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

const Root = @import("root.zig").Root;
const Server = @import("server.zig").Server;
const View = @import("view.zig").View;
const ViewStack = @import("view_stack.zig").ViewStack;

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

pub const Output = struct {
    const Self = @This();

    root: *Root,
    wlr_output: *c.wlr_output,
    listen_frame: c.wl_listener,

    pub fn init(self: *Self, root: *Root, 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) {
            // TODO: handle failure
            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.root = root;
        self.wlr_output = wlr_output;

        // Sets up a listener for the frame notify event.
        self.listen_frame.notify = handleFrame;
        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(root.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 handleFrame(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.root.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);

        // The first view in the list is "on top" so iterate in reverse.
        var it = ViewStack.reverseIterator(
            output.root.views.last,
            output.root.current_focused_tags,
        );
        while (it.next()) |view| {
            // This check prevents a race condition when a frame is requested
            // between mapping of a view and the first configure being handled.
            if (view.current_box.width == 0 or view.current_box.height == 0) {
                continue;
            }
            output.renderView(view, &now);
        }

        // 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 renderView(self: Self, view: *View, now: *c.struct_timespec) void {
        // If we have a stashed buffer, we are in the middle of a transaction
        // and need to render that buffer until the transaction is complete.
        if (view.stashed_buffer) |buffer| {
            var box = c.wlr_box{
                .x = view.current_box.x + @intCast(i32, view.root.border_width),
                .y = view.current_box.y + @intCast(i32, view.root.border_width),
                .width = @intCast(c_int, view.current_box.width - view.root.border_width * 2),
                .height = @intCast(c_int, view.current_box.height - view.root.border_width * 2),
            };

            // Scale the box to the output's current scaling factor
            scaleBox(&box, self.wlr_output.scale);

            var matrix: [9]f32 = undefined;
            c.wlr_matrix_project_box(
                &matrix,
                &box,
                c.enum_wl_output_transform.WL_OUTPUT_TRANSFORM_NORMAL,
                0.0,
                &self.wlr_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(
                self.root.server.wlr_renderer,
                buffer.texture,
                &matrix,
                1.0,
            );
        } else {
            // Since there is no stashed buffer, we are not in the middle of
            // a transaction and may simply render each toplevel surface.
            var rdata = RenderData{
                .output = self.wlr_output,
                .view = view,
                .renderer = self.root.server.wlr_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, renderSurface, &rdata);
        }
    }

    fn renderSurface(_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 = _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.root.wlr_output_layout, output, &ox, &oy);
        ox += @intToFloat(f64, view.current_box.x + @intCast(i32, view.root.border_width) + sx);
        oy += @intToFloat(f64, view.current_box.y + @intCast(i32, view.root.border_width) + sy);

        var box = c.wlr_box{
            .x = @floatToInt(c_int, ox),
            .y = @floatToInt(c_int, oy),
            .width = surface.current.width,
            .height = surface.current.height,
        };

        // Scale the box to the output's current scaling factor
        scaleBox(&box, output.scale);

        // 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.
        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);
    }
};

/// Scale a wlr_box, taking the possibility of fractional scaling into account.
fn scaleBox(box: *c.wlr_box, scale: f64) void {
    box.x = @floatToInt(c_int, @round(@intToFloat(f64, box.x) * scale));
    box.y = @floatToInt(c_int, @round(@intToFloat(f64, box.y) * scale));
    box.width = scaleLength(box.width, box.x, scale);
    box.height = scaleLength(box.height, box.x, scale);
}

/// Scales a width/height.
///
/// This might seem overly complex, but it needs to work for fractional scaling.
fn scaleLength(length: c_int, offset: c_int, scale: f64) c_int {
    return @floatToInt(c_int, @round(@intToFloat(f64, offset + length) * scale) -
        @round(@intToFloat(f64, offset) * scale));
}