import csv
import io
import re
from datetime import datetime
from typing import Dict, Any

from django.db import transaction
from core.models import Entry


# ==============================
# Helpers
# ==============================

def _decode_bytes(b: bytes) -> str:
    # Keep BOM-safe decoding
    return b.decode("utf-8-sig", errors="replace")


def _sniff_dialect(txt: str):
    try:
        return csv.Sniffer().sniff(txt[:4096], delimiters=[",", ";", "\t", "|"])
    except Exception:
        class _D: delimiter = ","
        return _D()


def _norm_header(h: str) -> str:
    """
    Normalize headers in a forgiving way:
    - lower-case
    - remove all non-alphanumerics
    - collapse spaces/underscores
    """
    if not h:
        return ""
    h = h.strip().lower()
    h = h.replace("_", " ")
    h = re.sub(r"\s+", " ", h)
    # drop everything non-alnum
    h = re.sub(r"[^a-z0-9 ]+", "", h)
    return h.replace(" ", "")


def _getv(row: Dict[str, Any], hdr_map: Dict[str, str], canon: str) -> str:
    # Look up using canonical key -> original header
    for orig, can in hdr_map.items():
        if can == canon:
            v = row.get(orig, "")
            return (v or "").strip()
    return ""


def _clip(s: str, n: int) -> str:
    s = (s or "").strip()
    return s[:n] if n and len(s) > n else s


def _parse_date(s: str):
    s = (s or "").strip()
    if not s:
        return None
    for fmt in ("%Y-%m-%d", "%Y/%m/%d", "%m/%d/%Y", "%m/%d/%y", "%Y.%m.%d", "%m-%d-%Y"):
        try:
            return datetime.strptime(s, fmt).date()
        except ValueError:
            continue
    return None


# ==============================
# Public: import_csv_bytes
# ==============================

def import_csv_bytes(
    csv_bytes: bytes,
    dry_run: bool = False,
    *,
    # tune these if you changed model field sizes
    max_source=255,
    max_code=128,
    max_talk_number=128,
    max_talk_title=512,
    max_scripture=512,
):
    """
    Import CSV seed in an idempotent/upsert fashion.

    Mapping (case/spacing-insensitive):
      Subject, Illustration, Application, Scripture, Source,
      Talk Title, Talk Number, Code, Date, Date Edited
    """
    text = _decode_bytes(csv_bytes)
    dialect = _sniff_dialect(text)
    f = io.StringIO(text)
    rdr = csv.DictReader(f, dialect=dialect)

    seen_headers = [h.strip() for h in (rdr.fieldnames or [])]

    # Build header normalization map
    # Canonical keys we expect:
    #  subject illustration application scripture source talktitle talknumber code date dateedited
    canon_targets = {
        "subject": "subject",
        "illustration": "illustration",
        "application": "application",
        "scripture": "scripture",
        "source": "source",
        "talktitle": "talk_title",
        "title": "talk_title",
        "talknumber": "talk_number",
        "number": "talk_number",
        "code": "code",
        "date": "date",
        "dateedited": "date_edited",
        "edited": "date_edited",
    }
    header_map = {}
    for h in seen_headers:
        header_map[h] = canon_targets.get(_norm_header(h), _norm_header(h))  # unknowns still map to their norm

    inserted = updated = skipped = 0
    errors = []
    scripture_parsed = 0

    with transaction.atomic():
        for idx, row in enumerate(rdr, start=2):  # data starts at line 2
            try:
                subject      = _getv(row, header_map, "subject")
                illustration = _getv(row, header_map, "illustration")
                application  = _getv(row, header_map, "application")

                scripture_raw = _clip(_getv(row, header_map, "scripture"), max_scripture)
                source        = _clip(_getv(row, header_map, "source"), max_source)
                talk_title    = _clip(_getv(row, header_map, "talk_title"), max_talk_title)
                talk_number   = _clip(_getv(row, header_map, "talk_number"), max_talk_number)
                entry_code    = _clip(_getv(row, header_map, "code"), max_code)

                date_added  = _parse_date(_getv(row, header_map, "date"))
                date_edited = _parse_date(_getv(row, header_map, "date_edited"))

                # Decide how to find an existing row:
                # 1) Prefer Code if present (treat as external key)
                # 2) Else fall back to (subject, illustration, application)
                obj = None
                if entry_code:
                    obj = Entry.objects.filter(entry_code=entry_code).first()
                if obj is None:
                    obj = Entry.objects.filter(
                        subject=subject, illustration=illustration, application=application
                    ).first()

                created = obj is None
                if created:
                    obj = Entry()

                # Assign fields
                obj.subject = subject
                obj.illustration = illustration
                obj.application = application
                obj.scripture_raw = scripture_raw
                obj.source = source
                obj.talk_title = talk_title
                obj.talk_number = talk_number
                obj.entry_code = entry_code
                if date_added:
                    obj.date_added = date_added
                if date_edited:
                    obj.date_edited = date_edited

                if dry_run:
                    updated += 1 if not created else 0
                    inserted += 1 if created else 0
                else:
                    obj.save()
                    if created:
                        inserted += 1
                    else:
                        updated += 1

                # (Optional) quick scripture counter — we’re not parsing here,
                # but keep a metric like your previous report
                if scripture_raw:
                    scripture_parsed += 1

            except Exception as e:
                skipped += 1
                # keep error list compact
                msg = str(e)
                if "value too long for type" in msg and max(msg.count("\n"), 0) == 0:
                    errors.append("value too long for type character varying(...)")
                else:
                    errors.append(msg)

    return {
        "rows": inserted + updated + skipped,
        "inserted": inserted,
        "updated": updated,
        "skipped": skipped,
        "errors": errors[:200],  # cap to avoid huge output
        "scripture_parsed": scripture_parsed,
        "scripture_failed": 0,
        "dialect_delimiter": dialect.delimiter,
        "used_headerless_mode": False,
        "seen_headers": [h.lower() for h in seen_headers],
    }