use serde::{Deserialize, Serialize};
use onioncoin_timing::TimingMetadata;

/// Transaction ID (hash of transaction)
pub type TxId = [u8; 32];

/// A transaction in the OnionCoin network
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Transaction {
    /// Protocol version
    pub version: u8,

    /// Transaction inputs
    pub inputs: Vec<TransactionInput>,

    /// Transaction outputs
    pub outputs: Vec<TransactionOutput>,

    /// Ring signatures for anonymity (simplified placeholder)
    pub ring_signatures: Vec<RingSignature>,

    /// Range proof to hide amounts (placeholder)
    pub range_proof: Vec<u8>,

    /// Encrypted transaction fee
    pub encrypted_fee: u64,

    /// Timing metadata for temporal privacy
    pub timing: TimingMetadata,
}

impl Transaction {
    /// Calculate transaction ID (hash)
    pub fn id(&self) -> TxId {
        let serialized = bincode::serialize(self).expect("Serialization should not fail");
        let hash = blake3::hash(&serialized);
        *hash.as_bytes()
    }

    /// Validate transaction structure
    pub fn validate(&self) -> Result<(), TransactionError> {
        // Must have at least one input and one output
        if self.inputs.is_empty() {
            return Err(TransactionError::NoInputs);
        }

        if self.outputs.is_empty() {
            return Err(TransactionError::NoOutputs);
        }

        // Ring signatures must match inputs
        if self.ring_signatures.len() != self.inputs.len() {
            return Err(TransactionError::InvalidRingSignatures);
        }

        // Validate timing metadata
        if !self.timing.validate(chrono::Utc::now()) {
            return Err(TransactionError::InvalidTimingMetadata);
        }

        Ok(())
    }

    /// Get size in bytes
    pub fn size(&self) -> usize {
        bincode::serialize(self)
            .map(|s| s.len())
            .unwrap_or(0)
    }
}

/// Transaction input
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub struct TransactionInput {
    /// Reference to previous transaction output
    pub previous_output: OutPoint,

    /// Key image (prevents double spending in ring signatures)
    pub key_image: [u8; 32],
}

/// Reference to a specific output in a previous transaction
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub struct OutPoint {
    /// Transaction ID
    pub txid: TxId,

    /// Output index
    pub vout: u32,
}

/// Transaction output
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
pub struct TransactionOutput {
    /// Encrypted amount (confidential transaction)
    pub encrypted_amount: Vec<u8>,

    /// One-time stealth address (public key)
    pub stealth_address: [u8; 32],

    /// Commitment to the amount (for verification)
    pub commitment: [u8; 32],
}

/// Ring signature for input anonymity
/// Simplified placeholder - production would use actual cryptographic implementation
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RingSignature {
    /// Public keys in the ring (decoy outputs + real output)
    pub ring: Vec<[u8; 32]>,

    /// Signature components
    pub c: [u8; 32],
    pub r: Vec<[u8; 32]>,

    /// Ring size (typically 11 for privacy)
    pub ring_size: usize,
}

impl RingSignature {
    /// Create a new ring signature with specified ring size
    pub fn new(ring_size: usize) -> Self {
        Self {
            ring: vec![[0u8; 32]; ring_size],
            c: [0u8; 32],
            r: vec![[0u8; 32]; ring_size],
            ring_size,
        }
    }

    /// Verify ring signature (placeholder)
    pub fn verify(&self) -> bool {
        // In production: actual ring signature verification
        self.ring.len() == self.ring_size && self.r.len() == self.ring_size
    }
}

#[derive(Debug, thiserror::Error)]
pub enum TransactionError {
    #[error("Transaction has no inputs")]
    NoInputs,

    #[error("Transaction has no outputs")]
    NoOutputs,

    #[error("Invalid ring signatures")]
    InvalidRingSignatures,

    #[error("Invalid timing metadata")]
    InvalidTimingMetadata,

    #[error("Transaction too large")]
    TooLarge,

    #[error("Invalid fee")]
    InvalidFee,
}

#[cfg(test)]
mod tests {
    use super::*;
    use chrono::Utc;

    fn create_test_transaction() -> Transaction {
        let seed = [42u8; 32];
        let timing = TimingMetadata::new(Utc::now(), &seed).unwrap();

        Transaction {
            version: 1,
            inputs: vec![TransactionInput {
                previous_output: OutPoint {
                    txid: [1u8; 32],
                    vout: 0,
                },
                key_image: [2u8; 32],
            }],
            outputs: vec![TransactionOutput {
                encrypted_amount: vec![0u8; 32],
                stealth_address: [3u8; 32],
                commitment: [4u8; 32],
            }],
            ring_signatures: vec![RingSignature::new(11)],
            range_proof: vec![0u8; 64],
            encrypted_fee: 1000,
            timing,
        }
    }

    #[test]
    fn test_transaction_id() {
        let tx1 = create_test_transaction();
        let tx2 = create_test_transaction();

        // Same transaction should have same ID
        assert_eq!(tx1.id(), tx2.id());
    }

    #[test]
    fn test_transaction_validation() {
        let tx = create_test_transaction();
        assert!(tx.validate().is_ok());
    }

    #[test]
    fn test_transaction_no_inputs() {
        let mut tx = create_test_transaction();
        tx.inputs.clear();

        assert!(matches!(
            tx.validate(),
            Err(TransactionError::NoInputs)
        ));
    }

    #[test]
    fn test_transaction_no_outputs() {
        let mut tx = create_test_transaction();
        tx.outputs.clear();

        assert!(matches!(
            tx.validate(),
            Err(TransactionError::NoOutputs)
        ));
    }

    #[test]
    fn test_ring_signature_verification() {
        let ring_sig = RingSignature::new(11);
        assert!(ring_sig.verify());
    }
}
