//
//  Blockchain.swift
//  Blockchain
//
//  Created by Victor BODINAUD on 27/02/2020.
//  Copyright © 2020 Victor BODINAUD. All rights reserved.
//

import Foundation

public class Blockchain {
    var chain = [Block]()
    let minDifficulty = 2
    let maxDifficulty = 6
    let targetBlockTime = 10.0 // en secondes

    static let genesisBlock: Block = {
        let block = Block()
        block.previousHash = "0000genesis0000"
        block.index = 0
        block.timestamp = 1701388800
        block.difficulty = 4
        block.nonce = 12345
        block.hash = "000088c1731bed4996680d2c50ea3d9b573c1507d2d61866c0deff33a7f8cf5e"
        return block
    }()

    init() {
        chain.append(Blockchain.genesisBlock)
        print("Genesis block initialized -- hash: \(Blockchain.genesisBlock.hash)")
    }

    func calculateNewDifficulty() -> Int {
        guard chain.count >= 2 else { return minDifficulty }

        let lastBlock = chain.last!
        let previousBlock = chain[chain.count - 2]
        let timeSpent = Double(lastBlock.timestamp - previousBlock.timestamp)

        if timeSpent < targetBlockTime / 2 {
            return min(lastBlock.difficulty + 1, maxDifficulty)
        } else if timeSpent > targetBlockTime * 2 {
            return max(lastBlock.difficulty - 1, minDifficulty)
        }

        return lastBlock.difficulty
    }

    func validateChain(_ chain: [Block]) -> Bool {
        guard let firstBlock = chain.first,
              firstBlock.hash == Blockchain.genesisBlock.hash
        else {
            print("Genesis block mismatch")
            return false
        }

        for i in 1..<chain.count {
            let block = chain[i]
            let previousBlock = chain[i - 1]

            if block.previousHash != previousBlock.hash {
                print("Invalid chain at block \(i): incorrect previous hash")
                return false
            }

            if !block.isValid() {
                print("Invalid chain at block \(i): invalid block hash")
                return false
            }
        }

        return true
    }

    func validateChainTotally(_ chain: [Block]) -> Bool {
        // Vérifier le genesis block
        guard let firstBlock = chain.first,
              firstBlock.hash == Blockchain.genesisBlock.hash
        else {
            print("Chain: Invalid genesis block")
            return false
        }

        // Vérifier la séquence des blocs
        for i in 1..<chain.count {
            let block = chain[i]
            let previousBlock = chain[i - 1]

            // Vérifier le chaînage
            if block.previousHash != previousBlock.hash {
                print("Chain: Invalid block sequence at height \(i)")
                return false
            }

            // Vérifier l'index
            if block.index != i {
                print("Chain: Invalid block index at height \(i)")
                return false
            }

            // Vérifier la chronologie
            if block.timestamp <= previousBlock.timestamp {
                print("Chain: Invalid timestamp at height \(i)")
                return false
            }

            // Vérifier la difficulté
            let expectedDifficulty = calculateExpectedDifficulty(at: i, chain: chain)
            if block.difficulty != expectedDifficulty {
                print("Chain: Invalid difficulty at height \(i)")
                return false
            }

            // Vérifier le bloc lui-même
            if !block.isValid() {
                print("Chain: Invalid block at height \(i)")
                return false
            }
        }

        return true
    }

    private func calculateExpectedDifficulty(at index: Int, chain: [Block]) -> Int {
        return chain[index].difficulty
    }
}