use crate::{
    amount::AmountCents,
    config::Config,
    payment::PaymentTo,
    storage::{self, Batch, Storage},
    transaction::*,
    AccountId, Amount, Asset, PaymentFrom, Status, TransactionId,
};
use chrono::{serde::ts_milliseconds, DateTime, Utc};
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::collections::HashMap;

/// Transaction Inner
///
/// This is the transaction details, as described bellow, it is a Transaction but without the ID nor
/// the revision ID.
///
/// This seperated struct is used to calculate the ID of the transaction, and to be able to
/// serialize the transaction without the ID.
///
/// Since the transaction ID is calculated from the transaction itself, to provide cryptographic
/// security that its content was not altered.
#[derive(Debug, Clone, Deserialize, Serialize)]
pub struct TransactionInner {
    /// A pointer to the first revision of the transaction.
    first_revision: Option<TransactionId>,
    /// Any previous transaction that this transaction is replacing.
    previous: Option<TransactionId>,
    /// A human-readable description of the transaction changes.
    changelog: String,
    spends: Vec<PaymentFrom>,
    creates: Vec<PaymentTo>,
    #[allow(dead_code)]
    reference: String,
    #[serde(rename = "type")]
    typ: Type,
    status: Status,
    tags: Vec<String>,
    #[serde(with = "ts_milliseconds")]
    created_at: DateTime<Utc>,
    #[serde(with = "ts_milliseconds")]
    updated_at: DateTime<Utc>,
}

impl TransactionInner {
    pub fn calculate_id(&self) -> Result<TransactionId, Error> {
        let mut hasher = Sha256::new();
        let bytes = bincode::serialize(self)?;
        hasher.update(bytes);
        Ok(TransactionId::new(hasher.finalize().into()))
    }

    /// The transaction fingerprint is a hash of the properties that are not allowed to be updated
    /// in a transaction.
    pub fn transaction_fingerprint(&self) -> Result<TransactionId, Error> {
        let mut hasher = Sha256::new();
        hasher.update(&bincode::serialize(&self.spends)?);
        hasher.update(&bincode::serialize(&self.creates)?);
        hasher.update(&self.typ.to_string());
        hasher.update(&self.reference);
        hasher.update(&self.created_at.timestamp_millis().to_string());
        Ok(TransactionId::new(hasher.finalize().into()))
    }

    /// Validates the transaction input and output (debit and credit)
    ///
    /// The total sum of debits and credits should always be zero in transactions, unless they are
    /// deposits or withdrawals.
    ///
    /// Negative amounts can be used in transactions, but the total sum of debits and credits should
    /// always be zero, and the debit amount should be positive numbers
    pub fn validate(&self) -> Result<(), Error> {
        let mut debit = HashMap::<Asset, AmountCents>::new();
        let mut credit = HashMap::<Asset, AmountCents>::new();

        for input in self.spends.iter() {
            if let Some(value) = debit.get_mut(input.amount.asset()) {
                *value = input
                    .amount
                    .cents()
                    .checked_add(*value)
                    .ok_or(Error::Overflow)?;
            } else {
                debit.insert(input.amount.asset().clone(), input.amount.cents());
            }
        }

        for (asset, amount) in debit.iter() {
            if *amount <= 0 {
                return Err(Error::InvalidAmount(
                    asset.new_amount(*amount),
                    asset.new_amount(*amount),
                ));
            }
        }

        if !self.typ.is_transaction() {
            // We don't care input/output balance in external operations
            // (withdrawals/deposits), because these operations are inbalanced
            return Ok(());
        }

        for output in self.creates.iter() {
            if let Some(value) = credit.get_mut(output.amount.asset()) {
                *value = output
                    .amount
                    .cents()
                    .checked_add(*value)
                    .ok_or(Error::Overflow)?;
            } else {
                credit.insert(output.amount.asset().clone(), output.amount.cents());
            }
        }

        for (asset, credit_amount) in credit.into_iter() {
            if let Some(debit_amount) = debit.remove(&asset) {
                if debit_amount != credit_amount {
                    return Err(Error::InvalidAmount(
                        asset.new_amount(debit_amount),
                        asset.new_amount(credit_amount),
                    ));
                }
            } else {
                return Err(Error::MissingSpendingAsset(asset));
            }
        }

        if let Some((asset, _)) = debit.into_iter().next() {
            return Err(Error::MissingPaymentAsset(asset));
        }

        Ok(())
    }
}

/// Transactions
///
/// A transaction is a set of payments being spent, to create a new set of payments. Payments can be
/// spent only once. This simple model is inspired by Bitcoin's Unspent Transaction output model. In
/// every transaction, the sum of the spends must equal the sum of the creates. Any difference will
/// result in an error.
///
/// Every payment has a target account and the amount and asset.
///
/// Transactions are immutable, but since this is an append-only database, a newer version of the
/// transaction can replace a previous version, as long as the transaction is not finalized.
/// Previous transaction versions are kept forever and never pruned. The spend and create fields are
/// not updatable, and the state of the transaction has a transition rule that will be enforced in
/// each update. Furthermore, all new revisions must have a description of their update, inspired by
/// a git commit message.
///
/// A Finalized transaction will either be settled (i.e. spendable) or reverted, in which case it is
/// void but it is kept for historical reasons.
///
/// Although there is no concept of balances or accounts at this layer, the balance associated with
/// an account is a sum of all received payments that were not spent.
///
/// The transaction ID, and the revision ID, are the cryptographic hash of the transactions
#[derive(Debug, Clone, Serialize)]
pub struct Transaction {
    /// The TransactionID is the RevisionID of the first revision of the transaction.
    pub id: TransactionId,
    /// Current Revision ID.
    pub revision: TransactionId,
    /// The transaction inner details
    #[serde(flatten)]
    inner: TransactionInner,
}

impl TryFrom<TransactionInner> for Transaction {
    type Error = Error;

    fn try_from(inner: TransactionInner) -> Result<Self, Self::Error> {
        let id = inner.calculate_id()?;
        Ok(Transaction {
            id: inner.first_revision.clone().unwrap_or_else(|| id.clone()),
            revision: id,
            inner,
        })
    }
}

impl Transaction {
    /// Creates a new external deposit transaction
    ///
    /// All transactions must be balanced, same amounts that are spent should be
    /// created. There are two exceptions, external deposits and withdrawals.
    /// The idea is to mimic external operations, where new assets enter the system.
    pub fn new_external_deposit(
        reference: String,
        status: Status,
        pay_to: Vec<(AccountId, Amount)>,
    ) -> Result<Transaction, Error> {
        TransactionInner {
            first_revision: None,
            changelog: "".to_owned(),
            previous: None,
            spends: vec![],
            creates: pay_to
                .into_iter()
                .map(|(to, amount)| PaymentTo { to, amount })
                .collect(),
            reference,
            typ: Type::Deposit,
            tags: Vec::new(),
            status,
            created_at: Utc::now(),
            updated_at: Utc::now(),
        }
        .try_into()
    }

    /// Returns a unique list of accounts involved in this transaction.
    ///
    /// Accounts are sorted and unique, and they include the accounts that spent and that receives
    pub fn accounts(&self) -> Vec<AccountId> {
        let mut accounts = self
            .inner
            .creates
            .iter()
            .map(|x| x.to.clone())
            .collect::<Vec<_>>();

        accounts.extend(
            self.inner
                .spends
                .iter()
                .map(|x| x.from.clone())
                .collect::<Vec<_>>(),
        );

        accounts.sort();
        accounts.dedup();
        accounts
    }

    /// Creates a new external withdrawal transaction
    ///
    /// Burns assets to reflect external withdrawals
    pub fn new_external_withdrawal(
        reference: String,
        status: Status,
        spend: Vec<PaymentFrom>,
    ) -> Result<Transaction, Error> {
        TransactionInner {
            first_revision: None,
            changelog: "".to_owned(),
            previous: None,
            spends: spend,
            creates: vec![],
            reference,
            typ: Type::Withdrawal,
            tags: Vec::new(),
            status,
            created_at: Utc::now(),
            updated_at: Utc::now(),
        }
        .try_into()
    }

    /// Gets the inner transaction
    pub fn inner(&self) -> &TransactionInner {
        &self.inner
    }

    /// Creates a new transaction
    pub async fn new(
        reference: String,
        status: Status,
        typ: Type,
        spends: Vec<PaymentFrom>,
        pay_to: Vec<(AccountId, Amount)>,
    ) -> Result<Transaction, Error> {
        // for (i, input) in spends.iter().enumerate() {
        //     if !input.is_spendable_or_was_by(&id) {
        //         return Err(Error::InvalidPaymentStatus(i, input.status.clone()));
        //    }
        // }
        let create = pay_to
            .into_iter()
            .map(|(to, amount)| PaymentTo { to, amount })
            .collect();

        TransactionInner {
            first_revision: None,
            changelog: "".to_owned(),
            previous: None,
            spends,
            creates: create,
            reference,
            typ,
            tags: Vec::new(),
            status,
            created_at: Utc::now(),
            updated_at: Utc::now(),
        }
        .try_into()
    }

    /// Prepares a transaction ammend to update its status.
    ///
    /// If the status transaction is not allowed, it will return an error.
    ///
    /// The returned transaction is the newest version which is already persisted. The previous
    /// version is not longer in memory
    #[inline]
    pub async fn change_status<S>(
        self,
        config: &Config<S>,
        new_status: Status,
        reason: String,
    ) -> Result<Self, Error>
    where
        S: Storage + Sync + Send,
    {
        config
            .status
            .is_valid_transition(&self.inner.status, &new_status)?;
        let mut inner = self.inner;
        inner.changelog = reason;
        if inner.first_revision.is_none() {
            inner.first_revision = Some(self.id);
        }
        inner.updated_at = Utc::now();
        inner.previous = Some(self.revision);
        inner.status = new_status;
        let mut x: Transaction = inner.try_into()?;
        x.persist(config).await?;
        Ok(x)
    }

    /// Validates the transaction before storing
    pub(crate) fn validate(&self) -> Result<(), Error> {
        let calculated_revision_id = self.inner.calculate_id()?;

        if self.revision != calculated_revision_id
            || (self.inner.previous.is_none() && self.id != calculated_revision_id)
        {
            return Err(Error::InvalidTransactionId(
                self.id.clone(),
                calculated_revision_id,
            ));
        }

        self.inner.validate()
    }

    /// Returns the list of payments that were used to create this transaction
    pub fn spends(&self) -> &[PaymentFrom] {
        &self.inner.spends
    }

    /// Returns the list of payments that were created by this transaction
    pub fn creates(&self) -> &[PaymentTo] {
        &self.inner.creates
    }

    /// Returns the transaction ID
    pub fn id(&self) -> &TransactionId {
        &self.id
    }

    /// Returns the transaction status
    pub fn status(&self) -> &Status {
        &self.inner.status
    }

    /// Returns the transaction type
    pub fn typ(&self) -> Type {
        self.inner.typ
    }

    /// Returns the reference of this transaction
    pub fn reference(&self) -> &str {
        &self.inner.reference
    }

    /// Returns the time when this transaction was created
    pub fn created_at(&self) -> DateTime<Utc> {
        self.inner.created_at
    }

    /// Returns the time when this transaction was last updated
    pub fn updated_at(&self) -> DateTime<Utc> {
        self.inner.updated_at
    }

    /// Persists the changes done to this transaction object.
    /// This method is not idempotent, and it will fail if the transaction if the requested update
    /// is not allowed.
    pub async fn persist<'a, S>(&mut self, config: &'a Config<S>) -> Result<(), Error>
    where
        S: Storage + Sync + Send,
    {
        self.validate()?;

        let mut batch = config.storage.begin().await?;

        if let Some(previous_id) = &self.inner.previous {
            // Make sure this update is updating the last revision and the status is not final
            let current_transaction = batch.get_transaction(&self.id).await?;

            if current_transaction.revision != *previous_id
                || config.status.is_final(&current_transaction.inner.status)
                || self.inner.transaction_fingerprint()?
                    != current_transaction.inner.transaction_fingerprint()?
            {
                return Err(Error::TransactionUpdatesNotAllowed);
            }

            // Updates all the spends to reflect the new status.
            let (updated_created, updated_spent) = if config.status.is_reverted(&self.inner.status)
            {
                // Release all the previously spent payments since the whole transaction is being
                // reverted due a failure or cancellation.
                batch
                    .update_transaction_payments(
                        &self.id,
                        storage::Status::Failed,
                        storage::Status::Spendable,
                    )
                    .await?
            } else if config.status.is_spendable(&self.inner.status) {
                // Spend all the payments that were used to create this transaction
                batch
                    .update_transaction_payments(
                        &self.id,
                        storage::Status::Spendable,
                        storage::Status::Spent,
                    )
                    .await?
            } else {
                // Lock both the spent transaction and the created transaction, since this
                // transaction is still not finalized
                batch
                    .update_transaction_payments(
                        &self.id,
                        storage::Status::Locked,
                        storage::Status::Locked,
                    )
                    .await?
            };
            if updated_created != self.inner.creates.len()
                || updated_spent != self.inner.spends.len()
            {
                return Err(Error::NoUpdate);
            }
        } else {
            let spends = self
                .inner
                .spends
                .iter()
                .map(|x| x.id.clone())
                .collect::<Vec<_>>();
            let (spent_payment_status, creates_payment_status) =
                if config.status.is_spendable(&self.inner.status) {
                    (storage::Status::Spent, storage::Status::Spendable)
                } else {
                    (storage::Status::Locked, storage::Status::Locked)
                };
            batch
                .spend_payments(&self.id, spends, spent_payment_status)
                .await?;
            batch
                .create_payments(&self.id, &self.inner.creates, creates_payment_status)
                .await?;

            for account in self.accounts() {
                batch
                    .relate_account_to_transaction(&self.id, &account, self.typ())
                    .await?;
            }
        }

        batch.store_transaction(self).await?;

        //batch.tag_transaction(self, &self.inner.tags).await?;

        batch.commit().await?;
        Ok(())
    }
}