// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package frontend

import (
	"fmt"
	"net/http"

	"github.com/google/safehtml/template"
	"golang.org/x/pkgsite/internal"
	"golang.org/x/pkgsite/internal/derrors"
	"golang.org/x/pkgsite/internal/log"
	"golang.org/x/pkgsite/internal/stdlib"
)

// errUnitNotFoundWithoutFetch returns a 404 with instructions to the user on
// how to manually fetch the package. No fetch button is provided. This is used
// for very large modules or modules that previously 500ed.
var errUnitNotFoundWithoutFetch = &serverError{
	status: http.StatusNotFound,
	epage: &errorPage{
		messageTemplate: template.MakeTrustedTemplate(`
					    <h3 class="Error-message">{{.StatusText}}</h3>
					    <p class="Error-message">Check that you entered the URL correctly or try fetching it following the
                        <a href="/about#adding-a-package">instructions here</a>.</p>`),
		MessageData: struct{ StatusText string }{http.StatusText(http.StatusNotFound)},
	},
}

func (s *Server) servePathNotFoundPage(w http.ResponseWriter, r *http.Request, ds internal.DataSource, fullPath, requestedVersion string) (err error) {
	defer derrors.Wrap(&err, "servePathNotFoundPage(w, r, %q, %q)", fullPath, requestedVersion)

	ctx := r.Context()
	path, err := stdlibPathForShortcut(ctx, ds, fullPath)
	if err != nil {
		// Log the error, but prefer a "path not found" error for a
		// better user experience.
		log.Error(ctx, err)
	}
	if path != "" {
		http.Redirect(w, r, fmt.Sprintf("/%s", path), http.StatusFound)
		return
	}
	if stdlib.Contains(fullPath) {
		return &serverError{status: http.StatusNotFound}
	}
	return pathNotFoundError(fullPath, requestedVersion)
}

// pathNotFoundError returns a page with an option on how to
// add a package or module to the site.
func pathNotFoundError(fullPath, requestedVersion string) error {
	if !isSupportedVersion(fullPath, requestedVersion) {
		return invalidVersionError(fullPath, requestedVersion)
	}
	if stdlib.Contains(fullPath) {
		return &serverError{status: http.StatusNotFound}
	}
	path := fullPath
	if requestedVersion != internal.LatestVersion {
		path = fmt.Sprintf("%s@%s", fullPath, requestedVersion)
	}
	return &serverError{
		status: http.StatusNotFound,
		epage: &errorPage{
			templateName: "fetch.tmpl",
			MessageData:  path,
		},
	}
}