"""Per-source ingest cursors (design §6; T06).

Tracks ``(path -> size, mtime)`` so sweeps re-ingest only changed/grown files.
Persisted as a small JSON sidecar. Ingest itself is idempotent on
``(session_uid, seq)`` in the store, so the cursor is an optimization, not a
correctness requirement — a lost cursor just means a full (still-idempotent)
re-scan.
"""

from __future__ import annotations

import json
import os
from typing import Optional


class Cursors:
    def __init__(self, path: str):
        self.path = path
        self._data: dict[str, dict] = {}
        if os.path.exists(path):
            try:
                with open(path, "r", encoding="utf-8") as f:
                    self._data = json.load(f)
            except (OSError, ValueError):
                self._data = {}

    def is_changed(self, file_path: str) -> bool:
        """True if the file is new or has changed size/mtime since last seen."""
        try:
            stat = os.stat(file_path)
        except OSError:
            return False
        prev = self._data.get(file_path)
        return prev is None or prev.get("size") != stat.st_size or prev.get("mtime") != stat.st_mtime

    def mark(self, file_path: str) -> None:
        try:
            stat = os.stat(file_path)
        except OSError:
            return
        self._data[file_path] = {"size": stat.st_size, "mtime": stat.st_mtime}

    def save(self) -> None:
        os.makedirs(os.path.dirname(self.path) or ".", exist_ok=True)
        tmp = self.path + ".tmp"
        with open(tmp, "w", encoding="utf-8") as f:
            json.dump(self._data, f)
        os.replace(tmp, self.path)