pi_gray 0.1.0

extern crate fnv;

use fnv::FnvHashMap;

pub trait GrayVersion {
    fn get_gray(&self) -> &Option<usize>;
    fn set_gray(&mut self, g: Option<usize>);
    fn get_id(&self) -> usize;
}

pub trait Gray {}

/**

* 灰度表
*/
pub struct GrayTab<T: Gray> {
    last: usize,
    tab: FnvHashMap<usize, T>,
}

impl<T: Gray> GrayTab<T> {
    //构建一个灰度表
    pub fn new(first: T) -> Self {
        let mut map = FnvHashMap::default();
        map.insert(0, first);
        GrayTab { last: 0, tab: map }
    }

    //取灰度
    pub fn get(&self, version: &usize) -> Option<&T> {
        self.tab.get(version)
    }

    //添加一个灰度
    pub fn add(&mut self, gray: T) -> usize {
        self.last += 1;
        self.tab.insert(self.last, gray);
        self.last
    }

    //移除灰度, 如果移除后
    pub fn remove(&mut self, version: &usize) -> Option<T> {
        //如果灰度列表中只存在一个灰度，则不能移除
        match self.last {
            0 => {
                println!("The only gray cannot be removed");
                return None;
            }
            _ => (),
        };

        //如果移除灰度版本未最新版本， 则更新最新版本未前一版本
        match version == &self.last {
            true => self.version_back(),
            false => (),
        }
        self.tab.remove(version)
    }

    //取到最新灰度
    pub fn get_last(&self) -> &T {
        self.tab.get(&self.last).unwrap()
    }

    fn version_back(&mut self) {
        self.last = self.last - 1;
        match self.tab.get(&self.last) {
            Some(_) => (),
            None => self.version_back(),
        }
    }
}