#include "../../include/mgui/scrollview.h"
#include "../../include/mgui/mgui.h"
#include "../../include/alloc.h"
#include <mgl/mgl.h>
#include <mgl/window/window.h>
#include <mgl/window/event.h>
#include <limits.h>
#include <assert.h>

#define SCROLL_ACCEL 20.0f
#define SCROLL_DEACCEL 10.0f

#define WIDGET_NATURAL_SIZE INT_MAX

static float max_float(float a, float b) {
    return a >= b ? a : b;
}

static int max_int(int a, int b) {
    return a >= b ? a : b;
}

static int min_int(int a, int b) {
    return a <= b ? a : b;
}

static float abs_float(float value) {
    return value >= 0.0f ? value : -value;
}

mgui_scrollview* mgui_scrollview_create() {
    mgui_scrollview *scrollview = mgui_alloc(sizeof(mgui_scrollview));
    mgui_widget_init(&scrollview->widget, MGUI_WIDGET_SCROLLVIEW);
    scrollview->child = NULL;
    scrollview->position = (mgl_vec2i){ 0, 0 };
    scrollview->scroll = (mgl_vec2i){ 0, 0 };
    scrollview->mouse_scroll = (mgl_vec2f){ 0.0f, 0.0f };
    return scrollview;
}

void mgui_scrollview_destroy(mgui_scrollview *scrollview) {
    if(scrollview->child)
        mgui_widget_destroy(scrollview->child);
    mgui_free(scrollview);
}

mgui_widget* mgui_scrollview_to_widget(mgui_scrollview *list) {
    return &list->widget;
}

mgui_scrollview* mgui_widget_to_scrollview(mgui_widget *widget) {
    assert(widget->type == MGUI_WIDGET_SCROLLVIEW);
    return (mgui_scrollview*)widget;
}

void mgui_scrollview_set_child(mgui_scrollview *self, mgui_widget *child) {
    assert(child != mgui_scrollview_to_widget(self));
    self->child = child;
    if(self->child) {
        mgui_widget_set_has_parent(self->child);
        mgui_widget_calculate_size(self->child, self->widget.size);
    }
}

void mgui_scrollview_set_position(mgui_scrollview *self, mgl_vec2i position) {
    self->position = position;
}

void mgui_scrollview_calculate_size(mgui_scrollview *self, mgl_vec2i max_size) {
    self->widget.size = max_size;
    if(self->widget.size.x == WIDGET_NATURAL_SIZE)
        self->widget.size.x = 500;

    if(self->widget.size.y == WIDGET_NATURAL_SIZE)
        self->widget.size.y = 600;

    if(self->child)
        mgui_widget_calculate_size(self->child, (mgl_vec2i){ WIDGET_NATURAL_SIZE, WIDGET_NATURAL_SIZE });
}

void mgui_scrollview_on_event(mgui_scrollview *self, mgl_window *window, mgl_event *event) {
    /* TODO: Allow keyboard navigation if scrollview has focus */
    if(event->type == MGL_EVENT_MOUSE_WHEEL_SCROLLED)
        self->mouse_scroll.y += (event->mouse_wheel_scroll.delta * SCROLL_ACCEL);

    if(self->child)
        mgui_widget_on_event(self->child, window, event);
}

/* TODO: Check if visible in scissor */

void mgui_scrollview_draw(mgui_scrollview *self, mgl_window *window) {
    const double frame_time = mgui_get_seconds_since_last_update();
    self->mouse_scroll.x *= max_float(0.0f, (1.0f - frame_time * SCROLL_DEACCEL));
    self->mouse_scroll.y *= max_float(0.0f, (1.0f - frame_time * SCROLL_DEACCEL));

    if(abs_float(self->mouse_scroll.x) < 0.0001f)
        self->mouse_scroll.x = 0.0f;

    if(abs_float(self->mouse_scroll.y) < 0.0001f)
        self->mouse_scroll.y = 0.0f;

    self->scroll.x += (int)self->mouse_scroll.x;
    self->scroll.y += (int)self->mouse_scroll.y;

    mgl_vec2i child_size;
    if(self->child)
        child_size = self->child->size;
    else
        child_size = (mgl_vec2i){ 0, 0 };

    if(child_size.x > self->widget.size.x) {
        self->scroll.x = min_int(self->scroll.x, 0);
        self->scroll.x = max_int(self->scroll.x, -child_size.x + self->widget.size.x);
    } else {
        self->scroll.x = 0;
    }

    if(child_size.y > self->widget.size.y) {
        self->scroll.y = min_int(self->scroll.y, 0);
        self->scroll.y = max_int(self->scroll.y, -child_size.y + self->widget.size.y);
    } else {
        self->scroll.y = 0;
    }

    if(self->child) {
        mgl_scissor prev_scissor;
        mgl_window_get_scissor(window, &prev_scissor);

        mgl_scissor new_scissor = {
            .position = self->position,
            .size = self->widget.size
        };
        mgl_window_set_scissor(window, &new_scissor);

        mgui_widget_set_position(self->child, (mgl_vec2i){ self->position.x + self->scroll.x, self->position.y + self->scroll.y });
        mgui_widget_draw(self->child, window);

        mgl_window_set_scissor(window, &prev_scissor);
    }
}