// Copyright 2021 MaidSafe.net limited.
//
// This SAFE Network Software is licensed to you under The General Public License (GPL), version 3.
// Unless required by applicable law or agreed to in writing, the SAFE Network Software distributed
// under the GPL Licence is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. Please review the Licences for the specific language governing
// permissions and limitations relating to use of the SAFE Network Software.

// Code required to mint Dbcs
// The in the most basic terms means
// a valid input DBC can be split into
// 1 or more DBCs as long as
// input is vaid
// Outputs <= input value

use std::collections::{BTreeMap, HashSet};

use crate::{
    Dbc, DbcContent, DbcContentHash, DbcTransaction, Error, KeyCache, KeyManager, PublicKey,
    Result, Signature,
};

#[derive(Default)]
struct SpendBook {
    transactions: BTreeMap<DbcContentHash, DbcTransaction>,
}

impl SpendBook {
    fn lookup(&self, dbc_hash: &DbcContentHash) -> Option<&DbcTransaction> {
        self.transactions.get(dbc_hash)
    }

    fn log(&mut self, dbc_hash: DbcContentHash, transaction: DbcTransaction) {
        self.transactions.insert(dbc_hash, transaction);
    }
}

#[derive(Debug, Clone)]
pub struct MintRequest {
    pub inputs: HashSet<Dbc>,
    pub outputs: HashSet<DbcContent>,
}

impl MintRequest {
    pub fn to_transaction(&self) -> DbcTransaction {
        DbcTransaction {
            inputs: self.inputs.iter().map(|i| i.name()).collect(),
            outputs: self.outputs.iter().map(|i| i.hash()).collect(),
        }
    }

    pub fn verify_transaction_balances(&self) -> Result<()> {
        let in_amount: u64 = self.inputs.iter().map(|input| input.amount()).sum();
        let out_amount: u64 = self.outputs.iter().map(|output| output.amount).sum();
        if in_amount != out_amount {
            Err(Error::DbcMintRequestDoesNotBalance)
        } else {
            Ok(())
        }
    }
}

pub struct Mint {
    pub(crate) key_mgr: KeyManager,
    spendbook: SpendBook,
}

impl Mint {
    pub fn genesis(amount: u64) -> (Self, Dbc) {
        let key_mgr = KeyManager::new_genesis();

        let genesis_input = [0u8; 32];

        let parents = vec![genesis_input].into_iter().collect();
        let content = DbcContent::new(parents, amount, 0);

        let transaction = DbcTransaction {
            inputs: vec![genesis_input].into_iter().collect(),
            outputs: vec![content.hash()].into_iter().collect(),
        };

        let mut spendbook = SpendBook::default();
        spendbook.log(genesis_input, transaction.clone());

        let transaction_sig = key_mgr.sign(&transaction.hash());

        let dbc = Dbc {
            content,
            transaction,
            transaction_sigs: vec![(genesis_input, (key_mgr.public_key(), transaction_sig))]
                .into_iter()
                .collect(),
        };

        (Self { key_mgr, spendbook }, dbc)
    }

    pub fn key_cache(&self) -> &KeyCache {
        self.key_mgr.key_cache()
    }

    pub fn public_key(&self) -> PublicKey {
        self.key_mgr.public_key()
    }

    pub fn reissue(
        &mut self,
        mint_request: MintRequest,
    ) -> Result<(
        DbcTransaction,
        BTreeMap<DbcContentHash, (PublicKey, Signature)>,
    )> {
        mint_request.verify_transaction_balances()?;
        self.validate_transaction_input_dbcs(&mint_request.inputs)?;
        let transaction = mint_request.to_transaction();
        let transaction_sigs = self.sign_transaction(&transaction);

        for input in mint_request.inputs.iter() {
            self.spendbook.log(input.name(), transaction.clone());
        }

        Ok((transaction, transaction_sigs))
    }

    fn validate_transaction_input_dbcs(&self, inputs: &HashSet<Dbc>) -> Result<()> {
        if inputs.len() == 0 {
            return Err(Error::TransactionMustHaveAnInput);
        }

        for input in inputs.iter() {
            input.confirm_valid(self.key_cache())?;

            if let Some(transaction) = self.spendbook.lookup(&input.name()).cloned() {
                // This input has already been spent, return the transaction to the user
                let transaction_sigs = self.sign_transaction(&transaction);
                return Err(Error::DbcAlreadySpent {
                    transaction,
                    transaction_sigs,
                });
            }
        }

        Ok(())
    }

    fn sign_transaction(
        &self,
        transaction: &DbcTransaction,
    ) -> BTreeMap<DbcContentHash, (PublicKey, Signature)> {
        let sig = self.key_mgr.sign(&transaction.hash());

        transaction
            .inputs
            .iter()
            .copied()
            .zip(std::iter::repeat((self.public_key(), sig)))
            .collect()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::collections::BTreeSet;

    use quickcheck_macros::quickcheck;

    use crate::tests::{TinyInt, TinyVec};

    #[quickcheck]
    fn prop_genesis() {
        let (mint, genesis_dbc) = Mint::genesis(1000);
        assert_eq!(genesis_dbc.content.amount, 1000);
        let validation = genesis_dbc.confirm_valid(&mint.key_cache());
        println!("Genesis DBC Validation {:?}", validation);
        assert!(validation.is_ok());
    }

    #[quickcheck]
    fn prop_splitting_the_genesis_dbc(output_amounts: TinyVec<TinyInt>) {
        let output_amount = output_amounts.vec().iter().map(|i| i.coerce::<u64>()).sum();

        let (mut genesis, genesis_dbc) = Mint::genesis(output_amount);

        let inputs: HashSet<_> = vec![genesis_dbc.clone()].into_iter().collect();
        let input_hashes: BTreeSet<_> = inputs.iter().map(|in_dbc| in_dbc.name()).collect();

        let outputs = output_amounts
            .vec()
            .iter()
            .enumerate()
            .map(|(i, amount)| DbcContent::new(input_hashes.clone(), amount.coerce(), i as u8))
            .collect();

        let mint_request = MintRequest { inputs, outputs };

        let (transaction, transaction_sigs) = genesis.reissue(mint_request.clone()).unwrap();

        // Verify transaction returned to us by the Mint matches our request
        assert_eq!(mint_request.to_transaction(), transaction);
        assert_eq!(
            transaction.inputs,
            mint_request.inputs.iter().map(|i| i.name()).collect()
        );
        assert_eq!(
            transaction.outputs,
            mint_request.outputs.iter().map(|o| o.hash()).collect()
        );

        // Verify signatures corespond to each input
        let (pubkey, sig) = transaction_sigs.values().cloned().next().unwrap();
        for input in mint_request.inputs.iter() {
            assert_eq!(transaction_sigs.get(&input.name()), Some(&(pubkey, sig)));
        }
        assert_eq!(transaction_sigs.len(), transaction.inputs.len());

        let output_dbcs: Vec<_> = mint_request
            .outputs
            .into_iter()
            .map(|content| Dbc {
                content,
                transaction: transaction.clone(),
                transaction_sigs: transaction_sigs.clone(),
            })
            .collect();

        let key_cache = KeyCache::from(vec![genesis.public_key()]);
        for dbc in output_dbcs.iter() {
            let expected_amount: u64 =
                output_amounts.vec()[dbc.content.output_number as usize].coerce();
            assert_eq!(dbc.amount(), expected_amount);
            assert!(dbc.confirm_valid(&key_cache).is_ok());
        }

        assert_eq!(
            output_dbcs.iter().map(|dbc| dbc.amount()).sum::<u64>(),
            output_amount
        );
    }

    #[test]
    fn test_double_spend_protection() {
        let (mut genesis, genesis_dbc) = Mint::genesis(1000);

        let inputs: HashSet<_> = vec![genesis_dbc.clone()].into_iter().collect();
        let input_hashes: BTreeSet<_> = vec![genesis_dbc.name()].into_iter().collect();

        let mint_request = MintRequest {
            inputs: inputs.clone(),
            outputs: vec![DbcContent::new(input_hashes.clone(), 1000, 0)]
                .into_iter()
                .collect(),
        };

        let (t, s) = genesis.reissue(mint_request).unwrap();

        let double_spend_mint_request = MintRequest {
            inputs,
            outputs: vec![DbcContent::new(input_hashes, 1000, 1)]
                .into_iter()
                .collect(),
        };

        let res = genesis.reissue(double_spend_mint_request);

        assert!(matches!(
            res,
            Err(Error::DbcAlreadySpent { transaction, transaction_sigs }) if transaction == t && transaction_sigs == s
        ));
    }

    #[quickcheck]
    fn prop_dbc_transaction_many_to_many(
        input_amounts: TinyVec<TinyInt>,
        output_amounts: TinyVec<TinyInt>,
    ) {
        let genesis_amount = input_amounts.vec().iter().map(|i| i.coerce::<u64>()).sum();

        let (mut genesis, genesis_dbc) = Mint::genesis(genesis_amount);

        let gen_inputs: HashSet<_> = vec![genesis_dbc.clone()].into_iter().collect();
        let gen_input_hashes: BTreeSet<_> = gen_inputs.iter().map(|in_dbc| in_dbc.name()).collect();
        let input_content: HashSet<_> = input_amounts
            .vec()
            .iter()
            .enumerate()
            .map(|(i, amount)| DbcContent::new(gen_input_hashes.clone(), amount.coerce(), i as u8))
            .collect();

        let mint_request = MintRequest {
            inputs: gen_inputs,
            outputs: input_content.clone(),
        };

        let (transaction, transaction_sigs) = genesis.reissue(mint_request.clone()).unwrap();

        let input_dbcs: HashSet<_> = input_content
            .into_iter()
            .map(|content| Dbc {
                content,
                transaction: transaction.clone(),
                transaction_sigs: transaction_sigs.clone(),
            })
            .collect();

        let input_hashes: BTreeSet<_> = input_dbcs.iter().map(|in_dbc| in_dbc.name()).collect();

        let outputs: HashSet<_> = output_amounts
            .vec()
            .iter()
            .enumerate()
            .map(|(i, amount)| DbcContent::new(input_hashes.clone(), amount.coerce(), i as u8))
            .collect();

        let mint_request = MintRequest {
            inputs: input_dbcs,
            outputs: outputs.clone(),
        };

        let many_to_many_result = genesis.reissue(mint_request.clone());

        match many_to_many_result {
            Ok((transaction, transaction_sigs)) => {
                let output_amount: u64 =
                    output_amounts.vec().iter().map(|i| i.coerce::<u64>()).sum();
                assert_eq!(genesis_amount, output_amount);

                let output_dbcs: Vec<_> = outputs
                    .into_iter()
                    .map(|content| Dbc {
                        content,
                        transaction: transaction.clone(),
                        transaction_sigs: transaction_sigs.clone(),
                    })
                    .collect();

                for dbc in output_dbcs.iter() {
                    let dbc_confirm_result =
                        dbc.confirm_valid(&KeyCache::from(vec![genesis.public_key()]));
                    println!("DBC confirm result {:?}", dbc_confirm_result);
                    assert!(dbc_confirm_result.is_ok());
                }

                assert_eq!(
                    output_dbcs.iter().map(|dbc| dbc.amount()).sum::<u64>(),
                    output_amount
                );
            }
            Err(Error::DbcMintRequestDoesNotBalance) => {
                let output_amount: u64 =
                    output_amounts.vec().iter().map(|i| i.coerce::<u64>()).sum();
                assert_ne!(genesis_amount, output_amount);
            }
            Err(Error::TransactionMustHaveAnInput) => {
                assert_eq!(input_amounts.vec().len(), 0);
            }
            err => panic!("Unexpected reissue err {:#?}", err),
        }
    }

    #[quickcheck]
    fn prop_dbc_ensure_outputs_are_numbered_uniquely() {
        todo!()
    }

    #[quickcheck]
    fn prop_in_progress_transaction_can_be_continued_across_churn() {
        todo!()
    }

    #[quickcheck]
    fn prop_reject_invalid_prefix() {
        todo!();
    }

    #[quickcheck]
    fn prop_output_parents_must_match_inputs() {
        todo!();
    }

    #[quickcheck]
    fn prop_input_ownership_proofs_are_checked() {
        todo!();
    }

    #[test]
    fn test_inputs_are_validated() {
        let (mut genesis, _) = Mint::genesis(1000);

        let input_content = DbcContent {
            parents: Default::default(),
            amount: 100,
            output_number: 0,
        };
        let input_content_hashes: BTreeSet<_> = vec![input_content.hash()].into_iter().collect();

        let fraudulant_reissue_result = genesis.reissue(MintRequest {
            inputs: vec![Dbc {
                content: input_content,
                transaction: DbcTransaction {
                    inputs: Default::default(),
                    outputs: input_content_hashes.clone(),
                },
                transaction_sigs: Default::default(),
            }]
            .into_iter()
            .collect(),
            outputs: vec![DbcContent {
                parents: input_content_hashes,
                amount: 100,
                output_number: 0,
            }]
            .into_iter()
            .collect(),
        });
        assert!(fraudulant_reissue_result.is_err());
    }
}