/*
 * Copyright DataStax, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.datastax.driver.core;

import com.google.common.base.Objects;

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

import static com.google.common.base.Preconditions.checkArgument;


/**
 * Represents a duration. A duration stores separately months, days, and seconds due to the fact that
 * the number of days in a month varies, and a day can have 23 or 25 hours if a daylight saving is involved.
 */
public final class Duration {

    static final long NANOS_PER_MICRO = 1000L;
    static final long NANOS_PER_MILLI = 1000 * NANOS_PER_MICRO;
    static final long NANOS_PER_SECOND = 1000 * NANOS_PER_MILLI;
    static final long NANOS_PER_MINUTE = 60 * NANOS_PER_SECOND;
    static final long NANOS_PER_HOUR = 60 * NANOS_PER_MINUTE;
    static final int DAYS_PER_WEEK = 7;
    static final int MONTHS_PER_YEAR = 12;

    /**
     * The Regexp used to parse the duration provided as String.
     */
    private static final Pattern STANDARD_PATTERN =
            Pattern.compile("\\G(\\d+)(y|Y|mo|MO|mO|Mo|w|W|d|D|h|H|s|S|ms|MS|mS|Ms|us|US|uS|Us|µs|µS|ns|NS|nS|Ns|m|M)");

    /**
     * The Regexp used to parse the duration when provided in the ISO 8601 format with designators.
     */
    private static final Pattern ISO8601_PATTERN =
            Pattern.compile("P((\\d+)Y)?((\\d+)M)?((\\d+)D)?(T((\\d+)H)?((\\d+)M)?((\\d+)S)?)?");

    /**
     * The Regexp used to parse the duration when provided in the ISO 8601 format with designators.
     */
    private static final Pattern ISO8601_WEEK_PATTERN = Pattern.compile("P(\\d+)W");

    /**
     * The Regexp used to parse the duration when provided in the ISO 8601 alternative format.
     */
    private static final Pattern ISO8601_ALTERNATIVE_PATTERN =
            Pattern.compile("P(\\d{4})-(\\d{2})-(\\d{2})T(\\d{2}):(\\d{2}):(\\d{2})");

    /**
     * The number of months.
     */
    private final int months;

    /**
     * The number of days.
     */
    private final int days;

    /**
     * The number of nanoseconds.
     */
    private final long nanoseconds;

    private Duration(int months, int days, long nanoseconds) {
        // Makes sure that all the values are negative if one of them is
        if ((months < 0 || days < 0 || nanoseconds < 0) && ((months > 0 || days > 0 || nanoseconds > 0))) {
            throw new IllegalArgumentException(String.format(
                    "All values must be either negative or positive, got %d months, %d days, %d nanoseconds", months, days, nanoseconds));
        }
        this.months = months;
        this.days = days;
        this.nanoseconds = nanoseconds;
    }

    /**
     * Creates a duration with the given number of months, days and nanoseconds.
     * <p/>
     * A duration can be negative. In this case, all the non zero values must be negative.
     *
     * @param months      the number of months
     * @param days        the number of days
     * @param nanoseconds the number of nanoseconds
     * @throws IllegalArgumentException if the values are not all negative or all positive
     */
    public static Duration newInstance(int months, int days, long nanoseconds) {
        return new Duration(months, days, nanoseconds);
    }

    /**
     * Converts a <code>String</code> into a duration.
     * <p>The accepted formats are:
     * <ul>
     * <li>multiple digits followed by a time unit like: 12h30m where the time unit can be:
     * <ul>
     * <li>{@code y}: years</li>
     * <li>{@code m}: months</li>
     * <li>{@code w}: weeks</li>
     * <li>{@code d}: days</li>
     * <li>{@code h}: hours</li>
     * <li>{@code m}: minutes</li>
     * <li>{@code s}: seconds</li>
     * <li>{@code ms}: milliseconds</li>
     * <li>{@code us} or {@code µs}: microseconds</li>
     * <li>{@code ns}: nanoseconds</li>
     * </ul>
     * </li>
     * <li>ISO 8601 format:  P[n]Y[n]M[n]DT[n]H[n]M[n]S or P[n]W</li>
     * <li>ISO 8601 alternative format: P[YYYY]-[MM]-[DD]T[hh]:[mm]:[ss]</li>
     * </ul>
     *
     * @param input the <code>String</code> to convert
     * @return a {@link Duration}
     */
    public static Duration from(String input) {
        boolean isNegative = input.startsWith("-");
        String source = isNegative ? input.substring(1) : input;

        if (source.startsWith("P")) {
            if (source.endsWith("W"))
                return parseIso8601WeekFormat(isNegative, source);

            if (source.contains("-"))
                return parseIso8601AlternativeFormat(isNegative, source);

            return parseIso8601Format(isNegative, source);
        }
        return parseStandardFormat(isNegative, source);
    }

    private static Duration parseIso8601Format(boolean isNegative, String source) {
        Matcher matcher = ISO8601_PATTERN.matcher(source);
        if (!matcher.matches())
            throw new IllegalArgumentException(String.format("Unable to convert '%s' to a duration", source));

        Builder builder = new Builder(isNegative);
        if (matcher.group(1) != null)
            builder.addYears(groupAsLong(matcher, 2));

        if (matcher.group(3) != null)
            builder.addMonths(groupAsLong(matcher, 4));

        if (matcher.group(5) != null)
            builder.addDays(groupAsLong(matcher, 6));

        // Checks if the String contains time information
        if (matcher.group(7) != null) {
            if (matcher.group(8) != null)
                builder.addHours(groupAsLong(matcher, 9));

            if (matcher.group(10) != null)
                builder.addMinutes(groupAsLong(matcher, 11));

            if (matcher.group(12) != null)
                builder.addSeconds(groupAsLong(matcher, 13));
        }
        return builder.build();
    }

    private static Duration parseIso8601AlternativeFormat(boolean isNegative, String source) {
        Matcher matcher = ISO8601_ALTERNATIVE_PATTERN.matcher(source);
        if (!matcher.matches())
            throw new IllegalArgumentException(String.format("Unable to convert '%s' to a duration", source));

        return new Builder(isNegative).addYears(groupAsLong(matcher, 1))
                .addMonths(groupAsLong(matcher, 2))
                .addDays(groupAsLong(matcher, 3))
                .addHours(groupAsLong(matcher, 4))
                .addMinutes(groupAsLong(matcher, 5))
                .addSeconds(groupAsLong(matcher, 6))
                .build();
    }

    private static Duration parseIso8601WeekFormat(boolean isNegative, String source) {
        Matcher matcher = ISO8601_WEEK_PATTERN.matcher(source);
        if (!matcher.matches())
            throw new IllegalArgumentException(String.format("Unable to convert '%s' to a duration", source));

        return new Builder(isNegative).addWeeks(groupAsLong(matcher, 1))
                .build();
    }

    private static Duration parseStandardFormat(boolean isNegative, String source) {
        Matcher matcher = STANDARD_PATTERN.matcher(source);
        if (!matcher.find())
            throw new IllegalArgumentException(String.format("Unable to convert '%s' to a duration", source));

        Builder builder = new Builder(isNegative);
        boolean done;

        do {
            long number = groupAsLong(matcher, 1);
            String symbol = matcher.group(2);
            add(builder, number, symbol);
            done = matcher.end() == source.length();
        }
        while (matcher.find());

        if (!done)
            throw new IllegalArgumentException(String.format("Unable to convert '%s' to a duration", source));

        return builder.build();
    }

    private static long groupAsLong(Matcher matcher, int group) {
        return Long.parseLong(matcher.group(group));
    }

    private static Builder add(Builder builder, long number, String symbol) {
        String s = symbol.toLowerCase();
        if (s.equals("y")) {
            return builder.addYears(number);
        } else if (s.equals("mo")) {
            return builder.addMonths(number);
        } else if (s.equals("w")) {
            return builder.addWeeks(number);
        } else if (s.equals("d")) {
            return builder.addDays(number);
        } else if (s.equals("h")) {
            return builder.addHours(number);
        } else if (s.equals("m")) {
            return builder.addMinutes(number);
        } else if (s.equals("s")) {
            return builder.addSeconds(number);
        } else if (s.equals("ms")) {
            return builder.addMillis(number);
        } else if (s.equals("us") || s.equals("µs")) {
            return builder.addMicros(number);
        } else if (s.equals("ns")) {
            return builder.addNanos(number);
        }
        throw new IllegalArgumentException(String.format("Unknown duration symbol '%s'", symbol));
    }

    /**
     * Appends the result of the division to the specified builder if the dividend is not zero.
     *
     * @param builder  the builder to append to
     * @param dividend the dividend
     * @param divisor  the divisor
     * @param unit     the time unit to append after the result of the division
     * @return the remainder of the division
     */
    private static long append(StringBuilder builder, long dividend, long divisor, String unit) {
        if (dividend == 0 || dividend < divisor)
            return dividend;

        builder.append(dividend / divisor).append(unit);
        return dividend % divisor;
    }

    /**
     * Returns the number of months in this duration.
     *
     * @return the number of months in this duration.
     */
    public int getMonths() {
        return months;
    }

    /**
     * Returns the number of days in this duration.
     *
     * @return the number of days in this duration.
     */
    public int getDays() {
        return days;
    }

    /**
     * Returns the number of nanoseconds in this duration.
     *
     * @return the number of months in this duration.
     */
    public long getNanoseconds() {
        return nanoseconds;
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(days, months, nanoseconds);
    }

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Duration))
            return false;

        Duration other = (Duration) obj;
        return days == other.days
                && months == other.months
                && nanoseconds == other.nanoseconds;
    }

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();

        if (months < 0 || days < 0 || nanoseconds < 0)
            builder.append('-');

        long remainder = append(builder, Math.abs(months), MONTHS_PER_YEAR, "y");
        append(builder, remainder, 1, "mo");

        append(builder, Math.abs(days), 1, "d");

        if (nanoseconds != 0) {
            remainder = append(builder, Math.abs(nanoseconds), NANOS_PER_HOUR, "h");
            remainder = append(builder, remainder, NANOS_PER_MINUTE, "m");
            remainder = append(builder, remainder, NANOS_PER_SECOND, "s");
            remainder = append(builder, remainder, NANOS_PER_MILLI, "ms");
            remainder = append(builder, remainder, NANOS_PER_MICRO, "us");
            append(builder, remainder, 1, "ns");
        }
        return builder.toString();
    }

    private static class Builder {
        /**
         * {@code true} if the duration is a negative one, {@code false} otherwise.
         */
        private final boolean isNegative;

        /**
         * The number of months.
         */
        private int months;

        /**
         * The number of days.
         */
        private int days;

        /**
         * The number of nanoseconds.
         */
        private long nanoseconds;

        /**
         * We need to make sure that the values for each units are provided in order.
         */
        private int currentUnitIndex;

        public Builder(boolean isNegative) {
            this.isNegative = isNegative;
        }

        /**
         * Adds the specified amount of years.
         *
         * @param numberOfYears the number of years to add.
         * @return this {@code Builder}
         */
        public Builder addYears(long numberOfYears) {
            validateOrder(1);
            validateMonths(numberOfYears, MONTHS_PER_YEAR);
            months += numberOfYears * MONTHS_PER_YEAR;
            return this;
        }

        /**
         * Adds the specified amount of months.
         *
         * @param numberOfMonths the number of months to add.
         * @return this {@code Builder}
         */
        public Builder addMonths(long numberOfMonths) {
            validateOrder(2);
            validateMonths(numberOfMonths, 1);
            months += numberOfMonths;
            return this;
        }

        /**
         * Adds the specified amount of weeks.
         *
         * @param numberOfWeeks the number of weeks to add.
         * @return this {@code Builder}
         */
        public Builder addWeeks(long numberOfWeeks) {
            validateOrder(3);
            validateDays(numberOfWeeks, DAYS_PER_WEEK);
            days += numberOfWeeks * DAYS_PER_WEEK;
            return this;
        }

        /**
         * Adds the specified amount of days.
         *
         * @param numberOfDays the number of days to add.
         * @return this {@code Builder}
         */
        public Builder addDays(long numberOfDays) {
            validateOrder(4);
            validateDays(numberOfDays, 1);
            days += numberOfDays;
            return this;
        }

        /**
         * Adds the specified amount of hours.
         *
         * @param numberOfHours the number of hours to add.
         * @return this {@code Builder}
         */
        public Builder addHours(long numberOfHours) {
            validateOrder(5);
            validateNanos(numberOfHours, NANOS_PER_HOUR);
            nanoseconds += numberOfHours * NANOS_PER_HOUR;
            return this;
        }

        /**
         * Adds the specified amount of minutes.
         *
         * @param numberOfMinutes the number of minutes to add.
         * @return this {@code Builder}
         */
        public Builder addMinutes(long numberOfMinutes) {
            validateOrder(6);
            validateNanos(numberOfMinutes, NANOS_PER_MINUTE);
            nanoseconds += numberOfMinutes * NANOS_PER_MINUTE;
            return this;
        }

        /**
         * Adds the specified amount of seconds.
         *
         * @param numberOfSeconds the number of seconds to add.
         * @return this {@code Builder}
         */
        public Builder addSeconds(long numberOfSeconds) {
            validateOrder(7);
            validateNanos(numberOfSeconds, NANOS_PER_SECOND);
            nanoseconds += numberOfSeconds * NANOS_PER_SECOND;
            return this;
        }

        /**
         * Adds the specified amount of milliseconds.
         *
         * @param numberOfMillis the number of milliseconds to add.
         * @return this {@code Builder}
         */
        public Builder addMillis(long numberOfMillis) {
            validateOrder(8);
            validateNanos(numberOfMillis, NANOS_PER_MILLI);
            nanoseconds += numberOfMillis * NANOS_PER_MILLI;
            return this;
        }

        /**
         * Adds the specified amount of microseconds.
         *
         * @param numberOfMicros the number of microseconds to add.
         * @return this {@code Builder}
         */
        public Builder addMicros(long numberOfMicros) {
            validateOrder(9);
            validateNanos(numberOfMicros, NANOS_PER_MICRO);
            nanoseconds += numberOfMicros * NANOS_PER_MICRO;
            return this;
        }

        /**
         * Adds the specified amount of nanoseconds.
         *
         * @param numberOfNanos the number of nanoseconds to add.
         * @return this {@code Builder}
         */
        public Builder addNanos(long numberOfNanos) {
            validateOrder(10);
            validateNanos(numberOfNanos, 1);
            nanoseconds += numberOfNanos;
            return this;
        }

        /**
         * Validates that the total number of months can be stored.
         *
         * @param units         the number of units that need to be added
         * @param monthsPerUnit the number of days per unit
         */
        private void validateMonths(long units, int monthsPerUnit) {
            validate(units, (Integer.MAX_VALUE - months) / monthsPerUnit, "months");
        }

        /**
         * Validates that the total number of days can be stored.
         *
         * @param units       the number of units that need to be added
         * @param daysPerUnit the number of days per unit
         */
        private void validateDays(long units, int daysPerUnit) {
            validate(units, (Integer.MAX_VALUE - days) / daysPerUnit, "days");
        }

        /**
         * Validates that the total number of nanoseconds can be stored.
         *
         * @param units        the number of units that need to be added
         * @param nanosPerUnit the number of nanoseconds per unit
         */
        private void validateNanos(long units, long nanosPerUnit) {
            validate(units, (Long.MAX_VALUE - nanoseconds) / nanosPerUnit, "nanoseconds");
        }

        /**
         * Validates that the specified amount is less than the limit.
         *
         * @param units    the number of units to check
         * @param limit    the limit on the number of units
         * @param unitName the unit name
         */
        private void validate(long units, long limit, String unitName) {
            checkArgument(units <= limit,
                    "Invalid duration. The total number of %s must be less or equal to %s",
                    unitName,
                    Integer.MAX_VALUE);
        }

        /**
         * Validates that the duration values are added in the proper order.
         *
         * @param unitIndex the unit index (e.g. years=1, months=2, ...)
         */
        private void validateOrder(int unitIndex) {
            if (unitIndex == currentUnitIndex)
                throw new IllegalArgumentException(String.format("Invalid duration. The %s are specified multiple times", getUnitName(unitIndex)));

            if (unitIndex <= currentUnitIndex)
                throw new IllegalArgumentException(String.format("Invalid duration. The %s should be after %s",
                        getUnitName(currentUnitIndex),
                        getUnitName(unitIndex)));

            currentUnitIndex = unitIndex;
        }

        /**
         * Returns the name of the unit corresponding to the specified index.
         *
         * @param unitIndex the unit index
         * @return the name of the unit corresponding to the specified index.
         */
        private String getUnitName(int unitIndex) {
            switch (unitIndex) {
                case 1:
                    return "years";
                case 2:
                    return "months";
                case 3:
                    return "weeks";
                case 4:
                    return "days";
                case 5:
                    return "hours";
                case 6:
                    return "minutes";
                case 7:
                    return "seconds";
                case 8:
                    return "milliseconds";
                case 9:
                    return "microseconds";
                case 10:
                    return "nanoseconds";
                default:
                    throw new AssertionError("unknown unit index: " + unitIndex);
            }
        }

        public Duration build() {
            return isNegative ? new Duration(-months, -days, -nanoseconds) : new Duration(months, days, nanoseconds);
        }
    }
}
