From 076b8c5a1f093f74a6b211bf0d7a81ef70b0687a Mon Sep 17 00:00:00 2001
From: I-Al-Istannen <i-al-istannen@users.noreply.github.com>
Date: Thu, 23 Apr 2020 18:29:20 +0200
Subject: [PATCH] Add download strategies to save bandwith

Only download files that are newer than the local version.
---
 PFERD/__init__.py            |  1 +
 PFERD/download_strategies.py | 80 ++++++++++++++++++++++++++++++++++++
 PFERD/ilias/downloader.py    |  4 +-
 PFERD/pferd.py               | 12 +++++-
 4 files changed, 93 insertions(+), 4 deletions(-)
 create mode 100644 PFERD/download_strategies.py

diff --git a/PFERD/__init__.py b/PFERD/__init__.py
index 87131ce..9759e22 100644
--- a/PFERD/__init__.py
+++ b/PFERD/__init__.py
@@ -7,6 +7,7 @@ more complex configuration, you need to import the other submodules manually.
 
 import logging
 
+from .download_strategies import *
 from .pferd import Pferd
 
 STYLE = "{"
diff --git a/PFERD/download_strategies.py b/PFERD/download_strategies.py
new file mode 100644
index 0000000..974fa61
--- /dev/null
+++ b/PFERD/download_strategies.py
@@ -0,0 +1,80 @@
+"""
+Contains a few default strategies for limiting the amount of downloaded files.
+"""
+
+import datetime
+import logging
+from abc import ABC, abstractmethod
+from pathlib import Path
+from typing import Optional
+
+from typing_extensions import Protocol, runtime_checkable
+
+from .organizer import Organizer
+from .utils import PrettyLogger
+
+LOGGER = logging.getLogger(__name__)
+PRETTY = PrettyLogger(LOGGER)
+
+
+@runtime_checkable
+class DownloadInfo(Protocol):
+    # pylint: disable=too-few-public-methods
+    """
+    This class describes some minimal information about a file you can download.
+    """
+
+    @property
+    def path(self) -> Path:
+        """
+        Returns the path.
+        """
+
+    @property
+    def modification_date(self) -> Optional[datetime.datetime]:
+        """
+        Returns the modification date or None if not known.
+        """
+
+
+class DownloadStrategy(ABC):
+    # pylint: disable=too-few-public-methods
+    """
+    A strategy deciding whether to download a given info.
+    """
+
+    @abstractmethod
+    def should_download(self, organizer: Organizer, info: DownloadInfo) -> bool:
+        """
+        Decides wether a given file should be downloaded.
+        """
+
+
+class DownloadEverythingStrategy(DownloadStrategy):
+    # pylint: disable=too-few-public-methods
+    """
+    A strategy that redownloads everything.
+    """
+
+    def should_download(self, organizer: Organizer, info: DownloadInfo) -> bool:
+        return True
+
+
+class DownloadNewOrModified(DownloadStrategy):
+    # pylint: disable=too-few-public-methods
+    """
+    A strategy that only downloads changed or new files.
+    """
+
+    def should_download(self, organizer: Organizer, info: DownloadInfo) -> bool:
+        resolved_file = organizer.resolve(info.path)
+        if not resolved_file.exists() or info.modification_date is None:
+            return True
+        resolved_mod_time_seconds = resolved_file.stat().st_mtime
+
+        # Download if the info is newer
+        if info.modification_date.timestamp() > resolved_mod_time_seconds:
+            return True
+
+        PRETTY.filtered_path(info.path, "Local file had newer or equal modification time")
+        return False
diff --git a/PFERD/ilias/downloader.py b/PFERD/ilias/downloader.py
index 88e6792..9a6c785 100644
--- a/PFERD/ilias/downloader.py
+++ b/PFERD/ilias/downloader.py
@@ -3,7 +3,7 @@
 import datetime
 from dataclasses import dataclass
 from pathlib import Path
-from typing import List
+from typing import List, Optional
 
 import bs4
 import requests
@@ -26,7 +26,7 @@ class IliasDownloadInfo(Transformable):
     """
 
     url: str
-    modification_date: datetime.datetime
+    modification_date: Optional[datetime.datetime]
     # parameters: Dict[str, Any] = field(default_factory=dict)
 
 
diff --git a/PFERD/pferd.py b/PFERD/pferd.py
index ff2743f..de61da5 100644
--- a/PFERD/pferd.py
+++ b/PFERD/pferd.py
@@ -2,6 +2,7 @@ from pathlib import Path
 from typing import Optional
 
 from .cookie_jar import CookieJar
+from .download_strategies import DownloadEverythingStrategy, DownloadStrategy
 from .ilias import (IliasAuthenticator, IliasCrawler, IliasDirectoryFilter,
                     IliasDownloader, KitShibbolethAuthenticator)
 from .organizer import Organizer
@@ -9,7 +10,6 @@ from .tmp_dir import TmpDir
 from .transform import Transform, apply_transform
 from .utils import Location
 
-
 # TODO save known-good cookies as soon as possible
 # TODO print synchronizer name before beginning synchronization
 
@@ -31,6 +31,7 @@ class Pferd(Location):
             cookies: Optional[Path],
             dir_filter: IliasDirectoryFilter,
             transform: Transform,
+            download_strategy: DownloadStrategy,
     ) -> None:
         cookie_jar = CookieJar(cookies)
         session = cookie_jar.create_session()
@@ -43,7 +44,12 @@ class Pferd(Location):
         cookie_jar.load_cookies()
         info = crawler.crawl()
         cookie_jar.save_cookies()
-        downloader.download_all(apply_transform(transform, info))
+        downloader.download_all(
+            [
+                info for info in apply_transform(transform, info)
+                if download_strategy.should_download(organizer, info)
+            ]
+        )
         cookie_jar.save_cookies()
 
     def ilias_kit(
@@ -55,6 +61,7 @@ class Pferd(Location):
             cookies: Optional[Path] = None,
             username: Optional[str] = None,
             password: Optional[str] = None,
+            download_strategy: DownloadStrategy = DownloadEverythingStrategy(),
     ) -> None:
         # This authenticator only works with the KIT ilias instance.
         authenticator = KitShibbolethAuthenticator(username=username, password=password)
@@ -66,4 +73,5 @@ class Pferd(Location):
             cookies=cookies,
             dir_filter=dir_filter,
             transform=transform,
+            download_strategy=download_strategy,
         )