// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

/**
 * @title CurrencyValidation
 * @notice Library for validating currency codes and types according to ISO 4217 compliance
 * @dev Ensures all currency references are either ISO 4217 compliant or explicitly identified as non-ISO
 */
library CurrencyValidation {
    /**
     * @notice Currency type enumeration
     */
    enum CurrencyType {
        ISO4217_FIAT,      // Standard ISO 4217 fiat currency (USD, EUR, etc.)
        ISO4217_CRYPTO,    // ISO 4217 cryptocurrency code (if applicable)
        NON_ISO_SYNTHETIC, // Non-ISO synthetic unit of account (e.g., GRU)
        NON_ISO_INTERNAL,  // Non-ISO internal accounting unit
        COMMODITY          // Commodity code (XAU, XAG, etc.)
    }

    /**
     * @notice Validate ISO 4217 currency code format
     * @dev ISO 4217 codes are exactly 3 uppercase letters
     * @param code Currency code to validate
     * @return isValid True if code matches ISO 4217 format
     */
    function isValidISO4217Format(string memory code) internal pure returns (bool isValid) {
        bytes memory codeBytes = bytes(code);
        if (codeBytes.length != 3) {
            return false;
        }
        
        for (uint256 i = 0; i < 3; i++) {
            uint8 char = uint8(codeBytes[i]);
            if (char < 65 || char > 90) { // Not A-Z
                return false;
            }
        }
        
        return true;
    }

    /**
     * @notice Check if currency code is a recognized ISO 4217 code
     * @dev This is a simplified check - in production, maintain a full registry
     * @param code Currency code
     * @return isISO4217 True if code is recognized ISO 4217
     */
    function isISO4217Currency(string memory code) internal pure returns (bool isISO4217) {
        if (!isValidISO4217Format(code)) {
            return false;
        }
        
        // Common ISO 4217 codes (extend as needed)
        bytes32 codeHash = keccak256(bytes(code));
        
        // Major currencies
        if (codeHash == keccak256("USD") || // US Dollar
            codeHash == keccak256("EUR") || // Euro
            codeHash == keccak256("GBP") || // British Pound
            codeHash == keccak256("JPY") || // Japanese Yen
            codeHash == keccak256("CNY") || // Chinese Yuan
            codeHash == keccak256("CHF") || // Swiss Franc
            codeHash == keccak256("CAD") || // Canadian Dollar
            codeHash == keccak256("AUD") || // Australian Dollar
            codeHash == keccak256("NZD") || // New Zealand Dollar
            codeHash == keccak256("SGD")) { // Singapore Dollar
            return true;
        }
        
        // In production, maintain a full registry or use oracle/external validation
        return false;
    }

    /**
     * @notice Check if code is GRU (Global Reserve Unit)
     * @dev GRU is a non-ISO 4217 synthetic unit of account
     * @param code Currency code
     * @return gru True if code is GRU
     */
    function isGRU(string memory code) internal pure returns (bool gru) {
        bytes32 codeHash = keccak256(bytes(code));
        return codeHash == keccak256("GRU") || 
               codeHash == keccak256("M00") || 
               codeHash == keccak256("M0") || 
               codeHash == keccak256("M1");
    }

    /**
     * @notice Check if code is XAU (Gold)
     * @dev XAU is the ISO 4217 commodity code for gold
     * @param code Currency code
     * @return xau True if code is XAU
     */
    function isXAU(string memory code) internal pure returns (bool xau) {
        return keccak256(bytes(code)) == keccak256("XAU");
    }

    /**
     * @notice Get currency type
     * @param code Currency code
     * @return currencyType Type of currency
     */
    function getCurrencyType(string memory code) internal pure returns (CurrencyType currencyType) {
        if (isXAU(code)) {
            return CurrencyType.COMMODITY;
        }
        
        if (isGRU(code)) {
            return CurrencyType.NON_ISO_SYNTHETIC;
        }
        
        if (isISO4217Currency(code)) {
            return CurrencyType.ISO4217_FIAT;
        }
        
        // If format is valid but not recognized, treat as potentially valid ISO 4217
        if (isValidISO4217Format(code)) {
            return CurrencyType.ISO4217_FIAT; // Assume valid but not in our list
        }
        
        return CurrencyType.NON_ISO_INTERNAL;
    }

    /**
     * @notice Validate that currency is legal tender (ISO 4217 fiat)
     * @param code Currency code
     * @return legalTender True if currency is ISO 4217 legal tender
     */
    function isLegalTender(string memory code) internal pure returns (bool legalTender) {
        CurrencyType currencyType = getCurrencyType(code);
        return currencyType == CurrencyType.ISO4217_FIAT;
    }

    /**
     * @notice Require currency to be legal tender or revert
     * @param code Currency code
     */
    function requireLegalTender(string memory code) internal pure {
        require(isLegalTender(code), "CurrencyValidation: not legal tender - must be ISO 4217");
    }

    /**
     * @notice Require currency to NOT be legal tender (for synthetic units)
     * @param code Currency code
     */
    function requireNonLegalTender(string memory code) internal pure {
        require(!isLegalTender(code), "CurrencyValidation: must be non-legal tender");
    }
}
