use crate::foundations::{elem, scope, Cast, Content, Packed, Smart};
use crate::introspection::{Locatable, Unqueriable};
use crate::layout::{Alignment, Em, Length, Rel};

/// Places content relatively to its parent container.
///
/// Placed content can be either overlaid (the default) or floating. Overlaid
/// content is aligned with the parent container according to the given
/// [`alignment`]($place.alignment), and shown over any other content added so
/// far in the container. Floating content is placed at the top or bottom of
/// the container, displacing other content down or up respectively. In both
/// cases, the content position can be adjusted with [`dx`]($place.dx) and
/// [`dy`]($place.dy) offsets without affecting the layout.
///
/// The parent can be any container such as a [`block`], [`box`],
/// [`rect`], etc. A top level `place` call will place content directly
/// in the text area of the current page. This can be used for absolute
/// positioning on the page: with a `top + left`
/// [`alignment`]($place.alignment), the offsets `dx` and `dy` will set the
/// position of the element's top left corner relatively to the top left corner
/// of the text area. For absolute positioning on the full page including
/// margins, you can use `place` in [`page.foreground`]($page.foreground) or
/// [`page.background`]($page.background).
///
/// # Examples
/// ```example
/// #set page(height: 120pt)
/// Hello, world!
///
/// #rect(
///   width: 100%,
///   height: 2cm,
///   place(horizon + right, square()),
/// )
///
/// #place(
///   top + left,
///   dx: -5pt,
///   square(size: 5pt, fill: red),
/// )
/// ```
///
/// # Effect on the position of other elements { #effect-on-other-elements }
/// Overlaid elements don't take space in the flow of content, but a `place`
/// call inserts an invisible block-level element in the flow. This can
/// affect the layout by breaking the current paragraph. To avoid this,
/// you can wrap the `place` call in a [`box`] when the call is made
/// in the middle of a paragraph. The alignment and offsets will then be
/// relative to this zero-size box. To make sure it doesn't interfere with
/// spacing, the box should be attached to a word using a word joiner.
///
/// For example, the following defines a function for attaching an annotation
/// to the following word:
///
/// ```example
/// >>> #set page(height: 70pt)
/// #let annotate(..args) = {
///   box(place(..args))
///   sym.wj
///   h(0pt, weak: true)
/// }
///
/// A placed #annotate(square(), dy: 2pt)
/// square in my text.
/// ```
///
/// The zero-width weak spacing serves to discard spaces between the function
/// call and the next word.
#[elem(scope, Locatable, Unqueriable)]
pub struct PlaceElem {
    /// Relative to which position in the parent container to place the content.
    ///
    /// - If `float` is `{false}`, then this can be any alignment other than `{auto}`.
    /// - If `float` is `{true}`, then this must be `{auto}`, `{top}`, or `{bottom}`.
    ///
    /// When `float` is `{false}` and no vertical alignment is specified, the
    /// content is placed at the current position on the vertical axis.
    #[positional]
    #[default(Smart::Custom(Alignment::START))]
    pub alignment: Smart<Alignment>,

    /// Relative to which containing scope something is placed.
    ///
    /// The parent scope is primarily used with figures and, for
    /// this reason, the figure function has a mirrored [`scope`
    /// parameter]($figure.scope). Nonetheless, it can also be more generally
    /// useful to break out of the columns. A typical example would be to
    /// [create a single-column title section]($guides/page-setup-guide/#columns)
    /// in a two-column document.
    ///
    /// Note that parent-scoped placement is currently only supported if `float`
    /// is `{true}`. This may change in the future.
    ///
    /// ```example
    /// #set page(height: 150pt, columns: 2)
    /// #place(
    ///   top + center,
    ///   scope: "parent",
    ///   float: true,
    ///   rect(width: 80%, fill: aqua),
    /// )
    ///
    /// #lorem(25)
    /// ```
    pub scope: PlacementScope,

    /// Whether the placed element has floating layout.
    ///
    /// Floating elements are positioned at the top or bottom of the parent
    /// container, displacing in-flow content. They are always placed in the
    /// in-flow order relative to each other, as well as before any content
    /// following a later [`place.flush`] element.
    ///
    /// ```example
    /// #set page(height: 150pt)
    /// #let note(where, body) = place(
    ///   center + where,
    ///   float: true,
    ///   clearance: 6pt,
    ///   rect(body),
    /// )
    ///
    /// #lorem(10)
    /// #note(bottom)[Bottom 1]
    /// #note(bottom)[Bottom 2]
    /// #lorem(40)
    /// #note(top)[Top]
    /// #lorem(10)
    /// ```
    pub float: bool,

    /// The spacing between the placed element and other elements in a floating
    /// layout.
    ///
    /// Has no effect if `float` is `{false}`.
    #[default(Em::new(1.5).into())]
    #[resolve]
    pub clearance: Length,

    /// The horizontal displacement of the placed content.
    ///
    /// ```example
    /// #set page(height: 100pt)
    /// #for i in range(16) {
    ///   let amount = i * 4pt
    ///   place(center, dx: amount - 32pt, dy: amount)[A]
    /// }
    /// ```
    ///
    /// This does not affect the layout of in-flow content.
    /// In other words, the placed content is treated as if it
    /// were wrapped in a [`move`] element.
    pub dx: Rel<Length>,

    /// The vertical displacement of the placed content.
    ///
    /// This does not affect the layout of in-flow content.
    /// In other words, the placed content is treated as if it
    /// were wrapped in a [`move`] element.
    pub dy: Rel<Length>,

    /// The content to place.
    #[required]
    pub body: Content,
}

/// `PlaceElem` must be locatable to support logical ordering of floats, but I
/// do not want to expose `query(place)` for now.
impl Unqueriable for Packed<PlaceElem> {}

#[scope]
impl PlaceElem {
    #[elem]
    type FlushElem;
}

/// Relative to which containing scope something shall be placed.
#[derive(Debug, Default, Copy, Clone, Eq, PartialEq, Hash, Cast)]
pub enum PlacementScope {
    /// Place into the current column.
    #[default]
    Column,
    /// Place relative to the parent, letting the content span over all columns.
    Parent,
}

/// Asks the layout algorithm to place pending floating elements before
/// continuing with the content.
///
/// This is useful for preventing floating figures from spilling
/// into the next section.
///
/// ```example
/// >>> #set page(height: 160pt, width: 150pt)
/// #lorem(15)
///
/// #figure(
///   rect(width: 100%, height: 50pt),
///   placement: auto,
///   caption: [A rectangle],
/// )
///
/// #place.flush()
///
/// This text appears after the figure.
/// ```
#[elem]
pub struct FlushElem {}