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extern crate consul_rust;
#[macro_use]
extern crate log;
extern crate rand;
extern crate url;

use core::diplomat::{Diplomat, Strategy};
use std::collections::HashMap;
use std::collections::HashSet;
use std::time::{SystemTime, UNIX_EPOCH};

pub mod core;

/// Discovery for target app address, with load balancing and fail over.
///
///    1. The discovery will refresh the service list every 10 seconds by
///       default. The selection strategy is roundrobin, for keeping the
///       connections balanced.
///    2. Once a connection to a specified host failed, discard the host and
///       try the next. And loop the process until find a connectable host
///       or the retry time reaches the max time. If all the hosts are
///       discarded, refresh the host list.
///    3. The discovery also accepts an extra address pair, for fallback
///       when the discovery agent is down. If no backup address found, zone
///       will try to pick one from the discarded addresses.
///
///

pub struct Discovery {
    // target means which service should to be found.
    // eg. comment for Comment service.
    target: String,

    // a fallback choice if discovery agent is down.
    address: String,

    // ttl specified the interval for the discovery to refresh the service list.
    ttl: u64,

    // the real woker to fetch the service list.
    diplomat: Diplomat,

    // record the last time the address is acessed,
    // used for refreshing the service list after time expired.
    last_cleanup_time: u64,

    // record the unnormal address to prevent failure.
    discarded_addr: HashSet<String>,

//   todo mu sync.Mutex
}

impl Default for Discovery {
    fn default() -> Discovery {
        Discovery {
            target: String::new(),
            address: String::new(),
            ttl: 10,
            diplomat: Diplomat::new(),
            discarded_addr: HashSet::new(),
            last_cleanup_time: 0,
        }
    }
}

fn get_unix_timestamp() -> u64 {
    let start = SystemTime::now();
    let since_the_epoch = start.duration_since(UNIX_EPOCH)
        .expect("Time went backwards");
    since_the_epoch.as_secs() * 1000
}

impl Discovery {
    pub fn new_discovery(target: String, address: Option<String>) -> Discovery {
        // todo verify address ip and port
        let mut discovery = Discovery { ..Default::default() };
        let mut addr = String::new();
        match address {
            Some(x) => { addr = x; }
            _ => {}
        }
        if target.is_empty() {
            if addr.is_empty() {
                panic!("Target name and address can not be null together");
            } else {
                discovery.address = addr;
            }
        } else {
            discovery.target = target;
        }
        discovery
    }
    pub fn get_address(&mut self) -> String {
        // todo Mutex
        let mut address = self.address.clone();
        if self.target.is_empty() {
            if address.is_empty() {
                panic!("Target null, no address available")
            }
            return address;
        }
        self.cleanup();

        let max_rr_time = self.discarded_addr.len() + 1;
        let mut rr_time: u32 = 0;

        loop {
            let service_entry = self.diplomat.select(self.target.clone(), Strategy::Roundrobin, false);
            match service_entry {
                Some(val) => {
                    let ret = format!("{}:{}", val.address, val.port);
                    if !self.discarded_addr.contains(&ret) {
                        address = ret;
                        break;
                    }
                    rr_time += 1;
                    if rr_time == max_rr_time as u32 {
                        if !self.address.is_empty() {
                            info!("No healthy addresses available, fallback to the given host-port pair.");
                            address = self.address.clone();
                        } else if self.discarded_addr.len() > 0 {
                            // random choice
                            for d in self.discarded_addr.iter() {
                                warn!("Fallback to a discarded address: {}", d);
                                address = d.clone();
                            }
                        } else {
                            panic!("Iterated on all the addresses, no healthy address available.")
                        }
                        break;
                    }
                }
                _ => { panic!("Can not discover available address"); }
            }
        }
        address
    }
    /// Cleanup the discarded addresses, the expiration time is the TTL.
    fn cleanup(&mut self) {
        let now = get_unix_timestamp();
        if self.last_cleanup_time != 0 {
            if self.last_cleanup_time + self.ttl <= now {
                self.discarded_addr.clear();
                self.last_cleanup_time = now;
            }
        } else {
            self.last_cleanup_time = now;
        }
    }


    /// Discard the given address for a period. The TTL is the one passed in the initializer.
    pub fn discard_address(&mut self, address: String) -> bool {
        if self.last_cleanup_time == 0 {
            self.last_cleanup_time = get_unix_timestamp()
        }
        if !self.discarded_addr.contains(&address) {
            self.discarded_addr.insert(address);
            true
        } else {
            false
        }
    }
}