use crate::blocks::block::{Block, UnminedBlock};
use crate::common::binary_conversions::hex_to_u64;
use crate::common::check_genesis::genesis_checkup;
use crate::common::types::Transaction;
use crate::encode;
use crate::miner::fairness::fairness_difficulty;
use crate::records::block_height::get_block_height::get_height;
use crate::records::memory::chain_state::{
    cached_chain_height, cached_tip_hash, cached_tip_header,
};
use crate::records::memory::network_mapping::NodeInfo;
use crate::records::unpack_block::unpack_header::load_block_header;
use crate::records::wallet_registry::resolve_pubkey_from_short_address;
use crate::sled::Db;
use crate::verifications::verification_service::VerificationService;
use crate::wallets::structures::Wallet;
use crate::Arc;
use crate::Utc;

const ALLOWED_FUTURE_BLOCK_SECONDS: u32 = 1;

impl Block {
    pub async fn verify(
        &self,
        db: &Db,
        verification_service: Arc<VerificationService>,
    ) -> Result<Vec<String>, String> {
        // block verification checks header validity first, then
        // delegates transaction verification to the shared service
        // get transactionsfrom block
        let transactions = &self.transactions;

        // verifiy the number of transactions is not more than 1000001
        let total_transactions = transactions.len() as u32;
        if total_transactions > 15_000_001 {
            return Err(format!(
                "Too many transactions in the block: {total_transactions}"
            ));
        }

        // get current timestamp
        let current_timestamp = Utc::now().timestamp() as u32;

        // get header from block
        let header = &self.vrf_block;

        // validate miner
        let miner = &header.unmined_block.miner;
        let miner_pubkey = resolve_pubkey_from_short_address(db, miner)
            .map_err(|e| e.to_string())?
            .ok_or_else(|| "This miner address is not registered".to_string())?;
        let miner_pubkey_hex = encode(&miner_pubkey);
        let block_number = current_chain_height(db).await + 1;

        if !NodeInfo::address_checkup(miner, block_number).await {
            return Err("This address is not eligable to mine".to_string());
        }

        // get variables from the block
        let timestamp = header.unmined_block.timestamp;
        let previous_hash = header.unmined_block.previous_hash.clone();
        let difficulty = header.unmined_block.next_block_difficulty;
        let vrf = header.vrf;
        let proof = &header.proof;

        // hash the header to validate the difficulty
        let unmined_header_hash = header.unmined_block.hash().await;

        // validate vrf number
        if !Wallet::vrf_verify_with_public_key(vrf, &unmined_header_hash, &miner_pubkey_hex, proof)
            .await
        {
            return Err("Invalid vrf.".to_string());
        }

        // hash the header to validate the difficulty
        let header_hash = header.hash().await;

        // get u64 value
        let hash = hex_to_u64(&header_hash).await?;

        // validate hash
        Self::validate_hash_difficulty(db, hash).await?;

        // Allow the same one-second clock skew tolerated during handshake,
        // while the parent timestamp check below still enforces block spacing.
        if timestamp > current_timestamp.saturating_add(ALLOWED_FUTURE_BLOCK_SECONDS) {
            return Err("Timestamp in the block is in the future.".to_string());
        }

        // We need to check if the genesis block exists to do
        // any previous block validations or we will get an error
        // trying to validate the genesis block as the block 0
        // won't load.
        if genesis_checkup().await {
            Self::not_genesis_block_checkup(db, miner, timestamp, previous_hash, difficulty)
                .await?;
        }

        let results = Self::send_transactions_to_validate(
            miner.to_string(),
            self.transactions.clone(),
            db.clone(),
            verification_service,
        )
        .await?;

        Ok(results)
    }

    async fn not_genesis_block_checkup(
        db: &Db,
        miner: &str,
        timestamp: u32,
        previous_hash: String,
        difficulty: u64,
    ) -> Result<(), String> {
        // non-genesis blocks must reference the current tip,
        // satisfy fairness rules, and carry the correct next difficulty
        // load the last block this is the current height
        // as we are always validating a height higher than
        // what is recorded.
        let previous_height = current_chain_height(db).await;
        let previous_block = match cached_tip_header(previous_height).await {
            Some(header) => header,
            None => load_block_header(previous_height).await?,
        };

        // check if miner is eligible based on
        // fairness difficulty checker
        if !fairness_difficulty(previous_height, miner).await {
            return Err(
                "You have not passed the fairness difficulty, You cannot mine this block."
                    .to_string(),
            );
        }

        // get previous block hash
        let calculated_previous_hash = match cached_tip_hash(previous_height).await {
            Some(hash) => hash,
            None => previous_block.hash().await,
        };

        // Validate recorded previous_hash is equal to
        // the previous block hash
        if calculated_previous_hash != previous_hash {
            return Err("Incorrect previous_block_hash.".to_string());
        }

        // validate that the current timestamp is greater the previous
        // block timestamp plus 2 seconds
        let current_timestamp = Utc::now().timestamp() as u32;
        if current_timestamp < previous_block.unmined_block.timestamp + 1 {
            return Err("Mining to quickly".to_string());
        }

        // validate that the timestamp of the current block we are
        // validating is greater than the previous block timestamp
        // plus 2 seconds
        if timestamp < previous_block.unmined_block.timestamp + 2 {
            return Err("Mining to quickly".to_string());
        }

        // get next block difficulty
        let difficulty_adjustment = UnminedBlock::adjust_difficulty(
            timestamp,
            db,
            previous_block.unmined_block.next_block_difficulty,
        )
        .await;

        // validate the listed next block difficulty matches what
        // we calculated it should be
        if difficulty_adjustment != difficulty {
            let e = "Incorrect value for next block difficulty".to_string();
            return Err(e);
        }
        Ok(())
    }

    async fn send_transactions_to_validate(
        miner: String,
        transactions: Vec<Transaction>,
        db: crate::sled::Db,
        verification_service: Arc<VerificationService>,
    ) -> Result<Vec<String>, String> {
        // transaction verification is centralized in the shared
        // verification service so block assembly stays lightweight
        verification_service
            .verify_block_transactions(miner, transactions, db)
            .await
    }

    async fn validate_hash_difficulty(db: &Db, hash: u64) -> Result<(), String> {
        // compare the reduced header hash against the previous
        // block's recorded target difficulty threshold
        if !genesis_checkup().await {
            let difficulty_target = 2000000000000000_u64;
            if hash <= difficulty_target {
                return Ok(());
            } else {
                return Err(
                    "Block hash does not satisfy the genesis difficulty threshold.".to_string(),
                );
            }
        }
        let current_block_number = current_chain_height(db).await + 1;
        let previous_block_height = current_block_number - 1;
        let previous_block = match cached_tip_header(previous_block_height).await {
            Some(header) => header,
            None => load_block_header(previous_block_height).await?,
        };
        let difficulty_target = previous_block.unmined_block.next_block_difficulty;
        if hash >= difficulty_target {
            Err(format!(
                "Block hash does not satisfy the required difficulty threshold: hash_value={hash} required_below={difficulty_target}"
            ))
        } else {
            Ok(())
        }
    }
}

async fn current_chain_height(db: &Db) -> u32 {
    cached_chain_height()
        .await
        .unwrap_or_else(|| get_height(db))
}