"""Import service for DAK Zweitmeinungs-Portal.

Handles:
- fall_id generation: YYYY-KW02d-fallgruppe-KVNR (or random suffix)
- Duplicate detection: by fall_id or (nachname, fallgruppe, datum, vorname, geburtsdatum)
- Preview/confirm flow: preview_import() checks for duplicates, confirm_import() inserts
- Import logging: writes ImportLog entry on each confirmed import
"""

import logging
import random
import re
import string

from sqlalchemy.orm import Session

from app.models.audit import ImportLog
from app.models.case import Case
from app.schemas.import_schemas import ImportPreview, ImportResult, ImportRow
from app.services.csv_parser import ParsedCase

logger = logging.getLogger(__name__)


def generate_random_suffix(length: int = 6) -> str:
    """Generate a random alphanumeric suffix (uppercase + digits)."""
    charset = string.ascii_uppercase + string.digits
    return "".join(random.choices(charset, k=length))


def generate_fall_id(parsed: ParsedCase) -> str:
    """Generate unique fall_id: YYYY-KW02d-fallgruppe-KVNR.

    Uses KVNR as identifier. Falls back to 6-char random suffix if
    KVNR is missing or empty.

    Examples:
        - 2026-06-onko-A123456789
        - 2026-12-kardio-X7K9M2  (random fallback)
    """
    suffix = parsed.kvnr if parsed.kvnr else generate_random_suffix()
    return f"{parsed.jahr}-{parsed.kw:02d}-{parsed.fallgruppe}-{suffix}"


# KVNR format: letter followed by 9 digits (e.g. A123456789)
KVNR_PATTERN = re.compile(r'^[A-Z]\d{9}$')


def has_random_suffix(fall_id: str | None) -> bool:
    """Check if a fall_id ends with a non-KVNR suffix.

    Returns True for random suffixes (6-char alphanumeric) and legacy
    Nachname-based suffixes. Returns False for KVNR suffixes.
    """
    if not fall_id:
        return False
    parts = fall_id.rsplit("-", 1)
    if len(parts) < 2:
        return False
    suffix = parts[1]
    # If it matches KVNR pattern, it's NOT a random suffix
    if KVNR_PATTERN.match(suffix):
        return False
    return True


def check_duplicate(db: Session, parsed: ParsedCase) -> bool:
    """Check if a case already exists in the database.

    Match criteria (OR):
    1. Exact fall_id match
    2. Personal data match: (nachname, fallgruppe, datum) plus optional
       (vorname, geburtsdatum) when available
    """
    fall_id = generate_fall_id(parsed)

    # Check by fall_id
    existing = db.query(Case).filter(Case.fall_id == fall_id).first()
    if existing:
        return True

    # Check by personal data combination
    query = db.query(Case).filter(
        Case.nachname == parsed.nachname,
        Case.fallgruppe == parsed.fallgruppe,
        Case.datum == parsed.datum,
    )
    if parsed.vorname:
        query = query.filter(Case.vorname == parsed.vorname)
    if parsed.geburtsdatum:
        query = query.filter(Case.geburtsdatum == parsed.geburtsdatum)

    return query.first() is not None


def preview_import(
    db: Session,
    parsed_cases: list[ParsedCase],
    filename: str,
) -> ImportPreview:
    """Check parsed cases against DB for duplicates, return preview.

    This is the first step of the two-phase import flow. It does NOT
    modify the database -- only reads to detect duplicates.
    """
    rows: list[ImportRow] = []
    duplicates = 0

    for i, pc in enumerate(parsed_cases, start=1):
        is_dup = check_duplicate(db, pc)
        if is_dup:
            duplicates += 1
        rows.append(
            ImportRow(
                row_number=i,
                nachname=pc.nachname,
                vorname=pc.vorname,
                geburtsdatum=pc.geburtsdatum,
                kvnr=pc.kvnr,
                fallgruppe=pc.fallgruppe,
                datum=pc.datum,
                is_duplicate=is_dup,
                fall_id=generate_fall_id(pc),
            )
        )

    logger.info(
        "Import preview for '%s': %d total, %d new, %d duplicates",
        filename,
        len(parsed_cases),
        len(parsed_cases) - duplicates,
        duplicates,
    )

    return ImportPreview(
        filename=filename,
        total_rows=len(parsed_cases),
        new_cases=len(parsed_cases) - duplicates,
        duplicates=duplicates,
        rows=rows,
    )


def confirm_import(
    db: Session,
    parsed_cases: list[ParsedCase],
    filename: str,
    user_id: int | None = None,
) -> ImportResult:
    """Insert non-duplicate cases into the database.

    This is the second step of the two-phase import flow. It:
    1. Re-checks each case for duplicates (in case of concurrent imports)
    2. Creates Case rows for new cases
    3. Logs the import in ImportLog
    4. Commits the transaction
    """
    imported = 0
    skipped = 0
    errors: list[str] = []

    for pc in parsed_cases:
        try:
            if check_duplicate(db, pc):
                skipped += 1
                continue

            case = Case(
                fall_id=generate_fall_id(pc),
                crm_ticket_id=pc.crm_ticket_id,
                jahr=pc.jahr,
                kw=pc.kw,
                datum=pc.datum,
                nachname=pc.nachname,
                vorname=pc.vorname,
                geburtsdatum=pc.geburtsdatum,
                kvnr=pc.kvnr,
                fallgruppe=pc.fallgruppe,
                import_source=filename,
            )
            db.add(case)
            imported += 1
        except Exception as e:
            errors.append(f"{pc.nachname}: {e}")
            logger.warning("Import error for case %s: %s", pc.nachname, e)

    # Flush to detect any DB-level constraint violations before logging
    db.flush()

    # Log the import
    log = ImportLog(
        filename=filename,
        import_type="csv_crm",
        cases_imported=imported,
        cases_skipped=skipped,
        cases_updated=0,
        errors="; ".join(errors) if errors else None,
        imported_by=user_id,
    )
    db.add(log)
    db.commit()

    logger.info(
        "Import confirmed for '%s': %d imported, %d skipped, %d errors",
        filename,
        imported,
        skipped,
        len(errors),
    )

    return ImportResult(
        imported=imported,
        skipped=skipped,
        updated=0,
        errors=errors,
    )