loop-agent-sdk 0.1.0

//! Loop Agent SDK - Webhook Handler
//! 
//! Unified handler for Fidel, Square, and Stripe webhooks.
//! 
//! ## Security
//! 
//! - Signature verification BEFORE any processing
//! - Privacy layer hashing BEFORE any logging
//! - Reject spoofed webhooks at the door
//! 
//! ## Flow
//! 
//! ```text
//! Webhook arrives
//!     ↓
//! Verify signature (reject if invalid)
//!     ↓
//! Extract card_id
//!     ↓
//! IMMEDIATELY hash to loop_fp_* (purge raw card_id)
//!     ↓
//! Lookup user by fingerprint
//!     ↓
//! Execute capture
//! ```

use crate::privacy::{LoopFingerprint, PrivacyLayer, PrivacyError};
use hmac::{Hmac, Mac};
use sha2::Sha256;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use tracing::{error, info, warn, instrument};

type HmacSha256 = Hmac<Sha256>;

// ============================================================================
// WEBHOOK CONFIGURATION
// ============================================================================

/// Webhook secrets for signature verification
#[derive(Debug, Clone)]
pub struct WebhookSecrets {
    /// Fidel webhook secrets by event type
    pub fidel: FidelSecrets,
    /// Square webhook signature key
    pub square: Option<String>,
    /// Stripe webhook signing secret
    pub stripe: Option<String>,
}

#[derive(Debug, Clone)]
pub struct FidelSecrets {
    /// transaction.auth event
    pub auth: String,
    /// transaction.clearing event (main one for captures)
    pub clearing: String,
    /// card.linked event
    pub card_linked: String,
}

impl WebhookSecrets {
    /// Load from environment variables
    pub fn from_env() -> Self {
        Self {
            fidel: FidelSecrets {
                auth: std::env::var("FIDEL_WEBHOOK_SECRET_AUTH")
                    .unwrap_or_default(),
                clearing: std::env::var("FIDEL_WEBHOOK_SECRET_CLEARING")
                    .unwrap_or_default(),
                card_linked: std::env::var("FIDEL_WEBHOOK_SECRET_CARD_LINKED")
                    .unwrap_or_default(),
            },
            square: std::env::var("SQUARE_WEBHOOK_SIGNATURE_KEY").ok(),
            stripe: std::env::var("STRIPE_WEBHOOK_SECRET").ok(),
        }
    }
}

// ============================================================================
// WEBHOOK SOURCE DETECTION
// ============================================================================

/// Detected webhook source
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub enum WebhookSource {
    Fidel,
    Square,
    Stripe,
    Unknown,
}

impl WebhookSource {
    /// Detect source from headers
    pub fn detect(headers: &HashMap<String, String>) -> Self {
        // Fidel uses X-Fidel-Signature
        if headers.contains_key("x-fidel-signature") || headers.contains_key("X-Fidel-Signature") {
            return Self::Fidel;
        }
        
        // Square uses X-Square-Signature
        if headers.contains_key("x-square-signature") || headers.contains_key("X-Square-Signature") {
            return Self::Square;
        }
        
        // Stripe uses Stripe-Signature
        if headers.contains_key("stripe-signature") || headers.contains_key("Stripe-Signature") {
            return Self::Stripe;
        }
        
        Self::Unknown
    }
}

// ============================================================================
// NORMALIZED TRANSACTION (Source-Agnostic)
// ============================================================================

/// Normalized transaction data from any webhook source
/// 
/// This is the internal representation after parsing webhook payloads.
/// All source-specific fields are mapped to this common structure.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct NormalizedTransaction {
    /// Loop fingerprint (hashed card_id)
    pub fingerprint: String,
    /// Last 4 digits of card (for display only)
    pub card_last4: String,
    /// Card brand (VISA, MASTERCARD, etc.)
    pub card_brand: String,
    /// Transaction amount in cents
    pub amount_cents: u64,
    /// Currency code (USD, EUR, etc.)
    pub currency: String,
    /// Merchant identifier
    pub merchant_id: String,
    /// Merchant name (for display)
    pub merchant_name: Option<String>,
    /// Location identifier (if available)
    pub location_id: Option<String>,
    /// Transaction timestamp (Unix seconds)
    pub timestamp: i64,
    /// Source-specific transaction ID (for dedup)
    pub source_txn_id: String,
    /// Original webhook source
    pub source: WebhookSource,
    /// Transaction type
    pub txn_type: TransactionType,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
pub enum TransactionType {
    /// Authorization (pending)
    Auth,
    /// Clearing (settled) - this is what we capture
    Clearing,
    /// Refund
    Refund,
}

// ============================================================================
// FIDEL WEBHOOK HANDLING
// ============================================================================

/// Fidel webhook payload (transaction.clearing event)
#[derive(Debug, Deserialize)]
pub struct FidelWebhookPayload {
    /// Transaction data
    pub transaction: FidelTransaction,
    /// Event type
    #[serde(rename = "type")]
    pub event_type: String,
}

#[derive(Debug, Deserialize)]
pub struct FidelTransaction {
    /// Fidel's transaction ID
    pub id: String,
    /// Card ID (THIS IS WHAT WE HASH)
    #[serde(rename = "cardId")]
    pub card_id: String,
    /// Last 4 digits
    #[serde(rename = "lastNumbers")]
    pub last_numbers: String,
    /// Card scheme (VISA, MASTERCARD)
    pub scheme: String,
    /// Amount in original currency
    pub amount: f64,
    /// Currency code
    pub currency: String,
    /// Merchant info
    #[serde(rename = "brandId")]
    pub brand_id: Option<String>,
    #[serde(rename = "merchantName")]
    pub merchant_name: Option<String>,
    #[serde(rename = "locationId")]
    pub location_id: Option<String>,
    /// Transaction date (ISO 8601)
    #[serde(rename = "datetime")]
    pub datetime: String,
    /// Auth vs Clearing
    #[serde(rename = "auth")]
    pub is_auth: Option<bool>,
}

/// Verify Fidel webhook signature
/// 
/// Fidel signs webhooks with HMAC-SHA256.
/// Header: X-Fidel-Signature
#[instrument(skip(body, secret))]
pub fn verify_fidel_signature(
    signature_header: &str,
    body: &[u8],
    secret: &str,
) -> Result<bool, WebhookError> {
    // Fidel signature format: sha256=<hex>
    let signature = signature_header
        .strip_prefix("sha256=")
        .ok_or_else(|| WebhookError::InvalidSignature("Missing sha256= prefix".into()))?;
    
    let expected_bytes = hex::decode(signature)
        .map_err(|e| WebhookError::InvalidSignature(format!("Invalid hex: {}", e)))?;
    
    let mut mac = HmacSha256::new_from_slice(secret.as_bytes())
        .map_err(|e| WebhookError::InvalidSignature(format!("HMAC error: {}", e)))?;
    
    mac.update(body);
    
    // Use constant-time comparison
    match mac.verify_slice(&expected_bytes) {
        Ok(_) => {
            info!("Fidel signature verified");
            Ok(true)
        }
        Err(_) => {
            warn!("Fidel signature verification failed");
            Ok(false)
        }
    }
}

/// Parse Fidel webhook and normalize
/// 
/// # Privacy Protocol
/// 
/// This function implements Double-Blind Vaulting:
/// 1. Parse the raw payload
/// 2. IMMEDIATELY hash card_id to fingerprint
/// 3. Drop the raw card_id (it's moved into the hasher)
/// 4. Return only normalized data with fingerprint
#[instrument(skip(body, privacy))]
pub fn parse_fidel_webhook(
    body: &[u8],
    privacy: &PrivacyLayer,
) -> Result<NormalizedTransaction, WebhookError> {
    // Parse JSON
    let payload: FidelWebhookPayload = serde_json::from_slice(body)
        .map_err(|e| WebhookError::ParseError(format!("Invalid JSON: {}", e)))?;
    
    let txn = payload.transaction;
    
    // CRITICAL: Hash the card_id IMMEDIATELY
    // The hash_card_id function takes ownership and zeroizes the original
    let fingerprint = privacy.hash_card_id(txn.card_id);
    
    // After this point, raw card_id no longer exists in memory
    // All subsequent operations use only the fingerprint
    
    // Parse timestamp
    let timestamp = chrono::DateTime::parse_from_rfc3339(&txn.datetime)
        .map(|dt| dt.timestamp())
        .unwrap_or_else(|_| chrono::Utc::now().timestamp());
    
    // Determine transaction type
    let txn_type = match payload.event_type.as_str() {
        "transaction.auth" => TransactionType::Auth,
        "transaction.clearing" => TransactionType::Clearing,
        "transaction.refund" => TransactionType::Refund,
        _ => TransactionType::Clearing, // Default to clearing
    };
    
    // Convert amount to cents
    let amount_cents = (txn.amount * 100.0).round() as u64;
    
    Ok(NormalizedTransaction {
        fingerprint: fingerprint.into_string(),
        card_last4: txn.last_numbers,
        card_brand: txn.scheme,
        amount_cents,
        currency: txn.currency,
        merchant_id: txn.brand_id.unwrap_or_else(|| "unknown".to_string()),
        merchant_name: txn.merchant_name,
        location_id: txn.location_id,
        timestamp,
        source_txn_id: txn.id,
        source: WebhookSource::Fidel,
        txn_type,
    })
}

// ============================================================================
// SQUARE WEBHOOK HANDLING
// ============================================================================

/// Square webhook payload (payment.completed event)
#[derive(Debug, Deserialize)]
pub struct SquareWebhookPayload {
    /// Event type
    #[serde(rename = "type")]
    pub event_type: String,
    /// Event data
    pub data: SquareEventData,
}

#[derive(Debug, Deserialize)]
pub struct SquareEventData {
    /// Object containing payment details
    pub object: SquarePaymentObject,
}

#[derive(Debug, Deserialize)]
pub struct SquarePaymentObject {
    pub payment: SquarePayment,
}

#[derive(Debug, Deserialize)]
pub struct SquarePayment {
    pub id: String,
    #[serde(rename = "amount_money")]
    pub amount_money: SquareMoney,
    #[serde(rename = "card_details")]
    pub card_details: Option<SquareCardDetails>,
    #[serde(rename = "location_id")]
    pub location_id: String,
    #[serde(rename = "created_at")]
    pub created_at: String,
}

#[derive(Debug, Deserialize)]
pub struct SquareMoney {
    pub amount: i64,
    pub currency: String,
}

#[derive(Debug, Deserialize)]
pub struct SquareCardDetails {
    pub card: SquareCard,
}

#[derive(Debug, Deserialize)]
pub struct SquareCard {
    /// Square's card fingerprint (we hash this too)
    pub fingerprint: Option<String>,
    #[serde(rename = "last_4")]
    pub last_4: Option<String>,
    #[serde(rename = "card_brand")]
    pub card_brand: Option<String>,
}

/// Verify Square webhook signature
#[instrument(skip(body, signature_key))]
pub fn verify_square_signature(
    signature_header: &str,
    body: &[u8],
    notification_url: &str,
    signature_key: &str,
) -> Result<bool, WebhookError> {
    // Square signature = Base64(HMAC-SHA256(notification_url + body))
    let mut mac = HmacSha256::new_from_slice(signature_key.as_bytes())
        .map_err(|e| WebhookError::InvalidSignature(format!("HMAC error: {}", e)))?;
    
    mac.update(notification_url.as_bytes());
    mac.update(body);
    
    let computed = base64::Engine::encode(
        &base64::engine::general_purpose::STANDARD,
        mac.finalize().into_bytes(),
    );
    
    if computed == signature_header {
        info!("Square signature verified");
        Ok(true)
    } else {
        warn!("Square signature verification failed");
        Ok(false)
    }
}

/// Parse Square webhook and normalize
#[instrument(skip(body, privacy))]
pub fn parse_square_webhook(
    body: &[u8],
    privacy: &PrivacyLayer,
    merchant_id: &str, // Square merchant ID
) -> Result<NormalizedTransaction, WebhookError> {
    let payload: SquareWebhookPayload = serde_json::from_slice(body)
        .map_err(|e| WebhookError::ParseError(format!("Invalid JSON: {}", e)))?;
    
    let payment = payload.data.object.payment;
    
    // Get card details
    let card_details = payment.card_details
        .ok_or_else(|| WebhookError::ParseError("No card details".into()))?;
    
    let card = card_details.card;
    
    // Get Square's fingerprint and hash it
    let raw_fingerprint = card.fingerprint
        .ok_or_else(|| WebhookError::ParseError("No card fingerprint".into()))?;
    
    // CRITICAL: Hash immediately
    let fingerprint = privacy.hash_card_id(raw_fingerprint);
    
    // Parse timestamp
    let timestamp = chrono::DateTime::parse_from_rfc3339(&payment.created_at)
        .map(|dt| dt.timestamp())
        .unwrap_or_else(|_| chrono::Utc::now().timestamp());
    
    Ok(NormalizedTransaction {
        fingerprint: fingerprint.into_string(),
        card_last4: card.last_4.unwrap_or_default(),
        card_brand: card.card_brand.unwrap_or_default(),
        amount_cents: payment.amount_money.amount as u64,
        currency: payment.amount_money.currency,
        merchant_id: merchant_id.to_string(),
        merchant_name: None,
        location_id: Some(payment.location_id),
        timestamp,
        source_txn_id: payment.id,
        source: WebhookSource::Square,
        txn_type: TransactionType::Clearing,
    })
}

// ============================================================================
// STRIPE WEBHOOK HANDLING
// ============================================================================

/// Verify Stripe webhook signature
#[instrument(skip(body, secret))]
pub fn verify_stripe_signature(
    signature_header: &str,
    body: &[u8],
    secret: &str,
) -> Result<bool, WebhookError> {
    // Stripe signature format: t=timestamp,v1=signature,v1=signature...
    let parts: HashMap<&str, &str> = signature_header
        .split(',')
        .filter_map(|part| {
            let mut kv = part.splitn(2, '=');
            Some((kv.next()?, kv.next()?))
        })
        .collect();
    
    let timestamp = parts.get("t")
        .ok_or_else(|| WebhookError::InvalidSignature("Missing timestamp".into()))?;
    
    let signature = parts.get("v1")
        .ok_or_else(|| WebhookError::InvalidSignature("Missing v1 signature".into()))?;
    
    // Construct signed payload
    let signed_payload = format!("{}.{}", timestamp, String::from_utf8_lossy(body));
    
    let mut mac = HmacSha256::new_from_slice(secret.as_bytes())
        .map_err(|e| WebhookError::InvalidSignature(format!("HMAC error: {}", e)))?;
    
    mac.update(signed_payload.as_bytes());
    
    let computed = hex::encode(mac.finalize().into_bytes());
    
    if computed == *signature {
        info!("Stripe signature verified");
        Ok(true)
    } else {
        warn!("Stripe signature verification failed");
        Ok(false)
    }
}

// ============================================================================
// UNIFIED WEBHOOK HANDLER
// ============================================================================

/// Unified webhook handler
/// 
/// This is the main entry point for all webhook processing.
/// It detects the source, verifies the signature, and normalizes the transaction.
pub struct WebhookHandler {
    privacy: PrivacyLayer,
    secrets: WebhookSecrets,
}

impl WebhookHandler {
    /// Create new webhook handler
    pub async fn new(secrets: WebhookSecrets) -> Result<Self, WebhookError> {
        let privacy = PrivacyLayer::new(&Default::default()).await
            .map_err(|e| WebhookError::InitError(e.to_string()))?;
        
        Ok(Self { privacy, secrets })
    }
    
    /// Process incoming webhook
    /// 
    /// Returns normalized transaction if valid, error if signature fails or parsing fails.
    #[instrument(skip(self, body))]
    pub async fn process(
        &self,
        headers: &HashMap<String, String>,
        body: &[u8],
        context: &WebhookContext,
    ) -> Result<NormalizedTransaction, WebhookError> {
        // 1. Detect source
        let source = WebhookSource::detect(headers);
        info!(?source, "Detected webhook source");
        
        // 2. Verify signature (BEFORE any parsing)
        match source {
            WebhookSource::Fidel => {
                let sig = headers.get("x-fidel-signature")
                    .or_else(|| headers.get("X-Fidel-Signature"))
                    .ok_or_else(|| WebhookError::InvalidSignature("Missing signature header".into()))?;
                
                // Determine which secret based on event type (peek at body)
                let secret = self.get_fidel_secret(body)?;
                
                if !verify_fidel_signature(sig, body, &secret)? {
                    return Err(WebhookError::SignatureVerificationFailed);
                }
            }
            WebhookSource::Square => {
                let sig = headers.get("x-square-signature")
                    .or_else(|| headers.get("X-Square-Signature"))
                    .ok_or_else(|| WebhookError::InvalidSignature("Missing signature header".into()))?;
                
                let secret = self.secrets.square.as_ref()
                    .ok_or_else(|| WebhookError::MissingSecret("Square".into()))?;
                
                let url = context.webhook_url.as_ref()
                    .ok_or_else(|| WebhookError::MissingContext("webhook_url".into()))?;
                
                if !verify_square_signature(sig, body, url, secret)? {
                    return Err(WebhookError::SignatureVerificationFailed);
                }
            }
            WebhookSource::Stripe => {
                let sig = headers.get("stripe-signature")
                    .or_else(|| headers.get("Stripe-Signature"))
                    .ok_or_else(|| WebhookError::InvalidSignature("Missing signature header".into()))?;
                
                let secret = self.secrets.stripe.as_ref()
                    .ok_or_else(|| WebhookError::MissingSecret("Stripe".into()))?;
                
                if !verify_stripe_signature(sig, body, secret)? {
                    return Err(WebhookError::SignatureVerificationFailed);
                }
            }
            WebhookSource::Unknown => {
                return Err(WebhookError::UnknownSource);
            }
        }
        
        // 3. Parse and normalize (with privacy layer)
        let transaction = match source {
            WebhookSource::Fidel => parse_fidel_webhook(body, &self.privacy)?,
            WebhookSource::Square => {
                let merchant_id = context.merchant_id.as_ref()
                    .ok_or_else(|| WebhookError::MissingContext("merchant_id".into()))?;
                parse_square_webhook(body, &self.privacy, merchant_id)?
            }
            WebhookSource::Stripe => {
                // TODO: Implement Stripe parsing
                return Err(WebhookError::NotImplemented("Stripe parsing".into()));
            }
            WebhookSource::Unknown => unreachable!(),
        };
        
        info!(
            source = ?source,
            fingerprint = %transaction.fingerprint,
            amount_cents = transaction.amount_cents,
            "Transaction normalized"
        );
        
        Ok(transaction)
    }
    
    /// Get the appropriate Fidel secret based on event type
    fn get_fidel_secret(&self, body: &[u8]) -> Result<String, WebhookError> {
        // Quick peek to determine event type
        #[derive(Deserialize)]
        struct EventPeek {
            #[serde(rename = "type")]
            event_type: String,
        }
        
        let peek: EventPeek = serde_json::from_slice(body)
            .map_err(|e| WebhookError::ParseError(format!("Cannot determine event type: {}", e)))?;
        
        let secret = match peek.event_type.as_str() {
            "transaction.auth" => &self.secrets.fidel.auth,
            "transaction.clearing" => &self.secrets.fidel.clearing,
            "card.linked" => &self.secrets.fidel.card_linked,
            _ => &self.secrets.fidel.clearing, // Default
        };
        
        if secret.is_empty() {
            return Err(WebhookError::MissingSecret(format!("Fidel {}", peek.event_type)));
        }
        
        Ok(secret.clone())
    }
}

/// Additional context for webhook processing
#[derive(Debug, Default)]
pub struct WebhookContext {
    /// Webhook URL (needed for Square signature)
    pub webhook_url: Option<String>,
    /// Merchant ID (for Square)
    pub merchant_id: Option<String>,
}

// ============================================================================
// ERRORS
// ============================================================================

#[derive(Debug, Clone)]
pub enum WebhookError {
    /// Signature header invalid or malformed
    InvalidSignature(String),
    /// Signature verification failed
    SignatureVerificationFailed,
    /// Could not parse webhook payload
    ParseError(String),
    /// Unknown webhook source
    UnknownSource,
    /// Missing required secret
    MissingSecret(String),
    /// Missing required context
    MissingContext(String),
    /// Feature not implemented
    NotImplemented(String),
    /// Initialization error
    InitError(String),
}

impl std::fmt::Display for WebhookError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::InvalidSignature(msg) => write!(f, "Invalid signature: {}", msg),
            Self::SignatureVerificationFailed => write!(f, "Signature verification failed"),
            Self::ParseError(msg) => write!(f, "Parse error: {}", msg),
            Self::UnknownSource => write!(f, "Unknown webhook source"),
            Self::MissingSecret(name) => write!(f, "Missing secret: {}", name),
            Self::MissingContext(name) => write!(f, "Missing context: {}", name),
            Self::NotImplemented(feature) => write!(f, "Not implemented: {}", feature),
            Self::InitError(msg) => write!(f, "Initialization error: {}", msg),
        }
    }
}

impl std::error::Error for WebhookError {}

#[cfg(test)]
mod tests {
    use super::*;
    
    #[test]
    fn detect_fidel_source() {
        let mut headers = HashMap::new();
        headers.insert("x-fidel-signature".to_string(), "sha256=abc".to_string());
        
        assert_eq!(WebhookSource::detect(&headers), WebhookSource::Fidel);
    }
    
    #[test]
    fn detect_square_source() {
        let mut headers = HashMap::new();
        headers.insert("x-square-signature".to_string(), "abc".to_string());
        
        assert_eq!(WebhookSource::detect(&headers), WebhookSource::Square);
    }
    
    #[test]
    fn detect_unknown_source() {
        let headers = HashMap::new();
        assert_eq!(WebhookSource::detect(&headers), WebhookSource::Unknown);
    }
}