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// 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.

#[cfg(not(feature = "std"))]
use alloc::boxed::Box;

use crate::{
    ast::{BinaryOperator, Expr, LockTable, LockTableType, Statement},
    dialect::Dialect,
    keywords::Keyword,
    parser::{Parser, ParserError},
};

/// A [`Dialect`] for [MySQL](https://www.mysql.com/)
#[derive(Debug)]
pub struct MySqlDialect {}

impl Dialect for MySqlDialect {
    fn is_identifier_start(&self, ch: char) -> bool {
        // See https://dev.mysql.com/doc/refman/8.0/en/identifiers.html.
        // Identifiers which begin with a digit are recognized while tokenizing numbers,
        // so they can be distinguished from exponent numeric literals.
        ch.is_alphabetic()
            || ch == '_'
            || ch == '$'
            || ch == '@'
            || ('\u{0080}'..='\u{ffff}').contains(&ch)
    }

    fn is_identifier_part(&self, ch: char) -> bool {
        self.is_identifier_start(ch) || ch.is_ascii_digit()
    }

    fn is_delimited_identifier_start(&self, ch: char) -> bool {
        ch == '`'
    }

    fn parse_infix(
        &self,
        parser: &mut crate::parser::Parser,
        expr: &crate::ast::Expr,
        _precedence: u8,
    ) -> Option<Result<crate::ast::Expr, ParserError>> {
        // Parse DIV as an operator
        if parser.parse_keyword(Keyword::DIV) {
            Some(Ok(Expr::BinaryOp {
                left: Box::new(expr.clone()),
                op: BinaryOperator::MyIntegerDivide,
                right: Box::new(parser.parse_expr().unwrap()),
            }))
        } else {
            None
        }
    }

    fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
        if parser.parse_keywords(&[Keyword::LOCK, Keyword::TABLES]) {
            Some(parse_lock_tables(parser))
        } else if parser.parse_keywords(&[Keyword::UNLOCK, Keyword::TABLES]) {
            Some(parse_unlock_tables(parser))
        } else {
            None
        }
    }
}

/// `LOCK TABLES`
/// <https://dev.mysql.com/doc/refman/8.0/en/lock-tables.html>
fn parse_lock_tables(parser: &mut Parser) -> Result<Statement, ParserError> {
    let tables = parser.parse_comma_separated(parse_lock_table)?;
    Ok(Statement::LockTables { tables })
}

// tbl_name [[AS] alias] lock_type
fn parse_lock_table(parser: &mut Parser) -> Result<LockTable, ParserError> {
    let table = parser.parse_identifier()?;
    let alias =
        parser.parse_optional_alias(&[Keyword::READ, Keyword::WRITE, Keyword::LOW_PRIORITY])?;
    let lock_type = parse_lock_tables_type(parser)?;

    Ok(LockTable {
        table,
        alias,
        lock_type,
    })
}

// READ [LOCAL] | [LOW_PRIORITY] WRITE
fn parse_lock_tables_type(parser: &mut Parser) -> Result<LockTableType, ParserError> {
    if parser.parse_keyword(Keyword::READ) {
        if parser.parse_keyword(Keyword::LOCAL) {
            Ok(LockTableType::Read { local: true })
        } else {
            Ok(LockTableType::Read { local: false })
        }
    } else if parser.parse_keyword(Keyword::WRITE) {
        Ok(LockTableType::Write {
            low_priority: false,
        })
    } else if parser.parse_keywords(&[Keyword::LOW_PRIORITY, Keyword::WRITE]) {
        Ok(LockTableType::Write { low_priority: true })
    } else {
        parser.expected("an lock type in LOCK TABLES", parser.peek_token())
    }
}

/// UNLOCK TABLES
/// <https://dev.mysql.com/doc/refman/8.0/en/lock-tables.html>
fn parse_unlock_tables(_parser: &mut Parser) -> Result<Statement, ParserError> {
    Ok(Statement::UnlockTables)
}