local LrApplication = import "LrApplication"
local LrDialogs = import "LrDialogs"
local LrExportSession = import "LrExportSession"
local LrPathUtils = import "LrPathUtils"
local LrProgressScope = import "LrProgressScope"
local LrTasks = import "LrTasks"

local catalog = LrApplication.activeCatalog ()
local photo = catalog:getTargetPhoto ()

local settings = {
    LR_DNG_compatibility = 117506048,
    LR_DNG_compressed = true,
    LR_DNG_conversionMethod = "preserveRAW",
    LR_DNG_embedCache = true,
    LR_DNG_embedRAW = false,
    LR_DNG_lossyCompression = true,
    LR_DNG_previewSize = "none",
    LR_embeddedMetadataOption = "all",
    LR_exportServiceProvider = "com.adobe.ag.export.file",
    LR_renamingTokensOn = true,
    LR_tokenCustomString = "",
    LR_tokens = "medium-lossless",
    LR_format = "DNG"}

settings.LR_export_destinationPathPrefix = 
    LrPathUtils.getStandardFilePath "desktop"

LrTasks.startAsyncTask (function ()

    for _, size in ipairs {"medium", "large"} do
    for _, compression in ipairs {false, true} do 
        settings.LR_DNG_previewSize = size
        settings.LR_DNG_lossyCompression = compression
        settings.LR_tokens = tostring (settings.LR_DNG_lossyCompression)
            .. "-" .. settings.LR_DNG_previewSize

        local session = LrExportSession {photosToExport = {photo}, 
            exportSettings = settings}
        session:doExportOnNewTask ()
        LrTasks.sleep (0.001) 
            --[[ If we don't sleep here, presumably to give the new export 
            task a chance to get started, we get "An internal error has 
            occurred. AgExportSession: startRendering: can not call twice 
            on the same session." Yet another LR race condition. ]]

        local scope = LrProgressScope {title = "Export " .. 
            LrPathUtils.leafName (photo.path)}
        local renditions = session:renditions {progressScope = scope, 
            renderProgressPortion = 1, stopIfCanceled = true}
        for _, rendition in renditions do
            local success, err = rendition:waitForRender ()
            LrDialogs.message ("waitForRender: " .. tostring (success) .. " " .. 
                err)
            end 
        scope:done ()
        end end
    end)