/*
 * Tiled layout for river, implemented in understandable, simple, commented code.
 * Reading this code should help you get a basic understanding of how to use
 * river-layout to create a basic layout generator.
 *
 * Q: Wow, this is a lot of code just for a layout!
 * A: No, it really is not. Most of the code here is just generic Wayland client
 *    boilerplate. The actual layout part is pretty small.
 *
 * Q: Can I use this to port dwm layouts to river?
 * A: Yes you can! You just need to replace the logic in layout_handle_layout_demand().
 *    You don't even need to fully understand the protocol if all you want to
 *    do is just port some simple layouts.
 *
 * Q: I have no idea how any of this works.
 * A: If all you want to do is create simple layouts, you do not need to
 *    understand the Wayland parts of the code. If you still want to understand
 *    it and are already familiar with how Wayland clients work, read the
 *    protocol. If you are new to writing Wayland client code, you can read
 *    https://wayland-book.com, then read the protocol.
 *
 * Q: How do I build this?
 * A: To build, you need to generate the header and code of the layout protocol
 *    extension and link against them. This is achieved with the following
 *    commands (You may want to setup a build system).
 *
 *        wayland-scanner private-code < river-layout-v2.xml > river-layout-v2.c
 *        wayland-scanner client-header < river-layout-v2.xml > river-layout-v2.h
 *        gcc -Wall -Wextra -Wpedantic -Wno-unused-parameter -c -o layout.o layout.c
 *        gcc -Wall -Wextra -Wpedantic -Wno-unused-parameter -c -o river-layout-v2.o river-layout-v2.c
 *        gcc -o layout layout.o river-layout-v2.o -lwayland-client
 */

#include<assert.h>
#include<stdbool.h>
#include<stdint.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#include<wayland-client.h>
#include<wayland-client-protocol.h>

#include"river-layout-v2.h"

/* A few macros to indulge the inner glibc user. */
#define MIN(a, b) ( a < b ? a : b )
#define MAX(a, b) ( a > b ? a : b )
#define CLAMP(a, b, c) ( MIN(MAX(b, c), MAX(MIN(b, c), a)) )

struct Output
{
	struct wl_list link;

	struct wl_output       *output;
	struct river_layout_v2 *layout;

	uint32_t main_count;
	double main_factor;
	uint32_t view_padding;
	uint32_t outer_padding;

	bool configured;
};

/* In Wayland it's a good idea to have your main data global, since you'll need
 * it everywhere anyway.
 */
struct wl_display  *wl_display;
struct wl_registry *wl_registry;
struct wl_callback *sync_callback;
struct river_layout_manager_v2 *layout_manager;
struct wl_list outputs;
bool loop = true;
int ret = EXIT_FAILURE;

static void layout_handle_layout_demand (void *data, struct river_layout_v2 *river_layout_v2,
		uint32_t view_count, uint32_t width, uint32_t height, uint32_t tags, uint32_t serial)
{
	struct Output *output = (struct Output *)data;

	/* Simple tiled layout with no frills.
	 *
	 * If you want to create your own simple layout, just rip the following
	 * code out and replace it with your own logic. All content un-aware
	 * dynamic tiling layouts you know, for example from dwm, can be easily
	 * ported to river this way. If you want to create layouts that are
	 * content aware, meaning they react to the currently visible windows,
	 * you have to create handlers for the advertise_view and advertise_done
	 * events. Happy hacking!
	 */
	width -= 2 * output->outer_padding, height -= 2 * output->outer_padding;
	unsigned int main_size, stack_size, view_x, view_y, view_width, view_height;
	if ( output->main_count == 0 )
	{
		main_size  = 0;
		stack_size = width;
	}
	else if ( view_count <= output->main_count )
	{
		main_size  = width;
		stack_size = 0;
	}
	else
	{
		main_size  = width * output->main_factor;
		stack_size = width - main_size;
	}
	for (unsigned int i = 0; i < view_count; i++)
	{
		if ( i < output->main_count ) /* main area. */
		{
			view_x      = 0;
			view_width  = main_size;
			view_height = height / MIN(output->main_count, view_count);
			view_y      = i * view_height;
		}
		else /* Stack area. */
		{
			view_x      = main_size;
			view_width  = stack_size;
			view_height = height / ( view_count - output->main_count);
			view_y      = (i - output->main_count) * view_height;
		}

		river_layout_v2_push_view_dimensions(output->layout, serial,
				view_x + output->view_padding + output->outer_padding,
				view_y + output->view_padding + output->outer_padding,
				view_width - (2 * output->view_padding),
				view_height - (2 * output->view_padding));
	}

	river_layout_v2_commit(output->layout, serial);
}

static void layout_handle_namespace_in_use (void *data, struct river_layout_v2 *river_layout_v2)
{
	/* Oh no, the namespace we choose is already used by another client!
	 * All we can do now is destroy the river_layout object. Because we are
	 * lazy, we just abort and let our cleanup mechanism destroy it. A more
	 * sophisticated client could instead destroy only the one single
	 * affected river_layout object and recover from this mishap. Writing
	 * such a client is left as an exercise for the reader.
	 */
	fputs("Namespace already in use.\n", stderr);
	loop = false;
}

static void layout_handle_set_int_value (void *data, struct river_layout_v2 *river_layout_v2,
		const char *name, int32_t value)
{
	/* This event is used by the server to tell us to change the value of
	 * one of our layout parameters, identified by name. A layout_demand
	 * event will be send immediately afterwards.
	 */
	struct Output *output = (struct Output *)data;

	/* All integer parameters of this layout only accept positive values. */
	if ( value < 0 )
		return;

	if ( strcmp(name, "main_count") == 0 )
		output->main_count = (uint32_t)value;
	else if ( strcmp(name, "view_padding") == 0 )
		output->view_padding = (uint32_t)value;
	else if ( strcmp(name, "outer_padding") == 0 )
		output->outer_padding = (uint32_t)value;
}

static void layout_handle_mod_int_value (void *data, struct river_layout_v2 *river_layout_v2,
		const char *name, int32_t delta)
{
	/* This event is used by the server to tell us to modify the value of
	 * one of our layout parameters by a delta, identified by name. A
	 * layout_demand event will be send immediately afterwards.
	 */
	struct Output *output = (struct Output *)data;
	if ( strcmp(name, "main_count") == 0 )
	{
		if ( (int32_t)output->main_count + delta >= 0 )
			output->main_count = output->main_count + delta;
	}
	else if ( strcmp(name, "view_padding") == 0 )
	{
		if ( (int32_t)output->view_padding + delta >= 0 )
			output->view_padding = output->view_padding + delta;
	}
	else if ( strcmp(name, "outer_padding") == 0 )
	{
		if ( (int32_t)output->outer_padding + delta >= 0 )
			output->outer_padding = output->outer_padding + delta;
	}
}

static void layout_handle_set_fixed_value (void *data, struct river_layout_v2 *river_layout_v2,
		const char *name, wl_fixed_t value)
{
	struct Output *output = (struct Output *)data;
	if ( strcmp(name, "main_factor") == 0 )
		output->main_factor = CLAMP(wl_fixed_to_double(value), 0.1, 0.9);
}

static void layout_handle_mod_fixed_value (void *data, struct river_layout_v2 *river_layout_v2,
		const char *name, wl_fixed_t delta)
{
	struct Output *output = (struct Output *)data;
	if ( strcmp(name, "main_factor") == 0 )
		output->main_factor = CLAMP(output->main_factor + wl_fixed_to_double(delta), 0.1, 0.9);
}

/* A no-op function we plug into listeners when we don't want to handle an event. */
static void noop () {}

static const struct river_layout_v2_listener layout_listener = {
	.namespace_in_use = layout_handle_namespace_in_use,
	.layout_demand    = layout_handle_layout_demand,
	.set_int_value    = layout_handle_set_int_value,
	.mod_int_value    = layout_handle_mod_int_value,
	.set_fixed_value  = layout_handle_set_fixed_value,
	.mod_fixed_value  = layout_handle_mod_fixed_value,
	.set_string_value = noop,
	.advertise_view   = noop,
	.advertise_done   = noop,
};

static void configure_output (struct Output *output)
{
	output->configured = true;

	/* The namespace of the layout is how the compositor chooses what layout
	 * to use. It can be any arbitrary string. It should describe roughly
	 * what kind of layout your client will create, so here we use "tile".
	 */
	output->layout = river_layout_manager_v2_get_layout(layout_manager,
			output->output, "tile");
	river_layout_v2_add_listener(output->layout, &layout_listener, output);
}

static bool create_output (struct wl_output *wl_output)
{
	struct Output *output = calloc(1, sizeof(struct Output));
	if ( output == NULL )
	{
		fputs("Failed to allocate.\n", stderr);
		return false;
	}

	output->output     = wl_output;
	output->layout     = NULL;
	output->configured = false;

	/* These are the parameters of our layout. In this case, they are the
	 * ones you'd typically expect from a dynamic tiling layout, but if you
	 * are creative, you can do more. You can use any arbitrary amount of
	 * integer, fixed and string values in your layout. If the user wants to
	 * change a value, the server lets us know using events of the
	 * river_layout object. They need to be initialiued with defaults though.
	 */
	output->main_count    = 1;
	output->main_factor   = 0.6;
	output->view_padding  = 5;
	output->outer_padding = 5;

	/* If we already have the river_layout_manager, we can get a
	 * river_layout for this output.
	 */
	if ( layout_manager != NULL )
		configure_output(output);

	wl_list_insert(&outputs, &output->link);
	return true;
}

static void destroy_output (struct Output *output)
{
	if ( output->layout != NULL )
		river_layout_v2_destroy(output->layout);
	wl_output_destroy(output->output);
	wl_list_remove(&output->link);
	free(output);
}

static void destroy_all_outputs ()
{
	struct Output *output, *tmp;
	wl_list_for_each_safe(output, tmp, &outputs, link)
		destroy_output(output);
}

static void registry_handle_global (void *data, struct wl_registry *registry,
		uint32_t name, const char *interface, uint32_t version)
{
	if (! strcmp(interface, river_layout_manager_v2_interface.name))
		layout_manager = wl_registry_bind(registry, name,
				&river_layout_manager_v2_interface, 1);
	else if (! strcmp(interface, wl_output_interface.name))
	{
		struct wl_output *wl_output = wl_registry_bind(registry, name,
				&wl_output_interface, version);
		if (! create_output(wl_output))
		{
			loop = false;
			ret = EXIT_FAILURE;
		}
	}
}

static const struct wl_registry_listener registry_listener = {
	.global        = registry_handle_global,
	.global_remove = noop
};

static void sync_handle_done (void *data, struct wl_callback *wl_callback,
		uint32_t irrelevant)
{
	wl_callback_destroy(wl_callback);
	sync_callback = NULL;

	/* When this function is called, the registry finished advertising all
	 * available globals. Let's check if we have everything we need.
	 */
	if ( layout_manager == NULL )
	{
		fputs("Wayland compositor does not support river-layout-v2.\n", stderr);
		ret = EXIT_FAILURE;
		loop = false;
		return;
	}

	/* If outputs were registered before the river_layout_manager is
	 * available, they won't have a river_layout, so we need to create those
	 * here.
	 */
	struct Output *output;
	wl_list_for_each(output, &outputs, link)
		if (! output->configured)
			configure_output(output);
}

static const struct wl_callback_listener sync_callback_listener = {
	.done = sync_handle_done,
};

static bool init_wayland (void)
{
	/* We query the display name here instead of letting wl_display_connect()
	 * figure it out itself, because libwayland (for legacy reasons) falls
	 * back to using "wayland-0" when $WAYLAND_DISPLAY is not set, which is
	 * generally not desirable.
	 */
	const char *display_name = getenv("WAYLAND_DISPLAY");
	if ( display_name == NULL )
	{
		fputs("WAYLAND_DISPLAY is not set.\n", stderr);
		return false;
	}

	wl_display = wl_display_connect(display_name);
	if ( wl_display == NULL )
	{
		fputs("Can not connect to Wayland server.\n", stderr);
		return false;
	}

	wl_list_init(&outputs);

	wl_registry = wl_display_get_registry(wl_display);
	wl_registry_add_listener(wl_registry, &registry_listener, NULL);

	/* The sync callback we attach here will be called when all previous
	 * requests have been handled by the server.
	 */
	sync_callback = wl_display_sync(wl_display);
	wl_callback_add_listener(sync_callback, &sync_callback_listener, NULL);

	return true;
}

static void finish_wayland (void)
{
	if ( wl_display == NULL )
		return;

	destroy_all_outputs();

	if ( sync_callback != NULL )
		wl_callback_destroy(sync_callback);
	if ( layout_manager != NULL )
		river_layout_manager_v2_destroy(layout_manager);

	wl_registry_destroy(wl_registry);
	wl_display_disconnect(wl_display);
}

int main (int argc, char *argv[])
{
	if (init_wayland())
	{
		ret = EXIT_SUCCESS;
		while ( loop && wl_display_dispatch(wl_display) != -1 );
	}
	finish_wayland();
	return ret;
}