/*
Copyright 2019 The KubeSphere Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package ldap

import (
	"errors"
	"log"
	"sync"

	"github.com/go-ldap/ldap"
)

// channelPool implements the Pool interface based on buffered channels.
type channelPool struct {
	// storage for our net.Conn connections
	mu    sync.Mutex
	conns chan ldap.Client

	name        string
	aliveChecks bool

	// net.Conn generator
	factory PoolFactory
	closeAt []uint16
}

// PoolFactory is a function to create new connections.
type PoolFactory func(string) (ldap.Client, error)

// newChannelPool returns a new pool based on buffered channels with an initial
// capacity and maximum capacity. Factory is used when initial capacity is
// greater than zero to fill the pool. A zero initialCap doesn't fill the Pool
// until a new Get() is called. During a Get(), If there is no new connection
// available in the pool, a new connection will be created via the Factory()
// method.
//
// closeAt will automagically mark the connection as unusable if the return code
// of the call is one of those passed, most likely you want to set this to something
// like
//   []uint8{ldap.LDAPResultTimeLimitExceeded, ldap.ErrorNetwork}
func newChannelPool(initialCap, maxCap int, name string, factory PoolFactory, closeAt []uint16) (Pool, error) {
	if initialCap < 0 || maxCap <= 0 || initialCap > maxCap {
		return nil, errors.New("invalid capacity settings")
	}

	c := &channelPool{
		conns:       make(chan ldap.Client, maxCap),
		name:        name,
		factory:     factory,
		closeAt:     closeAt,
		aliveChecks: true,
	}

	// create initial connections, if something goes wrong,
	// just close the pool error out.
	for i := 0; i < initialCap; i++ {
		conn, err := factory(c.name)
		if err != nil {
			c.Close()
			return nil, errors.New("factory is not able to fill the pool: " + err.Error())
		}
		c.conns <- conn
	}

	return c, nil
}

func (c *channelPool) AliveChecks(on bool) {
	c.mu.Lock()
	c.aliveChecks = on
	c.mu.Unlock()
}

func (c *channelPool) getConns() chan ldap.Client {
	c.mu.Lock()
	conns := c.conns
	c.mu.Unlock()
	return conns
}

// Get implements the Pool interfaces Get() method. If there is no new
// connection available in the pool, a new connection will be created via the
// Factory() method.
func (c *channelPool) Get() (*PoolConn, error) {
	conns := c.getConns()
	if conns == nil {
		return nil, ErrClosed
	}

	// wrap our connections with our ldap.Client implementation (wrapConn
	// method) that puts the connection back to the pool if it's closed.
	select {
	case conn := <-conns:
		if conn == nil {
			return nil, ErrClosed
		}
		if !c.aliveChecks || isAlive(conn) {
			return c.wrapConn(conn, c.closeAt), nil
		}
		conn.Close()
		return c.NewConn()
	default:
		return c.NewConn()
	}
}

func isAlive(conn ldap.Client) bool {
	_, err := conn.Search(&ldap.SearchRequest{BaseDN: "", Scope: ldap.ScopeBaseObject, Filter: "(&)", Attributes: []string{"1.1"}})
	return err == nil
}

func (c *channelPool) NewConn() (*PoolConn, error) {
	conn, err := c.factory(c.name)
	if err != nil {
		return nil, err
	}
	return c.wrapConn(conn, c.closeAt), nil
}

// put puts the connection back to the pool. If the pool is full or closed,
// conn is simply closed. A nil conn will be rejected.
func (c *channelPool) put(conn ldap.Client) {
	if conn == nil {
		log.Printf("connection is nil. rejecting")
		return
	}

	c.mu.Lock()
	defer c.mu.Unlock()

	if c.conns == nil {
		// pool is closed, close passed connection
		conn.Close()
		return
	}

	// put the resource back into the pool. If the pool is full, this will
	// block and the default case will be executed.
	select {
	case c.conns <- conn:
		return
	default:
		// pool is full, close passed connection
		conn.Close()
		return
	}
}

func (c *channelPool) Close() {
	c.mu.Lock()
	conns := c.conns
	c.conns = nil
	c.factory = nil
	c.mu.Unlock()

	if conns == nil {
		return
	}

	close(conns)
	for conn := range conns {
		conn.Close()
	}
	return
}

func (c *channelPool) Len() int { return len(c.getConns()) }

func (c *channelPool) wrapConn(conn ldap.Client, closeAt []uint16) *PoolConn {
	p := &PoolConn{c: c, closeAt: closeAt}
	p.Conn = conn
	return p
}