feat chat history

chatbot.py

@@ -2,7 +2,10 @@ import json
 import os
 import re
 import time
+import uuid
 from collections.abc import Callable
+from dataclasses import dataclass, field
+from datetime import datetime, timezone
 from pathlib import Path
 
 # CUDA 13.x moved its runtime DLLs to bin/x64, but llama_cpp's loader only
@@ -105,6 +108,81 @@ def extract_tool_calls(text: str) -> list[dict]:
     return calls
 
 
+# Chat sessions are persisted outside the repo, one JSON file per session, so
+# history survives closing the app and isn't lost on an app update/reinstall.
+CHATS_DIR = Path.home() / ".dev_assist_chatbot" / "chats"
+
+# Placeholder title for a session that hasn't received its first message yet;
+# used to detect when a title still needs to be derived from that message.
+DEFAULT_TITLE = "New chat"
+
+
+@dataclass
+class ChatSession:
+    id: str
+    title: str
+    created_at: str
+    updated_at: str
+    history: list[tuple[str, str]] = field(default_factory=list)
+
+
+def new_session() -> ChatSession:
+    now = datetime.now(timezone.utc).isoformat()
+    return ChatSession(id=uuid.uuid4().hex, title=DEFAULT_TITLE, created_at=now, updated_at=now)
+
+
+def derive_title(question: str, max_len: int = 40) -> str:
+    """First line of a session's opening question, trimmed to max_len - used
+    as its display title once it gets its first message."""
+    title = question.strip().splitlines()[0]
+    return title if len(title) <= max_len else title[: max_len - 1].rstrip() + "…"
+
+
+def _session_path(session_id: str) -> Path:
+    return CHATS_DIR / f"{session_id}.json"
+
+
+def save_session(session: ChatSession) -> None:
+    session.updated_at = datetime.now(timezone.utc).isoformat()
+    CHATS_DIR.mkdir(parents=True, exist_ok=True)
+    payload = {
+        "id": session.id,
+        "title": session.title,
+        "created_at": session.created_at,
+        "updated_at": session.updated_at,
+        "history": [[question, answer] for question, answer in session.history],
+    }
+    _session_path(session.id).write_text(json.dumps(payload, indent=2), encoding="utf-8")
+
+
+def delete_session(session_id: str) -> None:
+    _session_path(session_id).unlink(missing_ok=True)
+
+
+def list_sessions() -> list[ChatSession]:
+    """All persisted chat sessions, most recently updated first. A session
+    file that fails to parse is skipped rather than failing the whole list."""
+    if not CHATS_DIR.is_dir():
+        return []
+    sessions = []
+    for path in CHATS_DIR.glob("*.json"):
+        try:
+            data = json.loads(path.read_text(encoding="utf-8"))
+            sessions.append(
+                ChatSession(
+                    id=data["id"],
+                    title=data["title"],
+                    created_at=data["created_at"],
+                    updated_at=data["updated_at"],
+                    history=[tuple(turn) for turn in data["history"]],
+                )
+            )
+        except (json.JSONDecodeError, OSError, KeyError, TypeError):
+            continue
+    sessions.sort(key=lambda s: s.updated_at, reverse=True)
+    return sessions
+
+
 def build_messages(history: list[tuple[str, str]], question: str) -> list[dict[str, str]]:
     messages = [{"role": "system", "content": SYSTEM_PROMPT}]
     for user_turn, assistant_turn in history[-MAX_HISTORY_TURNS:]: