pragma solidity ^0.8.24;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/utils/cryptography/MerkleProof.sol";
import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
import "@openzeppelin/contracts/utils/Pausable.sol";
import "prb-math/contracts/PRBMath.sol";
import "hardhat/console.sol"; // For debugging purposes, can be removed in production

contract Launchpad is ReentrancyGuard, Pausable {
	
	// ================================
	// Custom Errors
	// ================================
	error Unauthorized();
	error InvalidParameter(string reason);
	error InvalidState(string reason);
	error InsufficientAmount(uint256 required, uint256 provided);
	error TransferFailed();
	error SaleNotConfigured();
	
	// ================================
	// State Variables
	// ================================
	
	// Core Configuration
	address public owner;
	address public saleTokenAddress; // Sale token address
	uint256 public totalTokensForSale; // Total tokens for sale
	address public paymentTokenAddress; // Payment tokens accepted for the sale
	uint256 public paymentTokenPrice; // Payment token price in terms of sale token
	uint256 public startTime; // Beginning time of the sale
	uint256 public endTime; // Ending time of the sale
	bytes32 public merkleRoot; // Merkle root for whitelisting

	// Sale Status
	uint256 public contributionTarget; // Target amount to be raised in the sale
	uint256 public totalContributionAmount; // Total contributed amount so far
	uint256 public totalContributionAmountWithoutFee;
	uint256 public totalContributionFee;
	bool public claimEnabled; // Whether claiming tokens is enabled
	uint256 public claimStartTime; // Start time for claiming tokens

	// User Data
	mapping(address => uint256) public userContributionAmount; // User's total contribution amount (including fee)
	mapping(address => uint256) public userBuyAmount; // User's buy amount (excluding fee)
	mapping(address => uint256) public userFeeAmount; // User's fee amount
	mapping(address => bool) public userClaimed; // Whether user has claimed their tokens
	uint256 public accountsCount; // Number of accounts that have contributed
	
	// Fee Configuration
	uint256 public feeBps; // Fee in basis points (bps)
	uint256 public constant MAX_FEE_BPS = 10000; // 100% in basis points
	uint256 public constant DECIMALS = 1e18;

	// ================================
	// Events
	// ================================
	event SaleCreated(address saleTokenAddress, uint256 totalTokensForSale);
	event Contributed(address user, uint256 amount, address paymentTokenAddress);
	event TokensClaimed(address user, uint256 tokensClaimed, uint256 refundAmount);
	event SaleCancelled(address saleTokenAddress, uint256 refundedAmount);
	event EnableClaimToken(bool enabled, uint256 claimStartTime);
	event DisableClaimToken(bool disabled);
	event OwnerChanged(address oldOwner, address newOwner);
	event SalePaymentUpdated(address paymentTokenAddress, uint256 tokenPrice);
	event MerkleRootUpdated(bytes32 newMerkleRoot);
	event FeeUpdated(uint256 oldFeeBps, uint256 newFeeBps);
	event RemainingTokensWithdrawn(address owner, uint256 amount);
	event PaymentsWithdrawn(address owner, uint256 amount, bool isOversubscribed);
	event EmergencyWithdraw(address owner, uint256 ethAmount, address[] tokenAddresses);
	event ContractPaused(address account);
	event ContractUnpaused(address account);

	// ================================
	// Constructor
	// ================================
	constructor() {
		owner = msg.sender;
		accountsCount = 0;
	}

	// ================================
	// Validation Functions
	// ================================
	
	/**
	 * @notice Validates basic sale parameters
	 */
	function _validateSaleParameters(
		address _saleTokenAddress,
		uint256 _saleTokenSupply,
		uint256 _contributionTarget,
		uint256 _saleStartTime,
		uint256 _saleEndTime,
		uint256 _tokenPrice,
		uint256 _feeBasisPoints
	) private pure {
		if (_saleTokenAddress == address(0)) revert InvalidParameter("Invalid token address");
		if (_saleTokenSupply == 0) revert InvalidParameter("Sale token supply must be greater than 0");
		if (_tokenPrice == 0) revert InvalidParameter("Price must be greater than 0");
		if (_contributionTarget == 0) revert InvalidParameter("Contribution target must be greater than 0");
		if (_saleStartTime >= _saleEndTime) revert InvalidParameter("Invalid time range");
		if (_feeBasisPoints > MAX_FEE_BPS) revert InvalidParameter("Fee cannot exceed 100%");
	}
	
	/**
	 * @notice Validates contribution target matches expected calculation
	 */
	function _validateContributionTarget(
		uint256 _saleTokenSupply,
		uint256 _tokenPrice,
		uint256 _contributionTarget
	) private pure {
		uint256 expectedContributionTarget = PRBMath.mulDiv(_saleTokenSupply, _tokenPrice, 1e18);
		if (_contributionTarget != expectedContributionTarget) revert InvalidParameter("Contribution target must equal saleTokenSupply * price");
	}
	
	/**
	 * @notice Validates sale state for cancellation
	 */
	function _validateSaleCancellation() private view {
		if (block.timestamp >= startTime) revert InvalidState("Sale already started");
		if (saleTokenAddress == address(0)) revert SaleNotConfigured();
	}
	
	/**
	 * @notice Validates claim enablement parameters
	 */
	function _validateClaimEnablement(uint256 _claimStartTimestamp) private view {
		if (_claimStartTimestamp < block.timestamp) revert InvalidParameter("Enable claim time must be in the future");
		if (_claimStartTimestamp < endTime) revert InvalidParameter("Claiming tokens can only be enabled after the sale ends");
	}
	
	/**
	 * @notice Validates withdrawal conditions
	 */
	function _validateWithdrawalConditions() private view {
		if (block.timestamp <= endTime) revert InvalidState("Sale is still active");
	}
	
	/**
	 * @notice Validates remaining token withdrawal conditions
	 */
	function _validateRemainingTokenWithdrawal() private view {
		_validateWithdrawalConditions();
		if (totalContributionAmountWithoutFee >= contributionTarget) revert InvalidState("All sold out, cannot withdraw remaining tokens");
	}
	
	/**
	 * @notice Validates contribution parameters for ETH
	 */
	function _validateETHContribution(
		uint256 _contributionAmount,
		uint256 _maxContributionAmount
	) private view {
		if (paymentTokenAddress != address(0)) revert InvalidState("Payment token must be ETH for this sale");
		if (_contributionAmount == 0) revert InvalidParameter("Must buy a positive amount");
		if (_contributionAmount > _maxContributionAmount) revert InvalidParameter("Buy amount exceeds max buy amount");
		if (msg.value < _contributionAmount) revert InsufficientAmount(_contributionAmount, msg.value);
		if (paymentTokenPrice == 0) revert InvalidState("Payment token not accepted for this sale");
	}
	
	/**
	 * @notice Validates contribution parameters for ERC20
	 */
	function _validateERC20Contribution(
		uint256 _contributionAmount,
		uint256 _maxContributionAmount
	) private view {
		if (_contributionAmount == 0) revert InvalidParameter("Must send a positive amount");
		if (_contributionAmount > _maxContributionAmount) revert InvalidParameter("Buy amount exceeds max buy amount");
		uint256 allowance = IERC20(paymentTokenAddress).allowance(msg.sender, address(this));
		if (allowance < _contributionAmount) revert InsufficientAmount(_contributionAmount, allowance);
	}
	
	/**
	 * @notice Validates Merkle proof
	 */
	function _validateMerkleProof(
		uint256 _maxContributionAmount,
		bytes32[] memory _merkleProof
	) private view {
		bytes32 leaf = keccak256(bytes.concat(keccak256(abi.encode(msg.sender, _maxContributionAmount))));
		if (!MerkleProof.verify(_merkleProof, merkleRoot, leaf)) revert InvalidParameter("Invalid proof");
	}
	
	/**
	 * @notice Validates user contribution limits
	 */
	function _validateUserContributionLimit(uint256 _maxContributionAmount) private view {
		if (userContributionAmount[msg.sender] > _maxContributionAmount) revert InvalidParameter("Buy amount exceeds max buy amount");
	}
	
	/**
	 * @notice Validates claim conditions
	 */
	function _validateClaimConditions() private view {
		if (block.timestamp <= endTime) revert InvalidState("Sale is still active");
		if (userContributionAmount[msg.sender] == 0) revert InvalidState("No tokens to claim");
		if (userClaimed[msg.sender]) revert InvalidState("Tokens already claimed");
	}
	
	/**
	 * @notice Validates owner address
	 */
	function _validateOwnerAddress(address _newOwnerAddress) private pure {
		if (_newOwnerAddress == address(0)) revert InvalidParameter("Invalid owner address");
	}
	
	/**
	 * @notice Validates price parameter
	 */
	function _validatePrice(uint256 _tokenPrice) private pure {
		if (_tokenPrice == 0) revert InvalidParameter("Price must be greater than 0");
	}
	
	/**
	 * @notice Validates fee basis points
	 */
	function _validateFeeBps(uint256 _feeBasisPoints) private pure {
		if (_feeBasisPoints > MAX_FEE_BPS) revert InvalidParameter("Fee cannot exceed 100%");
	}

	// ================================
	// Modifiers
	// ================================
	modifier onlyOwner() {
		if (msg.sender != owner) revert Unauthorized();
		_;
	}

	modifier saleActive() {
		if (merkleRoot == bytes32(0)) revert SaleNotConfigured();
		if (block.timestamp < startTime || block.timestamp > endTime) revert InvalidState("Sale is not active");
		_;
	}
	
	modifier validClaimTime() {
		if (!claimEnabled) revert InvalidState("Claiming tokens is not enabled");
		if (block.timestamp < claimStartTime) revert InvalidState("Claiming tokens not started yet");
		_;
	}

	// ================================
	// Owner Functions
	// ================================

	/**
	 * @notice Creates a new token sale with specified parameters.
	 * @param _saleTokenAddress The address of the token being sold.
	 * @param _saleTokenSupply The total supply of tokens allocated for this sale.
	 * @param _contributionTarget The fundraising target amount (not including fee).
	 * @param _saleStartTime The start time of the sale (timestamp).
	 * @param _saleEndTime The end time of the sale (timestamp).
	 * @param _paymentTokenAddress The address of the payment token (or address(0) for ETH).
	 * @param _tokenPrice The price per token in payment token units.
	 * @param _feeBasisPoints The fee in basis points (1/100 of a percent).
	 */
	function createSale(
		address _saleTokenAddress,
		uint256 _saleTokenSupply,
		uint256 _contributionTarget,
		uint256 _saleStartTime,
		uint256 _saleEndTime,
		address _paymentTokenAddress,
		uint256 _tokenPrice,
		uint256 _feeBasisPoints
	) public onlyOwner {
		// Validate all sale parameters
		_validateSaleParameters(_saleTokenAddress, _saleTokenSupply, _contributionTarget, _saleStartTime, _saleEndTime, _tokenPrice, _feeBasisPoints);
		
		// Validate parameter relationships
		// contributionTarget = saleTokenSupply × price
		// Note: _saleTokenSupply and _tokenPrice both contain 18 decimals, product needs to be divided by 1e18
		_validateContributionTarget(_saleTokenSupply, _tokenPrice, _contributionTarget);

		paymentTokenAddress = _paymentTokenAddress;
		paymentTokenPrice = _tokenPrice;
		saleTokenAddress = _saleTokenAddress;
		contributionTarget = _contributionTarget;
		totalTokensForSale = _saleTokenSupply;
		startTime = _saleStartTime;
		endTime = _saleEndTime;
		totalContributionAmount = 0;
		feeBps = _feeBasisPoints; // Set the fee in basis points
		merkleRoot = bytes32(0); // Reset Merkle root
		
		uint256 currentBalance = IERC20(_saleTokenAddress).balanceOf(address(this));
		if (currentBalance < _saleTokenSupply) {
			uint256 needToTransfer = _saleTokenSupply - currentBalance;
			IERC20(_saleTokenAddress).transferFrom(msg.sender, address(this), needToTransfer);
		}
		
		emit SaleCreated(saleTokenAddress, totalTokensForSale);
	}

	/**
	 * @notice Cancels the sale before it starts and refunds all tokens to the owner.
	 */
	function cancelSale() public onlyOwner {
		_validateSaleCancellation();
		uint256 balance = IERC20(saleTokenAddress).balanceOf(address(this));
		if (balance == 0) revert InvalidState("No tokens to refund");
		IERC20(saleTokenAddress).transfer(owner, balance); // Refund tokens to owner
		saleTokenAddress = address(0);
		totalTokensForSale = 0;
		totalContributionAmount = 0;
		startTime = 0;
		endTime = 0;
		merkleRoot = bytes32(0); // Reset Merkle root
		emit SaleCancelled(saleTokenAddress, balance);
	}

	/**
	 * @notice Enables claiming of purchased tokens after the sale ends.
	 * @param _claimStartTimestamp The timestamp when claiming is enabled.
	 */
	function enableClaimTokens(uint256 _claimStartTimestamp) public onlyOwner {
		_validateClaimEnablement(_claimStartTimestamp);
		claimEnabled = true;
		claimStartTime = _claimStartTimestamp; // Set claim start time to now
		emit EnableClaimToken(claimEnabled, claimStartTime);
	}

	/**
	 * @notice Disables claiming of purchased tokens.
	 */
	function disableClaimTokens() public onlyOwner {
		if (!claimEnabled) revert InvalidState("Claiming tokens is already disabled");
		claimEnabled = false;
		emit DisableClaimToken(claimEnabled);
	}

	/**
	 * @notice Withdraws any remaining unsold tokens to the owner after the sale ends.
	 */
	function withdrawRemainingTokens() public onlyOwner {
		_validateRemainingTokenWithdrawal();
		// Calculate sold tokens using PRBMath to prevent overflow and precision loss
		uint256 soldTokens = PRBMath.mulDiv(totalTokensForSale, totalContributionAmountWithoutFee, contributionTarget);
		uint256 remainingAmount = totalTokensForSale - soldTokens;
		IERC20(saleTokenAddress).transfer(owner, remainingAmount);
		emit RemainingTokensWithdrawn(owner, remainingAmount);
	}

	/**
	 * @notice Withdraws payment tokens from the contract to the owner.
	 * In case of oversubscription, withdraws the total amount for sold tokens plus fees.
	 * In normal subscription, withdraws all contributions.
	 */
	function withdrawPayments() public onlyOwner {
		_validateWithdrawalConditions();
		
		uint256 withdrawAmount = 0;
		// Use the new state variables to determine oversubscription
		bool isOversubscribed = totalContributionAmountWithoutFee > contributionTarget;
		
		// Check if oversubscribed
		if (isOversubscribed) {
			// Oversubscribed: all tokens are sold
			// Withdraw fixed amount: target amount + target fee
			uint256 targetFee = PRBMath.mulDiv(contributionTarget, feeBps, MAX_FEE_BPS);
			withdrawAmount = contributionTarget + targetFee;
			
			if (paymentTokenAddress == address(0)) {
				// Native token (ETH)
				if (withdrawAmount > 0 && address(this).balance >= withdrawAmount) {
					payable(owner).transfer(withdrawAmount);
				}
			} else {
				// ERC20 token
				uint256 balance = IERC20(paymentTokenAddress).balanceOf(address(this));
				if (withdrawAmount > 0 && balance >= withdrawAmount) {
					IERC20(paymentTokenAddress).transfer(owner, withdrawAmount);
				}
			}
			
			// Keep in contract:
			// Refund portion: totalContributionAmount - withdrawAmount
		} else {
			// Normal subscription: withdraw all contributions
			if (paymentTokenAddress == address(0)) {
				// Native token (ETH)
				withdrawAmount = address(this).balance;
				if (withdrawAmount > 0) {
					payable(owner).transfer(withdrawAmount);
				}
			} else {
				// ERC20 token
				withdrawAmount = IERC20(paymentTokenAddress).balanceOf(address(this));
				if (withdrawAmount > 0) {
					IERC20(paymentTokenAddress).transfer(owner, withdrawAmount);
				}
			}
		}
		
		emit PaymentsWithdrawn(owner, withdrawAmount, isOversubscribed);
	}

	/**
	 * @notice Emergency function to withdraw all assets from the contract.
	 * This function withdraws all ETH and all ERC20 tokens that the contract holds.
	 * Only callable by the owner in emergency situations.
	 * @param _tokenAddresses Array of ERC20 token addresses to withdraw.
	 */
	function emergencyWithdrawAll(address[] memory _tokenAddresses) public onlyOwner {
		// Withdraw all ETH
		uint256 ethBalance = address(this).balance;
		if (ethBalance > 0) {
			(bool success, ) = payable(owner).call{value: ethBalance}("");
			if (!success) revert TransferFailed();
		}
		
		// Withdraw all specified ERC20 tokens
		for (uint256 i = 0; i < _tokenAddresses.length; i++) {
			address tokenAddress = _tokenAddresses[i];
			if (tokenAddress != address(0)) {
				uint256 tokenBalance = IERC20(tokenAddress).balanceOf(address(this));
				if (tokenBalance > 0) {
					IERC20(tokenAddress).transfer(owner, tokenBalance);
				}
			}
		}
		
		emit EmergencyWithdraw(owner, ethBalance, _tokenAddresses);
	}

	// ================================
	// Configuration Functions
	// ================================

	/**
	 * @notice Transfers contract ownership to a new address.
	 * @param _newOwnerAddress The address of the new owner.
	 */
	function setOwner(address _newOwnerAddress) public onlyOwner {
		_validateOwnerAddress(_newOwnerAddress);
		address oldOwner = owner;
		owner = _newOwnerAddress;
		emit OwnerChanged(oldOwner, _newOwnerAddress);
	}

	/**
	 * @notice Sets the payment token and price for the sale.
	 * @param _paymentTokenAddress The address of the payment token.
	 * @param _tokenPrice The price per token in payment token units.
	 */
	function setSalePayment(address _paymentTokenAddress, uint256 _tokenPrice) public onlyOwner {
		_validatePrice(_tokenPrice);
		paymentTokenAddress = _paymentTokenAddress;
		paymentTokenPrice = _tokenPrice;
		emit SalePaymentUpdated(_paymentTokenAddress, _tokenPrice);
	}

	/**
	 * @notice Sets the Merkle root for whitelist verification.
	 * @param _newMerkleRoot The new Merkle root.
	 */
	function setMerkleRoot(bytes32 _newMerkleRoot) public onlyOwner {
		merkleRoot = _newMerkleRoot;
		emit MerkleRootUpdated(_newMerkleRoot);
	}

	/**
	 * @notice Sets the fee in basis points.
	 * @param _feeBasisPoints The fee in basis points (max 10000).
	 */
	function setFeeBps(uint256 _feeBasisPoints) public onlyOwner {
		_validateFeeBps(_feeBasisPoints);
		uint256 oldFeeBps = feeBps;
		feeBps = _feeBasisPoints; // Set the fee in basis points
		emit FeeUpdated(oldFeeBps, _feeBasisPoints);
	}

	/**
	 * @notice Pauses the contract, preventing most operations.
	 * @dev Only the owner can pause the contract.
	 */
	function pause() public onlyOwner {
		_pause();
		emit ContractPaused(msg.sender);
	}

	/**
	 * @notice Unpauses the contract, allowing normal operations to resume.
	 * @dev Only the owner can unpause the contract.
	 */
	function unpause() public onlyOwner {
		_unpause();
		emit ContractUnpaused(msg.sender);
	}

	// ================================
	// Getter Functions
	// ================================

	/**
	 * @notice Returns the address of the contract owner.
	 */
	function getOwner() public view returns (address) {
		return owner;
	}

	/**
	 * @notice Returns the address of the sale token.
	 */
	function getSaleToken() public view returns (address) {
		return saleTokenAddress;
	}

	/**
	 * @notice Returns the total number of tokens for sale.
	 */
	function getTotalTokensForSale() public view returns (uint256) {
		return totalTokensForSale;
	}

	/**
	 * @notice Returns the total contributed amount so far.
	 */
	function getTotalContributeAmount() public view returns (uint256) {
		return totalContributionAmount;
	}

	/**
	 * @notice Returns the sale start time.
	 */
	function getStartTime() public view returns (uint256) {
		return startTime;
	}

	/**
	 * @notice Returns the sale end time.
	 */
	function getEndTime() public view returns (uint256) {
		return endTime;
	}

	/**
	 * @notice Returns the payment token price.
	 */
	function getPaymentTokenPrice() public view returns (uint256) {
		return paymentTokenPrice;
	}

	/**
	 * @notice Returns the payment token address.
	 */
	function getPaymentTokens() public view returns (address) {
		return paymentTokenAddress;
	}

	/**
	 * @notice Returns the claim start time.
	 */
	function getClaimStartTime() public view returns (uint256) {
		return claimStartTime;
	}

	/**
	 * @notice Returns whether claiming is enabled.
	 */
	function isClaimEnabled() public view returns (bool) {
		return claimEnabled;
	}

	/**
	 * @notice Returns all sale details as a tuple.
	 */
	function getSaleDetails()
		public
		view
		returns (
			address _saleTokenAddress,
			uint256 _totalTokensForSale,
			uint256 _totalContributionAmount,
			uint256 _contributionTarget,
			uint256 _startTime,
			uint256 _endTime,
			bytes32 _merkleRoot,
			address _paymentTokenAddress,
			uint256 _paymentTokenPrice,
			uint256 _feeBps
		)
	{
		return (
			saleTokenAddress,
			totalTokensForSale,
			totalContributionAmount,
			contributionTarget,
			startTime,
			endTime,
			merkleRoot,
			paymentTokenAddress,
			paymentTokenPrice,
			feeBps
		);
	}

	/**
	 * @notice Returns the claimable tokens for a user.
	 * @param _user The address of the user.
	 */
	function getClaimableTokens(address _user) public view returns (uint256) {
		return userContributionAmount[_user];
	}

	/**
	 * @notice Returns the user's buy amount (excluding fee).
	 * @param _user The address of the user.
	 */
	function getUserBuyAmount(address _user) public view returns (uint256) {
		return userBuyAmount[_user];
	}

	/**
	 * @notice Returns the user's fee amount.
	 * @param _user The address of the user.
	 */
	function getUserFeeAmount(address _user) public view returns (uint256) {
		return userFeeAmount[_user];
	}

	/**
	 * @notice Returns whether the user has claimed their tokens.
	 * @param _user The address of the user.
	 */
	function hasUserClaimed(address _user) public view returns (bool) {
		return userClaimed[_user];
	}

	/**
	 * @notice Returns whether the contract is currently paused.
	 * @return True if the contract is paused, false otherwise.
	 */
	function isPaused() public view returns (bool) {
		return paused();
	}

	// ================================
	// Calculation Functions
	// ================================

	/**
	 * @notice Calculates the maximum contribution amount for a user (including fee).
	 * @param _maxTokenBuyAmount The maximum amount of tokens a user can buy.
	 * @return The maximum contribution amount including fee.
	 */
	function calculateMaxContributionAmount(uint256 _maxTokenBuyAmount) public view returns (uint256) {
		// Calculate buy amount value using PRBMath for high precision
		uint256 buyAmountValue = PRBMath.mulDiv(_maxTokenBuyAmount, paymentTokenPrice, 1e18);
		
		// Calculate total contribution amount (buy amount + fee) using PRBMath to prevent overflow
		// Total = buyAmount * (1 + feeBps/MAX_FEE_BPS) = buyAmount * (MAX_FEE_BPS + feeBps) / MAX_FEE_BPS
		return PRBMath.mulDiv(buyAmountValue, MAX_FEE_BPS + feeBps, MAX_FEE_BPS);
	}

	/**
	 * @notice Calculates the breakdown of a total payment amount into token purchase amount and platform fee.
	 * @param _totalPaymentAmount The total amount paid by user (including platform fee).
	 * @return _tokenPurchaseAmount The amount used to purchase tokens (excluding fee).
	 * @return _platformFeeAmount The platform fee amount.
	 */
	function calculateContributionBreakdown(uint256 _totalPaymentAmount) public view returns (uint256 _tokenPurchaseAmount, uint256 _platformFeeAmount) {
		// Platform fee is calculated based on token purchase amount, not total payment
		// Total payment = token purchase amount + platform fee
		// Platform fee = token purchase amount * feeBps / MAX_FEE_BPS
		// So: total payment = token purchase amount + (token purchase amount * feeBps / MAX_FEE_BPS)
		// Token purchase amount = total payment / (1 + feeBps / MAX_FEE_BPS)
		// Using PRBMath for high precision calculation
		_tokenPurchaseAmount = PRBMath.mulDiv(_totalPaymentAmount, MAX_FEE_BPS, MAX_FEE_BPS + feeBps);
		_platformFeeAmount = _totalPaymentAmount - _tokenPurchaseAmount;
		return (_tokenPurchaseAmount, _platformFeeAmount);
	}

	/**
	 * @notice Calculates the net contribution after deducting the fee.
	 * @param _contributionAmount The original contribution amount.
	 * @return The net contribution after fee deduction.
	 */
	function calculateNetContribution(uint256 _contributionAmount) public view returns (uint256) {
		// Fee is calculated based on buy amount, not total contribution
		// Use same logic as calculateContributionBreakdown
		// Using PRBMath for high precision calculation
		uint256 buyAmount = PRBMath.mulDiv(_contributionAmount, MAX_FEE_BPS, MAX_FEE_BPS + feeBps);
		return buyAmount;
	}

	// ================================
	// Main Functions
	// ================================

	/**
	 * @notice Contribute to the sale using ETH. Requires whitelist proof.
	 * @param _contributionAmount The amount of ETH to contribute.
	 * @param _maxContributionAmount The maximum allowed contribution for the user.
	 * @param _merkleProof The Merkle proof for whitelist verification.
	 * @dev nonReentrant modifier is used to prevent reentrancy attacks.
	 */
	function contributeWithETH(
		uint256 _contributionAmount,
		uint256 _maxContributionAmount,
		bytes32[] memory _merkleProof
	) public payable saleActive nonReentrant whenNotPaused {
		// Validate ETH contribution parameters
		_validateETHContribution(_contributionAmount, _maxContributionAmount);
		
		// Verify Merkle proof
		_validateMerkleProof(_maxContributionAmount, _merkleProof);

		// Calculate breakdown of total payment amount into token purchase payment and platform fee
		(uint256 buyAmount, uint256 feeAmount) = calculateContributionBreakdown(_contributionAmount);
		
		// Account count statistics
		if (userContributionAmount[msg.sender] == 0) {
			accountsCount++; // Increment accounts count only if this is the first contribution
		}

		// Payment amount statistics - separate token purchase payment and platform fee
		userContributionAmount[msg.sender] += _contributionAmount; // update user's total payment amount
		userBuyAmount[msg.sender] += buyAmount; // update user's payment amount for token purchase (excluding fee)
		userFeeAmount[msg.sender] += feeAmount; // update user's platform fee payment amount
		_validateUserContributionLimit(_maxContributionAmount);
		totalContributionAmount += _contributionAmount; // update total payment amount
		totalContributionAmountWithoutFee += buyAmount; // update total payment amount for token purchase (excluding fees)
		totalContributionFee += feeAmount; // update total platform fee amount
		if (msg.value > _contributionAmount) {
			payable(msg.sender).transfer(msg.value - _contributionAmount); //refund excess ETH
		}
		emit Contributed(msg.sender, _contributionAmount, address(0));
	}

	/**
	 * @notice Contribute to the sale using ERC20 tokens. Requires whitelist proof.
	 * @param _contributionAmount The amount of tokens to contribute.
	 * @param _maxContributionAmount The maximum allowed contribution for the user.
	 * @param _merkleProof The Merkle proof for whitelist verification.
	 * @dev nonReentrant modifier is used to prevent reentrancy attacks.
	 */
	function contributeWithERC20(
		uint256 _contributionAmount,
		uint256 _maxContributionAmount,
		bytes32[] memory _merkleProof
	) public saleActive nonReentrant whenNotPaused {
		// Validate ERC20 contribution parameters
		_validateERC20Contribution(_contributionAmount, _maxContributionAmount);
		
		// Verify Merkle proof
		_validateMerkleProof(_maxContributionAmount, _merkleProof);
		IERC20(paymentTokenAddress).transferFrom(msg.sender, address(this), _contributionAmount); // Transfer payment tokens from user account

		// Calculate breakdown of total payment amount into token purchase payment and platform fee
		(uint256 buyAmount, uint256 feeAmount) = calculateContributionBreakdown(_contributionAmount);
		
		if (userContributionAmount[msg.sender] == 0) {
			accountsCount++; // Increment accounts count only if this is the first contribution
		}
		userContributionAmount[msg.sender] += _contributionAmount; // update user's total payment amount
		userBuyAmount[msg.sender] += buyAmount; // update user's payment amount for token purchase (excluding fee)
		userFeeAmount[msg.sender] += feeAmount; // update user's platform fee payment amount
		_validateUserContributionLimit(_maxContributionAmount);
		totalContributionAmount += _contributionAmount; // update total payment amount
		totalContributionAmountWithoutFee += buyAmount; // update total payment amount for token purchase (excluding fees)
		totalContributionFee += feeAmount; // update total platform fee amount
		emit Contributed(msg.sender, _contributionAmount, paymentTokenAddress);
	}

	/**
	 * @notice Claim purchased tokens and receive refund if sale is oversubscribed.
	 * @dev nonReentrant modifier is used to prevent reentrancy attacks.
	 *      This function clears the user's contribution after claim to prevent double claim.
	 */
	function claimTokens() public validClaimTime whenNotPaused {
		_validateClaimConditions();
		uint256 contributeAmount = userContributionAmount[msg.sender];
		uint256 userBuyAmountValue = userBuyAmount[msg.sender];
		uint256 userFeeAmountValue = userFeeAmount[msg.sender];
		uint256 refundCost = 0;
		uint256 boughtToken = 0;
		
		if (totalContributionAmountWithoutFee <= contributionTarget) {
			// Normal subscription: use pre-calculated buy amount
			// Calculate token amount using PRBMath for high precision
			boughtToken = PRBMath.mulDiv(userBuyAmountValue, 1e18, paymentTokenPrice);
			IERC20(saleTokenAddress).transfer(msg.sender, boughtToken);
		} else {
			// Oversubscribed: all tokens are sold, user gets proportional share based on buy amount
			// Use the new state variable for total buy amount
			uint256 totalBuyAmount = totalContributionAmountWithoutFee;
			
			// User gets proportional share of all tokens based on their buy amount using PRBMath
			boughtToken = PRBMath.mulDiv(userBuyAmountValue, totalTokensForSale, totalBuyAmount);
			
			// Calculate how much the user actually pays for these tokens using PRBMath
			uint256 userEffectiveBuyAmount = PRBMath.mulDiv(boughtToken, paymentTokenPrice, 1e18);
			uint256 userEffectiveFeeAmount = PRBMath.mulDiv(userEffectiveBuyAmount, feeBps, MAX_FEE_BPS);
			
			// Calculate refund breakdown: both unused buy amount and unused fee
			uint256 refundBuyAmount = userBuyAmountValue - userEffectiveBuyAmount;
			uint256 refundFeeAmount = userFeeAmountValue - userEffectiveFeeAmount;
			// Use unchecked for addition since both values are guaranteed to be positive
			unchecked {
				refundCost = refundBuyAmount + refundFeeAmount;
			}
			
			// Refund
			if (paymentTokenAddress == address(0)) {
				(bool sent, ) = payable(msg.sender).call{ value: refundCost }("");
				if (!sent) revert TransferFailed();
			} else {
				IERC20(paymentTokenAddress).transfer(msg.sender, refundCost);
			}
			
			// Transfer tokens
			IERC20(saleTokenAddress).transfer(msg.sender, boughtToken);
		}
		
		// Mark user as claimed and clear user data
		userClaimed[msg.sender] = true;
		userContributionAmount[msg.sender] = 0;
		userBuyAmount[msg.sender] = 0;
		userFeeAmount[msg.sender] = 0;
		emit TokensClaimed(msg.sender, boughtToken, refundCost);
	}
}