import time
import threading
from typing import Optional
from pydantic import BaseModel, Field

# --- Redis Fallback & Import Guard ---
try:
    import redis
    HAS_REDIS = True
except ImportError:
    HAS_REDIS = False
    class DummyRedis:
        class ConnectionError(Exception):
            pass
        def __init__(self, *args, **kwargs):
            pass
    redis = DummyRedis()

# --- orjson Fallback Mechanism (Zero-Dependency Resilience) ---
try:
    import orjson
    HAS_ORJSON = True
except ImportError:
    import json
    HAS_ORJSON = False

def dumps_json(data: dict) -> bytes:
    if HAS_ORJSON:
        return orjson.dumps(data)
    else:
        return json.dumps(data).encode("utf-8")

def loads_json(data_bytes: bytes) -> dict:
    if HAS_ORJSON:
        return orjson.loads(data_bytes)
    else:
        return json.loads(data_bytes.decode("utf-8"))

def dumps_json_str(data: dict) -> str:
    return dumps_json(data).decode("utf-8")


# --- Pydantic v2 Schema Definitions ---

class WebhookPayload(BaseModel):
    event_id: str = Field(..., description="Unique event identifier from external provider")
    event_type: str = Field(..., description="Event type name (e.g. payment.succeeded)")
    amount: int = Field(..., ge=0, description="Transaction amount in minor units")
    merchant_id: str = Field(..., description="Target merchant account ID")

class WebhookResponse(BaseModel):
    status: str = Field(..., description="Processing status: success / duplicate_skipped / error")
    message: str = Field(..., description="Human-readable status detail")
    event_id: str = Field(..., description="Target event ID")


# --- Redis Distributed Lock Manager ---

class RedisWebhookLock:
    def __init__(self, redis_client: "redis.Redis", ttl_ms: int = 5000):
        self.redis = redis_client
        self.ttl_ms = ttl_ms

    def acquire_lock(self, event_id: str) -> bool:
        """
        Atomically acquires a lock using Redis SET with NX and PX options.
        - NX: Only set the key if it does not already exist.
        - PX: Set the specified expire time in milliseconds.
        """
        lock_key = f"webhook:lock:{event_id}"
        acquired = self.redis.set(lock_key, "locked", px=self.ttl_ms, nx=True)
        return bool(acquired)

    def release_lock(self, event_id: str) -> None:
        """
        Releases the lock by deleting the key.
        """
        lock_key = f"webhook:lock:{event_id}"
        self.redis.delete(lock_key)


# --- Webhook Processing Pipeline ---

def process_webhook(payload_bytes: bytes, redis_client: "redis.Redis") -> str:
    """
    Parses, validates, and processes incoming webhook payload with distributed lock concurrency control.
    """
    if not HAS_REDIS:
        error_resp = WebhookResponse(
            status="error",
            message="Redis package is not installed.",
            event_id="unknown"
        )
        return dumps_json_str(error_resp.model_dump())

    try:
        raw_data = loads_json(payload_bytes)
    except Exception as e:
        error_resp = WebhookResponse(
            status="error",
            message=f"Invalid JSON format: {e}",
            event_id="unknown"
        )
        return dumps_json_str(error_resp.model_dump())

    try:
        payload = WebhookPayload(**raw_data)
    except Exception as e:
        error_resp = WebhookResponse(
            status="error",
            message=f"Validation error: {e}",
            event_id=raw_data.get("event_id", "unknown")
        )
        return dumps_json_str(error_resp.model_dump())

    locker = RedisWebhookLock(redis_client, ttl_ms=3000)

    # Attempt atomic lock acquisition
    if not locker.acquire_lock(payload.event_id):
        # A concurrent worker is currently processing this event ID
        response = WebhookResponse(
            status="duplicate_skipped",
            message="Concurrent request detected. Webhook skipped to prevent double processing.",
            event_id=payload.event_id
        )
        return dumps_json_str(response.model_dump())

    try:
        # Simulate processing work (DB writes, external RPC, etc.)
        time.sleep(0.1)

        response = WebhookResponse(
            status="success",
            message="Webhook processed successfully.",
            event_id=payload.event_id
        )
        return dumps_json_str(response.model_dump())
    finally:
        locker.release_lock(payload.event_id)


# --- Concurrency Simulation Benchmark ---

def simulate_concurrent_webhooks():
    """
    Spawns concurrent worker threads dispatching identical event IDs to verify lock exclusivity.
    """
    if not HAS_REDIS:
        print("Error: 'redis' package is not installed. Please install it via 'pip install redis'.")
        return

    try:
        client = redis.Redis(host="localhost", port=6379, db=0)
        client.ping()
    except Exception:
        print("Redis server is not running on localhost:6379. Skipping live simulation.")
        return

    test_payload = WebhookPayload(
        event_id="evt_test_123456789",
        event_type="payment.succeeded",
        amount=5000,
        merchant_id="merchant_001"
    )
    payload_bytes = dumps_json(test_payload.model_dump())

    print(f"=== Concurrency Simulation Started (Event ID: {test_payload.event_id}) ===")
    print(f"JSON Engine: {'orjson' if HAS_ORJSON else 'json (fallback)'}")

    results = []
    threads = []
    lock = threading.Lock()

    def worker():
        res_str = process_webhook(payload_bytes, client)
        res_data = loads_json(res_str.encode("utf-8"))
        with lock:
            results.append(res_data["status"])

    thread_count = 10
    for _ in range(thread_count):
        t = threading.Thread(target=worker)
        threads.append(t)

    for t in threads:
        t.start()

    for t in threads:
        t.join()

    print("=== Simulation Results ===")
    success_count = results.count("success")
    skipped_count = results.count("duplicate_skipped")
    error_count = results.count("error")

    print(f"Total Requests: {thread_count}")
    print(f"Success: {success_count}")
    print(f"Duplicate Skipped: {skipped_count}")
    print(f"Errors: {error_count}")

    assert success_count == 1, f"Fatal Assertion: Success count is not 1 (got {success_count})"
    assert skipped_count == thread_count - 1, "Fatal Assertion: Concurrent duplicates were not correctly skipped"
    print(">>> Verification Succeeded: Distributed mutual exclusion lock completely stopped double-processing.")


if __name__ == "__main__":
    simulate_concurrent_webhooks()

python webhook_lock.py

=== Concurrency Simulation Started (Event ID: evt_test_123456789) ===
JSON Engine: orjson
=== Simulation Results ===
Total Requests: 10
Success: 1
Duplicate Skipped: 9
Errors: 0
>>> Verification Succeeded: Distributed mutual exclusion lock completely stopped double-processing.

   if redis.call("get", KEYS[1]) == ARGV[1] then
       return redis.call("del", KEYS[1])
   else
       return 0
   end

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