// Copyright 2016-2018, Pulumi Corporation.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package workspace

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"regexp"
	"runtime"
	"sort"
	"strings"
	"time"

	"github.com/blang/semver"
	"github.com/cheggaaa/pb"
	"github.com/djherbis/times"
	"github.com/pkg/errors"

	"github.com/pulumi/pulumi/sdk/v2/go/common/diag/colors"
	"github.com/pulumi/pulumi/sdk/v2/go/common/util/archive"
	"github.com/pulumi/pulumi/sdk/v2/go/common/util/contract"
	"github.com/pulumi/pulumi/sdk/v2/go/common/util/fsutil"
	"github.com/pulumi/pulumi/sdk/v2/go/common/util/httputil"
	"github.com/pulumi/pulumi/sdk/v2/go/common/util/logging"
	"github.com/pulumi/pulumi/sdk/v2/go/common/version"
	"github.com/pulumi/pulumi/sdk/v2/nodejs/npm"
	"github.com/pulumi/pulumi/sdk/v2/python"
)

const (
	windowsGOOS = "windows"
)

var (
	enableLegacyPluginBehavior = os.Getenv("PULUMI_ENABLE_LEGACY_PLUGIN_SEARCH") != ""
)

// MissingError is returned by functions that attempt to load plugins if a plugin can't be located.
type MissingError struct {
	// Info contains information about the plugin that was not found.
	Info PluginInfo
}

// NewMissingError allocates a new error indicating the given plugin info was not found.
func NewMissingError(info PluginInfo) error {
	return &MissingError{
		Info: info,
	}
}

func (err *MissingError) Error() string {
	if err.Info.Version != nil {
		return fmt.Sprintf("no %[1]s plugin '%[2]s-v%[3]s' found in the workspace or on your $PATH, "+
			"install the plugin using `pulumi plugin install %[1]s %[2]s v%[3]s`",
			err.Info.Kind, err.Info.Name, err.Info.Version)
	}

	return fmt.Sprintf("no %s plugin '%s' found in the workspace or on your $PATH",
		err.Info.Kind, err.Info.String())
}

// PluginInfo provides basic information about a plugin.  Each plugin gets installed into a system-wide
// location, by default `~/.pulumi/plugins/<kind>-<name>-<version>/`.  A plugin may contain multiple files,
// however the primary loadable executable must be named `pulumi-<kind>-<name>`.
type PluginInfo struct {
	Name         string          // the simple name of the plugin.
	Path         string          // the path that a plugin was loaded from.
	Kind         PluginKind      // the kind of the plugin (language, resource, etc).
	Version      *semver.Version // the plugin's semantic version, if present.
	Size         int64           // the size of the plugin, in bytes.
	InstallTime  time.Time       // the time the plugin was installed.
	LastUsedTime time.Time       // the last time the plugin was used.
	ServerURL    string          // an optional server to use when downloading this plugin.
	PluginDir    string          // if set, will be used as the root plugin dir instead of ~/.pulumi/plugins.
}

// Dir gets the expected plugin directory for this plugin.
func (info PluginInfo) Dir() string {
	dir := fmt.Sprintf("%s-%s", info.Kind, info.Name)
	if info.Version != nil {
		dir = fmt.Sprintf("%s-v%s", dir, info.Version.String())
	}
	return dir
}

// File gets the expected filename for this plugin.
func (info PluginInfo) File() string {
	return info.FilePrefix() + info.FileSuffix()
}

// FilePrefix gets the expected default file prefix for the plugin.
func (info PluginInfo) FilePrefix() string {
	return fmt.Sprintf("pulumi-%s-%s", info.Kind, info.Name)
}

// FileSuffix returns the suffix for the plugin (if any).
func (info PluginInfo) FileSuffix() string {
	if runtime.GOOS == windowsGOOS {
		return ".exe"
	}
	return ""
}

// DirPath returns the directory where this plugin should be installed.
func (info PluginInfo) DirPath() (string, error) {
	var err error
	dir := info.PluginDir
	if dir == "" {
		dir, err = GetPluginDir()
		if err != nil {
			return "", err
		}
	}

	return filepath.Join(dir, info.Dir()), nil
}

// LockFilePath returns the full path to the plugin's lock file used during installation
// to prevent concurrent installs.
func (info PluginInfo) LockFilePath() (string, error) {
	dir, err := info.DirPath()
	if err != nil {
		return "", err
	}
	return fmt.Sprintf("%s.lock", dir), nil
}

// PartialFilePath returns the full path to the plugin's partial file used during installation
// to indicate installation of the plugin hasn't completed yet.
func (info PluginInfo) PartialFilePath() (string, error) {
	dir, err := info.DirPath()
	if err != nil {
		return "", err
	}
	return fmt.Sprintf("%s.partial", dir), nil
}

// FilePath returns the full path where this plugin's primary executable should be installed.
func (info PluginInfo) FilePath() (string, error) {
	dir, err := info.DirPath()
	if err != nil {
		return "", err
	}
	return filepath.Join(dir, info.File()), nil
}

// Delete removes the plugin from the cache.  It also deletes any supporting files in the cache, which includes
// any files that contain the same prefix as the plugin itself.
func (info PluginInfo) Delete() error {
	dir, err := info.DirPath()
	if err != nil {
		return err
	}
	if err := os.RemoveAll(dir); err != nil {
		return err
	}
	// Attempt to delete any leftover .partial or .lock files.
	// Don't fail the operation if we can't delete these.
	contract.IgnoreError(os.Remove(fmt.Sprintf("%s.partial", dir)))
	contract.IgnoreError(os.Remove(fmt.Sprintf("%s.lock", dir)))
	return nil
}

// SetFileMetadata adds extra metadata from the given file, representing this plugin's directory.
func (info *PluginInfo) SetFileMetadata(path string) error {
	// Get the file info.
	file, err := os.Stat(path)
	if err != nil {
		return err
	}

	// Next, get the size from the directory (or, if there is none, just the file).
	size, err := getPluginSize(path)
	if err != nil {
		return errors.Wrapf(err, "getting plugin dir %s size", path)
	}
	info.Size = size

	// Next get the access times from the plugin binary itself.
	tinfo := times.Get(file)

	if tinfo.HasBirthTime() {
		info.InstallTime = tinfo.BirthTime()
	}

	info.LastUsedTime = tinfo.AccessTime()
	return nil
}

// Download fetches an io.ReadCloser for this plugin and also returns the size of the response (if known).
func (info PluginInfo) Download() (io.ReadCloser, int64, error) {
	// Figure out the OS/ARCH pair for the download URL.
	var os string
	switch runtime.GOOS {
	case "darwin", "linux", "windows":
		os = runtime.GOOS
	default:
		return nil, -1, errors.Errorf("unsupported plugin OS: %s", runtime.GOOS)
	}
	var arch string
	switch runtime.GOARCH {
	case "amd64", "arm64":
		arch = runtime.GOARCH
	default:
		return nil, -1, errors.Errorf("unsupported plugin architecture: %s", runtime.GOARCH)
	}

	// If the plugin has a server, associated with it, download from there.  Otherwise use the "default" location, which
	// is hosted by Pulumi.
	serverURL := info.ServerURL
	if serverURL == "" {
		serverURL = "https://get.pulumi.com/releases/plugins"
	}
	serverURL = strings.TrimSuffix(serverURL, "/")

	logging.V(1).Infof("%s downloading from %s", info.Name, serverURL)

	// URL escape the path value to ensure we have the correct path for S3/CloudFront.
	endpoint := fmt.Sprintf("%s/%s",
		serverURL,
		url.QueryEscape(fmt.Sprintf("pulumi-%s-%s-v%s-%s-%s.tar.gz", info.Kind, info.Name, info.Version, os, arch)))

	logging.V(9).Infof("full plugin download url: %s", endpoint)

	req, err := http.NewRequest("GET", endpoint, nil)
	if err != nil {
		return nil, -1, err
	}

	userAgent := fmt.Sprintf("pulumi-cli/1 (%s; %s)", version.Version, runtime.GOOS)
	req.Header.Set("User-Agent", userAgent)

	logging.V(9).Infof("plugin install request headers: %v", req.Header)

	resp, err := httputil.DoWithRetry(req, http.DefaultClient)
	if err != nil {
		return nil, -1, err
	}

	logging.V(9).Infof("plugin install response headers: %v", resp.Header)

	if resp.StatusCode < 200 || resp.StatusCode > 299 {
		return nil, -1, errors.Errorf("%d HTTP error fetching plugin from %s", resp.StatusCode, endpoint)
	}

	return resp.Body, resp.ContentLength, nil
}

// installLock acquires a file lock used to prevent concurrent installs.
func (info PluginInfo) installLock() (unlock func(), err error) {
	finalDir, err := info.DirPath()
	if err != nil {
		return nil, err
	}
	lockFilePath := fmt.Sprintf("%s.lock", finalDir)

	if err := os.MkdirAll(filepath.Dir(lockFilePath), 0700); err != nil {
		return nil, errors.Wrap(err, "creating plugin root")
	}

	mutex := fsutil.NewFileMutex(lockFilePath)
	if err := mutex.Lock(); err != nil {
		return nil, err
	}
	return func() {
		contract.IgnoreError(mutex.Unlock())
	}, nil
}

// Install installs a plugin's tarball into the cache. It validates that plugin names are in the expected format.
// Previous versions of Pulumi extracted the tarball to a temp directory first, and then renamed the temp directory
// to the final directory. The rename operation fails often enough on Windows due to aggressive virus scanners opening
// files in the temp directory. To address this, we now extract the tarball directly into the final directory, and use
// file locks to prevent concurrent installs.
// Each plugin has its own file lock, with the same name as the plugin directory, with a `.lock` suffix.
// During installation an empty file with a `.partial` suffix is created, indicating that installation is in-progress.
// The `.partial` file is deleted when installation is complete, indicating that the plugin has finished installing.
// If a failure occurs during installation, the `.partial` file will remain, indicating the plugin wasn't fully
// installed. The next time the plugin is installed, the old installation directory will be removed and replaced with
// a fresh install.
func (info PluginInfo) Install(tgz io.ReadCloser) error {
	defer contract.IgnoreClose(tgz)

	// Fetch the directory into which we will expand this tarball.
	finalDir, err := info.DirPath()
	if err != nil {
		return err
	}

	// Create a file lock file at <pluginsdir>/<kind>-<name>-<version>.lock.
	unlock, err := info.installLock()
	if err != nil {
		return err
	}
	defer unlock()

	// Cleanup any temp dirs from failed installations of this plugin from previous versions of Pulumi.
	if err := cleanupTempDirs(finalDir); err != nil {
		// We don't want to fail the installation if there was an error cleaning up these old temp dirs.
		// Instead, log the error and continue on.
		logging.V(5).Infof("Install: Error cleaning up temp dirs: %s", err.Error())
	}

	// Get the partial file path (e.g. <pluginsdir>/<kind>-<name>-<version>.partial).
	partialFilePath, err := info.PartialFilePath()
	if err != nil {
		return err
	}

	// Check whether the directory exists while we were waiting on the lock.
	_, finalDirStatErr := os.Stat(finalDir)
	if finalDirStatErr == nil {
		_, partialFileStatErr := os.Stat(partialFilePath)
		if partialFileStatErr != nil {
			if os.IsNotExist(partialFileStatErr) {
				// finalDir exists and there's no partial file, so the plugin is already installed.
				return nil
			}
			return partialFileStatErr
		}

		// The partial file exists, meaning a previous attempt at installing the plugin failed.
		// Delete finalDir so we can try installing again. There's no need to delete the partial
		// file since we'd just be recreating it again below anyway.
		if err := os.RemoveAll(finalDir); err != nil {
			return err
		}
	} else if !os.IsNotExist(finalDirStatErr) {
		return finalDirStatErr
	}

	// Create an empty partial file to indicate installation is in-progress.
	if err := ioutil.WriteFile(partialFilePath, nil, 0600); err != nil {
		return err
	}

	// Create the final directory.
	if err := os.MkdirAll(finalDir, 0700); err != nil {
		return err
	}

	// Uncompress the plugin.
	if err := archive.ExtractTGZ(tgz, finalDir); err != nil {
		return err
	}

	// Even though we deferred closing the tarball at the beginning of this function, go ahead and explicitly close
	// it now since we're finished extracting it, to prevent subsequent output from being displayed oddly with
	// the progress bar.
	contract.IgnoreClose(tgz)

	// Install dependencies, if needed.
	proj, err := LoadPluginProject(filepath.Join(finalDir, "PulumiPlugin.yaml"))
	if err != nil && !os.IsNotExist(err) {
		return errors.Wrap(err, "loading PulumiPlugin.yaml")
	}
	if proj != nil {
		runtime := strings.ToLower(proj.Runtime.Name())
		// For now, we only do this for Node.js and Python. For Go, the expectation is the binary is
		// already built. For .NET, similarly, a single self-contained binary could be used, but
		// otherwise `dotnet run` will implicitly run `dotnet restore`.
		// TODO[pulumi/pulumi#1334]: move to the language plugins so we don't have to hard code here.
		switch runtime {
		case "nodejs":
			var b bytes.Buffer
			if _, err := npm.Install(finalDir, &b, &b); err != nil {
				os.Stderr.Write(b.Bytes())
				return errors.Wrap(err, "installing plugin dependencies")
			}
		case "python":
			if err := python.InstallDependencies(finalDir, "venv", false /*showOutput*/); err != nil {
				return errors.Wrap(err, "installing plugin dependencies")
			}
		}
	}

	// Installation is complete. Remove the partial file.
	return os.Remove(partialFilePath)
}

// cleanupTempDirs cleans up leftover temp dirs from failed installs with previous versions of Pulumi.
func cleanupTempDirs(finalDir string) error {
	dir := filepath.Dir(finalDir)

	infos, err := ioutil.ReadDir(dir)
	if err != nil {
		return err
	}

	for _, info := range infos {
		// Temp dirs have a suffix of `.tmpXXXXXX` (where `XXXXXX`) is a random number,
		// from ioutil.TempFile.
		if info.IsDir() && installingPluginRegexp.MatchString(info.Name()) {
			path := filepath.Join(dir, info.Name())
			if err := os.RemoveAll(path); err != nil {
				return errors.Wrapf(err, "cleaning up temp dir %s", path)
			}
		}
	}

	return nil
}

func (info PluginInfo) String() string {
	var version string
	if v := info.Version; v != nil {
		version = fmt.Sprintf("-%s", v)
	}
	return info.Name + version
}

// PluginKind represents a kind of a plugin that may be dynamically loaded and used by Pulumi.
type PluginKind string

const (
	// AnalyzerPlugin is a plugin that can be used as a resource analyzer.
	AnalyzerPlugin PluginKind = "analyzer"
	// LanguagePlugin is a plugin that can be used as a language host.
	LanguagePlugin PluginKind = "language"
	// ResourcePlugin is a plugin that can be used as a resource provider for custom CRUD operations.
	ResourcePlugin PluginKind = "resource"
)

// IsPluginKind returns true if k is a valid plugin kind, and false otherwise.
func IsPluginKind(k string) bool {
	switch PluginKind(k) {
	case AnalyzerPlugin, LanguagePlugin, ResourcePlugin:
		return true
	default:
		return false
	}
}

// HasPlugin returns true if the given plugin exists.
func HasPlugin(plug PluginInfo) bool {
	dir, err := plug.DirPath()
	if err == nil {
		_, err := os.Stat(dir)
		if err == nil {
			partialFilePath, err := plug.PartialFilePath()
			if err == nil {
				if _, err := os.Stat(partialFilePath); os.IsNotExist(err) {
					return true
				}
			}
		}
	}
	return false
}

// HasPluginGTE returns true if the given plugin exists at the given version number or greater.
func HasPluginGTE(plug PluginInfo) (bool, error) {
	// If an exact match, return true right away.
	if HasPlugin(plug) {
		return true, nil
	}

	// Otherwise, load up the list of plugins and find one with the same name/type and >= version.
	plugs, err := GetPlugins()
	if err != nil {
		return false, err
	}

	// If we're not doing the legacy plugin behavior and we've been asked for a specific version, do the same plugin
	// search that we'd do at runtime. This ensures that `pulumi plugin install` works the same way that the runtime
	// loader does, to minimize confusion when a user has to install new plugins.
	if !enableLegacyPluginBehavior && plug.Version != nil {
		requestedVersion := semver.MustParseRange(plug.Version.String())
		_, err := SelectCompatiblePlugin(plugs, plug.Kind, plug.Name, requestedVersion)
		return err == nil, err
	}

	for _, p := range plugs {
		if p.Name == plug.Name &&
			p.Kind == plug.Kind &&
			(p.Version != nil && plug.Version != nil && p.Version.GTE(*plug.Version)) {
			return true, nil
		}
	}
	return false, nil
}

// GetPolicyDir returns the directory in which an organization's Policy Packs on the current machine are managed.
func GetPolicyDir(orgName string) (string, error) {
	return GetPulumiPath(PolicyDir, orgName)
}

// GetPolicyPath finds a PolicyPack by its name version, as well as a bool marked true if the path
// already exists and is a directory.
func GetPolicyPath(orgName, name, version string) (string, bool, error) {
	policiesDir, err := GetPolicyDir(orgName)
	if err != nil {
		return "", false, err
	}

	policyPackPath := path.Join(policiesDir, fmt.Sprintf("pulumi-analyzer-%s-v%s", name, version))

	file, err := os.Stat(policyPackPath)
	if err == nil && file.IsDir() {
		// PolicyPack exists. Return.
		return policyPackPath, true, nil
	} else if err != nil && !os.IsNotExist(err) {
		// Error trying to inspect PolicyPack FS entry. Return error.
		return "", false, err
	}

	// Not found. Return empty path.
	return policyPackPath, false, nil
}

// GetPluginDir returns the directory in which plugins on the current machine are managed.
func GetPluginDir() (string, error) {
	return GetPulumiPath(PluginDir)
}

// GetPlugins returns a list of installed plugins.
func GetPlugins() ([]PluginInfo, error) {
	// To get the list of plugins, simply scan the directory in the usual place.
	dir, err := GetPluginDir()
	if err != nil {
		return nil, err
	}
	return getPlugins(dir)
}

func getPlugins(dir string) ([]PluginInfo, error) {
	files, err := ioutil.ReadDir(dir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}

	// Now read the file infos and create the plugin infos.
	var plugins []PluginInfo
	for _, file := range files {
		// Skip anything that doesn't look like a plugin.
		if kind, name, version, ok := tryPlugin(file); ok {
			plugin := PluginInfo{
				Name:    name,
				Kind:    kind,
				Version: &version,
			}
			path := filepath.Join(dir, file.Name())
			if _, err := os.Stat(fmt.Sprintf("%s.partial", path)); err == nil {
				// Skip it if the partial file exists, meaning the plugin is not fully installed.
				continue
			} else if !os.IsNotExist(err) {
				return nil, err
			}
			if err = plugin.SetFileMetadata(path); err != nil {
				return nil, err
			}
			plugins = append(plugins, plugin)
		}
	}
	return plugins, nil
}

// GetPluginPath finds a plugin's path by its kind, name, and optional version.  It will match the latest version that
// is >= the version specified.  If no version is supplied, the latest plugin for that given kind/name pair is loaded,
// using standard semver sorting rules.  A plugin may be overridden entirely by placing it on your $PATH.
func GetPluginPath(kind PluginKind, name string, version *semver.Version) (string, string, error) {
	// If we have a version of the plugin on its $PATH, use it.  This supports development scenarios.
	filename := (&PluginInfo{Kind: kind, Name: name, Version: version}).FilePrefix()
	if path, err := exec.LookPath(filename); err == nil {
		logging.V(6).Infof("GetPluginPath(%s, %s, %v): found on $PATH %s", kind, name, version, path)
		return "", path, nil
	}

	// At some point in the future, language plugins will be located in the plugin cache, just like regular plugins
	// (see pulumi/pulumi#956 for some of the reasons why this isn't the case today). For now, they ship next to the
	// `pulumi` binary. While we encourage this folder to be on the $PATH (and so the check above would have found
	// the language plugin) it's possible someone is running `pulumi` with an explicit path on the command line or
	// has done symlink magic such that `pulumi` is on the path, but the language plugins are not. So, if possible,
	// look next to the instance of `pulumi` that is running to find this language plugin.
	if kind == LanguagePlugin {
		exePath, exeErr := os.Executable()
		if exeErr == nil {
			fullPath, fullErr := filepath.EvalSymlinks(exePath)
			if fullErr == nil {
				for _, ext := range getCandidateExtensions() {
					candidate := filepath.Join(filepath.Dir(fullPath), filename+ext)
					// Let's see if the file is executable. On Windows, os.Stat() returns a mode of "-rw-rw-rw" so on
					// on windows we just trust the fact that the .exe can actually be launched.
					if stat, err := os.Stat(candidate); err == nil &&
						(stat.Mode()&0100 != 0 || runtime.GOOS == windowsGOOS) {
						logging.V(6).Infof("GetPluginPath(%s, %s, %v): found next to current executable %s",
							kind, name, version, candidate)

						return "", candidate, nil
					}
				}
			}
		}
	}

	// Otherwise, check the plugin cache.
	plugins, err := GetPlugins()
	if err != nil {
		return "", "", errors.Wrapf(err, "loading plugin list")
	}

	var match *PluginInfo
	if !enableLegacyPluginBehavior && version != nil {
		logging.V(6).Infof("GetPluginPath(%s, %s, %s): enabling new plugin behavior", kind, name, version)
		candidate, err := SelectCompatiblePlugin(plugins, kind, name, semver.MustParseRange(version.String()))
		if err != nil {
			return "", "", NewMissingError(PluginInfo{
				Name:    name,
				Kind:    kind,
				Version: version,
			})
		}
		match = &candidate
	} else {
		for _, cur := range plugins {
			// Since the value of cur changes as we iterate, we can't save a pointer to it. So let's have a local that
			// we can take a pointer to if this plugin is the best match yet.
			plugin := cur
			if plugin.Kind == kind && plugin.Name == name {
				// Always pick the most recent version of the plugin available.  Even if this is an exact match, we
				// keep on searching just in case there's a newer version available.
				var m *PluginInfo
				if match == nil && version == nil {
					m = &plugin // no existing match, no version spec, take it.
				} else if match != nil &&
					(match.Version == nil || (plugin.Version != nil && plugin.Version.GT(*match.Version))) {
					m = &plugin // existing match, but this plugin is newer, prefer it.
				} else if version != nil && plugin.Version != nil && plugin.Version.GTE(*version) {
					m = &plugin // this plugin is >= the version being requested, use it.
				}

				if m != nil {
					match = m
					logging.V(6).Infof("GetPluginPath(%s, %s, %s): found candidate (#%s)",
						kind, name, version, match.Version)
				}
			}
		}
	}

	if match != nil {
		matchDir, err := match.DirPath()
		if err != nil {
			return "", "", err
		}
		matchPath, err := match.FilePath()
		if err != nil {
			return "", "", err
		}

		logging.V(6).Infof("GetPluginPath(%s, %s, %v): found in cache at %s", kind, name, version, matchPath)
		return matchDir, matchPath, nil
	}

	return "", "", nil
}

// SortedPluginInfo is a wrapper around PluginInfo that allows for sorting by version.
type SortedPluginInfo []PluginInfo

func (sp SortedPluginInfo) Len() int { return len(sp) }
func (sp SortedPluginInfo) Less(i, j int) bool {
	iVersion := sp[i].Version
	jVersion := sp[j].Version
	switch {
	case iVersion == nil && jVersion == nil:
		return false
	case iVersion == nil:
		return true
	case jVersion == nil:
		return false
	default:
		return iVersion.LT(*jVersion)
	}
}
func (sp SortedPluginInfo) Swap(i, j int) { sp[i], sp[j] = sp[j], sp[i] }

// SelectCompatiblePlugin selects a plugin from the list of plugins with the given kind and name that sastisfies the
// requested semver range. It returns the highest version plugin that satisfies the requested constraints, or an error
// if no such plugin could be found.
//
// If there exist plugins in the plugin list that don't have a version, SelectCompatiblePlugin will select them if there
// are no other compatible plugins available.
func SelectCompatiblePlugin(
	plugins []PluginInfo, kind PluginKind, name string, requested semver.Range) (PluginInfo, error) {
	logging.V(7).Infof("SelectCompatiblePlugin(..., %s): beginning", name)
	var bestMatch PluginInfo
	var hasMatch bool

	// Before iterating over the list of plugins, sort the list of plugins by version in ascending order. This ensures
	// that we can do a single pass over the plugin list, from lowest version to greatest version, and be confident that
	// the best match that we find at the end is the greatest possible compatible version for the requested plugin.
	//
	// Plugins without versions are treated as having the lowest version. Ties between plugins without versions are
	// resolved arbitrarily.
	sort.Sort(SortedPluginInfo(plugins))
	for _, plugin := range plugins {
		switch {
		case plugin.Kind != kind || plugin.Name != name:
			// Not the plugin we're looking for.
		case !hasMatch && plugin.Version == nil:
			// This is the plugin we're looking for, but it doesn't have a version. We haven't seen anything better yet,
			// so take it.
			logging.V(7).Infof(
				"SelectCompatiblePlugin(..., %s): best plugin %s: no version and no other candidates",
				name, plugin.String())
			hasMatch = true
			bestMatch = plugin
		case plugin.Version == nil:
			// This is a rare case - we've already seen a version-less plugin and we're seeing another here. Ignore this
			// one and defer to the one we previously selected.
			logging.V(7).Infof("SelectCompatiblePlugin(..., %s): skipping plugin %s: no version", name, plugin.String())
		case requested(*plugin.Version):
			// This plugin is compatible with the requested semver range. Save it as the best match and continue.
			logging.V(7).Infof("SelectCompatiblePlugin(..., %s): best plugin %s: semver match", name, plugin.String())
			hasMatch = true
			bestMatch = plugin
		default:
			logging.V(7).Infof(
				"SelectCompatiblePlugin(..., %s): skipping plugin %s: semver mismatch", name, plugin.String())
		}
	}

	if !hasMatch {
		logging.V(7).Infof("SelectCompatiblePlugin(..., %s): failed to find match", name)
		return PluginInfo{}, errors.New("failed to locate compatible plugin")
	}
	logging.V(7).Infof("SelectCompatiblePlugin(..., %s): selecting plugin '%s': best match ", name, bestMatch.String())
	return bestMatch, nil
}

// ReadCloserProgressBar displays a progress bar for the given closer and returns a wrapper closer to manipulate it.
func ReadCloserProgressBar(
	closer io.ReadCloser, size int64, message string, colorization colors.Colorization) io.ReadCloser {
	if size == -1 {
		return closer
	}

	// If we know the length of the download, show a progress bar.
	bar := pb.New(int(size))
	bar.Prefix(colorization.Colorize(colors.SpecUnimportant + message + ":"))
	bar.Postfix(colorization.Colorize(colors.Reset))
	bar.SetMaxWidth(80)
	bar.SetUnits(pb.U_BYTES)
	bar.Start()

	return &barCloser{
		bar:        bar,
		readCloser: bar.NewProxyReader(closer),
	}
}

// getCandidateExtensions returns a set of file extensions (including the dot seprator) which should be used when
// probing for an executable file.
func getCandidateExtensions() []string {
	if runtime.GOOS == windowsGOOS {
		return []string{".exe", ".cmd"}
	}

	return []string{""}
}

// pluginRegexp matches plugin directory names: pulumi-KIND-NAME-VERSION.
var pluginRegexp = regexp.MustCompile(
	"^(?P<Kind>[a-z]+)-" + // KIND
		"(?P<Name>[a-zA-Z0-9-]*[a-zA-Z0-9])-" + // NAME
		"v(?P<Version>.*)$") // VERSION

// installingPluginRegexp matches the name of temporary folders. Previous versions of Pulumi first extracted
// plugins to a temporary folder with a suffix of `.tmpXXXXXX` (where `XXXXXX`) is a random number, from
// ioutil.TempFile. We should ignore these folders.
var installingPluginRegexp = regexp.MustCompile(`\.tmp[0-9]+$`)

// tryPlugin returns true if a file is a plugin, and extracts information about it.
func tryPlugin(file os.FileInfo) (PluginKind, string, semver.Version, bool) {
	// Only directories contain plugins.
	if !file.IsDir() {
		logging.V(11).Infof("skipping file in plugin directory: %s", file.Name())
		return "", "", semver.Version{}, false
	}

	// Ignore plugins which are being installed
	if installingPluginRegexp.MatchString(file.Name()) {
		logging.V(11).Infof("skipping plugin %s which is being installed", file.Name())
		return "", "", semver.Version{}, false
	}

	// Filenames must match the plugin regexp.
	match := pluginRegexp.FindStringSubmatch(file.Name())
	if len(match) != len(pluginRegexp.SubexpNames()) {
		logging.V(11).Infof("skipping plugin %s with missing capture groups: expect=%d, actual=%d",
			file.Name(), len(pluginRegexp.SubexpNames()), len(match))
		return "", "", semver.Version{}, false
	}
	var kind PluginKind
	var name string
	var version *semver.Version
	for i, group := range pluginRegexp.SubexpNames() {
		v := match[i]
		switch group {
		case "Kind":
			// Skip invalid kinds.
			if IsPluginKind(v) {
				kind = PluginKind(v)
			} else {
				logging.V(11).Infof("skipping invalid plugin kind: %s", v)
			}
		case "Name":
			name = v
		case "Version":
			// Skip invalid versions.
			ver, err := semver.ParseTolerant(v)
			if err == nil {
				version = &ver
			} else {
				logging.V(11).Infof("skipping invalid plugin version: %s", v)
			}
		}
	}

	// If anything was missing or invalid, skip this plugin.
	if kind == "" || name == "" || version == nil {
		logging.V(11).Infof("skipping plugin with missing information: kind=%s, name=%s, version=%v",
			kind, name, version)
		return "", "", semver.Version{}, false
	}

	return kind, name, *version, true
}

// getPluginSize recursively computes how much space is devoted to a given plugin.
func getPluginSize(path string) (int64, error) {
	file, err := os.Stat(path)
	if err != nil {
		return 0, nil
	}

	size := int64(0)
	if file.IsDir() {
		subs, err := ioutil.ReadDir(path)
		if err != nil {
			return 0, err
		}
		for _, child := range subs {
			add, err := getPluginSize(filepath.Join(path, child.Name()))
			if err != nil {
				return 0, err
			}
			size += add
		}
	} else {
		size += file.Size()
	}
	return size, nil
}

type barCloser struct {
	bar        *pb.ProgressBar
	readCloser io.ReadCloser
}

func (bc *barCloser) Read(dest []byte) (int, error) {
	return bc.readCloser.Read(dest)
}

func (bc *barCloser) Close() error {
	bc.bar.Finish()
	return bc.readCloser.Close()
}