Implement basic frontend-engine interaction

Use a Flask-based Python server as an adapter to the engine's
stdin-stdout inferface.

adapter/adapter.py

@@ -0,0 +1,46 @@
+import os
+import subprocess
+
+import flask
+from flask_cors import CORS
+
+
+PIECE_TYPE = [("P", "pawn")]
+COLOR = [
+    ("W", "white"),
+    ("B", "black"),
+]
+
+HERE = os.path.abspath(os.path.dirname(__file__))
+app = flask.Flask(__name__)
+CORS(app)
+engine = subprocess.Popen(
+    [os.path.join(HERE, "../rs/target/debug/schach")],
+    stdin=subprocess.PIPE,
+    stdout=subprocess.PIPE,
+)
+
+
+def make_piece(piece_str):
+    piece_type, color, file, rank = piece_str
+    return {
+        "who": dict(PIECE_TYPE)[piece_type],
+        "color": dict(COLOR)[color],
+        "position": f"{file}{rank}",
+    }
+
+
+@app.route("/get_state/")
+def get_state():
+    engine.stdin.write(b"get_state\n")
+    engine.stdin.flush()
+    position_str = engine.stdout.readline().decode("ascii").strip()
+    position = [
+        make_piece(position_str[i : i + 4])
+        for i in range(0, len(position_str), 4)
+    ]
+    return flask.jsonify(position)
+
+
+if __name__ == "__main__":
+    app.run(debug=True, host="127.0.0.1", port=3000)