use core::ops::Deref;
use std::sync::{Arc, RwLock};

use async_trait::async_trait;

use sp_core::Decode;
use sp_application_crypto::{
  RuntimePublic as PublicTrait,
  sr25519::{Public, Signature},
};
use sp_keystore::CryptoStore;

use sp_staking::SessionIndex;
use sp_api::{BlockId, ProvideRuntimeApi};

use sc_client_api::HeaderBackend;

use tendermint_machine::ext::{BlockNumber, RoundNumber, Weights, Signer, SignatureScheme};

use sp_tendermint::TendermintApi;

use crate::{KEY_TYPE_ID, TendermintClient};

struct TendermintValidatorsStruct {
  session: SessionIndex,

  total_weight: u64,
  weights: Vec<u64>,

  lookup: Vec<Public>,
}

impl TendermintValidatorsStruct {
  fn from_module<T: TendermintClient>(client: &Arc<T::Client>) -> Self {
    let last = client.info().finalized_hash;
    let api = client.runtime_api();
    let session = api.current_session(&BlockId::Hash(last)).unwrap();
    let validators = api.validators(&BlockId::Hash(last)).unwrap();

    Self {
      session,

      // TODO
      total_weight: validators.len().try_into().unwrap(),
      weights: vec![1; validators.len()],

      lookup: validators,
    }
  }
}

// Wrap every access of the validators struct in something which forces calling refresh
struct Refresh<T: TendermintClient> {
  client: Arc<T::Client>,
  _refresh: Arc<RwLock<TendermintValidatorsStruct>>,
}

impl<T: TendermintClient> Refresh<T> {
  // If the session has changed, re-create the struct with the data on it
  fn refresh(&self) {
    let session = self._refresh.read().unwrap().session;
    let current_block = BlockId::Hash(self.client.info().finalized_hash);
    if session != self.client.runtime_api().current_session(&current_block).unwrap() {
      *self._refresh.write().unwrap() = TendermintValidatorsStruct::from_module::<T>(&self.client);
    }
  }
}

impl<T: TendermintClient> Deref for Refresh<T> {
  type Target = RwLock<TendermintValidatorsStruct>;
  fn deref(&self) -> &RwLock<TendermintValidatorsStruct> {
    self.refresh();
    &self._refresh
  }
}

/// Tendermint validators observer, providing data on the active validators.
pub struct TendermintValidators<T: TendermintClient>(Refresh<T>);
impl<T: TendermintClient> Clone for TendermintValidators<T> {
  fn clone(&self) -> Self {
    Self(Refresh { _refresh: self.0._refresh.clone(), client: self.0.client.clone() })
  }
}

impl<T: TendermintClient> TendermintValidators<T> {
  pub(crate) fn new(client: Arc<T::Client>) -> TendermintValidators<T> {
    TendermintValidators(Refresh {
      _refresh: Arc::new(RwLock::new(TendermintValidatorsStruct::from_module::<T>(&client))),
      client,
    })
  }
}

pub struct TendermintSigner<T: TendermintClient>(
  pub(crate) Arc<dyn CryptoStore>,
  pub(crate) TendermintValidators<T>,
);

impl<T: TendermintClient> Clone for TendermintSigner<T> {
  fn clone(&self) -> Self {
    Self(self.0.clone(), self.1.clone())
  }
}

impl<T: TendermintClient> TendermintSigner<T> {
  async fn get_public_key(&self) -> Public {
    let pubs = self.0.sr25519_public_keys(KEY_TYPE_ID).await;
    if pubs.is_empty() {
      self.0.sr25519_generate_new(KEY_TYPE_ID, None).await.unwrap()
    } else {
      pubs[0]
    }
  }
}

#[async_trait]
impl<T: TendermintClient> Signer for TendermintSigner<T> {
  type ValidatorId = u16;
  type Signature = Signature;

  async fn validator_id(&self) -> Option<u16> {
    let key = self.get_public_key().await;
    for (i, k) in (*self.1 .0).read().unwrap().lookup.iter().enumerate() {
      if k == &key {
        return Some(u16::try_from(i).unwrap());
      }
    }
    None
  }

  async fn sign(&self, msg: &[u8]) -> Signature {
    Signature::decode(
      &mut self
        .0
        .sign_with(KEY_TYPE_ID, &self.get_public_key().await.into(), msg)
        .await
        .unwrap()
        .unwrap()
        .as_ref(),
    )
    .unwrap()
  }
}

impl<T: TendermintClient> SignatureScheme for TendermintValidators<T> {
  type ValidatorId = u16;
  type Signature = Signature;
  type AggregateSignature = Vec<Signature>;
  type Signer = TendermintSigner<T>;

  fn verify(&self, validator: u16, msg: &[u8], sig: &Signature) -> bool {
    self.0.read().unwrap().lookup[usize::try_from(validator).unwrap()].verify(&msg, sig)
  }

  fn aggregate(sigs: &[Signature]) -> Vec<Signature> {
    sigs.to_vec()
  }

  fn verify_aggregate(&self, validators: &[u16], msg: &[u8], sigs: &Vec<Signature>) -> bool {
    if validators.len() != sigs.len() {
      return false;
    }
    for (v, sig) in validators.iter().zip(sigs.iter()) {
      if !self.verify(*v, msg, sig) {
        return false;
      }
    }
    true
  }
}

impl<T: TendermintClient> Weights for TendermintValidators<T> {
  type ValidatorId = u16;

  fn total_weight(&self) -> u64 {
    self.0.read().unwrap().total_weight
  }

  fn weight(&self, id: u16) -> u64 {
    self.0.read().unwrap().weights[usize::try_from(id).unwrap()]
  }

  // TODO: https://github.com/serai-dex/serai/issues/159
  fn proposer(&self, number: BlockNumber, round: RoundNumber) -> u16 {
    u16::try_from(
      (number.0 + u64::from(round.0)) % u64::try_from(self.0.read().unwrap().lookup.len()).unwrap(),
    )
    .unwrap()
  }
}