property |NSURL| : a reference to current application’s |NSURL|
property NSString : a reference to current application’s NSString
property NSImage : a reference to current application’s NSImage
property NSScreen : a reference to current application’s NSScreen
property NSNumber : a reference to current application’s NSNumber
property NSZeroPoint : a reference to current application’s NSZeroPoint
property PDFDocument : a reference to current application’s PDFDocument
property NSJPEGFileType : a reference to current application’s NSJPEGFileType
property NSCompositeCopy : a reference to current application’s NSCompositeCopy
property NSGraphicsContext : a reference to current application’s NSGraphicsContext
property NSBitmapImageRep : a reference to current application’s NSBitmapImageRep
property NSNumberFormatter : a reference to current application’s NSNumberFormatter
property NSImageInterpolationHigh : a reference to current application’s NSImageInterpolationHigh

tell application "Skim"
　　set docCount to count every document
　　if docCount = 0 then return
　　
　　tell front document
　　　　set curViewSets to view settings
　　　　set curMode to display mode of curViewSets
　　　　
　　　　if curMode is not in {two up, two up continuous} then
　　　　　　display dialog "２ページ見開きモードでないため、処理を終了します。" with title "error" with icon 0
　　　　　　return
　　　　end if
　　　　
　　　　set bMode to displays as book of curViewSets
　　　　if bMode = false then
　　　　　　display dialog "「書籍モード」でないため、処理を終了します。" with title "error" with icon 0
　　　　　　return
　　　　end if
　　　　
　　　　set curInd to index of current page
　　　　set docFile to file of it
　　end tell
end tell

–PDFのファイルパスから実際のPDFを求める
set aPOSIX to POSIX path of docFile
set aURL to (|NSURL|’s fileURLWithPath:aPOSIX)
set aPDFdoc to PDFDocument’s alloc()’s initWithURL:aURL

–PDFのページ数を求める
set pCount to aPDFdoc’s pageCount() –ページ数

if curInd = pCount then
　　display dialog "このページはPDFの最終ページなので、見開き表示になっていない可能性があります。" with title "エラー"
　　return
end if

if curInd = 1 then
　　display dialog "このページはPDFの最初のページなので、見開き表示になっていない可能性があります。" with title "エラー"
　　return
end if

–見開き中の選択ページが奇数（右ページ）だった場合の対処
if chkOddNum(curInd) = true then set curInd to curInd – 1

–Detect Retina Environment
set compFactor to 1.0 –1.0 — 0.0 = max jpeg compression, 1.0 = none

set retinaF to NSScreen’s mainScreen()’s backingScaleFactor()
if retinaF = 1.0 then
　　set aScale to 2.0 –Non Retina Env
else
　　set aScale to 1.0 –Retina Env
end if

–Pick Up a PDF page as an image (Left Side Page)
set thisPageL to (aPDFdoc’s pageAtIndex:(curInd – 1))
set imgL to (NSImage’s alloc()’s initWithData:(thisPageL’s dataRepresentation()))
set pageL to renderPDFPageToNSImage(imgL, (curInd – 1), aScale) of me

–Pick Up a PDF page as an image (Right Side Page)
set thisPageR to (aPDFdoc’s pageAtIndex:(curInd – 0))
set imgR to (NSImage’s alloc()’s initWithData:(thisPageR’s dataRepresentation()))
set pageR to renderPDFPageToNSImage(imgR, (curInd – 0), aScale) of me

–Calc 2 pages’ width and others
set origWidth to (pageR’s |size|()’s width)
set newWidth to origWidth * 2
set newHeight to pageR’s |size|()’s height

–Make 2 pages’ blank image
set aSize to current application’s NSMakeSize(newWidth, newHeight)
set newImage to NSImage’s alloc()’s initWithSize:aSize

–Compositte each Left and Right page image
overlayNSImageByLeftTopOrigin(newImage, pageL, {0, 0}) of me
overlayNSImageByLeftTopOrigin(newImage, pageR, {origWidth, 0}) of me

–Save Image as JPEG
set theData to newImage’s TIFFRepresentation()
set newRep to (NSBitmapImageRep’s imageRepWithData:theData)
set targData to (newRep’s representationUsingType:(NSJPEGFileType) |properties|:{NSImageCompressionFactor:compFactor, NSImageProgressive:false})
set zText to retZeroPaddingText((curInd + 1), 4) of me
set outPath to addString_beforeExtensionIn_addingExtension_("_" & zText, aPOSIX, "jpg")
(targData’s writeToFile:outPath atomically:true) –書き出し

on renderPDFPageToNSImage(anImage, aPageNum, aScale)
　　set pointSize to anImage’s |size|()
　　
　　set newSize to current application’s NSMakeSize((pointSize’s width) * aScale, (pointSize’s height) * aScale)
　　set newImage to (NSImage’s alloc()’s initWithSize:newSize)
　　
　　newImage’s lockFocus()
　　(anImage’s setSize:newSize)
　　(NSGraphicsContext’s currentContext()’s setImageInterpolation:(NSImageInterpolationHigh))
　　(anImage’s drawAtPoint:(NSZeroPoint) fromRect:(current application’s CGRectMake(0, 0, newSize’s width, newSize’s height)) operation:(NSCompositeCopy) fraction:2.0)
　　newImage’s unlockFocus()
　　return newImage
end renderPDFPageToNSImage

–ファイルパス（POSIX path）に対して、文字列（枝番）を追加。任意の拡張子を追加
on addString:extraString beforeExtensionIn:aPath addingExtension:aExt
　　set pathString to NSString’s stringWithString:aPath
　　set theExtension to pathString’s pathExtension()
　　set thePathNoExt to pathString’s stringByDeletingPathExtension()
　　
　　set newPath to (thePathNoExt’s stringByAppendingString:extraString)’s stringByAppendingPathExtension:aExt
　　return newPath as string
end addString:beforeExtensionIn:addingExtension:

on retZeroPaddingText(aNum, aLen)
　　set tText to ("0000000000" & aNum as text)
　　set tCount to length of tText
　　set resText to text (tCount – aLen + 1) thru tCount of tText
　　return resText
end retZeroPaddingText

–2つのNSImageを重ね合わせ合成してNSImageで返す（x,yで配置座標を指定） –newImageを参照渡し
on overlayNSImageByLeftTopOrigin(newImage, composeImage, aTargPos as list)
　　set backSize to newImage’s |size|()
　　set bHeight to (height of backSize)
　　
　　set overlaySize to composeImage’s |size|()
　　copy aTargPos to {x1, tempy1}
　　set x2 to (width of overlaySize)
　　set y2 to (height of overlaySize)
　　set y1 to bHeight – y2 + tempy1
　　
　　newImage’s lockFocus()
　　
　　set bRect to {{x1, y1}, {x2, y2}} –macOS 10.13 or later
　　set newImageRect to {{0, 0}, (newImage’s |size|)}
　　newImage’s drawInRect:newImageRect
　　composeImage’s drawInRect:bRect
　　
　　newImage’s unlockFocus()
end overlayNSImageByLeftTopOrigin

on retUUIDfilePath(aPath, aExt)
　　set aUUIDstr to (NSUUID’s UUID()’s UUIDString()) as string
　　set aPath to ((NSString’s stringWithString:aPath)’s stringByDeletingLastPathComponent()’s stringByAppendingPathComponent:aUUIDstr)’s stringByAppendingPathExtension:aExt
　　return aPath
end retUUIDfilePath

–NSImageを指定パスにPNG形式で保存
on saveNSImageAtPathAsPNG(anImage, outPath)
　　set imageRep to anImage’s TIFFRepresentation()
　　set aRawimg to NSBitmapImageRep’s imageRepWithData:imageRep
　　set pathString to NSString’s stringWithString:outPath
　　set newPath to pathString’s stringByExpandingTildeInPath()
　　set myNewImageData to (aRawimg’s representationUsingType:(NSPNGFileType) |properties|:(missing value))
　　set aRes to (myNewImageData’s writeToFile:newPath atomically:true) as boolean
　　return aRes –true/false
end saveNSImageAtPathAsPNG

–奇数かどうかチェック
on chkOddNum(aNum)
　　set a to aNum mod 2
　　if a = 1 then
　　　　return true
　　else
　　　　return false
　　end if
end chkOddNum

–偶数かどうかチェック
on chkEvenNum(aNum)
　　set a to aNum mod 2
　　if a = 0 then
　　　　return true
　　else
　　　　return false
　　end if
end chkEvenNum