/*
Copyright (c) 2023 Michał Wilczek, Michał Margos

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
associated documentation files (the “Software”), to deal in the Software without restriction,
including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial
portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

use geo_aid_derive::Parse;
use num_traits::Zero;

use crate::script::builtins;
use std::{
    fmt::{Debug, Display},
    iter::Peekable,
    marker::PhantomData,
};

use crate::span;

use super::{
    token::{
        number::CompExponent, Ampersant, Asterisk, At, Caret, Colon, Comma, Dollar, Dot, Eq,
        Exclamation, Gt, Gteq, Ident, LBrace, LParen, LSquare, Let, Lt, Lteq, Minus, NamedIdent,
        Number, Plus, Question, RBrace, RParen, RSquare, Semi, Slash, Span, StrLit, TokInteger,
        Token,
    },
    unit, ComplexUnit, Error,
};

pub trait Parse {
    type FirstToken: CheckParses;

    /// # Errors
    /// Returns an error if parsing was unsuccessful.
    fn parse<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &mut InputStream<'t, I>,
    ) -> Result<Self, Error>
    where
        Self: Sized;

    fn get_span(&self) -> Span;
}

pub trait CheckParses {
    fn check_parses<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &InputStream<'t, I>,
    ) -> Option<bool>;
}

impl<T: Parse> CheckParses for T {
    fn check_parses<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &InputStream<'t, I>,
    ) -> Option<bool> {
        Some(input.clone().parse::<Self>().is_ok())
    }
}

#[derive(Debug)]
pub struct TokenOr<T, U> {
    phantom_t: PhantomData<T>,
    phantom_u: PhantomData<U>,
}

impl<T: CheckParses, U: CheckParses> CheckParses for TokenOr<T, U> {
    fn check_parses<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &InputStream<'t, I>,
    ) -> Option<bool> {
        T::check_parses(input).or_else(|| U::check_parses(input))
    }
}

#[derive(Debug)]
pub struct Maybe<T> {
    phantom_t: PhantomData<T>,
}

impl<T: CheckParses> CheckParses for Maybe<T> {
    fn check_parses<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &InputStream<'t, I>,
    ) -> Option<bool> {
        T::check_parses(input).and_then(|x| if x { Some(x) } else { None })
    }
}

impl<T: Parse> Parse for Vec<T> {
    type FirstToken = Maybe<T::FirstToken>;

    fn parse<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &mut InputStream<'t, I>,
    ) -> Result<Self, Error>
    where
        Self: Sized,
    {
        let mut parsed = Self::new();

        while let Ok(Some(v)) = input.parse() {
            parsed.push(v);
        }

        Ok(parsed)
    }

    fn get_span(&self) -> Span {
        self.first().map_or(Span::empty(), |x| {
            x.get_span().join(self.last().unwrap().get_span())
        })
    }
}

impl<T: Parse, U: Parse> Parse for (T, U) {
    type FirstToken = T::FirstToken;

    fn parse<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &mut InputStream<'t, I>,
    ) -> Result<Self, Error>
    where
        Self: Sized,
    {
        Ok((input.parse()?, input.parse()?))
    }

    fn get_span(&self) -> Span {
        self.0.get_span().join(self.1.get_span())
    }
}

impl<T: Parse> Parse for Option<T> {
    type FirstToken = Maybe<T::FirstToken>;

    fn parse<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &mut InputStream<'t, I>,
    ) -> Result<Self, Error>
    where
        Self: Sized,
    {
        if T::FirstToken::check_parses(input) == Some(false) {
            Ok(None)
        } else {
            Ok(Some(input.parse()?))
        }
    }

    fn get_span(&self) -> Span {
        match self {
            Some(v) => v.get_span(),
            None => span!(0, 0, 0, 0),
        }
    }
}

#[derive(Debug, Clone)]
pub struct InputStream<'t, I: Iterator<Item = &'t Token> + Clone> {
    it: Peekable<I>,
}

impl<'t, I: Iterator<Item = &'t Token> + Clone> InputStream<'t, I> {
    #[must_use]
    pub fn new<It: IntoIterator<IntoIter = I>>(it: It) -> Self {
        Self {
            it: it.into_iter().peekable(),
        }
    }

    /// # Errors
    /// Returns an error if failed to parse
    pub fn parse<P: Parse>(&mut self) -> Result<P, Error> {
        P::parse(self)
    }

    /// # Errors
    /// Returns an EOF error if there is no next token.
    pub fn get_token(&mut self) -> Result<&'t Token, Error> {
        self.it.next().ok_or(Error::EndOfInput)
    }

    /// # Errors
    /// Returns an EOF error if there is no next token. Does not advance the inner iterator.
    pub fn expect_token(&mut self) -> Result<(), Error> {
        if self.eof() {
            Err(Error::EndOfInput)
        } else {
            Ok(())
        }
    }

    #[must_use]
    pub fn eof(&mut self) -> bool {
        self.it.peek().is_none()
    }
}

/// A binary operator, like `+`, `-`, `*` or `/`.
#[derive(Debug, Parse)]
pub enum BinaryOperator {
    /// Addition
    Add(Plus),
    /// Subtraction
    Sub(Minus),
    /// Multiplication
    Mul(Asterisk),
    /// Division
    Div(Slash),
}

impl ToString for BinaryOperator {
    fn to_string(&self) -> String {
        match self {
            BinaryOperator::Add(_) => String::from("+"),
            BinaryOperator::Sub(_) => String::from("-"),
            BinaryOperator::Mul(_) => String::from("*"),
            BinaryOperator::Div(_) => String::from("/"),
        }
    }
}

#[derive(Debug, Parse)]
#[parse(first_token = Ampersant)]
pub struct PointCollectionConstructor {
    pub ampersant: Ampersant,
    pub left_paren: LParen,
    pub points: Punctuated<Expression<false>, Comma>,
    pub right_paren: RParen,
}

/// Punctuated expressions.
#[derive(Debug)]
pub struct ImplicitIterator<const ITER: bool> {
    pub exprs: Punctuated<SimpleExpression, Comma>,
}

impl<const ITER: bool> ImplicitIterator<ITER> {
    #[must_use]
    pub fn get(&self, index: usize) -> Option<&SimpleExpression> {
        if ITER {
            self.exprs.get(index)
        } else {
            Some(&self.exprs.first)
        }
    }
}

impl<const ITER: bool> Parse for ImplicitIterator<ITER> {
    type FirstToken = <SimpleExpression as Parse>::FirstToken;

    fn parse<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &mut InputStream<'t, I>,
    ) -> Result<Self, Error>
    where
        Self: Sized,
    {
        if ITER {
            Ok(Self {
                exprs: input.parse()?,
            })
        } else {
            Ok(Self {
                exprs: Punctuated {
                    first: input.parse()?,
                    collection: Vec::new(),
                },
            })
        }
    }

    fn get_span(&self) -> Span {
        self.exprs.get_span()
    }
}

/// $id(a, b, ...).
#[derive(Debug)]
pub struct ExplicitIterator {
    pub dollar: Dollar,
    pub id_token: TokInteger,
    pub id: u8,
    pub left_paren: LParen,
    pub exprs: Punctuated<Expression<false>, Comma>,
    pub right_paren: RParen,
}

impl ExplicitIterator {
    #[must_use]
    pub fn get(&self, index: usize) -> Option<&Expression<false>> {
        self.exprs.get(index)
    }
}

impl Parse for ExplicitIterator {
    type FirstToken = Dollar;

    fn parse<'r, I: Iterator<Item = &'r Token> + Clone>(
        input: &mut InputStream<'r, I>,
    ) -> Result<Self, Error> {
        let mut parsed = Self {
            dollar: input.parse()?,
            id_token: input.parse()?,
            id: 0,
            left_paren: input.parse()?,
            exprs: input.parse()?,
            right_paren: input.parse()?,
        };

        parsed.id = parsed
            .id_token
            .parsed
            .parse()
            .map_err(|_| Error::NumberTooLarge {
                error_span: parsed.id_token.get_span(),
            })?;

        if parsed.exprs.len() == 1 {
            return Err(Error::SingleVariantExplicitIterator {
                error_span: parsed.dollar.span.join(parsed.right_paren.span),
            });
        }

        Ok(parsed)
    }

    fn get_span(&self) -> Span {
        self.dollar.span.join(self.right_paren.span)
    }
}

/// A parsed expression.
#[derive(Debug)]
pub enum Expression<const ITER: bool> {
    /// Simple values separated by a comma.
    ImplicitIterator(ImplicitIterator<ITER>),
    /// A binary operator expression.
    Binop(ExprBinop<ITER>),
}

impl<const ITER: bool> Parse for Expression<ITER> {
    type FirstToken = <SimpleExpression as Parse>::FirstToken;

    fn parse<'r, I: Iterator<Item = &'r Token> + Clone>(
        input: &mut InputStream<'r, I>,
    ) -> Result<Self, Error> {
        let mut expr = Expression::ImplicitIterator(input.parse()?);

        while let Ok(Some(op)) = input.parse() {
            let rhs = Expression::ImplicitIterator(input.parse()?);

            expr = dispatch_order(expr, op, rhs);
        }

        Ok(expr)
    }

    fn get_span(&self) -> Span {
        match self {
            Expression::ImplicitIterator(it) => it.get_span(),
            Expression::Binop(e) => e.lhs.get_span().join(e.rhs.get_span()),
        }
    }
}

/// A rational exponent.
#[derive(Debug)]
pub struct RationalExponent {
    pub lparen: LParen,
    pub nom: TokInteger,
    pub slash: Slash,
    pub denom: TokInteger,
    pub rparen: RParen,
}

impl Parse for RationalExponent {
    type FirstToken = LParen;

    fn parse<'r, I: Iterator<Item = &'r Token> + Clone>(
        input: &mut InputStream<'r, I>,
    ) -> Result<Self, Error> {
        let parsed = Self {
            lparen: input.parse()?,
            nom: input.parse()?,
            slash: input.parse()?,
            denom: input.parse()?,
            rparen: input.parse()?,
        };

        if parsed.denom.parsed.is_zero() {
            return Err(Error::ZeroDenominator {
                error_span: parsed.denom.span,
            });
        }

        Ok(parsed)
    }

    fn get_span(&self) -> Span {
        self.lparen.span.join(self.rparen.span)
    }
}

/// An integer or a ratio.
#[derive(Debug, Parse)]
pub enum Exponent {
    Simple(TokInteger),
    Parenthised(RationalExponent),
}

impl Exponent {
    /// # Errors
    /// Returns an error if the numbers can't fit.
    pub fn into_comp(&self) -> Result<CompExponent, Error> {
        match self {
            Self::Simple(i) => Ok(CompExponent::new(
                i.parsed
                    .parse()
                    .map_err(|_| Error::NumberTooLarge { error_span: i.span })?,
                1,
            )),
            Self::Parenthised(exp) => Ok(CompExponent::new(
                exp.nom.parsed.parse().map_err(|_| Error::NumberTooLarge {
                    error_span: exp.nom.span,
                })?,
                exp.denom
                    .parsed
                    .parse()
                    .map_err(|_| Error::NumberTooLarge {
                        error_span: exp.denom.span,
                    })?,
            )),
        }
    }
}

/// A value being raised to a rational power.
#[derive(Debug, Parse)]
pub struct Exponentiation {
    /// Caret token
    pub caret: Caret,
    /// Possible negation
    pub minus: Option<Minus>,
    /// The exponent.
    pub exponent: Exponent,
}

#[derive(Debug, Parse)]
pub struct FieldIndex {
    /// The indexed thing
    pub name: Box<Name>,
    /// The dot
    pub dot: Dot,
    /// The field
    pub field: Ident,
}

/// A name (field, method or variable).
#[derive(Debug)]
pub enum Name {
    // Variant order matters, as it defines the parsing priority
    Call(ExprCall),
    FieldIndex(FieldIndex),
    Ident(Ident),
    Expression(ExprParenthised),
}

impl Parse for Name {
    type FirstToken = TokenOr<Maybe<Ident>, LParen>;

    fn parse<'t, I: Iterator<Item = &'t Token> + Clone>(
        input: &mut InputStream<'t, I>,
    ) -> Result<Self, Error>
    where
        Self: Sized,
    {
        let mut name = if let Some(expr) = input.parse()? {
            Self::Expression(expr)
        } else {
            Self::Ident(input.parse()?)
        };

        loop {
            name = if let Some(dot) = input.parse::<Option<Dot>>()? {
                Self::FieldIndex(FieldIndex {
                    name: Box::new(name),
                    dot,
                    field: input.parse()?,
                })
            } else if let Some(lparen) = input.parse::<Option<LParen>>()? {
                Self::Call(ExprCall {
                    name: Box::new(name),
                    lparen,
                    params: input.parse()?,
                    rparen: input.parse()?,
                })
            } else {
                break Ok(name);
            };
        }
    }

    fn get_span(&self) -> Span {
        match self {
            Self::Call(v) => v.get_span(),
            Self::FieldIndex(v) => v.get_span(),
            Self::Expression(v) => v.get_span(),
            Self::Ident(v) => v.get_span(),
        }
    }
}

/// A parsed simple expression.
#[derive(Debug, Parse)]
pub struct SimpleExpression {
    /// Possible minus for negation.
    pub minus: Option<Minus>,
    /// The kind of the expression.
    pub kind: SimpleExpressionKind,
    /// Possible exponentiation.
    pub exponent: Option<Exponentiation>,
    /// The additional display information.
    pub display: Option<DisplayProperties>,
}

/// A parsed simple expression.
#[derive(Debug, Parse)]
pub enum SimpleExpressionKind {
    /// A named (variable, field or function call)
    Name(Name),
    /// A raw number
    Number(Number),
    /// An explicit iterator.
    ExplicitIterator(ExplicitIterator),
    /// A point collection construction
    PointCollection(PointCollectionConstructor),
}

/// A parsed function call
#[derive(Debug, Parse)]
pub struct ExprCall {
    /// The called thing.
    pub name: Box<Name>,
    /// The `(` token.
    pub lparen: LParen,
    /// Punctuated params. `None` if no params are given.
    pub params: Option<Punctuated<Expression<false>, Comma>>,
    /// The `)` token.
    pub rparen: RParen,
}

/// A parsed parenthesed expression
#[derive(Debug, Parse)]
pub struct ExprParenthised {
    /// The `(` token.
    pub lparen: LParen,
    /// The contained `Expression`.
    pub content: Box<Expression<true>>,
    /// The `)` token.
    pub rparen: RParen,
}

/// A parsed binary operator expression.
#[derive(Debug, Parse)]
pub struct ExprBinop<const ITER: bool> {
    /// Left hand side
    pub lhs: Box<Expression<ITER>>,
    /// The operator
    pub operator: BinaryOperator,
    /// Right hand side.
    pub rhs: Box<Expression<ITER>>,
}

impl BinaryOperator {
    fn index(&self) -> u8 {
        match self {
            BinaryOperator::Add(_) | BinaryOperator::Sub(_) => 1,
            BinaryOperator::Mul(_) | BinaryOperator::Div(_) => 2,
        }
    }
}

/// Inserts an operator with an rhs into a operator series, considering the order of operations.
fn dispatch_order<const ITER: bool>(
    lhs: Expression<ITER>,
    op: BinaryOperator,
    rhs: Expression<ITER>, // We have to trust, that it is a valid expression.
) -> Expression<ITER> {
    match lhs {
        // if lhs is simple, there is no order to consider.
        lhs @ Expression::ImplicitIterator(_) => Expression::Binop(ExprBinop {
            lhs: Box::new(lhs),
            operator: op,
            rhs: Box::new(rhs),
        }),
        // Otherwise we compare indices of the operators and act accordingly.
        Expression::Binop(lhs) => {
            if op.index() > lhs.operator.index() {
                Expression::Binop(ExprBinop {
                    lhs: lhs.lhs,
                    operator: lhs.operator,
                    rhs: Box::new(dispatch_order(*lhs.rhs, op, rhs)),
                })
            } else {
                Expression::Binop(ExprBinop {
                    lhs: Box::new(Expression::Binop(lhs)),
                    operator: op,
                    rhs: Box::new(rhs),
                })
            }
        }
    }
}

/// A builtin rule operator
#[derive(Debug, Parse)]
pub enum PredefinedRuleOperator {
    /// Equality
    Eq(Eq),
    /// Less than
    Lt(Lt),
    /// Greater than
    Gt(Gt),
    /// Less than or equal
    Lteq(Lteq),
    /// Greater than or equal
    Gteq(Gteq),
}

/// A rule operator.
#[derive(Debug, Parse)]
pub enum RuleOperator {
    /// A inverted rule operator (!op)
    Inverted(InvertedRuleOperator),
    Predefined(PredefinedRuleOperator),
    Defined(NamedIdent),
}

/// An inverted rule operator.
#[derive(Debug, Parse)]
#[parse(first_token = Exclamation)]
pub struct InvertedRuleOperator {
    /// The `!` token
    pub exlamation: Exclamation,
    /// The operator.
    pub operator: Box<RuleOperator>,
}

/// Defines the first half of a flag statement.
#[derive(Debug, Parse)]
pub struct FlagName {
    pub at: At,
    pub name: Punctuated<NamedIdent, Dot>,
    pub colon: Colon,
}

/// A set of flags.
#[derive(Debug, Parse)]
#[parse(first_token = LBrace)]
pub struct FlagSet {
    pub lbrace: LBrace,
    pub flags: Vec<FlagStatement>,
    pub rbrace: RBrace,
}

/// Defines the second half of a flag statement.
#[derive(Debug, Parse)]
pub enum FlagValue {
    Ident(NamedIdent),
    Set(FlagSet),
    Number(Number),
}

/// Defines a compiler flag or flagset.
#[derive(Debug, Parse)]
pub struct FlagStatement {
    pub name: FlagName,
    pub value: FlagValue,
}

/// A single variable definition. Contains its name and optional display properties
#[derive(Debug, Clone, Parse)]
pub struct VariableDefinition {
    /// Name of the variable.
    pub name: Ident,
    /// Display properties.
    pub display_properties: Option<DisplayProperties>,
}

/// `let <something> = <something else>`.
/// Defines variables and possibly adds rules to them.
#[derive(Debug, Parse)]
pub struct LetStatement {
    /// The `let` token.
    pub let_token: Let,
    /// The lhs ident iterator.
    pub ident: Punctuated<VariableDefinition, Comma>,
    /// The `=` token.
    pub eq: Eq,
    /// The rhs expression.
    pub expr: Expression<true>,
    /// The rules after the rhs expression.
    pub rules: Vec<(RuleOperator, Expression<true>)>,
    /// The ending semicolon.
    pub semi: Semi,
}

/// `lhs ruleop rhs`.
/// Defines a rule.
#[derive(Debug, Parse)]
pub struct RuleStatement {
    /// Display properties.
    pub display: Option<DisplayProperties>,
    /// Left hand side
    pub lhs: Expression<true>,
    /// Rule operator
    pub op: RuleOperator,
    /// Right hand side
    pub rhs: Expression<true>,
    /// The ending semicolon.
    pub semi: Semi,
}

/// `?expr`
#[derive(Debug, Parse)]
pub struct RefStatement {
    /// Display properties.
    pub display: Option<DisplayProperties>,
    /// The starting question mark.
    pub question: Question,
    /// Operand.
    pub operand: Expression<true>,
    /// The ending semicolon.
    pub semi: Semi,
}

/// A general statement.
#[derive(Debug, Parse)]
pub enum Statement {
    /// No operation
    Noop(Semi),
    /// let
    Let(LetStatement),
    /// Flag
    Flag(FlagStatement),
    /// Reference
    Ref(RefStatement),
    /// rule
    Rule(RuleStatement),
}

impl Statement {
    #[must_use]
    pub fn as_flag(&self) -> Option<&FlagStatement> {
        if let Self::Flag(v) = self {
            Some(v)
        } else {
            None
        }
    }
}

/// A utility struct for collections of parsed items with punctuators between them.
#[derive(Debug, Clone, Parse)]
pub struct Punctuated<T: Parse, P: Parse> {
    /// The first parsed item.
    pub first: Box<T>,
    /// The next items with punctuators.
    pub collection: Vec<(P, T)>,
}

impl<T: Parse, P: Parse> Punctuated<T, P> {
    /// Creates a new instance of `Punctuated`.
    #[must_use]
    pub fn new(first: T) -> Punctuated<T, P> {
        Self {
            first: Box::new(first),
            collection: Vec::new(),
        }
    }

    /// Turns the punctuated into an iterator on the items.
    pub fn iter(&self) -> impl Iterator<Item = &T> {
        vec![self.first.as_ref()]
            .into_iter()
            .chain(self.collection.iter().map(|x| &x.1))
    }

    /// Turns the punctuated into an iterator on the items.
    pub fn into_parsed_iter(self) -> impl Iterator<Item = T> {
        vec![*self.first]
            .into_iter()
            .chain(self.collection.into_iter().map(|x| x.1))
    }

    /// Gets the item count.
    #[must_use]
    pub fn len(&self) -> usize {
        self.collection.len() + 1
    }

    /// Checks if there are no items (always false).
    #[must_use]
    pub fn is_empty(&self) -> bool {
        false
    }

    /// Tries to get the element on `index`.
    #[must_use]
    pub fn get(&self, index: usize) -> Option<&T> {
        match index {
            0 => Some(&self.first),
            _ => self.collection.get(index - 1).map(|x| &x.1),
        }
    }
}

impl Parse for TokInteger {
    type FirstToken = Number;

    fn parse<'r, I: Iterator<Item = &'r Token> + Clone>(
        input: &mut InputStream<'r, I>,
    ) -> Result<Self, Error> {
        match input.get_token()? {
            Token::Number(Number::Integer(tok)) => Ok(tok.clone()),
            t => Err(Error::InvalidToken { token: t.clone() }),
        }
    }

    fn get_span(&self) -> Span {
        self.span
    }
}

impl Parse for NamedIdent {
    type FirstToken = Ident;

    fn parse<'r, I: Iterator<Item = &'r Token> + Clone>(
        input: &mut InputStream<'r, I>,
    ) -> Result<Self, Error> {
        match input.get_token()? {
            Token::Ident(Ident::Named(named)) => Ok(named.clone()),
            t => Err(Error::InvalidToken { token: t.clone() }),
        }
    }

    fn get_span(&self) -> Span {
        self.span
    }
}

impl<T: Parse> Parse for Box<T> {
    type FirstToken = T::FirstToken;

    fn parse<'r, I: Iterator<Item = &'r Token> + Clone>(
        input: &mut InputStream<'r, I>,
    ) -> Result<Self, Error> {
        Ok(Box::new(input.parse()?))
    }

    fn get_span(&self) -> Span {
        (**self).get_span()
    }
}

/// A builtin type.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Type {
    /// A point
    Point,
    /// A line
    Line,
    /// A scalar of a certain unit.
    Scalar(Option<ComplexUnit>),
    /// A point collection.
    PointCollection(usize),
    /// A circle
    Circle,
    /// A bundle type.
    Bundle(&'static str),
    /// Marks unknown type. Unknown type pretends to be valid, but isn't really.
    Unknown,
}

impl Type {
    #[must_use]
    pub fn as_scalar(&self) -> Option<&Option<ComplexUnit>> {
        if let Self::Scalar(v) = self {
            Some(v)
        } else {
            None
        }
    }
}

/// A user-defined type.
pub struct DefinedType {
    /// The type's name.
    pub name: String,
}

impl Display for Type {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Point => write!(f, "Point"),
            Self::Line => write!(f, "Line"),
            Self::Scalar(unit) => match unit {
                Some(unit) => write!(f, "Scalar ({unit})"),
                None => write!(f, "Scalar (no unit)"),
            },
            Self::PointCollection(l) => write!(f, "Point collection ({l})"),
            Self::Circle => write!(f, "Circle"),
            Self::Bundle(name) => write!(f, "{name}"),
            Type::Unknown => write!(f, "undefined"),
        }
    }
}

impl Type {
    /// Whether `self` can be cast to `into`.
    #[must_use]
    pub fn can_cast(&self, into: &Type) -> bool {
        match self {
            // A point can only be cast into another point or a point collection with length one.
            Type::Point => matches!(into, Type::Point | Type::PointCollection(1)),
            // A line can only be cast into another line.
            Type::Line => matches!(into, Type::Line),
            // A scalar with a defined unit can only be cast into another scalar with the same unit.
            Type::Scalar(Some(unit1)) => {
                if let Type::Scalar(Some(unit2)) = into {
                    unit1 == unit2
                } else {
                    false
                }
            }
            // A scalar with no defined unit can be cast into any other scalar, except angle.
            Type::Scalar(None) => match into {
                Type::Scalar(unit) => match unit {
                    Some(unit) => unit.0[1].is_zero(), // no angle
                    None => true,
                },
                _ => false,
            },
            Type::PointCollection(l) => match into {
                Type::Point => *l == 1,
                Type::Line => *l == 2,
                Type::Scalar(Some(u)) => *u == unit::DISTANCE && *l == 2,
                Type::PointCollection(v) => v == l || *v == 0,
                _ => false,
            },
            Type::Circle => matches!(into, Type::Circle),
            Type::Bundle(name) => {
                if into == self {
                    true
                } else if let Type::PointCollection(count) = into {
                    builtins::get_bundle_pc(name) == *count
                } else {
                    false
                }
            }
            Type::Unknown => false,
        }
    }
}

/// A property
#[derive(Debug, Clone, Parse)]
pub struct Property {
    /// Property name.
    pub name: NamedIdent,
    /// '='
    pub eq: Eq,
    /// Property value.
    pub value: PropertyValue,
}

/// A property's value
#[derive(Debug, Clone, Parse)]
pub enum PropertyValue {
    Number(Number),
    Ident(Ident),
    RawString(RawString),
    String(StrLit),
}

impl Display for PropertyValue {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Number(n) => write!(f, "{n}"),
            Self::Ident(i) => write!(f, "{i}"),
            Self::RawString(s) => write!(f, "!{}", s.lit),
            Self::String(s) => write!(f, "{s}"),
        }
    }
}

#[derive(Debug, Clone, Parse)]
pub struct RawString {
    pub excl: Exclamation,
    pub lit: StrLit,
}

pub trait FromProperty: Sized {
    /// # Errors
    /// Causes an error if the value is not properly convertible.
    fn from_property(property: PropertyValue) -> Result<Self, Error>;
}

impl<T: FromProperty> FromProperty for Result<T, Error> {
    fn from_property(property: PropertyValue) -> Result<Self, Error> {
        Ok(T::from_property(property))
    }
}

impl FromProperty for bool {
    fn from_property(property: PropertyValue) -> Result<Self, Error> {
        match property {
            PropertyValue::Ident(ident) => match ident {
                Ident::Named(ident) => match ident.ident.as_str() {
                    "enabled" | "on" | "true" | "yes" => Ok(true),
                    "disabled" | "off" | "false" | "no" => Ok(false),
                    _ => Err(Error::BooleanExpected {
                        error_span: ident.get_span(),
                    }),
                },
                Ident::Collection(_) => Err(Error::BooleanExpected {
                    error_span: ident.get_span(),
                }),
            },
            PropertyValue::Number(num) => match num {
                Number::Integer(i) => match i.parsed.parse::<u8>() {
                    Ok(0) => Ok(false),
                    Ok(1) => Ok(true),
                    _ => Err(Error::BooleanExpected { error_span: i.span }),
                },
                Number::Float(f) => Err(Error::BooleanExpected { error_span: f.span }),
            },
            PropertyValue::String(s) => match s.content.as_str() {
                "enabled" | "on" | "true" | "yes" => Ok(true),
                "disabled" | "off" | "false" | "no" => Ok(false),
                _ => Err(Error::BooleanExpected {
                    error_span: s.get_span(),
                }),
            },
            PropertyValue::RawString(s) => Err(Error::BooleanExpected {
                error_span: s.get_span(),
            }),
        }
    }
}

impl FromProperty for String {
    fn from_property(property: PropertyValue) -> Result<String, Error> {
        match property {
            PropertyValue::Ident(ident) => Ok(ident.to_string()),
            PropertyValue::Number(num) => Err(Error::StringExpected {
                error_span: num.get_span(),
            }),
            PropertyValue::RawString(s) => Ok(s.lit.content),
            PropertyValue::String(s) => Ok(s.content),
        }
    }
}

/// Properties related to displaying things.
#[derive(Debug, Clone, Parse)]
pub struct DisplayProperties {
    /// '['
    pub lsquare: LSquare,
    /// Properties
    pub properties: Punctuated<Property, Semi>,
    /// ']'
    pub rsquare: RSquare,
}