/*
 * Copyright (c) 2006-2017 DMDirc Developers
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
 * documentation files (the "Software"), to deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
 * OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

package com.dmdirc.config.provider;

import com.dmdirc.util.validators.DisabledOptionValidator;
import com.dmdirc.util.validators.NumericalValidator;
import com.dmdirc.util.validators.OptionalValidator;
import com.dmdirc.util.validators.PermissiveValidator;
import com.dmdirc.util.validators.Validator;
import com.dmdirc.util.validators.ValidatorChain;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

/**
 * A source of configuration settings that can only be read from.
 *
 * <p>
 * This implementation supports the idea of optional/disabled settings. This is where values may be
 * prefixed with the strings <code>true:</code> or <code>false:</code>, where the former has no
 * effect on the value of the setting, and the latter indicates that the user wishes to disable the
 * setting.
 *
 * <p>
 * Disabled settings allow for optional settings to have default values; a value can be added with
 * the <code>false:</code> prefix which effectively disables the default value and makes the setting
 * act as though it does not have a value.
 */
public interface ReadOnlyConfigProvider {

    /** A permissive validator to use when callers don't specify one. */
    Validator<String> PERMISSIVE_VALIDATOR = new PermissiveValidator<>();

    /** A validator for integer settings. */
    Validator<String> INT_VALIDATOR = new OptionalValidator(new NumericalValidator(-1, -1));

    /**
     * Retrieves the specified option from this config source.
     *
     * @param domain The domain of the option
     * @param option The name of the option
     *
     * @return The value of the option, or null if it doesn't exist
     */
    default String getOption(final String domain, final String option) {
        return getOption(domain, option, PERMISSIVE_VALIDATOR);
    }

    /**
     * Retrieves the first value for the specified option that matches the specified validator.
     *
     * @param domain    The domain of the option
     * @param option    The name of the option
     * @param validator The validator to use to check legal values
     *
     * @return The value of the option, or null if no matching values exist
     */
    String getOption(String domain, String option, Validator<String> validator);

    /**
     * Determines if this source has a value for the specified option which matches the specified
     * validator.
     *
     * @param domain    The domain of the option
     * @param option    The name of the option
     * @param validator The validator to use to check legal values
     *
     * @return True iff a matching option exists, false otherwise.
     */
    boolean hasOption(String domain, String option, Validator<String> validator);

    /**
     * Retrieves a boolean representation of the specified option.
     *
     * @param domain The domain of the option
     * @param option The name of the option
     *
     * @return The boolean representation of the option
     */
    default boolean getOptionBool(final String domain, final String option) {
        return Boolean.parseBoolean(getOption(domain, option));
    }

    /**
     * Retrieves the specified option as a character.
     *
     * @param domain The domain of the option
     * @param option The name of the option
     *
     * @return The value of the option
     */
    default char getOptionChar(final String domain, final String option) {
        return getOption(domain, option).charAt(0);
    }

    /**
     * Retrieves an integral representation of the specified option.
     *
     * @param domain    The domain of the option
     * @param option    The name of the option
     * @param fallbacks An ordered array of further domains and options (in pairs) to try if the
     *                  specified domain/option isn't found
     *
     * @return The integer representation of the option
     */
    default Integer getOptionInt(final String domain, final String option,
            final String... fallbacks) {
        return getOptionInt(domain, option, true, fallbacks);
    }

    /**
     * Retrieves an integral representation of the specified option.
     *
     * @param domain    The domain of the option
     * @param option    The name of the option
     * @param required  Whether this option is required or optional
     * @param fallbacks An ordered array of further domains and options (in pairs) to try if the
     *                  specified domain/option isn't found
     *
     * @return The integer representation of the option
     *
     * @since 0.6.5
     */
    default Integer getOptionInt(final String domain, final String option, final boolean required,
            final String... fallbacks) {
        final String value = getOptionString(domain, option, required, INT_VALIDATOR, fallbacks);

        return value == null ? null : Integer.parseInt(value.trim());
    }

    /**
     * Retrieves a list representation of the specified option.
     *
     * @param domain    The domain of the option
     * @param option    The name of the option
     * @param trimEmpty Whether or not to trim empty lines
     *
     * @return The list representation of the option
     */
    default List<String> getOptionList(final String domain, final String option,
            final boolean trimEmpty) {
        final List<String> res = new ArrayList<>();

        if (hasOption(domain, option, PERMISSIVE_VALIDATOR)) {
            for (String line : getOption(domain, option).split("\n")) {
                if (!line.isEmpty() || !trimEmpty) {
                    res.add(line);
                }
            }
        }

        return res;
    }

    /**
     * Retrieves a list representation of the specified option, trimming empty lines by default.
     *
     * @param domain The domain of the option
     * @param option The name of the option
     *
     * @return The list representation of the option
     */
    default List<String> getOptionList(final String domain, final String option) {
        return getOptionList(domain, option, true);
    }

    /**
     * Retrieves the specified option as a String, if it exists and satisfies the specified
     * validator.
     * <p>
     * If no fallback settings are supplied (or if fallback settings are supplied and execution
     * reaches the last fallback setting) AND if the 'required' parameter is true, then all disabled
     * values (i.e., those starting with <code>false:</code>) will be ignored. To check if a valid
     * non-disabled value exists, call {@link #hasOptionString(String, String, Validator)}.
     *
     * @param domain    The domain of the option
     * @param option    The name of the option
     * @param required  Whether the specified option is required or not
     * @param validator The validator to use to check the value
     * @param fallbacks An ordered array of further domains and options (in pairs) to try if the
     *                  specified domain/option isn't found
     *
     * @return The string representation of the option or null if optional setting is not specified
     */
    default String getOptionString(final String domain, final String option, final boolean required,
            final Validator<String> validator, final String... fallbacks) {
        final String value;

        final Validator<String> newValidator = required && fallbacks.length == 0
                ? ValidatorChain.<String>builder().addValidator(
                new DisabledOptionValidator()).addValidator(validator).build()
                : validator;

        if (!hasOption(domain, option, newValidator)
                || (value = getOption(domain, option, newValidator)).startsWith("false:")) {
            return fallbacks.length >= 2 ? getOptionString(fallbacks[0],
                    fallbacks[1], required, validator,
                    Arrays.copyOfRange(fallbacks, 2, fallbacks.length)) : null;
        } else if (value.startsWith("true:")) {
            return value.substring(5);
        } else {
            return value;
        }
    }

    /**
     * Retrieves the specified option as a String, if it exists.
     *
     * @param domain    The domain of the option
     * @param option    The name of the option
     * @param fallbacks An ordered array of further domains and options (in pairs) to try if the
     *                  specified domain/option isn't found
     *
     * @return The string representation of the option or null if optional setting is not specified
     */
    default String getOptionString(final String domain, final String option,
            final String... fallbacks) {
        return getOptionString(domain, option, true, PERMISSIVE_VALIDATOR, fallbacks);
    }

    /**
     * Retrieves a boolean representation of the specified option.
     *
     * @param domain The domain of the option
     * @param option The name of the option
     *
     * @return The boolean representation of the option
     */
    default boolean hasOptionBool(final String domain, final String option) {
        return hasOption(domain, option, PERMISSIVE_VALIDATOR);
    }

    /**
     * Determines if this source has the specified character option.
     *
     * @param domain The domain of the option
     * @param option The name of the option
     *
     * @return True iff the option exists and is parsable as a char, false otherwise.
     */
    default boolean hasOptionChar(final String domain, final String option) {
        return hasOptionString(domain, option);
    }

    /**
     * Determines if this source has the specified integer option.
     *
     * @param domain The domain of the option
     * @param option The name of the option
     *
     * @return True iff the option exists and is parsable as an integer, false otherwise.
     */
    default boolean hasOptionInt(final String domain, final String option) {
        return hasOptionString(domain, option, INT_VALIDATOR);
    }

    /**
     * Determines if this source has the specified String option.
     *
     * <p>A String option is considered to exist if:
     *
     * <ul>
     *     <li>there is a value for the specified option,
     *     <li>that value is not empty, and
     *     <li>that value is not disabled (i.e., it doesn't begin with "false:")
     * </ul>
     *
     * @param domain The domain of the option
     * @param option The name of the option
     *
     * @return True iff the option exists and is not empty, false otherwise
     */
    default boolean hasOptionString(final String domain, final String option) {
        return hasOptionString(domain, option, PERMISSIVE_VALIDATOR);
    }

    /**
     * Determines if this source has the specified String option.
     *
     * <p>A String option is considered to exist if:
     *
     * <ul>
     *     <li>there is a value for the specified option that satisfies the specified validator,
     *     <li>that value is not empty, and
     *     <li>that value is not disabled (i.e., it doesn't begin with "false:")
     * </ul>
     *
     * @param domain    The domain of the option
     * @param option    The name of the option
     * @param validator The validator to use to check legal values
     *
     * @return True iff the option exists and is not empty, false otherwise
     */
    default boolean hasOptionString(final String domain, final String option,
            final Validator<String> validator) {
        final String value;

        return hasOption(domain, option, validator)
                && !(value = getOption(domain, option, validator)).isEmpty()
                && !value.startsWith("false:");
    }

    /**
     * Returns the name of all the options in the specified domain. If the domain doesn't exist, an
     * empty list is returned.
     *
     * @param domain The domain to search
     *
     * @return A list of options in the specified domain
     */
    Map<String, String> getOptions(String domain);

}