package seedu.address.logic.parser;

import seedu.address.commons.exceptions.IllegalValueException;
import seedu.address.commons.util.StringUtil;
import seedu.address.logic.commands.*;
import seedu.address.logic.parser.ArgumentTokenizer.*;

import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import static seedu.address.commons.core.Messages.MESSAGE_INVALID_COMMAND_FORMAT;
import static seedu.address.commons.core.Messages.MESSAGE_UNKNOWN_COMMAND;

/**
 * Parses user input.
 */
public class Parser {

    /**
     * Used for initial separation of command word and args.
     */
    private static final Pattern BASIC_COMMAND_FORMAT = Pattern.compile("(?<commandWord>\\S+)(?<arguments>.*)");

    private static final Pattern PERSON_INDEX_ARGS_FORMAT = Pattern.compile("(?<targetIndex>.+)");

    private static final Pattern KEYWORDS_ARGS_FORMAT =
            Pattern.compile("(?<keywords>\\S+(?:\\s+\\S+)*)"); // one or more keywords separated by whitespace
    public static final Prefix phoneNumberPrefix = new Prefix("p/");
    public static final Prefix emailPrefix = new Prefix("e/");
    public static final Prefix addressPrefix = new Prefix("a/");
    public static final Prefix tagsPrefix = new Prefix("t/");

    public Parser() {}

    /**
     * Parses user input into command for execution.
     *
     * @param userInput full user input string
     * @return the command based on the user input
     */
    public Command parseCommand(String userInput) {
        final Matcher matcher = BASIC_COMMAND_FORMAT.matcher(userInput.trim());
        if (!matcher.matches()) {
            return new IncorrectCommand(String.format(MESSAGE_INVALID_COMMAND_FORMAT, HelpCommand.MESSAGE_USAGE));
        }

        final String commandWord = matcher.group("commandWord");
        final String arguments = matcher.group("arguments");
        switch (commandWord) {

        case AddCommand.COMMAND_WORD:
            return prepareAdd(arguments);

        case SelectCommand.COMMAND_WORD:
            return prepareSelect(arguments);

        case DeleteCommand.COMMAND_WORD:
            return prepareDelete(arguments);

        case ClearCommand.COMMAND_WORD:
            return new ClearCommand();

        case FindCommand.COMMAND_WORD:
            return prepareFind(arguments);

        case ListCommand.COMMAND_WORD:
            return new ListCommand();

        case ExitCommand.COMMAND_WORD:
            return new ExitCommand();

        case HelpCommand.COMMAND_WORD:
            return new HelpCommand();

        default:
            return new IncorrectCommand(MESSAGE_UNKNOWN_COMMAND);
        }
    }

    /**
     * Parses arguments in the context of the add person command.
     *
     * @param args full command args string
     * @return the prepared command
     */
    private Command prepareAdd(String args){
        ArgumentTokenizer argsTokenizer = new ArgumentTokenizer(phoneNumberPrefix, emailPrefix,
                                                                addressPrefix, tagsPrefix);
        argsTokenizer.tokenize(args);
        try {
            return new AddCommand(
                    argsTokenizer.getPreamble().get(),
                    argsTokenizer.getValue(phoneNumberPrefix).get(),
                    argsTokenizer.getValue(emailPrefix).get(),
                    argsTokenizer.getValue(addressPrefix).get(),
                    toSet(argsTokenizer.getAllValues(tagsPrefix))
            );
        } catch (NoSuchElementException nsee) {
            return new IncorrectCommand(String.format(MESSAGE_INVALID_COMMAND_FORMAT, AddCommand.MESSAGE_USAGE));
        } catch (IllegalValueException ive) {
            return new IncorrectCommand(ive.getMessage());
        }
    }

    private Set<String> toSet(Optional<List<String>> tagsOptional) {
        List<String> tags = tagsOptional.orElse(Collections.emptyList());
        return new HashSet<>(tags);
    }

    /**
     * Parses arguments in the context of the delete person command.
     *
     * @param args full command args string
     * @return the prepared command
     */
    private Command prepareDelete(String args) {

        Optional<Integer> index = parseIndex(args);
        if (!index.isPresent()) {
            return new IncorrectCommand(
                    String.format(MESSAGE_INVALID_COMMAND_FORMAT, DeleteCommand.MESSAGE_USAGE));
        }

        return new DeleteCommand(index.get());
    }

    /**
     * Parses arguments in the context of the select person command.
     *
     * @param args full command args string
     * @return the prepared command
     */
    private Command prepareSelect(String args) {
        Optional<Integer> index = parseIndex(args);
        if (!index.isPresent()) {
            return new IncorrectCommand(
                    String.format(MESSAGE_INVALID_COMMAND_FORMAT, SelectCommand.MESSAGE_USAGE));
        }

        return new SelectCommand(index.get());
    }

    /**
     * Returns the specified index in the {@code command} if it is a positive unsigned integer
     * Returns an {@code Optional.empty()} otherwise.
     */
    private Optional<Integer> parseIndex(String command) {
        final Matcher matcher = PERSON_INDEX_ARGS_FORMAT.matcher(command.trim());
        if (!matcher.matches()) {
            return Optional.empty();
        }

        String index = matcher.group("targetIndex");
        if (!StringUtil.isUnsignedInteger(index)) {
            return Optional.empty();
        }
        return Optional.of(Integer.parseInt(index));

    }

    /**
     * Parses arguments in the context of the find person command.
     *
     * @param args full command args string
     * @return the prepared command
     */
    private Command prepareFind(String args) {
        final Matcher matcher = KEYWORDS_ARGS_FORMAT.matcher(args.trim());
        if (!matcher.matches()) {
            return new IncorrectCommand(String.format(MESSAGE_INVALID_COMMAND_FORMAT,
                    FindCommand.MESSAGE_USAGE));
        }

        // keywords delimited by whitespace
        final String[] keywords = matcher.group("keywords").split("\\s+");
        final Set<String> keywordSet = new HashSet<>(Arrays.asList(keywords));
        return new FindCommand(keywordSet);
    }

}

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Fix checkstyle warning for Parser