use crate::*;


pub struct SyntacticParser {
    tokeniser: Tokeniser,
    /// The name of the most recently parsed label.
    label_name: String,
    /// The name of the macro being parsed.
    macro_name: Option<String>,
}

impl SyntacticParser {
    pub fn from_source_code<P: Into<PathBuf>>(source_code: &str, path: Option<P>) -> Self {
        let mut tokeniser = Tokeniser::new(source_code, path);
        tokeniser.add_delimiters(&['@','&','%',';',':','{','}','(','[','#','~']);
        Self {
            tokeniser,
            label_name: String::new(),
            macro_name: None,
        }
    }
}


impl Iterator for SyntacticParser {
    type Item = SyntacticToken;

    /// Sequentially parse tokens from the source code.
    fn next(&mut self) -> Option<SyntacticToken> {
        use SyntacticTokenVariant as SynVar;
        use SyntacticParseError as SynErr;
        let t = &mut self.tokeniser;

        t.drop_whitespace();
        t.mark_start_position();

        let variant = match t.eat_char()? {
            '@' => {
                self.label_name = t.eat_token();
                SynVar::LabelDefinition(self.label_name.clone())
            }
            '&' => {
                let token = t.eat_token();
                SynVar::LabelDefinition(format!("{}/{token}", self.label_name))
            }
            '%' => {
                let macro_name = t.eat_token();
                self.macro_name = Some(macro_name.clone());
                SynVar::MacroDefinition(macro_name)
            }
            ';' => {
                self.macro_name = None;
                SynVar::MacroDefinitionTerminator
            }
            '[' => match t.eat_to_delimiter(']') {
                Some(string) => {
                    let constant = ConstantExpression::from_str(&string, t);
                    SynVar::ConstantExpression(constant)
                }
                None => SynVar::Error(SynErr::UnterminatedConstantExpression),
            }
            '{' => SynVar::BlockOpen,
            '}' => SynVar::BlockClose,
            '(' => match t.eat_to_delimiter(')') {
                Some(string) => SynVar::Comment(string),
                None => SynVar::Error(SynErr::UnterminatedComment),
            }
            '#' => {
                let token = t.eat_token();
                let pbl = PackedBinaryLiteral::from_str(&token, t);
                SynVar::PackedBinaryLiteral(pbl)
            },
            '~' => {
                let token = t.eat_token();
                SynVar::Symbol(format!("{}/{token}", self.label_name))
            }
            ':' => SynVar::Separator,
            c => {
                let token = format!("{c}{}", t.eat_token());
                if let Some(hex_string) = token.strip_prefix("0x") {
                    match usize::from_str_radix(hex_string, 16) {
                        Ok(hex) => SynVar::HexadecimalLiteral(hex),
                        Err(_) => SynVar::Error(SynErr::InvalidHexadecimalLiteral(token)),
                    }
                } else {
                    match usize::from_str_radix(&token, 10) {
                        Ok(value) => SynVar::DecimalLiteral(value),
                        Err(_) => SynVar::Symbol(token),
                    }
                }
            }
        };

        // Parse source path comments.
        if let SynVar::Comment(comment) = &variant {
            // Check if the comment fills the entire line.
            if t.start_position.column == 0 && t.end_of_line() {
                if let Some(path) = comment.strip_prefix(": ") {
                    t.source_path = Some(PathBuf::from(path.trim()));
                    t.embedded_first_line = t.start_position.line + 1;
                }
            }
        }

        let source = t.mark_end_position();
        Some( SyntacticToken { source, variant } )
    }
}