package driver

import (
	"fmt"
	"runtime"
	"strings"
	"syscall"
	"time"

	"github.com/hashicorp/nomad/client/config"
	"github.com/hashicorp/nomad/client/executor"
	"github.com/hashicorp/nomad/nomad/structs"
)

// ExecDriver is the simplest possible driver. It literally just
// fork/execs tasks. It should probably not be used for most things,
// but is useful for testing purposes or for very simple tasks.
type ExecDriver struct {
	DriverContext
}

// execHandle is returned from Start/Open as a handle to the PID
type execHandle struct {
	cmd    executor.Executor
	waitCh chan error
	doneCh chan struct{}
}

// NewExecDriver is used to create a new exec driver
func NewExecDriver(ctx *DriverContext) Driver {
	return &ExecDriver{*ctx}
}

func (d *ExecDriver) Fingerprint(cfg *config.Config, node *structs.Node) (bool, error) {
	// Only enable if we are root when running on non-windows systems.
	if runtime.GOOS != "windows" && syscall.Geteuid() != 0 {
		d.logger.Printf("[DEBUG] driver.exec: must run as root user, disabling")
		return false, nil
	}

	node.Attributes["driver.exec"] = "1"
	return true, nil
}

func (d *ExecDriver) Start(ctx *ExecContext, task *structs.Task) (DriverHandle, error) {
	// Get the command
	command, ok := task.Config["command"]
	if !ok || command == "" {
		return nil, fmt.Errorf("missing command for exec driver")
	}

	// Look for arguments
	argRaw, ok := task.Config["args"]
	var args []string
	if ok {
		args = strings.Split(argRaw, " ")
	}

	// Setup the command
	cmd := executor.Command(command, args...)
	if err := cmd.Limit(task.Resources); err != nil {
		return nil, fmt.Errorf("failed to constrain resources: %s", err)
	}

	// Populate environment variables
	cmd.Command().Env = PopulateEnvironment(ctx, task)

	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("failed to start command: %v", err)
	}

	// Return a driver handle
	h := &execHandle{
		cmd:    cmd,
		doneCh: make(chan struct{}),
		waitCh: make(chan error, 1),
	}
	go h.run()
	return h, nil
}

func (d *ExecDriver) Open(ctx *ExecContext, handleID string) (DriverHandle, error) {
	// Find the process
	cmd, err := executor.OpenId(handleID)
	if err != nil {
		return nil, fmt.Errorf("failed to open ID %v: %v", handleID, err)
	}

	// Return a driver handle
	h := &execHandle{
		cmd:    cmd,
		doneCh: make(chan struct{}),
		waitCh: make(chan error, 1),
	}
	go h.run()
	return h, nil
}

func (h *execHandle) ID() string {
	id, _ := h.cmd.ID()
	return id
}

func (h *execHandle) WaitCh() chan error {
	return h.waitCh
}

func (h *execHandle) Update(task *structs.Task) error {
	// Update is not possible
	return nil
}

func (h *execHandle) Kill() error {
	h.cmd.Shutdown()
	select {
	case <-h.doneCh:
		return nil
	case <-time.After(5 * time.Second):
		return h.cmd.ForceStop()
	}
}

func (h *execHandle) run() {
	err := h.cmd.Wait()
	close(h.doneCh)
	if err != nil {
		h.waitCh <- err
	}
	close(h.waitCh)
}