//! Expressions in function headers.

use std::fmt::{self, Debug, Formatter};
use std::ops::Deref;
use std::str::FromStr;
use std::u8;

use crate::Feedback;
use crate::length::Length;
use super::span::Spanned;
use super::tokens::is_identifier;
use super::value::Value;

/// An argument or return value.
#[derive(Clone, PartialEq)]
pub enum Expr {
    /// An identifier: `ident`.
    Ident(Ident),
    /// A string: `"string"`.
    Str(String),
    /// A number: `1.2, 200%`.
    Number(f64),
    /// A length: `2cm, 5.2in`.
    Length(Length),
    /// A bool: `true, false`.
    Bool(bool),
    /// A color value, including the alpha channel: `#f79143ff`.
    Color(RgbaColor),
    /// A tuple: `(false, 12cm, "hi")`.
    Tuple(Tuple),
    /// A named tuple: `cmyk(37.7, 0, 3.9, 1.1)`.
    NamedTuple(NamedTuple),
    /// An object: `{ fit: false, width: 12pt }`.
    Object(Object),
    /// An operator that negates the contained expression.
    Neg(Box<Spanned<Expr>>),
    /// An operator that adds the contained expressions.
    Add(Box<Spanned<Expr>>, Box<Spanned<Expr>>),
    /// An operator that subtracts contained expressions.
    Sub(Box<Spanned<Expr>>, Box<Spanned<Expr>>),
    /// An operator that multiplies the contained expressions.
    Mul(Box<Spanned<Expr>>, Box<Spanned<Expr>>),
    /// An operator that divides the contained expressions.
    Div(Box<Spanned<Expr>>, Box<Spanned<Expr>>),
}

impl Expr {
    /// A natural-language name of the type of this expression, e.g. "identifier".
    pub fn name(&self) -> &'static str {
        use Expr::*;
        match self {
            Ident(_) => "identifier",
            Str(_) => "string",
            Number(_) => "number",
            Length(_) => "length",
            Bool(_) => "bool",
            Color(_) => "color",
            Tuple(_) => "tuple",
            NamedTuple(_) => "named tuple",
            Object(_) => "object",
            Neg(_) => "negation",
            Add(_, _) => "addition",
            Sub(_, _) => "subtraction",
            Mul(_, _) => "multiplication",
            Div(_, _) => "division",
        }
    }
}

impl Debug for Expr {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        use Expr::*;
        match self {
            Ident(i) => i.fmt(f),
            Str(s) => s.fmt(f),
            Number(n) => n.fmt(f),
            Length(s) => s.fmt(f),
            Bool(b) => b.fmt(f),
            Color(c) => c.fmt(f),
            Tuple(t) => t.fmt(f),
            NamedTuple(t) => t.fmt(f),
            Object(o) => o.fmt(f),
            Neg(e) => write!(f, "-{:?}", e),
            Add(a, b) => write!(f, "({:?} + {:?})", a, b),
            Sub(a, b) => write!(f, "({:?} - {:?})", a, b),
            Mul(a, b) => write!(f, "({:?} * {:?})", a, b),
            Div(a, b) => write!(f, "({:?} / {:?})", a, b),
        }
    }
}

/// A unicode identifier.
///
/// # Example
/// ```typst
/// [func: "hi", ident]
///  ^^^^        ^^^^^
/// ```
#[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub struct Ident(pub String);

impl Ident {
    /// Create a new identifier from a string checking that it is a valid
    /// unicode identifier.
    pub fn new<S>(ident: S) -> Option<Ident> where S: AsRef<str> + Into<String> {
        if is_identifier(ident.as_ref()) {
            Some(Ident(ident.into()))
        } else {
            None
        }
    }

    /// Return a reference to the underlying string.
    pub fn as_str(&self) -> &str {
        self.0.as_str()
    }
}

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

/// An 8-bit RGBA color.
///
/// # Example
/// ```typst
/// [page: background=#423abaff]
///                   ^^^^^^^^
/// ```
#[derive(Copy, Clone, Eq, PartialEq, Hash)]
pub struct RgbaColor {
    /// Red channel.
    pub r: u8,
    /// Green channel.
    pub g: u8,
    /// Blue channel.
    pub b: u8,
    /// Alpha channel.
    pub a: u8,
    /// Indicates whether this is a user-provided value or a
    /// default value provided as a fail-over by the parser.
    /// This color may be overwritten if this property is true.
    pub healed: bool,
}

impl RgbaColor {
    /// Constructs a new color.
    pub fn new(r: u8, g: u8, b: u8, a: u8) -> RgbaColor {
        RgbaColor { r, g, b, a, healed: false }
    }

    /// Constructs a new color with the healed property set to true.
    pub fn new_healed(r: u8, g: u8, b: u8, a: u8) -> RgbaColor {
        RgbaColor { r, g, b, a, healed: true }
    }
}

impl FromStr for RgbaColor {
    type Err = ParseColorError;

    /// Constructs a new color from a hex string like `7a03c2`.
    /// Do not specify a leading `#`.
    fn from_str(hex_str: &str) -> Result<RgbaColor, Self::Err> {
        if !hex_str.is_ascii() {
            return Err(ParseColorError);
        }

        let len = hex_str.len();
        let long =  len == 6 || len == 8;
        let short = len == 3 || len == 4;
        let alpha = len == 4 || len == 8;

        if !long && !short {
            return Err(ParseColorError);
        }

        let mut values: [u8; 4] = [255; 4];

        for elem in if alpha { 0..4 } else { 0..3 } {
            let item_len = if long { 2 } else { 1 };
            let pos = elem * item_len;

            let item = &hex_str[pos..(pos+item_len)];
            values[elem] = u8::from_str_radix(item, 16)
                .map_err(|_| ParseColorError)?;

            if short {
                // Duplicate number for shorthand notation, i.e. `a` -> `aa`
                values[elem] += values[elem] * 16;
            }
        }

        Ok(RgbaColor::new(values[0], values[1], values[2], values[3]))
    }
}

impl Debug for RgbaColor {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        if f.alternate() {
            write!(
                f,
                "rgba({:02}, {:02}, {:02}, {:02})",
                self.r, self.g, self.b, self.a,
            )?;
        } else {
            write!(
                f,
                "#{:02x}{:02x}{:02x}{:02x}",
                self.r, self.g, self.b, self.a,
            )?;
        }
        if self.healed {
            f.write_str(" [healed]")?;
        }
        Ok(())
    }
}

/// The error returned when parsing a [`RgbaColor`] from a string fails.
#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub struct ParseColorError;

impl std::error::Error for ParseColorError {}

impl fmt::Display for ParseColorError {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        f.write_str("invalid color")
    }
}

/// An untyped sequence of expressions.
///
/// # Example
/// ```typst
/// (false, 12cm, "hi")
/// ```
#[derive(Default, Clone, PartialEq)]
pub struct Tuple(pub Vec<Spanned<Expr>>);

impl Tuple {
    /// Create an empty tuple.
    pub fn new() -> Tuple {
        Tuple(vec![])
    }

    /// Add an element.
    pub fn push(&mut self, item: Spanned<Expr>) {
        self.0.push(item);
    }

    /// Expect a specific value type and generate errors for every argument
    /// until an argument of the value type is found.
    pub fn expect<V: Value>(&mut self, f: &mut Feedback) -> Option<V> {
        while !self.0.is_empty() {
            let item = self.0.remove(0);
            if let Some(val) = V::parse(item, f) {
                return Some(val);
            }
        }
        None
    }

    /// Extract the first argument of the value type if there is any.
    pub fn get<V: Value>(&mut self) -> Option<V> {
        for (i, item) in self.0.iter().enumerate() {
            if let Some(val) = V::parse(item.clone(), &mut Feedback::new()) {
                self.0.remove(i);
                return Some(val);
            }
        }
        None
    }

    /// Extract all arguments of the value type.
    pub fn all<'a, V: Value>(&'a mut self) -> impl Iterator<Item = V> + 'a {
        let mut i = 0;
        std::iter::from_fn(move || {
            while i < self.0.len() {
               let val = V::parse(self.0[i].clone(), &mut Feedback::new());
               if val.is_some() {
                   self.0.remove(i);
                   return val;
               } else {
                   i += 1;
               }
            }
            None
        })
    }
}

impl Debug for Tuple {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        f.debug_list().entries(&self.0).finish()
    }
}

/// A named, untyped sequence of expressions.
///
/// # Example
/// ```typst
/// hsl(93, 10, 19.4)
/// ```
#[derive(Debug, Clone, PartialEq)]
pub struct NamedTuple {
    /// The name of the tuple and where it is in the user source.
    pub name: Spanned<Ident>,
    /// The elements of the tuple.
    pub tuple: Spanned<Tuple>,
}

impl NamedTuple {
    /// Create a named tuple from a tuple.
    pub fn new(name: Spanned<Ident>, tuple: Spanned<Tuple>) -> NamedTuple {
        NamedTuple { name, tuple }
    }
}

impl Deref for NamedTuple {
    type Target = Tuple;

    fn deref(&self) -> &Self::Target {
        &self.tuple.v
    }
}

/// A key-value collection of identifiers and associated expressions.
///
/// # Example
/// ```typst
/// { fit: false, width: 12cm, items: (1, 2, 3) }
/// ```
#[derive(Default, Clone, PartialEq)]
pub struct Object(pub Vec<Spanned<Pair>>);

/// A key-value pair in an object.
#[derive(Debug, Clone, PartialEq)]
pub struct Pair {
    /// The key part.
    /// ```typst
    /// key: value
    /// ^^^
    /// ```
    pub key: Spanned<Ident>,
    /// The value part.
    /// ```typst
    /// key: value
    ///      ^^^^^
    /// ```
    pub value: Spanned<Expr>,
}

impl Object {
    /// Create an empty object.
    pub fn new() -> Object {
        Object(vec![])
    }

    /// Add a pair to object.
    pub fn push(&mut self, pair: Spanned<Pair>) {
        self.0.push(pair);
    }

    /// Extract an argument with the given key if there is any.
    ///
    /// Generates an error if there is a matching key, but the value is of the
    /// wrong type.
    pub fn get<V: Value>(&mut self, key: &str, f: &mut Feedback) -> Option<V> {
        for (i, pair) in self.0.iter().enumerate() {
            if pair.v.key.v.as_str() == key {
                let pair = self.0.remove(i);
                return V::parse(pair.v.value, f);
            }
        }
        None
    }

    /// Extract all key-value pairs where the value is of the given type.
    pub fn all<'a, V: Value>(&'a mut self)
        -> impl Iterator<Item = (Spanned<Ident>, V)> + 'a
    {
        let mut i = 0;
        std::iter::from_fn(move || {
            while i < self.0.len() {
               let val = V::parse(self.0[i].v.value.clone(), &mut Feedback::new());
               if let Some(val) = val {
                   let pair = self.0.remove(i);
                   return Some((pair.v.key, val));
               } else {
                   i += 1;
               }
            }
            None
        })
    }
}

impl Debug for Object {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        f.debug_map()
            .entries(self.0.iter().map(|p| (&p.v.key.v, &p.v.value.v)))
            .finish()
    }
}