#!/bin/bash

# timein--Shows the current time in the specified time zone or
# geographic zone. Without any argument, this shows UTC/GMT.
# Use the word "list" to see a list of known geographic regions.
# Note that it's possible to match zone directories (regions),
# but that only time zone files (cities) are valid specifications.

# Time zone database ref: http://www.twinsun.com/tz/tz-link.htm

zonedir="/usr/share/zoneinfo"

if [ ! -d $zonedir ] ; then
    echo "No time zone database at $zonedir." >&2
    exit 1
fi

if [ -d "$zonedir/posix" ] ; then
    zonedir=$zonedir/posix # Modern Linux systems
fi

if [ $# -eq 0 ] ; then
    timezone="UTC"
    mixedzone="UTC"
elif [ "$1" = "list" ] ; then
    (
    echo "All know time zones and regions defined on this system:"
    cd $zonedir
    find -L * -type f -print | xargs -n 2 | \
        awk '{printf " %-38s\n", $1, $2 }'
    ) | more
    exit 0
else

    region="$(dirname $1)"
    zone="$(basename $1)"

    # Is the given time zone a direct match? If so, we're good to go.
    # Otherwise we need to dig around a bit to find things. Start by
    # just counting matches.

    matchcnt="$(find -L $zonedir -name $zone -type f -print |\
        wc -l | sed 's/[^[:digit:]]//g')"

    # Check if at least one file matches.
    if [ "$matchcnt" -gt 0 ] ; then
        # But exit if more than one file matches.
        if [ $matchcnt -gt 1 ] ; then
            echo "\"$zone\" matches more than one possible time zone record." >&2
            echo "Please use 'list' to see all known regions and time zones." >&2
            exit 1
        fi
        match="$(find -L $zonedir -name $zone -type f -print)"
        mixedzone="$zone"
    else # Maybe we can find a matching time zone region, ratgher than a specifications
        # time zone.
        # First letter capitlized, rest of word lowercase for region + zone
        mixedreegion="$(echo ${region%${region#?}} \
            | tr '[[:lower:]]' '[[:upper:]]') \
            $(echo ${region#?} | tr '[[:upper:]]' '[[:lower:]]')"
                    mixedzone="$(echo ${zone%${zone#?}} | tr '[[:lower:]]' '[[:upper:]]') \
                        $(echo ${zone#?} | tr '[[:upper:]]' '[[:lower:]]')"

        if [ "$mixedregion" != "." ] ; then
            # Only look for specified zone in specified region
            # to let users specify unique matches when there's
            # more than one possibility (e.g., "Atlantic").
            match="$(find -L $zondir/$mixedregion -type f -name $mixedzone -print)"
        else
            match="$(find -L $zonedir -name $mixedzone -type f -print)"
        fi

        # If file exactly matched the specified pattern
        if [ -z "$match" ] ; then
            # Check if the pattern was too ambiguous.
            if [ ! -z $(find -L $zonedir -name $mixedzone -type d -print) ] ; then
                echo "The region \"$1\" has more than one time zone. " >&2
            else # Or if it just didn't produce any matches at all
                echo "Can't find an exact match for \"$1\". " >&2
            fi
            echo "Please use 'list' to see all known regions and time zones." >&2
            exit 1
        fi
    fi
    timezone="$match"
fi

nicetz=$(echo $timezone | sed "s|$zonedir/||g") # Pretty up the output.

echo It\'s $(TZ=$timezone date '+%A, %B %e, %Y, at %l:%M %p') in $nicetz

exit 0
