package chef

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"path"
	"regexp"
	"strings"
	"sync"
	"text/template"
	"time"

	"github.com/hashicorp/terraform/communicator"
	"github.com/hashicorp/terraform/communicator/remote"
	"github.com/hashicorp/terraform/helper/schema"
	"github.com/hashicorp/terraform/terraform"
	"github.com/mitchellh/go-homedir"
	"github.com/mitchellh/go-linereader"
)

const (
	clienrb         = "client.rb"
	defaultEnv      = "_default"
	firstBoot       = "first-boot.json"
	logfileDir      = "logfiles"
	linuxChefCmd    = "chef-client"
	linuxConfDir    = "/etc/chef"
	linuxNoOutput   = "> /dev/null 2>&1"
	linuxGemCmd     = "/opt/chef/embedded/bin/gem"
	linuxKnifeCmd   = "knife"
	secretKey       = "encrypted_data_bag_secret"
	windowsChefCmd  = "cmd /c chef-client"
	windowsConfDir  = "C:/chef"
	windowsNoOutput = "> nul 2>&1"
	windowsGemCmd   = "C:/opscode/chef/embedded/bin/gem"
	windowsKnifeCmd = "cmd /c knife"
)

const clientConf = `
log_location            STDOUT
chef_server_url         "{{ .ServerURL }}"
node_name               "{{ .NodeName }}"
{{ if .UsePolicyfile }}
use_policyfile true
policy_group 	 "{{ .PolicyGroup }}"
policy_name 	 "{{ .PolicyName }}"
{{ end -}}

{{ if .HTTPProxy }}
http_proxy          "{{ .HTTPProxy }}"
ENV['http_proxy'] = "{{ .HTTPProxy }}"
ENV['HTTP_PROXY'] = "{{ .HTTPProxy }}"
{{ end -}}

{{ if .HTTPSProxy }}
https_proxy          "{{ .HTTPSProxy }}"
ENV['https_proxy'] = "{{ .HTTPSProxy }}"
ENV['HTTPS_PROXY'] = "{{ .HTTPSProxy }}"
{{ end -}}

{{ if .NOProxy }}
no_proxy          "{{ join .NOProxy "," }}"
ENV['no_proxy'] = "{{ join .NOProxy "," }}"
{{ end -}}

{{ if .SSLVerifyMode }}
ssl_verify_mode  {{ .SSLVerifyMode }}
{{- end -}}

{{ if .DisableReporting }}
enable_reporting false
{{ end -}}

{{ if .ClientOptions }}
{{ join .ClientOptions "\n" }}
{{ end }}
`

type provisionFn func(terraform.UIOutput, communicator.Communicator) error

type provisioner struct {
	Attributes            map[string]interface{}
	ClientOptions         []string
	DisableReporting      bool
	Environment           string
	FetchChefCertificates bool
	LogToFile             bool
	UsePolicyfile         bool
	PolicyGroup           string
	PolicyName            string
	HTTPProxy             string
	HTTPSProxy            string
	NamedRunList          string
	NOProxy               []string
	NodeName              string
	OhaiHints             []string
	OSType                string
	RecreateClient        bool
	PreventSudo           bool
	RunList               []string
	SecretKey             string
	ServerURL             string
	SkipInstall           bool
	SkipRegister          bool
	SSLVerifyMode         string
	UserName              string
	UserKey               string
	Vaults                map[string][]string
	Version               string

	cleanupUserKeyCmd     string
	createConfigFiles     provisionFn
	installChefClient     provisionFn
	fetchChefCertificates provisionFn
	generateClientKey     provisionFn
	configureVaults       provisionFn
	runChefClient         provisionFn
	useSudo               bool
}

// Provisioner returns a Chef provisioner
func Provisioner() terraform.ResourceProvisioner {
	return &schema.Provisioner{
		Schema: map[string]*schema.Schema{
			"node_name": &schema.Schema{
				Type:     schema.TypeString,
				Required: true,
			},
			"server_url": &schema.Schema{
				Type:     schema.TypeString,
				Required: true,
			},
			"user_name": &schema.Schema{
				Type:     schema.TypeString,
				Required: true,
			},
			"user_key": &schema.Schema{
				Type:     schema.TypeString,
				Required: true,
			},

			"attributes_json": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"client_options": &schema.Schema{
				Type:     schema.TypeList,
				Elem:     &schema.Schema{Type: schema.TypeString},
				Optional: true,
			},
			"disable_reporting": &schema.Schema{
				Type:     schema.TypeBool,
				Optional: true,
			},
			"environment": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
				Default:  defaultEnv,
			},
			"fetch_chef_certificates": &schema.Schema{
				Type:     schema.TypeBool,
				Optional: true,
			},
			"log_to_file": &schema.Schema{
				Type:     schema.TypeBool,
				Optional: true,
			},
			"use_policyfile": &schema.Schema{
				Type:     schema.TypeBool,
				Optional: true,
			},
			"policy_group": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"policy_name": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"http_proxy": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"https_proxy": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"no_proxy": &schema.Schema{
				Type:     schema.TypeList,
				Elem:     &schema.Schema{Type: schema.TypeString},
				Optional: true,
			},
			"named_run_list": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"ohai_hints": &schema.Schema{
				Type:     schema.TypeList,
				Elem:     &schema.Schema{Type: schema.TypeString},
				Optional: true,
			},
			"os_type": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"recreate_client": &schema.Schema{
				Type:     schema.TypeBool,
				Optional: true,
			},
			"prevent_sudo": &schema.Schema{
				Type:     schema.TypeBool,
				Optional: true,
			},
			"run_list": &schema.Schema{
				Type:     schema.TypeList,
				Elem:     &schema.Schema{Type: schema.TypeString},
				Optional: true,
			},
			"secret_key": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"skip_install": &schema.Schema{
				Type:     schema.TypeBool,
				Optional: true,
			},
			"skip_register": &schema.Schema{
				Type:     schema.TypeBool,
				Optional: true,
			},
			"ssl_verify_mode": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"vault_json": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
			"version": &schema.Schema{
				Type:     schema.TypeString,
				Optional: true,
			},
		},

		ApplyFunc:    applyFn,
		ValidateFunc: validateFn,
	}
}

// TODO: Support context cancelling (Provisioner Stop)
func applyFn(ctx context.Context) error {
	o := ctx.Value(schema.ProvOutputKey).(terraform.UIOutput)
	d := ctx.Value(schema.ProvConfigDataKey).(*schema.ResourceData)

	// Decode the raw config for this provisioner
	p, err := decodeConfig(d)
	if err != nil {
		return err
	}

	if p.OSType == "" {
		switch t := d.State().Ephemeral.ConnInfo["type"]; t {
		case "ssh", "": // The default connection type is ssh, so if the type is empty assume ssh
			p.OSType = "linux"
		case "winrm":
			p.OSType = "windows"
		default:
			return fmt.Errorf("Unsupported connection type: %s", t)
		}
	}

	// Set some values based on the targeted OS
	switch p.OSType {
	case "linux":
		p.cleanupUserKeyCmd = fmt.Sprintf("rm -f %s", path.Join(linuxConfDir, p.UserName+".pem"))
		p.createConfigFiles = p.linuxCreateConfigFiles
		p.installChefClient = p.linuxInstallChefClient
		p.fetchChefCertificates = p.fetchChefCertificatesFunc(linuxKnifeCmd, linuxConfDir)
		p.generateClientKey = p.generateClientKeyFunc(linuxKnifeCmd, linuxConfDir, linuxNoOutput)
		p.configureVaults = p.configureVaultsFunc(linuxGemCmd, linuxKnifeCmd, linuxConfDir)
		p.runChefClient = p.runChefClientFunc(linuxChefCmd, linuxConfDir)
		p.useSudo = !p.PreventSudo && d.State().Ephemeral.ConnInfo["user"] != "root"
	case "windows":
		p.cleanupUserKeyCmd = fmt.Sprintf("cd %s && del /F /Q %s", windowsConfDir, p.UserName+".pem")
		p.createConfigFiles = p.windowsCreateConfigFiles
		p.installChefClient = p.windowsInstallChefClient
		p.fetchChefCertificates = p.fetchChefCertificatesFunc(windowsKnifeCmd, windowsConfDir)
		p.generateClientKey = p.generateClientKeyFunc(windowsKnifeCmd, windowsConfDir, windowsNoOutput)
		p.configureVaults = p.configureVaultsFunc(windowsGemCmd, windowsKnifeCmd, windowsConfDir)
		p.runChefClient = p.runChefClientFunc(windowsChefCmd, windowsConfDir)
		p.useSudo = false
	default:
		return fmt.Errorf("Unsupported os type: %s", p.OSType)
	}

	// Get a new communicator
	comm, err := communicator.New(d.State())
	if err != nil {
		return err
	}

	// Wait and retry until we establish the connection
	err = retryFunc(comm.Timeout(), func() error {
		return comm.Connect(o)
	})
	if err != nil {
		return err
	}
	defer comm.Disconnect()

	// Make sure we always delete the user key from the new node!
	var once sync.Once
	cleanupUserKey := func() {
		o.Output("Cleanup user key...")
		if err := p.runCommand(o, comm, p.cleanupUserKeyCmd); err != nil {
			o.Output("WARNING: Failed to cleanup user key on new node: " + err.Error())
		}
	}
	defer once.Do(cleanupUserKey)

	if !p.SkipInstall {
		if err := p.installChefClient(o, comm); err != nil {
			return err
		}
	}

	o.Output("Creating configuration files...")
	if err := p.createConfigFiles(o, comm); err != nil {
		return err
	}

	if !p.SkipRegister {
		if p.FetchChefCertificates {
			o.Output("Fetch Chef certificates...")
			if err := p.fetchChefCertificates(o, comm); err != nil {
				return err
			}
		}

		o.Output("Generate the private key...")
		if err := p.generateClientKey(o, comm); err != nil {
			return err
		}
	}

	if p.Vaults != nil {
		o.Output("Configure Chef vaults...")
		if err := p.configureVaults(o, comm); err != nil {
			return err
		}
	}

	// Cleanup the user key before we run Chef-Client to prevent issues
	// with rights caused by changing settings during the run.
	once.Do(cleanupUserKey)

	o.Output("Starting initial Chef-Client run...")
	if err := p.runChefClient(o, comm); err != nil {
		return err
	}

	return nil
}

func validateFn(d *schema.ResourceData) (ws []string, es []error) {
	p, err := decodeConfig(d)
	if err != nil {
		es = append(es, err)
		return ws, es
	}

	if !p.UsePolicyfile && p.RunList == nil {
		es = append(es, errors.New("Key not found: run_list"))
	}
	if p.UsePolicyfile && p.PolicyName == "" {
		es = append(es, errors.New("Policyfile enabled but key not found: policy_name"))
	}
	if p.UsePolicyfile && p.PolicyGroup == "" {
		es = append(es, errors.New("Policyfile enabled but key not found: policy_group"))
	}

	return ws, es
}

func (p *provisioner) deployConfigFiles(o terraform.UIOutput, comm communicator.Communicator, confDir string) error {
	// Copy the user key to the new instance
	pk := strings.NewReader(p.UserKey)
	if err := comm.Upload(path.Join(confDir, p.UserName+".pem"), pk); err != nil {
		return fmt.Errorf("Uploading user key failed: %v", err)
	}

	if p.SecretKey != "" {
		// Copy the secret key to the new instance
		s := strings.NewReader(p.SecretKey)
		if err := comm.Upload(path.Join(confDir, secretKey), s); err != nil {
			return fmt.Errorf("Uploading %s failed: %v", secretKey, err)
		}
	}

	// Make sure the SSLVerifyMode value is written as a symbol
	if p.SSLVerifyMode != "" && !strings.HasPrefix(p.SSLVerifyMode, ":") {
		p.SSLVerifyMode = fmt.Sprintf(":%s", p.SSLVerifyMode)
	}

	// Make strings.Join available for use within the template
	funcMap := template.FuncMap{
		"join": strings.Join,
	}

	// Create a new template and parse the client config into it
	t := template.Must(template.New(clienrb).Funcs(funcMap).Parse(clientConf))

	var buf bytes.Buffer
	err := t.Execute(&buf, p)
	if err != nil {
		return fmt.Errorf("Error executing %s template: %s", clienrb, err)
	}

	// Copy the client config to the new instance
	if err = comm.Upload(path.Join(confDir, clienrb), &buf); err != nil {
		return fmt.Errorf("Uploading %s failed: %v", clienrb, err)
	}

	// Create a map with first boot settings
	fb := make(map[string]interface{})
	if p.Attributes != nil {
		fb = p.Attributes
	}

	// Check if the run_list was also in the attributes and if so log a warning
	// that it will be overwritten with the value of the run_list argument.
	if _, found := fb["run_list"]; found {
		log.Printf("[WARNING] Found a 'run_list' specified in the configured attributes! " +
			"This value will be overwritten by the value of the `run_list` argument!")
	}

	// Add the initial runlist to the first boot settings
	if !p.UsePolicyfile {
		fb["run_list"] = p.RunList
	}

	// Marshal the first boot settings to JSON
	d, err := json.Marshal(fb)
	if err != nil {
		return fmt.Errorf("Failed to create %s data: %s", firstBoot, err)
	}

	// Copy the first-boot.json to the new instance
	if err := comm.Upload(path.Join(confDir, firstBoot), bytes.NewReader(d)); err != nil {
		return fmt.Errorf("Uploading %s failed: %v", firstBoot, err)
	}

	return nil
}

func (p *provisioner) deployOhaiHints(o terraform.UIOutput, comm communicator.Communicator, hintDir string) error {
	for _, hint := range p.OhaiHints {
		// Open the hint file
		f, err := os.Open(hint)
		if err != nil {
			return err
		}
		defer f.Close()

		// Copy the hint to the new instance
		if err := comm.Upload(path.Join(hintDir, path.Base(hint)), f); err != nil {
			return fmt.Errorf("Uploading %s failed: %v", path.Base(hint), err)
		}
	}

	return nil
}

func (p *provisioner) fetchChefCertificatesFunc(
	knifeCmd string,
	confDir string) func(terraform.UIOutput, communicator.Communicator) error {
	return func(o terraform.UIOutput, comm communicator.Communicator) error {
		clientrb := path.Join(confDir, clienrb)
		cmd := fmt.Sprintf("%s ssl fetch -c %s", knifeCmd, clientrb)

		return p.runCommand(o, comm, cmd)
	}
}

func (p *provisioner) generateClientKeyFunc(knifeCmd string, confDir string, noOutput string) provisionFn {
	return func(o terraform.UIOutput, comm communicator.Communicator) error {
		options := fmt.Sprintf("-c %s -u %s --key %s",
			path.Join(confDir, clienrb),
			p.UserName,
			path.Join(confDir, p.UserName+".pem"),
		)

		// See if we already have a node object
		getNodeCmd := fmt.Sprintf("%s node show %s %s %s", knifeCmd, p.NodeName, options, noOutput)
		node := p.runCommand(o, comm, getNodeCmd) == nil

		// See if we already have a client object
		getClientCmd := fmt.Sprintf("%s client show %s %s %s", knifeCmd, p.NodeName, options, noOutput)
		client := p.runCommand(o, comm, getClientCmd) == nil

		// If we have a client, we can only continue if we are to recreate the client
		if client && !p.RecreateClient {
			return fmt.Errorf(
				"Chef client %q already exists, set recreate_client=true to automatically recreate the client", p.NodeName)
		}

		// If the node exists, try to delete it
		if node {
			deleteNodeCmd := fmt.Sprintf("%s node delete %s -y %s",
				knifeCmd,
				p.NodeName,
				options,
			)
			if err := p.runCommand(o, comm, deleteNodeCmd); err != nil {
				return err
			}
		}

		// If the client exists, try to delete it
		if client {
			deleteClientCmd := fmt.Sprintf("%s client delete %s -y %s",
				knifeCmd,
				p.NodeName,
				options,
			)
			if err := p.runCommand(o, comm, deleteClientCmd); err != nil {
				return err
			}
		}

		// Create the new client object
		createClientCmd := fmt.Sprintf("%s client create %s -d -f %s %s",
			knifeCmd,
			p.NodeName,
			path.Join(confDir, "client.pem"),
			options,
		)

		return p.runCommand(o, comm, createClientCmd)
	}
}

func (p *provisioner) configureVaultsFunc(gemCmd string, knifeCmd string, confDir string) provisionFn {
	return func(o terraform.UIOutput, comm communicator.Communicator) error {
		if err := p.runCommand(o, comm, fmt.Sprintf("%s install chef-vault", gemCmd)); err != nil {
			return err
		}

		options := fmt.Sprintf("-c %s -u %s --key %s",
			path.Join(confDir, clienrb),
			p.UserName,
			path.Join(confDir, p.UserName+".pem"),
		)

		for vault, items := range p.Vaults {
			for _, item := range items {
				updateCmd := fmt.Sprintf("%s vault update %s %s -C %s -M client %s",
					knifeCmd,
					vault,
					item,
					p.NodeName,
					options,
				)
				if err := p.runCommand(o, comm, updateCmd); err != nil {
					return err
				}
			}
		}

		return nil
	}
}

func (p *provisioner) runChefClientFunc(chefCmd string, confDir string) provisionFn {
	return func(o terraform.UIOutput, comm communicator.Communicator) error {
		fb := path.Join(confDir, firstBoot)
		var cmd string

		// Policyfiles do not support chef environments, so don't pass the `-E` flag.
		switch {
		case p.UsePolicyfile && p.NamedRunList == "":
			cmd = fmt.Sprintf("%s -j %q", chefCmd, fb)
		case p.UsePolicyfile && p.NamedRunList != "":
			cmd = fmt.Sprintf("%s -j %q -n %q", chefCmd, fb, p.NamedRunList)
		default:
			cmd = fmt.Sprintf("%s -j %q -E %q", chefCmd, fb, p.Environment)
		}

		if p.LogToFile {
			if err := os.MkdirAll(logfileDir, 0755); err != nil {
				return fmt.Errorf("Error creating logfile directory %s: %v", logfileDir, err)
			}

			logFile := path.Join(logfileDir, p.NodeName)
			f, err := os.Create(path.Join(logFile))
			if err != nil {
				return fmt.Errorf("Error creating logfile %s: %v", logFile, err)
			}
			f.Close()

			o.Output("Writing Chef Client output to " + logFile)
			o = p
		}

		return p.runCommand(o, comm, cmd)
	}
}

// Output implementation of terraform.UIOutput interface
func (p *provisioner) Output(output string) {
	logFile := path.Join(logfileDir, p.NodeName)
	f, err := os.OpenFile(logFile, os.O_APPEND|os.O_WRONLY, 0666)
	if err != nil {
		log.Printf("Error creating logfile %s: %v", logFile, err)
		return
	}
	defer f.Close()

	// These steps are needed to remove any ANSI escape codes used to colorize
	// the output and to make sure we have proper line endings before writing
	// the string to the logfile.
	re := regexp.MustCompile(`\x1b\[[0-9;]+m`)
	output = re.ReplaceAllString(output, "")
	output = strings.Replace(output, "\r", "\n", -1)

	if _, err := f.WriteString(output); err != nil {
		log.Printf("Error writing output to logfile %s: %v", logFile, err)
	}

	if err := f.Sync(); err != nil {
		log.Printf("Error saving logfile %s to disk: %v", logFile, err)
	}
}

// runCommand is used to run already prepared commands
func (p *provisioner) runCommand(o terraform.UIOutput, comm communicator.Communicator, command string) error {
	// Unless prevented, prefix the command with sudo
	if p.useSudo {
		command = "sudo " + command
	}

	outR, outW := io.Pipe()
	errR, errW := io.Pipe()
	outDoneCh := make(chan struct{})
	errDoneCh := make(chan struct{})
	go p.copyOutput(o, outR, outDoneCh)
	go p.copyOutput(o, errR, errDoneCh)

	cmd := &remote.Cmd{
		Command: command,
		Stdout:  outW,
		Stderr:  errW,
	}

	err := comm.Start(cmd)
	if err != nil {
		return fmt.Errorf("Error executing command %q: %v", cmd.Command, err)
	}

	cmd.Wait()
	if cmd.ExitStatus != 0 {
		err = fmt.Errorf(
			"Command %q exited with non-zero exit status: %d", cmd.Command, cmd.ExitStatus)
	}

	// Wait for output to clean up
	outW.Close()
	errW.Close()
	<-outDoneCh
	<-errDoneCh

	return err
}

func (p *provisioner) copyOutput(o terraform.UIOutput, r io.Reader, doneCh chan<- struct{}) {
	defer close(doneCh)
	lr := linereader.New(r)
	for line := range lr.Ch {
		o.Output(line)
	}
}

// retryFunc is used to retry a function for a given duration
func retryFunc(timeout time.Duration, f func() error) error {
	finish := time.After(timeout)
	for {
		err := f()
		if err == nil {
			return nil
		}
		log.Printf("Retryable error: %v", err)

		select {
		case <-finish:
			return err
		case <-time.After(3 * time.Second):
		}
	}
}

func decodeConfig(d *schema.ResourceData) (*provisioner, error) {
	p := &provisioner{
		ClientOptions:         getStringList(d.Get("client_options")),
		DisableReporting:      d.Get("disable_reporting").(bool),
		Environment:           d.Get("environment").(string),
		FetchChefCertificates: d.Get("fetch_chef_certificates").(bool),
		LogToFile:             d.Get("log_to_file").(bool),
		UsePolicyfile:         d.Get("use_policyfile").(bool),
		PolicyGroup:           d.Get("policy_group").(string),
		PolicyName:            d.Get("policy_name").(string),
		HTTPProxy:             d.Get("http_proxy").(string),
		HTTPSProxy:            d.Get("https_proxy").(string),
		NOProxy:               getStringList(d.Get("no_proxy")),
		NamedRunList:          d.Get("named_run_list").(string),
		NodeName:              d.Get("node_name").(string),
		OhaiHints:             getStringList(d.Get("ohai_hints")),
		OSType:                d.Get("os_type").(string),
		RecreateClient:        d.Get("recreate_client").(bool),
		PreventSudo:           d.Get("prevent_sudo").(bool),
		RunList:               getStringList(d.Get("run_list")),
		SecretKey:             d.Get("secret_key").(string),
		ServerURL:             d.Get("server_url").(string),
		SkipInstall:           d.Get("skip_install").(bool),
		SkipRegister:          d.Get("skip_register").(bool),
		SSLVerifyMode:         d.Get("ssl_verify_mode").(string),
		UserName:              d.Get("user_name").(string),
		UserKey:               d.Get("user_key").(string),
		Version:               d.Get("version").(string),
	}

	// Make sure the supplied URL has a trailing slash
	p.ServerURL = strings.TrimSuffix(p.ServerURL, "/") + "/"

	for i, hint := range p.OhaiHints {
		hintPath, err := homedir.Expand(hint)
		if err != nil {
			return nil, fmt.Errorf("Error expanding the path %s: %v", hint, err)
		}
		p.OhaiHints[i] = hintPath
	}

	if attrs, ok := d.GetOk("attributes_json"); ok {
		var m map[string]interface{}
		if err := json.Unmarshal([]byte(attrs.(string)), &m); err != nil {
			return nil, fmt.Errorf("Error parsing attributes_json: %v", err)
		}
		p.Attributes = m
	}

	if vaults, ok := d.GetOk("vault_json"); ok {
		var m map[string]interface{}
		if err := json.Unmarshal([]byte(vaults.(string)), &m); err != nil {
			return nil, fmt.Errorf("Error parsing vault_json: %v", err)
		}

		v := make(map[string][]string)
		for vault, items := range m {
			switch items := items.(type) {
			case []interface{}:
				for _, item := range items {
					if item, ok := item.(string); ok {
						v[vault] = append(v[vault], item)
					}
				}
			case interface{}:
				if item, ok := items.(string); ok {
					v[vault] = append(v[vault], item)
				}
			}
		}

		p.Vaults = v
	}

	return p, nil
}

func getStringList(v interface{}) []string {
	if v == nil {
		return nil
	}
	switch l := v.(type) {
	case []string:
		return l
	case []interface{}:
		arr := make([]string, len(l))
		for i, x := range l {
			arr[i] = x.(string)
		}
		return arr
	default:
		panic(fmt.Sprintf("Unsupported type: %T", v))
	}
}