Working code

25 files changed, 967 insertions, 0 deletions

diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..e208a16
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,3 @@
+/gradlew        text eol=lf
+*.bat           text eol=crlf
+
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..750a400
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+.gradle
+build
+.idea
+.autoupdates
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..f387ae2
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,8 @@
+Copyright (c) 2022 Linnea Gräf.
+
+Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
+
+    1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/build.gradle.kts b/build.gradle.kts
new file mode 100644
index 0000000..2cf2eb9
--- /dev/null
+++ b/build.gradle.kts
@@ -0,0 +1,68 @@
+plugins {
+    `maven-publish`
+    signing
+    java
+}
+
+group = "moe.nea"
+version = "0.1.0"
+
+allprojects {
+    apply(plugin = "java")
+    tasks.withType(JavaCompile::class) {
+        sourceCompatibility = "1.8"
+        targetCompatibility = "1.8"
+    }
+    repositories {
+        mavenCentral()
+    }
+}
+
+project(":updater") {
+    tasks.jar {
+        archiveFileName.set("updater.jar")
+        manifest {
+            attributes(
+                mapOf(
+                    "Main-Class" to "moe.nea.libautoupdate.postexit.PostExitMain"
+                )
+            )
+        }
+    }
+}
+
+dependencies {
+    compileOnly("org.projectlombok:lombok:1.18.24")
+    annotationProcessor("org.projectlombok:lombok:1.18.24")
+    implementation("com.google.code.gson:gson:2.2.4")
+}
+
+
+tasks.processResources {
+    val updateJar = tasks.getByPath(":updater:jar")
+    from(updateJar.outputs)
+}
+
+publishing {
+    publications {
+        create<MavenPublication>("maven") {
+            from(components["java"])
+            pom {
+                licenses {
+                    license {
+                        name.set("BSD-2-Clause")
+                    }
+                }
+                developers {
+                    developer {
+                        name.set("Linnea Gräf")
+                    }
+                }
+                scm {
+                    url.set("https://git.nea.moe/nea/libautoupdate")
+                }
+            }
+        }
+    }
+    repositories { }
+}
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..249e583
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.jar
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000..ae04661
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.5.1-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/gradlew b/gradlew
new file mode 100755
index 0000000..a69d9cb
--- /dev/null
+++ b/gradlew
@@ -0,0 +1,240 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# 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
+#
+#      https://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.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"
diff --git a/gradlew.bat b/gradlew.bat
new file mode 100644
index 0000000..f127cfd
--- /dev/null
+++ b/gradlew.bat
@@ -0,0 +1,91 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/settings.gradle.kts b/settings.gradle.kts
new file mode 100644
index 0000000..fb48404
--- /dev/null
+++ b/settings.gradle.kts
@@ -0,0 +1,3 @@
+rootProject.name = "libautoupdate"
+
+include("updater")
diff --git a/src/main/java/moe/nea/libautoupdate/CurrentVersion.java b/src/main/java/moe/nea/libautoupdate/CurrentVersion.java
new file mode 100644
index 0000000..52b8372
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/CurrentVersion.java
@@ -0,0 +1,9 @@
+package moe.nea.libautoupdate;
+
+public interface CurrentVersion {
+    int getCurrentVersionNumber();
+
+    static CurrentVersion of(int number) {
+        return () -> number;
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/DeleteAndSaveInSameFolderUpdateTarget.java b/src/main/java/moe/nea/libautoupdate/DeleteAndSaveInSameFolderUpdateTarget.java
new file mode 100644
index 0000000..3e07f45
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/DeleteAndSaveInSameFolderUpdateTarget.java
@@ -0,0 +1,22 @@
+package moe.nea.libautoupdate;
+
+import lombok.SneakyThrows;
+import lombok.Value;
+
+import java.io.File;
+import java.util.Arrays;
+import java.util.List;
+
+@Value
+public class DeleteAndSaveInSameFolderUpdateTarget implements UpdateTarget {
+    File file;
+
+    @SneakyThrows
+    @Override
+    public List<UpdateAction> generateUpdateActions(PotentialUpdate update) {
+        return Arrays.asList(
+                new UpdateAction.DeleteFile(file),
+                new UpdateAction.MoveDownloadedFile(update.getUpdateJarStorage(), new File(file.getParentFile(), update.getFileName()))
+        );
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/ExitHookInvoker.java b/src/main/java/moe/nea/libautoupdate/ExitHookInvoker.java
new file mode 100644
index 0000000..55436a2
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/ExitHookInvoker.java
@@ -0,0 +1,62 @@
+package moe.nea.libautoupdate;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
+
+public class ExitHookInvoker {
+
+    private static boolean isExitHookRegistered = false;
+    private static List<UpdateAction> actions;
+    private static File updaterJar;
+    private static boolean cancelled = false;
+
+
+    public static synchronized void setExitHook(File updaterJar, List<UpdateAction> actions) {
+        if (!isExitHookRegistered) {
+            Runtime.getRuntime().addShutdownHook(new Thread(ExitHookInvoker::runExitHook));
+
+            isExitHookRegistered = true;
+        }
+        ExitHookInvoker.cancelled = false;
+        ExitHookInvoker.actions = actions;
+        ExitHookInvoker.updaterJar = updaterJar;
+    }
+
+    public static synchronized void cancelUpdate() {
+        cancelled = true;
+    }
+
+    private static synchronized String[] buildInvocation() {
+        boolean isWindows = System.getProperty("os.name", "").startsWith("Windows");
+        File javaBinary = new File(System.getProperty("java.home"), "bin/java" + (isWindows ? ".exe" : ""));
+
+
+        List<String> arguments = new ArrayList<>();
+        arguments.add(javaBinary.getAbsolutePath());
+        arguments.add("-jar");
+        arguments.add(updaterJar.getAbsolutePath());
+
+        for (UpdateAction action : actions) {
+            action.encode(arguments);
+        }
+
+        return arguments.toArray(new String[0]);
+    }
+
+    private static void runExitHook() {
+        try {
+            if (cancelled) {
+                System.out.println("Skipping cancelled update");
+                return;
+            }
+            String[] invocation = buildInvocation();
+            System.out.println("Running post updater using: " + String.join(" ", invocation));
+            Runtime.getRuntime().exec(invocation);
+        } catch (Throwable t) {
+            t.printStackTrace();
+        }
+    }
+
+
+}
diff --git a/src/main/java/moe/nea/libautoupdate/GistSource.java b/src/main/java/moe/nea/libautoupdate/GistSource.java
new file mode 100644
index 0000000..a8ae5df
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/GistSource.java
@@ -0,0 +1,19 @@
+package moe.nea.libautoupdate;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+
+import java.util.concurrent.CompletableFuture;
+
+@Value
+@EqualsAndHashCode(callSuper = false)
+public class GistSource extends JsonUpdateSource {
+    String owner;
+    String gistId;
+    private static final String GIST_RAW_URL = "https://gist.githubusercontent.com/%s/%s/raw/%s.json";
+
+    @Override
+    public CompletableFuture<UpdateData> checkUpdate(String updateStream) {
+        return getJsonFromURL(String.format(GIST_RAW_URL, owner, gistId, updateStream), UpdateData.class);
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/JsonUpdateSource.java b/src/main/java/moe/nea/libautoupdate/JsonUpdateSource.java
new file mode 100644
index 0000000..ffbfa9a
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/JsonUpdateSource.java
@@ -0,0 +1,31 @@
+package moe.nea.libautoupdate;
+
+import com.google.gson.Gson;
+import lombok.val;
+
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.nio.charset.StandardCharsets;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+
+public abstract class JsonUpdateSource implements UpdateSource {
+    private static final Gson gson = new Gson();
+
+    protected Gson getGson() {
+        return gson;
+    }
+
+    protected <T> CompletableFuture<T> getJsonFromURL(String url, Class<T> clazz) {
+        return CompletableFuture.supplyAsync(() -> {
+            try {
+                try (val is = new URL(url).openStream()) {
+                    return getGson().fromJson(new InputStreamReader(is, StandardCharsets.UTF_8), clazz);
+                }
+            } catch (IOException e) {
+                throw new CompletionException(e);
+            }
+        });
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/Main.java b/src/main/java/moe/nea/libautoupdate/Main.java
new file mode 100644
index 0000000..5d98df1
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/Main.java
@@ -0,0 +1,22 @@
+package moe.nea.libautoupdate;
+
+public class Main {
+    public static void main(String[] args) {
+
+        UpdateContext updater = new UpdateContext(
+                UpdateSource.gistSource("romangraef", "9b62fe32bc41c09d2d7e2d3153f14ee8"),
+                UpdateTarget.deleteAndSaveInTheSameFolder(Main.class),
+                CurrentVersion.of(10000),
+                "test"
+        );
+        updater.cleanup();
+        System.out.println("Update cleaned");
+        System.out.println("Created update context: " + updater);
+        updater.checkUpdate("stable").thenCompose(it -> {
+            System.out.println("Checked for update on stable: " + it);
+            System.out.println("Can update: " + it.isUpdateAvailable());
+            System.out.println("Executing update.");
+            return it.launchUpdate();
+        }).join();
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/PotentialUpdate.java b/src/main/java/moe/nea/libautoupdate/PotentialUpdate.java
new file mode 100644
index 0000000..2e6142d
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/PotentialUpdate.java
@@ -0,0 +1,94 @@
+package moe.nea.libautoupdate;
+
+import lombok.Value;
+import lombok.val;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.net.MalformedURLException;
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+
+@Value
+public class PotentialUpdate {
+    UpdateData update;
+    UpdateContext context;
+    UUID updateUUID = UUID.randomUUID();
+
+    public File getUpdateDirectory() {
+        return new File(".autoupdates", context.getIdentifier() + "/" + updateUUID);
+    }
+
+
+    public boolean isUpdateAvailable() {
+        if (update == null) return false;
+        return update.getVersionNumber() > context.getCurrentVersion().getCurrentVersionNumber();
+    }
+
+    private File getFile(String name) {
+        getUpdateDirectory().mkdirs();
+        return new File(getUpdateDirectory(), name);
+    }
+
+    public File getUpdateJarStorage() {
+        return getFile("next.jar");
+    }
+
+    public String getFileName() throws MalformedURLException {
+        val split = update.getDownloadAsURL().getPath().split("/");
+        return split[split.length - 1];
+    }
+
+
+    public void extractUpdater() throws IOException {
+        val file = getFile("updater.jar");
+        try (val from = getClass().getResourceAsStream("/updater.jar");
+             val to = new FileOutputStream(file)) {
+            UpdateUtils.connect(from, to);
+        }
+    }
+
+    public void downloadUpdate() throws IOException {
+        try (val from = update.getDownloadAsURL().openStream();
+             val to = new FileOutputStream(getUpdateJarStorage())) {
+            UpdateUtils.connect(from, to);
+        }
+        try (val check = new FileInputStream(getUpdateJarStorage())) {
+            val updateSha = UpdateUtils.sha256sum(check);
+            if (!update.getSha256().equalsIgnoreCase(updateSha)) {
+                throw new UpdateException(
+                        "Hash of downloaded file " + getUpdateJarStorage() +
+                                " (" + updateSha + ") does not match expected hash of " +
+                                update.getSha256());
+            }
+        }
+    }
+
+    public void prepareUpdate() throws IOException {
+        extractUpdater();
+        downloadUpdate();
+    }
+
+
+    public void executeUpdate() throws IOException {
+        prepareUpdate();
+        ExitHookInvoker.setExitHook(getFile("updater.jar"),
+                context.getTarget().generateUpdateActions(this));
+    }
+
+
+    public CompletableFuture<Void> launchUpdate() {
+        return CompletableFuture.supplyAsync(() -> {
+            try {
+                executeUpdate();
+            } catch (IOException e) {
+                throw new CompletionException(e);
+            }
+            return null;
+        });
+    }
+
+}
diff --git a/src/main/java/moe/nea/libautoupdate/ReplaceJarUpdateTarget.java b/src/main/java/moe/nea/libautoupdate/ReplaceJarUpdateTarget.java
new file mode 100644
index 0000000..f31481c
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/ReplaceJarUpdateTarget.java
@@ -0,0 +1,20 @@
+package moe.nea.libautoupdate;
+
+import lombok.Value;
+
+import java.io.File;
+import java.util.Arrays;
+import java.util.List;
+
+@Value
+public class ReplaceJarUpdateTarget implements UpdateTarget {
+    File file;
+
+    @Override
+    public List<UpdateAction> generateUpdateActions(PotentialUpdate update) {
+        return Arrays.asList(
+                new UpdateAction.DeleteFile(file),
+                new UpdateAction.MoveDownloadedFile(update.getUpdateJarStorage(), file)
+        );
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/UpdateAction.java b/src/main/java/moe/nea/libautoupdate/UpdateAction.java
new file mode 100644
index 0000000..ae9852e
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/UpdateAction.java
@@ -0,0 +1,43 @@
+package moe.nea.libautoupdate;
+
+import lombok.EqualsAndHashCode;
+import lombok.NonNull;
+import lombok.Value;
+
+import java.io.File;
+import java.util.List;
+
+public abstract class UpdateAction {
+    private UpdateAction() {
+    }
+
+    public abstract void encode(List<String> arguments);
+
+    @Value
+    @EqualsAndHashCode(callSuper = false)
+    public static class DeleteFile extends UpdateAction {
+        @NonNull File toDelete;
+
+        @Override
+        public void encode(List<String> arguments) {
+            arguments.add("delete");
+            arguments.add(toDelete.getAbsolutePath());
+        }
+    }
+
+    @Value
+    @EqualsAndHashCode(callSuper = false)
+    public static class MoveDownloadedFile extends UpdateAction {
+        @NonNull File whereFrom;
+        @NonNull File whereTo;
+
+        @Override
+        public void encode(List<String> arguments) {
+            arguments.add("move");
+            arguments.add(whereFrom.getAbsolutePath());
+            arguments.add(whereTo.getAbsolutePath());
+        }
+    }
+
+
+}
diff --git a/src/main/java/moe/nea/libautoupdate/UpdateContext.java b/src/main/java/moe/nea/libautoupdate/UpdateContext.java
new file mode 100644
index 0000000..fa8b8d5
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/UpdateContext.java
@@ -0,0 +1,32 @@
+package moe.nea.libautoupdate;
+
+
+import lombok.NonNull;
+import lombok.Value;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.concurrent.CompletableFuture;
+
+@Value
+public class UpdateContext {
+    @NonNull UpdateSource source;
+    @NonNull UpdateTarget target;
+    @NonNull CurrentVersion currentVersion;
+    @NonNull String identifier;
+
+
+    public void cleanup() {
+        File file = new File(".autoupdates", identifier).getAbsoluteFile();
+        try {
+            UpdateUtils.deleteDirectory(file.toPath());
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    public CompletableFuture<PotentialUpdate> checkUpdate(String updateStream) {
+        return source.checkUpdate(updateStream)
+                .thenApply(it -> new PotentialUpdate(it, this));
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/UpdateData.java b/src/main/java/moe/nea/libautoupdate/UpdateData.java
new file mode 100644
index 0000000..276ae5f
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/UpdateData.java
@@ -0,0 +1,22 @@
+package moe.nea.libautoupdate;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.net.MalformedURLException;
+import java.net.URL;
+
+@Data
+@NoArgsConstructor
+@AllArgsConstructor
+public class UpdateData {
+    String versionName;
+    int versionNumber;
+    String sha256;
+    String download;
+
+    public URL getDownloadAsURL() throws MalformedURLException {
+        return new URL(download);
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/UpdateException.java b/src/main/java/moe/nea/libautoupdate/UpdateException.java
new file mode 100644
index 0000000..482263b
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/UpdateException.java
@@ -0,0 +1,7 @@
+package moe.nea.libautoupdate;
+
+public class UpdateException extends RuntimeException {
+    public UpdateException(String message) {
+        super(message);
+    }
+}
diff --git a/src/main/java/moe/nea/libautoupdate/UpdateSource.java b/src/main/java/moe/nea/libautoupdate/UpdateSource.java
new file mode 100644
index 0000000..1407063
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/UpdateSource.java
@@ -0,0 +1,11 @@
+package moe.nea.libautoupdate;
+
+import java.util.concurrent.CompletableFuture;
+
+public interface UpdateSource {
+    static UpdateSource gistSource(String owner, String gistId) {
+        return new GistSource(owner, gistId);
+    }
+
+    CompletableFuture<UpdateData> checkUpdate(String updateStream);
+}
diff --git a/src/main/java/moe/nea/libautoupdate/UpdateTarget.java b/src/main/java/moe/nea/libautoupdate/UpdateTarget.java
new file mode 100644
index 0000000..fcaaa3e
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/UpdateTarget.java
@@ -0,0 +1,19 @@
+package moe.nea.libautoupdate;
+
+import java.io.File;
+import java.util.List;
+
+public interface UpdateTarget {
+    List<UpdateAction> generateUpdateActions(PotentialUpdate update);
+
+    static UpdateTarget replaceJar(Class<?> containedClass) {
+        File file = UpdateUtils.getJarFileContainingClass(containedClass);
+        return new ReplaceJarUpdateTarget(file);
+    }
+
+    static UpdateTarget deleteAndSaveInTheSameFolder(Class<?> containedClass) {
+        File file = UpdateUtils.getJarFileContainingClass(containedClass);
+        return new DeleteAndSaveInSameFolderUpdateTarget(file);
+    }
+
+}
diff --git a/src/main/java/moe/nea/libautoupdate/UpdateUtils.java b/src/main/java/moe/nea/libautoupdate/UpdateUtils.java
new file mode 100644
index 0000000..ce09c0b
--- /dev/null
+++ b/src/main/java/moe/nea/libautoupdate/UpdateUtils.java
@@ -0,0 +1,86 @@
+package moe.nea.libautoupdate;
+
+import lombok.val;
+import lombok.var;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.math.BigInteger;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.nio.file.FileVisitResult;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Locale;
+
+public class UpdateUtils {
+    private UpdateUtils() {
+    }
+
+    public static File getJarFileContainingClass(Class<?> clazz) {
+        val location = clazz.getProtectionDomain().getCodeSource().getLocation();
+        if (location == null)
+            return null;
+        var path = location.toString();
+        path = path.split("!", 2)[0];
+        if (path.startsWith("jar:")) {
+            path = path.substring(4);
+        }
+        try {
+            return new File(new URI(path));
+        } catch (URISyntaxException e) {
+            e.printStackTrace();
+            return null;
+        }
+    }
+
+    public static void connect(InputStream from, OutputStream to) throws IOException {
+        val buf = new byte[4096];
+        int r;
+        while ((r = from.read(buf)) != -1) {
+            to.write(buf, 0, r);
+        }
+    }
+
+    public static String sha256sum(InputStream stream) throws IOException {
+        try {
+            val digest = MessageDigest.getInstance("SHA-256");
+            int r;
+            val buf = new byte[4096];
+            while ((r = stream.read(buf)) != -1) {
+                digest.update(buf, 0, r);
+            }
+            return String.format("%64s",
+                            new BigInteger(1, digest.digest())
+                                    .toString(16))
+                    .replace(' ', '0')
+                    .toLowerCase(Locale.ROOT);
+        } catch (NoSuchAlgorithmException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public static void deleteDirectory(Path path) throws IOException {
+        if (!Files.exists(path)) return;
+        Files.walkFileTree(path, new SimpleFileVisitor<Path>() {
+            @Override
+            public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
+                Files.delete(dir);
+                return FileVisitResult.CONTINUE;
+            }
+
+            @Override
+            public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
+                Files.delete(file);
+                return FileVisitResult.CONTINUE;
+            }
+        });
+    }
+}
+
diff --git a/updater/src/main/java/moe/nea/libautoupdate/postexit/PostExitMain.java b/updater/src/main/java/moe/nea/libautoupdate/postexit/PostExitMain.java
new file mode 100644
index 0000000..d143fee
--- /dev/null
+++ b/updater/src/main/java/moe/nea/libautoupdate/postexit/PostExitMain.java
@@ -0,0 +1,46 @@
+package moe.nea.libautoupdate.postexit;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.PrintStream;
+import java.nio.file.Files;
+import java.nio.file.StandardCopyOption;
+
+public class PostExitMain {
+    public static void main(String[] args) throws IOException {
+        File outputFile = new File(".autoupdates", "postexit.log");
+        outputFile.getParentFile().mkdirs();
+        PrintStream printStream = new PrintStream(new FileOutputStream(outputFile, true));
+        System.setErr(printStream);
+        System.setOut(printStream);
+
+        for (int i = 0; i < args.length; i++) {
+            switch (args[i].intern()) {
+                case "delete":
+                    File file = new File(args[++i]);
+                    System.out.println("Deleting " + file);
+                    file.delete();
+                    break;
+                case "move":
+                    File from = new File(args[++i]);
+                    File to = new File(args[++i]);
+                    System.out.println("Moving " + from + " to " + to);
+                    // Use Files.move instead of File.renameTo, since renameTo is not well-defined.
+                    Files.move(from.toPath(), to.toPath(), StandardCopyOption.REPLACE_EXISTING);
+                    break;
+                default:
+                    System.out.println("Unknown instruction " + args[i]);
+                    System.exit(1);
+            }
+        }
+    }
+
+    public void unlockedFile(File file) throws InterruptedException {
+        while (!file.exists() || !file.renameTo(file)) {
+            Thread.sleep(1000L);
+        }
+        file.getParentFile().mkdirs();
+    }
+
+}