#!/bin/bash 

# changetrack--Tracks a given URL and, if it's changed since the last
#   visit, emails the new page to the specified address.

setglobal sendmail = $[which sendmail]         
setglobal sitearchive = '"/tmp/changetrack'"
setglobal tmpchanges = ""$sitearchive/changes.$Pid""  # Temp file
setglobal fromaddr = '"webscraper@intuitive.com'"
setglobal dirperm = '755'        # read+write+execute for dir owner
setglobal fileperm = '644'       # read+write for owner, read only for others

trap "$[which rm] -f $tmpchanges" 0 1 15  # Remove temp file on exit

if test $Argc -ne 2  {
  echo "Usage: $[basename $0] url email" > !2
  echo "  tip: to have changes displayed on screen, use email addr '-'" > !2
  exit 1
}

if test ! -d $sitearchive  {
  if ! mkdir $sitearchive  {
    echo "$[basename $0] failed: couldn't create $sitearchive." > !2
    exit 1
  }
  chmod $dirperm $sitearchive
}

if test $[echo $1 | cut -c1-5] != "http:"  {
  echo "Please use fully qualified URLs (e.g. start with 'http://')" > !2
  exit 1
}

setglobal fname = $[echo $1 | sed 's/http:\/\///g' | tr '/?&' '...]
setglobal baseurl = ""$[echo $1 | cut -d/ -f1-3]/""

# Grab a copy of the Web page and put it in an archive file. Note that we 
#   can track changes by looking just at the content (that is, -dump, not
#   -source), so we can skip any HTML parsing....

lynx  -dump $1 | uniq > $sitearchive/$(fname).new

if test -f "$sitearchive/$fname"  {
  # We've seen this site before, so compare the two with diff.
  diff $sitearchive/$fname $sitearchive/$(fname).new > $tmpchanges
  if test -s $tmpchanges  {
    echo "Status: Site $1 has changed since our last check."
  } else {
    echo "Status: No changes for site $1 since last check"
    rm -f $sitearchive/$(fname).new     # Nothing new...
    exit 0                              # No change--we're outta here.
  }
} else {
  echo "Status: first visit to $1. Copy archived for future analysis."
  mv $sitearchive/$(fname).new $sitearchive/$fname
  chmod $fileperm $sitearchive/$fname
  exit 0
}

# If we're here, the site has changed, and we need to send the contents
#   of the .new file to the user and replace the original with the .new
#   for the next invocation of the script.

if test $2 != "-"  {

shell { echo "Content-type: text/html"
  echo "From: $fromaddr (Web Site Change Tracker)"
  echo "Subject: Web Site $1 Has Changed"
  echo "To: $2"
  echo ""

   curl -s -dump $1 | \
   sed -e "s|src=\"|SRC=\"$baseurl|gi" \
       -e "s|href=\"|HREF=\"$baseurl|gi" \
       -e "s|$baseurl\/http:|http:|g"
} | $sendmail -t

} else {
  # Just showing the differences on the screen– is ugly. Solution?

  diff $sitearchive/$fname $sitearchive/$(fname).new
}

# Update the saved snapshot of the website.

mv $sitearchive/$(fname).new $sitearchive/$fname
chmod 755 $sitearchive/$fname
exit 0