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use crate::{utils::DebugPunctuated, Expr, Spanned, Stmt, VariableDeclaration};
use proc_macro2::Span;
use std::fmt;
use syn::{
    parenthesized,
    parse::{discouraged::Speculative, Parse, ParseStream},
    punctuated::Punctuated,
    token::Paren,
    Result, Token,
};

/// A variable declaration statement: `uint256 foo = 42;`.
///
/// Solidity Reference:
/// <https://docs.soliditylang.org/en/latest/grammar.html#a4.SolidityParser.variableDeclarationStatement>
#[derive(Clone)]
pub struct StmtVarDecl {
    pub declaration: VarDeclDecl,
    pub assignment: Option<(Token![=], Expr)>,
    pub semi_token: Token![;],
}

impl fmt::Debug for StmtVarDecl {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("StmtVarDecl")
            .field("declaration", &self.declaration)
            .field("assignment", &self.assignment)
            .finish()
    }
}

impl Parse for StmtVarDecl {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        let declaration: VarDeclDecl = input.parse()?;

        // tuple requires assignment
        let assignment = if matches!(declaration, VarDeclDecl::Tuple(_)) || input.peek(Token![=]) {
            Some((input.parse()?, input.parse()?))
        } else {
            None
        };

        let semi_token = input.parse()?;

        Ok(Self {
            declaration,
            assignment,
            semi_token,
        })
    }
}

impl Spanned for StmtVarDecl {
    fn span(&self) -> Span {
        let span = self.declaration.span();
        self.assignment
            .as_ref()
            .and_then(|(_, expr)| expr.span().join(span))
            .unwrap_or(span)
    }

    fn set_span(&mut self, span: Span) {
        self.declaration.set_span(span);
        if let Some((eq, expr)) = &mut self.assignment {
            eq.span = span;
            expr.set_span(span);
        }
        self.semi_token.span = span;
    }
}

impl StmtVarDecl {
    pub fn parse_or_expr(input: ParseStream<'_>) -> Result<Stmt> {
        // TODO: Figure if we can do this without forking
        let speculative_parse = || {
            let fork = input.fork();
            match fork.parse() {
                Ok(var) => {
                    input.advance_to(&fork);
                    Ok(Stmt::VarDecl(var))
                }
                Err(_) => input.parse().map(Stmt::Expr),
            }
        };

        if input.peek(Paren) {
            if input.peek2(Token![=]) {
                speculative_parse()
            } else {
                input.parse().map(Stmt::Expr)
            }
        } else {
            speculative_parse()
        }
    }
}

/// The declaration of the variable(s) in a variable declaration statement.
#[derive(Clone, Debug)]
pub enum VarDeclDecl {
    VarDecl(VariableDeclaration),
    Tuple(VarDeclTuple),
}

impl Parse for VarDeclDecl {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        if input.peek(Paren) {
            input.parse().map(Self::Tuple)
        } else {
            VariableDeclaration::parse_with_name(input).map(Self::VarDecl)
        }
    }
}

impl Spanned for VarDeclDecl {
    fn span(&self) -> Span {
        match self {
            Self::VarDecl(decl) => decl.span(),
            Self::Tuple(decl) => decl.span(),
        }
    }

    fn set_span(&mut self, span: Span) {
        match self {
            Self::VarDecl(decl) => decl.set_span(span),
            Self::Tuple(decl) => decl.set_span(span),
        }
    }
}

/// A declaration of variables in a tuple: `(,,uint256 foo,string memory bar)`.
///
/// Solidity Reference:
/// <https://docs.soliditylang.org/en/latest/grammar.html#a4.SolidityParser.variableDeclarationTuple>
#[derive(Clone)]
pub struct VarDeclTuple {
    pub paren_token: Paren,
    /// The list of variables being declared. The list can't be empty, but it
    /// can contain `None` elements, indicating the field is empty.
    pub vars: Punctuated<Option<VariableDeclaration>, Token![,]>,
}

impl fmt::Debug for VarDeclTuple {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("VarDeclTuple")
            .field("vars", DebugPunctuated::new(&self.vars))
            .finish()
    }
}

impl Parse for VarDeclTuple {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        let content;
        Ok(Self {
            paren_token: parenthesized!(content in input),
            vars: content.parse_terminated(Self::parse_var_opt, Token![,])?,
        })
    }
}

impl Spanned for VarDeclTuple {
    fn span(&self) -> Span {
        self.paren_token.span.join()
    }

    fn set_span(&mut self, span: Span) {
        self.paren_token = Paren(span);
    }
}

impl VarDeclTuple {
    fn parse_var_opt(input: ParseStream<'_>) -> Result<Option<VariableDeclaration>> {
        if input.peek(Token![,]) {
            Ok(None)
        } else {
            input.parse().map(Some)
        }
    }
}