[wikiart] add extractor for single paintings (closes #1233)

There is no API endpoint for single paintings from what I can tell,
so this uses the site's search.

gallery_dl/extractor/wikiart.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-# Copyright 2019-2020 Mike Fährmann
+# Copyright 2019-2021 Mike Fährmann
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 as
@@ -40,7 +40,7 @@ class WikiartExtractor(Extractor):
     def paintings(self):
         """Return an iterable containing all relevant 'painting' objects"""
 
-    def _pagination(self, url, extra_params=None, key="Paintings"):
+    def _pagination(self, url, extra_params=None, key="Paintings", stop=False):
         headers = {
             "X-Requested-With": "XMLHttpRequest",
             "Referer": url,
@@ -60,6 +60,8 @@ class WikiartExtractor(Extractor):
             if not items:
                 return
             yield from items
+            if stop:
+                return
             params["page"] += 1
 
 
@@ -67,7 +69,7 @@ class WikiartArtistExtractor(WikiartExtractor):
     """Extractor for an artist's paintings on wikiart.org"""
     subcategory = "artist"
     directory_fmt = ("{category}", "{artist[artistName]}")
-    pattern = BASE_PATTERN + r"/(?!\w+-by-)([\w-]+)"
+    pattern = BASE_PATTERN + r"/(?!\w+-by-)([\w-]+)/?$"
     test = ("https://www.wikiart.org/en/thomas-cole", {
         "url": "5ba2fbe6783fcce34e65014d16e5fbc581490c98",
         "keyword": "6d92913c55675e05553f000cfee5daff0b4107cf",
@@ -75,18 +77,50 @@ class WikiartArtistExtractor(WikiartExtractor):
 
     def __init__(self, match):
         WikiartExtractor.__init__(self, match)
-        self.artist = match.group(2)
+        self.artist_name = match.group(2)
+        self.artist = None
 
     def metadata(self):
-        url = "{}/{}/{}?json=2".format(self.root, self.lang, self.artist)
-        return {"artist": self.request(url).json()}
+        url = "{}/{}/{}?json=2".format(self.root, self.lang, self.artist_name)
+        self.artist = self.request(url).json()
+        return {"artist": self.artist}
 
     def paintings(self):
         url = "{}/{}/{}/mode/all-paintings".format(
-            self.root, self.lang, self.artist)
+            self.root, self.lang, self.artist_name)
         return self._pagination(url)
 
 
+class WikiartImageExtractor(WikiartArtistExtractor):
+    """Extractor for individual paintings on wikiart.org"""
+    subcategory = "image"
+    pattern = BASE_PATTERN + r"/(?!(?:paintings|artists)-by-)([\w-]+)/([\w-]+)"
+    test = (
+        ("https://www.wikiart.org/en/thomas-cole/the-departure-1838", {
+            "url": "4d9fd87680a2620eaeaf1f13e3273475dec93231",
+            "keyword": "a1b083d500ce2fd364128e35b026e4ca526000cc",
+        }),
+        # no year or '-' in slug
+        ("https://www.wikiart.org/en/huang-shen/summer", {
+            "url": "d7f60118c34067b2b37d9577e412dc1477b94207",
+        }),
+    )
+
+    def __init__(self, match):
+        WikiartArtistExtractor.__init__(self, match)
+        self.title = match.group(3)
+
+    def paintings(self):
+        title, sep, year = self.title.rpartition("-")
+        if not sep or not year.isdecimal():
+            title = self.title
+        url = "{}/{}/Search/{} {}".format(
+            self.root, self.lang,
+            self.artist.get("artistName") or self.artist_name, title,
+        )
+        return self._pagination(url, stop=True)
+
+
 class WikiartArtworksExtractor(WikiartExtractor):
     """Extractor for artwork collections on wikiart.org"""
     subcategory = "artworks"