use crate::{
    storage::{Batch, Storage},
    transaction::Type,
    AccountId, Amount, AssetManager, Error, Payment, Status, Transaction, TransactionId,
};
use std::{cmp::Ordering, collections::HashMap};

#[derive(Clone, Debug)]
pub struct Ledger<'a, B, S>
where
    B: Batch<'a>,
    S: Storage<'a, B> + Sync + Send,
{
    storage: S,
    asset_manager: AssetManager,
    _phantom: std::marker::PhantomData<&'a B>,
}

impl<'a, B, S> Ledger<'a, B, S>
where
    B: Batch<'a>,
    S: Storage<'a, B> + Sync + Send,
{
    pub fn new(storage: S, asset_manager: AssetManager) -> Self {
        Self {
            storage,
            asset_manager,
            _phantom: std::marker::PhantomData,
        }
    }

    pub fn parse_amount(&self, asset: &str, amount: &str) -> Result<Amount, Error> {
        Ok(self.asset_manager.human_amount_by_name(asset, amount)?)
    }

    /// Selects the unspent payments to be used as inputs of the new transaction.
    ///
    /// This function also returns a list of transactions that will be used as
    /// exchanged transactions, to make sure the main transaction doesn't hold
    /// extra funds, by splitting any large unspent payments into two, one that
    /// matches exactly the needed amount, and another one that will be used as
    /// change. These exchange transaction are internal transactions and they
    /// are created as settled.
    async fn create_inputs_to_pay_from_accounts(
        &self,
        payments: Vec<(AccountId, Amount)>,
    ) -> Result<(Vec<Transaction>, Vec<Payment>), Error> {
        let mut to_spend = HashMap::new();

        for (account_id, amount) in payments.into_iter() {
            let id = (account_id, *amount.asset());
            if let Some(value) = to_spend.get_mut(&id) {
                *value += amount.cents();
            } else {
                to_spend.insert(id, amount.cents());
            }
        }

        let mut change_transactions = vec![];
        let mut payments: Vec<Payment> = vec![];

        for ((account, asset), mut to_spend_cents) in to_spend.into_iter() {
            let iterator = self
                .storage
                .get_unspent_payments(&account, asset.id, to_spend_cents)
                .await?;
            for payment in iterator.into_iter() {
                let cents = payment.amount.cents();
                to_spend_cents -= cents;
                payments.push(payment);
                match to_spend_cents.cmp(&0) {
                    Ordering::Equal => {
                        // No change amount, we are done with this input
                        break;
                    }
                    Ordering::Less => {
                        // There is a change amount, we need to split the last
                        // input into two payment_ids into the same accounts in
                        // a transaction that will settle immediately, otherwise
                        // the change amount will be unspentable until this
                        // transaction settles. By doing so the current
                        // operation will have no change and it can safely take
                        // its time to settle without making any change amount
                        // unspentable.
                        let to_spend_cents = to_spend_cents.abs();
                        let input = payments
                            .pop()
                            .ok_or(Error::InsufficientBalance(account.clone(), asset.id))?;
                        let split_input = Transaction::new(
                            "Exchange transaction".to_owned(),
                            // Set the change transaction as settled. This is an
                            // internal transaction to split an existing payment
                            // into two. Since this is an internal transaction it
                            // can be settled immediately.
                            //
                            // Because this internal transaction is being settled
                            // immediately, the other payment can be used right away,
                            // otherwise it would be locked until the main
                            // transaction settles.
                            Status::Settled,
                            Type::Internal,
                            vec![input],
                            vec![
                                (account.clone(), asset.new_amount(cents - to_spend_cents)),
                                (account.clone(), asset.new_amount(to_spend_cents)),
                            ],
                        )
                        .await?;
                        // Spend the new payment
                        payments.push(split_input.creates()[0].clone());
                        // Return the split payment transaction to be executed
                        // later as a pre-requisite for the new transaction
                        change_transactions.push(split_input);

                        // Go to the next payment input or exit the loop
                        break;
                    }
                    _ => {
                        // We need more funds, continue to the selecting the
                        // available payment if any
                    }
                }
            }

            if to_spend_cents > 0 {
                // We don't have enough payment to cover the to_spend_cents
                // Return an insufficient balance error
                return Err(Error::InsufficientBalance(account, asset.id));
            }
        }

        Ok((change_transactions, payments))
    }

    /// Creates a new transaction and returns it.
    ///
    /// The input is pretty simple, take this amounts from these given accounts
    /// and send them to these accounts (and amounts). The job of this function
    /// is to figure it out how to do it. This function will make sure that each
    /// account has enough balance, selecting the unspent payments from each
    /// account that will be spent. It will also return a list of transactions
    /// that will be used to return the change to the accounts, these accounts
    /// can be settled immediately so no other funds required to perform the
    /// transaction are locked.
    ///
    /// This functions performs read only operations on top of the storage layer
    /// and it will guarantee execution (meaning that it will not lock any
    /// funds, so these transactions may fail if any selected payment is spent
    /// between the time the transaction is created and executed).
    ///
    /// A NewTransaction struct is returned, the change_transactions should be
    /// executed and set as settled before the transaction is executed,
    /// otherwise it will fail. A failure in any execution will render the
    /// entire operation as failed but no funds will be locked.
    pub async fn new_transaction(
        &'a self,
        reference: String,
        status: Status,
        from: Vec<(AccountId, Amount)>,
        to: Vec<(AccountId, Amount)>,
    ) -> Result<Transaction, Error> {
        let (change_transactions, payments) = self.create_inputs_to_pay_from_accounts(from).await?;

        for mut change_tx in change_transactions.into_iter() {
            change_tx.persist(&self.storage).await?;
        }

        let mut transaction =
            Transaction::new(reference, status, Type::Transaction, payments, to).await?;
        transaction.persist(&self.storage).await?;
        Ok(transaction)
    }

    /// Return the balances from a given account
    ///
    /// The balance is a vector of Amounts, one for each asset. The balance will
    /// return only spendable amounts, meaning that any amount that is locked in
    /// a transaction will not be returned.
    ///
    /// TODO: Return locked funds as well.
    pub async fn get_balance(&self, account: &AccountId) -> Result<Vec<Amount>, Error> {
        Ok(self.storage.get_balance(account).await?)
    }

    pub async fn deposit(
        &'a self,
        account: &AccountId,
        amount: Amount,
        status: Status,
        reference: String,
    ) -> Result<Transaction, Error> {
        let mut transaction =
            Transaction::new_external_deposit(reference, status, vec![(account.clone(), amount)])?;
        println!("{}", serde_json::to_string_pretty(&transaction).unwrap());
        transaction.persist(&self.storage).await?;
        Ok(transaction)
    }

    pub async fn withdrawal(
        &'a self,
        account: &AccountId,
        amount: Amount,
        status: Status,
        reference: String,
    ) -> Result<Transaction, Error> {
        let (change_transactions, payments) = self
            .create_inputs_to_pay_from_accounts(vec![(account.clone(), amount)])
            .await?;
        for mut change_tx in change_transactions.into_iter() {
            change_tx.persist(&self.storage).await?;
        }
        let mut transaction = Transaction::new_external_withdrawal(reference, status, payments)?;
        transaction.persist(&self.storage).await?;
        Ok(transaction)
    }

    /// Returns the transaction object by a given transaction id
    pub async fn get_transaction(
        &'a self,
        transaction_id: &TransactionId,
    ) -> Result<Transaction, Error> {
        Ok(self
            .storage
            .get_transaction(transaction_id)
            .await?
            .try_into()?)
    }

    /// Returns all transactions from a given account. It can be optionally be
    /// sorted by transaction type. The transactions are sorted from newest to
    /// oldest.
    pub async fn get_transactions(
        &'a self,
        account_id: &AccountId,
        typ: Option<Type>,
    ) -> Result<Vec<Transaction>, Error> {
        let r = self
            .storage
            .get_transactions(account_id, typ)
            .await?
            .into_iter()
            .map(|x| x.try_into())
            .collect::<Result<Vec<Transaction>, _>>()?;

        Ok(r)
    }

    /// Attemps to change the status of a given transaction id. On success the
    /// new transaction object is returned, otherwise an error is returned.
    pub async fn change_status(
        &'a self,
        transaction_id: &TransactionId,
        new_status: Status,
    ) -> Result<Transaction, Error> {
        let mut tx: Transaction = self
            .storage
            .get_transaction(transaction_id)
            .await?
            .try_into()?;
        tx.change_status(new_status)?;
        tx.persist(&self.storage).await?;
        Ok(tx)
    }
}