import csv
import xml.etree.ElementTree as ET
from collections import defaultdict
from dataclasses import dataclass
from decimal import Decimal, InvalidOperation
from pathlib import Path

from clients import calculate_customer, find_xml_files


@dataclass(frozen=True)
class SummaryResult:
    xml_count: int
    customer_count: int


def extract_session(xml_path: Path) -> tuple[str, Decimal] | None:
    try:
        root = ET.parse(xml_path).getroot()
    except ET.ParseError:
        return None

    session = root.find("Session")
    if session is None:
        return None

    client_description = session.find("SessionDescription[@Name='ClientName']")
    client_name = "" if client_description is None else client_description.get("Description", "")
    duration = session.get("Duration", "").strip()
    if not client_name.strip() or not duration:
        return None

    try:
        return calculate_customer(client_name), Decimal(duration)
    except InvalidOperation:
        return None


def write_summary(rows: list[dict[str, str]], output: Path) -> None:
    output.parent.mkdir(parents=True, exist_ok=True)
    with output.open("w", newline="", encoding="latin-1", errors="replace") as csv_file:
        writer = csv.DictWriter(csv_file, fieldnames=["Kunde", "AnzahlSitzungen", "Dauer"], delimiter=";")
        writer.writeheader()
        writer.writerows(rows)


def format_duration(duration: Decimal) -> str:
    value = format(duration, "f")
    if "." in value:
        value = value.rstrip("0").rstrip(".")
    return value or "0"


def run(directory: Path, output: Path) -> SummaryResult:
    if not directory.is_dir():
        raise ValueError(f"Das Verzeichnis existiert nicht: {directory}")

    totals: defaultdict[str, list[Decimal | int]] = defaultdict(lambda: [0, Decimal("0")])
    checked_count = 0
    for xml_file in find_xml_files(directory):
        checked_count += 1
        session = extract_session(xml_file)
        if session is None:
            continue
        customer, duration = session
        totals[customer][0] += 1
        totals[customer][1] += duration

    rows = [
        {
            "Kunde": customer,
            "AnzahlSitzungen": str(values[0]),
            "Dauer": format_duration(values[1]),
        }
        for customer, values in sorted(totals.items(), key=lambda item: item[0].casefold())
    ]
    write_summary(rows, output)
    return SummaryResult(xml_count=checked_count, customer_count=len(rows))