#!/bin/sh -pe

lang=$1
validated_language=

test -n "$lang" || exit 1

langtoolsdir=/usr/share/language-tools

#
# discard possible fallback languages
#
lang=${lang%%:*}

#
# remove possible encoding part
#
if [ $lang != ${lang%.utf8*} ]; then
    lang=${lang%.*}${lang#*.utf8}
elif [ $lang != ${lang%.UTF-8*} ]; then
    lang=${lang%.*}${lang#*.UTF-8}
fi

#
# make sure that the output is a valid language option
#
options=$( $langtoolsdir/language-options )

# exact match
for opt in $options; do
    if [ $opt = $lang ]; then
        validated_language=$lang
        break
    fi
done

if [ -z "$validated_language" ]; then
    langcode=${lang%%[_@]*}

    # try the "main" country code if any
    main_country=
    is_variant=false
    while read line; do
        if [ "${line%%[[:space:]]*}" = $langcode ]; then
            main_country=${line##*[[:space:]]}
            if [ $lang != ${lang#*@} ]; then
                main_country=$main_country@${lang#*@}
                is_variant=true
            fi
            break
        fi
    done < $langtoolsdir/main-countries
    if [ -n "$main_country" ]; then
        for opt in $options; do
            if [ $main_country = $opt ]; then
                validated_language=$main_country
                break
            fi
        done
    fi

    # try out fitting language option without paying regard to
    # country code
    if [ -z "$validated_language" ]; then
        for opt in $options; do
            if [ "${opt%%[_@]*}" = $langcode -a $langcode != 'zh' ]; then
                if $is_variant && [ $opt = ${opt#*@} ]; then
                    continue
                fi
                validated_language=$opt
                break
            fi
        done
    fi
fi

if [ -z "$validated_language" ]; then
    validated_language='en'
fi

echo $validated_language