Add optional tweaking of the .gv output

Solves wireviz#174 intermediately by allowing low level .gv tweaking.

docs/syntax.md

@@ -35,6 +35,8 @@ additional_bom_items:  # custom items to add to BOM
   - <bom-item>           # BOM item (see below)
   ...
 
+tweak:  # optional tweaking of .gv output
+  ...
 ```
 
 ## Metadata entries
@@ -327,6 +329,30 @@ Alternatively items can be added to just the BOM by putting them in the section
   manufacturer: <str>  # manufacturer name  
 ```
 
+## Tweak entries
+
+```yaml
+  # Optional tweaking of the .gv output.
+  # This feature is experimental and might change
+  # or be removed in future versions.
+
+  override:  # dict of .gv entries to override
+    # Each entry is identified by its leading string
+    # in lines beginning with a TAB character.
+    # The leading string might be in "quotes" in 
+    # the .gv output. This leading string must be
+    # followed by attributes in [square brackets].
+    # Entries containing HTML in an attribute are
+    # not supported.
+    <str>:  # leading string of .gv entry
+      <str> : <str>  # attribute and its new value
+      # Any number of attributes can be overridden
+      # for each entry
+
+  append:  # single or list of .gv entries to append
+    <str>  # strings to append might have multiple lines
+```
+
 ## Colors
 
 Colors are defined via uppercase, two character strings.
@@ -403,6 +429,7 @@ The following attributes accept multiline strings:
 - `manufacturer`
 - `mpn`
 - `image.caption`
+- `tweak.append`
 
 ### Method 1
 

src/wireviz/DataClasses.py

@@ -59,6 +59,12 @@ def __post_init__(self):
             self.bgcolor_bundle = self.bgcolor_cable
 
 
+@dataclass
+class Tweak:
+    override: Optional[Dict[Designator, Dict[str, str]]] = None
+    append: Union[str, List[str], None] = None
+
+
 @dataclass
 class Image:
     gv_dir: InitVar[Path] # Directory of .gv file injected as context during parsing

src/wireviz/Harness.py

@@ -10,7 +10,7 @@
 import re
 
 from wireviz import wv_colors, __version__, APP_NAME, APP_URL
-from wireviz.DataClasses import Metadata, Options, Connector, Cable
+from wireviz.DataClasses import Metadata, Options, Tweak, Connector, Cable
 from wireviz.wv_colors import get_color_hex, translate_color
 from wireviz.wv_gv_html import nested_html_table, html_colorbar, html_image, \
     html_caption, remove_links, html_line_breaks
@@ -25,6 +25,7 @@
 class Harness:
     metadata: Metadata
     options: Options
+    tweak: Tweak
 
     def __post_init__(self):
         self.connectors = {}
@@ -344,6 +345,44 @@ def create_graph(self) -> Graph:
             dot.node(cable.name, label=f'<\n{html}\n>', shape='box',
                      style=style, fillcolor=translate_color(bgcolor, "HEX"))
 
+        def typecheck(name: str, var, type) -> None:
+            if not isinstance(var, type):
+                raise Exception(f'Unexpected value type of {name}: {var}')
+
+        # TODO?: Differ between override attributes and HTML?
+        if self.tweak.override is not None:
+            typecheck('tweak.override', self.tweak.override, dict)
+            for k, d in self.tweak.override.items():
+                typecheck(f'tweak.override.{k} key', k, str)
+                typecheck(f'tweak.override.{k} value', d, dict)
+                for a, v in d.items():
+                    typecheck(f'tweak.override.{k}.{a} key', a, str)
+                    typecheck(f'tweak.override.{k}.{a} value', v, str)
+
+            # Override generated attributes of selected entries matching tweak.override.
+            for i, entry in enumerate(dot.body):
+                if isinstance(entry, str):
+                    # Find a possibly quoted keyword after leading TAB(s) and followed by [ ].
+                    match = re.match(r'^\t*(")?((?(1)[^"]|[^ "])+)(?(1)") \[.*\]$', entry, re.S)
+                    keyword = match and match[2]
+                    if keyword in self.tweak.override.keys():
+                        for attr, value in self.tweak.override[keyword].items():
+                            if len(value) == 0 or ' ' in value:
+                                value = value.replace('"', r'\"')
+                                value = f'"{value}"'
+                            # TODO?: If value is None: delete attr, and if attr not found: append it?
+                            entry = re.sub(f'{attr}=("[^"]*"|[^] ]*)', f'{attr}={value}', entry)
+                        dot.body[i] = entry
+
+        if self.tweak.append is not None:
+            if isinstance(self.tweak.append, list):
+                for i, element in enumerate(self.tweak.append, 1):
+                    typecheck(f'tweak.append[{i}]', element, str)
+                dot.body.extend(self.tweak.append)
+            else:
+                typecheck(f'tweak.append', self.tweak.append, str)
+                dot.body.append(self.tweak.append)
+
         return dot
 
     @property

src/wireviz/wireviz.py

@@ -13,7 +13,7 @@
     sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..'))
 
 from wireviz import __version__
-from wireviz.DataClasses import Metadata, Options
+from wireviz.DataClasses import Metadata, Options, Tweak
 from wireviz.Harness import Harness
 from wireviz.wv_helper import expand, open_file_read
 
@@ -38,6 +38,7 @@ def parse(yaml_input: str, file_out: (str, Path) = None, return_types: (None, st
     harness = Harness(
         metadata = Metadata(**yaml_data.get('metadata', {})),
         options = Options(**yaml_data.get('options', {})),
+        tweak = Tweak(**yaml_data.get('tweak', {})),
     )
     if 'title' not in harness.metadata:
         harness.metadata['title'] = Path(file_out).stem