apprt: add Layout type

src/apprt.zig

@@ -18,6 +18,7 @@ pub const gtk = @import("apprt/gtk.zig");
 pub const none = @import("apprt/none.zig");
 pub const browser = @import("apprt/browser.zig");
 pub const embedded = @import("apprt/embedded.zig");
+pub const layout = @import("apprt/layout.zig");
 pub const surface = @import("apprt/surface.zig");
 
 pub const Action = action.Action;
@@ -55,5 +56,6 @@ test {
     _ = Runtime;
     _ = runtime;
     _ = action;
+    _ = layout;
     _ = structs;
 }

src/apprt/layout.zig

@@ -0,0 +1,56 @@
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+const configpkg = @import("../config.zig");
+const datastruct = @import("../datastruct/main.zig");
+
+/// SplitTree represents a desired layout of splits and their associated
+/// surface configurations. This is used by apprts to launch and modify
+/// predefined terminal layouts.
+///
+/// This only represents a desired split tree; it doesn't represent
+/// tabs, windows, or any other higher-level constructs. These will
+/// be represented elsewhere. To start, we only support single-tab
+/// layouts.
+pub const SplitTree = datastruct.SplitTree(struct {
+    const View = @This();
+
+    /// A unique identifier for this leaf node. This is guaranteed to
+    /// forever unique and not reused during the lifetime of the
+    /// layout. This allows layouts to change at runtime and the apprt
+    /// to diff them.
+    ///
+    /// It is up to the creator of the layout to ensure uniqueness
+    /// when creating or updating layouts.
+    id: u64,
+
+    /// The configuration associated with this leaf node when creating
+    /// the associated terminal surface.
+    config: configpkg.Config,
+
+    /// The reference count for this layout node. When it reaches
+    /// zero it will be freed.
+    refs: usize = 1,
+
+    pub fn ref(self: *View, _: Allocator) Allocator.Error!*View {
+        self.refs += 1;
+        return self;
+    }
+
+    pub fn unref(self: *View, alloc: Allocator) void {
+        self.refs -= 1;
+        if (self.refs == 0) {
+            self.config.deinit();
+            alloc.destroy(self);
+        }
+    }
+
+    pub const CApi = struct {
+        pub fn get_id(self: *const View) callconv(.c) u64 {
+            return self.id;
+        }
+
+        pub fn get_config(self: *const View) callconv(.c) *const configpkg.Config {
+            return &self.config;
+        }
+    };
+});