package ca.uhn.fhir.util;

import com.google.common.annotations.VisibleForTesting;
import org.apache.commons.lang3.time.DateUtils;

import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.Date;
import java.util.LinkedList;
import java.util.concurrent.TimeUnit;

import static org.apache.commons.lang3.StringUtils.isNotBlank;

/*
 * #%L
 * HAPI FHIR - Core Library
 * %%
 * Copyright (C) 2014 - 2019 University Health Network
 * %%
 * 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.
 * #L%
 */

/**
 * A multipurpose stopwatch which can be used to time tasks and produce
 * human readable output about task duration, throughput, estimated task completion,
 * etc.
 * <p>
 * <p>
 * <b>Thread Safety Note: </b> StopWatch is not intended to be thread safe.
 * </p>
 *
 * @since HAPI FHIR 3.3.0
 */
public class StopWatch {

        private static Long ourNowForUnitTest;
        private long myStarted = now();
        private TaskTiming myCurrentTask;
        private LinkedList<TaskTiming> myTasks;
        /**
         * Constructor
         */
        public StopWatch() {
                super();
        }
        /**
         * Constructor
         *
         * @param theStart The time to record as the start for this timer
         */
        public StopWatch(Date theStart) {
                myStarted = theStart.getTime();
        }

        private void addNewlineIfContentExists(StringBuilder theB) {
                if (theB.length() > 0) {
                        theB.append("\n");
                }
        }

        /**
         * Finish the counter on the current task (which was started by calling
         * {@link #startTask(String)}. This method has no effect if no task
         * is currently started so it's ok to call it more than once.
         */
        public void endCurrentTask() {
                ensureTasksListExists();
                if (myCurrentTask != null) {
                        myCurrentTask.setEnd(now());
                }
                myCurrentTask = null;
        }

        private void ensureTasksListExists() {
                if (myTasks == null) {
                        myTasks = new LinkedList<>();
                }
        }

        /**
         * Returns a nice human-readable display of the time taken per
         * operation. Note that this may not actually output the number
         * of milliseconds if the time taken per operation was very long (over
         * 10 seconds)
         *
         * @see #formatMillis(long)
         */
        public String formatMillisPerOperation(long theNumOperations) {
                double millisPerOperation = (((double) getMillis()) / Math.max(1.0, theNumOperations));
                return formatMillis(millisPerOperation);
        }

        /**
         * Returns a string providing the durations of all tasks collected by {@link #startTask(String)}
         */
        public String formatTaskDurations() {

                ensureTasksListExists();
                StringBuilder b = new StringBuilder();

                if (myTasks.size() > 0) {
                        long delta = myTasks.getFirst().getStart() - myStarted;
                        if (delta > 10) {
                                addNewlineIfContentExists(b);
                                b.append("Before first task");
                                b.append(": ");
                                b.append(formatMillis(delta));
                        }
                }

                TaskTiming last = null;
                for (TaskTiming nextTask : myTasks) {

                        if (last != null) {
                                long delta = nextTask.getStart() - last.getEnd();
                                if (delta > 10) {
                                        addNewlineIfContentExists(b);
                                        b.append("Between");
                                        b.append(": ");
                                        b.append(formatMillis(delta));
                                }
                        }

                        addNewlineIfContentExists(b);
                        b.append(nextTask.getTaskName());
                        b.append(": ");
                        long delta = nextTask.getMillis();
                        b.append(formatMillis(delta));

                        last = nextTask;
                }

                if (myTasks.size() > 0) {
                        long delta = now() - myTasks.getLast().getEnd();
                        if (delta > 10) {
                                addNewlineIfContentExists(b);
                                b.append("After last task");
                                b.append(": ");
                                b.append(formatMillis(delta));
                        }
                }

                return b.toString();
        }

        /**
         * Determine the current throughput per unit of time (specified in theUnit)
         * assuming that theNumOperations operations have happened.
         * <p>
         * For example, if this stopwatch has 2 seconds elapsed, and this method is
         * called for theNumOperations=30 and TimeUnit=SECONDS,
         * this method will return 15
         * </p>
         *
         * @see #getThroughput(long, TimeUnit)
         */
        public String formatThroughput(long theNumOperations, TimeUnit theUnit) {
                double throughput = getThroughput(theNumOperations, theUnit);
                return new DecimalFormat("0.0").format(throughput);
        }

        /**
         * Given an amount of something completed so far, and a total amount, calculates how long it will take for something to complete
         *
         * @param theCompleteToDate The amount so far
         * @param theTotal          The total (must be higher than theCompleteToDate
         * @return A formatted amount of time
         */
        public String getEstimatedTimeRemaining(double theCompleteToDate, double theTotal) {
                double millis = getMillis();
                long millisRemaining = (long) (((theTotal / theCompleteToDate) * millis) - (millis));
                return formatMillis(millisRemaining);
        }

        public long getMillis(Date theNow) {
                return theNow.getTime() - myStarted;
        }

        public long getMillis() {
                long now = now();
                return now - myStarted;
        }

        public long getMillisAndRestart() {
                long now = now();
                long retVal = now - myStarted;
                myStarted = now;
                return retVal;
        }

        /**
         * @param theNumOperations Ok for this to be 0, it will be treated as 1
         */
        public long getMillisPerOperation(long theNumOperations) {
                return (long) (((double) getMillis()) / Math.max(1.0, theNumOperations));
        }

        public Date getStartedDate() {
                return new Date(myStarted);
        }

        /**
         * Determine the current throughput per unit of time (specified in theUnit)
         * assuming that theNumOperations operations have happened.
         * <p>
         * For example, if this stopwatch has 2 seconds elapsed, and this method is
         * called for theNumOperations=30 and TimeUnit=SECONDS,
         * this method will return 15
         * </p>
         *
         * @see #formatThroughput(long, TimeUnit)
         */
        public double getThroughput(long theNumOperations, TimeUnit theUnit) {
                if (theNumOperations <= 0) {
                        return 0.0f;
                }

                long millisElapsed = Math.max(1, getMillis());
                long periodMillis = theUnit.toMillis(1);

                double denominator = ((double) millisElapsed) / ((double) periodMillis);

                return (double) theNumOperations / denominator;
        }

        public void restart() {
                myStarted = now();
        }

        /**
         * Starts a counter for a sub-task
         * <p>
         * <b>Thread Safety Note: </b> This method is not threadsafe! Do not use subtasks in a
         * multithreaded environment.
         * </p>
         *
         * @param theTaskName Note that if theTaskName is blank or empty, no task is started
         */
        public void startTask(String theTaskName) {
                endCurrentTask();
                if (isNotBlank(theTaskName)) {
                        myCurrentTask = new TaskTiming()
                                .setTaskName(theTaskName)
                                .setStart(now());
                        myTasks.add(myCurrentTask);
                }
        }

        /**
         * Formats value in an appropriate format. See {@link #formatMillis(long)}}
         * for a description of the format
         *
         * @see #formatMillis(long)
         */
        @Override
        public String toString() {
                return formatMillis(getMillis());
        }

        private static class TaskTiming {
                private long myStart;
                private long myEnd;
                private String myTaskName;

                public long getEnd() {
                        if (myEnd == 0) {
                                return now();
                        }
                        return myEnd;
                }

                public TaskTiming setEnd(long theEnd) {
                        myEnd = theEnd;
                        return this;
                }

                public long getMillis() {
                        return getEnd() - getStart();
                }

                public long getStart() {
                        return myStart;
                }

                public TaskTiming setStart(long theStart) {
                        myStart = theStart;
                        return this;
                }

                public String getTaskName() {
                        return myTaskName;
                }

                public TaskTiming setTaskName(String theTaskName) {
                        myTaskName = theTaskName;
                        return this;
                }
        }

        private static NumberFormat getDayFormat() {
                return new DecimalFormat("0.0");
        }

        private static NumberFormat getTenDayFormat() {
                return new DecimalFormat("0");
        }

        private static NumberFormat getSubMillisecondMillisFormat() {
                return new DecimalFormat("0.000");
        }

        /**
         * Append a right-aligned and zero-padded numeric value to a `StringBuilder`.
         */
        static private void append(StringBuilder tgt, String pfx, int dgt, long val) {
                tgt.append(pfx);
                if (dgt > 1) {
                        int pad = (dgt - 1);
                        for (long xa = val; xa > 9 && pad > 0; xa /= 10) {
                                pad--;
                        }
                        for (int xa = 0; xa < pad; xa++) {
                                tgt.append('0');
                        }
                }
                tgt.append(val);
        }

        /**
         * Formats a number of milliseconds for display (e.g.
         * in a log file), tailoring the output to how big
         * the value actually is.
         * <p>
         * Example outputs:
         * </p>
         * <ul>
         * <li>133ms</li>
         * <li>00:00:10.223</li>
         * <li>1.7 days</li>
         * <li>64 days</li>
         * </ul>
         */
        public static String formatMillis(long theMillis) {
                return formatMillis((double) theMillis);
        }

        /**
         * Formats a number of milliseconds for display (e.g.
         * in a log file), tailoring the output to how big
         * the value actually is.
         * <p>
         * Example outputs:
         * </p>
         * <ul>
         * <li>133ms</li>
         * <li>00:00:10.223</li>
         * <li>1.7 days</li>
         * <li>64 days</li>
         * </ul>
         */
        public static String formatMillis(double theMillis) {
                StringBuilder buf = new StringBuilder(20);
                if (theMillis > 0.0 && theMillis < 1.0) {
                        buf.append(getSubMillisecondMillisFormat().format(theMillis));
                        buf.append("ms");
                } else if (theMillis < (10 * DateUtils.MILLIS_PER_SECOND)) {
                        buf.append((int) theMillis);
                        buf.append("ms");
                } else if (theMillis >= DateUtils.MILLIS_PER_DAY) {
                        double days = theMillis / DateUtils.MILLIS_PER_DAY;
                        if (days >= 10) {
                                buf.append(getTenDayFormat().format(days));
                                buf.append(" days");
                        } else if (days != 1.0f) {
                                buf.append(getDayFormat().format(days));
                                buf.append(" days");
                        } else {
                                buf.append(getDayFormat().format(days));
                                buf.append(" day");
                        }
                } else {
                        long millisAsLong = (long) theMillis;
                        append(buf, "", 2, ((millisAsLong % DateUtils.MILLIS_PER_DAY) / DateUtils.MILLIS_PER_HOUR));
                        append(buf, ":", 2, ((millisAsLong % DateUtils.MILLIS_PER_HOUR) / DateUtils.MILLIS_PER_MINUTE));
                        append(buf, ":", 2, ((millisAsLong % DateUtils.MILLIS_PER_MINUTE) / DateUtils.MILLIS_PER_SECOND));
                        if (theMillis <= DateUtils.MILLIS_PER_MINUTE) {
                                append(buf, ".", 3, (millisAsLong % DateUtils.MILLIS_PER_SECOND));
                        }
                }
                return buf.toString();
        }

        private static long now() {
                if (ourNowForUnitTest != null) {
                        return ourNowForUnitTest;
                }
                return System.currentTimeMillis();
        }

        @VisibleForTesting
        static void setNowForUnitTestForUnitTest(Long theNowForUnitTest) {
                ourNowForUnitTest = theNowForUnitTest;
        }

}