sql/src/parser.ts

import * as AST from "./ast";
import Error, { isError } from "./error";
import Token, { TokenKind } from "./token";

export default class Parser {
  public tokens: Token[];
  public position: number;

  constructor(tokens: Token[]) {
    this.tokens = tokens;
    this.position = 0;
  }

  public parse(): AST.Statement[] | Error {
    const tree: AST.Statement[] = [];

    while (!this.atEnd()) {
      const stmt = this.statement();
      if (isError(stmt)) {
        return stmt;
      } else {
        tree.push(stmt);
      }
    }

    return tree;
  }

  private statement(): AST.Statement | Error {
    const token = this.currentToken();

    switch (token.kind) {
      case TokenKind.SELECT:
        return this.select();
    }

    return new Error(`Unexpected token: ${token.repr()}`, token.line);
  }

  private select(): AST.Statement | Error {
    this.eat(TokenKind.SELECT);
    const args = this.selectArguments();
    if (isError(args)) {
      return args;
    }

    const from = this.match(TokenKind.FROM) ? this.from() : null;
    if (isError(from)) {
      return from;
    }

    const where = this.match(TokenKind.WHERE) ? this.where() : null;
    if (isError(where)) {
      return where;
    }

    return new AST.SelectStatement({
      arguments: args,
      from,
      where,
    });
  }

  private selectArguments(): AST.SelectArgument[] | Error {
    const args = [];

    while (true) {
      const arg = this.expr();
      if (isError(arg)) {
        return arg;
      }
      args.push(arg);

      if (this.match(TokenKind.COMMA)) {
        this.eat(TokenKind.COMMA);
      } else {
        break;
      }
    }

    return args;
  }

  private from(): AST.FromTarget | Error {
    this.eat(TokenKind.FROM);
    return this.fromTarget();
  }

  private fromTarget(): AST.FromTarget | Error {
    if (this.match(TokenKind.LPAREN)) {
      this.eat(TokenKind.LPAREN);
      const stmt = this.select();
      if (isError(stmt)) {
        return stmt;
      }

      const rparen = this.eat(TokenKind.RPAREN);
      if (isError(rparen)) {
        return rparen;
      }

      if (this.match(TokenKind.AS)) {
        return this.alias(stmt);
      }

      return stmt;
    }

    const primary = this.backtickOrIdentifier();
    if (isError(primary)) {
      return primary;
    }

    return this.alias(primary);
  }

  private alias<T extends AST.Expr | AST.Statement>(obj: T): AST.Alias | T | Error {
    if (!this.match(TokenKind.AS)) {
      return obj;
    }

    this.eat(TokenKind.AS);

    const token = this.currentToken();
    const alias = this.match(TokenKind.BACKTICK)
      ? this.backtick()
      : this.match(TokenKind.IDENTIFIER)
        ? this.identifier()
        : new Error(`Unexpected token: ${token.repr()}`, token.line);

    if (isError(alias)) {
      return alias;
    }

    return new AST.Alias(obj, alias);
  }

  private where(): AST.Expr | Error {
    this.eat(TokenKind.WHERE);
    return this.expr();
  }

  private expr(): AST.Expr | Error {
    return this.or();
  }

  private or(): AST.Expr | Error {
    let left = this.and();
    if (isError(left)) {
      return left;
    }

    while (this.match(TokenKind.OR)) {
      this.eat(TokenKind.OR);
      const right = this.and();
      if (isError(right)) {
        return right;
      }

      left = new AST.Binary({
        left,
        right,
        type: AST.BinaryExpressionTypes.OR,
      });
    }

    return left;
  }

  private and(): AST.Expr | Error {
    let left = this.equality();
    if (isError(left)) {
      return left;
    }

    while (this.match(TokenKind.AND)) {
      this.eat(TokenKind.AND);
      const right = this.equality();
      if (isError(right)) {
        return right;
      }

      left = new AST.Binary({
        left,
        right,
        type: AST.BinaryExpressionTypes.AND,
      });
    }

    return left;
  }

  private equality(): AST.Expr | Error {
    const left = this.addition();
    if (isError(left)) {
      return left;
    }

    if (this.match(TokenKind.EQUALS)) {
      this.eat(TokenKind.EQUALS);
      const right = this.addition();
      if (isError(right)) {
        return right;
      }

      return new AST.Binary({
        left,
        right,
        type: AST.BinaryExpressionTypes.EQUALITY,
      });
    }

    return left;
  }

  private addition(): AST.Expr | Error {
    const left = this.multiplication();
    if (isError(left)) {
      return left;
    }

    if (this.match(TokenKind.PLUS)) {
      this.eat(TokenKind.PLUS);
      const right = this.multiplication();
      if (isError(right)) {
        return right;
      }

      return new AST.Binary({
        left,
        right,
        type: AST.BinaryExpressionTypes.ADDITION,
      });
    }

    if (this.match(TokenKind.MINUS)) {
      this.eat(TokenKind.MINUS);
      const right = this.multiplication();
      if (isError(right)) {
        return right;
      }

      return new AST.Binary({
        left,
        right,
        type: AST.BinaryExpressionTypes.SUBTRACTION,
      });
    }

    return left;
  }

  private multiplication(): AST.Expr | Error {
    const left = this.primary();
    if (isError(left)) {
      return left;
    }

    if (this.match(TokenKind.STAR)) {
      this.eat(TokenKind.STAR);
      const right = this.primary();
      if (isError(right)) {
        return right;
      }

      return new AST.Binary({
        left,
        right,
        type: AST.BinaryExpressionTypes.MULTIPLICATION,
      });
    }

    if (this.match(TokenKind.SLASH)) {
      this.eat(TokenKind.SLASH);
      const right = this.primary();
      if (isError(right)) {
        return right;
      }

      return new AST.Binary({
        left,
        right,
        type: AST.BinaryExpressionTypes.DIVISION,
      });
    }

    return left;
  }

  private primary(): AST.Expr | Error {
    const token = this.currentToken();

    const primary = (() => {
      switch (token.kind) {
        case TokenKind.NUMBER:
          return this.number();
        case TokenKind.IDENTIFIER:
          return this.identifier();
        case TokenKind.BACKTICK:
          return this.backtick();
        case TokenKind.LPAREN:
          return this.group();
        default:
          return new Error(`Unexpected token: ${token.repr()}`, token.line);
      }
    })();

    if (isError(primary)) {
      return primary;
    }

    if (this.match(TokenKind.AS)) {
      this.eat(TokenKind.AS);

      const name = this.match(TokenKind.BACKTICK) ? this.backtick() : this.identifier();

      if (isError(name)) {
        return name;
      }

      return new AST.Alias(primary, name);
    } else if (this.match(TokenKind.DOT)) {
      this.eat(TokenKind.DOT);

      const right = this.match(TokenKind.BACKTICK) ? this.backtick() : this.identifier();
      if (isError(right)) {
        return right;
      }

      return new AST.Binary({
        left: primary,
        right,
        type: AST.BinaryExpressionTypes.DOT,
      });
    }

    return primary;
  }

  private group(): AST.Expr | Error {
    this.eat(TokenKind.LPAREN);
    const expr = this.expr();
    const rparen = this.eat(TokenKind.RPAREN);
    if (isError(rparen)) {
      return rparen;
    }
    return expr;
  }

  private backtickOrIdentifier(): AST.Backtick | AST.Identifier | Error {
    const token = this.currentToken();
    switch (token.kind) {
      case TokenKind.BACKTICK:
        return this.backtick();
      case TokenKind.IDENTIFIER:
        return this.identifier();
      default:
        return new Error(`Unexpected token: ${token.repr()}`, token.line);
    }
  }

  private backtick(): AST.Backtick | Error {
    this.eat(TokenKind.BACKTICK);
    const identifier = this.identifier();
    if (isError(identifier)) {
      return identifier;
    }

    const closeTick = this.eat(TokenKind.BACKTICK);
    if (isError(closeTick)) {
      return closeTick;
    }

    return new AST.Backtick(identifier);
  }

  private identifier(): AST.Identifier | Error {
    const identifier = this.eat(TokenKind.IDENTIFIER);
    if (isError(identifier)) {
      return identifier;
    }
    return new AST.Identifier(identifier.value || "");
  }

  private number(): AST.Number | Error {
    const n = this.eat(TokenKind.NUMBER);
    if (isError(n)) {
      return n;
    }
    return new AST.Number(parseFloat(n.value || ""));
  }

  private eat(kind: TokenKind) {
    const token = this.currentToken();
    if (token.kind === kind) {
      this.advance();
      return token;
    }

    return new Error(`Unexpected token: ${token.repr()}`, token.line);
  }

  private match(kind: TokenKind): boolean {
    return this.currentToken().kind === kind;
  }

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

  private advance() {
    this.position += 1;
  }

  private atEnd(): boolean {
    return this.match(TokenKind.EOF);
  }
}