use std::fmt::{self, Debug, Formatter};
use std::num::NonZeroUsize;

use ecow::EcoString;

use crate::engine::Engine;
use crate::foundations::{func, scope, ty, Repr};
use crate::layout::Position;
use crate::model::Numbering;

/// Identifies an element in the document.
///
/// A location uniquely identifies an element in the document and lets you
/// access its absolute position on the pages. You can retrieve the current
/// location with the [`here`] function and the location of a queried or shown
/// element with the [`location()`]($content.location) method on content.
///
/// # Locatable elements { #locatable }
/// Currently, only a subset of element functions is locatable. Aside from
/// headings and figures, this includes equations, references, quotes and all
/// elements with an explicit label. As a result, you _can_ query for e.g.
/// [`strong`] elements, but you will find only those that have an explicit
/// label attached to them. This limitation will be resolved in the future.
#[ty(scope)]
#[derive(Copy, Clone, Eq, PartialEq, Hash)]
pub struct Location(u128);

impl Location {
    /// Create a new location from a unique hash.
    pub fn new(hash: u128) -> Self {
        Self(hash)
    }

    /// Extract the raw hash.
    pub fn hash(self) -> u128 {
        self.0
    }

    /// Produces a well-known variant of this location.
    ///
    /// This is a synthetic location created from another one and is used, for
    /// example, in bibliography management to create individual linkable
    /// locations for reference entries from the bibliography's location.
    pub fn variant(self, n: usize) -> Self {
        Self(typst_utils::hash128(&(self.0, n)))
    }
}

#[scope]
impl Location {
    /// Returns the page number for this location.
    ///
    /// Note that this does not return the value of the [page counter]($counter)
    /// at this location, but the true page number (starting from one).
    ///
    /// If you want to know the value of the page counter, use
    /// `{counter(page).at(loc)}` instead.
    ///
    /// Can be used with [`here`] to retrieve the physical page position
    /// of the current context:
    /// ```example
    /// #context [
    ///   I am located on
    ///   page #here().page()
    /// ]
    /// ```
    #[func]
    pub fn page(self, engine: &mut Engine) -> NonZeroUsize {
        engine.introspector.page(self)
    }

    /// Returns a dictionary with the page number and the x, y position for this
    /// location. The page number starts at one and the coordinates are measured
    /// from the top-left of the page.
    ///
    /// If you only need the page number, use `page()` instead as it allows
    /// Typst to skip unnecessary work.
    #[func]
    pub fn position(self, engine: &mut Engine) -> Position {
        engine.introspector.position(self)
    }

    /// Returns the page numbering pattern of the page at this location. This
    /// can be used when displaying the page counter in order to obtain the
    /// local numbering. This is useful if you are building custom indices or
    /// outlines.
    ///
    /// If the page numbering is set to `{none}` at that location, this function
    /// returns `{none}`.
    #[func]
    pub fn page_numbering(self, engine: &mut Engine) -> Option<Numbering> {
        engine.introspector.page_numbering(self).cloned()
    }
}

impl Debug for Location {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        write!(f, "Location({})", self.0)
    }
}

impl Repr for Location {
    fn repr(&self) -> EcoString {
        "..".into()
    }
}

/// Makes this element as locatable through the introspector.
pub trait Locatable {}

/// Marks this element as not being queryable even though it is locatable for
/// internal reasons.
pub trait Unqueriable {}