/**

 * Relational pipes

 * Copyright © 2020 František Kučera (Frantovo.cz, GlobalCode.info)

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, version 3.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program. If not, see <http://www.gnu.org/licenses/>.

 */

#pragma once

#include <sstream>

#include <stdexcept>

#include <string>

namespace relpipe {

namespace tr {

namespace sql {

/**

 * An SQL script may consist of several SQL statements separated by „;“ character.

 * But this character may also occur in literal values or quoted identifiers where it does not separate SQL statements.

 * This scanner reads SQL script character by character and separates particular SQL statements.

 * It recognizes comments, literals, quoted values and other parts (see enum State),

 * so it is able to distinguish which „;“ separates SQL statements from other „;“ that should be ignored.

 * 

 * Usage:

 * Append characters using append() and when it returns true,

 * call getAndReset() and use the returned statement.

 * If there are any remaining characters on the input, start again with appending…

 */

class SqlInputScanner {

private:

	enum class State {

		/** SQL code like keywords, functions, operators or identifiers (not quoted ones) */

		SQL,

		/** classic SQL comment: -- terminated by the line end */

		COMMENT_SINGLE,

		/** comment like this one */

		COMMENT_MULTI,

		/** quoted identifier like "column_name" */

		IDENTIFIER,

		/** string literal like 'some value' */

		STRING_VALUE

	};

	State state = State::SQL;

	bool includeSeparators = true;

	std::wstringstream current;

	wchar_t last = L'\0';

public:

	/**

	 * @param ch next character from the input stream

	 * @return whether the accumulated SQL statement is complete – then call getAndReset(), otherwise continue appending

	 */

	bool append(wchar_t ch);

	/**

	 * Returns current buffer and empties it, so append() can be called again (building new SQL statement)

	 * @return accumulated SQL statement

	 */

	std::wstring getAndReset();

	/**

	 * @param includeSeparators whether „;“ separators should be appended to the buffer

	 * and then returned from getAndReset() as part of the SQL statement

	 */

	void setIncludeSeparators(bool includeSeparators) {

		this->includeSeparators = includeSeparators;

	}

};

bool SqlInputScanner::append(wchar_t ch) {

	if (state != State::SQL || (ch != L';') || (includeSeparators && ch == L';')) current << ch;

	if (state == State::SQL) {

		if (ch == L'"') state = State::IDENTIFIER;

		else if (ch == L'\'') state = State::STRING_VALUE;

		else if (ch == L'-' && last == L'-') state = State::COMMENT_SINGLE;

		else if (ch == L'*' && last == L'/') state = State::COMMENT_MULTI;

	} else if (state == State::COMMENT_SINGLE) {

		if (ch == L'\n') state = State::SQL;

	} else if (state == State::COMMENT_MULTI) {

		if (ch == L'/' && last == L'*') state = State::SQL;

	} else if (state == State::IDENTIFIER) {

		if (ch == L'"') state = State::SQL;

	} else if (state == State::STRING_VALUE) {

		if (ch == L'\'') state = State::SQL;

	} else {

		throw std::domain_error("Unsupported SqlInputScanner state (bug in code)");

	}

	last = ch;

	return state == State::SQL && ch == L';';

};

std::wstring SqlInputScanner::getAndReset() {

	std::wstring str = current.str();

	current.str(L"");

	current.clear();

	return str;

}

}

}

}