// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package relui

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"context"
	"crypto/sha256"
	"fmt"
	"io"
	"io/fs"
	"math/rand"
	"net/http"
	"path"
	"strings"
	"sync"
	"time"

	"cloud.google.com/go/storage"
	"github.com/google/go-cmp/cmp"
	"golang.org/x/build/buildlet"
	"golang.org/x/build/dashboard"
	"golang.org/x/build/internal/gcsfs"
	"golang.org/x/build/internal/releasetargets"
	"golang.org/x/build/internal/relui/db"
	"golang.org/x/build/internal/relui/sign"
	"golang.org/x/build/internal/task"
	"golang.org/x/build/internal/workflow"
	wf "golang.org/x/build/internal/workflow"
	"golang.org/x/net/context/ctxhttp"
)

// DefinitionHolder holds workflow definitions.
type DefinitionHolder struct {
	mu          sync.Mutex
	definitions map[string]*wf.Definition
}

// NewDefinitionHolder creates a new DefinitionHolder,
// initialized with a sample "echo" wf.
func NewDefinitionHolder() *DefinitionHolder {
	return &DefinitionHolder{definitions: map[string]*wf.Definition{
		"echo": newEchoWorkflow(),
	}}
}

// Definition returns the initialized wf.Definition registered
// for a given name.
func (h *DefinitionHolder) Definition(name string) *wf.Definition {
	h.mu.Lock()
	defer h.mu.Unlock()
	return h.definitions[name]
}

// RegisterDefinition registers a definition with a name.
// If a definition with the same name already exists, RegisterDefinition panics.
func (h *DefinitionHolder) RegisterDefinition(name string, d *wf.Definition) {
	h.mu.Lock()
	defer h.mu.Unlock()
	if _, exist := h.definitions[name]; exist {
		panic("relui: multiple registrations for " + name)
	}
	h.definitions[name] = d
}

// Definitions returns the names of all registered definitions.
func (h *DefinitionHolder) Definitions() map[string]*wf.Definition {
	h.mu.Lock()
	defer h.mu.Unlock()
	defs := make(map[string]*wf.Definition)
	for k, v := range h.definitions {
		defs[k] = v
	}
	return defs
}

// Release parameter definitions.
var (
	targetDateParam = wf.ParamDef[task.Date]{
		Name: "Target Release Date",
		ParamType: wf.ParamType[task.Date]{
			HTMLElement:   "input",
			HTMLInputType: "date",
		},
		Doc: `Target Release Date is the date on which the release is scheduled.

It must be three to seven days after the pre-announcement as documented in the security policy.`,
	}
	securityPreAnnParam = wf.ParamDef[string]{
		Name: "Security Content",
		ParamType: workflow.ParamType[string]{
			HTMLElement: "select",
			HTMLSelectOptions: []string{
				"the standard library",
				"the toolchain",
				"the standard library and the toolchain",
			},
		},
		Doc: `Security Content is the security content to be included in the release pre-announcement.

It must not reveal details beyond what's allowed by the security policy.`,
	}

	securitySummaryParameter = wf.ParamDef[string]{
		Name: "Security Summary (optional)",
		Doc: `Security Summary is an optional sentence describing security fixes included in this release.

It shows up in the release tweet.

The empty string means there are no security fixes to highlight.

Past examples:
• "Includes a security fix for crypto/tls (CVE-2021-34558)."
• "Includes a security fix for the Wasm port (CVE-2021-38297)."
• "Includes security fixes for encoding/pem (CVE-2022-24675), crypto/elliptic (CVE-2022-28327), crypto/x509 (CVE-2022-27536)."`,
	}

	securityFixesParameter = wf.ParamDef[[]string]{
		Name:      "Security Fixes (optional)",
		ParamType: wf.SliceLong,
		Doc: `Security Fixes is a list of descriptions, one for each distinct security fix included in this release, in Markdown format.

It shows up in the announcement mail.

The empty list means there are no security fixes included.

Past examples:
• "encoding/pem: fix stack overflow in Decode

   A large (more than 5 MB) PEM input can cause a stack overflow in Decode,
   leading the program to crash.

   Thanks to Juho Nurminen of Mattermost who reported the error.

   This is CVE-2022-24675 and Go issue https://go.dev/issue/51853."
• "crypto/elliptic: tolerate all oversized scalars in generic P-256

   A crafted scalar input longer than 32 bytes can cause P256().ScalarMult
   or P256().ScalarBaseMult to panic. Indirect uses through crypto/ecdsa and
   crypto/tls are unaffected. amd64, arm64, ppc64le, and s390x are unaffected.

   This was discovered thanks to a Project Wycheproof test vector.

   This is CVE-2022-28327 and Go issue https://go.dev/issue/52075."`,
		Example: `encoding/pem: fix stack overflow in Decode

A large (more than 5 MB) PEM input can cause a stack overflow in Decode,
leading the program to crash.

Thanks to Juho Nurminen of Mattermost who reported the error.

This is CVE-2022-24675 and Go issue https://go.dev/issue/51853.`,
	}

	releaseCoordinators = wf.ParamDef[[]string]{
		Name:      "Release Coordinator Usernames (optional)",
		ParamType: wf.SliceShort,
		Doc: `Release Coordinator Usernames is an optional list of the coordinators of the release.

Their first names will be included at the end of the release announcement, and CLs will be mailed to them.`,
		Example: "heschi",
	}
)

// newEchoWorkflow returns a runnable wf.Definition for
// development.
func newEchoWorkflow() *wf.Definition {
	wd := wf.New()
	wf.Output(wd, "greeting", wf.Task1(wd, "greeting", echo, wf.Param(wd, wf.ParamDef[string]{Name: "greeting"})))
	wf.Output(wd, "farewell", wf.Task1(wd, "farewell", echo, wf.Param(wd, wf.ParamDef[string]{Name: "farewell"})))
	return wd
}

func echo(ctx *wf.TaskContext, arg string) (string, error) {
	ctx.Printf("echo(%v, %q)", ctx, arg)
	return arg, nil
}

func checkTaskApproved(ctx *wf.TaskContext, p db.PGDBTX) (bool, error) {
	q := db.New(p)
	t, err := q.Task(ctx, db.TaskParams{
		Name:       ctx.TaskName,
		WorkflowID: ctx.WorkflowID,
	})
	if !t.ReadyForApproval {
		_, err := q.UpdateTaskReadyForApproval(ctx, db.UpdateTaskReadyForApprovalParams{
			ReadyForApproval: true,
			Name:             ctx.TaskName,
			WorkflowID:       ctx.WorkflowID,
		})
		if err != nil {
			return false, err
		}
	}
	return t.ApprovedAt.Valid, err
}

// ApproveActionDep returns a function for defining approval Actions.
//
// ApproveActionDep takes a single *pgxpool.Pool argument, which is
// used to query the database to determine if a task has been marked
// approved.
//
// ApproveActionDep marks the task as requiring approval in the
// database once the task is started. This can be used to show an
// "approve" control in the UI.
//
//	waitAction := wf.ActionN(wd, "Wait for Approval", ApproveActionDep(db), wf.After(someDependency))
func ApproveActionDep(p db.PGDBTX) func(*wf.TaskContext) error {
	return func(ctx *wf.TaskContext) error {
		_, err := task.AwaitCondition(ctx, 5*time.Second, func() (int, bool, error) {
			done, err := checkTaskApproved(ctx, p)
			return 0, done, err
		})
		return err
	}
}

// RegisterReleaseWorkflows registers workflows for issuing Go releases.
func RegisterReleaseWorkflows(ctx context.Context, h *DefinitionHolder, build *BuildReleaseTasks, milestone *task.MilestoneTasks, version *task.VersionTasks, comm task.CommunicationTasks) error {
	// Register prod release workflows.
	if err := registerProdReleaseWorkflows(ctx, h, build, milestone, version, comm); err != nil {
		return err
	}

	// Register pre-announcement workflows.
	currentMajor, err := version.GetCurrentMajor(ctx)
	if err != nil {
		return err
	}
	releases := []struct {
		kinds []task.ReleaseKind
		name  string
	}{
		{[]task.ReleaseKind{task.KindCurrentMinor, task.KindPrevMinor}, fmt.Sprintf("next minor release for Go 1.%d and 1.%d", currentMajor, currentMajor-1)},
		{[]task.ReleaseKind{task.KindCurrentMinor}, fmt.Sprintf("next minor release for Go 1.%d", currentMajor)},
		{[]task.ReleaseKind{task.KindPrevMinor}, fmt.Sprintf("next minor release for Go 1.%d", currentMajor-1)},
	}
	for _, r := range releases {
		wd := wf.New()

		versions := wf.Task1(wd, "Get next versions", version.GetNextVersions, wf.Const(r.kinds))
		targetDate := wf.Param(wd, targetDateParam)
		securityContent := wf.Param(wd, securityPreAnnParam)
		coordinators := wf.Param(wd, releaseCoordinators)

		sentMail := wf.Task4(wd, "mail-pre-announcement", comm.PreAnnounceRelease, versions, targetDate, securityContent, coordinators)
		wf.Output(wd, "Pre-announcement URL", wf.Task1(wd, "await-pre-announcement", comm.AwaitAnnounceMail, sentMail))

		h.RegisterDefinition("pre-announce "+r.name, wd)
	}

	// Register dry-run release workflows.
	registerBuildTestSignOnlyWorkflow(h, version, build, currentMajor+1, task.KindBeta)

	return nil
}

func registerProdReleaseWorkflows(ctx context.Context, h *DefinitionHolder, build *BuildReleaseTasks, milestone *task.MilestoneTasks, version *task.VersionTasks, comm task.CommunicationTasks) error {
	currentMajor, err := version.GetCurrentMajor(ctx)
	if err != nil {
		return err
	}
	releases := []struct {
		kind   task.ReleaseKind
		major  int
		suffix string
	}{
		{task.KindMajor, currentMajor + 1, "final"},
		{task.KindRC, currentMajor + 1, "next RC"},
		{task.KindBeta, currentMajor + 1, "next beta"},
		{task.KindCurrentMinor, currentMajor, "next minor"},
		{task.KindPrevMinor, currentMajor - 1, "next minor"},
	}
	for _, r := range releases {
		wd := wf.New()

		coordinators := wf.Param(wd, releaseCoordinators)

		versionPublished := addSingleReleaseWorkflow(build, milestone, version, wd, r.major, r.kind, coordinators)

		securitySummary := wf.Const("")
		securityFixes := wf.Slice[string]()
		if r.kind == task.KindCurrentMinor || r.kind == task.KindPrevMinor {
			securitySummary = wf.Param(wd, securitySummaryParameter)
			securityFixes = wf.Param(wd, securityFixesParameter)
		}
		addCommTasks(wd, build, comm, wf.Slice(versionPublished), securitySummary, securityFixes, coordinators)

		h.RegisterDefinition(fmt.Sprintf("Go 1.%d %s", r.major, r.suffix), wd)
	}

	wd, err := createMinorReleaseWorkflow(build, milestone, version, comm, currentMajor-1, currentMajor)
	if err != nil {
		return err
	}
	h.RegisterDefinition(fmt.Sprintf("Minor releases for Go 1.%d and 1.%d", currentMajor-1, currentMajor), wd)

	return nil
}

func registerBuildTestSignOnlyWorkflow(h *DefinitionHolder, version *task.VersionTasks, build *BuildReleaseTasks, major int, kind task.ReleaseKind) {
	wd := wf.New()

	nextVersion := wf.Task1(wd, "Get next version", version.GetNextVersion, wf.Const(kind))
	branch := fmt.Sprintf("release-branch.go1.%d", major)
	if kind == task.KindBeta {
		branch = "master"
	}
	branchVal := wf.Const(branch)
	source := wf.Task3(wd, "Build source archive", build.buildSource, branchVal, wf.Const(""), nextVersion)
	artifacts := build.addBuildTasks(wd, major, nextVersion, source)
	wf.Output(wd, "Artifacts", artifacts)

	h.RegisterDefinition(fmt.Sprintf("dry-run (build, test, and sign only): Go 1.%d next beta", major), wd)
}

func createMinorReleaseWorkflow(build *BuildReleaseTasks, milestone *task.MilestoneTasks, version *task.VersionTasks, comm task.CommunicationTasks, prevMajor, currentMajor int) (*wf.Definition, error) {
	wd := wf.New()

	coordinators := wf.Param(wd, releaseCoordinators)
	v1Published := addSingleReleaseWorkflow(build, milestone, version, wd.Sub(fmt.Sprintf("Go 1.%d", currentMajor)), currentMajor, task.KindCurrentMinor, coordinators)
	v2Published := addSingleReleaseWorkflow(build, milestone, version, wd.Sub(fmt.Sprintf("Go 1.%d", prevMajor)), prevMajor, task.KindPrevMinor, coordinators)

	securitySummary := wf.Param(wd, securitySummaryParameter)
	securityFixes := wf.Param(wd, securityFixesParameter)
	addCommTasks(wd, build, comm, wf.Slice(v1Published, v2Published), securitySummary, securityFixes, coordinators)

	return wd, nil
}

func addCommTasks(
	wd *wf.Definition, build *BuildReleaseTasks, comm task.CommunicationTasks,
	versions wf.Value[[]string], securitySummary wf.Value[string], securityFixes, coordinators wf.Value[[]string],
) {
	okayToAnnounceAndTweet := wf.Action0(wd, "Wait to Announce", build.ApproveAction, wf.After(versions))

	// Announce that a new Go release has been published.
	sentMail := wf.Task3(wd, "mail-announcement", comm.AnnounceRelease, versions, securityFixes, coordinators, wf.After(okayToAnnounceAndTweet))
	announcementURL := wf.Task1(wd, "await-announcement", comm.AwaitAnnounceMail, sentMail)
	tweetURL := wf.Task3(wd, "post-tweet", comm.TweetRelease, versions, securitySummary, announcementURL, wf.After(okayToAnnounceAndTweet))

	wf.Output(wd, "Announcement URL", announcementURL)
	wf.Output(wd, "Tweet URL", tweetURL)
}

func addSingleReleaseWorkflow(
	build *BuildReleaseTasks, milestone *task.MilestoneTasks, version *task.VersionTasks,
	wd *wf.Definition, major int, kind task.ReleaseKind, coordinators wf.Value[[]string],
) (versionPublished wf.Value[string]) {
	kindVal := wf.Const(kind)
	branch := fmt.Sprintf("release-branch.go1.%d", major)
	if kind == task.KindBeta {
		branch = "master"
	}
	branchVal := wf.Const(branch)
	startingHead := wf.Task1(wd, "Read starting branch head", version.ReadBranchHead, branchVal)

	// Select version, check milestones.
	nextVersion := wf.Task1(wd, "Get next version", version.GetNextVersion, kindVal)
	milestones := wf.Task2(wd, "Pick milestones", milestone.FetchMilestones, nextVersion, kindVal)
	checked := wf.Action3(wd, "Check blocking issues", milestone.CheckBlockers, milestones, nextVersion, kindVal)

	securityRef := wf.Param(wd, wf.ParamDef[string]{Name: "Ref from the private repository to build from (optional)"})
	source := wf.Task3(wd, "Build source archive", build.buildSource, startingHead, securityRef, nextVersion, wf.After(checked))

	// Build, test, and sign release.
	signedAndTestedArtifacts := build.addBuildTasks(wd, major, nextVersion, source)
	okayToTagAndPublish := wf.Action0(wd, "Wait for Release Coordinator Approval", build.ApproveAction, wf.After(signedAndTestedArtifacts))

	dlcl := wf.Task3(wd, "Mail DL CL", version.MailDLCL, wf.Slice(nextVersion), coordinators, wf.Const(false), wf.After(okayToTagAndPublish))
	dlclCommit := wf.Task2(wd, "Wait for DL CL", version.AwaitCL, dlcl, wf.Const(""))
	wf.Output(wd, "Download CL submitted", dlclCommit)

	// Tag version and upload to CDN/website.
	// If we're releasing a beta from master, tagging is easy; we just tag the
	// commit we started from. Otherwise, we're going to submit a VERSION CL,
	// and we need to make sure that that CL is submitted on top of the same
	// state we built from. For security releases that state may not have
	// been public when we started, but it should be now.
	tagCommit := startingHead
	if branch != "master" {
		publishingHead := wf.Task3(wd, "Check branch state matches source archive", build.checkSourceMatch, branchVal, nextVersion, source, wf.After(okayToTagAndPublish))
		versionCL := wf.Task3(wd, "Mail version CL", version.CreateAutoSubmitVersionCL, branchVal, coordinators, nextVersion, wf.After(publishingHead))
		tagCommit = wf.Task2(wd, "Wait for version CL submission", version.AwaitCL, versionCL, publishingHead)
	}
	tagged := wf.Action2(wd, "Tag version", version.TagRelease, nextVersion, tagCommit, wf.After(okayToTagAndPublish))
	uploaded := wf.Action1(wd, "Upload artifacts to CDN", build.uploadArtifacts, signedAndTestedArtifacts, wf.After(tagged))
	pushed := wf.Action3(wd, "Push issues", milestone.PushIssues, milestones, nextVersion, kindVal, wf.After(tagged))
	versionPublished = wf.Task2(wd, "Publish to website", build.publishArtifacts, nextVersion, signedAndTestedArtifacts, wf.After(uploaded, pushed))
	if kind == task.KindMajor {
		updateStdlibIndexCL := wf.Task3(wd, fmt.Sprintf("Mail update stdlib index CL for 1.%d", major), version.CreateUpdateStdlibIndexCL, wf.Const("master"), coordinators, versionPublished)
		wf.Output(wd, "Stdlib regeneration CL", updateStdlibIndexCL)
	}
	wf.Output(wd, "Released version", versionPublished)
	return versionPublished
}

// addBuildTasks registers tasks to build, test, and sign the release onto wd.
// It returns the output from the last task, a slice of signed and tested artifacts.
func (tasks *BuildReleaseTasks) addBuildTasks(wd *wf.Definition, major int, version wf.Value[string], source wf.Value[artifact]) wf.Value[[]artifact] {
	targets := releasetargets.TargetsForGo1Point(major)
	skipTests := wf.Param(wd, wf.ParamDef[[]string]{Name: "Targets to skip testing (or 'all') (optional)", ParamType: wf.SliceShort})
	artifacts := []wf.Value[artifact]{source}
	// Build, test and sign binary artifacts for all targets.
	var testsPassed []wf.Dependency
	for _, target := range targets {
		targetVal := wf.Const(target)
		wd := wd.Sub(target.Name)

		// Build release artifacts for the platform.
		// Also create installers and perform platform-specific signing where applicable.
		bin := wf.Task2(wd, "Build binary archive", tasks.buildBinary, targetVal, source)
		switch target.GOOS {
		case "darwin":
			pkg := wf.Task3(wd, "Build PKG installer", tasks.buildDarwinPKG, targetVal, version, bin)
			signedPKG := wf.Task2(wd, "Sign PKG installer", tasks.signArtifact, pkg, wf.Const(sign.BuildMacOS))
			signedTGZ := wf.Task2(wd, "Convert to .tgz", tasks.convertPKGToTGZ, targetVal, signedPKG)
			artifacts = append(artifacts, signedPKG, signedTGZ)
		case "windows":
			msi := wf.Task2(wd, "Build MSI installer", tasks.buildWindowsMSI, targetVal, bin)
			signedMSI := wf.Task2(wd, "Sign MSI installer", tasks.signArtifact, msi, wf.Const(sign.BuildWindows))
			zip := wf.Task2(wd, "Convert to .zip", tasks.convertTGZToZip, targetVal, bin)
			artifacts = append(artifacts, signedMSI, zip)
		default:
			artifacts = append(artifacts, bin)
		}

		if target.BuildOnly {
			continue
		}
		short := wf.Action4(wd, "Run short tests", tasks.runTests, targetVal, wf.Const(dashboard.Builders[target.Builder]), skipTests, bin)
		testsPassed = append(testsPassed, short)
		if target.LongTestBuilder != "" {
			long := wf.Action4(wd, "Run long tests", tasks.runTests, targetVal, wf.Const(dashboard.Builders[target.Builder]), skipTests, bin)
			testsPassed = append(testsPassed, long)
		}
	}
	signedArtifacts := wf.Task1(wd, "Compute GPG signature for artifacts", tasks.computeGPG, wf.Slice(artifacts...))

	// Run advisory trybots.
	var advisoryResults []wf.Value[tryBotResult]
	for _, bc := range advisoryTryBots(major) {
		result := wf.Task3(wd, "Run advisory TryBot "+bc.Name, tasks.runAdvisoryTryBot, wf.Const(bc), skipTests, source)
		advisoryResults = append(advisoryResults, result)
	}
	tryBotsApproved := wf.Action1(wd, "Approve any TryBot failures", tasks.checkAdvisoryTrybots, wf.Slice(advisoryResults...))

	signedAndTested := wf.Task2(wd, "Wait for signing and tests", func(ctx *wf.TaskContext, artifacts []artifact, version string) ([]artifact, error) {
		// Note: Note this needs to happen somewhere, doesn't matter where. Maybe move it to a nicer place later.
		for i, a := range artifacts {
			if a.Target != nil {
				artifacts[i].Filename = version + "." + a.Target.Name + "." + a.Suffix
			} else {
				artifacts[i].Filename = version + "." + a.Suffix
			}
		}

		return artifacts, nil
	}, signedArtifacts, version, wf.After(testsPassed...), wf.After(tryBotsApproved))
	return signedAndTested
}

func advisoryTryBots(major int) []*dashboard.BuildConfig {
	usedBuilders := map[string]bool{}
	for _, t := range releasetargets.TargetsForGo1Point(major) {
		usedBuilders[t.Builder] = true
		usedBuilders[t.LongTestBuilder] = true
	}

	var extras []*dashboard.BuildConfig
	for name, bc := range dashboard.Builders {
		if !usedBuilders[name] &&
			bc.BuildsRepoPostSubmit("go", fmt.Sprintf("release-branch.go1.%d", major), "") &&
			bc.HostConfig().IsGoogle() &&
			len(bc.KnownIssues) == 0 {
			extras = append(extras, bc)
		}
	}
	return extras
}

// BuildReleaseTasks serves as an adapter to the various build tasks in the task package.
type BuildReleaseTasks struct {
	GerritClient           task.GerritClient
	GerritHTTPClient       *http.Client
	GerritURL              string
	PrivateGerritURL       string
	GCSClient              *storage.Client
	ScratchURL, ServingURL string // ScratchURL is a gs:// or file:// URL, no trailing slash. E.g., "gs://golang-release-staging/relui-scratch".
	DownloadURL            string
	PublishFile            func(*task.WebsiteFile) error
	CreateBuildlet         func(context.Context, string) (buildlet.RemoteClient, error)
	SignService            sign.Service
	ApproveAction          func(*wf.TaskContext) error
}

func (b *BuildReleaseTasks) buildSource(ctx *wf.TaskContext, revision, securityRevision, version string) (artifact, error) {
	return b.runBuildStep(ctx, nil, nil, artifact{}, "src.tar.gz", func(_ *task.BuildletStep, _ io.Reader, w io.Writer) error {
		if securityRevision != "" {
			return task.WriteSourceArchive(ctx, b.GerritHTTPClient, b.PrivateGerritURL, securityRevision, version, w)
		}
		return task.WriteSourceArchive(ctx, b.GerritHTTPClient, b.GerritURL, revision, version, w)
	})
}

func (b *BuildReleaseTasks) checkSourceMatch(ctx *wf.TaskContext, branch, version string, source artifact) (head string, _ error) {
	head, err := b.GerritClient.ReadBranchHead(ctx, "go", branch)
	if err != nil {
		return "", err
	}
	_, err = b.runBuildStep(ctx, nil, nil, source, "", func(_ *task.BuildletStep, r io.Reader, _ io.Writer) error {
		branchArchive := &bytes.Buffer{}
		if err := task.WriteSourceArchive(ctx, b.GerritHTTPClient, b.GerritURL, head, version, branchArchive); err != nil {
			return err
		}
		branchHashes, err := tarballHashes(branchArchive)
		if err != nil {
			return fmt.Errorf("hashing branch tarball: %v", err)
		}
		archiveHashes, err := tarballHashes(r)
		if err != nil {
			return fmt.Errorf("hashing archive tarball: %v", err)
		}
		if diff := cmp.Diff(branchHashes, archiveHashes); diff != "" {
			return fmt.Errorf("branch state doesn't match source archive (-branch, +archive):\n%v", diff)
		}
		return nil
	})
	return head, err
}

func tarballHashes(r io.Reader) (map[string]string, error) {
	gzr, err := gzip.NewReader(r)
	if err != nil {
		return nil, err
	}
	defer gzr.Close()
	tr := tar.NewReader(gzr)
	hashes := map[string]string{}
	for {
		header, err := tr.Next()
		if err == io.EOF {
			break
		} else if err != nil {
			return nil, fmt.Errorf("reading tar header: %v", err)
		}
		h := sha256.New()
		if _, err := io.CopyN(h, tr, header.Size); err != nil {
			return nil, fmt.Errorf("reading file %q: %v", header.Name, err)
		}
		hashes[header.Name] = fmt.Sprintf("%X", h.Sum(nil))
	}
	return hashes, nil
}

func (b *BuildReleaseTasks) buildBinary(ctx *wf.TaskContext, target *releasetargets.Target, source artifact) (artifact, error) {
	bc := dashboard.Builders[target.Builder]
	return b.runBuildStep(ctx, target, bc, source, "tar.gz", func(bs *task.BuildletStep, r io.Reader, w io.Writer) error {
		return bs.BuildBinary(ctx, r, w)
	})
}

func (b *BuildReleaseTasks) buildDarwinPKG(ctx *wf.TaskContext, target *releasetargets.Target, version string, binary artifact) (artifact, error) {
	bc := dashboard.Builders[target.Builder]
	return b.runBuildStep(ctx, target, bc, binary, "pkg", func(bs *task.BuildletStep, r io.Reader, w io.Writer) error {
		return bs.BuildDarwinPKG(ctx, r, version, w)
	})
}
func (b *BuildReleaseTasks) convertPKGToTGZ(ctx *wf.TaskContext, target *releasetargets.Target, pkg artifact) (tgz artifact, _ error) {
	bc := dashboard.Builders[target.Builder]
	return b.runBuildStep(ctx, target, bc, pkg, "tar.gz", func(bs *task.BuildletStep, r io.Reader, w io.Writer) error {
		return bs.ConvertPKGToTGZ(ctx, r, w)
	})
}

func (b *BuildReleaseTasks) buildWindowsMSI(ctx *wf.TaskContext, target *releasetargets.Target, binary artifact) (artifact, error) {
	bc := dashboard.Builders[target.Builder]
	return b.runBuildStep(ctx, target, bc, binary, "msi", func(bs *task.BuildletStep, r io.Reader, w io.Writer) error {
		return bs.BuildWindowsMSI(ctx, r, w)
	})
}
func (b *BuildReleaseTasks) convertTGZToZip(ctx *wf.TaskContext, target *releasetargets.Target, binary artifact) (artifact, error) {
	return b.runBuildStep(ctx, target, nil, binary, "zip", func(_ *task.BuildletStep, r io.Reader, w io.Writer) error {
		return task.ConvertTGZToZIP(r, w)
	})
}

// computeGPG performs GPG signing on artifacts, and sets their GPGSignature field.
func (b *BuildReleaseTasks) computeGPG(ctx *wf.TaskContext, artifacts []artifact) ([]artifact, error) {
	// doGPG reports whether to do GPG signature computation for artifact a.
	doGPG := func(a artifact) bool {
		return a.Suffix == "src.tar.gz" || a.Suffix == "tar.gz"
	}

	// Start a signing job on all artifacts that want to do GPG signing and await its results.
	var in []string
	for _, a := range artifacts {
		if !doGPG(a) {
			continue
		}

		in = append(in, b.ScratchURL+"/"+a.ScratchPath)
	}
	out, err := b.signArtifacts(ctx, sign.BuildGPG, in)
	if err != nil {
		return nil, err
	} else if len(out) != len(in) {
		return nil, fmt.Errorf("got %d outputs, want %d .asc signatures", len(out), len(in))
	}
	// All done, we have our GPG signatures.
	// Put them in a base name → scratch path map.
	var signatures = make(map[string]string)
	for _, o := range out {
		scratchPath, ok := cutPrefix(o, b.ScratchURL+"/")
		if !ok {
			return nil, fmt.Errorf("got signed URL %q outside of scratch space %q, which is unsupported", o, b.ScratchURL+"/")
		}
		signatures[path.Base(o)] = scratchPath
	}

	// Set the artifacts' GPGSignature field.
	scratchFS, err := gcsfs.FromURL(ctx, b.GCSClient, b.ScratchURL)
	if err != nil {
		return nil, err
	}
	for i, a := range artifacts {
		if !doGPG(a) {
			continue
		}

		sigPath, ok := signatures[path.Base(a.ScratchPath)+".asc"]
		if !ok {
			return nil, fmt.Errorf("no GPG signature for %q", path.Base(a.ScratchPath))
		}
		sig, err := fs.ReadFile(scratchFS, sigPath)
		if err != nil {
			return nil, err
		}
		artifacts[i].GPGSignature = string(sig)
	}

	return artifacts, nil
}

// signArtifact signs a single artifact of specified type.
func (b *BuildReleaseTasks) signArtifact(ctx *wf.TaskContext, a artifact, bt sign.BuildType) (signed artifact, _ error) {
	// Sign the unsigned artifact located at ScratchPath, and
	// update ScratchPath to point to the new signed artifact.
	signedURL, err := b.signArtifacts(ctx, bt, []string{b.ScratchURL + "/" + a.ScratchPath})
	if err != nil {
		return artifact{}, err
	} else if len(signedURL) != 1 {
		return artifact{}, fmt.Errorf("got %d outputs, want 1 signed artifact", len(signedURL))
	}
	var ok bool
	a.ScratchPath, ok = cutPrefix(signedURL[0], b.ScratchURL+"/")
	if !ok {
		return artifact{}, fmt.Errorf("got signed URL %q outside of scratch space %q, which is unsupported", signedURL[0], b.ScratchURL+"/")
	}
	scratchFS, err := gcsfs.FromURL(ctx, b.GCSClient, b.ScratchURL)
	if err != nil {
		return artifact{}, err
	}

	// Update the Size and SHA256 fields.
	f, err := scratchFS.Open(a.ScratchPath)
	if err != nil {
		return artifact{}, err
	}
	var hash = sha256.New()
	n, err := io.Copy(hash, f)
	if err != nil {
		f.Close()
		return artifact{}, err
	}
	err = f.Close()
	if err != nil {
		return artifact{}, err
	}
	a.Size = int(n)
	a.SHA256 = fmt.Sprintf("%x", string(hash.Sum([]byte(nil))))

	return a, nil
}

// signArtifacts starts signing on the artifacts provided via the gs:// URL inputs,
// waits for signing to complete, and returns the gs:// URLs of the signed outputs.
func (b *BuildReleaseTasks) signArtifacts(ctx *wf.TaskContext, bt sign.BuildType, inURLs []string) (outURLs []string, _ error) {
	jobID, err := b.SignService.SignArtifact(ctx, bt, inURLs)
	if err != nil {
		return nil, err
	}
	outURLs, jobError := task.AwaitCondition(ctx, time.Minute, func() (out []string, done bool, _ error) {
		statusContext, cancel := context.WithTimeout(ctx, time.Minute)
		defer cancel()
		t := time.Now()
		status, desc, out, err := b.SignService.ArtifactSigningStatus(statusContext, jobID)
		if err != nil {
			ctx.Printf("ArtifactSigningStatus ran into a retryable communication error after %v: %v\n", time.Since(t), err)
			return nil, false, nil
		}
		switch status {
		case sign.StatusCompleted:
			return out, true, nil // All done.
		case sign.StatusFailed:
			if desc != "" {
				return nil, true, fmt.Errorf("signing attempt failed: %s", desc)
			}
			return nil, true, fmt.Errorf("signing attempt failed")
		default:
			if desc != "" {
				ctx.Printf("still waiting: %s\n", desc)
			}
			return nil, false, nil // Still waiting.
		}
	})
	if jobError != nil {
		// If ctx is canceled, also cancel the signing request.
		if ctx.Err() != nil {
			cancelContext, cancel := context.WithTimeout(context.Background(), time.Minute)
			defer cancel()
			t := time.Now()
			err := b.SignService.CancelSigning(cancelContext, jobID)
			if err != nil {
				ctx.Printf("CancelSigning error after %v: %v\n", time.Since(t), err)
			}
		}

		return nil, jobError
	}
	return outURLs, nil
}

func (b *BuildReleaseTasks) runTests(ctx *wf.TaskContext, target *releasetargets.Target, build *dashboard.BuildConfig, skipTests []string, binary artifact) error {
	for _, skip := range skipTests {
		if skip == "all" || target.Name == skip {
			ctx.Printf("Skipping test")
			return nil
		}
	}
	_, err := b.runBuildStep(ctx, target, build, binary, "", func(bs *task.BuildletStep, r io.Reader, _ io.Writer) error {
		return bs.TestTarget(ctx, r)
	})
	return err
}

type tryBotResult struct {
	Name   string
	Passed bool
}

func (b *BuildReleaseTasks) runAdvisoryTryBot(ctx *wf.TaskContext, bc *dashboard.BuildConfig, skipTests []string, source artifact) (tryBotResult, error) {
	for _, skip := range skipTests {
		if skip == "all" || bc.Name == skip {
			ctx.Printf("Skipping test")
			return tryBotResult{bc.Name, true}, nil
		}
	}

	passed := false
	_, err := b.runBuildStep(ctx, nil, bc, source, "", func(bs *task.BuildletStep, r io.Reader, w io.Writer) error {
		var err error
		passed, err = bs.RunTryBot(ctx, r)
		return err
	})
	return tryBotResult{bc.Name, passed}, err
}

func (b *BuildReleaseTasks) checkAdvisoryTrybots(ctx *wf.TaskContext, results []tryBotResult) error {
	var fails []string
	for _, r := range results {
		if !r.Passed {
			fails = append(fails, r.Name)
		}
	}
	if len(fails) == 0 {
		return nil
	}
	ctx.Printf("Some advisory TryBots failed. Check their logs and approve this task if it's okay:\n%v", strings.Join(fails, "\n"))
	return b.ApproveAction(ctx)
}

// runBuildStep is a convenience function that manages resources a build step might need.
// If target and build config are specified, a BuildletStep will be passed to f.
// If input with a scratch file is specified, its content will be opened and passed as a Reader to f.
// If outputSuffix is specified, a unique filename will be generated based off
// it (and the target name, if any), the file will be opened and passed as a
// Writer to f, and an artifact representing it will be returned as the result.
func (b *BuildReleaseTasks) runBuildStep(
	ctx *wf.TaskContext,
	target *releasetargets.Target,
	build *dashboard.BuildConfig,
	input artifact,
	outputSuffix string,
	f func(*task.BuildletStep, io.Reader, io.Writer) error,
) (artifact, error) {
	var step *task.BuildletStep
	if build != nil {
		ctx.Printf("Creating buildlet %v.", build.Name)
		client, err := b.CreateBuildlet(ctx, build.Name)
		if err != nil {
			return artifact{}, err
		}
		defer client.Close()
		w := &task.LogWriter{Logger: ctx}
		go w.Run(ctx)
		step = &task.BuildletStep{
			Target:      target,
			Buildlet:    client,
			BuildConfig: build,
			LogWriter:   w,
		}
		ctx.Printf("Buildlet ready.")
	}

	scratchFS, err := gcsfs.FromURL(ctx, b.GCSClient, b.ScratchURL)
	if err != nil {
		return artifact{}, err
	}
	var in io.ReadCloser
	if input.ScratchPath != "" {
		in, err = scratchFS.Open(input.ScratchPath)
		if err != nil {
			return artifact{}, err
		}
		defer in.Close()
	}
	var out io.WriteCloser
	var scratchPath string
	hash := sha256.New()
	size := &sizeWriter{}
	var multiOut io.Writer
	if outputSuffix != "" {
		scratchName := outputSuffix
		if target != nil {
			scratchName = target.Name + "." + outputSuffix
		}
		scratchPath = fmt.Sprintf("%v/%v-%v", ctx.WorkflowID.String(), rand.Int63(), scratchName)
		out, err = gcsfs.Create(scratchFS, scratchPath)
		if err != nil {
			return artifact{}, err
		}
		defer out.Close()
		multiOut = io.MultiWriter(out, hash, size)
	}
	// Hide in's Close method from the task, which may assert it to Closer.
	nopIn := io.NopCloser(in)
	if err := f(step, nopIn, multiOut); err != nil {
		return artifact{}, err
	}
	if step != nil {
		if err := step.Buildlet.Close(); err != nil {
			return artifact{}, err
		}
	}
	if in != nil {
		if err := in.Close(); err != nil {
			return artifact{}, err
		}
	}
	if out != nil {
		if err := out.Close(); err != nil {
			return artifact{}, err
		}
	}
	return artifact{
		Target:      target,
		ScratchPath: scratchPath,
		Suffix:      outputSuffix,
		SHA256:      fmt.Sprintf("%x", string(hash.Sum([]byte(nil)))),
		Size:        size.size,
	}, nil
}

// An artifact represents a file as it moves through the release process. Most
// files will appear on go.dev/dl eventually.
type artifact struct {
	// The target platform of this artifact, or nil for source.
	Target *releasetargets.Target
	// The scratch path of this artifact within the scratch directory.
	// <workflow-id>/<random-number>-<filename>
	ScratchPath string
	// The contents of the GPG signature for this artifact (.asc file).
	GPGSignature string
	// The filename suffix of the artifact, e.g. "tar.gz" or "src.tar.gz",
	// combined with the version and Target name to produce Filename.
	Suffix string
	// The final Filename of this artifact as it will be downloaded.
	Filename string
	SHA256   string
	Size     int
}

type sizeWriter struct {
	size int
}

func (w *sizeWriter) Write(p []byte) (n int, err error) {
	w.size += len(p)
	return len(p), nil
}

func (tasks *BuildReleaseTasks) uploadArtifacts(ctx *wf.TaskContext, artifacts []artifact) error {
	scratchFS, err := gcsfs.FromURL(ctx, tasks.GCSClient, tasks.ScratchURL)
	if err != nil {
		return err
	}
	servingFS, err := gcsfs.FromURL(ctx, tasks.GCSClient, tasks.ServingURL)
	if err != nil {
		return err
	}

	todo := map[string]bool{} // URLs we're waiting on becoming available.
	for _, a := range artifacts {
		if err := uploadArtifact(scratchFS, servingFS, a); err != nil {
			return err
		}
		todo[tasks.DownloadURL+"/"+a.Filename] = true
		todo[tasks.DownloadURL+"/"+a.Filename+".sha256"] = true
		if a.GPGSignature != "" {
			todo[tasks.DownloadURL+"/"+a.Filename+".asc"] = true
		}
	}

	check := func() (int, bool, error) {
		for url := range todo {
			ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
			defer cancel()
			resp, err := ctxhttp.Head(ctx, http.DefaultClient, url)
			if err != nil && err != context.DeadlineExceeded {
				return 0, false, err
			}
			resp.Body.Close()
			cancel()
			if resp.StatusCode == http.StatusOK {
				delete(todo, url)
			}
		}
		return 0, len(todo) == 0, nil
	}
	_, err = task.AwaitCondition(ctx, 30*time.Second, check)
	return err
}

// uploadArtifact copies the artifact a and its metadata files
// from scratchFS to servingFS.
func uploadArtifact(scratchFS, servingFS fs.FS, a artifact) error {
	in, err := scratchFS.Open(a.ScratchPath)
	if err != nil {
		return err
	}
	defer in.Close()

	out, err := gcsfs.Create(servingFS, a.Filename)
	if err != nil {
		return err
	}
	defer out.Close()
	if _, err := io.Copy(out, in); err != nil {
		return err
	}
	if err := out.Close(); err != nil {
		return err
	}

	if err := gcsfs.WriteFile(servingFS, a.Filename+".sha256", []byte(a.SHA256)); err != nil {
		return err
	}
	if a.GPGSignature != "" {
		if err := gcsfs.WriteFile(servingFS, a.Filename+".asc", []byte(a.GPGSignature)); err != nil {
			return err
		}
	}

	return nil
}

// publishArtifacts publishes artifacts for version (typically so they appear at https://go.dev/dl/).
// It returns version, the Go version that has been successfully published.
//
// The version string uses the same format as Go tags. For example, "go1.19rc1".
func (tasks *BuildReleaseTasks) publishArtifacts(ctx *wf.TaskContext, version string, artifacts []artifact) (publishedVersion string, _ error) {
	for _, a := range artifacts {
		f := &task.WebsiteFile{
			Filename:       a.Filename,
			Version:        version,
			ChecksumSHA256: a.SHA256,
			Size:           int64(a.Size),
		}
		if a.Target != nil {
			f.OS = a.Target.GOOS
			f.Arch = a.Target.GOARCH
			if a.Target.GOARCH == "arm" {
				f.Arch = "armv6l"
			}
		}
		switch a.Suffix {
		case "src.tar.gz":
			f.Kind = "source"
		case "tar.gz", "zip":
			f.Kind = "archive"
		case "msi", "pkg":
			f.Kind = "installer"
		}
		if err := tasks.PublishFile(f); err != nil {
			return "", err
		}
	}
	ctx.Printf("Published %v artifacts for %v", len(artifacts), version)
	return version, nil
}

// cutPrefix returns s without the provided leading prefix string
// and reports whether it found the prefix.
// If s doesn't start with prefix, cutPrefix returns s, false.
// If prefix is the empty string, cutPrefix returns s, true.
// TODO: After Go 1.21 is out, delete in favor of strings.CutPrefix.
func cutPrefix(s, prefix string) (after string, found bool) {
	if !strings.HasPrefix(s, prefix) {
		return s, false
	}
	return s[len(prefix):], true
}