import random
from typing import Mapping

_USER_AGENTS = (
    # Chrome Desktop (Windows)
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36",
    # Chrome Desktop (Mac)
    "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36",
    # Safari Desktop (Mac)
    "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.4 Safari/605.1.15",
    # Chrome Android
    "Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Mobile Safari/537.36",
    # Safari iOS
    "Mozilla/5.0 (iPhone; CPU iPhone OS 17_5 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.0 Mobile/15E148 Safari/605.1.15",
)

_CLIENT_HINTS = (
    {
        "sec-ch-ua": '"Not/A)Brand";v="8", "Chromium";v="126", "Google Chrome";v="126"',
        "sec-ch-ua-mobile": "?0",
        "sec-ch-ua-platform": '"Windows"',
    },
    {
        "sec-ch-ua": '"Not/A)Brand";v="8", "Chromium";v="126", "Google Chrome";v="126"',
        "sec-ch-ua-mobile": "?0",
        "sec-ch-ua-platform": '"macOS"',
    },
    {
        "sec-ch-ua": '"Not/A)Brand";v="8", "Chromium";v="126", "Google Chrome";v="126"',
        "sec-ch-ua-mobile": "?1",
        "sec-ch-ua-platform": '"Android"',
    },
)


def get_random_user_agent() -> str:
    """Return a random modern browser User-Agent string."""
    return random.choice(_USER_AGENTS)


def get_browser_headers() -> dict[str, str]:
    """Return a full set of realistic browser request headers."""
    ua = get_random_user_agent()
    hints = random.choice(_CLIENT_HINTS)
    headers = {
        "User-Agent": ua,
        "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webkit,video/mp4,video/*;q=0.8,*/*;q=0.5",
        "Accept-Language": "en-US,en;q=0.9,uk;q=0.8",
        "Accept-Encoding": "gzip, deflate, br",
        "Sec-Fetch-Dest": "document",
        "Sec-Fetch-Mode": "navigate",
        "Sec-Fetch-Site": "same-origin",
        "Sec-Fetch-User": "?1",
    }
    headers.update(hints)
    return headers


def merge_browser_headers(custom_headers: Mapping[str, str] | None = None) -> dict[str, str]:
    """Merge custom headers with default browser headers, preserving custom overrides."""
    base = get_browser_headers()
    if custom_headers:
        base.update(dict(custom_headers))
    return base