)
+    buffer.usePinned { p ->
+        platform.posix.sprintf(p.addressOf(0), format, *args)
+    }
+    return buffer.stringFromUtf8()
+}

core/src/jvmMain/kotlin/org/isoron/uhabits/database/JavaDatabase.kt

@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.database
+
+import org.isoron.uhabits.utils.*
+import java.sql.Connection
+import java.sql.DriverManager
+import java.sql.PreparedStatement
+import java.sql.ResultSet
+
+class JavaPreparedStatement(private var stmt : PreparedStatement) : org.isoron.uhabits.utils.PreparedStatement {
+
+    private var rs: ResultSet? = null
+    private var hasExecuted = false
+
+    override fun step(): StepResult {
+        if (!hasExecuted) {
+            hasExecuted = true
+            val hasResult = stmt.execute()
+            if (hasResult) rs = stmt.resultSet
+        }
+
+        if (rs == null || !rs!!.next()) return StepResult.DONE
+        return StepResult.ROW
+    }
+
+    override fun finalize() {
+        stmt.close()
+    }
+
+    override fun getInt(index: Int): Int {
+        return rs!!.getInt(index + 1)
+    }
+
+    override fun getText(index: Int): String {
+        return rs!!.getString(index + 1)
+    }
+
+    override fun bindInt(index: Int, value: Int) {
+        stmt.setInt(index, value)
+    }
+
+    override fun bindText(index: Int, value: String) {
+        stmt.setString(index, value)
+    }
+
+    override fun reset() {
+        stmt.clearParameters()
+    }
+}
+
+class JavaDatabase(private var conn: Connection,
+                   private val log: Log) : Database {
+
+    override fun prepareStatement(sql: String): org.isoron.uhabits.utils.PreparedStatement {
+        log.debug("Running SQL: ${sql}")
+        return JavaPreparedStatement(conn.prepareStatement(sql))
+    }
+    override fun close() {
+        conn.close()
+    }
+}
+
+class JavaDatabaseOpener(private val log: Log) : DatabaseOpener {
+    override fun open(file: UserFile): Database {
+        val platformFile = file as JavaUserFile
+        val conn = DriverManager.getConnection("jdbc:sqlite:${platformFile.path}")
+        return JavaDatabase(conn, log)
+    }
+}

core/src/jvmMain/kotlin/org/isoron/uhabits/utils/JavaFiles.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+import java.nio.file.Files
+import java.nio.file.Path
+import java.nio.file.Paths
+
+class JavaResourceFile(private val path: Path) : ResourceFile {
+    override fun readLines(): List<String> {
+        return Files.readAllLines(path)
+    }
+}
+
+class JavaUserFile(val path: Path) : UserFile {
+    override fun exists(): Boolean {
+        return Files.exists(path)
+    }
+
+    override fun delete() {
+        Files.delete(path)
+    }
+}
+
+class JavaFileOpener : FileOpener {
+    override fun openUserFile(filename: String): UserFile {
+        val path = Paths.get("/tmp/$filename")
+        return JavaUserFile(path)
+    }
+
+    override fun openResourceFile(filename: String): ResourceFile {
+        val rootFolders = listOf("assets/main",
+                                 "assets/test")
+        for (root in rootFolders) {
+            val path = Paths.get("$root/$filename")
+            if (Files.exists(path) && Files.isReadable(path)) {
+                return JavaResourceFile(path)
+            }
+        }
+        throw RuntimeException("file not found")
+    }
+}

core/src/jvmMain/kotlin/org/isoron/uhabits/utils/JavaLog.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+class JavaLog : Log {
+    override fun info(msg: String) {
+        println("[I] $msg")
+    }
+
+    override fun debug(msg: String) {
+        println("[D] $msg")
+    }
+}

core/src/jvmMain/kotlin/org/isoron/uhabits/utils/Strings.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+actual fun sprintf(format: String, vararg args: Any?): String {
+    return String.format(format, *args)
+}

core/src/jvmTest/kotlin/org/isoron/uhabits/BackendTest.kt

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits
+
+import junit.framework.Assert.assertEquals
+import junit.framework.Assert.assertTrue
+import org.junit.Test
+
+class BackendTest : BaseTest() {
+    @Test
+    fun testBackend() {
+//        val backend = Backend(databaseOpener, fileOpener)
+//        assertEquals(backend.getHabitList().size, 0)
+//
+//        backend.createHabit("Brush teeth")
+//        backend.createHabit("Wake up early")
+
+//        var result = backend.getHabitList()
+//        assertEquals(2, result.size)
+//        assertEquals(result[0]["name"], "Brush teeth")
+//        assertEquals(result[0]["name"], "Wake up early")
+//
+//        backend.deleteHabit(1)
+//        result = backend.getHabitList()
+//        assertEquals(result.size, 1)
+//
+//        backend.updateHabit(2, "Wake up late")
+//        result = backend.getHabitList()
+//        assertEquals(result[2]["name"], "Wake up late")
+    }
+}

core/src/jvmTest/kotlin/org/isoron/uhabits/BaseTest.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits
+
+import org.isoron.uhabits.utils.JavaFileOpener
+import org.isoron.uhabits.database.JavaDatabaseOpener
+import org.isoron.uhabits.utils.JavaLog
+
+open class BaseTest {
+    val fileOpener = JavaFileOpener()
+    val databaseOpener = JavaDatabaseOpener(JavaLog())
+}

core/src/jvmTest/kotlin/org/isoron/uhabits/database/JavaDatabaseTest.kt

@@ -0,0 +1,82 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.database
+
+import org.isoron.uhabits.BaseTest
+import org.isoron.uhabits.utils.*
+import org.junit.Before
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class JavaDatabaseTest : BaseTest() {
+    private lateinit var db: Database
+
+    @Before
+    fun setup() {
+        val dbFile = fileOpener.openUserFile("test.sqlite3")
+        if (dbFile.exists()) dbFile.delete()
+        db = databaseOpener.open(dbFile)
+    }
+
+    @Test
+    fun testUsage() {
+        db.setVersion(0)
+        assertEquals(db.getVersion(), 0)
+
+        db.setVersion(23)
+        assertEquals(db.getVersion(), 23)
+
+        var stmt = db.prepareStatement("drop table if exists demo")
+        stmt.step()
+        stmt.finalize()
+
+        stmt = db.prepareStatement("create table if not exists demo(key int, value text)")
+        stmt.step()
+        stmt.finalize()
+
+        stmt = db.prepareStatement("insert into demo(key, value) values (?1, ?2)")
+        stmt.bindInt(1, 42)
+        stmt.bindText(2, "Hello World")
+        stmt.step()
+        stmt.finalize()
+
+        stmt = db.prepareStatement("select * from demo where key > ?1")
+        stmt.bindInt(1, 10)
+
+        var result = stmt.step()
+        assertEquals(result, StepResult.ROW)
+        assertEquals(stmt.getInt(0), 42)
+        assertEquals(stmt.getText(1), "Hello World")
+
+        result = stmt.step()
+        assertEquals(result, StepResult.DONE)
+
+        stmt.finalize()
+        db.close()
+    }
+
+    @Test
+    fun testMigrateTo() {
+        assertEquals(0, db.getVersion())
+        db.migrateTo(22, fileOpener)
+        assertEquals(22, db.getVersion())
+        db.execute("select * from habits")
+    }
+}

core/src/jvmTest/kotlin/org/isoron/uhabits/utils/JavaFilesTest.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2016-2019 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.utils
+
+import org.isoron.uhabits.BaseTest
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class JavaFilesTest : BaseTest() {
+    @Test
+    fun testReadLines() {
+        val hello = fileOpener.openResourceFile("hello.txt")
+        var lines = hello.readLines()
+        assertEquals("Hello World!", lines[0])
+        assertEquals("This is a resource.", lines[1])
+
+        val migration = fileOpener.openResourceFile("migrations/012.sql")
+        lines = migration.readLines()
+        assertEquals("delete from Score", lines[0])
+    }
+}