"""
SSH/SCP helper functions dùng chung cho cả 2 luồng flash.

Không chứa logic nghiệp vụ — chỉ là transport layer:
  _create_ssh_client()     — kết nối SSH với retry
  _upload_firmware()       — upload file qua SCP lên /tmp/
  _verify_firmware()       — kiểm tra file tồn tại trên device
  _sync_and_sysupgrade()   — sync + sysupgrade, trả về "DONE" / "FAIL: ..."
"""

import os
import time

import paramiko
from scp import SCPClient


def _create_ssh_client(ip, user, password, timeout=15):
    """Tạo SSH client với AutoAddPolicy, có retry 3 lần."""
    last_err = None
    for attempt in range(3):
        try:
            client = paramiko.SSHClient()
            client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
            client.connect(
                ip, username=user, password=password,
                timeout=timeout, look_for_keys=False, allow_agent=False,
            )
            return client
        except paramiko.AuthenticationException:
            # Sai password — retry không giúp ích gì
            raise
        except Exception as e:
            last_err = e
            if attempt < 2:
                time.sleep(1)
    raise last_err


def _upload_firmware(client, firmware_path, status_cb=None):
    """
    Upload firmware qua SCP lên /tmp/<filename>.
    Trả về remote_path khi thành công, raise RuntimeError nếu thất bại.
    """
    if status_cb:
        status_cb("Uploading firmware via SCP...")

    filename    = os.path.basename(firmware_path)
    remote_path = f"/tmp/{filename}"

    last_err = None
    for attempt in range(3):
        try:
            scp = SCPClient(client.get_transport(), socket_timeout=350)
            scp.put(firmware_path, remote_path)
            scp.close()
            time.sleep(2)
            return remote_path
        except Exception as e:
            last_err = e
            time.sleep(1.5)

    raise RuntimeError(f"SCP upload failed (Check Network) — {last_err}")


def _verify_firmware(client, remote_path, status_cb=None):
    """
    Xác nhận file firmware tồn tại trên thiết bị.
    Raise RuntimeError nếu file không có.
    """
    if status_cb:
        status_cb("Verifying firmware...")

    _, stdout, _ = client.exec_command(
        f"test -f {remote_path} && ls -lh {remote_path}", timeout=10
    )
    output = stdout.read().decode("utf-8", errors="ignore").strip()
    if not output:
        raise RuntimeError("Firmware file not found on device after upload")


def _sync_and_sysupgrade(client, remote_path, status_cb=None):
    """
    Sync filesystem rồi chạy sysupgrade.
    Trả về "DONE" khi thành công, "FAIL: ..." khi sysupgrade lỗi sớm.
    Connection drop trong lúc sysupgrade = thành công (thiết bị đang reboot).
    """
    if status_cb:
        status_cb("Syncing filesystem...")
    client.exec_command("sync", timeout=10)
    time.sleep(2)

    if status_cb:
        status_cb("Flashing firmware (sysupgrade)...")

    try:
        # -F: bỏ qua kiểm tra metadata (cần cho uImage)
        # -v: verbose  -n: không giữ cấu hình cũ
        _, stdout, _ = client.exec_command(
            f"sysupgrade -F -v -n {remote_path} > /tmp/sysup.log 2>&1"
        )
        # Chờ tối đa 4 giây — nếu exit quá sớm thì coi như lỗi
        time.sleep(4)

        if stdout.channel.exit_status_ready():
            exit_code = stdout.channel.recv_exit_status()
            _, log_out, _ = client.exec_command("cat /tmp/sysup.log")
            err_msg = log_out.read().decode("utf-8", errors="ignore").strip()
            return (
                f"FAIL: sysupgrade terminated early "
                f"(Code {exit_code}). Details:\n{err_msg}"
            )
    except Exception:
        # Connection drop = device đang reboot = thành công
        pass

    if status_cb:
        status_cb("Rebooting...")
    time.sleep(3)
    return "DONE"