// Copyright (c) 2014-2016 The btcsuite developers
// Copyright (c) 2015-2021 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package blockchain_test

import (
	"context"
	"fmt"
	"os"
	"path/filepath"

	"github.com/decred/dcrd/blockchain/v4"
	"github.com/decred/dcrd/chaincfg/v3"
	"github.com/decred/dcrd/database/v3"
	_ "github.com/decred/dcrd/database/v3/ffldb"
	"github.com/decred/dcrd/dcrutil/v4"
	"github.com/syndtr/goleveldb/leveldb"
	"github.com/syndtr/goleveldb/leveldb/filter"
	"github.com/syndtr/goleveldb/leveldb/opt"
)

// This example demonstrates how to create a new chain instance and use
// ProcessBlock to attempt to add a block to the chain.  As the package
// overview documentation describes, this includes all of the Decred consensus
// rules.  This example intentionally attempts to insert a duplicate genesis
// block to illustrate how an invalid block is handled.
func ExampleBlockChain_ProcessBlock() {
	// Create a new database to store the accepted blocks into.  Typically
	// this would be opening an existing database and would not be deleting
	// and creating a new database like this, but it is done here so this is
	// a complete working example and does not leave temporary files laying
	// around.
	mainNetParams := chaincfg.MainNetParams()
	dbPath := filepath.Join(os.TempDir(), "exampleprocessblock")
	_ = os.RemoveAll(dbPath)
	db, err := database.Create("ffldb", dbPath, mainNetParams.Net)
	if err != nil {
		fmt.Printf("Failed to create database: %v\n", err)
		return
	}
	defer os.RemoveAll(dbPath)
	defer db.Close()

	// Additionally, create a new database to store the UTXO set.
	utxoDbPath := filepath.Join(os.TempDir(), "exampleprocessblockutxodb")
	_ = os.RemoveAll(utxoDbPath)
	opts := opt.Options{
		Strict:      opt.DefaultStrict,
		Compression: opt.NoCompression,
		Filter:      filter.NewBloomFilter(10),
	}
	utxoDb, err := leveldb.OpenFile(utxoDbPath, &opts)
	if err != nil {
		fmt.Printf("Failed to create UTXO database: %v\n", err)
		return
	}
	defer os.RemoveAll(utxoDbPath)
	defer utxoDb.Close()

	// Create a new BlockChain instance using the underlying database for
	// the main bitcoin network.  This example does not demonstrate some
	// of the other available configuration options such as specifying a
	// notification callback and signature cache.  Also, the caller would
	// ordinarily keep a reference to the median time source and add time
	// values obtained from other peers on the network so the local time is
	// adjusted to be in agreement with other peers.
	chain, err := blockchain.New(context.Background(),
		&blockchain.Config{
			DB:          db,
			ChainParams: mainNetParams,
			TimeSource:  blockchain.NewMedianTime(),
			UtxoCache: blockchain.NewUtxoCache(&blockchain.UtxoCacheConfig{
				Backend: blockchain.NewLevelDbUtxoBackend(utxoDb),
				FlushBlockDB: func() error {
					return nil
				},
				MaxSize: 100 * 1024 * 1024, // 100 MiB
			}),
		})
	if err != nil {
		fmt.Printf("Failed to create chain instance: %v\n", err)
		return
	}

	// Process a block.  For this example, intentionally cause an error by
	// trying to process the genesis block which already exists.
	genesisBlock := dcrutil.NewBlock(mainNetParams.GenesisBlock)
	forkLen, err := chain.ProcessBlock(genesisBlock)
	if err != nil {
		fmt.Printf("Failed to create chain instance: %v\n", err)
		return
	}
	isMainChain := forkLen == 0
	fmt.Printf("Block accepted. Is it on the main chain?: %v", isMainChain)

	// This output is dependent on the genesis block, and needs to be
	// updated if the mainnet genesis block is updated.
	// Output:
	// Failed to process block: already have block 267a53b5ee86c24a48ec37aee4f4e7c0c4004892b7259e695e9f5b321f1ab9d2
}