//! 虚拟机栈实现

use thiserror::Error;

const MAX_STACK_SIZE: usize = 1024;

#[derive(Debug, Error)]
pub enum StackError {
    #[error("栈溢出")]
    Overflow,
    #[error("栈下溢")]
    Underflow,
}

/// 虚拟机栈
#[derive(Debug, Clone)]
pub struct Stack {
    data: Vec<u64>,
    max_size: usize,
}

impl Stack {
    pub fn new() -> Self {
        Stack {
            data: Vec::new(),
            max_size: MAX_STACK_SIZE,
        }
    }
    
    pub fn with_capacity(capacity: usize) -> Self {
        Stack {
            data: Vec::with_capacity(capacity),
            max_size: capacity,
        }
    }
    
    /// 压栈
    pub fn push(&mut self, value: u64) -> Result<(), StackError> {
        if self.data.len() >= self.max_size {
            return Err(StackError::Overflow);
        }
        self.data.push(value);
        Ok(())
    }
    
    /// 出栈
    pub fn pop(&mut self) -> Result<u64, StackError> {
        self.data.pop().ok_or(StackError::Underflow)
    }
    
    /// 查看栈顶元素
    pub fn peek(&self) -> Result<u64, StackError> {
        self.data.last().copied().ok_or(StackError::Underflow)
    }
    
    /// 复制栈顶元素
    pub fn dup(&mut self) -> Result<(), StackError> {
        let value = self.peek()?;
        self.push(value)
    }
    
    /// 交换栈顶两个元素
    pub fn swap(&mut self) -> Result<(), StackError> {
        if self.data.len() < 2 {
            return Err(StackError::Underflow);
        }
        let len = self.data.len();
        self.data.swap(len - 1, len - 2);
        Ok(())
    }
    
    /// 获取栈大小
    pub fn size(&self) -> usize {
        self.data.len()
    }
    
    /// 检查栈是否为空
    pub fn is_empty(&self) -> bool {
        self.data.is_empty()
    }
    
    /// 清空栈
    pub fn clear(&mut self) {
        self.data.clear();
    }
}

impl Default for Stack {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_stack_push_pop() {
        let mut stack = Stack::new();
        assert!(stack.push(42).is_ok());
        assert!(stack.push(100).is_ok());
        
        assert_eq!(stack.pop().expect("mainnet: handle error"), 100);
        assert_eq!(stack.pop().expect("mainnet: handle error"), 42);
        assert!(stack.pop().is_err());
    }

    #[test]
    fn test_stack_peek() {
        let mut stack = Stack::new();
        stack.push(42).expect("FIX-006: unexpected None/Err");
        
        assert_eq!(stack.peek().expect("mainnet: handle error"), 42);
        assert_eq!(stack.size(), 1);
    }

    #[test]
    fn test_stack_dup() {
        let mut stack = Stack::new();
        stack.push(42).expect("FIX-006: unexpected None/Err");
        stack.dup().expect("FIX-006: unexpected None/Err");
        
        assert_eq!(stack.size(), 2);
        assert_eq!(stack.pop().expect("mainnet: handle error"), 42);
        assert_eq!(stack.pop().expect("mainnet: handle error"), 42);
    }

    #[test]
    fn test_stack_swap() {
        let mut stack = Stack::new();
        stack.push(1).expect("FIX-006: unexpected None/Err");
        stack.push(2).expect("FIX-006: unexpected None/Err");
        stack.swap().expect("FIX-006: unexpected None/Err");
        
        assert_eq!(stack.pop().expect("mainnet: handle error"), 1);
        assert_eq!(stack.pop().expect("mainnet: handle error"), 2);
    }

    #[test]
    fn test_stack_overflow() {
        let mut stack = Stack::with_capacity(2);
        assert!(stack.push(1).is_ok());
        assert!(stack.push(2).is_ok());
        assert!(stack.push(3).is_err());
    }
}