//! Dynamic typesetting functions.

use std::any::Any;
use std::collections::HashMap;
use std::fmt::{self, Debug, Formatter};

use crate::font::FontClass;
use crate::layout::{layout, Layout, LayoutContext, LayoutResult};
use crate::layout::flex::FlexLayout;
use crate::parsing::{parse, ParseContext, ParseError, ParseResult};
use crate::syntax::{SyntaxTree, FuncHeader};


/// Typesetting function types.
///
/// These types have to be able to parse tokens into themselves and store the relevant information
/// from the parsing to do their role in typesetting later.
///
/// The trait `FunctionBounds` is automatically implemented for types which can be used as
/// functions, that is they fulfill the bounds `Debug + PartialEq + 'static`.
pub trait Function: FunctionBounds {
    /// Parse the header and body into this function given a context.
    fn parse(header: &FuncHeader, body: Option<&str>, ctx: ParseContext)
        -> ParseResult<Self> where Self: Sized;

    /// Layout this function given a context.
    ///
    /// Returns optionally the resulting layout and a new context if changes to the context should
    /// be made.
    fn layout(&self, ctx: LayoutContext) -> LayoutResult<Option<Layout>>;
}

impl PartialEq for dyn Function {
    fn eq(&self, other: &dyn Function) -> bool {
        self.help_eq(other)
    }
}

/// A helper trait that describes requirements for types that can implement [`Function`].
///
/// Automatically implemented for all types which fulfill to the bounds `Debug + PartialEq +
/// 'static`. There should be no need to implement this manually.
pub trait FunctionBounds: Debug {
    /// Cast self into `Any`.
    fn help_cast_as_any(&self) -> &dyn Any;

    /// Compare self with another function.
    fn help_eq(&self, other: &dyn Function) -> bool;
}

impl<T> FunctionBounds for T where T: Debug + PartialEq + 'static {
    fn help_cast_as_any(&self) -> &dyn Any {
        self
    }

    fn help_eq(&self, other: &dyn Function) -> bool {
        if let Some(other) = other.help_cast_as_any().downcast_ref::<Self>() {
            self == other
        } else {
            false
        }
    }
}

/// A map from identifiers to functions.
pub struct Scope {
    parsers: HashMap<String, Box<ParseFunc>>,
}

/// A function which parses a function invocation into a function type.
type ParseFunc = dyn Fn(&FuncHeader, Option<&str>, ParseContext)
                       -> ParseResult<Box<dyn Function>>;

impl Scope {
    /// Create a new empty scope.
    pub fn new() -> Scope {
        Scope { parsers: HashMap::new() }
    }

    /// Create a new scope with the standard functions contained.
    pub fn with_std() -> Scope {
        let mut std = Scope::new();
        std.add::<BoldFunc>("bold");
        std.add::<ItalicFunc>("italic");
        std.add::<MonospaceFunc>("mono");
        std
    }

    /// Add a function type to the scope giving it a name.
    pub fn add<F: Function + 'static>(&mut self, name: &str) {
        self.parsers.insert(
            name.to_owned(),
            Box::new(|h, b, c| {
                F::parse(h, b, c).map(|func| Box::new(func) as Box<dyn Function>)
            })
        );
    }

    /// Return the parser with the given name if there is one.
    pub(crate) fn get_parser(&self, name: &str) -> Option<&ParseFunc> {
        self.parsers.get(name).map(|x| &**x)
    }
}

impl Debug for Scope {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        write!(f, "Scope ")?;
        write!(f, "{:?}", self.parsers.keys())
    }
}

/// Creates style functions like bold and italic.
macro_rules! style_func {
    ($(#[$outer:meta])* pub struct $struct:ident { $name:expr },
     $style:ident => $style_change:block) => {
        $(#[$outer])*
        #[derive(Debug, PartialEq)]
        pub struct $struct { body: SyntaxTree }
        impl Function for $struct {
            fn parse(header: &FuncHeader, body: Option<&str>, ctx: ParseContext)
                -> ParseResult<Self> where Self: Sized {
                // Accept only invocations without arguments and with body.
                if header.args.is_empty() && header.kwargs.is_empty() {
                    if let Some(body) = body {
                        Ok($struct { body: parse(body, ctx)? })
                    } else {
                        Err(ParseError::new(format!("expected body for function `{}`", $name)))
                    }
                } else {
                    Err(ParseError::new(format!("unexpected arguments to function `{}`", $name)))
                }
            }

            fn layout(&self, ctx: LayoutContext) -> LayoutResult<Option<Layout>> {
                // Change the context.
                let mut $style = ctx.style.clone();
                $style_change

                // Create a box and put it into a flex layout.
                let boxed = layout(&self.body, LayoutContext {
                    style: &$style,
                    .. ctx
                })?;
                let flex = FlexLayout::from_box(boxed);

                Ok(Some(Layout::Flex(flex)))
            }
        }
    };
}

style_func! {
    /// Typesets text in bold.
    pub struct BoldFunc { "bold" },
    style => { style.toggle_class(FontClass::Bold) }
}

style_func! {
    /// Typesets text in italics.
    pub struct ItalicFunc { "italic" },
    style => { style.toggle_class(FontClass::Italic) }
}

style_func! {
    /// Typesets text in monospace.
    pub struct MonospaceFunc { "mono" },
    style => { style.toggle_class(FontClass::Monospace) }
}