package agent

import (
	"bytes"
	"github.com/hashicorp/consul/consul/structs"
	"log"
	"os/exec"
	"runtime"
	"sync"
	"syscall"
	"time"
)

// CheckNotifier interface is used by the CheckMonitor
// to notify when a check has a status update. The update
// should take care to be idempotent.
type CheckNotifier interface {
	UpdateCheck(checkID, status string)
}

// CheckMonitor is used to periodically invoke a script to
// determine the health of a given check. It is compatible with
// nagios plugins and expects the output in the same format.
type CheckMonitor struct {
	Notify   CheckNotifier
	CheckID  string
	Script   string
	Interval time.Duration
	Logger   *log.Logger

	stop     bool
	stopCh   chan struct{}
	stopLock sync.Mutex
}

// Start is used to start a check monitor.
// Monitor runs until stop is called
func (c *CheckMonitor) Start() {
	c.stopLock.Lock()
	defer c.stopLock.Unlock()
	c.stop = false
	c.stopCh = make(chan struct{})
	go c.run()
}

// Stop is used to stop a check monitor.
func (c *CheckMonitor) Stop() {
	c.stopLock.Lock()
	defer c.stopLock.Unlock()
	if !c.stop {
		c.stop = true
		close(c.stopCh)
	}
}

// run is invoked by a goroutine to run until Stop() is called
func (c *CheckMonitor) run() {
	next := time.After(0)
	for {
		select {
		case <-next:
			c.check()
			next = time.After(c.Interval)
		case <-c.stopCh:
			return
		}
	}
}

// check is invoked periodically to perform the script check
func (c *CheckMonitor) check() {
	// Determine the shell invocation based on OS
	var shell, flag string
	if runtime.GOOS == "windows" {
		shell = "cmd"
		flag = "/C"
	} else {
		shell = "/bin/sh"
		flag = "-c"
	}

	// Create the command
	cmd := exec.Command(shell, flag, c.Script)

	// Collect the output
	var output bytes.Buffer
	cmd.Stdout = &output
	cmd.Stderr = &output

	// Start the check
	if err := cmd.Start(); err != nil {
		c.Logger.Printf("[ERR] agent: failed to invoke '%s': %s", c.Script, err)
		c.Notify.UpdateCheck(c.CheckID, structs.HealthUnknown)
		return
	}

	// Wait for the check to complete
	err := cmd.Wait()
	c.Logger.Printf("[DEBUG] agent: check '%s' script '%s' output: %s",
		c.CheckID, c.Script, output.Bytes())

	// Check if the check passed
	if err == nil {
		c.Logger.Printf("[DEBUG] Check '%v' is passing", c.CheckID)
		c.Notify.UpdateCheck(c.CheckID, structs.HealthPassing)
		return
	}

	// If the exit code is 1, set check as warning
	exitErr, ok := err.(*exec.ExitError)
	if ok {
		if status, ok := exitErr.Sys().(syscall.WaitStatus); ok {
			code := status.ExitStatus()
			if code == 1 {
				c.Logger.Printf("[WARN] Check '%v' is now warning", c.CheckID)
				c.Notify.UpdateCheck(c.CheckID, structs.HealthWarning)
				return
			}
		}
	}

	// Set the health as critical
	c.Logger.Printf("[WARN] Check '%v' is now critical", c.CheckID)
	c.Notify.UpdateCheck(c.CheckID, structs.HealthCritical)
}