Expose server build information

Co-authored-by: Zach Brown <1254957+zachbr@users.noreply.github.com>
Co-authored-by: Kyle Wood <kyle@denwav.dev>
Co-authored-by: Mark Vainomaa <mikroskeem@mikroskeem.eu>
Co-authored-by: Riley Park <rileysebastianpark@gmail.com>
Co-authored-by: Jake Potrebic <jake.m.potrebic@gmail.com>
Co-authored-by: masmc05 <masmc05@gmail.com>

paper-server/src/main/java/com/destroystokyo/paper/VersionHistoryManager.java

@@ -0,0 +1,153 @@
+package com.destroystokyo.paper;
+
+import com.google.common.base.MoreObjects;
+import com.google.gson.Gson;
+import com.google.gson.JsonSyntaxException;
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
+import java.util.Objects;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import org.bukkit.Bukkit;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+public enum VersionHistoryManager {
+    INSTANCE;
+
+    private final Gson gson = new Gson();
+
+    private final Logger logger = Bukkit.getLogger();
+
+    private VersionData currentData = null;
+
+    VersionHistoryManager() {
+        final Path path = Paths.get("version_history.json");
+
+        if (Files.exists(path)) {
+            // Basic file santiy checks
+            if (!Files.isRegularFile(path)) {
+                if (Files.isDirectory(path)) {
+                    logger.severe(path + " is a directory, cannot be used for version history");
+                } else {
+                    logger.severe(path + " is not a regular file, cannot be used for version history");
+                }
+                // We can't continue
+                return;
+            }
+
+            try (final BufferedReader reader = Files.newBufferedReader(path, StandardCharsets.UTF_8)) {
+                currentData = gson.fromJson(reader, VersionData.class);
+            } catch (final IOException e) {
+                logger.log(Level.SEVERE, "Failed to read version history file '" + path + "'", e);
+                return;
+            } catch (final JsonSyntaxException e) {
+                logger.log(Level.SEVERE, "Invalid json syntax for file '" + path + "'", e);
+                return;
+            }
+
+            final String version = Bukkit.getVersion();
+            if (version == null) {
+                logger.severe("Failed to retrieve current version");
+                return;
+            }
+
+            if (currentData == null) {
+                // Empty file
+                currentData = new VersionData();
+                currentData.setCurrentVersion(version);
+                writeFile(path);
+                return;
+            }
+
+            if (!version.equals(currentData.getCurrentVersion())) {
+                // The version appears to have changed
+                currentData.setOldVersion(currentData.getCurrentVersion());
+                currentData.setCurrentVersion(version);
+                writeFile(path);
+            }
+        } else {
+            // File doesn't exist, start fresh
+            currentData = new VersionData();
+            // oldVersion is null
+            currentData.setCurrentVersion(Bukkit.getVersion());
+            writeFile(path);
+        }
+    }
+
+    private void writeFile(@Nonnull final Path path) {
+        try (final BufferedWriter writer = Files.newBufferedWriter(
+            path,
+            StandardCharsets.UTF_8,
+            StandardOpenOption.WRITE,
+            StandardOpenOption.CREATE,
+            StandardOpenOption.TRUNCATE_EXISTING
+        )) {
+            gson.toJson(currentData, writer);
+        } catch (final IOException e) {
+            logger.log(Level.SEVERE, "Failed to write to version history file", e);
+        }
+    }
+
+    @Nullable
+    public VersionData getVersionData() {
+        return currentData;
+    }
+
+    public static class VersionData {
+        private String oldVersion;
+
+        private String currentVersion;
+
+        @Nullable
+        public String getOldVersion() {
+            return oldVersion;
+        }
+
+        public void setOldVersion(@Nullable String oldVersion) {
+            this.oldVersion = oldVersion;
+        }
+
+        @Nullable
+        public String getCurrentVersion() {
+            return currentVersion;
+        }
+
+        public void setCurrentVersion(@Nullable String currentVersion) {
+            this.currentVersion = currentVersion;
+        }
+
+        @Override
+        public String toString() {
+            return MoreObjects.toStringHelper(this)
+                .add("oldVersion", oldVersion)
+                .add("currentVersion", currentVersion)
+                .toString();
+        }
+
+        @Override
+        public boolean equals(@Nullable Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (o == null || getClass() != o.getClass()) {
+                return false;
+            }
+            final VersionData versionData = (VersionData) o;
+            return Objects.equals(oldVersion, versionData.oldVersion) &&
+                Objects.equals(currentVersion, versionData.currentVersion);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(oldVersion, currentVersion);
+        }
+    }
+}