set api_key "some api key"
set user "some user"

package require http
package require tdom

#procedure to read metadata from id3tag
proc ___readMetadata {fn} {
        catch {set fh [open $fn r]} status
        if {[string match "*couldn't open*" $status]} {
                return -1
        }
        fconfigure $fh -encoding binary -translation binary
        seek $fh -128 end
        set tag [read $fh]
        close $fh
        binary scan $tag A3 id
        if {$id eq "TAG"} {
                binary scan $tag A3A30A30A30A4A28ccc id title artist album  year comment zero track genre
                return [list $title $artist $album $year $comment]
        } else {
                return -1
        }
}

#last.fm api
#artist.getInfo
proc ___artistGetInfo {artist} {
        global api_key
        set method "artist.getInfo"
        set query [::http::formatQuery method $method api_key $api_key artist $artist]
        return [___requestData $query]
}

#album.getinfo
proc ___albumGetInfo {artist album} {
        global api_key
        global user
        set method "album.getinfo"
        set query [::http::formatQuery method $method api_key $api_key artist $artist album $album user $user]
        return [___requestData $query]
}

#run query and return received data
proc ___requestData {query} {
        set r [::http::geturl http://ws.audioscrobbler.com/2.0/ -query $query]
        set data [::http::data $r]
        ::http::cleanup $r
        return $data        
}

#parse received xml
proc ___parseXML {xml data} {
        global xmlStruct
        set dom [dom parse $xml]
        set doc [$dom documentElement]
        foreach n $data {
                catch {set path $xmlStruct($n)} status
                if {[string match "*can't read*" $status]} {
                        puts "Element $n is not defined"
                        continue
                }
                set node [$doc selectNodes $path]
                if {[string length $node] > 0} {
                        lappend res [list $n [string trimleft [$node text]]]
                } else {
                        lappend res [list $n ""]
                }
        }
        return $res
}

#save picture under name for entered ulr
proc ___savePicture {name url path} {
        catch {set fh [open [file join $path $name] w]} status
        if {[string match "*couldn't open*" $status]} {
                return -1
        }        
        fconfigure $fh -translation binary
        set imgtok [http::geturl $url -binary true -channel $fh]
        set Stat [::http::status $imgtok]
        flush $fh
        close $fh
        http::cleanup $imgtok
}



#define position of name artist and release date in the xml
set xmlStruct(album) "/lfm/album/name"
set xmlStruct(artist) "/lfm/album/artist"
set xmlStruct(releasedate) "/lfm/album/releasedate"
set xmlStruct(picture) {/lfm/album/image[@size='large']}

#example how to check album info, extract cover url and save it
proc ___getMetadata {artist album {path ""}} {
        set ret [___parseXML [___albumGetInfo $artist $album] {album artist releasedate picture}]
        foreach n $ret {
                puts $n
                switch [lindex $n 0] {
                        "picture" {
                                if {[string length [lindex $n 1]] > 5} {
                                        set nName [file split [lindex $n 1]]
                                        set nName [lindex $nName [expr [llength $nName] -1]]
                                        ___savePicture $nName [lindex $n 1] $path
                                        return $nName
                                }
                        }
                }
        }
}

#scan file, check metainfo via last.fm and save cove art
proc prepareCover {fileN path} {
        lassign [___readMetadata [file join $path $fileN]] title artist album year comment
        set pName [___getMetadata $artist $album]
}

prepareCover 02_test.mp3 ./