package gocql

import (
	"fmt"
	"log"
	"strings"
	"sync"
	"time"
)

//ConnectionPool is the interface gocql expects to be exposed for a connection pool.
type ConnectionPool interface {
	Pick(*Query) *Conn
	Size() int
	HandleError(*Conn, error, bool)
	Close()
}

//NewPoolFunc is the type used by ClusterConfig to create a pool of a specific type.
type NewPoolFunc func(*ClusterConfig) ConnectionPool

//SimplePool is the current implementation of the connection pool inside gocql. This
//pool is meant to be a simple default used by gocql so users can get up and running
//quickly.
type SimplePool struct {
	cfg      *ClusterConfig
	hostPool *RoundRobin
	connPool map[string]*RoundRobin
	conns    map[*Conn]struct{}
	keyspace string
	mu       sync.Mutex

	cFillingPool chan int

	quit     bool
	quitWait chan bool
	quitOnce sync.Once
}

//NewSimplePool is the function used by gocql to create the simple connection pool.
//This is the default if no other pool type is specified.
func NewSimplePool(cfg *ClusterConfig) ConnectionPool {
	pool := SimplePool{
		cfg:          cfg,
		hostPool:     NewRoundRobin(),
		connPool:     make(map[string]*RoundRobin),
		conns:        make(map[*Conn]struct{}),
		quitWait:     make(chan bool),
		cFillingPool: make(chan int, 1),
		keyspace:     cfg.Keyspace,
	}
	//Walk through connecting to hosts. As soon as one host connects
	//defer the remaining connections to cluster.fillPool()
	for i := 0; i < len(pool.cfg.Hosts); i++ {
		addr := strings.TrimSpace(pool.cfg.Hosts[i])
		if strings.Index(addr, ":") < 0 {
			addr = fmt.Sprintf("%s:%d", addr, pool.cfg.DefaultPort)
		}
		if pool.connect(addr) == nil {
			pool.cFillingPool <- 1
			go pool.fillPool()
			break
		}

	}
	return &pool
}

func (c *SimplePool) connect(addr string) error {
	cfg := ConnConfig{
		ProtoVersion:  c.cfg.ProtoVersion,
		CQLVersion:    c.cfg.CQLVersion,
		Timeout:       c.cfg.Timeout,
		NumStreams:    c.cfg.NumStreams,
		Compressor:    c.cfg.Compressor,
		Authenticator: c.cfg.Authenticator,
		Keepalive:     c.cfg.SocketKeepalive,
	}

	for {
		conn, err := Connect(addr, cfg, c)
		if err != nil {
			log.Printf("failed to connect to %q: %v", addr, err)
			return err
		}
		return c.addConn(conn)
	}
}

func (c *SimplePool) addConn(conn *Conn) error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.quit {
		conn.Close()
		return nil
	}
	//Set the connection's keyspace if any before adding it to the pool
	if c.keyspace != "" {
		if err := conn.UseKeyspace(c.keyspace); err != nil {
			log.Printf("error setting connection keyspace. %v", err)
			conn.Close()
			return err
		}
	}
	connPool := c.connPool[conn.Address()]
	if connPool == nil {
		connPool = NewRoundRobin()
		c.connPool[conn.Address()] = connPool
		c.hostPool.AddNode(connPool)
	}
	connPool.AddNode(conn)
	c.conns[conn] = struct{}{}
	return nil
}

//fillPool manages the pool of connections making sure that each host has the correct
//amount of connections defined. Also the method will test a host with one connection
//instead of flooding the host with number of connections defined in the cluster config
func (c *SimplePool) fillPool() {
	//Debounce large amounts of requests to fill pool
	select {
	case <-time.After(1 * time.Millisecond):
		return
	case <-c.cFillingPool:
		defer func() { c.cFillingPool <- 1 }()
	}

	c.mu.Lock()
	isClosed := c.quit
	c.mu.Unlock()
	//Exit if cluster(session) is closed
	if isClosed {
		return
	}
	//Walk through list of defined hosts
	for i := 0; i < len(c.cfg.Hosts); i++ {
		addr := strings.TrimSpace(c.cfg.Hosts[i])
		if strings.Index(addr, ":") < 0 {
			addr = fmt.Sprintf("%s:%d", addr, c.cfg.DefaultPort)
		}
		var numConns int = 1
		//See if the host already has connections in the pool
		c.mu.Lock()
		conns, ok := c.connPool[addr]
		c.mu.Unlock()

		if ok {
			//if the host has enough connections just exit
			numConns = conns.Size()
			if numConns >= c.cfg.NumConns {
				continue
			}
		} else {
			//See if the host is reachable
			if err := c.connect(addr); err != nil {
				continue
			}
		}
		//This is reached if the host is responsive and needs more connections
		//Create connections for host synchronously to mitigate flooding the host.
		go func(a string, conns int) {
			for ; conns < c.cfg.NumConns; conns++ {
				c.connect(addr)
			}
		}(addr, numConns)
	}
}

// Should only be called if c.mu is locked
func (c *SimplePool) removeConnLocked(conn *Conn) {
	conn.Close()
	connPool := c.connPool[conn.addr]
	if connPool == nil {
		return
	}
	connPool.RemoveNode(conn)
	if connPool.Size() == 0 {
		c.hostPool.RemoveNode(connPool)
		delete(c.connPool, conn.addr)
	}
	delete(c.conns, conn)
}

func (c *SimplePool) removeConn(conn *Conn) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.removeConnLocked(conn)
}

//HandleError is called by a Connection object to report to the pool an error has occured.
//Logic is then executed within the pool to clean up the erroroneous connection and try to
//top off the pool.
func (c *SimplePool) HandleError(conn *Conn, err error, closed bool) {
	if !closed {
		// ignore all non-fatal errors
		return
	}
	c.removeConn(conn)
	if !c.quit {
		go c.fillPool() // top off pool.
	}
}

//Pick selects a connection to be used by the query.
func (c *SimplePool) Pick(qry *Query) *Conn {
	//Check if connections are available
	c.mu.Lock()
	conns := len(c.conns)
	c.mu.Unlock()

	if conns == 0 {
		//try to populate the pool before returning.
		c.fillPool()
	}

	return c.hostPool.Pick(qry)
}

//Size returns the number of connections currently active in the pool
func (p *SimplePool) Size() int {
	p.mu.Lock()
	conns := len(p.conns)
	p.mu.Unlock()
	return conns
}

//Close kills the pool and all associated connections.
func (c *SimplePool) Close() {
	c.quitOnce.Do(func() {
		c.mu.Lock()
		defer c.mu.Unlock()
		c.quit = true
		close(c.quitWait)
		for conn := range c.conns {
			c.removeConnLocked(conn)
		}
	})
}