/**
 * Relational pipes
 * Copyright © 2019 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 <memory>
#include <string>
#include <sstream>
#include <regex>
#include <vector>
#include <locale>
#include <codecvt>
#include <unistd.h>
#include <cassert>
#include <sys/stat.h>

#include <sqlite3.h>

#include <relpipe/reader/typedefs.h>
#include <relpipe/reader/TypeId.h>
#include <relpipe/reader/handlers/RelationalReaderValueHandler.h>
#include <relpipe/reader/handlers/AttributeMetadata.h>

#include <relpipe/writer/Factory.h>

#include "Configuration.h"
#include "SqlException.h"
#include "PreparedStatement.h"

namespace relpipe {
namespace tr {
namespace sql {

using namespace std;
using namespace relpipe;
using namespace relpipe::reader;
using namespace relpipe::reader::handlers;

class Connection {
private:
	sqlite3* db;

	void begin() {
		sqlite3_exec(db, "BEGIN", nullptr, nullptr, nullptr);
	}

public:

	Connection(const char* filename) {
		int result = sqlite3_open(filename, &db);
		if (result != SQLITE_OK) {
			sqlite3_close(db);
			throw SqlException(L"Unable to open SQLite database.");
		}
		begin();
	}

	virtual ~Connection() {
		sqlite3_close(db);
	}

	PreparedStatement* prepareStatement(const char* sql) {
		const char* remaining;
		sqlite3_stmt *stmt;
		int result = sqlite3_prepare(db, sql, -1, &stmt, &remaining);
		if (result == SQLITE_OK) return new PreparedStatement(stmt);
		else throw SqlException(L"Unable to prepare SQLite statement.");
	}

	bool getAutoCommit() {
		return sqlite3_get_autocommit(db);
	}

	void setAutoCommit(bool autoCommit) {
		bool autoCommitOld = getAutoCommit();
		if (autoCommit && !autoCommitOld) commit();
		else if (!autoCommit && autoCommitOld) begin();
	}

	void commit() {
		sqlite3_exec(db, "COMMIT", nullptr, nullptr, nullptr);
	}

	void rollback() {
		sqlite3_exec(db, "ROLLBACK", nullptr, nullptr, nullptr);
	}

};

class SqlHandler : public RelationalReaderValueHandler {
private:
	Configuration configuration;
	boolean_t fileAlreadyExisted = false;
	writer::RelationalWriter* relationalWriter;
	std::wstring_convert<codecvt_utf8<wchar_t>> convertor; // TODO: support also other encodings
	vector<AttributeMetadata> currentReaderMetadata;
	integer_t currentAttributeIndex = 0;
	std::unique_ptr<Connection> connection;
	std::unique_ptr<PreparedStatement> currentInsert;

	bool readNextSqlStatement(std::wistream* input, std::wstringstream* sql) {
		sql->str(L"");
		sql->clear();

		for (wchar_t ch; *input >> ch;) {
			*sql << ch;
			if (ch == L';' && sqlite3_complete(convertor.to_bytes(sql->str()).c_str())) return true;
		}

		string_t remainingSql = sql->str();
		for (wchar_t ch : remainingSql) if (ch != L' ' && ch != L'\n' && ch != L'\r' && ch != L'\t') throw SqlException(L"Unexpected EOF, missing „;“ after: „" + remainingSql + L"“");

		return false;
	}

	void processSqlInput(std::wistream* input) {
		if (input == nullptr) return;
		*input >> std::ws >> std::noskipws;
		for (std::wstringstream sql; readNextSqlStatement(input, &sql);) {
			std::unique_ptr<PreparedStatement> prepared(connection->prepareStatement(convertor.to_bytes(sql.str()).c_str()));
			while (prepared->next());
		}
	}

	relpipe::writer::TypeId findType(string_t columnName, int columnIndex, const Statement& statement, std::shared_ptr<PreparedStatement> preparedStatement) {
		for (TypeCast typeCast : statement.typeCasts) if (typeCast.name == columnName) return relationalWriter->toTypeId(typeCast.type);
		return preparedStatement->getColumType(columnIndex);
	}

	void processStatement(const Statement& statement) {
		std::shared_ptr<PreparedStatement> prepared(connection->prepareStatement(convertor.to_bytes(statement.sql).c_str()));
		int columnCount = prepared->getColumnCount();
		int parameterCount = statement.parameters.size();

		for (int i = 0; i < parameterCount; i++) {
			prepared->setString(i + 1, convertor.to_bytes(statement.parameters[i].value));
		}

		std::vector<relpipe::writer::AttributeMetadata> metadata;
		for (int i = 0; i < columnCount; i++) {
			string_t columnName = convertor.from_bytes(prepared->getColumName(i).c_str());
			metadata.push_back({columnName, findType(columnName, i, statement, prepared)});
		}
		relationalWriter->startRelation(statement.relation, metadata, true);

		while (prepared->next()) {
			for (int i = 0; i < columnCount; i++) {
				relationalWriter->writeAttribute(convertor.from_bytes(prepared->getString(i)));
			}
		}
	}

	std::vector<string_t> getAllRelations() {
		std::vector<string_t> relations;
		std::unique_ptr<PreparedStatement> prepared(connection->prepareStatement("SELECT name FROM sqlite_master WHERE type IN ('table', 'view')"));
		while (prepared->next()) relations.push_back(convertor.from_bytes(prepared->getString(0)));
		return relations;
	}

	void copyRelations(const CopyRelations& copy) {
		std::wregex pattern(copy.pattern);
		for (string_t relation : getAllRelations()) {
			if (regex_match(relation, pattern)) {
				std::wstringstream select;
				select << L"SELECT * FROM ";
				writeIdentifier(select, relation);

				Statement statement;
				statement.relation = copy.replace ? regex_replace(relation, pattern, copy.replacement) : relation;
				statement.sql = select.str();
				processStatement(statement);
			}
		}
	}

	relpipe::writer::string_t toSQLType(relpipe::reader::TypeId typeId) {
		if (typeId == relpipe::reader::TypeId::BOOLEAN) return L"integer"; // TODO: map selected values back to booleans or allow optional storage as string 
		else if (typeId == relpipe::reader::TypeId::INTEGER) return L"integer";
		else return L"text";
	}

	void writeIdentifier(std::wstringstream& output, relpipe::writer::string_t identifier) {
		output << L'"';
		for (auto & ch : identifier) {
			if (ch == L'"') output << L"\"\"";
			else output << ch;
		}
		output << L'"';
	}

public:

	SqlHandler(writer::RelationalWriter* relationalWriter, Configuration& configuration) : relationalWriter(relationalWriter), configuration(configuration) {
		std::string file;
		if (configuration.file.size()) {
			file = convertor.to_bytes(configuration.file);

			// in C++17 we can use: std::filesystem::exists()
			struct stat fileStat;
			fileAlreadyExisted = (stat(file.c_str(), &fileStat) == 0);
		} else {
			file = ":memory:";
		}

		connection.reset(new Connection(file.c_str()));
		connection->setAutoCommit(false);
	}

	virtual ~SqlHandler() {
	}

	void startRelation(string_t name, vector<AttributeMetadata> attributes) override {
		currentReaderMetadata = attributes;

		// CREATE TABLE:
		std::wstringstream sql;
		// TODO: if already exist just append new columns
		sql << L"CREATE TABLE ";
		writeIdentifier(sql, name);
		sql << L" (\n";
		for (int i = 0; i < attributes.size(); i++) {
			sql << L"\t";
			writeIdentifier(sql, attributes[i].getAttributeName());
			sql << L" " << toSQLType(attributes[i].getTypeId());
			if (i < attributes.size() - 1) sql << L",\n";
		}
		sql << L"\n)";

		std::unique_ptr<PreparedStatement> createTable(connection->prepareStatement(convertor.to_bytes(sql.str()).c_str()));
		createTable->next();

		// prepare INSERT:
		sql = wstringstream();
		sql << L"INSERT INTO ";
		writeIdentifier(sql, name);
		sql << L" VALUES (";
		for (int i = 0; i < attributes.size(); i++) {
			sql << L"?";
			if (i < attributes.size() - 1) sql << L",";
		}
		sql << L")";
		currentInsert.reset(connection->prepareStatement(convertor.to_bytes(sql.str()).c_str()));
	}

	void attribute(const void* value, const std::type_info& typeInfo) override {
		relpipe::reader::TypeId type = currentReaderMetadata[currentAttributeIndex].getTypeId();
		currentAttributeIndex++;

		switch (type) {
			case relpipe::reader::TypeId::BOOLEAN:
			{
				assert(typeInfo == typeid (boolean_t));
				auto* typedValue = static_cast<const boolean_t*> (value);
				currentInsert->setBoolean(currentAttributeIndex, *typedValue);
				break;
			}
			case relpipe::reader::TypeId::INTEGER:
			{
				assert(typeInfo == typeid (integer_t));
				auto* typedValue = static_cast<const integer_t*> (value);
				currentInsert->setInteger(currentAttributeIndex, *typedValue);
				break;
			}
			case relpipe::reader::TypeId::STRING:
			{
				assert(typeInfo == typeid (string_t));
				auto* typedValue = static_cast<const string_t*> (value);
				currentInsert->setString(currentAttributeIndex, convertor.to_bytes(*typedValue).c_str());
				break;
			}
			default:
				throw SqlException(L"Unsupported type in attribute()");
		}

		if (currentAttributeIndex % currentReaderMetadata.size() == 0) {
			currentInsert->next();
			currentInsert->reset();
			currentAttributeIndex = 0;
		}
	}

	void endOfPipe() {
		// process optional SQL input
		processSqlInput(configuration.sqlBeforeRelational);

		// run the transformation – process all statements:
		for (const Statement& statement : configuration.statements) processStatement(statement);

		// process optional SQL input
		processSqlInput(configuration.sqlAfterRelational);

		// pass-through some relations:
		for (const CopyRelations& copy : configuration.copyRelations) copyRelations(copy);

		connection->commit();

		// delete or keep the file:
		if (configuration.file.size()) {
			if (configuration.keepFile == KeepFile::Never || (configuration.keepFile == KeepFile::Automatic && !fileAlreadyExisted)) {
				std::wcerr << L"will unlink file" << std::endl;
				int result = unlink(convertor.to_bytes(configuration.file).c_str());
				if (result) throw SqlException(L"Unable to delete SQLite file.");
			}
		} // else: we had no file, everything was in memory
	}

};

}
}
}