moss/src/parser.ts

import { AST } from './ast';
import { Error } from './error';
import Token, { TokenTypes } from './token';

export class ParserError implements Error {
  public message: string;
  public line: number;
  public module?: string;

  public constructor(message: string, line: number, module?: string) {
    this.message = message;
    this.line = line;
    this.module = module;
  }
}

export type ParserResult = { tree: AST.Node[]; module?: string } | ParserError;

export default class Parser {
  private tokens: Token[];
  private module?: string;
  private tree: AST.Node[];
  private position: number;

  public constructor(lexerResult: { tokens: Token[]; module?: string }) {
    this.tokens = lexerResult.tokens;
    this.module = lexerResult.module;
    this.tree = [];
    this.position = 0;
  }

  public parse(): ParserResult {
    while (this.currentToken().type != TokenTypes.EOF) {
      const expr = this.expr();
      if (expr instanceof ParserError) return expr;
      this.tree.push(expr);
    }

    this.eat(TokenTypes.EOF);

    return {
      tree: this.tree,
      module: this.module,
    };
  }

  private expr(): AST.Node | ParserError {
    const currentToken = this.currentToken();
    switch (currentToken.type) {
      case TokenTypes.LITERAL:
      case TokenTypes.IDENTIFIER:
        return this.value();
      case TokenTypes.LPAREN:
        if (
          this.nextToken() &&
          this.nextToken().type === TokenTypes.FUNCTION_NAME
        ) {
          switch (this.nextToken().value) {
            case 'let':
              return this.let();
            case 'media':
              return this.mediaQuery();
            case 'keyframes':
              return this.keyframes();
            case 'mixin':
              return this.mixin();
            default:
              return this.application();
          }
          return this.error(
            `Undefined function '${this.nextToken().value}`,
            this.nextToken()
          );
        }
        return this.ruleSet();
      default:
        return this.error(`Unexpected ${currentToken.type}`, currentToken);
    }

    return this.error(`Unexpected ${currentToken.type}`, currentToken);
  }

  private let(): AST.Let | ParserError {
    const lParen = this.eat(TokenTypes.LPAREN);
    if (lParen instanceof ParserError) return lParen;

    const letToken = this.eat(TokenTypes.FUNCTION_NAME);
    if (letToken instanceof ParserError) return letToken;

    const bindings: AST.Binding[] = [];

    while (this.currentToken().type === TokenTypes.IDENTIFIER) {
      const identifier = this.identifier();
      if (identifier instanceof ParserError) return identifier;
      const value = this.value();
      if (value instanceof ParserError) return value;
      bindings.push(new AST.Binding(identifier, value));
    }

    const children: AST.Node[] = [];

    while (this.currentToken().type === TokenTypes.LPAREN) {
      const body = this.expr();
      if (body instanceof ParserError) return body;
      children.push(body);
    }

    const rParen = this.eat(TokenTypes.RPAREN);
    if (rParen instanceof ParserError) return rParen;

    return new AST.Let(bindings, children);
  }

  private mediaQuery(): AST.MediaQuery | ParserError {
    const lParen = this.eat(TokenTypes.LPAREN);
    if (lParen instanceof ParserError) return lParen;

    const mediaToken = this.eat(TokenTypes.FUNCTION_NAME);
    if (mediaToken instanceof ParserError) return mediaToken;

    const propertyToken = this.eat(TokenTypes.PROPERTY);
    if (propertyToken instanceof ParserError) return propertyToken;
    const property = new AST.Property(propertyToken);
    const value = this.value();
    if (value instanceof ParserError) return value;

    const predicate = new AST.MediaQueryPredicate(property, value);

    const children: AST.Node[] = [];

    while (this.currentToken().type === TokenTypes.LPAREN) {
      const body = this.expr();
      if (body instanceof ParserError) return body;
      children.push(body);
    }

    const rParen = this.eat(TokenTypes.RPAREN);
    if (rParen instanceof ParserError) return rParen;

    return new AST.MediaQuery(predicate, children);
  }

  private keyframes(): AST.Keyframes | ParserError {
    const lParen = this.eat(TokenTypes.LPAREN);
    if (lParen instanceof ParserError) return lParen;

    const keyframesToken = this.eat(TokenTypes.FUNCTION_NAME);
    if (keyframesToken instanceof ParserError) return keyframesToken;

    const name = this.literal();
    if (name instanceof ParserError) return name;

    const children: AST.Node[] = [];

    while (this.currentToken().type === TokenTypes.LPAREN) {
      const body = this.expr();
      if (body instanceof ParserError) return body;
      children.push(body);
    }

    const rParen = this.eat(TokenTypes.RPAREN);
    if (rParen instanceof ParserError) return rParen;

    return new AST.Keyframes(name, children);
  }

  private mixin(): AST.Mixin | ParserError {
    const lParen = this.eat(TokenTypes.LPAREN);
    if (lParen instanceof ParserError) return lParen;

    const mixinToken = this.eat(TokenTypes.FUNCTION_NAME);
    if (mixinToken instanceof ParserError) return mixinToken;

    const name = this.eat(TokenTypes.LITERAL);
    if (name instanceof ParserError) return name;

    const rules: AST.Rule[] = [];

    const openParen = this.eat(TokenTypes.LPAREN);
    if (openParen instanceof ParserError) return openParen;

    const parameters: AST.Identifier[] = [];

    while (this.currentToken().type === TokenTypes.IDENTIFIER) {
      const param = this.identifier();
      if (param instanceof ParserError) return param;
      parameters.push(param);
    }

    const closeParen = this.eat(TokenTypes.RPAREN);
    if (closeParen instanceof ParserError) return closeParen;

    while (this.currentToken().type === TokenTypes.PROPERTY) {
      const property = this.property();
      if (property instanceof ParserError) return property;
      const value = this.value();
      if (value instanceof ParserError) return value;
      rules.push(new AST.Rule(property, value));
    }

    const rParen = this.eat(TokenTypes.RPAREN);
    if (rParen instanceof ParserError) return rParen;

    return new AST.Mixin(name, parameters, rules);
  }

  private application(): AST.Application | ParserError {
    const lParen = this.eat(TokenTypes.LPAREN);
    if (lParen instanceof ParserError) return lParen;

    const functionToken = this.eat(TokenTypes.FUNCTION_NAME);
    if (functionToken instanceof ParserError) return functionToken;

    const functionName = new AST.Literal(functionToken);

    const args: AST.Node[] = [];
    while (this.currentToken().type !== TokenTypes.RPAREN) {
      const argument = this.expr();
      if (argument instanceof ParserError) return argument;

      args.push(argument);
    }

    const rParen = this.eat(TokenTypes.RPAREN);
    if (rParen instanceof ParserError) return rParen;

    return new AST.Application(functionName, args);
  }

  private ruleSet(parents: AST.Selector[] = []): AST.RuleSet | ParserError {
    const lParen = this.eat(TokenTypes.LPAREN);
    if (lParen instanceof ParserError) return lParen;

    const selectors: AST.Selector[] = [];

    const selector = this.selector(parents);
    if (selector instanceof ParserError) return selector;
    selectors.push(selector);

    while (this.currentToken().type === TokenTypes.COMMA) {
      this.eat(TokenTypes.COMMA);
      const selector = this.selector(parents);
      if (selector instanceof ParserError) return selector;
      selectors.push(selector);
    }

    const children: (AST.Rule | AST.RuleSet)[] = [];

    while (
      [TokenTypes.PROPERTY, TokenTypes.LPAREN].includes(
        this.currentToken().type
      )
    ) {
      if (this.currentToken().type === TokenTypes.PROPERTY) {
        const propertyToken = this.eat(TokenTypes.PROPERTY);
        if (propertyToken instanceof ParserError) return propertyToken;

        const property = new AST.Property(propertyToken);

        const value = this.value();
        if (value instanceof ParserError) return value;

        children.push(new AST.Rule(property, value));
      } else if (this.currentToken().type === TokenTypes.LPAREN) {
        const ruleSet = this.ruleSet(selectors);
        if (ruleSet instanceof ParserError) return ruleSet;
        children.push(ruleSet);
      }
    }

    const rParen = this.eat(TokenTypes.RPAREN);
    if (rParen instanceof ParserError) return rParen;

    return new AST.RuleSet(selectors, children);
  }

  private value():
    | AST.Literal
    | AST.Identifier
    | AST.Application
    | ParserError {
    const type = this.currentToken().type;
    switch (type) {
      case TokenTypes.LITERAL:
        return this.literal();
      case TokenTypes.IDENTIFIER:
        return this.identifier();
      case TokenTypes.LPAREN:
        if (this.nextToken().type === TokenTypes.FUNCTION_NAME)
          return this.application();
      default:
        return this.error(`Unexpected ${type}`, this.currentToken());
    }
  }

  private literal(): AST.Literal | ParserError {
    const literal = this.eat(TokenTypes.LITERAL);
    if (literal instanceof ParserError) return literal;
    return new AST.Literal(literal);
  }

  private property(): AST.Property | ParserError {
    const property = this.eat(TokenTypes.PROPERTY);
    if (property instanceof ParserError) return property;
    return new AST.Property(property);
  }

  private identifier(): AST.Identifier | ParserError {
    const identifier = this.eat(TokenTypes.IDENTIFIER);
    if (identifier instanceof ParserError) return identifier;
    return new AST.Identifier(identifier);
  }

  private selector(parents: AST.Selector[] = []): AST.Selector | ParserError {
    const literal = this.literal();
    if (literal instanceof ParserError) return literal;
    return new AST.Selector(literal.value, parents);
  }

  private eat(type: TokenTypes): Token | ParserError {
    const token = this.currentToken();
    if (type === token.type) {
      this.position += 1;
      return token;
    }
    return this.error(`Unexpected ${token.type}; expected ${type}`, token);
  }

  private currentToken(): Token {
    return this.tokens[this.position];
  }

  private nextToken(): Token {
    return this.tokens[this.position + 1];
  }

  private error(message: string, token: Token) {
    return new ParserError(message, token.line, token.module);
  }
}