"""本地转发器的无状态报文解析与改写函数。"""

from urllib.parse import urlsplit


HTTP_METHODS = (
    b"CONNECT ", b"GET ", b"POST ", b"PUT ", b"DELETE ",
    b"HEAD ", b"OPTIONS ", b"PATCH ",
)


def starts_with_http_method(data: bytes) -> bool:
    return any(data.startswith(method) for method in HTTP_METHODS)


def inject_proxy_auth(data: bytes, basic_auth: str) -> bytes:
    """为完整 HTTP 代理请求注入上游 Basic Authorization。"""
    if not starts_with_http_method(data):
        return data
    end = data.find(b"\r\n\r\n")
    if end == -1:
        return data
    head = data[:end]
    first_end = head.find(b"\r\n")
    request_line = head if first_end == -1 else head[:first_end]
    headers = b"" if first_end == -1 else head[first_end + 2:]
    for line in headers.split(b"\r\n"):
        if b":" not in line:
            continue
        name = line[:line.index(b":")].strip().lower()
        if name == b"authorization":
            return data
    auth_line = f"Authorization: Basic {basic_auth}\r\n".encode()
    return request_line + b"\r\n" + auth_line + headers + data[end:]


def parse_connect_authority(first_line: str):
    """从 CONNECT 首行提取 ``(host, port)``，失败时返回 ``None``。"""
    parts = first_line.split(" ")
    if len(parts) < 2:
        return None
    authority = parts[1]
    if authority.startswith("[") and "]" in authority:
        try:
            host = authority[1:authority.index("]")]
            tail = authority[authority.index("]") + 1:]
            if tail.startswith(":") and tail[1:].isdigit():
                return host, int(tail[1:])
        except ValueError:
            pass
    if ":" not in authority:
        return None
    host, _, port_s = authority.rpartition(":")
    if not host or not port_s.isdigit():
        return None
    return host, int(port_s)


def parse_http_absolute(first_line: str):
    """从明文 HTTP 代理首行提取 ``(host, port)``，失败时返回 ``None``。"""
    parts = first_line.split(" ")
    if len(parts) < 2 or not parts[1].lower().startswith(("http://", "https://")):
        return None
    parsed = urlsplit(parts[1])
    if not parsed.hostname:
        return None
    port = parsed.port or (443 if parsed.scheme == "https" else 80)
    return parsed.hostname, port


def force_http_close(buffer: bytes) -> bytes:
    """直连明文 HTTP 时强制 Connection: close，避免错复用连接。"""
    end = buffer.find(b"\r\n\r\n")
    if end == -1:
        return buffer
    head, tail = buffer[:end], buffer[end:]
    lines = head.split(b"\r\n")
    out = [lines[0]]
    conn_seen = False
    for line in lines[1:]:
        low = line.lower()
        if low.startswith(b"connection:"):
            out.append(b"Connection: close")
            conn_seen = True
        elif low.startswith(b"proxy-connection:"):
            continue
        else:
            out.append(line)
    if not conn_seen:
        out.append(b"Connection: close")
    return b"\r\n".join(out) + tail