local pstring  = require( 'Module:GetString' ) local p856     = require( 'Module:GetP856' ) local images   = require( 'Module:GetImage' ) local items    = require( 'Module:GetItem' )  -- returns nil, if both values are equal, otherwise the value -- similar to the SQL function nullif() local function nilIf ( value, equalValue )     if ( value == nil ) then       return nil    elseif ( tostring ( value ) == tostring ( equalValue ) ) then       return nil    else       return value    end  end  -- returns the first value that is not nil -- similar to the SQL function coalesce() local function coalesce ( value1, value2, value3 )    return value1 or value2 or value3 end  -- returns a manually created quickbar row local function createTr ( text, label, trClass )     -- check for valid text    -- if there is no text, then display nothing    if text == '' then         return ''     else        -- displaying the given info       local tr = mw.html.create ( 'tr' )       tr:addClass('voy-qb-item ' .. trClass )          :tag('th')          :addClass('voy-qb-item-key')          :wikitext( label )       tr:tag('td')          :addClass( 'voy-qb-item-value1' )          :wikitext( text )       return tostring ( tr )    end  end  local qbAirline = {}  function qbAirline.qb_airline ( frame )       -- copying and lowering the given parameters    local templateArgs = {}    for key,value in pairs ( frame.args ) do       templateArgs[string.lower(key)] = value    end    for key,value in pairs ( frame:getParent().args ) do       templateArgs[string.lower(key)] = value    end     -- variables for the whole quickbar content and the categories    local display = ''        -- getting or determining (if needed) the wikidata-ID    if templateArgs.id == '' then templateArgs.id = nil end    local qbID = nilIf ( nilIf ( templateArgs.id, 'self' ), '' ) or mw.wikibase.getEntityIdForCurrentPage() or ''     -- starting the quickbar table    display = display .. '<div class="voy-qb-rightdiv"><table cellspacing="0" class="voy-qb voy-qb-airline">'     -- Logo    -- always taken from Wikidata    display = display .. images.GetImage().getEmblemsQuickbar ( qbID, 'L' )     -- the main image    -- taken from Wikidata, if not provided    display = display .. images.GetImage().getMainImageQuickbar ( qbID, coalesce ( templateArgs["bild"], '' ) )     -- heading    -- is mandatory, even if you do not provide it, its shown (with the sitename)    -- initialising with given heading    local qbNamen = coalesce ( templateArgs["namen"], '' )        -- if no heading is provided, get the sitename    if qbNamen == '' then       local page = {}       page = mw.title.getCurrentTitle()         if qbID ~= '' then           qbNamen = coalesce ( mw.wikibase.getSitelink( qbID, 'dewikivoyage' ), page.text, 'Fluggesellschaft')       else          qbNamen = coalesce ( page.text, 'Fluggesellschaft')       end    end        -- creating the row with the heading    local trHeader = mw.html.create ( 'tr' )    trHeader:addClass( 'voy-qb-item' )    trHeader:tag('td')       :attr('colspan', 2 )       :addClass('voy-qb-header' )       :wikitext(qbNamen)    -- adding it to the quickbar    display = display .. tostring ( trHeader )     -- variable for a single quickbar row    local tr = ''        -- general information:    -- an entry is only added when the parameter is used    -- if the parameter is empty, the information is fetched from Wikidata    -- if the parameter is not empty, the local information is used, but mostly compared Wikidata, and maintenance categories are used    -- the parameter with the value "no" deactivates the entry     -- IATA Code    -- always shown and take from Wikidata    display = display .. pstring.GetString().getStringsQuickbar ( qbID, 'P229', nil, coalesce ( templateArgs["iata"], '' ) )     -- headquarters    display = display .. items.GetItem().getItemsQuickbar ( qbID, 'P159', coalesce ( templateArgs["sitz"], ''), 'Sitz' )     -- main hub    display = display .. items.GetItem().getItemsQuickbar ( qbID, 'P113', coalesce ( templateArgs["drehkreuz"], '' ) )     -- passengers    display = display .. createTr ( coalesce ( templateArgs["passagieraufkommen"], '' ), 'Passagieraufkommen', 'voy-qb-passengers' )     -- destinations    display = display .. createTr ( coalesce ( templateArgs["ziele"], '' ), 'Ziele', 'voy-qb-destinations' )     -- alliance    display = display .. items.GetItem().getItemsQuickbar ( qbID, 'P114', coalesce ( templateArgs["allianz"], '' ) )     -- reward program    display = display .. items.GetItem().getItemsQuickbar ( qbID, 'P4446', coalesce ( templateArgs["bonusprogramm"], '' ) )        -- subsidiaries    display = display .. items.GetItem().getItemsQuickbar ( qbID, 'P355', coalesce ( templateArgs["tochtergesellschaften"], '' ) )        -- website    display = display .. p856.GetP856().getUrlAsLinkWithHostQuickbar ( qbID, coalesce ( templateArgs["webseite"], '' ) )     -- phone number    -- not from Wikidata because it's country specific    display = display .. createTr ( coalesce ( templateArgs["telefon"], '' ), 'Telefon', 'voy-qb-phone' )     -- finishing the HTML table    display = display .. '</table></div>'     return display     end  return qbAirline