First commit with entire first rendition of the project

spectra/trigger.py

@@ -0,0 +1,63 @@
+import json
+import os
+import threading
+
+_TRIGGER_LOCK = threading.Lock()
+
+
+def cache_dir():
+    env = os.environ.get("SPECTRA_CACHE_DIR")
+    if env:
+        os.makedirs(env, exist_ok=True)
+        return env
+    try:
+        d = "/var/cache/spectra"
+        os.makedirs(d, exist_ok=True)
+        return d
+    except PermissionError:
+        d = os.path.expanduser("~/.cache/spectra")
+        os.makedirs(d, exist_ok=True)
+        return d
+
+
+def _trigger_path():
+    return os.path.join(cache_dir(), "trigger.json")
+
+
+def write_trigger(data):
+    path = _trigger_path()
+    with _TRIGGER_LOCK:
+        os.makedirs(os.path.dirname(path), exist_ok=True)
+        with open(path, "w") as f:
+            json.dump(data, f)
+
+
+def read_trigger():
+    path = _trigger_path()
+    try:
+        with _TRIGGER_LOCK:
+            with open(path) as f:
+                return json.load(f)
+    except (FileNotFoundError, json.JSONDecodeError):
+        return None
+
+
+def clear_trigger():
+    path = _trigger_path()
+    with _TRIGGER_LOCK:
+        try:
+            os.remove(path)
+        except FileNotFoundError:
+            pass
+
+
+def read_and_clear_trigger():
+    path = _trigger_path()
+    with _TRIGGER_LOCK:
+        try:
+            with open(path) as f:
+                data = json.load(f)
+            os.remove(path)
+            return data
+        except (FileNotFoundError, json.JSONDecodeError):
+            return None