import requests
import os
import time
from datetime import datetime, timedelta

class OAuth2Client:
    def __init__(self, token_url, client_id, client_secret, scope=None):
        self.token_url = token_url
        self.client_id = client_id
        self.client_secret = client_secret
        self.scope = scope
        self.access_token = None
        self.expires_at = None # datetime object when token expires

    def _get_new_token(self):
        print("Requesting new OAuth2 access token...")
        headers = {
            "Content-Type": "application/x-www-form-urlencoded"
        }
        data = {
            "grant_type": "client_credentials",
            "client_id": self.client_id,
            "client_secret": self.client_secret
        }
        if self.scope:
            data["scope"] = self.scope

        try:
            response = requests.post(self.token_url, headers=headers, data=data)
            response.raise_for_status() # Raise an HTTPError for bad responses (4xx or 5xx)
            token_data = response.json()

            self.access_token = token_data.get("access_token")
            expires_in = token_data.get("expires_in") # seconds until expiration

            if self.access_token and expires_in:
                # Set expiration time a bit before actual expiration for safety (e.g., 60 seconds)
                self.expires_at = datetime.now() + timedelta(seconds=expires_in - 60)
                print(f"Successfully obtained new token. Expires at: {self.expires_at}")
            else:
                raise ValueError("Access token or expiration time missing from response.")

        except requests.exceptions.RequestException as e:
            print(f"Error obtaining OAuth2 token: {e}")
            self.access_token = None
            self.expires_at = None
            raise

    def get_access_token(self):
        # Check if token is still valid or needs refreshing
        if not self.access_token or (self.expires_at and datetime.now() >= self.expires_at):
            self._get_new_token()
        return self.access_token

    def make_api_request(self, api_url, method="GET", **kwargs):
        token = self.get_access_token()
        if not token:
            raise Exception("Could not obtain access token.")

        headers = kwargs.pop("headers", {})
        headers["Authorization"] = f"Bearer {token}"
        
        try:
            response = requests.request(method, api_url, headers=headers, **kwargs)
            response.raise_for_status()
            return response.json()
        except requests.exceptions.HTTPError as e:
            if e.response.status_code == 401: # Token might be invalid, try to refresh and retry
                print("API request failed with 401. Attempting to refresh token and retry...")
                self.access_token = None # Invalidate current token
                token = self.get_access_token() # Get new token
                if not token:
                    raise Exception("Could not refresh token after 401.")
                headers["Authorization"] = f"Bearer {token}"
                response = requests.request(method, api_url, headers=headers, **kwargs) # Retry request
                response.raise_for_status()
                return response.json()
            raise # Re-raise other HTTP errors
        except requests.exceptions.RequestException as e:
            print(f"API request failed: {e}")
            raise

# --- Usage Example ---
if __name__ == "__main__":
    # --- Configuration (ideally from environment variables) ---
    TOKEN_URL = os.getenv("OAUTH_TOKEN_URL", "https://your-oauth-server.com/oauth/token")
    CLIENT_ID = os.getenv("OAUTH_CLIENT_ID", "your_client_id")
    CLIENT_SECRET = os.getenv("OAUTH_CLIENT_SECRET", "your_client_secret")
    API_BASE_URL = os.getenv("API_BASE_URL", "https://your-resource-server.com/api/v1")
    API_SCOPE = "read write" # Optional scope

    if "your_client_id" in CLIENT_ID or "your-oauth-server" in TOKEN_URL:
         print("WARNING: Please configure OAUTH_TOKEN_URL, OAUTH_CLIENT_ID, OAUTH_CLIENT_SECRET, and API_BASE_URL environment variables or update values in script.")
         # Exit or use dummy values for demonstration if not configured
         TOKEN_URL = "https://example.com/oauth/token" # Placeholder
         CLIENT_ID = "test_client" # Placeholder
         CLIENT_SECRET = "test_secret" # Placeholder
         API_BASE_URL = "https://example.com/api/v1" # Placeholder


    client = OAuth2Client(TOKEN_URL, CLIENT_ID, CLIENT_SECRET, scope=API_SCOPE)

    try:
        # First API call - token will be obtained
        print("
--- Making first API call ---")
        data = client.make_api_request(f"{API_BASE_URL}/data")
        print(f"API Response (first call): {data}")

        # Simulate token expiration (for testing, do not do this in production)
        # client.expires_at = datetime.now() - timedelta(seconds=10) 
        
        # Second API call - if token is still valid, it will be reused
        print("
--- Making second API call (should reuse token) ---")
        data = client.make_api_request(f"{API_BASE_URL}/another-endpoint")
        print(f"API Response (second call): {data}")

        # Wait until just before theoretical token expiration to force refresh
        print("
--- Waiting to force token refresh ---")
        # In a real scenario, client.expires_at would be set correctly.
        # Here, we'll simulate waiting by making expires_at expire soon
        if client.expires_at:
            wait_time = (client.expires_at - datetime.now()).total_seconds() + 5 # Wait 5 seconds past expiration
            if wait_time > 0:
                print(f"Waiting for {int(wait_time)} seconds to force token refresh...")
                time.sleep(wait_time)
            else:
                print("Token already expired or about to expire, will refresh on next call.")
        else:
             print("Cannot determine token expiration, assuming it will be refreshed if needed.")
             time.sleep(2) # Give it some time if expires_at was not set


        # Third API call - token should be refreshed
        print("
--- Making third API call (should trigger token refresh) ---")
        data = client.make_api_request(f"{API_BASE_URL}/status")
        print(f"API Response (third call, after refresh): {data}")

    except Exception as e:
        print(f"An error occurred during API interaction: {e}")