<!-- Courtsey ruler
 p {
     font: 14px ariel, sans serif;
 #errorMsg {
     font:bold 18px arial,sans-serif;
 .chartContainer {
     padding: 2px;
 img.chart {
  Script: power.php
  Description: This scripts generates on the server charts showing
  power data spanning the period supplied by the user.  The script
  does the following:
     - converts user supplied dates to  epoch time
     - gets the times of the first and last data point in the round
       robin database (RRD)
     - from above validates user supplied begin and end dates
     - creates charts of the specified period
  Copyright 2020 Jeff Owrey
     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, either version 3 of the License, or
     (at your option) any later version.
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     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
  Revision History
    * v10 released 11 Jan 2021 by J L Owrey; first release
 # Define global constants
 # debug mode
 define("_DEBUG", false);
 # round robin database file
 define("_RRD_FILE", str_replace("public_html/power/power.php",
 # charts html directory
 define("_CHART_DIRECTORY", str_replace("power.php",
 # standard chart width in pixels
 define("_CHART_WIDTH", 600);
 # standard chart height in pixels
 define("_CHART_HEIGHT", 150);
 # Set error handling modes.
 # Get user supplied chart begin and end dates.
 $beginDate = $_POST["beginDate"];
 $endDate =  $_POST["endDate"];
 # Convert the user supplied dates to epoch time stamps.
 $beginDateEp = strtotime($beginDate);
 $endDateEp = strtotime($endDate);
 # Get the time stamp of the earliest data point in the RRD file.
 $cmd = sprintf("rrdtool first %s --rraindex 1", _RRD_FILE);
 $firstDP = shell_exec($cmd);
 # Get the time stamp of the latest data point in the RRD file.
 $cmd = sprintf("rrdtool last %s", _RRD_FILE);
 $lastDP = shell_exec($cmd);
 # Determine validity of user supplied dates.  User supplied begin
 # date must be less than user supplied end date.  Furthermore both
 # dates must be within the range of dates stored in the RRD.
 if ($beginDateEp > $endDateEp) {
     echo "<p id=\"errorMsg\">" .
          "End date must be after begin date.</p>";
 } elseif ($beginDateEp < $firstDP || $endDateEp > $lastDP) {
     echo "<p id=\"errorMsg\">" .
           "Date range must be between " .
           date('m / d / Y', $firstDP) . " and " . 
           date('m / d / Y', $lastDP) . ".</p>";
 } else {
     generateCharts($beginDateEp, $endDateEp);
 function sendChartsToClient() {
     # Send html commands to client browser.
     echo "<div class=\"chartContainer\">" .
          "<img class=\"chart\" src=\"dynamic/custom_current.png\">" .
     echo "<div class=\"chartContainer\">" .
          "<img class=\"chart\" src=\"dynamic/custom_voltage.png\">" .
     echo "<div class=\"chartContainer\">" .
          "<img class=\"chart\" src=\"dynamic/custom_power.png\">" .
     echo "<div class=\"chartContainer\">" .
          "<img class=\"chart\" src=\"dynamic/custom_battemp.png\">" .
     echo "<div class=\"chartContainer\">" .
          "<img class=\"chart\" src=\"dynamic/custom_ambtemp.png\">" .
 function generateCharts($beginDateEp, $endDateEp) {
     # Generate charts from validated user supplied dates.
     if (_DEBUG) {
         echo "<p>Date range: " . $beginDateEp . " thru " .
               $endDateEp . "</p>";
     createChart('custom_current', 'CUR', 'Amps', 
                 'Current', $beginDateEp, $endDateEp,
                  0, 0, 2, false);
     createChart('custom_voltage', 'VOLT', 'Volts', 
                 'Voltage', $beginDateEp, $endDateEp,
                  0, 0, 0, false);
     createChart('custom_power', 'PWR', 'Watts', 
                 'Power', $beginDateEp, $endDateEp,
                  0, 0, 2, false);
     createChart('custom_battemp', 'BTMP', 'deg\ F', 
                 'Battery\ Temperature', $beginDateEp, $endDateEp,
                  0, 0, 0, false);
     createChart('custom_ambtemp', 'ATMP', 'deg\ F', 
                 'Ambient\ Temperature', $beginDateEp, $endDateEp,
                  0, 0, 0, false);
 function createChart($chartFile, $dataItem, $label, $title, $begin,
                      $end, $lower, $upper, $addTrend, $autoScale) {
     Uses rrdtool to create a chart of specified aredn node data item.
        fileName - name of the created chart file
        dataItem - data item to be charted
        label - string containing a label for the item to be charted
        title - string containing a title for the chart
        begin - beginning time of the chart data
        end   - ending time of the data to be charted
        lower - lower bound for chart ordinate #NOT USED
        upper - upper bound for chart ordinate #NOT USED
        addTrend - 0, show only chart data
                   1, show only a trend line
                   2, show a trend line and the chart data
        autoScale - if True, then use vertical axis auto scaling
            (lower and upper parameters are ignored), otherwise use
            lower and upper parameters to set vertical axis scale
     Returns: True if successful, False otherwise
     # Define path on server to chart files.
     $chartPath = _CHART_DIRECTORY . $chartFile . ".png";
     # Format the rrdtool chart command.
     # Set chart file name, start time, end time, height, and width.
     $cmdfmt = "rrdtool graph %s -a PNG -s %s -e %s -w %s -h %s ";
     $cmd = sprintf($cmdfmt, $chartPath, $begin, $end, _CHART_WIDTH,
     $cmdfmt = "-l %s -u %s -r ";
     # Set upper and lower ordinate bounds.
     if ($lower < $upper) {
         $cmd .= sprintf($cmdfmt, $lower, $upper);
     } elseif ($autoScale) {
         $cmd .= "-A ";
     $cmd .= "-Y ";
     # Set the chart ordinate label and chart title. 
     $cmdfmt = "-v %s -t %s ";
     $cmd .= sprintf($cmdfmt, $label, $title);
     # Define moving average window width.
     $trendWindow = floor(($end - $begin) / 12);
     # Show the data, or a moving average trend line over
     # the data, or both.
     $cmdfmt = "DEF:dSeries=%s:%s:LAST ";
     $cmd .= sprintf($cmdfmt, _RRD_FILE, $dataItem);
     if ($addTrend == 0) {
         $cmd .= "LINE1:dSeries#0400ff ";
     } elseif ($addTrend == 1) {
         $cmdfmt = "CDEF:smoothed=dSeries,%s,TREND LINE3:smoothed#006600 ";
         $cmd .= sprintf($cmdfmt, $trendWindow);
     } elseif ($addTrend == 2) {
         $cmd .= "LINE1:dSeries#0400ff ";
         $cmdfmt = "CDEF:smoothed=dSeries,%s,TREND LINE3:smoothed#006600 ";
         $cmd .=  sprintf($cmdfmt, $trendWindow);
     # Execute the formatted rrdtool command in the shell. The rrdtool
     # command will complete execution before the html image tags get
     # sent to the browser.  This assures that the charts are available
     # when the client browser executes the html code that loads the
     # charts into the document displayed by the client browser.
     if (_DEBUG) {
         echo "<p>chart command:<br>" . $cmd . "</p>";
     $result = shell_exec($cmd . " 2>&1");
     if (_DEBUG) {
         echo "<p>result:<br>" . $result . "</p>";