use crate::core::ElementMaybeSignal;
use crate::{watch_with_options, WatchOptions};
use default_struct_builder::DefaultBuilder;
use leptos::*;
use std::cell::RefCell;
use std::marker::PhantomData;
use std::rc::Rc;
use wasm_bindgen::prelude::*;

/// Reactive [IntersectionObserver](https://developer.mozilla.org/en-US/docs/Web/API/IntersectionObserver).
///
/// Detects that a target element's visibility inside the viewport.
///
/// ## Demo
///
/// [Link to Demo](https://github.com/Synphonyte/leptos-use/tree/main/examples/use_intersection_observer)
///
/// ## Usage
///
/// ```
/// # use leptos::*;
/// # use leptos_use::use_intersection_observer;
/// #
/// # #[component]
/// # fn Demo(cx: Scope) -> impl IntoView {
/// let el = create_node_ref(cx);
/// let (is_visible, set_visible) = create_signal(cx, false);
///
/// use_intersection_observer(
///     cx,
///     el,
///     move |entries, _| {
///         set_visible(entries[0].is_intersecting());
///     },
/// );
///
/// view! { cx,
///     <div node_ref=el>
///         <h1>"Hello World"</h1>
///     </div>
/// }
/// # }
/// ```
///
/// ## See also
///
/// * [`use_element_visibility`]
pub fn use_intersection_observer<El, T, F>(
    cx: Scope,
    target: El,
    callback: F,
) -> UseIntersectionObserverReturn<impl Fn() + Clone, impl Fn() + Clone, impl Fn() + Clone>
where
    (Scope, El): Into<ElementMaybeSignal<T, web_sys::Element>>,
    T: Into<web_sys::Element> + Clone + 'static,
    F: FnMut(Vec<web_sys::IntersectionObserverEntry>, web_sys::IntersectionObserver)
        + Clone
        + 'static,
{
    use_intersection_observer_with_options::<El, T, web_sys::Element, web_sys::Element, F>(
        cx,
        target,
        callback,
        UseIntersectionObserverOptions::default(),
    )
}

/// Version of [`use_intersection_observer`] that takes a [`UseIntersectionObserverOptions`]. See [`use_intersection_observer`] for how to use.
pub fn use_intersection_observer_with_options<El, T, RootEl, RootT, F>(
    cx: Scope,
    target: El,
    callback: F,
    options: UseIntersectionObserverOptions<RootEl, RootT>,
) -> UseIntersectionObserverReturn<impl Fn() + Clone, impl Fn() + Clone, impl Fn() + Clone>
where
    (Scope, El): Into<ElementMaybeSignal<T, web_sys::Element>>,
    T: Into<web_sys::Element> + Clone + 'static,
    (Scope, RootEl): Into<ElementMaybeSignal<RootT, web_sys::Element>>,
    RootT: Into<web_sys::Element> + Clone + 'static,
    F: FnMut(Vec<web_sys::IntersectionObserverEntry>, web_sys::IntersectionObserver)
        + Clone
        + 'static,
{
    let UseIntersectionObserverOptions {
        immediate,
        root,
        root_margin,
        thresholds,
        ..
    } = options;

    let (is_active, set_active) = create_signal(cx, immediate);

    let observer: Rc<RefCell<Option<web_sys::IntersectionObserver>>> = Rc::new(RefCell::new(None));

    let obs = Rc::clone(&observer);
    let cleanup = move || {
        if let Some(o) = obs.take() {
            o.disconnect();
        }
    };

    let target = (cx, target).into();
    let root = root.map(|root| (cx, root).into());
    let clean = cleanup.clone();

    let stop_watch = watch_with_options(
        cx,
        move || {
            (
                target.get(),
                root.as_ref().map(|root| root.get()),
                is_active.get(),
            )
        },
        move |values, _, _| {
            let (target, root, is_active) = values;

            clean();

            if !is_active {
                return;
            }

            if let Some(target) = target {
                let mut callback = callback.clone();
                let closure =
                    Closure::<dyn FnMut(js_sys::Array, web_sys::IntersectionObserver)>::new(
                        move |entries: js_sys::Array, observer| {
                            callback(
                                entries
                                    .to_vec()
                                    .into_iter()
                                    .map(|v| {
                                        v.unchecked_into::<web_sys::IntersectionObserverEntry>()
                                    })
                                    .collect(),
                                observer,
                            );
                        },
                    );

                let mut options = web_sys::IntersectionObserverInit::new();
                options.root_margin(&root_margin).threshold(
                    &thresholds
                        .iter()
                        .copied()
                        .map(JsValue::from)
                        .collect::<js_sys::Array>(),
                );

                if let Some(Some(root)) = root {
                    let root: web_sys::Element = root.clone().into();
                    options.root(Some(&root));
                }

                let obs = web_sys::IntersectionObserver::new_with_options(
                    closure.as_ref().unchecked_ref(),
                    &options,
                )
                .expect("failed to create IntersectionObserver");

                closure.forget();

                let target: web_sys::Element = target.clone().into();
                obs.observe(&target);

                observer.replace(Some(obs));
            }
        },
        WatchOptions::default().immediate(immediate),
    );

    let clean = cleanup.clone();

    let stop = move || {
        clean();
        stop_watch();
    };

    on_cleanup(cx, stop.clone());

    let clean = cleanup.clone();

    UseIntersectionObserverReturn {
        is_active: is_active.into(),
        pause: move || {
            clean();
            set_active(false);
        },
        resume: move || {
            cleanup();
            set_active(true);
        },
        stop,
    }
}

/// Options for [`use_intersection_observer_with_options`].
#[derive(DefaultBuilder)]
pub struct UseIntersectionObserverOptions<El, T>
where
    (Scope, El): Into<ElementMaybeSignal<T, web_sys::Element>>,
    T: Into<web_sys::Element> + Clone + 'static,
{
    /// If `true`, the `IntersectionObserver` will be attached immediately. Otherwise it
    /// will only be attached after the returned `resume` closure is called. That is
    /// `use_intersections_observer` will be started "paused".
    immediate: bool,

    /// A `web_sys::Element` or `web_sys::Document` object which is an ancestor of the intended `target`,
    /// whose bounding rectangle will be considered the viewport.
    /// Any part of the target not visible in the visible area of the `root` is not considered visible.
    /// Defaults to `None` (which means the root `document` will be used).
    /// Please note that setting this to a `Some(document)` may not be supported by all browsers.
    /// See [Browser Compatibility](https://developer.mozilla.org/en-US/docs/Web/API/IntersectionObserver/IntersectionObserver#browser_compatibility)
    root: Option<El>,

    /// A string which specifies a set of offsets to add to the root's [bounding box](https://developer.mozilla.org/en-US/docs/Glossary/Bounding_box)
    /// when calculating intersections, effectively shrinking or growing the root for calculation purposes. The syntax is approximately the same as that for the CSS
    /// [`margin`](https://developer.mozilla.org/en-US/docs/Web/CSS/margin) property; see
    /// [The intersection root and root margin](https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API#the_intersection_root_and_root_margin)
    /// for more information on how the margin works and the syntax. The default is `"0px"`.
    #[builder(into)]
    root_margin: String,

    // TODO : validate that each number is between 0 and 1 ?
    /// A `Vec` of numbers between 0.0 and 1.0, specifying a ratio of intersection area to total
    /// bounding box area for the observed target. A value of 0.0 means that even a single
    /// visible pixel counts as the target being visible. 1.0 means that the entire target
    /// element is visible. See [Thresholds](https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API#thresholds)
    /// for a more in-depth description of how thresholds are used.
    /// The default is a single threshold of `[0.0]`.
    thresholds: Vec<f64>,

    #[builder(skip)]
    _marker: PhantomData<T>,
}

impl Default for UseIntersectionObserverOptions<web_sys::Element, web_sys::Element> {
    fn default() -> Self {
        Self {
            immediate: true,
            root: None,
            root_margin: "0px".into(),
            thresholds: vec![0.0],
            _marker: PhantomData,
        }
    }
}

/// The return value of [`use_intersection_observer`].
pub struct UseIntersectionObserverReturn<StopFn, PauseFn, ResumeFn>
where
    StopFn: Fn() + Clone,
    PauseFn: Fn() + Clone,
    ResumeFn: Fn() + Clone,
{
    /// Pauses the `IntersectionObserver` observations. Will cause `is_active = false`.
    pub pause: PauseFn,
    /// Resumes the `IntersectionObserver` observations. Will cause `is_active = true`.
    pub resume: ResumeFn,
    /// Stops the `IntersectionObserver` observations altogether.
    pub stop: StopFn,
    /// A signal which is `true` when the `IntersectionObserver` is active, and `false` when paused or stopped.
    pub is_active: Signal<bool>,
}