use ore_api::prelude::*;
use solana_nostd_keccak::hash;
use solana_program::slot_hashes::SlotHashes;
use steel::*;

/// Mine a block.
pub fn process_mine(accounts: &[AccountInfo<'_>], data: &[u8]) -> ProgramResult {
    // Parse data.
    let args = Mine::try_from_bytes(data)?;
    let amount = u64::from_le_bytes(args.amount);

    // Load accounts.
    let clock = Clock::get()?;
    let [signer_info, authority_info, block_info, commitment_info, market_info, miner_info, mint_hash_info, mint_ore_info, permit_info, recipient_info, treasury_info, system_program, token_program, slot_hashes_sysvar] =
        accounts
    else {
        return Err(ProgramError::NotEnoughAccountKeys);
    };
    signer_info.is_signer()?;
    authority_info.is_writable()?;
    let block = block_info
        .as_account_mut::<Block>(&ore_api::ID)?
        .assert_mut(|b| clock.slot >= b.start_slot)?
        .assert_mut(|b| clock.slot < b.start_slot + 1500)?;
    commitment_info
        .is_writable()?
        .as_associated_token_account(block_info.key, mint_hash_info.key)?;
    let market = market_info
        .as_account::<Market>(&ore_api::ID)?
        .assert(|m| m.id == block.id)?;
    mint_hash_info.has_address(&market.base.mint)?.as_mint()?;
    mint_ore_info.has_address(&MINT_ADDRESS)?.as_mint()?;
    let miner = miner_info
        .as_account_mut::<Miner>(&ore_api::ID)?
        .assert_mut(|m| m.authority == *authority_info.key)?;
    let permit = permit_info
        .as_account_mut::<Permit>(&ore_api::ID)?
        .assert_mut(|p| p.authority == miner.authority)?
        .assert_mut(|p| p.block_id == block.id)?
        .assert_mut(|p| p.executor == *signer_info.key || p.executor == Pubkey::default())?;
    recipient_info
        .is_writable()?
        .as_associated_token_account(&miner.authority, &MINT_ADDRESS)?;
    treasury_info.has_address(&TREASURY_ADDRESS)?;
    system_program.is_program(&system_program::ID)?;
    token_program.is_program(&spl_token::ID)?;
    slot_hashes_sysvar.is_sysvar(&sysvar::slot_hashes::ID)?;

    // Reduce permit amount.
    let amount = permit.amount.min(amount);
    permit.amount -= amount;

    // Pay executor fee.
    if permit.fee > 0 {
        permit_info.send(permit.fee * amount, signer_info);
    }

    // Close permit account, if empty.
    if permit.amount == 0 {
        permit_info.close(authority_info)?;
    }

    // Burn hash tokens.
    burn_signed(
        commitment_info,
        mint_hash_info,
        block_info,
        token_program,
        amount,
        &[BLOCK, &block.id.to_le_bytes()],
    )?;

    // Set block slot hash.
    if block.slot_hash == [0; 32] {
        let slot_hashes =
            bincode::deserialize::<SlotHashes>(slot_hashes_sysvar.data.borrow().as_ref()).unwrap();
        let Some(slot_hash) = slot_hashes.get(&block.start_slot) else {
            // If mine is not called within ~2.5 minutes of the block starting,
            // then the slot hash will be unavailable and secure hashes cannot be generated.
            return Ok(());
        };
        block.slot_hash = slot_hash.to_bytes();
    }

    // Reset miner hash if mining new block.
    if miner.block_id != block.id {
        miner.block_id = block.id;
        let mut args = [0u8; 96];
        args[..32].copy_from_slice(&block.id.to_le_bytes());
        args[32..64].copy_from_slice(&block.slot_hash);
        args[64..].copy_from_slice(&miner.authority.to_bytes());
        miner.hash = hash(&args);
    }

    // Mine and accumulate rewards.
    let mut miner_reward = 0;
    for _ in 0..amount {
        // Update stats
        block.total_hashes += 1;
        miner.total_hashes += 1;

        // Generate hash.
        miner.hash = hash(miner.hash.as_ref());

        // Score and increment rewards.
        let score = difficulty(miner.hash) as u64;
        if score >= block.reward.difficulty_threshold {
            block.winning_hashes += 1;
            miner.winning_hashes += 1;
            miner_reward += block.reward.difficulty_reward;
        }

        // If hash is best hash, update best hash.
        if miner.hash < block.reward.best_hash {
            block.reward.best_hash = miner.hash;
            block.reward.best_hash_authority = miner.authority;
        }
    }

    // Payout ORE.
    block.total_rewards += miner_reward;
    miner.total_rewards += miner_reward;
    mint_to_signed(
        mint_ore_info,
        recipient_info,
        treasury_info,
        token_program,
        miner_reward,
        &[TREASURY],
    )?;

    Ok(())
}

/// Returns the number of leading zeros on a 32 byte buffer.
pub fn difficulty(hash: [u8; 32]) -> u32 {
    let mut count = 0;
    for &byte in &hash {
        let lz = byte.leading_zeros();
        count += lz;
        if lz < 8 {
            break;
        }
    }
    count
}