buildmimetree.py: keep track of last I/O operation

diff --git a/.config/neomutt/buildmimetree.py b/.config/neomutt/buildmimetree.py
index 32fc17c005b613055a3dc42fdb8f744f148652e4..2ad671a839d632a87eae622358efab1dccaa086d 100755 (executable)
--- a/.config/neomutt/buildmimetree.py
+++ b/.config/neomutt/buildmimetree.py
@@ -46,6 +46,7 @@ import mimetypes
 import bs4
 import xml.etree.ElementTree as etree
 import io
+import enum
 from collections import namedtuple, OrderedDict
 from markdown.extensions import Extension
 from markdown.blockprocessors import BlockProcessor
@@ -171,6 +172,11 @@ def parse_cli_args(*args, **kwargs):
 
 
 class File:
+
+    class Op(enum.Enum):
+        R = enum.auto()
+        W = enum.auto()
+
     def __init__(self, path=None, mode="r", content=None, **kwargs):
         if path:
             if content:
@@ -185,8 +191,11 @@ class File:
         if content and not re.search(r"[r+]", mode):
             raise RuntimeError("Cannot specify content without read mode")
 
-        self._rcache = [content] if content else []
-        self._wcache = []
+        self._cache = {
+            File.Op.R: [content] if content else [],
+            File.Op.W: []
+        }
+        self._lastop = None
         self._mode = mode
         self._kwargs = kwargs
         self._file = None
@@ -209,48 +218,57 @@ class File:
     def close(self):
         self._file.close()
         self._file = None
-        self._rcache = self._wcache
-
-    def _get_rcache(self):
-        return (b"" if "b" in self._mode else "").join(self._rcache)
+        self._cache[File.Op.R] = self._cache[File.Op.W]
+        self._lastop = None
 
-    def _get_wcache(self):
-        return (b"" if "b" in self._mode else "").join(self._wcache)
+    def _get_cache(self, op):
+        return (b"" if "b" in self._mode else "").join(self._cache[op])
 
-    def _add_to_rcache(self, s):
-        self._rcache.append(s)
-
-    def _add_to_wcache(self, s):
-        self._wcache.append(s)
+    def _add_to_cache(self, op, s):
+        self._cache[op].append(s)
 
     def read(self, *, cache=True):
-        if cache and self._rcache:
-            return self._get_rcache()
+        if cache and self._cache[File.Op.R]:
+            return self._get_cache(File.Op.R)
 
         if not self._file:
             with self as f:
                 return f.read(cache=cache)
 
-        self._file.seek(0)
+        if self._lastop == File.Op.W:
+            try:
+                self._file.seek(0)
+            except io.UnsupportedOperation:
+                pass
+
+        self._lastop = File.Op.R
+
         if cache:
-            self._add_to_rcache(self._file.read())
-            return self._get_rcache()
+            self._add_to_cache(File.Op.R, self._file.read())
+            return self._get_cache(File.Op.R)
         else:
             return self._file.read()
 
     def write(self, s, *, cache=True):
+
         if not self._file:
             with self as f:
                 return f.write(s, cache=cache)
 
-        self._file.seek(0)
-        self._rcache = self._wcache
+        if self._lastop == File.Op.R:
+            try:
+                self._file.seek(0)
+            except io.UnsupportedOperation:
+                pass
 
         if cache:
-            self._add_to_wcache(s)
+            self._add_to_cache(File.Op.W, s)
+
+        self._cache[File.Op.R] = self._cache[File.Op.W]
 
         written = self._file.write(s)
         self._file.flush()
+        self._lastop = File.Op.W
         return written
 
     path = property(lambda s: s._path)