// ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
// ┃ ██████ ██████ ██████       █      █      █      █      █ █▄  ▀███ █       ┃
// ┃ ▄▄▄▄▄█ █▄▄▄▄▄ ▄▄▄▄▄█  ▀▀▀▀▀█▀▀▀▀▀ █ ▀▀▀▀▀█ ████████▌▐███ ███▄  ▀█ █ ▀▀▀▀▀ ┃
// ┃ █▀▀▀▀▀ █▀▀▀▀▀ █▀██▀▀ ▄▄▄▄▄ █ ▄▄▄▄▄█ ▄▄▄▄▄█ ████████▌▐███ █████▄   █ ▄▄▄▄▄ ┃
// ┃ █      ██████ █  ▀█▄       █ ██████      █      ███▌▐███ ███████▄ █       ┃
// ┣━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
// ┃ Copyright (c) 2017, the Perspective Authors.                              ┃
// ┃ ╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌ ┃
// ┃ This file is part of the Perspective library, distributed under the terms ┃
// ┃ of the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). ┃
// ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛

// Forked from https://github.com/AircastDev/yew-virtual-scroller (Apache 2.0)
// Adds support for Yew 0.19, auto-width and a simplified message structure.

use std::ops::Range;
use std::rc::Rc;

use itertools::Itertools;
use web_sys::Element;
use yew::prelude::*;
use yew::virtual_dom::VChild;

use super::scroll_panel_item::ScrollPanelItem;
use crate::utils::*;

#[derive(Properties)]
pub struct ScrollPanelProps {
    #[prop_or_default]
    pub children: Vec<VChild<ScrollPanelItem>>,

    #[prop_or_default]
    pub viewport_ref: Option<NodeRef>,

    #[prop_or_default]
    pub initial_width: Option<f64>,

    #[prop_or_default]
    pub class: Classes,

    #[prop_or_default]
    pub id: &'static str,

    #[prop_or_default]
    pub dragenter: Callback<DragEvent>,

    #[prop_or_default]
    pub dragover: Callback<DragEvent>,

    #[prop_or_default]
    pub dragleave: Callback<DragEvent>,

    #[prop_or_default]
    pub on_resize: Option<Rc<PubSub<()>>>,

    #[prop_or_default]
    pub on_auto_width: Callback<f64>,

    #[prop_or_default]
    pub on_dimensions_reset: Option<Rc<PubSub<()>>>,

    #[prop_or_default]
    pub drop: Callback<DragEvent>,

    #[prop_or_default]
    pub omit_autosize_div: bool,
}

impl ScrollPanelProps {
    /// Calculate the total virtual height of this scroll panel from the `size`
    /// prop of its children.
    fn total_height(&self) -> f64 {
        self.children
            .iter()
            .map(|x| x.props.get_size())
            .reduce(|x, y| x + y)
            .unwrap_or_default()
    }
}

impl PartialEq for ScrollPanelProps {
    fn eq(&self, _rhs: &Self) -> bool {
        false
    }
}

#[doc(hidden)]
pub enum ScrollPanelMsg {
    CalculateWindowContent,
    UpdateViewportDimensions,
    ResetAutoWidth,
    ChildrenChanged,
}

pub struct ScrollPanel {
    viewport_ref: NodeRef,
    viewport_height: f64,
    viewport_width: f64,
    content_window: Option<ContentWindow>,
    needs_rerender: bool,
    total_height: f64,
    _dimensions_reset_sub: Option<Subscription>,
    _resize_sub: Option<Subscription>,
}

impl Component for ScrollPanel {
    type Message = ScrollPanelMsg;
    type Properties = ScrollPanelProps;

    fn create(ctx: &Context<Self>) -> Self {
        let _dimensions_reset_sub = ctx.props().on_dimensions_reset.as_ref().map(|pubsub| {
            let link = ctx.link().clone();
            pubsub.add_listener(move |_| {
                link.send_message_batch(vec![
                    ScrollPanelMsg::ResetAutoWidth,
                    ScrollPanelMsg::CalculateWindowContent,
                ])
            })
        });

        let _resize_sub = ctx.props().on_resize.as_ref().map(|pubsub| {
            let link = ctx.link().clone();
            pubsub.add_listener(move |_| {
                link.send_message_batch(vec![
                    ScrollPanelMsg::UpdateViewportDimensions,
                    ScrollPanelMsg::CalculateWindowContent,
                ])
            })
        });

        let total_height = ctx.props().total_height();
        Self {
            viewport_ref: Default::default(),
            viewport_height: 0f64,
            viewport_width: ctx.props().initial_width.unwrap_or_default(),
            content_window: None,
            needs_rerender: true,
            total_height,
            _dimensions_reset_sub,
            _resize_sub,
        }
    }

    fn update(&mut self, ctx: &Context<Self>, msg: Self::Message) -> bool {
        match msg {
            ScrollPanelMsg::ResetAutoWidth => {
                self.viewport_width = 0.0;
                self.calculate_window_content(ctx)
            },

            // TODO don't hardcode pixel offsets - fix the CSS container to not
            // require pixel offsets to work.
            ScrollPanelMsg::UpdateViewportDimensions => {
                let viewport = self.viewport_elem(ctx);
                let rect = viewport.get_bounding_client_rect();
                let viewport_height = rect.height() - 8.0;
                let scroll_offset = if ctx.props().omit_autosize_div {
                    0.0
                } else {
                    6.0
                };

                let viewport_width = self.viewport_width.max(rect.width() - scroll_offset);
                let re_render = self.viewport_height != viewport_height
                    || self.viewport_width != viewport_width;

                self.viewport_height = rect.height() - 8.0;
                self.viewport_width = self.viewport_width.max(rect.width() - scroll_offset);
                ctx.props().on_auto_width.emit(self.viewport_width);
                re_render
            },
            ScrollPanelMsg::CalculateWindowContent => self.calculate_window_content(ctx),
            ScrollPanelMsg::ChildrenChanged => true,
        }
    }

    /// If the new total row height is different than last time this component
    /// was rendered, we need to double-render to read the container's
    /// potentially updated height.
    fn changed(&mut self, ctx: &Context<Self>, _old: &Self::Properties) -> bool {
        let total_height = ctx.props().total_height();
        self.needs_rerender =
            self.needs_rerender || (self.total_height - total_height).abs() > 0.1f64;
        self.total_height = total_height;
        ctx.link().send_message_batch(vec![
            ScrollPanelMsg::UpdateViewportDimensions,
            ScrollPanelMsg::CalculateWindowContent,
            ScrollPanelMsg::ChildrenChanged,
        ]);

        false
    }

    fn view(&self, ctx: &Context<Self>) -> Html {
        let content_style = format!("height:{}px", self.total_height);
        let (window_style, windowed_items) = match &self.content_window {
            None => ("".to_string(), &[][..]),
            Some(cw) => (
                format!(
                    "position:sticky;top:0;transform:translateY({}px);",
                    cw.start_y - cw.scroll_top
                ),
                (&ctx.props().children[cw.visible_range.clone()]),
            ),
        };

        let width_style = format!("width:{}px", self.viewport_width.max(0.0));
        let items = if !windowed_items.is_empty() {
            let onscroll = ctx.link().batch_callback(|_| {
                vec![
                    ScrollPanelMsg::UpdateViewportDimensions,
                    ScrollPanelMsg::CalculateWindowContent,
                ]
            });

            // TODO This glitches - we should use the `sticky` positioning strategy that
            // `regular-table` uses.
            html! {
                <div
                    ref={self.viewport(ctx)}
                    id={ctx.props().id}
                    {onscroll}
                    ondragover={&ctx.props().dragover}
                    ondragenter={&ctx.props().dragenter}
                    ondragleave={&ctx.props().dragleave}
                    ondrop={&ctx.props().drop}
                    class={ctx.props().class.clone()}
                >
                    <div class="scroll-panel-container" style={window_style}>
                        { for windowed_items.iter().cloned().map(Html::from) }
                        if !ctx.props().omit_autosize_div {
                            <div
                                key="__scroll-panel-auto-width__"
                                class="scroll-panel-auto-width"
                                style={width_style}
                            />
                        }
                    </div>
                    <div class="scroll-panel-content" style={content_style} />
                </div>
            }
        } else {
            html! {
                <div
                    ref={self.viewport(ctx)}
                    id={ctx.props().id}
                    class={ctx.props().class.clone()}
                >
                    <div style={content_style} />
                </div>
            }
        };

        html! { <>{ items }</> }
    }

    fn rendered(&mut self, ctx: &Context<Self>, _first_render: bool) {
        ctx.link().send_message_batch(vec![
            ScrollPanelMsg::UpdateViewportDimensions,
            ScrollPanelMsg::CalculateWindowContent,
        ]);
    }
}

impl ScrollPanel {
    fn viewport<'a, 'b: 'a, 'c: 'a>(&'b self, ctx: &'c Context<Self>) -> &'a NodeRef {
        ctx.props()
            .viewport_ref
            .as_ref()
            .unwrap_or(&self.viewport_ref)
    }

    fn viewport_elem(&self, ctx: &Context<Self>) -> Element {
        self.viewport(ctx).cast::<Element>().unwrap()
    }
}

#[derive(PartialEq)]
struct ContentWindow {
    scroll_top: f64,
    start_y: f64,
    visible_range: Range<usize>,
}

impl ScrollPanel {
    fn calculate_window_content(&mut self, ctx: &Context<Self>) -> bool {
        let viewport = self.viewport_elem(ctx);
        let scroll_top = viewport.scroll_top() as f64;
        let mut start_node = 0;
        let mut start_y = 0_f64;
        let mut offset = 0_f64;
        let end_node = ctx
            .props()
            .children
            .iter()
            .enumerate()
            .find_or_last(|(i, x)| {
                if offset + x.props.get_size() < scroll_top {
                    start_node = *i + 1;
                    start_y = offset + x.props.get_size();
                }

                offset += x.props.get_size();
                offset > scroll_top + self.viewport_height
            })
            .map(|x| x.0)
            .unwrap_or_default();

        // Why is this `end_node + 2`, I can see you asking yourself? `end_node` is the
        // index of the last visible child, but [`Range`] is an open interval so we must
        // increment by 1. The next rendered element is always occluded by the parent
        // container, it may seem unnecessary to render it, however not doing so causing
        // scroll glitching in Chrome:
        // * When the first pixel of the `end_node + 1` child is scrolled into view, the
        //   container element it is embedded in will expand past the end of the scroll
        //   container.
        // * Chrome detects this and helpfully scrolls this new element into view,
        //   re-triggering the on scroll callback.
        let visible_range = start_node..ctx.props().children.len().min(end_node + 2);
        let content_window = Some(ContentWindow {
            scroll_top,
            start_y,
            visible_range,
        });

        let re_render = self.content_window != content_window;
        self.content_window = content_window;
        re_render
    }
}
