"""
Email notification module.
Sends HTML-formatted detection reports via SMTP SSL.
Credentials are read from environment variables — never hardcoded.
"""
import logging
import os
import smtplib
import ssl
from datetime import datetime, timezone
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from pathlib import Path

logger = logging.getLogger(__name__)

SMTP_HOST = os.environ.get("SMTP_HOST", "smtp.gmail.com")
SMTP_PORT = int(os.environ.get("SMTP_PORT", "465"))
SMTP_USER = os.environ.get("SMTP_USER", "vedangofficeserver@gmail.com")
SMTP_PASS = os.environ.get("SMTP_PASS", "")

TEMPLATE_PATH = Path(__file__).resolve().parent.parent / "templates" / "ChangeDetection.html"


def _load_template() -> str:
    """Read the HTML email template from disk."""
    if not TEMPLATE_PATH.exists():
        logger.error("Email template not found at %s", TEMPLATE_PATH)
        return "<p>Change Detection report — template file missing.</p>"
    return TEMPLATE_PATH.read_text(encoding="utf-8")


def _build_region_rows(regions: list) -> str:
    """Render region rows as HTML <tr> elements for the email template."""
    if not regions:
        return ""
    rows = []
    for r in regions[:20]:
        bg = "#f9f9fb" if r.get("id", 0) % 2 == 0 else "#ffffff"
        sub = r.get("subType") or "—"
        conf = f'{r.get("confidence", 0) * 100:.0f}%'
        area = f'{r.get("area", 0):,}'
        rows.append(
            f'<tr style="background:{bg};">'
            f'<td style="padding:6px 10px;">{r.get("id","")}</td>'
            f'<td style="padding:6px 10px;">{r.get("objectType","")}</td>'
            f'<td style="padding:6px 10px;">{sub}</td>'
            f'<td style="padding:6px 10px;">{conf}</td>'
            f'<td style="padding:6px 10px; text-align:right;">{area}</td>'
            f"</tr>"
        )
    return "\n".join(rows)


def build_email_body(
    title: str,
    method: str,
    zone: str,
    village: str,
    change_pct: float,
    changed_px: int,
    total_px: int,
    regions: list,
) -> str:
    """Populate the HTML template with detection results."""
    html = _load_template()
    location = ", ".join(filter(None, [village, zone])) or "—"
    region_rows = _build_region_rows(regions)
    now = datetime.now(timezone.utc).strftime("%Y-%m-%d %H:%M UTC")

    replacements = {
        "{{title}}": title or "Untitled run",
        "{{method}}": method or "—",
        "{{location}}": location,
        "{{change_pct}}": f"{change_pct:.2f}",
        "{{changed_px}}": f"{changed_px:,}",
        "{{total_px}}": f"{total_px:,}",
        "{{regions_count}}": str(len(regions)),
        "{{region_rows}}": region_rows,
        "{{timestamp}}": now,
    }
    for key, val in replacements.items():
        html = html.replace(key, val)

    # Handle conditional regions block
    if regions:
        html = html.replace("{{#regions}}", "").replace("{{/regions}}", "")
    else:
        import re
        html = re.sub(r"\{\{#regions\}\}.*?\{\{/regions\}\}", "", html, flags=re.DOTALL)

    return html


def send_notification(
    recipient: str,
    title: str,
    method: str,
    zone: str,
    village: str,
    change_pct: float,
    changed_px: int,
    total_px: int,
    regions: list,
) -> bool:
    """
    Send detection report email to the recipient.
    Returns True on success, False on failure (never raises).
    """
    if not SMTP_PASS:
        logger.warning("SMTP_PASS not set — skipping email notification")
        return False

    html_body = build_email_body(
        title, method, zone, village, change_pct, changed_px, total_px, regions
    )

    msg = MIMEMultipart("alternative")
    msg["Subject"] = f"Change Detection Report — {title or 'Untitled run'}"
    msg["From"] = SMTP_USER
    msg["To"] = recipient
    msg.attach(MIMEText(html_body, "html", "utf-8"))

    try:
        context = ssl.create_default_context()
        with smtplib.SMTP_SSL(SMTP_HOST, SMTP_PORT, context=context) as server:
            server.login(SMTP_USER, SMTP_PASS)
            server.sendmail(SMTP_USER, recipient, msg.as_string())
        logger.info("Notification email sent to %s", recipient)
        return True
    except Exception as e:
        logger.error("Failed to send notification email: %s", e)
        return False