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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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.

use regex::Regex;
use sqlparser::keywords::ALL_KEYWORDS;

/// `Dialect` to use for Unparsing
///
/// The default dialect tries to avoid quoting identifiers unless necessary (e.g. `a` instead of `"a"`)
/// but this behavior can be overridden as needed
///
/// **Note**: This trait will eventually be replaced by the Dialect in the SQLparser package
///
/// See <https://github.com/sqlparser-rs/sqlparser-rs/pull/1170>
/// See also the discussion in <https://github.com/apache/datafusion/pull/10625>
pub trait Dialect {
    /// Return the character used to quote identifiers.
    fn identifier_quote_style(&self, _identifier: &str) -> Option<char>;

    /// Does the dialect support specifying `NULLS FIRST/LAST` in `ORDER BY` clauses?
    fn supports_nulls_first_in_sort(&self) -> bool {
        true
    }
}
pub struct DefaultDialect {}

impl Dialect for DefaultDialect {
    fn identifier_quote_style(&self, identifier: &str) -> Option<char> {
        let identifier_regex = Regex::new(r"^[a-zA-Z_][a-zA-Z0-9_]*$").unwrap();
        if ALL_KEYWORDS.contains(&identifier.to_uppercase().as_str())
            || !identifier_regex.is_match(identifier)
        {
            Some('"')
        } else {
            None
        }
    }
}

pub struct PostgreSqlDialect {}

impl Dialect for PostgreSqlDialect {
    fn identifier_quote_style(&self, _: &str) -> Option<char> {
        Some('"')
    }
}

pub struct MySqlDialect {}

impl Dialect for MySqlDialect {
    fn identifier_quote_style(&self, _: &str) -> Option<char> {
        Some('`')
    }

    fn supports_nulls_first_in_sort(&self) -> bool {
        false
    }
}

pub struct SqliteDialect {}

impl Dialect for SqliteDialect {
    fn identifier_quote_style(&self, _: &str) -> Option<char> {
        Some('`')
    }
}

pub struct CustomDialect {
    identifier_quote_style: Option<char>,
}

impl CustomDialect {
    pub fn new(identifier_quote_style: Option<char>) -> Self {
        Self {
            identifier_quote_style,
        }
    }
}

impl Dialect for CustomDialect {
    fn identifier_quote_style(&self, _: &str) -> Option<char> {
        self.identifier_quote_style
    }
}