// Copyright (c) 2018 HyperHQ Inc.
//
// SPDX-License-Identifier: Apache-2.0
//
// cache implements base vm factory on top of other base vm factory.

package cache

import (
	"context"
	"fmt"
	"sync"

	pb "github.com/kata-containers/runtime/protocols/cache"
	vc "github.com/kata-containers/runtime/virtcontainers"
	"github.com/kata-containers/runtime/virtcontainers/factory/base"
)

type cache struct {
	base base.FactoryBase

	cacheCh   chan *vc.VM
	closed    chan<- int
	wg        sync.WaitGroup
	closeOnce sync.Once

	vmm     map[*vc.VM]interface{}
	vmmLock sync.RWMutex
}

// New creates a new cached vm factory.
func New(ctx context.Context, count uint, b base.FactoryBase) base.FactoryBase {
	if count < 1 {
		return b
	}

	cacheCh := make(chan *vc.VM)
	closed := make(chan int, count)
	c := cache{
		base:    b,
		cacheCh: cacheCh,
		closed:  closed,
		vmm:     make(map[*vc.VM]interface{}),
	}
	for i := 0; i < int(count); i++ {
		c.wg.Add(1)
		go func() {
			for {
				vm, err := b.GetBaseVM(ctx, c.Config())
				if err != nil {
					c.wg.Done()
					c.CloseFactory(ctx)
					return
				}
				c.addToVmm(vm)

				select {
				case cacheCh <- vm:
					// Because vm will not be relased or changed
					// by cacheServer.GetBaseVM or removeFromVmm.
					// So removeFromVmm can be called after vm send to cacheCh.
					c.removeFromVmm(vm)
				case <-closed:
					c.removeFromVmm(vm)
					vm.Stop()
					c.wg.Done()
					return
				}
			}
		}()
	}
	return &c
}

func (c *cache) addToVmm(vm *vc.VM) {
	c.vmmLock.Lock()
	defer c.vmmLock.Unlock()

	c.vmm[vm] = nil
}

func (c *cache) removeFromVmm(vm *vc.VM) {
	c.vmmLock.Lock()
	defer c.vmmLock.Unlock()

	delete(c.vmm, vm)
}

// Config returns cache vm factory's base factory config.
func (c *cache) Config() vc.VMConfig {
	return c.base.Config()
}

// GetVMStatus returns the status of the cached VMs.
func (c *cache) GetVMStatus() []*pb.GrpcVMStatus {
	vs := []*pb.GrpcVMStatus{}

	c.vmmLock.RLock()
	defer c.vmmLock.RUnlock()

	for vm := range c.vmm {
		vs = append(vs, vm.GetVMStatus())
	}

	return vs
}

// GetBaseVM returns a base VM from cache factory's base factory.
func (c *cache) GetBaseVM(ctx context.Context, config vc.VMConfig) (*vc.VM, error) {
	vm, ok := <-c.cacheCh
	if ok {
		return vm, nil
	}
	return nil, fmt.Errorf("cache factory is closed")
}

// CloseFactory closes the cache factory.
func (c *cache) CloseFactory(ctx context.Context) {
	c.closeOnce.Do(func() {
		for len(c.closed) < cap(c.closed) { // send sufficient closed signal
			c.closed <- 0
		}
		c.wg.Wait()
		close(c.cacheCh)
		c.base.CloseFactory(ctx)
	})
}