#!/bin/sh
# author jjm2473

BING_BASE=http://www.bing.com
CACHE=/var/run/argon_bing.url
WRLOCK=/var/lock/argon_bing.lock

fetch_url_path() {
    curl --fail --show-error --max-time 1 \
        "$BING_BASE/HPImageArchive.aspx?format=js&idx=0&n=1&mkt=en-US" 2>/dev/null \
        | jsonfilter -q -e '@.images[0].url'
}

try_update() {
    local lock="$WRLOCK"
    exec 200>$lock

    if flock -n 200 >/dev/null 2>&1; then
        local path=`fetch_url_path`
        if [ -n "$path" ]; then
            echo "${BING_BASE}${path}" | tee "$CACHE"
        else
            if [ -s "$CACHE" ]; then
                cat "$CACHE"
            else
                touch "$CACHE"
            fi
        fi
        flock -u 200 >/dev/null 2>&1
    elif [ -s "$CACHE" ]; then
        cat "$CACHE"
    fi
}

get_url() {
    if [ -f "$CACHE" ]; then
        local idle_t=$((`date '+%s'` - `date -r "$CACHE" '+%s' 2>/dev/null || echo '0'`))
        if [ -s "$CACHE" ]; then
            if [ $idle_t -le 43200 ]; then
                cat "$CACHE"
                return
            fi
        else
            if [ $idle_t -le 120 ]; then
                return
            fi
        fi
    fi
    try_update
}

get_url