Edit Book: When using the arrange into folders tool do not change the case of already existing folders in the book. Fixes #1633875 [Editor:Arrange Folders problem on Windows](https://bugs.launchpad.net/calibre/+bug/1633875)

src/calibre/ebooks/oeb/polish/container.py

@@ -484,7 +484,7 @@ class Container(ContainerBase):  # {{{
         return name_to_abspath(name, self.root)
 
     def exists(self, name):
-        ''' True iff a file corresponding to the canonical name exists. Note
+        ''' True iff a file/directory corresponding to the canonical name exists. Note
         that this function suffers from the limitations of the underlying OS
         filesystem, in particular case (in)sensitivity. So on a case
         insensitive filesystem this will return True even if the case of name

src/calibre/ebooks/oeb/polish/replace.py

@@ -267,10 +267,25 @@ def get_recommended_folders(container, names):
     return {n:recommendations.get(mt_to_category(container, guess_type(os.path.basename(n))), opf_folder) for n in names}
 
 
+def normalize_case(container, val):
+    parts = val.split('/')
+    ans = []
+    for i in range(len(parts)):
+        q = '/'.join(parts[:i+1])
+        x = container.name_to_abspath(q)
+        xl = parts[i].lower()
+        candidates = [c for c in os.listdir(os.path.dirname(x)) if c != parts[i] and c.lower() == xl]
+        ans.append(candidates[0] if candidates else parts[i])
+    return '/'.join(ans)
+
+
 def rationalize_folders(container, folder_type_map):
     all_names = set(container.mime_map)
     new_names = set()
     name_map = {}
+    for key in tuple(folder_type_map):
+        val = folder_type_map[key]
+        folder_type_map[key] = normalize_case(container, val)
     for name in all_names:
         if name.startswith('META-INF/'):
             continue

src/calibre/ebooks/oeb/polish/tests/container.py

@@ -12,7 +12,7 @@ from zipfile import ZipFile
 from calibre import CurrentDir
 from calibre.ebooks.oeb.polish.tests.base import BaseTest, get_simple_book, get_split_book
 from calibre.ebooks.oeb.polish.container import get_container as _gc, clone_container, OCF_NS
-from calibre.ebooks.oeb.polish.replace import rename_files
+from calibre.ebooks.oeb.polish.replace import rename_files, rationalize_folders
 from calibre.ebooks.oeb.polish.split import split, merge
 from calibre.utils.filenames import nlinks_file
 from calibre.ptempfile import TemporaryFile, TemporaryDirectory
@@ -264,3 +264,12 @@ class ContainerTests(BaseTest):
                 self.assertTrue(os.path.exists('.git/xxx'))
                 self.assertTrue(os.path.exists('images/test-container.xyz'))
                 self.assertFalse(os.path.exists('images/cover.jpg'))
+
+    def test_folder_type_map_case(self):
+        book = get_simple_book()
+        c = get_container(book)
+        c.add_file('Image/testcase.png', b'xxx')
+        rationalize_folders(c, {'image':'image'})
+        self.assertTrue(c.has_name('Image/testcase.png'))
+        self.assertTrue(c.exists('Image/testcase.png'))
+        self.assertFalse(c.has_name('image/testcase.png'))