// Copyright 2019-2020 Google LLC.
// SPDX-License-Identifier: Apache-2.0
//
// besadii is a small CLI tool that runs as a Gerrit hook (currently
// 'ref-updated') to trigger various actions:
//
// - Buildkite CI builds
// - SourceGraph (cs.tvl.fyi) repository index updates
package main

import (
	"bytes"
	"encoding/json"
	"flag"
	"fmt"
	"io/ioutil"
	"log/syslog"
	"net/http"
	"os"
	"path"
	"strings"
)

var branchPrefix = "refs/heads/"

// refUpdated is a struct representing the information passed to
// besadii when it is invoked as Gerrit's refUpdated hook.
//
// https://gerrit.googlesource.com/plugins/hooks/+/HEAD/src/main/resources/Documentation/hooks.md#ref_updated
type refUpdated struct {
	project   string
	branch    string
	commit    string
	submitter string
	email     string
}

type Author struct {
	Name  string `json:"name"`
	Email string `json:"email"`
}

// Build is the representation of a Buildkite build as described on
// https://buildkite.com/docs/apis/rest-api/builds#create-a-build
type Build struct {
	Commit  string `json:"commit"`
	Branch  string `json:"branch"`
	Message string `json:"message"`
	Author  Author `json:"author"`
}

// Trigger a build of a given branch & commit on Buildkite
func triggerBuild(log *syslog.Writer, token string, update *refUpdated) error {
	build := Build{
		Commit:  update.commit,
		Branch:  update.branch,
		Message: fmt.Sprintf("Build of %q branch %q at %q", update.project, update.branch, update.commit),
		Author: Author{
			Name:  update.submitter,
			Email: update.email,
		},
	}

	body, _ := json.Marshal(build)
	reader := ioutil.NopCloser(bytes.NewReader(body))

	req, err := http.NewRequest("POST", "https://api.buildkite.com/v2/organizations/tvl/pipelines/depot/builds", reader)
	if err != nil {
		return fmt.Errorf("failed to create an HTTP request: %w", err)
	}

	req.Header.Add("Authorization", "Bearer "+token)
	req.Header.Add("Content-Type", "application/json")

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		// This might indicate a temporary error on the Buildkite side.
		return fmt.Errorf("failed to send Buildkite request: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != 201 {
		respBody, _ := ioutil.ReadAll(resp.Body)
		log.Err(fmt.Sprintf("received non-success response from Buildkite: %s (%v)", respBody, resp.Status))
	} else {
		fmt.Fprintf(log, "triggered Buildkite build for branch %q at commit %q", update.branch, update.commit)
	}

	return nil
}

// Trigger a Sourcegraph repository index update on cs.tvl.fyi.
//
// https://docs.sourcegraph.com/admin/repo/webhooks
func triggerIndexUpdate(token string) error {
	req, err := http.NewRequest("POST", "https://cs.tvl.fyi/.api/repos/depot/-/refresh", nil)
	if err != nil {
		return err
	}

	req.Header.Add("Authorization", "token "+token)

	_, err = http.DefaultClient.Do(req)
	return err
}

func refUpdatedFromFlags() (*refUpdated, error) {
	if path.Base(os.Args[0]) != "ref-updated" {
		return nil, fmt.Errorf("besadii must be invoked as the 'ref-updated' hook")
	}

	var update refUpdated

	flag.StringVar(&update.project, "project", "", "Gerrit project")
	flag.StringVar(&update.commit, "newrev", "", "new revision")
	flag.StringVar(&update.email, "submitter", "", "Submitter email")
	flag.StringVar(&update.submitter, "submitter-username", "", "Submitter username")
	ref := flag.String("refname", "", "updated reference name")

	// Gerrit passes more flags than we want, but Rob Pike decided[0] in
	// 2013 that the Go art project will not allow users to ignore flags
	// because he "doesn't like it". The following code ignores the
	// flags.
	//
	// [0]: https://github.com/golang/go/issues/6112#issuecomment-66083768
	var _old string
	flag.StringVar(&_old, "oldrev", "", "")

	flag.Parse()

	if update.project == "" || *ref == "" || update.commit == "" || update.submitter == "" {
		// If we get here, the user is probably being a dummy and invoking
		// this manually - but incorrectly.
		return nil, fmt.Errorf("'ref-updated' hook invoked without required arguments")
	}

	if update.project != "depot" {
		// this is not an error, but also not something we handle.
		return nil, nil
	}

	if !strings.HasPrefix(*ref, branchPrefix) {
		return nil, fmt.Errorf("besadii only supports branch updates at the moment (got %q)", *ref)
	}

	update.branch = strings.TrimPrefix(*ref, branchPrefix)

	return &update, nil
}

func main() {
	log, err := syslog.New(syslog.LOG_INFO|syslog.LOG_USER, "besadii")
	if err != nil {
		fmt.Printf("failed to open syslog: %s\n", err)
		os.Exit(1)
	}

	buildkiteToken, err := ioutil.ReadFile("/etc/secrets/buildkite-besadii")
	if err != nil {
		log.Alert(fmt.Sprintf("buildkite token could not be read: %s", err))
		os.Exit(1)
	}

	sourcegraphToken, err := ioutil.ReadFile("/etc/secrets/sourcegraph-token")
	if err != nil {
		log.Alert(fmt.Sprintf("sourcegraph token could not be read: %s", err))
		os.Exit(1)
	}

	update, err := refUpdatedFromFlags()
	if err != nil {
		log.Err(fmt.Sprintf("failed to parse ref update: %s", err))
		os.Exit(1)
	}

	if update == nil { // the project was not 'depot'
		os.Exit(0)
	}

	err = triggerBuild(log, string(buildkiteToken), update)
	if err != nil {
		log.Err(fmt.Sprintf("failed to trigger Buildkite build: %s", err))
	}

	err = triggerIndexUpdate(string(sourcegraphToken))
	if err != nil {
		log.Err(fmt.Sprintf("failed to trigger sourcegraph index update: %s", err))
	}
	log.Info("triggered sourcegraph index update")
}