#![allow(dead_code)] // Allow dead code for demo purposes

use md5;
use rand::{self, Rng};

// Add `rand = "0.8"` and `md5 = "0.7"` to your Cargo.toml

#[derive(Debug, Clone)] // Derive Clone to simplify state updates in the example
enum WebhookProcessingState {
    AwaitingPayload { webhook_id: String },
    PayloadReceived { webhook_id: String, payload_hash: String },
    Processing { webhook_id: String, handler_id: String, start_time_ms: u64 },
    Completed { webhook_id: String, status_code: u16, end_time_ms: u64 },
    Failed { webhook_id: String, error_reason: String, failed_time_ms: u64 },
}

impl WebhookProcessingState {
    /// Attempts to transition the webhook state safely.
    /// Returns a new state or an error if the transition is invalid.
    /// This prevents transitioning to an illogical state or accessing irrelevant data.
    fn try_advance(self) -> Result<Self, String> {
        match self {
            WebhookProcessingState::AwaitingPayload { webhook_id } => {
                println!("Webhook {} received payload.", webhook_id);
                Ok(WebhookProcessingState::PayloadReceived {
                    webhook_id: webhook_id,
                    payload_hash: format!("{:x}", md5::compute(format!("{}-payload", webhook_id))), // Simulate payload hashing
                })
            }
            WebhookProcessingState::PayloadReceived { webhook_id, payload_hash } => {
                println!("Webhook {} (hash {}) starting processing.", webhook_id, payload_hash);
                Ok(WebhookProcessingState::Processing {
                    webhook_id: webhook_id,
                    handler_id: "worker-node-1".to_string(),
                    start_time_ms: 1_678_886_400_000, // Example timestamp
                })
            }
            WebhookProcessingState::Processing { webhook_id, handler_id, start_time_ms } => {
                println!("Webhook {} processed by {} started at {}.", webhook_id, handler_id, start_time_ms);
                let mut rng = rand::thread_rng();
                if rng.gen_bool(0.7) { // 70% chance of success
                    Ok(WebhookProcessingState::Completed {
                        webhook_id: webhook_id,
                        status_code: 200,
                        end_time_ms: 1_678_886_401_000, // Example timestamp
                    })
                } else {
                    Ok(WebhookProcessingState::Failed {
                        webhook_id: webhook_id,
                        error_reason: "Simulated processing error".to_string(),
                        failed_time_ms: 1_678_886_401_000, // Example timestamp
                    })
                }
            }
            // All other states (Completed, Failed) are terminal and cannot be advanced from.
            _ => Err(format!("Cannot advance from terminal state: {:?}", self)),
        }
    }
}

fn main() {
    let mut state = WebhookProcessingState::AwaitingPayload { webhook_id: "wh-001".to_string() };
    println!("Initial: {:?}", state);

    state = state.try_advance().expect("Failed to advance state");
    println!("-> {:?}", state);

    state = state.try_advance().expect("Failed to advance state");
    println!("-> {:?}", state);

    state = state.try_advance().expect("Failed to advance state");
    println!("-> {:?}", state);

    // This will likely result in an error as it's a terminal state
    match state.try_advance() {
        Ok(s) => println!("-> {:?}", s),
        Err(e) => println!("Error advancing: {}", e),
    }
}