"""
display all images in a directory as thumbnail image buttons that display 
the full image when clicked; requires PIL for JPEGs and thumbnail image 
creation;  to do: add scrolling if too many thumbs for window!
"""

import os, sys, math
from tkinter import *
from PIL import Image                   # <== required for thumbs
from PIL.ImageTk import PhotoImage      # <== required for JPEG display

def makeThumbs(imgdir, size=(100, 100), subdir='thumbs'):
    """
    get thumbnail images for all images in a directory; for each image, create 
    and save a new thumb, or load and return an existing thumb;  makes thumb  
    dir if needed;  returns a list of (image filename, thumb image object);  
    caller can also run listdir on thumb dir to load;  on bad file types may 
    raise IOError, or other;  caveat: could also check file timestamps;
    """
    thumbdir = os.path.join(imgdir, subdir)
    if not os.path.exists(thumbdir):
        os.mkdir(thumbdir)

    thumbs = []
    for imgfile in os.listdir(imgdir):
        thumbpath = os.path.join(thumbdir, imgfile)
        if os.path.exists(thumbpath):
            thumbobj = Image.open(thumbpath)            # use already created
            thumbs.append((imgfile, thumbobj))
        else:
            print('making', thumbpath)
            imgpath = os.path.join(imgdir, imgfile)
            try:
                imgobj = Image.open(imgpath)            # make new thumb
                imgobj.thumbnail(size, Image.ANTIALIAS) # best downsize filter
                imgobj.save(thumbpath)                  # type via ext or passed
                thumbs.append((imgfile, imgobj))
            except:                                     # not always IOError
                print("Skipping: ", imgpath)
    return thumbs

class ViewOne(Toplevel):
    """
    open a single image in a pop-up window when created;  photoimage
    object must be saved: images are erased if object is reclaimed;
    """
    def __init__(self, imgdir, imgfile):
        Toplevel.__init__(self)
        self.title(imgfile)
        imgpath = os.path.join(imgdir, imgfile)
        imgobj  = PhotoImage(file=imgpath)
        Label(self, image=imgobj).pack()
        print(imgpath, imgobj.width(), imgobj.height())   # size in pixels
        self.savephoto = imgobj                           # keep reference on me

def viewer(imgdir, kind=Toplevel, cols=None):
    """
    make thumb links window for an image directory: one thumb button per image; 
    use kind=Tk to show in main  app window, or Frame container (pack);  imgfile
    differs per loop: must save with a default;  photoimage objs must be saved: 
    erased if reclaimed; packed row frames (versus grids, fixed-sizes, canvas); 
    """
    win = kind()
    win.title('Viewer: ' + imgdir)
    quit = Button(win, text='Quit', command=win.quit)          # pack first:
    quit.pack(fill=X, side=BOTTOM)                             # so clip last
    thumbs = makeThumbs(imgdir)
    if not cols:
        cols = int(math.ceil(math.sqrt(len(thumbs))))          # fixed or N x N

    savephotos = []
    while thumbs:
        thumbsrow, thumbs = thumbs[:cols], thumbs[cols:]
        row = Frame(win)
        row.pack(fill=BOTH, expand=YES)
        for (imgfile, imgobj) in thumbsrow:
            photo   = PhotoImage(imgobj)
            link    = Button(row, image=photo)
            handler = lambda savefile=imgfile: ViewOne(imgdir, savefile)
            link.config(command=handler)
            link.pack(side=LEFT, expand=YES, fill=X)
            savephotos.append(photo)
    return win, savephotos

if __name__ == '__main__':
    imgdir = (len(sys.argv) > 1 and sys.argv[1]) or 'images'
    main, save = viewer(imgdir, kind=Tk)
    main.mainloop()