use std::{
    collections::{HashMap, HashSet, VecDeque},
    hash::Hash,
};

use log::debug;
use nssa_core::{
    BlockId, Commitment, Nullifier, PrivacyPreservingCircuitOutput, Timestamp,
    account::{Account, AccountId, AccountWithMetadata},
    program::{
        ChainedCall, Claim, DEFAULT_PROGRAM_ID, ProgramId, compute_public_authorized_pdas,
        validate_execution,
    },
};

use crate::{
    V03State, ensure,
    error::{InvalidProgramBehaviorError, NssaError},
    privacy_preserving_transaction::{
        PrivacyPreservingTransaction, circuit::Proof, message::Message,
    },
    program::Program,
    program_deployment_transaction::ProgramDeploymentTransaction,
    public_transaction::PublicTransaction,
    state::MAX_NUMBER_CHAINED_CALLS,
};

pub struct StateDiff {
    pub signer_account_ids: Vec<AccountId>,
    pub public_diff: HashMap<AccountId, Account>,
    pub new_commitments: Vec<Commitment>,
    pub new_nullifiers: Vec<Nullifier>,
    pub program: Option<Program>,
}

/// The validated output of executing or verifying a transaction, ready to be applied to the state.
///
/// Can only be constructed by the transaction validation functions inside this crate, ensuring the
/// diff has been checked before any state mutation occurs.
pub struct ValidatedStateDiff(StateDiff);

impl ValidatedStateDiff {
    pub fn from_public_transaction(
        tx: &PublicTransaction,
        state: &V03State,
        block_id: BlockId,
        timestamp: Timestamp,
    ) -> Result<Self, NssaError> {
        let message = tx.message();
        let witness_set = tx.witness_set();

        // All account_ids must be different
        ensure!(
            message.account_ids.iter().collect::<HashSet<_>>().len() == message.account_ids.len(),
            NssaError::InvalidInput("Duplicate account_ids found in message".into(),)
        );

        // Check exactly one nonce is provided for each signature
        ensure!(
            message.nonces.len() == witness_set.signatures_and_public_keys.len(),
            NssaError::InvalidInput(
                "Mismatch between number of nonces and signatures/public keys".into(),
            )
        );

        // Check the signatures are valid
        ensure!(
            witness_set.is_valid_for(message),
            NssaError::InvalidInput("Invalid signature for given message and public key".into())
        );

        let signer_account_ids = tx.signer_account_ids();
        // Check nonces corresponds to the current nonces on the public state.
        for (account_id, nonce) in signer_account_ids.iter().zip(&message.nonces) {
            let current_nonce = state.get_account_by_id(*account_id).nonce;
            ensure!(
                current_nonce == *nonce,
                NssaError::InvalidInput("Nonce mismatch".into())
            );
        }

        // Build pre_states for execution
        let input_pre_states: Vec<_> = message
            .account_ids
            .iter()
            .map(|account_id| {
                AccountWithMetadata::new(
                    state.get_account_by_id(*account_id),
                    signer_account_ids.contains(account_id),
                    *account_id,
                )
            })
            .collect();

        let mut state_diff: HashMap<AccountId, Account> = HashMap::new();

        let initial_call = ChainedCall {
            program_id: message.program_id,
            instruction_data: message.instruction_data.clone(),
            pre_states: input_pre_states,
            pda_seeds: vec![],
        };

        #[expect(
            clippy::items_after_statements,
            reason = "More readable to keep it behind the place where it's used"
        )]
        #[derive(Debug)]
        struct CallerData {
            program_id: Option<ProgramId>,
            authorized_accounts: HashSet<AccountId>,
        }

        let initial_caller_data = CallerData {
            program_id: None,
            authorized_accounts: signer_account_ids.iter().copied().collect(),
        };

        let mut chained_calls =
            VecDeque::<(ChainedCall, CallerData)>::from_iter([(initial_call, initial_caller_data)]);
        let mut chain_calls_counter = 0;

        while let Some((chained_call, caller_data)) = chained_calls.pop_front() {
            ensure!(
                chain_calls_counter <= MAX_NUMBER_CHAINED_CALLS,
                NssaError::MaxChainedCallsDepthExceeded
            );

            // Check that the `program_id` corresponds to a deployed program
            let Some(program) = state.programs().get(&chained_call.program_id) else {
                return Err(NssaError::InvalidInput("Unknown program".into()));
            };

            debug!(
                "Program {:?} pre_states: {:?}, instruction_data: {:?}",
                chained_call.program_id, chained_call.pre_states, chained_call.instruction_data
            );
            let mut program_output = program.execute(
                caller_data.program_id,
                &chained_call.pre_states,
                &chained_call.instruction_data,
            )?;
            debug!(
                "Program {:?} output: {:?}",
                chained_call.program_id, program_output
            );

            let authorized_pdas =
                compute_public_authorized_pdas(caller_data.program_id, &chained_call.pda_seeds);

            // Account is authorized if it is either in the caller's authorized accounts or in the
            // list of PDAs the caller has authorized.
            let is_authorized = |account_id: &AccountId| {
                authorized_pdas.contains(account_id)
                    || caller_data.authorized_accounts.contains(account_id)
            };

            for pre in &program_output.pre_states {
                let account_id = pre.account_id;
                // Check that the program output pre_states coincide with the values in the public
                // state or with any modifications to those values during the chain of calls.
                let expected_pre = state_diff
                    .get(&account_id)
                    .cloned()
                    .unwrap_or_else(|| state.get_account_by_id(account_id));
                ensure!(
                    pre.account == expected_pre,
                    InvalidProgramBehaviorError::InconsistentAccountPreState {
                        account_id,
                        expected: Box::new(expected_pre),
                        actual: Box::new(pre.account.clone())
                    }
                );

                // Check that the program output pre_states marked as authorized are indeed
                // authorized.
                let is_indeed_authorized = is_authorized(&account_id);
                ensure!(
                    !pre.is_authorized || is_indeed_authorized,
                    InvalidProgramBehaviorError::InvalidAccountAuthorization { account_id }
                );
            }

            // Verify that the program output's self_program_id matches the expected program ID.
            ensure!(
                program_output.self_program_id == chained_call.program_id,
                InvalidProgramBehaviorError::MismatchedProgramId {
                    expected: chained_call.program_id,
                    actual: program_output.self_program_id
                }
            );

            // Verify that the program output's caller_program_id matches the actual caller.
            ensure!(
                program_output.caller_program_id == caller_data.program_id,
                InvalidProgramBehaviorError::MismatchedCallerProgramId {
                    expected: caller_data.program_id,
                    actual: program_output.caller_program_id,
                }
            );

            // Verify execution corresponds to a well-behaved program.
            // See the # Programs section for the definition of the `validate_execution` method.
            validate_execution(
                &program_output.pre_states,
                &program_output.post_states,
                chained_call.program_id,
            )
            .map_err(InvalidProgramBehaviorError::ExecutionValidationFailed)?;

            // Verify validity window
            ensure!(
                program_output.block_validity_window.is_valid_for(block_id)
                    && program_output
                        .timestamp_validity_window
                        .is_valid_for(timestamp),
                NssaError::OutOfValidityWindow
            );

            for (i, post) in program_output.post_states.iter_mut().enumerate() {
                let Some(claim) = post.required_claim() else {
                    continue;
                };
                let pre = &program_output.pre_states[i];
                let account_id = pre.account_id;

                // The invoked program can only claim accounts with default program id.
                ensure!(
                    post.account().program_owner == DEFAULT_PROGRAM_ID,
                    InvalidProgramBehaviorError::ClaimedNonDefaultAccount { account_id }
                );

                match claim {
                    Claim::Authorized => {
                        // The program can only claim accounts that were authorized by the signer.
                        ensure!(
                            pre.is_authorized,
                            InvalidProgramBehaviorError::ClaimedUnauthorizedAccount { account_id }
                        );
                    }
                    Claim::Pda(seed) => {
                        // The program can only claim accounts that correspond to the PDAs it is
                        // authorized to claim. The public-execution path only sees public
                        // accounts, so the public-PDA derivation is the correct formula here.
                        let pda = AccountId::for_public_pda(&chained_call.program_id, &seed);
                        ensure!(
                            account_id == pda,
                            InvalidProgramBehaviorError::MismatchedPdaClaim {
                                expected: pda,
                                actual: account_id
                            }
                        );
                    }
                }

                post.account_mut().program_owner = chained_call.program_id;
            }

            // Update the state diff
            for (pre, post) in program_output
                .pre_states
                .iter()
                .zip(program_output.post_states.iter())
            {
                state_diff.insert(pre.account_id, post.account().clone());
            }

            let authorized_accounts: HashSet<_> = program_output
                .pre_states
                .iter()
                .filter(|pre| pre.is_authorized)
                .map(|pre| pre.account_id)
                .collect();
            for new_call in program_output.chained_calls.into_iter().rev() {
                chained_calls.push_front((
                    new_call,
                    CallerData {
                        program_id: Some(chained_call.program_id),
                        authorized_accounts: authorized_accounts.clone(),
                    },
                ));
            }

            chain_calls_counter = chain_calls_counter
                .checked_add(1)
                .expect("we check the max depth at the beginning of the loop");
        }

        // Check that all modified uninitialized accounts where claimed
        for (account_id, post) in state_diff.iter().filter_map(|(account_id, post)| {
            let pre = state.get_account_by_id(*account_id);
            if pre.program_owner != DEFAULT_PROGRAM_ID {
                return None;
            }
            if pre == *post {
                return None;
            }
            Some((*account_id, post))
        }) {
            ensure!(
                post.program_owner != DEFAULT_PROGRAM_ID,
                InvalidProgramBehaviorError::DefaultAccountModifiedWithoutClaim { account_id }
            );
        }

        Ok(Self(StateDiff {
            signer_account_ids,
            public_diff: state_diff,
            new_commitments: vec![],
            new_nullifiers: vec![],
            program: None,
        }))
    }

    pub fn from_privacy_preserving_transaction(
        tx: &PrivacyPreservingTransaction,
        state: &V03State,
        block_id: BlockId,
        timestamp: Timestamp,
    ) -> Result<Self, NssaError> {
        let message = &tx.message;
        let witness_set = &tx.witness_set;

        // 1. Commitments or nullifiers are non empty
        ensure!(
            !message.new_commitments.is_empty() || !message.new_nullifiers.is_empty(),
            NssaError::InvalidInput(
                "Empty commitments and empty nullifiers found in message".into(),
            )
        );

        // 2. Check there are no duplicate account_ids in the public_account_ids list.
        ensure!(
            n_unique(&message.public_account_ids) == message.public_account_ids.len(),
            NssaError::InvalidInput("Duplicate account_ids found in message".into())
        );

        // Check there are no duplicate nullifiers in the new_nullifiers list
        ensure!(
            n_unique(&message.new_nullifiers) == message.new_nullifiers.len(),
            NssaError::InvalidInput("Duplicate nullifiers found in message".into())
        );

        // Check there are no duplicate commitments in the new_commitments list
        ensure!(
            n_unique(&message.new_commitments) == message.new_commitments.len(),
            NssaError::InvalidInput("Duplicate commitments found in message".into())
        );

        // 3. Nonce checks and Valid signatures
        // Check exactly one nonce is provided for each signature
        ensure!(
            message.nonces.len() == witness_set.signatures_and_public_keys.len(),
            NssaError::InvalidInput(
                "Mismatch between number of nonces and signatures/public keys".into(),
            )
        );

        // Check the signatures are valid
        ensure!(
            witness_set.signatures_are_valid_for(message),
            NssaError::InvalidInput("Invalid signature for given message and public key".into())
        );

        let signer_account_ids = tx.signer_account_ids();
        // Check nonces corresponds to the current nonces on the public state.
        for (account_id, nonce) in signer_account_ids.iter().zip(&message.nonces) {
            let current_nonce = state.get_account_by_id(*account_id).nonce;
            ensure!(
                current_nonce == *nonce,
                NssaError::InvalidInput("Nonce mismatch".into())
            );
        }

        // Verify validity window
        ensure!(
            message.block_validity_window.is_valid_for(block_id)
                && message.timestamp_validity_window.is_valid_for(timestamp),
            NssaError::OutOfValidityWindow
        );

        // Build pre_states for proof verification
        let public_pre_states: Vec<_> = message
            .public_account_ids
            .iter()
            .map(|account_id| {
                AccountWithMetadata::new(
                    state.get_account_by_id(*account_id),
                    signer_account_ids.contains(account_id),
                    *account_id,
                )
            })
            .collect();

        // 4. Proof verification
        check_privacy_preserving_circuit_proof_is_valid(
            &witness_set.proof,
            &public_pre_states,
            message,
        )?;

        // 5. Commitment freshness
        state.check_commitments_are_new(&message.new_commitments)?;

        // 6. Nullifier uniqueness
        state.check_nullifiers_are_valid(&message.new_nullifiers)?;

        let public_diff = message
            .public_account_ids
            .iter()
            .copied()
            .zip(message.public_post_states.clone())
            .collect();
        let new_nullifiers = message
            .new_nullifiers
            .iter()
            .copied()
            .map(|(nullifier, _)| nullifier)
            .collect();

        Ok(Self(StateDiff {
            signer_account_ids,
            public_diff,
            new_commitments: message.new_commitments.clone(),
            new_nullifiers,
            program: None,
        }))
    }

    pub fn from_program_deployment_transaction(
        tx: &ProgramDeploymentTransaction,
        state: &V03State,
    ) -> Result<Self, NssaError> {
        // TODO: remove clone
        let program = Program::new(tx.message.bytecode.clone())?;
        if state.programs().contains_key(&program.id()) {
            return Err(NssaError::ProgramAlreadyExists);
        }
        Ok(Self(StateDiff {
            signer_account_ids: vec![],
            public_diff: HashMap::new(),
            new_commitments: vec![],
            new_nullifiers: vec![],
            program: Some(program),
        }))
    }

    /// Returns the public account changes produced by this transaction.
    ///
    /// Used by callers (e.g. the sequencer) to inspect the diff before committing it, for example
    /// to enforce that system accounts are not modified by user transactions.
    #[must_use]
    pub fn public_diff(&self) -> HashMap<AccountId, Account> {
        self.0.public_diff.clone()
    }

    pub(crate) fn into_state_diff(self) -> StateDiff {
        self.0
    }
}

fn check_privacy_preserving_circuit_proof_is_valid(
    proof: &Proof,
    public_pre_states: &[AccountWithMetadata],
    message: &Message,
) -> Result<(), NssaError> {
    let output = PrivacyPreservingCircuitOutput {
        public_pre_states: public_pre_states.to_vec(),
        public_post_states: message.public_post_states.clone(),
        ciphertexts: message
            .encrypted_private_post_states
            .iter()
            .cloned()
            .map(|value| value.ciphertext)
            .collect(),
        new_commitments: message.new_commitments.clone(),
        new_nullifiers: message.new_nullifiers.clone(),
        block_validity_window: message.block_validity_window,
        timestamp_validity_window: message.timestamp_validity_window,
    };
    proof
        .is_valid_for(&output)
        .then_some(())
        .ok_or(NssaError::InvalidPrivacyPreservingProof)
}

fn n_unique<T: Eq + Hash>(data: &[T]) -> usize {
    let set: HashSet<&T> = data.iter().collect();
    set.len()
}

#[cfg(test)]
mod tests {
    use nssa_core::account::{AccountId, Nonce};

    use crate::{
        PrivateKey, PublicKey, V03State,
        program::Program,
        public_transaction::{Message, WitnessSet},
        validated_state_diff::ValidatedStateDiff,
    };

    /// Demonstrates the authorization-injection vulnerability:
    /// two malicious programs (injector + launderer) drain a victim's balance
    /// without the victim signing anything.
    ///
    /// Attack flow:
    ///   Transaction (attacker signs) → P1 (`malicious_injector`)
    ///     → injects `victim(is_authorized=true)` into chained call `pre_states` for P2
    ///   P2 (`malicious_launderer`)
    ///     → outputs empty pre/post states (victim never checked against authorized set)
    ///     → `authorized_accounts` for `authenticated_transfer` built from
    /// `program_output.pre_states` = {victim}   `authenticated_transfer`
    ///     → `victim.is_authorized=true` passes check ({victim}.contains(victim))
    ///     → transfer executes.
    #[test]
    fn malicious_programs_drain_victim_without_signature() {
        // p2_id, auth_transfer_id, victim_id_raw, victim_balance, victim_nonce,
        // victim_program_owner, recipient_id_raw, amount.
        // Primitives only — AccountId/Account cannot round-trip through instruction_data
        // via risc0_zkvm::serde (SerializeDisplay issue).
        type InjectorInstruction = (
            nssa_core::program::ProgramId, // p2_id
            nssa_core::program::ProgramId, // auth_transfer_id
            [u8; 32],                      // victim_id_raw
            u128,                          // victim_balance
            u128,                          // victim_nonce
            nssa_core::program::ProgramId, // victim_program_owner
            [u8; 32],                      // recipient_id_raw
            u128,                          // amount
        );

        let attacker_key = PrivateKey::try_new([10; 32]).unwrap();
        let attacker_id = AccountId::from(&PublicKey::new_from_private_key(&attacker_key));

        let victim_key = PrivateKey::try_new([20; 32]).unwrap();
        let victim_id = AccountId::from(&PublicKey::new_from_private_key(&victim_key));

        let recipient_id = AccountId::new([42; 32]);

        let victim_balance = 5_000_u128;
        let mut state = V03State::new_with_genesis_accounts(
            &[
                (attacker_id, 100),
                (victim_id, victim_balance),
                (recipient_id, 0),
            ],
            vec![],
            0,
        );

        state.insert_program(Program::malicious_injector());
        state.insert_program(Program::malicious_launderer());

        // Read victim state from chain, exactly as the attacker would.
        let victim_account = state.get_account_by_id(victim_id);

        let instruction: InjectorInstruction = (
            Program::malicious_launderer().id(),
            Program::authenticated_transfer_program().id(),
            *victim_id.value(),
            victim_account.balance,
            victim_account.nonce.0,
            victim_account.program_owner,
            *recipient_id.value(),
            victim_balance,
        );

        let message = Message::try_new(
            Program::malicious_injector().id(),
            vec![attacker_id],
            vec![Nonce(0)],
            instruction,
        )
        .unwrap();

        let witness_set = WitnessSet::for_message(&message, &[&attacker_key]);
        let tx = crate::PublicTransaction::new(message, witness_set);

        let result = ValidatedStateDiff::from_public_transaction(&tx, &state, 1, 0);

        assert!(
            result.is_err(),
            "attack transaction should be rejected by the fixed validator"
        );

        // Confirm the victim's balance is untouched.
        let victim_balance_after = state.get_account_by_id(victim_id).balance;
        let recipient_balance_after = state.get_account_by_id(recipient_id).balance;

        assert_eq!(
            victim_balance_after, victim_balance,
            "victim balance should be unchanged"
        );
        assert_eq!(
            recipient_balance_after, 0,
            "recipient should receive nothing"
        );
    }
}