chore: add exchange_user_to_page_token helper

exchange_user_to_page_token.py

@@ -0,0 +1,86 @@
+"""Exchange a Facebook short-lived user token for a long-lived user token and obtain a page access token.
+Saves `FB_PAGE_ACCESS_TOKEN` into `.env` (replacing existing value) and appends a masked entry to `log.txt`.
+
+Do NOT print full tokens to stdout.
+"""
+from dotenv import load_dotenv
+import os
+import requests
+from pathlib import Path
+
+ROOT = Path.cwd()
+load_dotenv()
+
+def mask(tok: str) -> str:
+    if not tok:
+        return ''
+    return tok[:4] + '...' + tok[-4:]
+
+app_id = os.getenv('FB_APP_ID')
+app_secret = os.getenv('FB_APP_SECRET')
+user_token = os.getenv('FB_USER_TOKEN')
+page_id = os.getenv('FB_PAGE_ID')
+
+if not app_id or not app_secret or not user_token or not page_id:
+    print('Missing one of FB_APP_ID, FB_APP_SECRET, FB_USER_TOKEN, or FB_PAGE_ID in environment. Aborting.')
+    raise SystemExit(2)
+
+try:
+    # Exchange short-lived user token for long-lived token
+    exch_url = f"https://graph.facebook.com/oauth/access_token?grant_type=fb_exchange_token&client_id={app_id}&client_secret={app_secret}&fb_exchange_token={user_token}"
+    r = requests.get(exch_url, timeout=15)
+    r.raise_for_status()
+    data = r.json()
+    long_user_token = data.get('access_token')
+except Exception as e:
+    print('Failed to exchange user token:', e)
+    raise
+
+try:
+    # Obtain page access token using the long-lived user token
+    page_url = f"https://graph.facebook.com/{page_id}?fields=access_token&access_token={long_user_token}"
+    r2 = requests.get(page_url, timeout=15)
+    r2.raise_for_status()
+    page_data = r2.json()
+    page_token = page_data.get('access_token')
+    if not page_token:
+        # fallback: try listing accounts from user
+        accounts_url = f"https://graph.facebook.com/me/accounts?access_token={long_user_token}"
+        r3 = requests.get(accounts_url, timeout=15)
+        r3.raise_for_status()
+        accounts = r3.json().get('data', [])
+        for acct in accounts:
+            if str(acct.get('id')) == str(page_id):
+                page_token = acct.get('access_token')
+                break
+except Exception as e:
+    print('Failed to obtain page token:', e)
+    raise
+
+if not page_token:
+    print('Could not retrieve page access token from Graph API. Aborting.')
+    raise SystemExit(3)
+
+# Save to .env (replace or append)
+env_path = ROOT / '.env'
+lines = []
+if env_path.exists():
+    lines = env_path.read_text(encoding='utf-8').splitlines()
+found = False
+for i,l in enumerate(lines):
+    if l.startswith('FB_PAGE_ACCESS_TOKEN='):
+        lines[i] = f'FB_PAGE_ACCESS_TOKEN={page_token}'
+        found = True
+        break
+if not found:
+    lines.append(f'FB_PAGE_ACCESS_TOKEN={page_token}')
+env_path.write_text('\n'.join(lines) + '\n', encoding='utf-8')
+
+# Append masked log
+try:
+    with open('log.txt', 'a', encoding='utf-8') as lf:
+        lf.write(f"[{__import__('time').strftime('%Y-%m-%d %H:%M:%S')}] FB_PAGE_TOKEN_CREATED page={page_id} token={mask(page_token)}\n")
+except Exception:
+    pass
+
+print('Successfully obtained page access token and saved to .env (token masked).')