"""Carga robusta de CSV desde bytes (uploads)."""
from __future__ import annotations

import csv as _csv
import os
import tempfile
from collections import Counter
from typing import Optional

import pandas as pd

_CANDIDATE_DELIMITERS = ["|", ";", "\t", ",", ":"]


def _detect_delimiter_from_sample(sample: str) -> str:
  if not sample:
    return ","
  try:
    dialect = _csv.Sniffer().sniff(sample, delimiters="".join(_CANDIDATE_DELIMITERS))
    sniffed = dialect.delimiter
  except _csv.Error:
    sniffed = None

  lines = [ln for ln in sample.splitlines() if ln.strip()]
  if not lines:
    return sniffed or ","

  scores: dict[str, tuple[int, int]] = {}
  for delim in _CANDIDATE_DELIMITERS:
    counts = [ln.count(delim) for ln in lines[:50]]
    if not counts or max(counts) == 0:
      continue
    mode_count, mode_freq = Counter(counts).most_common(1)[0]
    if mode_count == 0:
      continue
    scores[delim] = (mode_count, mode_freq)

  if scores:
    best = max(scores.items(), key=lambda kv: (kv[1][0], kv[1][1]))
    if sniffed and sniffed in scores:
      sniffed_score = scores[sniffed]
      if sniffed_score[0] >= best[1][0] - 1:
        return sniffed
    return best[0]
  return sniffed or ","


def load_csv_bytes(content: bytes, filename: str = "upload.csv") -> tuple[pd.DataFrame, str]:
  """Carga un CSV desde bytes. Devuelve `(df, delimiter)`."""
  if not content:
    raise RuntimeError(f"El archivo {filename} está vacío")

  sample = ""
  for enc in ("utf-8-sig", "utf-8", "latin-1", "cp1252"):
    try:
      sample = content[:65536].decode(enc, errors="replace")
      break
    except Exception:
      continue
  delimiter = _detect_delimiter_from_sample(sample)

  suffix = os.path.splitext(filename)[1] or ".csv"
  with tempfile.NamedTemporaryFile(delete=False, suffix=suffix) as tmp:
    tmp.write(content)
    tmp_path = tmp.name

  last_error: Optional[Exception] = None
  try:
    for enc in ("utf-8-sig", "utf-8", "latin-1", "cp1252"):
      try:
        df = pd.read_csv(
          tmp_path,
          delimiter=delimiter,
          dtype=str,
          encoding=enc,
          engine="python",
          on_bad_lines="skip",
          keep_default_na=False,
        )
        df.columns = [str(c).strip() for c in df.columns]
        return df, delimiter
      except Exception as exc:  # noqa: BLE001
        last_error = exc
    raise RuntimeError(f"No se pudo leer el CSV {filename}: {last_error}")
  finally:
    try:
      os.unlink(tmp_path)
    except OSError:
      pass