// cms is a free and open source content management system.
package main

import (
	"context"
	"log"
	"net/http"
	"strings"
	"time"

	"git.sr.ht/~evanj/cms/pkg/flushresp"
)

type App struct {
	log *log.Logger

	// NOTE: Concurrent read (only) is OK. This is never wrote (but defined on
	// server startup).
	handlers map[string]http.Handler
}

func (a *App) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	parts := strings.Split(r.URL.Path, "/")
	if len(parts) < 2 {
		http.NotFound(w, r)
		return
	}

	namespace := parts[1]
	if namespace == "" {
		namespace = "user"
	}

	h, ok := a.handlers[namespace]
	if !ok {
		http.NotFound(w, r)
		return
	}

	a.handleWithRetry(w, r, h)
}

// handleWithRetry will retry requests when we're approaching long request
// times in an effort to lower tail latency.
func (a *App) handleWithRetry(w http.ResponseWriter, r *http.Request, h http.Handler) {
	var (
		// Effective max request time is 30 seconds (ten seconds will be retried
		// three times).
		maxAttempts = 3
		maxTime     = 10 * time.Second
		err         error
	)

	for i := 0; i < maxAttempts; i++ {
		var (
			ctx, cancel = context.WithTimeout(context.Background(), maxTime)
			wWrap       = flushresp.New(w)
			successCh   = handle(wWrap, r.WithContext(ctx), h)
		)
		defer cancel()

		select {
		case <-ctx.Done():
			err = ctx.Err()
		case <-successCh:
			if _, err := wWrap.Flush(); err != nil {
				// TODO: Is there a more appropriate way to handle an error here?...
				a.log.Println(err)
			}
			return
		}
	}

	// TODO: Probably want a better error message.
	w.WriteHeader(http.StatusInternalServerError)
	w.Write([]byte(err.Error()))
}

func handle(w http.ResponseWriter, r *http.Request, h http.Handler) chan struct{} {
	c := make(chan struct{})

	go func(c chan struct{}) {
		h.ServeHTTP(w, r)
		c <- struct{}{}
	}(c)

	return c
}