Updater: continue on implementing Updater.inform

src/Updater.zig

@@ -111,9 +111,43 @@ fn resetConnection(self: *Updater) !void {
     self.conn_err = .none;
 }
 
+const SortContext = struct {
+    object: std.json.ObjectMap,
+
+    pub fn lessThan(ctx: SortContext, a_index: usize, b_index: usize) bool {
+        const keys = ctx.object.keys();
+        const a_version = std.SemanticVersion.parse(keys[a_index]) catch unreachable;
+        const b_version = std.SemanticVersion.parse(keys[b_index]) catch unreachable;
+        return a_version.order(b_version).compare(.gt);
+    }
+};
+
 /// Informs about running version to given `Writer` by desired `Channel`.
-pub fn inform(self: *Updater, channel: Channel, writer: std.Io.Writer) void {
+pub fn inform(self: *Updater, channel: Channel, writer: *std.Io.Writer) !void {
     const versions = try self.getVersions();
+    defer self.resetConnection() catch {};
+
+    switch (channel) {
+        .stable => {
+            var stable = versions.object;
+            // Get rid of `nightly`.
+            lp.assert(stable.swapRemove("nightly"), "Updater.inform: incorrect JSON", .{});
+
+            // Sort and retrieve the newest.
+            stable.sort(SortContext{ .object = stable });
+            // Newest is at the beginning.
+            const newest = stable.values()[0].object;
+            const version = (newest.get("version") orelse return error.IncorrectJson).string;
+            try writer.print("Latest stable Lightpanda version is {s}.\n", .{version});
+            return writer.flush();
+        },
+        .nightly => {
+            const nightly = (versions.object.get("nightly") orelse return error.IncorrectJson).object;
+            const version = (nightly.get("version") orelse return error.IncorrectJson).string;
+            try writer.print("Latest nightly Lightpanda version is {s}.\n", .{version});
+            return writer.flush();
+        },
+    }
 }
 
 /// Invoked by `Connection` when there are body bytes.

src/lightpanda.zig

@@ -227,12 +227,15 @@ fn dumpContent(app: *App, mode: Config.DumpFormat, dump_opts: dump.Opts, frame:
 
 /// Check `Config.zig` for `options`.
 pub fn update(allocator: std.mem.Allocator, config: *const Config, options: anytype) !void {
-    if (options.channel == .nightly) @panic("TODO");
-
     var client = try Updater.init(allocator, config);
     defer client.deinit();
 
-    try client.getVersions();
+    var stdout = std.fs.File.stdout();
+    var buf: [4096]u8 = undefined;
+    var writer = stdout.writer(&buf);
+    const w = &writer.interface;
+    // Inform to stdout about version.
+    try client.inform(options.channel, w);
 }
 
 // Writes a single page's result object. Framing (the enclosing array and any