// Copyright 2016 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 trie

import (
	"sync"

	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/rlp"
)

// hasher is a type used for the trie Hash operation. A hasher has some
// internal preallocated temp space
type hasher struct {
	sha      crypto.KeccakState
	tmp      []byte
	encbuf   rlp.EncoderBuffer
	parallel bool // Whether to use parallel threads when hashing
}

// hasherPool holds pureHashers
var hasherPool = sync.Pool{
	New: func() interface{} {
		return &hasher{
			tmp:    make([]byte, 0, 550), // cap is as large as a full fullNode.
			sha:    crypto.NewKeccakState(),
			encbuf: rlp.NewEncoderBuffer(nil),
		}
	},
}

func newHasher(parallel bool) *hasher {
	h := hasherPool.Get().(*hasher)
	h.parallel = parallel

	return h
}

func returnHasherToPool(h *hasher) {
	hasherPool.Put(h)
}

// hash collapses a node down into a hash node.
func (h *hasher) hash(n node, force bool) node {
	// Return the cached hash if it's available
	if hash, _ := n.cache(); hash != nil {
		return hash
	}
	// Trie not processed yet, walk the children
	switch n := n.(type) {
	case *shortNode:
		collapsed := h.hashShortNodeChildren(n)
		hashed := h.shortnodeToHash(collapsed, force)
		if hn, ok := hashed.(hashNode); ok {
			n.flags.hash = hn
		} else {
			n.flags.hash = nil
		}
		return hashed
	case *fullNode:
		collapsed := h.hashFullNodeChildren(n)
		hashed := h.fullnodeToHash(collapsed, force)
		if hn, ok := hashed.(hashNode); ok {
			n.flags.hash = hn
		} else {
			n.flags.hash = nil
		}
		return hashed
	default:
		// Value and hash nodes don't have children, so they're left as were
		return n
	}
}

// hashShortNodeChildren returns a copy of the supplied shortNode, with its child
// being replaced by either the hash or an embedded node if the child is small.
func (h *hasher) hashShortNodeChildren(n *shortNode) *shortNode {
	var collapsed shortNode
	collapsed.Key = hexToCompact(n.Key)
	switch n.Val.(type) {
	case *fullNode, *shortNode:
		collapsed.Val = h.hash(n.Val, false)
	default:
		collapsed.Val = n.Val
	}
	return &collapsed
}

// hashFullNodeChildren returns a copy of the supplied fullNode, with its child
// being replaced by either the hash or an embedded node if the child is small.
func (h *hasher) hashFullNodeChildren(n *fullNode) *fullNode {
	var children [17]node
	if h.parallel {
		var wg sync.WaitGroup

		wg.Add(16)

		for i := 0; i < 16; i++ {
			go func(i int) {
				hasher := newHasher(false)
				if child := n.Children[i]; child != nil {
					children[i] = hasher.hash(child, false)
				} else {
					children[i] = nilValueNode
				}

				returnHasherToPool(hasher)
				wg.Done()
			}(i)
		}
		wg.Wait()
	} else {
		for i := 0; i < 16; i++ {
			if child := n.Children[i]; child != nil {
				children[i] = h.hash(child, false)
			} else {
				children[i] = nilValueNode
			}
		}
	}
	if n.Children[16] != nil {
		children[16] = n.Children[16]
	}
	return &fullNode{flags: nodeFlag{}, Children: children}
}

// shortnodeToHash computes the hash of the given shortNode. The shortNode must
// first be collapsed, with its key converted to compact form. If the RLP-encoded
// node data is smaller than 32 bytes, the node itself is returned.
func (h *hasher) shortnodeToHash(n *shortNode, force bool) node {
	n.encode(h.encbuf)
	enc := h.encodedBytes()

	if len(enc) < 32 && !force {
		return n // Nodes smaller than 32 bytes are stored inside their parent
	}

	return h.hashData(enc)
}

// fullnodeToHash computes the hash of the given fullNode. If the RLP-encoded
// node data is smaller than 32 bytes, the node itself is returned.
func (h *hasher) fullnodeToHash(n *fullNode, force bool) node {
	n.encode(h.encbuf)
	enc := h.encodedBytes()

	if len(enc) < 32 && !force {
		return n // Nodes smaller than 32 bytes are stored inside their parent
	}

	return h.hashData(enc)
}

// encodedBytes returns the result of the last encoding operation on h.encbuf.
// This also resets the encoder buffer.
//
// All node encoding must be done like this:
//
//	node.encode(h.encbuf)
//	enc := h.encodedBytes()
//
// This convention exists because node.encode can only be inlined/escape-analyzed when
// called on a concrete receiver type.
func (h *hasher) encodedBytes() []byte {
	h.tmp = h.encbuf.AppendToBytes(h.tmp[:0])
	h.encbuf.Reset(nil)

	return h.tmp
}

// hashData hashes the provided data
func (h *hasher) hashData(data []byte) hashNode {
	n := make(hashNode, 32)

	h.sha.Reset()
	h.sha.Write(data)
	h.sha.Read(n)

	return n
}

// hashDataTo hashes the provided data to the given destination buffer. The caller
// must ensure that the dst buffer is of appropriate size.
func (h *hasher) hashDataTo(dst, data []byte) {
	h.sha.Reset()
	h.sha.Write(data)
	h.sha.Read(dst)
}

// proofHash is used to construct trie proofs, and returns the 'collapsed'
// node (for later RLP encoding) as well as the hashed node -- unless the
// node is smaller than 32 bytes, in which case it will be returned as is.
// This method does not do anything on value- or hash-nodes.
func (h *hasher) proofHash(original node) (collapsed, hashed node) {
	switch n := original.(type) {
	case *shortNode:
		sn := h.hashShortNodeChildren(n)
		return sn, h.shortnodeToHash(sn, false)
	case *fullNode:
		fn := h.hashFullNodeChildren(n)
		return fn, h.fullnodeToHash(fn, false)
	default:
		// Value and hash nodes don't have children, so they're left as were
		return n, n
	}
}
