system-design-game/main.go

package main

import (
	"fmt"
	"net/http"
	"os"
	"strconv"
	"strings"

	"github.com/gofrs/uuid"
)

const startupMessage = `                                ▄▄           ▄  ▄▄                              
                                 ▄▄           ▄▄    ▄                           
                                ▄              ▄▄▄    ▄                         
                                  ▄ ▄          ▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄          ▄▄▄▄▄▄▄ 
                                 ▄ ▄  ▄▄  ▄▄▄▄       ▄        ▄▄▄▄▄▄           ▄
  ▄            ▄   ▄▄▄   ▄       ▄   ▄▄▄▄▄▄▄▄       ▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄
            ▄  ▄    ▄ ▄  ▄  ▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄        ▄▄▄▄ ▄▄    ▄▄▄  ▄▄        ▄▄ 
 ▄      ▄      ▄▄ ▄▄▄▄▄▄▄ ▄▄▄▄▄▄▄▄▄▄▄    ▄   ▄   ▄▄▄  ▄ ▄▄   ▄ ▄▄▄▄▄▄       ▄   
               ▄    ▄▄  ▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄    ▄▄  ▄▄▄▄▄▄▄▄▄▄▄▄     
                                     ▄▄▄  ▄▄▄▄▄▄▄▄▄▄▄ ▄   ▄  ▄▄▄         ▄      
                                            ▄▄ ▄▄  ▄   ▄▄▄▄▄▄▄ ▄▄▄▄▄▄ ▄▄▄       
            ▄                               ▄▄     ▄  ▄     ▄▄▄▄▄▄   ▄          
               ▄  ▄   ▄▄      ▄   ▄  ▄▄▄▄     ▄▄▄▄▄▄▄▄       ▄▄▄▄  ▄▄ ▄         
                 ▄  ▄▄    ▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄  ▄▄                ▄▄          
                                    ▄▄               ▄▄▄▄▄▄ ▄▄▄▄▄▄              
`

func logRequest(r *http.Request) {
	uri := r.RequestURI
	method := r.Method
	fmt.Println("Got request!", method, uri)
}

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		logRequest(r)
		fmt.Fprintf(w, "Hello! you've requested %s\n", r.URL.Path)
	})

	http.HandleFunc("/cached", func(w http.ResponseWriter, r *http.Request) {
		logRequest(r)
		maxAgeParams, ok := r.URL.Query()["max-age"]
		if ok && len(maxAgeParams) > 0 {
			maxAge, _ := strconv.Atoi(maxAgeParams[0])
			w.Header().Set("Cache-Control", fmt.Sprintf("max-age=%d", maxAge))
		}
		responseHeaderParams, ok := r.URL.Query()["headers"]
		if ok {
			for _, header := range responseHeaderParams {
				h := strings.Split(header, ":")
				w.Header().Set(h[0], strings.TrimSpace(h[1]))
			}
		}
		statusCodeParams, ok := r.URL.Query()["status"]
		if ok {
			statusCode, _ := strconv.Atoi(statusCodeParams[0])
			w.WriteHeader(statusCode)
		}
		requestID := uuid.Must(uuid.NewV4())
		fmt.Fprint(w, requestID.String())
	})

	http.HandleFunc("/headers", func(w http.ResponseWriter, r *http.Request) {
		logRequest(r)
		keys, ok := r.URL.Query()["key"]
		if ok && len(keys) > 0 {
			fmt.Fprint(w, r.Header.Get(keys[0]))
			return
		}
		headers := []string{}
		headers = append(headers, fmt.Sprintf("host=%s", r.Host))
		for key, values := range r.Header {
			headers = append(headers, fmt.Sprintf("%s=%s", key, strings.Join(values, ",")))
		}
		fmt.Fprint(w, strings.Join(headers, "\n"))
	})

	http.HandleFunc("/env", func(w http.ResponseWriter, r *http.Request) {
		logRequest(r)
		keys, ok := r.URL.Query()["key"]
		if ok && len(keys) > 0 {
			fmt.Fprint(w, os.Getenv(keys[0]))
			return
		}
		envs := []string{}
		envs = append(envs, os.Environ()...)
		fmt.Fprint(w, strings.Join(envs, "\n"))
	})

	http.HandleFunc("/status", func(w http.ResponseWriter, r *http.Request) {
		logRequest(r)
		codeParams, ok := r.URL.Query()["code"]
		if ok && len(codeParams) > 0 {
			statusCode, _ := strconv.Atoi(codeParams[0])
			if statusCode >= 200 && statusCode < 600 {
				w.WriteHeader(statusCode)
			}
		}
		requestID := uuid.Must(uuid.NewV4())
		fmt.Fprint(w, requestID.String())
	})

	port := os.Getenv("PORT")
	if port == "" {
		port = "80"
	}

	for _, encodedRoute := range strings.Split(os.Getenv("ROUTES"), ",") {
		if encodedRoute == "" {
			continue
		}
		pathAndBody := strings.SplitN(encodedRoute, "=", 2)
		path, body := pathAndBody[0], pathAndBody[1]
		http.HandleFunc("/"+path, func(w http.ResponseWriter, r *http.Request) {
			fmt.Fprint(w, body)
		})
	}

	bindAddr := fmt.Sprintf(":%s", port)
	lines := strings.Split(startupMessage, "\n")
	fmt.Println()
	for _, line := range lines {
		fmt.Println(line)
	}
	fmt.Println()
	fmt.Printf("==> Server listening at %s 🚀\n", bindAddr)

	if err := http.ListenAndServe(bindAddr, nil); err != nil {
		panic(err)
	}
}