package chain

import (
	"blockchain/config"
	"crypto/sha256"
	"encoding/hex"
	"strconv"
	"strings"
)

type Block struct {
	Height       int
	Transactions []*Transaction
	PrevHash     string
	Hash         string
	Nonce        int
}

func NewBlock(height int, txs []*Transaction, prevHash string) *Block {
	return &Block{
		Height:       height,
		Transactions: txs,
		PrevHash:     prevHash,
	}
}

// HashBase returns the pre-computed prefix for nonce iteration.
func (b *Block) HashBase() string {
	var sb strings.Builder
	sb.WriteString(strconv.Itoa(b.Height))
	for _, tx := range b.Transactions {
		sb.WriteString(tx.TxID())
	}
	sb.WriteString(b.PrevHash)
	return sb.String()
}

func (b *Block) CalcHash() string {
	data := b.HashBase() + strconv.Itoa(b.Nonce)
	hash := sha256.Sum256([]byte(data))
	return hex.EncodeToString(hash[:])
}

func (b *Block) CheckProofOfWork() bool {
	prefix := strings.Repeat("0", config.Default.Chain.Difficulty)
	return b.Hash == b.CalcHash() && strings.HasPrefix(b.Hash, prefix)
}