feat: add simple web server for mermaid diagrams preview

Procfile.dev

@@ -2,3 +2,4 @@
 # text only UI and force loading / no cache
 mpf: mpf both -Xtav -c development
 monitor: mpf monitor
+docs: cd web && flask run

README.md

@@ -9,6 +9,16 @@ Machine](http://www.ipdb.org/machine.cgi?id=1072) by Williams.
 
 ![Playfield](https://github.com/deathsave/grand-prix/raw/main/monitor/playfield.jpg)
 
+### Docs
+
+A simple web server is included to serve up the markdown docs and
+Mermaid diagrams. To setup, run `pip install -r requirements.txt`
+in the `./web/` root. Then to run it, use `bin/docs`.
+
+```mermaid
+graph TD
+    TODO --> DIAGRAM["Diagram Modes"]
+```
 
 Proposed OPP Build
 ------------------

web/app.py

@@ -0,0 +1,26 @@
+import os
+import markdown
+import markdown_mermaidjs
+
+from flask import Flask
+from settings import MACHINE_ROOT
+
+SIMPLE_CSS = '<link rel="stylesheet" ' \
+    'href="https://unpkg.com/simpledotcss/simple.min.css">' \
+    '<style>' \
+    'h1,h2,h3,h4,h5,h6 { margin: 0.5rem; }' \
+    'p { margin: 0.5rem; }' \
+    '</style>'
+
+app = Flask(__name__)
+
+@app.route('/')
+def readme():
+    with open(os.path.join(MACHINE_ROOT, 'README.md')) as f:
+        html = markdown.markdown(
+            f.read(), extensions=["markdown_mermaidjs"]
+        )
+        return SIMPLE_CSS + html
+
+if __name__ == '__main__':
+    app.run()

web/requirements.txt

@@ -0,0 +1,3 @@
+mistune
+flask
+markdown-mermaidjs

web/settings.py

@@ -0,0 +1,4 @@
+import os
+# __file__ refers to the file settings.py
+APP_ROOT = os.path.dirname(os.path.abspath(__file__))
+MACHINE_ROOT = os.path.join(APP_ROOT, '../')