GitHubのPull Requestが作成されたら自動でレビューアをアサインする

WebHookから呼ばれることが前提

roulette.go

package main

import (
    "encoding/json"
    "io"
    "log"
    "math/rand"
    "net/http"
    "os"
    "strings"
)

var (
    githubToken = os.Getenv("GITHUB_TOKEN")
    githubUsers = strings.Split(os.Getenv("GITHUB_REVIEWERS"), ",")
)

// assign reviewer
func assign(url string, user string) error {
    assignBody := "{\"assignee\":\"" + user + "\"}"

    // update state
    r, _ := http.NewRequest("PATCH", url, strings.NewReader(assignBody))
    r.Header.Add("Authorization", "token "+githubToken)
    r.Header.Add("Content-Type", "application/json")
    client := &http.Client{}
    resp, err := client.Do(r)
    defer resp.Body.Close()
    if err != nil {
        log.Print(err)
        return err
    }
    return nil
}

func comment(url string, user string) error {
    body := "{\"body\":\"@" + user + "please review\"}"
    r, _ := http.NewRequest("POST", url, strings.NewReader(body))
    r.Header.Add("Authorization", "token "+githubToken)
    r.Header.Add("Content-Type", "application/json")
    client := &http.Client{}
    resp, err := client.Do(r)
    defer resp.Body.Close()
    if err != nil {
        log.Print(err)
        return err
    }
    return nil
}

func Hook(w http.ResponseWriter, req *http.Request) {
    err := req.ParseForm()
    if err != nil {
        log.Print(err)
        // TODO: 500 error
        return
    }

    v := req.FormValue("payload")
    var m map[string]interface{}
    err = json.Unmarshal([]byte(v), &m)
    if err != nil {
        log.Print(err)
        // TODO: 500 error
        return
    }

    if m["action"] != "opened" {
        return
    }

    links := m["pull_request"].(map[string]interface{})["_links"].(map[string]interface{})
    assignUrl := links["issue"].(map[string]interface{})["href"].(string)
    commentUrl := links["comments"].(map[string]interface{})["href"].(string)
    reviewer := githubUsers[rand.Intn(len(githubUsers))]
    assign(assignUrl, reviewer)
    comment(commentUrl, reviewer)
}

func ping(w http.ResponseWriter, req *http.Request) {
    io.WriteString(w, "pong\n")
}

func main() {
    log.Printf("reviewer candidates are %v", githubUsers)
    port := os.Getenv("PORT")
    if len(port) == 0 {
        port = "8000"
    }
    http.HandleFunc("/", Hook)
    http.HandleFunc("/ping", ping)
    log.Printf("start server. port: %v", port)
    err := http.ListenAndServe(":"+port, nil)

    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}