Create app.py

app.py

@@ -0,0 +1,146 @@
+import os
+import hmac
+import hashlib
+from typing import Optional
+from dotenv import load_dotenv
+from fastapi import FastAPI, Request, HTTPException, Header, status
+from pydantic import BaseModel, Field
+
+# Load environment variables from .env file
+load_dotenv()
+
+app = FastAPI(
+    title="GitHub PR Reviewer Bot Webhook Listener",
+    description="Listens for GitHub PR events and initiates Langgraph workflows."
+)
+
+# --- Configuration ---
+#GITHUB_WEBHOOK_SECRET = os.getenv("GITHUB_WEBHOOK_SECRET")
+GITHUB_WEBHOOK_SECRET ="d62UMC1iQ6n5PHq9w9bSvPHiWXBqhKX4"
+
+if not GITHUB_WEBHOOK_SECRET:
+    raise ValueError("GITHUB_WEBHOOK_SECRET environment variable not set. Please create a .env file.")
+
+# --- Pydantic Models for Payload Parsing ---
+
+class Repository(BaseModel):
+    id: int
+    full_name: str
+    html_url: str
+    clone_url: str
+
+class PullRequestUser(BaseModel):
+    login: str
+    id: int
+    type: str
+
+class PullRequest(BaseModel):
+    id: int
+    url: str
+    html_url: str
+    diff_url: str # This is the changelist URL (diff URL)
+    state: str
+    title: str
+    user: PullRequestUser
+    base: dict # Contains info about the base branch/repo
+    head: dict # Contains info about the head branch/repo
+
+class GitHubWebhookPayload(BaseModel):
+    action: str
+    pull_request: PullRequest
+    repository: Repository
+    sender: PullRequestUser
+
+# --- Helper Function for Signature Verification ---
+
+def verify_signature(x_hub_signature_256: str, payload_body: bytes) -> bool:
+    """
+    Verifies the GitHub webhook signature.
+    """
+    if not GITHUB_WEBHOOK_SECRET:
+        return False # Should be caught by the initial check, but for safety
+
+    # GitHub sends x-hub-signature-256 in the format 'sha256=<signature>'
+    # We need to extract just the signature part
+    expected_signature = x_hub_signature_256.split('sha256=')[1]
+
+    # Calculate the HMAC SHA256 signature
+    mac = hmac.new(
+        GITHUB_WEBHOOK_SECRET.encode('utf-8'),
+        msg=payload_body,
+        digestmod=hashlib.sha256
+    )
+    calculated_signature = mac.hexdigest()
+
+    # Use hmac.compare_digest for constant-time comparison to prevent timing attacks
+    return hmac.compare_digest(calculated_signature, expected_signature)
+
+# --- Webhook Endpoint ---
+
+@app.post("/webhook")
+async def github_webhook(
+    request: Request,
+    x_github_event: str = Header(..., alias="X-GitHub-Event"),
+    x_hub_signature_256: str = Header(..., alias="X-Hub-Signature-256"),
+):
+    """
+    Receives and processes GitHub webhook events for new Pull Request creation.
+    """
+    # Ensure it's a pull_request event first
+    if x_github_event != "pull_request":
+        print(f"Received non-pull_request event: {x_github_event}. Skipping.")
+        return {"message": f"Event type '{x_github_event}' ignored."}
+
+    payload_body = await request.body()
+
+    # 1. Signature Verification
+    if not verify_signature(x_hub_signature_256, payload_body):
+        print("Webhook signature verification failed!")
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid signature"
+        )
+    print("Webhook signature verified successfully.")
+
+    # 2. Payload Parsing
+    try:
+        payload = GitHubWebhookPayload.model_validate_json(payload_body)
+        print("Payload parsed successfully.")
+    except Exception as e:
+        print(f"Error parsing JSON payload: {e}")
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail=f"Invalid JSON payload: {e}"
+        )
+
+    # --- Filter for only 'opened' PR actions ---
+    if payload.action != "opened":
+        print(f"Received PR event with action '{payload.action}'. Only 'opened' events are processed. Skipping.")
+        return {"message": f"PR event action '{payload.action}' ignored."}
+
+    # If we reach here, it's an 'opened' pull_request event
+    print(f"New PR creation event detected! Action: {payload.action}")
+
+    # Extract crucial information
+    #pr_id = payload.pull_request.id
+    #pr_id = payload.pull_request.number
+    repo_id = payload.repository.id
+    pr_repo_name = payload.repository.full_name
+    changelist_url = payload.pull_request.diff_url
+    pr_id = int(changelist_url.split('/pull/')[1].split('.')[0])
+
+    repository_clone_url = payload.repository.clone_url
+    pr_action = payload.action # This will now always be "opened"
+    pr_title = payload.pull_request.title
+
+
+    print(f"Received PR event: Action={pr_action}, PR ID={pr_id}, Repo ID={repo_id}")
+    print(f"Changelist URL (Diff URL): {changelist_url}")
+    print(f"Repository Clone URL: {repository_clone_url}")
+    print(f"PR Title: {pr_title}")
+    print(f"pr_repo_name: {pr_repo_name} ")
+          
+
+@app.get("/")
+async def read_root():
+    return {"message": "PR Reviewer Bot is running!"}