/**
 * 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 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 <vector>
#include <filesystem>
#include <regex>
#include <memory>
#include <sstream>
#include <unistd.h>

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

#include "RequestedField.h"
#include "SubProcess.h"
#include "AttributeFinder.h"
#include "StreamletMsg.h"

namespace relpipe {
namespace in {
namespace filesystem {

namespace fs = std::filesystem;
using namespace relpipe::writer;

class StreamletAttributeFinder : public AttributeFinder {
private:
	std::wstring_convert<codecvt_utf8<wchar_t>> convertor; // TODO: support also other encodings.
	std::map<int, std::shared_ptr<SubProcess>> subProcesses;
	std::map<int, std::vector<AttributeMetadata>> cachedMetadata;

	std::vector<string_t> splitBySeparator(const string_t& originalString, const wchar_t separator = L':', const wchar_t escape = L'\\') {
		std::vector<string_t> result;
		std::wstringstream current;
		for (int i = 0, size = originalString.size(); i < size; i++) {
			wchar_t ch = originalString[i];
			if (ch == escape) {
				if (i + 1 < size) {
					ch = originalString[++i];
					if (ch == separator || ch == escape) current.put(ch);
					else RelpipeWriterException(L"Invalid escape sequence at position " + std::to_wstring(i) + L" of: " + originalString);
				} else {
					throw RelpipeWriterException(L"Invalid use of escape character at the end of: " + originalString);
				}
			} else if (ch == separator || i + 1 == size) {
				if (current.str().size()) result.push_back(current.str());
				current.str(L"");
				current.clear();
			} else {
				current.put(ch);
			}
		}
		return result;
	}

	string_t getStreamletCommand(const RequestedField& field) {
		const char* streamletPathChars = getenv("RELPIPE_IN_FILESYSTEM_STREAMLET_PATH");
		if (streamletPathChars) {
			for (string_t path : splitBySeparator(convertor.from_bytes(streamletPathChars))) {
				fs::path file = fs::path(path) / fs::path(field.name);
				if (fs::exists(file) && ::access(file.c_str(), X_OK) == 0) return file.wstring();  // n.b. must be set executable using e.g. chmod – files executable through only ACL, are actually not executable
			}
			throw RelpipeWriterException(L"Streamlet „" + field.name + L"“ was not found at $RELPIPE_IN_FILESYSTEM_STREAMLET_PATH");
		} else {
			throw RelpipeWriterException(L"Missing environment variable RELPIPE_IN_FILESYSTEM_STREAMLET_PATH → unable to find streamlet.");
		}
	}

protected:

	void startFile(const fs::path& file, const string& fileRaw, bool exists) override {
		AttributeFinder::startFile(file, fileRaw, exists);
		if (exists) {
			for (auto subProcess : subProcesses) {
				subProcess.second->write({StreamletMsg::INPUT_ATTRIBUTE, L"0", convertor.from_bytes(currentFileRaw), L"false"}); // index, value, isNull
				subProcess.second->write({StreamletMsg::WAITING_FOR_OUTPUT_ATTRIBUTES});
			}
		}
	}

	virtual void writeFieldOfExistingFile(RelationalWriter* writer, const string_t& relationName, const RequestedField & field) override {
		// TODO: paralelize also over records → fork multiple processes and distribute records across them; then collect results (with a lock)
		if (field.group == RequestedField::GROUP_STREAMLET) {
			for (auto metadata : cachedMetadata[field.id]) {
				SubProcess::Message m = subProcesses[field.id]->read();
				if (m.code == StreamletMsg::OUTPUT_ATTRIBUTE) writer->writeAttribute(m.parameters[0]);
				else throw RelpipeWriterException(L"Protocol violation from exec sub-process while reading: „" + metadata.attributeName + L"“. Expected OUTPUT_ATTRIBUTE but got: " + m.toString());
			}

			SubProcess::Message m = subProcesses[field.id]->read();
			if (m.code != StreamletMsg::WAITING_FOR_INPUT_ATTRIBUTES) throw RelpipeWriterException(L"Protocol violation from exec sub-process. Expected WAITING_FOR_INPUT_ATTRIBUTES but got: " + m.toString());
			// TODO: generic protocol violation error messages / method for checking responses
		}
	}

public:

	virtual vector<AttributeMetadata> toMetadata(RelationalWriter* writer, const string_t& relationName, const RequestedField & field) override {
		if (field.group == RequestedField::GROUP_STREAMLET) {

			if (cachedMetadata.count(field.id)) {
				return cachedMetadata[field.id];
			} else {

				std::vector<string_t> commandLine = {getStreamletCommand(field)};
				std::map<string_t, string_t> environment;

				for (auto mn : StreamletMsg::getMessageNames()) {
					environment[L"EXEC_MSG_" + mn.second] = std::to_wstring(mn.first);
					environment[L"EXEC_MSG_" + std::to_wstring(mn.first)] = mn.second;
				}

				shared_ptr<SubProcess> subProcess(SubProcess::create(commandLine, environment));
				subProcesses[field.id] = subProcess;

				string_t version = L"1";
				subProcess->write({StreamletMsg::VERSION_SUPPORTED, version});
				subProcess->write({StreamletMsg::WAITING_FOR_VERSION});
				SubProcess::Message versionMessage = subProcess->read();
				if (versionMessage.code == StreamletMsg::VERSION_ACCEPTED && versionMessage.parameters[0] == version) {
					subProcess->write({StreamletMsg::RELATION_START, relationName});
					subProcess->write({StreamletMsg::INPUT_ATTRIBUTE_METADATA, L"path", L"string"});
					for (string_t alias : field.getAliases()) subProcess->write({StreamletMsg::OUTPUT_ATTRIBUTE_ALIAS, alias});
					for (int i = 0; i < field.options.size();) subProcess->write({StreamletMsg::OPTION, field.options[i++], field.options[i++]});
					subProcess->write({StreamletMsg::WAITING_FOR_OUTPUT_ATTRIBUTES_METADATA});

					vector<AttributeMetadata> metadata;
					while (true) {
						SubProcess::Message m = subProcess->read();
						if (m.code == StreamletMsg::OUTPUT_ATTRIBUTE_METADATA) metadata.push_back({m.parameters[0], writer->toTypeId(m.parameters[1])});
						else if (m.code == StreamletMsg::WAITING_FOR_INPUT_ATTRIBUTES) break;
					}

					cachedMetadata[field.id] = metadata;
					return metadata;
				} else {
					throw RelpipeWriterException(L"Incompatible exec sub-process version or message: " + versionMessage.toString());
				}
			}
		} else {
			return {};
		}
	}

	virtual ~StreamletAttributeFinder() override {
		for (auto s : subProcesses) {
			try {
				s.second->write({StreamletMsg::RELATION_END});
				s.second->wait();
			} catch (...) {
				std::wcerr << L"Exception caught during closing sub-process #" + std::to_wstring(s.first) + L" and waiting for its end." << std::endl;
			}
		}
	}
};

}
}
}