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

const Server = @import("server.zig").Server;
const View = @import("view.zig").View;

const RenderData = struct {
    output: *c.wlr_output,
    renderer: *c.wlr_renderer,
    view: *View,
    when: *c.struct_timespec,
};

pub const Output = struct {
    server: *Server,
    wlr_output: *c.wlr_output,
    listen_frame: c.wl_listener,

    pub fn init(self: *@This(), server: *Server, wlr_output: *c.wlr_output) !void {
        // 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) {
            const 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 error.CantCommitWlrOutputMode;
            }
        }

        self.server = server;
        self.wlr_output = wlr_output;

        // Sets up a listener for the frame notify event.
        self.listen_frame.notify = handle_frame;
        c.wl_signal_add(&wlr_output.events.frame, &self.listen_frame);

        // Add the new output to the 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.wlr_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);
    }

    fn handle_frame(listener: ?*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).
        const output = @fieldParentPtr(Output, "listen_frame", listener.?);
        const renderer = output.server.wlr_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 view is rendered on top of the last.
        // The first view in the list is "on top" so iterate in reverse.
        var it = output.server.views.last;
        while (it) |node| : (it = node.prev) {
            const view = &node.data;
            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.wlr_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 render_surface(opt_surface: ?*c.wlr_surface, sx: c_int, sy: c_int, data: ?*c_void) callconv(.C) void {
        // wlroots says this will never be null
        const surface = opt_surface.?;
        // This function is called for every surface that needs to be rendered.
        const rdata = @ptrCast(*RenderData, @alignCast(@alignOf(RenderData), data));
        const view = rdata.view;
        const output = rdata.output;

        // We first obtain a wlr_texture, which is a GPU resource. wlroots
        // automatically handles negotiating these with the client. The underlying
        // resource could be an opaque handle passed from the client, or the client
        // could have sent a pixel buffer which we copied to the GPU, or a few other
        // means. You don't have to worry about this, wlroots takes care of it.
        const texture = c.wlr_surface_get_texture(surface);
        if (texture == null) {
            return;
        }

        // The view has a position in layout coordinates. If you have two displays,
        // one next to the other, both 1080p, a view on the rightmost display might
        // have layout coordinates of 2000,100. We need to translate that to
        // output-local coordinates, or (2000 - 1920).
        var ox: f64 = 0.0;
        var oy: f64 = 0.0;
        c.wlr_output_layout_output_coords(view.server.wlr_output_layout, output, &ox, &oy);
        ox += @intToFloat(f64, view.x + sx);
        oy += @intToFloat(f64, view.y + sy);

        // We also have to apply the scale factor for HiDPI outputs. This is only
        // part of the puzzle, TinyWL does not fully support HiDPI.
        const box = c.wlr_box{
            .x = @floatToInt(c_int, ox * output.scale),
            .y = @floatToInt(c_int, oy * output.scale),
            .width = @floatToInt(c_int, @intToFloat(f32, surface.current.width) * output.scale),
            .height = @floatToInt(c_int, @intToFloat(f32, surface.current.height) * output.scale),
        };

        // Those familiar with OpenGL are also familiar with the role of matricies
        // in graphics programming. We need to prepare a matrix to render the view
        // with. wlr_matrix_project_box is a helper which takes a box with a desired
        // x, y coordinates, width and height, and an output geometry, then
        // prepares an orthographic projection and multiplies the necessary
        // transforms to produce a model-view-projection matrix.
        //
        // Naturally you can do this any way you like, for example to make a 3D
        // compositor.
        var matrix: [9]f32 = undefined;
        const transform = c.wlr_output_transform_invert(surface.current.transform);
        c.wlr_matrix_project_box(&matrix, &box, transform, 0.0, &output.transform_matrix);

        // This takes our matrix, the texture, and an alpha, and performs the actual
        // rendering on the GPU.
        _ = c.wlr_render_texture_with_matrix(rdata.renderer, texture, &matrix, 1.0);

        // This lets the client know that we've displayed that frame and it can
        // prepare another one now if it likes.
        c.wlr_surface_send_frame_done(surface, rdata.when);
    }
};