syn-rsx 0.7.0

//! RSX Parser

use proc_macro2::{TokenStream, TokenTree};
use std::iter;
use syn::{
    ext::IdentExt,
    parse::{discouraged::Speculative, Parse, ParseStream, Parser as _, Peek},
    punctuated::Punctuated,
    token::{Brace, Colon},
    Expr, ExprBlock, ExprLit, ExprPath, Ident, Path, PathSegment, Result, Token,
};

use crate::{node::*, punctuation::*};

/// Configures the `Parser` behavior
#[derive(Debug, Clone, Default)]
pub struct ParserConfig {
    flat_tree: bool,
    number_of_top_level_nodes: Option<usize>,
    type_of_top_level_nodes: Option<NodeType>,
}

impl ParserConfig {
    /// Create new `ParserConfig` with default config
    pub fn new() -> ParserConfig {
        ParserConfig::default()
    }

    /// Return flat tree instead of nested tree
    pub fn flat_tree(mut self) -> Self {
        self.flat_tree = true;
        self
    }

    /// Exact number of required top level nodes
    pub fn number_of_top_level_nodes(mut self, number: usize) -> Self {
        self.number_of_top_level_nodes = Some(number);
        self
    }

    /// Enforce the `NodeType` of top level nodes
    pub fn type_of_top_level_nodes(mut self, node_type: NodeType) -> Self {
        self.type_of_top_level_nodes = Some(node_type);
        self
    }
}

/// RSX Parser
pub struct Parser {
    config: ParserConfig,
}

impl Parser {
    /// Create a new parser with the given config
    pub fn new(config: ParserConfig) -> Parser {
        Parser { config }
    }

    /// Parse a given `syn::ParseStream`
    pub fn parse(&self, input: ParseStream) -> Result<Vec<Node>> {
        let mut nodes = vec![];
        while !input.cursor().eof() {
            if let Some(number_of_top_level_nodes) = &self.config.number_of_top_level_nodes {
                if &nodes.len() != number_of_top_level_nodes {
                    return Err(input.error(format!(
                        "Exact number of required top level nodes: {}",
                        number_of_top_level_nodes
                    )));
                }
            }

            let parsed_nodes = &mut self.node(input)?;

            if let Some(type_of_top_level_nodes) = &self.config.type_of_top_level_nodes {
                if &parsed_nodes[0].node_type != type_of_top_level_nodes {
                    return Err(input.error(format!(
                        "Top level nodes need to be of type {}",
                        type_of_top_level_nodes
                    )));
                }
            }

            nodes.append(parsed_nodes);
        }

        Ok(nodes)
    }

    fn node(&self, input: ParseStream) -> Result<Vec<Node>> {
        let node = if input.peek(Token![<]) {
            self.element(input)
        } else if input.peek(Brace) {
            self.block(input)
        } else {
            self.text(input)
        }?;

        let mut nodes = vec![node];
        if self.config.flat_tree {
            let mut children = vec![];
            children.append(&mut nodes[0].children);
            nodes.append(&mut children);
        }

        Ok(nodes)
    }

    fn text(&self, input: ParseStream) -> Result<Node> {
        let text = input.parse::<ExprLit>()?.into();

        Ok(Node {
            name: None,
            value: Some(text),
            node_type: NodeType::Text,
            attributes: vec![],
            children: vec![],
        })
    }

    fn block(&self, input: ParseStream) -> Result<Node> {
        let block = self.block_expr(input)?;

        Ok(Node {
            name: None,
            value: Some(block),
            node_type: NodeType::Block,
            attributes: vec![],
            children: vec![],
        })
    }

    fn block_expr(&self, input: ParseStream) -> Result<Expr> {
        let fork = input.fork();
        let parser = move |input: ParseStream| input.parse();
        let group: TokenTree = fork.parse()?;
        let block: ExprBlock = parser.parse2(iter::once(group).collect())?;
        input.advance_to(&fork);

        Ok(block.into())
    }

    fn element(&self, input: ParseStream) -> Result<Node> {
        let fork = &input.fork();
        if let Ok(_) = self.tag_close(&input.fork()) {
            return Err(fork.error("close tag has no corresponding open tag"));
        }
        let (name, attributes, selfclosing) = self.tag_open(fork)?;

        let mut children = vec![];
        if !selfclosing {
            loop {
                if !self.has_children(&name, fork)? {
                    break;
                }

                children.append(&mut self.node(fork)?);
            }

            self.tag_close(fork)?;
        }
        input.advance_to(fork);

        Ok(Node {
            name: Some(name),
            value: None,
            node_type: NodeType::Element,
            attributes,
            children,
        })
    }

    fn has_children(&self, tag_open_name: &NodeName, input: ParseStream) -> Result<bool> {
        // an empty input at this point means the tag wasn't closed
        if input.is_empty() {
            return Err(input.error("open tag has no corresponding close tag"));
        }

        if let Ok(tag_close_name) = self.tag_close(&input.fork()) {
            if tag_open_name == &tag_close_name {
                // if the next token is a matching close tag then there are no child nodes
                return Ok(false);
            } else {
                // if the next token is a closing tag with a different name it's an invalid tree
                return Err(input.error("close tag has no corresponding open tag"));
            }
        }

        Ok(true)
    }

    fn tag_open(&self, input: ParseStream) -> Result<(NodeName, Vec<Node>, bool)> {
        input.parse::<Token![<]>()?;
        let name = self.node_name(input)?;

        let mut attributes = TokenStream::new();
        let selfclosing = loop {
            if let Ok(selfclosing) = self.tag_open_end(input) {
                break selfclosing;
            }

            if input.is_empty() {
                return Err(input.error("expected valid attribute or closing caret >"));
            }

            let next: TokenTree = input.parse()?;
            attributes.extend(Some(next));
        };

        let parser = move |input: ParseStream| self.attributes(input);
        let attributes = parser.parse2(attributes)?;

        Ok((name, attributes, selfclosing))
    }

    fn tag_open_end(&self, input: ParseStream) -> Result<bool> {
        let selfclosing = input.parse::<Option<Token![/]>>()?.is_some();
        input.parse::<Token![>]>()?;

        Ok(selfclosing)
    }

    fn tag_close(&self, input: ParseStream) -> Result<NodeName> {
        input.parse::<Token![<]>()?;
        input.parse::<Token![/]>()?;
        let name = self.node_name(input)?;
        input.parse::<Token![>]>()?;

        Ok(name)
    }

    fn attributes(&self, input: ParseStream) -> Result<Vec<Node>> {
        let mut nodes = vec![];

        loop {
            if input.is_empty() {
                break;
            }

            nodes.push(self.attribute(input)?);
        }

        Ok(nodes)
    }

    fn attribute(&self, input: ParseStream) -> Result<Node> {
        let fork = &input.fork();
        if fork.peek(Brace) {
            let value = Some(self.block_expr(fork)?);
            input.advance_to(fork);

            Ok(Node {
                name: None,
                node_type: NodeType::Block,
                value,
                attributes: vec![],
                children: vec![],
            })
        } else {
            let key = self.node_name(fork)?;
            let eq = fork.parse::<Option<Token![=]>>()?;
            let value = if eq.is_some() {
                if fork.is_empty() {
                    return Err(fork.error("missing attribute value"));
                }

                if fork.peek(Brace) {
                    Some(self.block_expr(fork)?)
                } else {
                    Some(fork.parse()?)
                }
            } else {
                None
            };
            input.advance_to(fork);

            Ok(Node {
                name: Some(key),
                node_type: NodeType::Attribute,
                value,
                attributes: vec![],
                children: vec![],
            })
        }
    }

    fn node_name(&self, input: ParseStream) -> Result<NodeName> {
        let node_name = self
            .node_name_punctuated_ident::<Dash, fn(_) -> Dash>(input, Dash)
            .map(|ok| NodeName::Dash(ok))
            .or_else(|_| {
                self.node_name_punctuated_ident::<Colon, fn(_) -> Colon>(input, Colon)
                    .map(|ok| NodeName::Colon(ok))
            })
            .or_else(|_| self.node_name_mod_style(input))
            .or(Err(input.error("invalid tag name or attribute key")))?;

        Ok(node_name)
    }

    fn node_name_punctuated_ident<T: Parse, F: Peek>(
        &self,
        input: ParseStream,
        punct: F,
    ) -> Result<Punctuated<Ident, T>> {
        let fork = &input.fork();
        let mut segments = Punctuated::<Ident, T>::new();

        while !fork.is_empty() && fork.peek(Ident::peek_any) {
            let ident = Ident::parse_any(fork)?;
            segments.push_value(ident.clone());

            if fork.peek(punct) {
                segments.push_punct(fork.parse()?);
            } else {
                break;
            }
        }

        if segments.len() > 1 {
            input.advance_to(fork);
            Ok(segments)
        } else {
            Err(fork.error("expected punctuated node name"))
        }
    }

    // Modified version of `Path::parse_mod_style` that uses `Ident::peek_any`
    // in order to allow parsing reserved keywords
    //
    // https://docs.rs/syn/1.0.30/src/syn/path.rs.html#388-418
    // TODO: consider PR upstream
    fn node_name_mod_style(&self, input: ParseStream) -> Result<NodeName> {
        let given_input = input;
        let input = &input.fork();

        let path = Path {
            leading_colon: input.parse()?,
            segments: {
                let mut segments = Punctuated::new();
                loop {
                    if !input.peek(Ident::peek_any)
                        && !input.peek(Token![super])
                        && !input.peek(Token![self])
                        && !input.peek(Token![Self])
                        && !input.peek(Token![crate])
                    {
                        break;
                    }
                    let ident = Ident::parse_any(input)?;
                    segments.push_value(PathSegment::from(ident));
                    if !input.peek(Token![::]) {
                        break;
                    }
                    let punct = input.parse()?;
                    segments.push_punct(punct);
                }
                if segments.is_empty() {
                    return Err(input.error("expected path"));
                } else if segments.trailing_punct() {
                    return Err(input.error("expected path segment"));
                }
                segments
            },
        };
        given_input.advance_to(input);

        Ok(NodeName::Path(ExprPath {
            attrs: vec![],
            qself: None,
            path,
        }))
    }
}