/**
 * 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 of the License.
 *
 * 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 <cstdlib>
#include <iostream>
#include <memory>
#include <vector>

#include <yaml.h>

#include <relpipe/writer/RelationalWriter.h>
#include <relpipe/writer/typedefs.h>

namespace relpipe {
namespace in {
namespace yaml {

class YAMLCommand {
private:
	std::wstring_convert<codecvt_utf8<wchar_t>> convertor; // YAML strings are in UTF-8

	class YAMLEvent {
	private:
		yaml_event_t event;
	public:

		YAMLEvent(yaml_event_t event) : event(event) {
		}

		virtual ~YAMLEvent() {
			yaml_event_delete(&event);
		}

		const yaml_event_type_t getType() const {
			return event.type;
		}

		const relpipe::writer::string_t getTypeName() const {
			return findTypeName(event.type);
		}

		/** Just for debugging and error handling */
		static const relpipe::writer::string_t findTypeName(const yaml_event_type_t eventType) {
			if (eventType == YAML_NO_EVENT) return L"NO";
			else if (eventType == YAML_STREAM_START_EVENT) return L"STREAM_START";
			else if (eventType == YAML_STREAM_END_EVENT) return L"STREAM_END";
			else if (eventType == YAML_DOCUMENT_START_EVENT) return L"DOCUMENT_START";
			else if (eventType == YAML_DOCUMENT_END_EVENT) return L"DOCUMENT_END";
			else if (eventType == YAML_ALIAS_EVENT) return L"ALIAS";
			else if (eventType == YAML_SCALAR_EVENT) return L"SCALAR";
			else if (eventType == YAML_SEQUENCE_START_EVENT) return L"SEQUENCE_START";
			else if (eventType == YAML_SEQUENCE_END_EVENT) return L"SEQUENCE_END";
			else if (eventType == YAML_MAPPING_START_EVENT) return L"MAPPING_START";
			else if (eventType == YAML_MAPPING_END_EVENT) return L"MAPPING_END";
			else return L"UNKNOWN";
		}

		const yaml_event_t* getEvent() const {
			return &event;
		}

		YAMLEvent(const YAMLEvent&) = delete;
		YAMLEvent& operator=(const YAMLEvent&) = delete;
	};

	class YAMLParser {
	private:
		yaml_parser_t yamlParser;
		std::istream* input = nullptr;

		static int readFromInput(void* instance, unsigned char* buffer, size_t size, size_t* length) {
			std::istream* input = ((YAMLParser*) instance)->input;
			input->read((char*) buffer, size);
			*length = input->gcount();
			return (input->good() || input->eof()) ? 1 : 0;
		}
	public:

		YAMLParser() {
			yaml_parser_initialize(&yamlParser);
		}

		virtual ~YAMLParser() {
			yaml_parser_delete(&yamlParser);
		}

		YAMLParser(const YAMLParser&) = delete;
		YAMLParser& operator=(const YAMLParser&) = delete;

		void setInput(std::istream* input) {
			this->input = input;
			yaml_parser_set_input(&yamlParser, readFromInput, (void*) this);
		}

		YAMLEvent* next() {
			yaml_event_t event;
			int result = yaml_parser_parse(&yamlParser, &event);
			return result == 1 && event.type != yaml_event_type_e::YAML_NO_EVENT ? new YAMLEvent(event) : nullptr; // 1 = OK in yaml.h; YAML_NO_EVENT = end
		}
	};

	using YAMLEvent_p = std::shared_ptr<YAMLEvent>;

	YAMLParser parser;
	std::shared_ptr<relpipe::writer::RelationalWriter> writer;

	relpipe::writer::string_t relationName;
	std::vector<relpipe::writer::string_t> record;
	std::vector<relpipe::writer::AttributeMetadata> attributesMetadata;

	relpipe::writer::string_t y2s(const yaml_char_t* value) {
		return value ? convertor.from_bytes((const char*) value) : L"";
	}

	relpipe::writer::string_t fetchScalarValue(YAMLEvent_p event) {
		if (event->getType() == YAML_SCALAR_EVENT) return y2s(event->getEvent()->data.scalar.value);
		else throw relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: expected SCALAR but got: " + event->getTypeName());
	}

	void consumeEvent(const yaml_event_type_t expectedEventType, relpipe::writer::string_t expectedScalarValue = L"") {
		YAMLEvent_p event = YAMLEvent_p(parser.next());
		if (!event) throw relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: missing event: " + YAMLEvent::findTypeName(expectedEventType));
		if (event->getType() != expectedEventType) throw relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: expected event: " + YAMLEvent::findTypeName(expectedEventType) + L", but got: " + event->getTypeName());
		if (expectedEventType == YAML_SCALAR_EVENT && expectedScalarValue.size() && expectedScalarValue != fetchScalarValue(event)) throw relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: expected scalar value: " + expectedScalarValue + L", but got " + fetchScalarValue(event));
	}

	relpipe::writer::string_t consumeScalarEvent() {
		YAMLEvent_p event = YAMLEvent_p(parser.next());
		if (event && event->getType() == YAML_SCALAR_EVENT) return fetchScalarValue(event);
		else throw relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: expected SCALAR, but got: " + event->getTypeName());
	}

	bool until(const yaml_event_type_t until, YAMLEvent_p& event) {
		event = YAMLEvent_p(parser.next());
		return event && event->getType() != until;
	}

	void processRelation() {
		YAMLEvent_p event = YAMLEvent_p(parser.next());
		if (event->getType() == YAML_MAPPING_START_EVENT) processRelationWithMetadata();
		else if (event->getType() == YAML_SEQUENCE_START_EVENT)processRelationWithoutMetadata();
		else throw relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: expected MAPPING or SEQUENCE, but got: " + event->getTypeName());
	}

	void processRelationWithMetadata() {
		consumeEvent(YAML_SCALAR_EVENT, L"attribute-metadata");
		consumeEvent(YAML_SEQUENCE_START_EVENT);

		for (YAMLEvent_p event; until(YAML_SEQUENCE_END_EVENT, event);) {
			if (event->getType() != YAML_MAPPING_START_EVENT) throw relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: expected MAPPING (attribute-metadata), but got: " + event->getTypeName());
			relpipe::writer::string_t name;
			relpipe::writer::string_t type = L"string";
			for (YAMLEvent_p event; until(YAML_MAPPING_END_EVENT, event);) {
				auto key = fetchScalarValue(event);
				auto value = consumeScalarEvent();
				if (key == L"name") name = value;
				else if (key == L"type") type = value;
				else; // unsupported metadata, later there might be something useful
			}
			attributesMetadata.push_back({name, writer->toTypeId(type)});
		}

		writer->startRelation(relationName, attributesMetadata, true);

		YAMLEvent_p event = YAMLEvent_p(parser.next());
		if (event->getType() == YAML_SCALAR_EVENT && fetchScalarValue(event) == L"record") {
			consumeEvent(YAML_SEQUENCE_START_EVENT);
			processRecords();
			consumeEvent(YAML_MAPPING_END_EVENT);
		} else if (event->getType() == YAML_MAPPING_END_EVENT) {
			// empty relation, no records
		} else {
			relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: expected 'record' or MAPPING_END, but got: " + event->getTypeName());
		}
	}

	void processRelationWithoutMetadata() {
		// First record:
		consumeEvent(YAML_MAPPING_START_EVENT);
		record.clear();
		for (YAMLEvent_p event; until(YAML_MAPPING_END_EVENT, event);) {
			auto name = fetchScalarValue(event);
			auto value = consumeScalarEvent();
			attributesMetadata.push_back({name, relpipe::writer::TypeId::STRING});
			record.push_back(value);
		}
		writer->startRelation(relationName, attributesMetadata, true);
		for (auto value : record) writer->writeAttribute(value);

		// Following records:
		processRecords();
	}

	void processRecords() {
		for (YAMLEvent_p event; until(YAML_SEQUENCE_END_EVENT, event);) {
			if (event->getType() != YAML_MAPPING_START_EVENT) throw relpipe::writer::RelpipeWriterException(L"Invalid YAML structure: expected MAPPING (record), but got: " + event->getTypeName());
			record.clear();
			record.resize(attributesMetadata.size());
			for (YAMLEvent_p event; until(YAML_MAPPING_END_EVENT, event);) {
				auto name = fetchScalarValue(event);
				auto value = consumeScalarEvent();
				for (int i = 0; i < attributesMetadata.size(); i++) {
					if (name == attributesMetadata[i].attributeName) {
						record[i] = value;
						break;
					}
				}
			}
			for (auto value : record) writer->writeAttribute(value);
		}
	}


public:

	YAMLCommand() {
	}

	virtual ~YAMLCommand() {
	}

	void process(std::istream& input, std::shared_ptr<relpipe::writer::RelationalWriter> writer) {
		parser.setInput(&input);
		this->writer = writer;

		consumeEvent(YAML_STREAM_START_EVENT);
		consumeEvent(YAML_DOCUMENT_START_EVENT);
		consumeEvent(YAML_MAPPING_START_EVENT);

		for (YAMLEvent_p event; until(YAML_MAPPING_END_EVENT, event);) {
			relationName = fetchScalarValue(event);
			attributesMetadata.clear();
			processRelation();
		}

		consumeEvent(YAML_DOCUMENT_END_EVENT);
		consumeEvent(YAML_STREAM_END_EVENT);
	}
};

}
}
}