"""
utils/scheduler.py — Daily completion report email scheduler.

Runs a background daemon thread that wakes every minute, checks whether
the configured send_time (HH:MM) has been reached today, and sends the
summary report via SMTP if it hasn't been sent yet.

Configuration (config.ini [email] section):
    enabled      = true/false
    smtp_host    = smtp.example.com
    smtp_port    = 587
    smtp_user    = sender@example.com
    smtp_password= secret
    use_tls      = true
    recipients   = admin@example.com, manager@example.com
    send_time    = 18:00        (24-hour HH:MM, local time)

Call start() once after login succeeds (admin only).
Call stop() on logout/shutdown.
"""

import configparser
import datetime
import logging
import os
import smtplib
import threading
from email.mime.multipart import MIMEMultipart
from email.mime.text      import MIMEText

logger = logging.getLogger("scheduler")

CONFIG_FILE = "config.ini"
_scheduler_thread: "threading.Thread | None" = None
_stop_event = threading.Event()


# ─── Config helpers ───────────────────────────────────────────────────────────

def load_email_config() -> dict:
    from utils.config_crypto import decrypt_value
    cfg = configparser.ConfigParser()
    if not os.path.exists(CONFIG_FILE):
        return {}
    cfg.read(CONFIG_FILE, encoding="utf-8")
    if "email" not in cfg:
        return {}
    s = cfg["email"]
    # security field: "starttls" | "ssl" | "none"
    # Falls back from legacy use_tls boolean for existing configs.
    security = s.get("security", "")
    if not security:
        security = "starttls" if s.getboolean("use_tls", fallback=True) else "none"
    return {
        "enabled":       s.getboolean("enabled",      fallback=False),
        "smtp_host":     s.get("smtp_host",   ""),
        "smtp_port":     s.getint("smtp_port", fallback=587),
        "smtp_user":     s.get("smtp_user",   ""),
        "smtp_password": decrypt_value(s.get("smtp_password", "")),
        "security":      security,
        "use_tls":       security == "starttls",   # kept for compatibility
        "recipients":    [r.strip() for r in s.get("recipients", "").split(",") if r.strip()],
        "send_time":     s.get("send_time", "18:00"),
    }


def save_email_config(enabled: bool, smtp_host: str, smtp_port: int,
                      smtp_user: str, smtp_password: str, security: str,
                      recipients: str, send_time: str):
    from utils.config_crypto import encrypt_value
    cfg = configparser.ConfigParser()
    cfg.read(CONFIG_FILE, encoding="utf-8")
    # Preserve last_sent_date if present
    last_sent = cfg.get("email", "last_sent_date", fallback="")
    cfg["email"] = {
        "enabled":         str(enabled).lower(),
        "smtp_host":       smtp_host,
        "smtp_port":       str(smtp_port),
        "smtp_user":       smtp_user,
        "smtp_password":   encrypt_value(smtp_password),
        "security":        security,
        "use_tls":         str(security == "starttls").lower(),  # legacy compat
        "recipients":      recipients,
        "send_time":       send_time,
    }
    if last_sent:
        cfg["email"]["last_sent_date"] = last_sent
    with open(CONFIG_FILE, "w", encoding="utf-8") as fh:
        cfg.write(fh)
    logger.info(f"Email configuration saved (security={security}, encrypted).")


def _make_smtp_server(smtp_host: str, smtp_port: int,
                      security: str) -> "smtplib.SMTP":
    """
    Open and return a ready-to-login SMTP connection.
    security: "starttls" | "ssl" | "none"

    Explicit ehlo() calls are required on Windows — smtplib's automatic
    greeting is unreliable there and causes 'Connection unexpectedly closed'
    on many servers (Office 365, Exchange, Google Workspace) when omitted.
    """
    if security == "ssl":
        server = smtplib.SMTP_SSL(smtp_host, smtp_port, timeout=15)
        server.ehlo()
    elif security == "starttls":
        server = smtplib.SMTP(smtp_host, smtp_port, timeout=15)
        server.ehlo()
        server.starttls()
        server.ehlo()          # re-identify after TLS upgrade — mandatory
    else:
        server = smtplib.SMTP(smtp_host, smtp_port, timeout=15)
        server.ehlo()
    return server


def test_smtp_connection(smtp_host: str, smtp_port: int,
                         smtp_user: str, smtp_password: str,
                         security: str) -> tuple:
    """
    Step-by-step SMTP diagnostic. Returns (success: bool, message: str).
    Each step is attempted independently so the error message tells the
    admin exactly where the failure occurred:
      Step 1 — DNS resolution
      Step 2 — TCP connect
      Step 3 — TLS handshake (if applicable)
      Step 4 — Authentication
    """
    import socket

    # Step 1: DNS resolution
    try:
        addr = socket.getaddrinfo(smtp_host, smtp_port,
                                  socket.AF_UNSPEC, socket.SOCK_STREAM)
        if not addr:
            raise OSError("No addresses returned")
        ip = addr[0][4][0]
        logger.info(f"SMTP test: {smtp_host} resolved to {ip}")
    except OSError as e:
        return False, (
            f"Step 1 FAILED — DNS: Cannot resolve '{smtp_host}'.\n"
            f"Check the hostname and your network connection.\n({e})"
        )

    # Step 2: TCP connect (raw socket, before any SMTP protocol)
    try:
        sock = socket.create_connection((smtp_host, smtp_port), timeout=8)
        sock.close()
        logger.info(f"SMTP test: TCP connect to {smtp_host}:{smtp_port} OK")
    except OSError as e:
        return False, (
            f"Step 2 FAILED — TCP: Cannot reach {smtp_host}:{smtp_port}.\n"
            f"The port may be blocked by a firewall or the server is down.\n({e})"
        )

    # Steps 3 + 4: SMTP protocol, TLS handshake, authentication
    try:
        server = _make_smtp_server(smtp_host, smtp_port, security)
        logger.info(f"SMTP test: TLS/connection OK (security={security})")
    except smtplib.SMTPConnectError as e:
        return False, (
            f"Step 3 FAILED — SMTP connect: {e}\n"
            f"Try a different Security mode or port."
        )
    except smtplib.SMTPException as e:
        return False, (
            f"Step 3 FAILED — TLS handshake: {e}\n"
            f"Try switching Security mode (e.g. SSL/TLS on port 465)."
        )
    except OSError as e:
        return False, (
            f"Step 3 FAILED — connection dropped: {e}\n"
            f"Try switching Security mode or port."
        )

    try:
        server.login(smtp_user, smtp_password)
        server.quit()
        logger.info("SMTP test: authentication OK")
        return True, (
            f"All steps passed.\n"
            f"Connected to {smtp_host}:{smtp_port} "
            f"({security.upper()}) and authenticated successfully."
        )
    except smtplib.SMTPAuthenticationError as e:
        try:
            server.quit()
        except Exception:
            pass
        return False, (
            f"Step 4 FAILED — Authentication: username or password rejected.\n"
            f"For Gmail/Google Workspace use an App Password, not your account password.\n({e})"
        )
    except smtplib.SMTPException as e:
        return False, f"Step 4 FAILED — SMTP error during login: {e}"
    except Exception as e:
        return False, f"Step 4 FAILED — Unexpected error: {e}"


def send_test_email(smtp_host: str, smtp_port: int,
                    smtp_user: str, smtp_password: str,
                    security: str, recipients: list) -> tuple:
    """
    Send a real test email through the full pipeline.
    Returns (success: bool, message: str).
    """
    try:
        subject = "Website Checker — SMTP Test"
        body = (
            "<html><body style='font-family:Segoe UI,Arial,sans-serif;color:#1a1a2e'>"
            "<h3 style='color:#5b4de8'>Website Checker — SMTP Test</h3>"
            "<p>This is a test email confirming your SMTP configuration is working.</p>"
            "<p>You can now enable daily reports from the Email Settings panel.</p>"
            "</body></html>"
        )
        msg = MIMEMultipart("alternative")
        msg["Subject"] = subject
        msg["From"]    = smtp_user
        msg["To"]      = ", ".join(recipients)
        msg.attach(MIMEText(body, "html", "utf-8"))

        server = _make_smtp_server(smtp_host, smtp_port, security)
        server.login(smtp_user, smtp_password)
        server.sendmail(smtp_user, recipients, msg.as_string())
        server.quit()
        logger.info(f"Test email sent to {recipients} via {smtp_host}:{smtp_port}")
        return True, f"Test email sent successfully to: {', '.join(recipients)}"
    except smtplib.SMTPAuthenticationError as e:
        return False, (
            f"Authentication failed — check username and password.\n"
            f"For Gmail/Google Workspace use an App Password.\n({e})"
        )
    except smtplib.SMTPConnectError as e:
        return False, f"Could not connect to {smtp_host}:{smtp_port} — {e}"
    except smtplib.SMTPException as e:
        return False, f"SMTP error: {e}"
    except OSError as e:
        return False, f"Network error: {e}"
    except Exception as e:
        return False, str(e)


# ─── Report builder ───────────────────────────────────────────────────────────

def _build_html_report() -> str:
    """Build a simple HTML daily summary table."""
    try:
        from models import get_admin_dashboard_stats
        stats = get_admin_dashboard_stats()
    except Exception as e:
        return f"<p>Error generating report: {e}</p>"

    today = datetime.date.today().strftime("%A, %d %B %Y")
    rows  = stats.get("user_stats", [])

    table_rows = ""
    skipped_no_shift = 0
    for r in rows:
        total = int(r.get("total_sites") or 0)
        # Skip users with no shifts scheduled today — they have no expected
        # work for this day and showing them as "0 / 0 — 0%" is misleading.
        if total == 0:
            skipped_no_shift += 1
            continue
        pct   = float(r.get("pct_complete") or 0)
        color = "#388e3c" if pct >= 100 else "#f57c00" if pct > 0 else "#d32f2f"
        table_rows += (
            f"<tr>"
            f"<td style='padding:8px 12px'>{r['username']}</td>"
            f"<td style='padding:8px 12px'>{r['full_name'] or ''}</td>"
            f"<td style='padding:8px 12px;text-align:center'>{int(r['checked_count'] or 0)}</td>"
            f"<td style='padding:8px 12px;text-align:center'>{total}</td>"
            f"<td style='padding:8px 12px;text-align:center;"
            f"color:{color};font-weight:bold'>{pct:.0f}%</td>"
            f"</tr>"
        )
    if not table_rows:
        table_rows = (
            "<tr><td colspan='5' style='padding:12px;color:#6b6b80;"
            "text-align:center'>No users with active shifts today.</td></tr>"
        )
    no_shift_note = (
        f"<p style='color:#6b6b80;font-size:11px'>"
        f"{skipped_no_shift} user(s) had no shifts scheduled today and are "
        f"excluded from this report.</p>"
    ) if skipped_no_shift else ""

    return f"""
<html><body style="font-family:Segoe UI,Arial,sans-serif;color:#1a1a2e">
<h2 style="color:#5b4de8">Website Checker — Daily Report</h2>
<p style="color:#6b6b80">{today}</p>
<table border="0" cellspacing="0" cellpadding="0"
       style="border-collapse:collapse;width:100%;max-width:600px">
  <thead>
    <tr style="background:#e0dff8">
      <th style="padding:10px 12px;text-align:left">Username</th>
      <th style="padding:10px 12px;text-align:left">Full Name</th>
      <th style="padding:10px 12px;text-align:center">Checked</th>
      <th style="padding:10px 12px;text-align:center">Total</th>
      <th style="padding:10px 12px;text-align:center">Completion</th>
    </tr>
  </thead>
  <tbody>{table_rows}</tbody>
</table>
{no_shift_note}
<p style="color:#6b6b80;font-size:12px;margin-top:24px">
  Sent automatically by Website Checker at {datetime.datetime.now().strftime('%H:%M')}.
</p>
</body></html>
"""


def _send_report(cfg: dict):
    """Build and send the daily report email."""
    html    = _build_html_report()
    today   = datetime.date.today().strftime("%d %b %Y")
    subject = f"Website Checker — Daily Report {today}"

    msg = MIMEMultipart("alternative")
    msg["Subject"] = subject
    msg["From"]    = cfg["smtp_user"]
    msg["To"]      = ", ".join(cfg["recipients"])
    msg.attach(MIMEText(html, "html", "utf-8"))

    try:
        security = cfg.get("security", "starttls")
        server = _make_smtp_server(
            cfg["smtp_host"], cfg["smtp_port"], security)
        server.login(cfg["smtp_user"], cfg["smtp_password"])
        server.sendmail(cfg["smtp_user"], cfg["recipients"], msg.as_string())
        server.quit()
        logger.info(f"Daily report emailed to: {cfg['recipients']}")
    except smtplib.SMTPAuthenticationError as e:
        logger.error(f"Failed to send daily report — authentication error: {e}")
    except smtplib.SMTPConnectError as e:
        logger.error(f"Failed to send daily report — connection error: {e}")
    except smtplib.SMTPException as e:
        logger.error(f"Failed to send daily report — SMTP error: {e}")
    except OSError as e:
        logger.error(f"Failed to send daily report — network error: {e}")
    except Exception as e:
        logger.error(f"Failed to send daily report email: {e}")


def _get_last_sent_date() -> "datetime.date | None":
    """Read the last-sent date from config.ini [email] last_sent_date key."""
    cfg = configparser.ConfigParser()
    if not os.path.exists(CONFIG_FILE):
        return None
    cfg.read(CONFIG_FILE, encoding="utf-8")
    raw = cfg.get("email", "last_sent_date", fallback="")
    if not raw:
        return None
    try:
        return datetime.date.fromisoformat(raw)
    except ValueError:
        return None


def _set_last_sent_date(d: "datetime.date"):
    """Persist the last-sent date to config.ini [email] last_sent_date key."""
    cfg = configparser.ConfigParser()
    if os.path.exists(CONFIG_FILE):
        cfg.read(CONFIG_FILE, encoding="utf-8")
    if "email" not in cfg:
        cfg["email"] = {}
    cfg["email"]["last_sent_date"] = d.isoformat()
    with open(CONFIG_FILE, "w", encoding="utf-8") as fh:
        cfg.write(fh)


# ─── Scheduler loop ───────────────────────────────────────────────────────────

def _scheduler_loop():
    # Seed from persisted value so a restart after send_time does not re-send.
    last_sent_date = _get_last_sent_date()

    while not _stop_event.is_set():
        _stop_event.wait(60)   # sleep 60 seconds between checks
        if _stop_event.is_set():
            break

        cfg = load_email_config()
        if not cfg.get("enabled") or not cfg.get("smtp_host") or not cfg.get("recipients"):
            continue

        try:
            send_h, send_m = map(int, cfg["send_time"].split(":"))
        except Exception:
            continue

        now   = datetime.datetime.now()
        today = now.date()

        if (now.hour > send_h or (now.hour == send_h and now.minute >= send_m)):
            if last_sent_date != today:
                last_sent_date = today
                _set_last_sent_date(today)
                logger.info(f"Scheduler: sending daily report at {now.strftime('%H:%M')}.")
                _send_report(cfg)


def start():
    """Start the background scheduler thread. Call once after successful login."""
    global _scheduler_thread, _stop_event
    # Guard against double-start: if a thread is already alive (e.g. admin
    # logs out and back in), stop it cleanly before spawning a new one.
    # Without this guard, _stop_event.clear() would unblock the sleeping
    # thread while a second thread also starts, resulting in two scheduler
    # threads firing simultaneously and potentially sending duplicate emails.
    if _scheduler_thread is not None and _scheduler_thread.is_alive():
        logger.info("Email scheduler already running - stopping before restart.")
        _stop_event.set()
        _scheduler_thread.join(timeout=5)
    # Create a fresh Event so there is no residual set-state from a prior stop()
    _stop_event = threading.Event()
    _scheduler_thread = threading.Thread(target=_scheduler_loop,
                                          name="EmailScheduler", daemon=True)
    _scheduler_thread.start()
    logger.info("Email scheduler started.")


def stop():
    """Signal the scheduler to stop cleanly."""
    global _stop_event
    _stop_event.set()
    logger.info("Email scheduler stopped.")