package main

import (
	"fmt"
	"hash/fnv"
	"io"
	"io/fs"
	"log"
	"log/slog"
	"mime"
	"net"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	cfg "website/internal/config"

	"github.com/ardanlabs/conf/v3"
	"github.com/getsentry/sentry-go"
	sentryhttp "github.com/getsentry/sentry-go/http"
	"github.com/pkg/errors"
	"github.com/shengyanli1982/law"
)

type Config struct {
	Production             bool    `conf:"default:false"`
	ListenAddress          string  `conf:"default:localhost"`
	Port                   uint16  `conf:"default:3000,short:p"`
	BaseURL                cfg.URL `conf:"default:http://localhost:3000,short:b"`
	RedirectOtherHostnames bool    `conf:"default:false"`
}

var Commit string

var config *cfg.Config

type File struct {
	filename string
	etag     string
}

var files = map[string]File{}

func hashFile(filename string) (string, error) {
	f, err := os.Open(filename)
	if err != nil {
		return "", err
	}
	defer f.Close()
	hash := fnv.New64a()
	if _, err := io.Copy(hash, f); err != nil {
		return "", err
	}
	return fmt.Sprintf(`W/"%x"`, hash.Sum(nil)), nil
}

func registerFile(urlpath string, filepath string) error {
	if files[urlpath] != (File{}) {
		log.Printf("registerFile called with duplicate file, urlPath: %s", urlpath)
		return nil
	}
	hash, err := hashFile(filepath)
	if err != nil {
		return err
	}
	files[urlpath] = File{
		filename: filepath,
		etag:     hash,
	}
	return nil
}

func registerContentFiles(root string) error {
	err := filepath.WalkDir(root, func(filePath string, f fs.DirEntry, err error) error {
		if err != nil {
			return errors.WithMessagef(err, "failed to access path %s", filePath)
		}
		relPath, err := filepath.Rel(root, filePath)
		if err != nil {
			return errors.WithMessagef(err, "failed to make path relative, path: %s", filePath)
		}
		urlPath, _ := strings.CutSuffix(relPath, "index.html")
		if !f.IsDir() {
			slog.Debug("registering file", "urlpath", "/"+urlPath)
			return registerFile("/"+urlPath, filePath)
		}
		return nil
	})
	if err != nil {
		return err
	}
	return nil
}

type HTTPError struct {
	Error   error
	Message string
	Code    int
}

func canonicalisePath(path string) (cPath string, differs bool) {
	if strings.HasSuffix(path, "/index.html") {
		cPath, differs = strings.CutSuffix(path, "index.html")
	} else if !strings.HasSuffix(path, "/") && files[path+"/"] != (File{}) {
		cPath, differs = path+"/", true
	}
	return path, differs
}

func serveFile(w http.ResponseWriter, r *http.Request) *HTTPError {
	urlPath, shouldRedirect := canonicalisePath(r.URL.Path)
	if shouldRedirect {
		http.Redirect(w, r, urlPath, 302)
		return nil
	}
	file := files[urlPath]
	if file == (File{}) {
		return &HTTPError{
			Message: "File not found",
			Code:    http.StatusNotFound,
		}
	}
	w.Header().Add("ETag", file.etag)
	w.Header().Add("Vary", "Accept-Encoding")
	for k, v := range config.Extra.Headers {
		w.Header().Add(k, v)
	}

	http.ServeFile(w, r, files[urlPath].filename)
	return nil
}

type webHandler func(http.ResponseWriter, *http.Request) *HTTPError

func (fn webHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	defer func() {
		if fail := recover(); fail != nil {
			w.WriteHeader(http.StatusInternalServerError)
			slog.Error("runtime panic!", "error", fail)
		}
	}()
	w.Header().Set("Server", fmt.Sprintf("website (%s)", Commit))
	if err := fn(w, r); err != nil {
		if strings.Contains(r.Header.Get("Accept"), "text/html") {
			w.WriteHeader(err.Code)
			notFoundPage := "website/private/404.html"
			http.ServeFile(w, r, notFoundPage)
		} else {
			http.Error(w, err.Message, err.Code)
		}
	}
}

var newMIMEs = map[string]string{
	".xsl": "text/xsl",
}

func fixupMIMETypes() {
	for ext, newType := range newMIMEs {
		if err := mime.AddExtensionType(ext, newType); err != nil {
			slog.Error("could not update mime type", "ext", ext, "mime", newType)
		}
	}
}

type loggingResponseWriter struct {
	http.ResponseWriter
	statusCode int
}

func (lrw *loggingResponseWriter) WriteHeader(code int) {
	lrw.statusCode = code
	// avoids warning: superfluous response.WriteHeader call
	if lrw.statusCode != http.StatusOK {
		lrw.ResponseWriter.WriteHeader(code)
	}
}

func NewLoggingResponseWriter(w http.ResponseWriter) *loggingResponseWriter {
	return &loggingResponseWriter{w, http.StatusOK}
}

type wrappedHandlerOptions struct {
	defaultHostname string
	logger          io.Writer
}

func wrapHandlerWithLogging(wrappedHandler http.Handler, opts wrappedHandlerOptions) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		scheme := r.Header.Get("X-Forwarded-Proto")
		if scheme == "" {
			scheme = "http"
		}
		host := r.Header.Get("Host")
		if host == "" {
			host = opts.defaultHostname
		}
		lw := NewLoggingResponseWriter(w)
		wrappedHandler.ServeHTTP(lw, r)
		statusCode := lw.statusCode
		fmt.Fprintf(
			opts.logger,
			"%s %s %d %s %s %s\n",
			scheme,
			r.Method,
			statusCode,
			host,
			r.URL.Path,
			lw.Header().Get("Location"),
		)
	})
}

func main() {
	if os.Getenv("DEBUG") != "" {
		slog.SetLogLoggerLevel(slog.LevelDebug)
	}

	fixupMIMETypes()

	runtimeConfig := Config{}
	help, err := conf.Parse("", &runtimeConfig)
	if err != nil {
		if errors.Is(err, conf.ErrHelpWanted) {
			fmt.Println(help)
			os.Exit(1)
		}
		log.Panicf("parsing runtime configuration: %v", err)
	}

	config, err = cfg.GetConfig()
	if err != nil {
		log.Panicf("parsing configuration file: %v", err)
	}

	cwd, err := os.Getwd()
	if err != nil {
		log.Panicf("don't know where I am")
	}
	slog.Debug("starting at", "wd", cwd)

	prefix := "website/public"
	slog.Debug("registering content files", "prefix", prefix)
	err = registerContentFiles(prefix)
	if err != nil {
		log.Panicf("registering content files: %v", err)
	}

	env := "development"
	if runtimeConfig.Production {
		env = "production"
	}
	err = sentry.Init(sentry.ClientOptions{
		EnableTracing:    true,
		TracesSampleRate: 1.0,
		Dsn:              os.Getenv("SENTRY_DSN"),
		Release:          Commit,
		Environment:      env,
	})
	if err != nil {
		log.Panic("could not set up sentry")
	}
	defer sentry.Flush(2 * time.Second)
	sentryHandler := sentryhttp.New(sentryhttp.Options{
		Repanic: true,
	})

	mux := http.NewServeMux()
	slog.Debug("binding main handler to", "host", runtimeConfig.BaseURL.Hostname()+"/")
	mux.Handle(runtimeConfig.BaseURL.Hostname()+"/", webHandler(serveFile))

	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		newURL := runtimeConfig.BaseURL.String() + r.URL.String()
		http.Redirect(w, r, newURL, 301)
	})

	var logWriter io.Writer
	if runtimeConfig.Production {
		logWriter = law.NewWriteAsyncer(os.Stdout, nil)
	} else {
		logWriter = os.Stdout
	}
	http.Handle("/",
		sentryHandler.Handle(
			wrapHandlerWithLogging(mux, wrappedHandlerOptions{
				defaultHostname: runtimeConfig.BaseURL.Hostname(),
				logger:          logWriter,
			}),
		),
	)
	// no logging, no sentry
	http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
	})

	listenAddress := net.JoinHostPort(runtimeConfig.ListenAddress, fmt.Sprint(runtimeConfig.Port))
	log.Fatal(http.ListenAndServe(listenAddress, nil))
}