kiwisdr_com-update

#! /bin/sh
# KiwiSDR.com receiver list extractor for dyatlov map maker
# Copyright 2017 Pierre Ynard
# Licensed under GPLv3+
#
# This script fetches the KiwiSDR.com receiver list, parses it, and
# updates a javascript file with the extracted data, to be sourced by
# the dyatlov map maker. It can run interactively, or in an automated
# way.
#
# The target directory for the javascript data files can be passed
# as an optional first argument to the script; by default, the
# script directory will be used. If setting up automated updates, it
# is strongly recommended for security reasons to use a separate,
# unprivileged target directory.

# Input and output configuration
SOURCE_URL='http://kiwisdr.com/public/'
JS_FILENAME='kiwisdr_com.js'

# Check dependencies, probe available features and switch color output
if ! which wget > /dev/null 2>&1; then
	echo 'Cannot find `wget`, aborting. This script requires `wget`, please install it.' >&2
	exit 1
fi

if which diffstat > /dev/null 2>&1; then
	[ -t 1 ] && diffstat='diffstat -C' || diffstat='diffstat'
else
	diffstat=''
	# Interactive only, don't nag in error logs or cron emails
	[ -t 2 ] && echo 'Consider installing `diffstat` for improved functionality.' >&2
fi

# Check if `diff --color` is supported on this version of `diff`
if [ -t 1 ] && diff --color /dev/null /dev/null > /dev/null 2>&1; then
	diff_color='--color'
else
	diff_color=''
fi

# Directory magic to find parser script
bindir="$(dirname -- "$0")"
parser="${bindir}/kiwisdr_com-parse"

if [ ! -x "$parser" ]; then
	echo 'Cannot run parser script `'"$parser"'`, aborting.' >&2
	exit 1
fi

# Determine target data directory, use optional first argument
datadir="${1:-$bindir}"

if ! [ -d "$datadir" -a -w "$datadir" ]; then
	echo "Cannot write into target directory '$datadir', aborting." >&2
	exit 1
fi

# Target data files
prev_js="${datadir}/${JS_FILENAME}"
new_js="${datadir}/${JS_FILENAME}.tmp"

# Cleaning this up may be more robust
rm -f -- "$new_js"

# Fetch and parse source data
wget_status=$({
	{
		if [ -t 2 ]; then
			# Interactive: verbose output with progress bar
			wget -O - -- "$SOURCE_URL" >&3
			echo $? >&4
		else
			# Non-interactive: non-verbose output, and also
			# filter out download logs to keep only real error
			# messages
			{
				wget -nv -O - -- "$SOURCE_URL" 2>&1 >&3
				echo $? >&4
			} | grep -v -- '\]$' >&2
		fi
	} 3>&1 | "$parser" >| "$new_js"
} 4>&1) || exit $?

[ $wget_status -eq 0 ] || exit $wget_status

# Heurisitic check that output isn't empty of any data. This should
# catch source format changes making the parser script completely fail.
js_real_lines=$(
	grep -c -- '[A-Za-z]' "$new_js"
	grep_status=$?
	[ $grep_status -lt 2 ] || exit $grep_status
) || exit $?

if [ "$js_real_lines" -lt 10 ]; then
	echo "Parsing of '$SOURCE_URL' failed: output too short. Aborting." >&2
	exit 1
fi

# Output diff to stdout for control or logging purposes
diff $diff_color -uN -- "$prev_js" "$new_js"
if [ -n "$diffstat" ]; then
	diff -uN -- "$prev_js" "$new_js" | $diffstat
fi

# If interactive, ask before replacing file
if [ -t 0 -a -t 2 -a -e "$prev_js" ]; then
	read -p "Update '$prev_js'? (Y/n) " update >&2
	case "$update" in
		Y*|y*|'') true;;
		*) exit 0;;
	esac
fi

# Update data
mv -f -- "$new_js" "$prev_js"