///! # 借贷协议
///!
///! Lending Protocol
///! 提供抵押借贷、利率计算和清算机制
///!
///! **版本**: v1.0
///! **模块**: charter-std/defi/lending.ch

use utils::math::{safe_mul, safe_div, safe_add, safe_sub, percentage};
use utils::crypto::sha3_384_hash;

// ============================================================================
// 借贷状态枚举
// ============================================================================

/// 贷款状态
pub enum LoanStatus {
    /// 活跃
    Active,
    
    /// 已还清
    Repaid,
    
    /// 已清算
    Liquidated,
    
    /// 违约
    Defaulted
}

/// 利率模式
pub enum InterestRateMode {
    /// 固定利率
    Fixed,
    
    /// 浮动利率
    Variable
}

// ============================================================================
// 借贷结构
// ============================================================================

/// 贷款信息
struct Loan {
    /// 贷款ID
    loan_id: Hash,
    
    /// 借款人
    borrower: Address,
    
    /// 抵押资产
    collateral_asset: Address,
    
    /// 抵押数量
    collateral_amount: u256,
    
    /// 借款资产
    borrow_asset: Address,
    
    /// 借款数量
    borrow_amount: u256,
    
    /// 利率（年化，基点）
    interest_rate: u16,
    
    /// 利率模式
    rate_mode: InterestRateMode,
    
    /// 创建时间
    created_at: Timestamp,
    
    /// 到期时间
    due_date: Timestamp,
    
    /// 已还本金
    repaid_principal: u256,
    
    /// 已还利息
    repaid_interest: u256,
    
    /// 贷款状态
    status: LoanStatus,
    
    /// 最后更新时间
    last_updated: Timestamp
}

/// 资产池信息
struct AssetPool {
    /// 资产地址
    asset: Address,
    
    /// 总存款
    total_deposits: u256,
    
    /// 总借款
    total_borrows: u256,
    
    /// 可用流动性
    available_liquidity: u256,
    
    /// 基础利率（年化，基点）
    base_rate: u16,
    
    /// 最优利用率（基点）
    optimal_utilization: u16,
    
    /// 斜率1（基点）
    slope1: u16,
    
    /// 斜率2（基点）
    slope2: u16,
    
    /// 抵押率（基点，例如8000表示80%）
    collateral_factor: u16,
    
    /// 清算阈值（基点，例如8500表示85%）
    liquidation_threshold: u16,
    
    /// 清算奖励（基点，例如500表示5%）
    liquidation_bonus: u16
}

/// 用户账户信息
struct UserAccount {
    /// 用户地址
    user: Address,
    
    /// 存款 (asset => amount)
    deposits: Map<Address, u256>,
    
    /// 借款 (asset => amount)
    borrows: Map<Address, u256>,
    
    /// 总抵押价值（USD）
    total_collateral_value: u256,
    
    /// 总借款价值（USD）
    total_borrow_value: u256,
    
    /// 健康因子（基点）
    health_factor: u16
}

// ============================================================================
// 借贷事件
// ============================================================================

/// 存款事件
event Deposit {
    user: Address,
    asset: Address,
    amount: u256,
    timestamp: Timestamp
}

/// 提款事件
event Withdraw {
    user: Address,
    asset: Address,
    amount: u256,
    timestamp: Timestamp
}

/// 借款事件
event Borrow {
    loan_id: Hash,
    borrower: Address,
    collateral_asset: Address,
    collateral_amount: u256,
    borrow_asset: Address,
    borrow_amount: u256,
    interest_rate: u16,
    timestamp: Timestamp
}

/// 还款事件
event Repay {
    loan_id: Hash,
    borrower: Address,
    repaid_principal: u256,
    repaid_interest: u256,
    timestamp: Timestamp
}

/// 清算事件
event Liquidate {
    loan_id: Hash,
    borrower: Address,
    liquidator: Address,
    collateral_liquidated: u256,
    debt_covered: u256,
    timestamp: Timestamp
}

// ============================================================================
// 借贷协议
// ============================================================================

/// 借贷协议
certificate LendingProtocol {
    /// 资产池 (asset => pool)
    let _pools: Map<Address, AssetPool>;
    
    /// 贷款 (loan_id => loan)
    let _loans: Map<Hash, Loan>;
    
    /// 用户账户 (user => account)
    let _accounts: Map<Address, UserAccount>;
    
    /// 用户贷款索引 (user => loan_ids)
    let _user_loans: Map<Address, Vec<Hash>>;
    
    /// 价格预言机（简化，实际需要外部预言机）
    let _prices: Map<Address, u256>;
    
    /// 管理员地址
    let _admin: Address;
    
    /// 清算奖励接收地址
    let _treasury: Address;
    
    // ========== 构造函数 ==========
    
    constructor(treasury: Address) {
        require(!treasury.is_zero(), "Invalid treasury");
        
        self._admin = msg.sender;
        self._treasury = treasury;
    }
    
    // ========== 资产池管理 ==========
    
    /// 创建资产池
    ///
    /// # 参数
    /// - `asset`: 资产地址
    /// - `base_rate`: 基础利率（基点）
    /// - `optimal_utilization`: 最优利用率（基点）
    /// - `slope1`: 斜率1（基点）
    /// - `slope2`: 斜率2（基点）
    /// - `collateral_factor`: 抵押率（基点）
    /// - `liquidation_threshold`: 清算阈值（基点）
    /// - `liquidation_bonus`: 清算奖励（基点）
    ///
    /// # 返回
    /// - `bool`: 是否成功
    pub fn create_pool(
        asset: Address,
        base_rate: u16,
        optimal_utilization: u16,
        slope1: u16,
        slope2: u16,
        collateral_factor: u16,
        liquidation_threshold: u16,
        liquidation_bonus: u16
    ) -> bool {
        require(msg.sender == self._admin, "Only admin");
        require(!asset.is_zero(), "Invalid asset");
        require(!self._pools.contains_key(asset), "Pool already exists");
        require(collateral_factor <= 10000, "Invalid collateral factor");
        require(liquidation_threshold <= 10000, "Invalid liquidation threshold");
        require(collateral_factor < liquidation_threshold, "CF must be < LT");
        
        let pool = AssetPool {
            asset: asset,
            total_deposits: 0,
            total_borrows: 0,
            available_liquidity: 0,
            base_rate: base_rate,
            optimal_utilization: optimal_utilization,
            slope1: slope1,
            slope2: slope2,
            collateral_factor: collateral_factor,
            liquidation_threshold: liquidation_threshold,
            liquidation_bonus: liquidation_bonus
        };
        
        self._pools[asset] = pool;
        
        return true;
    }
    
    /// 获取资产池信息
    ///
    /// # 参数
    /// - `asset`: 资产地址
    ///
    /// # 返回
    /// - `AssetPool`: 资产池信息
    pub fn get_pool(asset: Address) -> AssetPool {
        require(self._pools.contains_key(asset), "Pool not found");
        return self._pools[asset];
    }
    
    /// 计算当前借款利率
    ///
    /// # 参数
    /// - `asset`: 资产地址
    ///
    /// # 返回
    /// - `u16`: 借款利率（基点）
    pub fn get_borrow_rate(asset: Address) -> u16 {
        require(self._pools.contains_key(asset), "Pool not found");
        
        let pool = self._pools[asset];
        
        if pool.total_deposits == 0 {
            return pool.base_rate;
        }
        
        // 计算利用率
        let utilization = safe_mul(pool.total_borrows, 10000) / pool.total_deposits;
        
        if utilization <= pool.optimal_utilization as u256 {
            // 利用率 <= 最优利用率
            // rate = base_rate + (utilization / optimal) * slope1
            let rate_increase = safe_mul(utilization, pool.slope1 as u256) / pool.optimal_utilization as u256;
            return pool.base_rate + rate_increase as u16;
        } else {
            // 利用率 > 最优利用率
            // rate = base_rate + slope1 + ((utilization - optimal) / (10000 - optimal)) * slope2
            let excess_utilization = safe_sub(utilization, pool.optimal_utilization as u256);
            let excess_range = safe_sub(10000, pool.optimal_utilization as u256);
            let rate_increase = safe_mul(excess_utilization, pool.slope2 as u256) / excess_range;
            return pool.base_rate + pool.slope1 + rate_increase as u16;
        }
    }
    
    /// 计算存款利率
    ///
    /// # 参数
    /// - `asset`: 资产地址
    ///
    /// # 返回
    /// - `u16`: 存款利率（基点）
    pub fn get_deposit_rate(asset: Address) -> u16 {
        require(self._pools.contains_key(asset), "Pool not found");
        
        let pool = self._pools[asset];
        
        if pool.total_deposits == 0 {
            return 0;
        }
        
        // 存款利率 = 借款利率 * 利用率
        let borrow_rate = self.get_borrow_rate(asset);
        let utilization = safe_mul(pool.total_borrows, 10000) / pool.total_deposits;
        
        return safe_mul(borrow_rate as u256, utilization) / 10000 as u16;
    }
    
    // ========== 存款和提款 ==========
    
    /// 存款
    ///
    /// # 参数
    /// - `asset`: 资产地址
    /// - `amount`: 数量
    ///
    /// # 返回
    /// - `bool`: 是否成功
    pub fn deposit(asset: Address, amount: u256) -> bool {
        require(self._pools.contains_key(asset), "Pool not found");
        require(amount > 0, "Amount must be positive");
        
        // 实际实现需要调用资产合约的transferFrom
        
        // 更新资产池
        let mut pool = self._pools[asset];
        pool.total_deposits = safe_add(pool.total_deposits, amount);
        pool.available_liquidity = safe_add(pool.available_liquidity, amount);
        self._pools[asset] = pool;
        
        // 更新用户账户
        if !self._accounts.contains_key(msg.sender) {
            self._accounts[msg.sender] = UserAccount {
                user: msg.sender,
                deposits: Map::new(),
                borrows: Map::new(),
                total_collateral_value: 0,
                total_borrow_value: 0,
                health_factor: 10000
            };
        }
        
        let mut account = self._accounts[msg.sender];
        let current_deposit = account.deposits.get(asset).unwrap_or(0);
        account.deposits[asset] = safe_add(current_deposit, amount);
        self._accounts[msg.sender] = account;
        
        emit Deposit {
            user: msg.sender,
            asset: asset,
            amount: amount,
            timestamp: block.timestamp
        };
        
        return true;
    }
    
    /// 提款
    ///
    /// # 参数
    /// - `asset`: 资产地址
    /// - `amount`: 数量
    ///
    /// # 返回
    /// - `bool`: 是否成功
    pub fn withdraw(asset: Address, amount: u256) -> bool {
        require(self._pools.contains_key(asset), "Pool not found");
        require(amount > 0, "Amount must be positive");
        require(self._accounts.contains_key(msg.sender), "No account");
        
        let mut account = self._accounts[msg.sender];
        let deposit = account.deposits.get(asset).unwrap_or(0);
        require(deposit >= amount, "Insufficient deposit");
        
        // 检查是否有足够的流动性
        let pool = self._pools[asset];
        require(pool.available_liquidity >= amount, "Insufficient liquidity");
        
        // 检查健康因子
        // 提款后健康因子不能低于1.0
        let new_health_factor = self._calculate_health_factor_after_withdraw(
            msg.sender,
            asset,
            amount
        );
        require(new_health_factor >= 10000, "Would break health factor");
        
        // 更新资产池
        let mut pool = self._pools[asset];
        pool.total_deposits = safe_sub(pool.total_deposits, amount);
        pool.available_liquidity = safe_sub(pool.available_liquidity, amount);
        self._pools[asset] = pool;
        
        // 更新用户账户
        account.deposits[asset] = safe_sub(deposit, amount);
        self._accounts[msg.sender] = account;
        
        // 实际实现需要调用资产合约的transfer
        
        emit Withdraw {
            user: msg.sender,
            asset: asset,
            amount: amount,
            timestamp: block.timestamp
        };
        
        return true;
    }
    
    // ========== 借款和还款 ==========
    
    /// 借款
    ///
    /// # 参数
    /// - `collateral_asset`: 抵押资产
    /// - `collateral_amount`: 抵押数量
    /// - `borrow_asset`: 借款资产
    /// - `borrow_amount`: 借款数量
    /// - `duration`: 借款期限（秒）
    ///
    /// # 返回
    /// - `Hash`: 贷款ID
    pub fn borrow(
        collateral_asset: Address,
        collateral_amount: u256,
        borrow_asset: Address,
        borrow_amount: u256,
        duration: Duration
    ) -> Hash {
        require(self._pools.contains_key(collateral_asset), "Collateral pool not found");
        require(self._pools.contains_key(borrow_asset), "Borrow pool not found");
        require(collateral_amount > 0, "Collateral must be positive");
        require(borrow_amount > 0, "Borrow amount must be positive");
        require(duration > 0, "Duration must be positive");
        
        let collateral_pool = self._pools[collateral_asset];
        let borrow_pool = self._pools[borrow_asset];
        
        // 检查流动性
        require(
            borrow_pool.available_liquidity >= borrow_amount,
            "Insufficient liquidity"
        );
        
        // 计算抵押价值和借款价值
        let collateral_price = self._get_price(collateral_asset);
        let borrow_price = self._get_price(borrow_asset);
        
        let collateral_value = safe_mul(collateral_amount, collateral_price) / 1e18;
        let borrow_value = safe_mul(borrow_amount, borrow_price) / 1e18;
        
        // 检查抵押率
        let max_borrow_value = safe_mul(
            collateral_value,
            collateral_pool.collateral_factor as u256
        ) / 10000;
        
        require(borrow_value <= max_borrow_value, "Insufficient collateral");
        
        // 计算利率
        let interest_rate = self.get_borrow_rate(borrow_asset);
        
        // 生成贷款ID
        let loan_id = self._generate_loan_id(msg.sender, collateral_asset, borrow_asset);
        
        let loan = Loan {
            loan_id: loan_id,
            borrower: msg.sender,
            collateral_asset: collateral_asset,
            collateral_amount: collateral_amount,
            borrow_asset: borrow_asset,
            borrow_amount: borrow_amount,
            interest_rate: interest_rate,
            rate_mode: InterestRateMode::Variable,
            created_at: block.timestamp,
            due_date: block.timestamp + duration,
            repaid_principal: 0,
            repaid_interest: 0,
            status: LoanStatus::Active,
            last_updated: block.timestamp
        };
        
        self._loans[loan_id] = loan;
        
        // 更新用户贷款索引
        if !self._user_loans.contains_key(msg.sender) {
            self._user_loans[msg.sender] = Vec::new();
        }
        self._user_loans[msg.sender].push(loan_id);
        
        // 更新资产池
        let mut borrow_pool = self._pools[borrow_asset];
        borrow_pool.total_borrows = safe_add(borrow_pool.total_borrows, borrow_amount);
        borrow_pool.available_liquidity = safe_sub(borrow_pool.available_liquidity, borrow_amount);
        self._pools[borrow_asset] = borrow_pool;
        
        // 转移抵押资产（实际需要调用资产合约）
        // 转移借款资产给借款人（实际需要调用资产合约）
        
        emit Borrow {
            loan_id: loan_id,
            borrower: msg.sender,
            collateral_asset: collateral_asset,
            collateral_amount: collateral_amount,
            borrow_asset: borrow_asset,
            borrow_amount: borrow_amount,
            interest_rate: interest_rate,
            timestamp: block.timestamp
        };
        
        return loan_id;
    }
    
    /// 还款
    ///
    /// # 参数
    /// - `loan_id`: 贷款ID
    /// - `amount`: 还款数量
    ///
    /// # 返回
    /// - `bool`: 是否成功
    pub fn repay(loan_id: Hash, amount: u256) -> bool {
        require(self._loans.contains_key(loan_id), "Loan not found");
        require(amount > 0, "Amount must be positive");
        
        let mut loan = self._loans[loan_id];
        require(loan.borrower == msg.sender, "Not the borrower");
        require(loan.status == LoanStatus::Active, "Loan not active");
        
        // 计算应还利息
        let interest = self._calculate_interest(loan_id);
        let total_debt = safe_add(
            safe_sub(loan.borrow_amount, loan.repaid_principal),
            safe_sub(interest, loan.repaid_interest)
        );
        
        require(amount <= total_debt, "Amount exceeds debt");
        
        // 先还利息，再还本金
        let remaining_interest = safe_sub(interest, loan.repaid_interest);
        
        let interest_payment = if amount <= remaining_interest {
            amount
        } else {
            remaining_interest
        };
        
        let principal_payment = safe_sub(amount, interest_payment);
        
        loan.repaid_interest = safe_add(loan.repaid_interest, interest_payment);
        loan.repaid_principal = safe_add(loan.repaid_principal, principal_payment);
        loan.last_updated = block.timestamp;
        
        // 检查是否还清
        if loan.repaid_principal == loan.borrow_amount &&
           loan.repaid_interest == interest {
            loan.status = LoanStatus::Repaid;
            
            // 返还抵押品（实际需要调用资产合约）
        }
        
        self._loans[loan_id] = loan;
        
        // 更新资产池
        let mut pool = self._pools[loan.borrow_asset];
        pool.total_borrows = safe_sub(pool.total_borrows, principal_payment);
        pool.available_liquidity = safe_add(pool.available_liquidity, amount);
        self._pools[loan.borrow_asset] = pool;
        
        emit Repay {
            loan_id: loan_id,
            borrower: msg.sender,
            repaid_principal: principal_payment,
            repaid_interest: interest_payment,
            timestamp: block.timestamp
        };
        
        return true;
    }
    
    // ========== 清算 ==========
    
    /// 清算
    ///
    /// # 参数
    /// - `loan_id`: 贷款ID
    ///
    /// # 返回
    /// - `bool`: 是否成功
    pub fn liquidate(loan_id: Hash) -> bool {
        require(self._loans.contains_key(loan_id), "Loan not found");
        
        let mut loan = self._loans[loan_id];
        require(loan.status == LoanStatus::Active, "Loan not active");
        
        // 检查是否可以清算
        require(self._is_liquidatable(loan_id), "Cannot liquidate");
        
        // 计算债务
        let interest = self._calculate_interest(loan_id);
        let total_debt = safe_add(
            safe_sub(loan.borrow_amount, loan.repaid_principal),
            safe_sub(interest, loan.repaid_interest)
        );
        
        // 计算清算奖励
        let collateral_pool = self._pools[loan.collateral_asset];
        let liquidation_amount = safe_mul(
            loan.collateral_amount,
            (10000 + collateral_pool.liquidation_bonus) as u256
        ) / 10000;
        
        loan.status = LoanStatus::Liquidated;
        self._loans[loan_id] = loan;
        
        // 转移抵押品给清算人（实际需要调用资产合约）
        // 清算人需要支付债务（实际需要调用资产合约）
        
        emit Liquidate {
            loan_id: loan_id,
            borrower: loan.borrower,
            liquidator: msg.sender,
            collateral_liquidated: liquidation_amount,
            debt_covered: total_debt,
            timestamp: block.timestamp
        };
        
        return true;
    }
    
    /// 检查贷款是否可以清算
    ///
    /// # 参数
    /// - `loan_id`: 贷款ID
    ///
    /// # 返回
    /// - `bool`: 是否可以清算
    pub fn is_liquidatable(loan_id: Hash) -> bool {
        return self._is_liquidatable(loan_id);
    }
    
    // ========== 查询函数 ==========
    
    /// 获取贷款信息
    ///
    /// # 参数
    /// - `loan_id`: 贷款ID
    ///
    /// # 返回
    /// - `Loan`: 贷款信息
    pub fn get_loan(loan_id: Hash) -> Loan {
        require(self._loans.contains_key(loan_id), "Loan not found");
        return self._loans[loan_id];
    }
    
    /// 获取用户贷款列表
    ///
    /// # 参数
    /// - `user`: 用户地址
    ///
    /// # 返回
    /// - `Vec<Hash>`: 贷款ID列表
    pub fn get_user_loans(user: Address) -> Vec<Hash> {
        return self._user_loans.get(user).unwrap_or(Vec::new());
    }
    
    /// 计算应还利息
    ///
    /// # 参数
    /// - `loan_id`: 贷款ID
    ///
    /// # 返回
    /// - `u256`: 应还利息
    pub fn calculate_interest(loan_id: Hash) -> u256 {
        return self._calculate_interest(loan_id);
    }
    
    // ========== 内部函数 ==========
    
    /// 生成贷款ID
    fn _generate_loan_id(
        borrower: Address,
        collateral_asset: Address,
        borrow_asset: Address
    ) -> Hash {
        let mut data = Bytes::new();
        data.extend(borrower.as_bytes());
        data.extend(collateral_asset.as_bytes());
        data.extend(borrow_asset.as_bytes());
        data.extend(block.timestamp.to_bytes());
        data.extend(tx.hash.as_bytes());
        return sha3_384_hash(data);
    }
    
    /// 计算利息
    fn _calculate_interest(loan_id: Hash) -> u256 {
        let loan = self._loans[loan_id];
        
        let time_elapsed = safe_sub(block.timestamp, loan.last_updated);
        let principal = safe_sub(loan.borrow_amount, loan.repaid_principal);
        
        // 年化利率转换为秒利率
        // interest = principal * rate * time / (365 * 24 * 3600 * 10000)
        let interest = safe_mul(
            safe_mul(principal, loan.interest_rate as u256),
            time_elapsed
        ) / (365 * 24 * 3600 * 10000);
        
        return safe_add(loan.repaid_interest, interest);
    }
    
    /// 检查是否可以清算
    fn _is_liquidatable(loan_id: Hash) -> bool {
        let loan = self._loans[loan_id];
        
        if loan.status != LoanStatus::Active {
            return false;
        }
        
        // 检查是否过期
        if block.timestamp > loan.due_date {
            return true;
        }
        
        // 检查健康因子
        let collateral_pool = self._pools[loan.collateral_asset];
        let borrow_pool = self._pools[loan.borrow_asset];
        
        let collateral_price = self._get_price(loan.collateral_asset);
        let borrow_price = self._get_price(loan.borrow_asset);
        
        let collateral_value = safe_mul(loan.collateral_amount, collateral_price) / 1e18;
        
        let interest = self._calculate_interest(loan_id);
        let total_debt = safe_add(
            safe_sub(loan.borrow_amount, loan.repaid_principal),
            safe_sub(interest, loan.repaid_interest)
        );
        let debt_value = safe_mul(total_debt, borrow_price) / 1e18;
        
        // 健康因子 = (抵押价值 * 清算阈值) / 债务价值
        let health_factor = safe_mul(
            collateral_value,
            collateral_pool.liquidation_threshold as u256
        ) / debt_value;
        
        // 健康因子 < 1.0 可以清算
        return health_factor < 10000;
    }
    
    /// 计算提款后的健康因子
    fn _calculate_health_factor_after_withdraw(
        user: Address,
        asset: Address,
        amount: u256
    ) -> u16 {
        // 简化实现，实际需要重新计算所有抵押和借款
        return 10000;
    }
    
    /// 获取价格（简化，实际需要预言机）
    fn _get_price(asset: Address) -> u256 {
        return self._prices.get(asset).unwrap_or(1e18);
    }
    
    // ========== 管理函数 ==========
    
    /// 设置价格（简化，实际应该使用预言机）
    pub fn set_price(asset: Address, price: u256) -> bool {
        require(msg.sender == self._admin, "Only admin");
        self._prices[asset] = price;
        return true;
    }
}