package agent

import (
	"fmt"
	"io"
	"log"
	"os"
	"sync"

	"github.com/hashicorp/nomad/client"
	"github.com/hashicorp/nomad/nomad"
)

// Agent is a long running daemon that is used to run both
// clients and servers. Servers are responsible for managing
// state and making scheduling decisions. Clients can be
// scheduled to, and are responsible for interfacing with
// servers to run allocations.
type Agent struct {
	config    *Config
	logger    *log.Logger
	logOutput io.Writer

	server *nomad.Server
	client *client.Client

	shutdown     bool
	shutdownCh   chan struct{}
	shutdownLock sync.Mutex
}

// NewAgent is used to create a new agent with the given configuration
func NewAgent(config *Config, logOutput io.Writer) (*Agent, error) {
	// Ensure we have a log sink
	if logOutput == nil {
		logOutput = os.Stderr
	}

	a := &Agent{
		config:     config,
		logger:     log.New(logOutput, "", log.LstdFlags),
		logOutput:  logOutput,
		shutdownCh: make(chan struct{}),
	}

	if err := a.setupServer(); err != nil {
		return nil, err
	}
	if err := a.setupClient(); err != nil {
		return nil, err
	}
	if a.client == nil && a.server == nil {
		return nil, fmt.Errorf("must have at least client or server mode enabled")
	}
	return a, nil
}

// setupServer is used to setup the server if enabled
func (a *Agent) setupServer() error {
	if !a.config.Server.Enabled {
		return nil
	}

	// Setup the configuration
	conf := nomad.DefaultConfig()
	conf.LogOutput = a.logOutput
	conf.DevMode = a.config.DevMode

	// TODO: Merge configuration

	server, err := nomad.NewServer(conf)
	if err != nil {
		return fmt.Errorf("server setup failed: %v", err)
	}
	a.server = server
	return nil
}

// setupClient is used to setup the client if enabled
func (a *Agent) setupClient() error {
	if !a.config.Client.Enabled {
		return nil
	}

	// Setup the configuration
	conf := client.DefaultConfig()
	if a.server != nil {
		conf.RPCHandler = a.server
	}
	conf.LogOutput = a.logOutput
	conf.DevMode = a.config.DevMode

	// TODO: Merge configuration

	client, err := client.NewClient(conf)
	if err != nil {
		return fmt.Errorf("client setup failed: %v", err)
	}
	a.client = client
	return nil
}

// Leave is used gracefully exit. Clients will inform servers
// of their departure so that allocations can be rescheduled.
func (a *Agent) Leave() error {
	if a.client != nil {
		if err := a.client.Leave(); err != nil {
			a.logger.Printf("[ERR] agent: client leave failed: %v", err)
		}
	}
	if a.server != nil {
		if err := a.server.Leave(); err != nil {
			a.logger.Printf("[ERR] agent: server leave failed: %v", err)
		}
	}
	return nil
}

// Shutdown is used to terminate the agent.
func (a *Agent) Shutdown() error {
	a.shutdownLock.Lock()
	defer a.shutdownLock.Unlock()

	if a.shutdown {
		return nil
	}

	a.logger.Println("[INFO] agent: requesting shutdown")
	if a.client != nil {
		if err := a.client.Shutdown(); err != nil {
			a.logger.Printf("[ERR] agent: client shutdown failed: %v", err)
		}
	}
	if a.server != nil {
		if err := a.server.Shutdown(); err != nil {
			a.logger.Printf("[ERR] agent: server shutdown failed: %v", err)
		}
	}

	a.logger.Println("[INFO] agent: shutdown complete")
	a.shutdown = true
	close(a.shutdownCh)
	return nil
}

// RPC is used to make an RPC call to the Nomad servers
func (a *Agent) RPC(method string, args interface{}, reply interface{}) error {
	if a.server != nil {
		return a.server.RPC(method, args, reply)
	}
	return a.client.RPC(method, args, reply)
}

// Client returns the configured client or nil
func (a *Agent) Client() *client.Client {
	return a.client
}

// Server returns the configured server or nil
func (a *Agent) Server() *nomad.Server {
	return a.server
}