Begin implementing strategy selection

Right now this is still unexposed to the users.
Pretty-printing the foliating plan is somewhat of
a problem. Hopefully they are always quite small.

foliator.py

@@ -1,9 +1,10 @@
 #!/usr/bin/env python3
 
 import argparse
-from pypdf import PaperSize, PdfReader, PdfWriter, Transformation
-from pypdf.annotations import Line
+import numpy as np
+from pypdf import PaperSize, PdfReader, PdfWriter, Transformation, PageObject
 from pypdf.generic import ArrayObject, FloatObject, NameObject
+from pypdf.annotations import Line
 import math
 
 
@@ -38,7 +39,7 @@ def append_folio_A6(input_pdf, offset, size, append_to):
 # num_sheets = max_folio_size * a + (max_folio_size - k) * b
 # where k is minimal. We let n = max_folio_size and L = num_sheets.
 # Note that when L > n^2, then k = 1 must succeed.
-def find_partition(num_sheets, max_folio_size):
+def find_partition_mink(num_sheets, max_folio_size):
     max_a = num_sheets // max_folio_size
     for k in range(1, max_folio_size):
         # We want to solve a*k = L (mod n-k). This happens iff
@@ -57,7 +58,12 @@ def find_partition(num_sheets, max_folio_size):
         # substracting almost mprime.
         candidate = max_a - tosub
         if (candidate >= 0):
-            return (candidate, k)
+            b = (num_sheets - max_folio_size * candidate)//(max_folio_size - k)
+            return [max_folio_size] * candidate + [max_folio_size - k] * b
+
+def find_partition_greedy(num_sheets, max_folio_size):
+    q = num_sheets//max_folio_size
+    return [max_folio_size] * q + [num_sheets - q*max_folio_size]
 
 # Interprets input_pdf as a list of A6 pages, and appends to append_to with
 # A5 pages using the following rules:
@@ -65,23 +71,29 @@ def find_partition(num_sheets, max_folio_size):
 #      with "mirror around **short** edge"
 #   b. when grouped as consecutive sequences of max_folio_size or less, the printed
 #      sheets can be folded in the middle and assembled as a folio
-def foliate_A6(input_pdf, max_folio_size=-1, append_to=PdfWriter()):
-    current_page = 0
+def foliate_A6(input_pdf, strat_func, max_folio_size, append_to=PdfWriter()):
     doc_length = len(input_pdf.pages)
     writer = append_to
-    if max_folio_size < 0:
-        max_folio_size = doc_length
+
+    num_sheets = math.ceil(doc_length/4.0)
+    print("Using", num_sheets, "two-sided A5 sheets")
+
+    L = [num_sheets]
+    if max_folio_size > 0:
+        L = strat_func(num_sheets, max_folio_size)
+
+    if(np.sum(L) != num_sheets):
+        print("[ERROR] strategy gave", np.sum(L), " A5 sheets")
+        exit(1)
 
     folio_page_size = 0
-    while(current_page < doc_length):
-        # max_folio_size is a number of _sheets_, each containing 4 pages
-        folio_page_size = min(doc_length - current_page, 4*max_folio_size)
+    current_page = 0
+    for l in L:
+        # l is a number of _sheets_, each containing 4 pages
+        folio_page_size = min(doc_length - current_page, 4*l)
         append_folio_A6(input_pdf, current_page, folio_page_size, append_to)
         current_page += folio_page_size
 
-    print("Dangling folio has",folio_page_size,"pages",
-          "(",int(math.ceil(folio_page_size/4.0)),"sheets).")
-
     return writer
 
 # Take an A5 printing plan, with odd/even pages being understood
@@ -106,7 +118,7 @@ def blit_to_A4(input_pdf, append_to=PdfWriter()):
             writer.add_annotation(front_page, midline)
 
         front = input_pdf.pages[k]
-        back = input_pdf.pages[k+1] if (k+1<L) else create_blank_page(None, PaperSize.A5.width, PaperSize.A5.height)
+        back = input_pdf.pages[k+1] if (k+1<L) else PageObject.create_blank_page(None, PaperSize.A5.width, PaperSize.A5.height)
 
         front.mediabox = front_page.mediabox
         back.mediabox  = back_page.mediabox
@@ -129,7 +141,7 @@ parser.add_argument("-fs", help="maximum folio size, in sheets",
 args = parser.parse_args()
 
 input_pdf = PdfReader(args.infile)
-a5 = foliate_A6(input_pdf, args.fs)
+a5 = foliate_A6(input_pdf, find_partition_greedy, args.fs)
 if (args.a5):
     a5.write(args.outfile)
 else:

shell.nix

@@ -6,6 +6,7 @@ pkgs.mkShell {
   packages = [
   (pkgs.python3.withPackages (pythonPackages: with python3Packages; [
     pypdf
+    numpy
   ]))
   ];
 }