"""
Progress tracking (JSON) and CSV writing.
"""

import csv
import json
import logging
from pathlib import Path
from typing import Iterator

log = logging.getLogger(__name__)


class ProgressTracker:
    """
    Tracks successfully downloaded URLs in a JSON file so runs can be resumed.

    Public API (all external code should use only these methods):
      is_done(url)    — True if url has been downloaded
      mark_done(url)  — Record url as complete (call save() to persist)
      discard(url)    — Remove url from the completed set
      iter_urls()     — Iterate over all completed URLs
      __len__()       — Number of completed URLs
      save()          — Flush state to disk
    """

    def __init__(self, path: Path) -> None:
        self.path = path
        self._done: set[str] = set()
        self._load()

    def _load(self) -> None:
        if self.path.exists():
            try:
                data = json.loads(self.path.read_text())
                self._done = set(data.get("completed_urls", []))
                log.info("Resuming: %d URLs already downloaded.", len(self._done))
            except Exception:
                log.warning("Could not read progress file; starting fresh.")

    def is_done(self, url: str) -> bool:
        return url in self._done

    def mark_done(self, url: str) -> None:
        self._done.add(url)

    def discard(self, url: str) -> None:
        """Remove a URL from the completed set (re-queues it for download)."""
        self._done.discard(url)

    def iter_urls(self) -> Iterator[str]:
        """Iterate over all completed URLs."""
        return iter(self._done)

    def __len__(self) -> int:
        return len(self._done)

    def save(self) -> None:
        self.path.parent.mkdir(parents=True, exist_ok=True)
        tmp = self.path.with_suffix(".json.tmp")
        tmp.write_text(
            json.dumps({"completed_urls": sorted(self._done)}, indent=2)
        )
        tmp.replace(self.path)  # atomic on POSIX; avoids corrupt JSON on crash


class CsvWriter:
    """Append-mode CSV writer that writes a header on first creation."""

    def __init__(self, path: Path, fields: list[str]) -> None:
        is_new = not path.exists()
        path.parent.mkdir(parents=True, exist_ok=True)
        self._fh = open(path, "a", newline="", encoding="utf-8")
        self._writer = csv.DictWriter(self._fh, fieldnames=fields)
        if is_new:
            self._writer.writeheader()
        self._fields = fields

    def write(self, row: dict) -> None:
        self._writer.writerow({f: row.get(f, "") for f in self._fields})
        self._fh.flush()

    def close(self) -> None:
        self._fh.close()