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// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package core

import (
    "fmt"

    "github.com/dexon-foundation/dexon/consensus"
    "github.com/dexon-foundation/dexon/core/state"
    "github.com/dexon-foundation/dexon/core/types"
    "github.com/dexon-foundation/dexon/params"
)

// BlockValidator is responsible for validating block headers, uncles and
// processed state.
//
// BlockValidator implements Validator.
type BlockValidator struct {
    config *params.ChainConfig // Chain configuration options
    bc     *BlockChain         // Canonical block chain
    engine consensus.Engine    // Consensus engine used for validating
}

// NewBlockValidator returns a new block validator which is safe for re-use
func NewBlockValidator(config *params.ChainConfig, blockchain *BlockChain, engine consensus.Engine) *BlockValidator {
    validator := &BlockValidator{
        config: config,
        engine: engine,
        bc:     blockchain,
    }
    return validator
}

// ValidateBody validates the given block's uncles and verifies the block
// header's transaction and uncle roots. The headers are assumed to be already
// validated at this point.
func (v *BlockValidator) ValidateBody(block *types.Block) error {
    // Check whether the block's known, and if not, that it's linkable
    if v.bc.HasBlockAndState(block.Hash(), block.NumberU64()) {
        return ErrKnownBlock
    }
    // Header validity is known at this point, check the uncles and transactions
    header := block.Header()
    if err := v.engine.VerifyUncles(v.bc, block); err != nil {
        return err
    }
    if hash := types.CalcUncleHash(block.Uncles()); hash != header.UncleHash {
        return fmt.Errorf("uncle root hash mismatch: have %x, want %x", hash, header.UncleHash)
    }
    if hash := types.DeriveSha(block.Transactions()); hash != header.TxHash {
        return fmt.Errorf("transaction root hash mismatch: have %x, want %x", hash, header.TxHash)
    }
    if !v.bc.HasBlockAndState(block.ParentHash(), block.NumberU64()-1) {
        if !v.bc.HasBlock(block.ParentHash(), block.NumberU64()-1) {
            return consensus.ErrUnknownAncestor
        }
        return consensus.ErrPrunedAncestor
    }
    return nil
}

// ValidateState validates the various changes that happen after a state
// transition, such as amount of used gas, the receipt roots and the state root
// itself. ValidateState returns a database batch if the validation was a success
// otherwise nil and an error is returned.
func (v *BlockValidator) ValidateState(block, parent *types.Block, statedb *state.StateDB, receipts types.Receipts, usedGas uint64) error {
    header := block.Header()
    if block.GasUsed() != usedGas {
        return fmt.Errorf("invalid gas used (remote: %d local: %d)", block.GasUsed(), usedGas)
    }
    // Validate the received block's bloom with the one derived from the generated receipts.
    // For valid blocks this should always validate to true.
    rbloom := types.CreateBloom(receipts)
    if rbloom != header.Bloom {
        return fmt.Errorf("invalid bloom (remote: %x  local: %x)", header.Bloom, rbloom)
    }
    // Tre receipt Trie's root (R = (Tr [[H1, R1], ... [Hn, R1]]))
    receiptSha := types.DeriveSha(receipts)
    if receiptSha != header.ReceiptHash {
        return fmt.Errorf("invalid receipt root hash (remote: %x local: %x)", header.ReceiptHash, receiptSha)
    }
    // Validate the state root against the received state root and throw
    // an error if they don't match.
    if root := statedb.IntermediateRoot(v.config.IsEIP158(header.Number)); header.Root != root {
        return fmt.Errorf("invalid merkle root (remote: %x local: %x)", header.Root, root)
    }
    return nil
}

func (v *BlockValidator) ValidateWitnessData(height uint64, data types.WitnessData) error {
    currentBlock := v.bc.CurrentBlock()
    if height > currentBlock.NumberU64() && height != 0 {
        pendingBlock := v.bc.GetPendingBlockByNumber(height)

        if pendingBlock.Root() != data.Root {
            return fmt.Errorf("invalid witness root %s vs %s",
                pendingBlock.Root().String(), data.Root.String())
        }
        if pendingBlock.ReceiptHash() != data.ReceiptHash {
            return fmt.Errorf("invalid witness receipt hash %s vs %s",
                pendingBlock.ReceiptHash().String(), data.ReceiptHash.String())
        }
    }
    return nil
}

// CalcGasLimit computes the gas limit of the next block after parent. It aims
// to keep the baseline gas above the provided floor, and increase it towards the
// ceil if the blocks are full. If the ceil is exceeded, it will always decrease
// the gas allowance.
func CalcGasLimit(parent *types.Block, gasFloor, gasCeil uint64) uint64 {
    // contrib = (parentGasUsed * 3 / 2) / 1024
    contrib := (parent.GasUsed() + parent.GasUsed()/2) / params.GasLimitBoundDivisor

    // decay = parentGasLimit / 1024 -1
    decay := parent.GasLimit()/params.GasLimitBoundDivisor - 1

    /*
        strategy: gasLimit of block-to-mine is set based on parent's
        gasUsed value.  if parentGasUsed > parentGasLimit * (2/3) then we
        increase it, otherwise lower it (or leave it unchanged if it's right
        at that usage) the amount increased/decreased depends on how far away
        from parentGasLimit * (2/3) parentGasUsed is.
    */
    limit := parent.GasLimit() - decay + contrib
    if limit < params.MinGasLimit {
        limit = params.MinGasLimit
    }
    // If we're outside our allowed gas range, we try to hone towards them
    if limit < gasFloor {
        limit = parent.GasLimit() + decay
        if limit > gasFloor {
            limit = gasFloor
        }
    } else if limit > gasCeil {
        limit = parent.GasLimit() - decay
        if limit < gasCeil {
            limit = gasCeil
        }
    }
    return limit
}