Obsidian session logger

log_event.py

#!/usr/bin/env python3
"""
Claude Code -> Obsidian session logger.

Called by Claude Code hooks (see settings.json snippet). Reads hook JSON
from stdin, writes one markdown note per event into a per-session folder
in your Obsidian vault, and chains them together with wikilinks.

Usage (set by the hook command):
    python3 log_event.py prompt      # UserPromptSubmit
    python3 log_event.py tool_call   # PreToolUse
    python3 log_event.py result      # PostToolUse
"""
import sys, json, os, re, datetime, pathlib

# --- CONFIGURE THIS ---
VAULT = pathlib.Path(os.path.expanduser("~/ObsidianVaults/ClaudeSessions"))
# -----------------------


def slugify(s, maxlen=40):
    s = re.sub(r"[^a-zA-Z0-9._-]+", "-", s).strip("-")
    return s[:maxlen] or "note"


def load_state(session_dir):
    p = session_dir / ".state.json"
    if p.exists():
        try:
            return json.loads(p.read_text())
        except json.JSONDecodeError:
            pass
    return {"seq": 0, "last_note": None, "pending": {}}


def save_state(session_dir, state):
    (session_dir / ".state.json").write_text(json.dumps(state))


def append_index(session_dir, note_name, kind):
    idx = session_dir / "_session-index.md"
    if not idx.exists():
        idx.write_text("---\ntype: session-index\ntags: [session-index]\n---\n\n# Session log\n\n")
    with idx.open("a") as f:
        f.write(f"- [[{note_name}]] — {kind}\n")


def write_note(session_dir, note_name, frontmatter, body):
    fm = "\n".join(f"{k}: {v}" for k, v in frontmatter.items())
    (session_dir / f"{note_name}.md").write_text(f"---\n{fm}\n---\n\n{body}\n")


def main():
    if len(sys.argv) < 2:
        sys.exit(0)  # never block the session over a bad invocation
    kind = sys.argv[1]

    try:
        data = json.load(sys.stdin)
    except json.JSONDecodeError:
        sys.exit(0)

    session_id = data.get("session_id", "unknown")
    date = datetime.date.today().isoformat()
    session_dir = VAULT / f"{date}-{session_id[:8]}"
    session_dir.mkdir(parents=True, exist_ok=True)

    state = load_state(session_dir)
    state["seq"] += 1
    seq = state["seq"]
    ts = datetime.datetime.now().isoformat(timespec="seconds")

    if kind == "prompt":
        prompt = data.get("prompt", "")
        note_name = f"{seq:03d}-prompt"
        links = "\n\n## Links\n"
        if state["last_note"]:
            links += f"- Previous: [[{state['last_note']}]]\n"
        write_note(
            session_dir, note_name,
            {"type": "prompt", "seq": seq, "session": session_id, "timestamp": ts, "tags": "[prompt]"},
            prompt + links,
        )
        append_index(session_dir, note_name, "prompt")
        state["last_note"] = note_name

    elif kind == "tool_call":
        tool_name = data.get("tool_name", "unknown_tool")
        tool_input = data.get("tool_input", {})
        tool_use_id = data.get("tool_use_id", "")
        note_name = f"{seq:03d}-call-{slugify(tool_name)}"
        body = f"**Tool:** `{tool_name}`\n\n```json\n{json.dumps(tool_input, indent=2)}\n```"
        links = "\n\n## Links\n"
        if state["last_note"]:
            links += f"- Triggered by: [[{state['last_note']}]]\n"
        write_note(
            session_dir, note_name,
            {"type": "tool_call", "seq": seq, "session": session_id, "timestamp": ts,
             "tool": tool_name, "tags": "[tool_call]"},
            body + links,
        )
        append_index(session_dir, note_name, f"tool_call: {tool_name}")
        state["last_note"] = note_name
        if tool_use_id:
            state["pending"][tool_use_id] = note_name

    elif kind == "result":
        tool_name = data.get("tool_name", "unknown_tool")
        tool_use_id = data.get("tool_use_id", "")
        resp = data.get("tool_response", "")
        resp_str = resp if isinstance(resp, str) else json.dumps(resp, indent=2)
        if len(resp_str) > 4000:
            resp_str = resp_str[:4000] + "\n... [truncated]"
        note_name = f"{seq:03d}-result-{slugify(tool_name)}"
        body = f"**Tool:** `{tool_name}`\n\n```\n{resp_str}\n```"
        links = "\n\n## Links\n"
        call_note = state["pending"].pop(tool_use_id, None)
        if call_note:
            links += f"- Produced by: [[{call_note}]]\n"
        elif state["last_note"]:
            links += f"- Previous: [[{state['last_note']}]]\n"
        write_note(
            session_dir, note_name,
            {"type": "result", "seq": seq, "session": session_id, "timestamp": ts,
             "tool": tool_name, "tags": "[result]"},
            body + links,
        )
        append_index(session_dir, note_name, f"result: {tool_name}")
        state["last_note"] = note_name

    save_state(session_dir, state)
    sys.exit(0)


if __name__ == "__main__":
    main()