const std = @import("std");
const c = @import("c.zig").c;

const Output = struct {
    server: *Server,
    wlr_output: *c.wlr_output,
    frame: c.wl_listener,
};

fn output_frame(listener: [*c]c.wl_listener, data: ?*c_void) callconv(.C) void {
    // This function is called every time an output is ready to display a frame,
    // generally at the output's refresh rate (e.g. 60Hz).
    var output = @fieldParentPtr(Output, "frame", listener);
    var renderer = output.*.server.*.renderer;

    var now: c.struct_timespec = undefined;
    _ = c.clock_gettime(c.CLOCK_MONOTONIC, &now);

    // wlr_output_attach_render makes the OpenGL context current.
    if (!c.wlr_output_attach_render(output.*.wlr_output, null)) {
        return;
    }
    // The "effective" resolution can change if you rotate your outputs.
    var width: c_int = undefined;
    var height: c_int = undefined;
    c.wlr_output_effective_resolution(output.*.wlr_output, &width, &height);
    // Begin the renderer (calls glViewport and some other GL sanity checks)
    c.wlr_renderer_begin(renderer, width, height);

    const color = [_]f32{ 0.3, 0.3, 0.3, 1.0 };
    c.wlr_renderer_clear(renderer, &color);

    // Each subsequent window we render is rendered on top of the last. Because
    //  our view list is ordered front-to-back, we iterate over it backwards.
    for (output.*.server.views.span()) |*view| {
        if (!view.*.mapped) {
            // An unmapped view should not be rendered.
            continue;
        }
        var rdata = RenderData{
            .output = output.*.wlr_output,
            .view = view,
            .renderer = renderer,
            .when = &now,
        };
        // This calls our render_surface function for each surface among the
        // xdg_surface's toplevel and popups.
        c.wlr_xdg_surface_for_each_surface(view.*.xdg_surface, render_surface, &rdata);
    }

    // Hardware cursors are rendered by the GPU on a separate plane, and can be
    // moved around without re-rendering what's beneath them - which is more
    // efficient. However, not all hardware supports hardware cursors. For this
    // reason, wlroots provides a software fallback, which we ask it to render
    // here. wlr_cursor handles configuring hardware vs software cursors for you,
    // and this function is a no-op when hardware cursors are in use.
    c.wlr_output_render_software_cursors(output.*.wlr_output, null);

    // Conclude rendering and swap the buffers, showing the final frame
    // on-screen.
    c.wlr_renderer_end(renderer);
    // TODO: handle failure
    _ = c.wlr_output_commit(output.*.wlr_output);
}

fn server_new_output(listener: [*c]c.wl_listener, data: ?*c_void) callconv(.C) void {
    var server = @fieldParentPtr(Server, "new_output", listener);
    var wlr_output = @ptrCast(*c.wlr_output, @alignCast(@alignOf(*c.wlr_output), data));

    // Some backends don't have modes. DRM+KMS does, and we need to set a mode
    // before we can use the output. The mode is a tuple of (width, height,
    // refresh rate), and each monitor supports only a specific set of modes. We
    // just pick the monitor's preferred mode, a more sophisticated compositor
    // would let the user configure it.

    // if not empty
    if (c.wl_list_empty(&wlr_output.*.modes) == 0) {
        var mode = c.wlr_output_preferred_mode(wlr_output);
        c.wlr_output_set_mode(wlr_output, mode);
        c.wlr_output_enable(wlr_output, true);
        if (!c.wlr_output_commit(wlr_output)) {
            return;
        }
    }

    // Allocates and configures our state for this output
    server.*.outputs.append(Output{
        .server = undefined,
        .wlr_output = undefined,
        .frame = undefined,
    }) catch unreachable;
    var output = &server.*.outputs.span()[server.*.outputs.span().len - 1];
    output.*.wlr_output = wlr_output;
    output.*.server = server;

    // Sets up a listener for the frame notify event.
    output.*.frame.notify = output_frame;
    c.wl_signal_add(&wlr_output.*.events.frame, &output.*.frame);

    // Adds this to the output layout. The add_auto function arranges outputs
    // from left-to-right in the order they appear. A more sophisticated
    // compositor would let the user configure the arrangement of outputs in the
    // layout.
    c.wlr_output_layout_add_auto(server.*.output_layout, wlr_output);

    // Creating the global adds a wl_output global to the display, which Wayland
    // clients can see to find out information about the output (such as
    // DPI, scale factor, manufacturer, etc).
    c.wlr_output_create_global(wlr_output);
}