datafusion 0.2.9

// Copyright 2018 Grove Enterprises LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! SQL Tokenizer

use std::collections::HashSet;
use std::iter::Peekable;
use std::str::Chars;

/// SQL Token enumeration
#[derive(Debug, Clone, PartialEq)]
pub enum Token {
    /// SQL identifier e.g. table or column name
    Identifier(String),
    /// SQL keyword  e.g. Keyword("SELECT")
    Keyword(String),
    /// Numeric literal
    Number(String),
    /// String literal
    String(String),
    /// Comma
    Comma,
    /// Whitespace (space, tab, etc)
    Whitespace,
    /// Equality operator `=`
    Eq,
    /// Not Equals operator `!=` or `<>`
    Neq,
    /// Less Than operator `<`
    Lt,
    /// Greater han operator `>`
    Gt,
    /// Less Than Or Equals operator `<=`
    LtEq,
    /// Greater Than Or Equals operator `>=`
    GtEq,
    /// Plus operator `+`
    Plus,
    /// Minus operator `-`
    Minus,
    /// Multiplication operator `*`
    Mult,
    /// Division operator `/`
    Div,
    /// Left parenthesis `(`
    LParen,
    /// Right parenthesis `)`
    RParen,
    /// Period (used for compound identifiers or projections into nested types)
    Period,
}

/// Tokenizer error
#[derive(Debug)]
pub struct TokenizerError(String);

/// SQL keywords
static KEYWORDS: &'static [&'static str] = &[
    "SELECT", "FROM", "WHERE", "LIMIT", "ORDER", "GROUP", "BY", "HAVING", "UNION", "ALL", "INSERT",
    "UPDATE", "DELETE", "IN", "NOT", "NULL", "SET", "CREATE", "EXTERNAL", "TABLE", "ASC", "DESC",
    "AND", "OR", "AS",
    "VARCHAR", "FLOAT", "DOUBLE", "INT", "INTEGER"
];

/// SQL Tokenizer
pub struct Tokenizer {
    keywords: HashSet<String>,
    pub query: String,
}

impl Tokenizer {
    /// Create a new SQL tokenizer for the specified SQL statement
    pub fn new(query: &str) -> Self {
        let mut tokenizer = Tokenizer {
            keywords: HashSet::new(),
            query: query.to_string(),
        };
        KEYWORDS.into_iter().for_each(|k| {
            tokenizer.keywords.insert(k.to_string());
        });
        tokenizer
    }

    /// Tokenize the statement and produce a vector of tokens
    pub fn tokenize(&mut self) -> Result<Vec<Token>, TokenizerError> {
        let mut peekable = self.query.chars().peekable();

        let mut tokens: Vec<Token> = vec![];

        while let Some(token) = self.next_token(&mut peekable)? {
            tokens.push(token);
        }

        Ok(tokens
            .into_iter()
            .filter(|t| match t {
                &Token::Whitespace => false,
                _ => true,
            })
            .collect())
    }

    /// Get the next token or return None
    fn next_token(&self, chars: &mut Peekable<Chars>) -> Result<Option<Token>, TokenizerError> {
        match chars.peek() {
            Some(&ch) => match ch {
                // whitespace
                ' ' | '\t' | '\n' => {
                    chars.next(); // consume
                    Ok(Some(Token::Whitespace))
                }
                // identifier or keyword
                'a'...'z' | 'A'...'Z' | '_' | '@' => {
                    let mut s = String::new();
                    while let Some(&ch) = chars.peek() {
                        match ch {
                            'a'...'z' | 'A'...'Z' | '_' | '0'...'9' => {
                                chars.next(); // consume
                                s.push(ch);
                            }
                            _ => break,
                        }
                    }
                    if self.keywords.contains(&s) {
                        Ok(Some(Token::Keyword(s)))
                    } else {
                        Ok(Some(Token::Identifier(s)))
                    }
                }
                // string
                '\'' => {
                    //TODO: handle escaped quotes in string
                    //TODO: handle EOF before terminating quote
                    let mut s = String::new();
                    chars.next(); // consume
                    while let Some(&ch) = chars.peek() {
                        match ch {
                            '\'' => {
                                chars.next(); // consume
                                break;
                            }
                            _ => {
                                chars.next(); // consume
                                s.push(ch);
                            }
                        }
                    }
                    Ok(Some(Token::String(s)))
                }
                // numbers
                '0'...'9' => {
                    let mut s = String::new();
                    while let Some(&ch) = chars.peek() {
                        match ch {
                            '0'...'9' | '.' => {
                                chars.next(); // consume
                                s.push(ch);
                            }
                            _ => break,
                        }
                    }
                    Ok(Some(Token::Number(s)))
                }
                // punctuation
                ',' => {
                    chars.next();
                    Ok(Some(Token::Comma))
                }
                '(' => {
                    chars.next();
                    Ok(Some(Token::LParen))
                }
                ')' => {
                    chars.next();
                    Ok(Some(Token::RParen))
                }
                // operators
                '+' => {
                    chars.next();
                    Ok(Some(Token::Plus))
                }
                '-' => {
                    chars.next();
                    Ok(Some(Token::Minus))
                }
                '*' => {
                    chars.next();
                    Ok(Some(Token::Mult))
                }
                '/' => {
                    chars.next();
                    Ok(Some(Token::Div))
                }
                '=' => {
                    chars.next();
                    Ok(Some(Token::Eq))
                }
                '.' => {
                    chars.next();
                    Ok(Some(Token::Period))
                }
                '!' => {
                    chars.next(); // consume
                    match chars.peek() {
                        Some(&ch) => match ch {
                            '=' => {
                                chars.next();
                                Ok(Some(Token::Neq))
                            }
                            _ => Err(TokenizerError(format!("TBD"))),
                        },
                        None => Err(TokenizerError(format!("TBD"))),
                    }
                }
                '<' => {
                    chars.next(); // consume
                    match chars.peek() {
                        Some(&ch) => match ch {
                            '=' => {
                                chars.next();
                                Ok(Some(Token::LtEq))
                            }
                            '>' => {
                                chars.next();
                                Ok(Some(Token::Neq))
                            }
                            _ => Ok(Some(Token::Lt)),
                        },
                        None => Ok(Some(Token::Lt)),
                    }
                }
                '>' => {
                    chars.next(); // consume
                    match chars.peek() {
                        Some(&ch) => match ch {
                            '=' => {
                                chars.next();
                                Ok(Some(Token::GtEq))
                            }
                            _ => Ok(Some(Token::Gt)),
                        },
                        None => Ok(Some(Token::Gt)),
                    }
                }
                _ => Err(TokenizerError(String::from(format!(
                    "unhandled char '{}' in tokenizer",
                    ch
                )))),
            },
            None => Ok(None),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn tokenize_select_1() {
        let sql = String::from("SELECT 1");
        let mut tokenizer = Tokenizer::new(&sql);
        let tokens = tokenizer.tokenize().unwrap();

        let expected = vec![
            Token::Keyword(String::from("SELECT")),
            Token::Number(String::from("1")),
        ];

        compare(expected, tokens);
    }

    #[test]
    fn tokenize_scalar_function() {
        let sql = String::from("SELECT sqrt(1)");
        let mut tokenizer = Tokenizer::new(&sql);
        let tokens = tokenizer.tokenize().unwrap();

        let expected = vec![
            Token::Keyword(String::from("SELECT")),
            Token::Identifier(String::from("sqrt")),
            Token::LParen,
            Token::Number(String::from("1")),
            Token::RParen,
        ];

        compare(expected, tokens);
    }

    #[test]
    fn tokenize_simple_select() {
        let sql = String::from("SELECT * FROM customer WHERE id = 1 LIMIT 5");
        let mut tokenizer = Tokenizer::new(&sql);
        let tokens = tokenizer.tokenize().unwrap();

        let expected = vec![
            Token::Keyword(String::from("SELECT")),
            Token::Mult,
            Token::Keyword(String::from("FROM")),
            Token::Identifier(String::from("customer")),
            Token::Keyword(String::from("WHERE")),
            Token::Identifier(String::from("id")),
            Token::Eq,
            Token::Number(String::from("1")),
            Token::Keyword(String::from("LIMIT")),
            Token::Number(String::from("5")),
        ];

        compare(expected, tokens);
    }

    #[test]
    fn tokenize_string_predicate() {
        let sql = String::from("SELECT * FROM customer WHERE salary != 'Not Provided'");
        let mut tokenizer = Tokenizer::new(&sql);
        let tokens = tokenizer.tokenize().unwrap();

        let expected = vec![
            Token::Keyword(String::from("SELECT")),
            Token::Mult,
            Token::Keyword(String::from("FROM")),
            Token::Identifier(String::from("customer")),
            Token::Keyword(String::from("WHERE")),
            Token::Identifier(String::from("salary")),
            Token::Neq,
            Token::String(String::from("Not Provided")),
        ];

        compare(expected, tokens);
    }

    fn compare(expected: Vec<Token>, actual: Vec<Token>) {
        //println!("------------------------------");
        //println!("tokens   = {:?}", actual);
        //println!("expected = {:?}", expected);
        //println!("------------------------------");
        assert_eq!(expected, actual);
    }

}