package trie

import (
	"fmt"
	"io"
	"reflect"

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

// rawNode is a simple binary blob used to differentiate between collapsed trie
// nodes and already encoded RLP binary blobs (while at the same time store them
// in the same cache fields).
type rawNode []byte

func (n rawNode) cache() (hashNode, bool)   { panic("this should never end up in a live trie") }
func (n rawNode) fstring(ind string) string { panic("this should never end up in a live trie") }

func (n rawNode) EncodeRLP(w io.Writer) error {
	_, err := w.Write(n)
	return err
}

// rawFullNode represents only the useful data content of a full node, with the
// caches and flags stripped out to minimize its data storage. This type honors
// the same RLP encoding as the original parent.
type rawFullNode [17]node

func (n rawFullNode) cache() (hashNode, bool)   { panic("this should never end up in a live trie") }
func (n rawFullNode) fstring(ind string) string { panic("this should never end up in a live trie") }

func (n rawFullNode) EncodeRLP(w io.Writer) error {
	eb := rlp.NewEncoderBuffer(w)
	n.encode(eb)
	return eb.Flush()
}

// rawShortNode represents only the useful data content of a short node, with the
// caches and flags stripped out to minimize its data storage. This type honors
// the same RLP encoding as the original parent.
type rawShortNode struct {
	Key []byte
	Val node
}

func (n rawShortNode) cache() (hashNode, bool)   { panic("this should never end up in a live trie") }
func (n rawShortNode) fstring(ind string) string { panic("this should never end up in a live trie") }

// cachedNode is all the information we know about a single cached trie node
// in the memory database write layer.
type cachedNode struct {
	node node   // Cached collapsed trie node, or raw rlp data
	size uint16 // Byte size of the useful cached data

	parents  uint32                 // Number of live nodes referencing this one
	children map[common.Hash]uint16 // External children referenced by this node

	flushPrev common.Hash // Previous node in the flush-list
	flushNext common.Hash // Next node in the flush-list
}

// cachedNodeSize is the raw size of a cachedNode data structure without any
// node data included. It's an approximate size, but should be a lot better
// than not counting them.
var cachedNodeSize = int(reflect.TypeOf(cachedNode{}).Size())

// cachedNodeChildrenSize is the raw size of an initialized but empty external
// reference map.
const cachedNodeChildrenSize = 48

// rlp returns the raw rlp encoded blob of the cached trie node, either directly
// from the cache, or by regenerating it from the collapsed node.
func (n *cachedNode) rlp() []byte {
	if node, ok := n.node.(rawNode); ok {
		return node
	}
	return nodeToBytes(n.node)
}

// obj returns the decoded and expanded trie node, either directly from the cache,
// or by regenerating it from the rlp encoded blob.
func (n *cachedNode) obj(hash common.Hash) node {
	if node, ok := n.node.(rawNode); ok {
		// The raw-blob format nodes are loaded either from the
		// clean cache or the database, they are all in their own
		// copy and safe to use unsafe decoder.
		return mustDecodeNodeUnsafe(hash[:], node)
	}
	return expandNode(hash[:], n.node)
}

// forChilds invokes the callback for all the tracked children of this node,
// both the implicit ones from inside the node as well as the explicit ones
// from outside the node.
func (n *cachedNode) forChilds(onChild func(hash common.Hash)) {
	for child := range n.children {
		onChild(child)
	}
	if _, ok := n.node.(rawNode); !ok {
		forGatherChildren(n.node, onChild)
	}
}

// forGatherChildren traverses the node hierarchy of a collapsed storage node and
// invokes the callback for all the hashnode children.
func forGatherChildren(n node, onChild func(hash common.Hash)) {
	switch n := n.(type) {
	case *rawShortNode:
		forGatherChildren(n.Val, onChild)
	case rawFullNode:
		for i := 0; i < 16; i++ {
			forGatherChildren(n[i], onChild)
		}
	case hashNode:
		onChild(common.BytesToHash(n))
	case valueNode, nil, rawNode:
	default:
		panic(fmt.Sprintf("unknown node type: %T", n))
	}
}

// simplifyNode traverses the hierarchy of an expanded memory node and discards
// all the internal caches, returning a node that only contains the raw data.
func simplifyNode(n node) node {
	switch n := n.(type) {
	case *shortNode:
		// Short nodes discard the flags and cascade
		return &rawShortNode{Key: n.Key, Val: simplifyNode(n.Val)}

	case *fullNode:
		// Full nodes discard the flags and cascade
		node := rawFullNode(n.Children)
		for i := 0; i < len(node); i++ {
			if node[i] != nil {
				node[i] = simplifyNode(node[i])
			}
		}
		return node

	case valueNode, hashNode, rawNode:
		return n

	default:
		panic(fmt.Sprintf("unknown node type: %T", n))
	}
}

// expandNode traverses the node hierarchy of a collapsed storage node and converts
// all fields and keys into expanded memory form.
func expandNode(hash hashNode, n node) node {
	switch n := n.(type) {
	case *rawShortNode:
		// Short nodes need key and child expansion
		return &shortNode{
			Key: compactToHex(n.Key),
			Val: expandNode(nil, n.Val),
			flags: nodeFlag{
				hash: hash,
			},
		}

	case rawFullNode:
		// Full nodes need child expansion
		node := &fullNode{
			flags: nodeFlag{
				hash: hash,
			},
		}
		for i := 0; i < len(node.Children); i++ {
			if n[i] != nil {
				node.Children[i] = expandNode(nil, n[i])
			}
		}
		return node

	case valueNode, hashNode:
		return n

	default:
		panic(fmt.Sprintf("unknown node type: %T", n))
	}
}