// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package web

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

	apimodel "code.superseriousbusiness.org/gotosocial/internal/api/model"
	apiutil "code.superseriousbusiness.org/gotosocial/internal/api/util"
	"code.superseriousbusiness.org/gotosocial/internal/gtserror"
	"github.com/gin-gonic/gin"
)

func (m *Module) threadGETHandler(c *gin.Context) {
	ctx := c.Request.Context()

	// We'll need the instance later, and we can also use it
	// before then to make it easier to return a web error.
	instance, errWithCode := m.processor.InstanceGetV1(ctx)
	if errWithCode != nil {
		apiutil.WebErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
		return
	}

	// Return instance we already got from the db,
	// don't try to fetch it again when erroring.
	instanceGet := func(ctx context.Context) (*apimodel.InstanceV1, gtserror.WithCode) {
		return instance, nil
	}

	// Parse account requestedUser and status ID from the URL.
	requestedUser, errWithCode := apiutil.ParseUsername(c.Param(apiutil.UsernameKey))
	if errWithCode != nil {
		apiutil.WebErrorHandler(c, errWithCode, instanceGet)
		return
	}

	statusID, errWithCode := apiutil.ParseWebStatusID(c.Param(apiutil.WebStatusIDKey))
	if errWithCode != nil {
		apiutil.WebErrorHandler(c, errWithCode, instanceGet)
		return
	}

	// Normalize requested username + status ID:
	//
	//   - Usernames on our instance are (currently) always lowercase.
	//   - StatusIDs on our instance are (currently) always ULIDs.
	//
	// todo: Update this logic when different username patterns
	// are allowed, and/or when status slugs are introduced.
	requestedUser = strings.ToLower(requestedUser)
	statusID = strings.ToUpper(statusID)

	// Check what type of content is being requested. If we're getting an AP
	// request on this endpoint we should render the AP representation instead.
	accept, err := apiutil.NegotiateAccept(c, apiutil.HTMLOrActivityPubHeaders...)
	if err != nil {
		apiutil.WebErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), instanceGet)
		return
	}

	if apiutil.ASContentType(accept) {
		// AP status representation has been requested.
		status, errWithCode := m.processor.Fedi().StatusGet(c.Request.Context(), requestedUser, statusID)
		if errWithCode != nil {
			apiutil.WebErrorHandler(c, errWithCode, instanceGet)
			return
		}

		apiutil.JSONType(c, http.StatusOK, accept, status)
		return
	}

	// text/html has been requested. Proceed with getting the web view of the status.

	// Fetch the target account so we can do some checks on it.
	acct, errWithCode := m.processor.Account().GetWeb(ctx, requestedUser)
	if errWithCode != nil {
		apiutil.WebErrorHandler(c, errWithCode, instanceGet)
		return
	}

	// If requested account is suspended, this page should not be visible.
	if acct.Suspended {
		err := gtserror.Newf("account %s is suspended", requestedUser)
		apiutil.WebErrorHandler(c, gtserror.NewErrorNotFound(err), instanceGet)
		return
	}

	// Get the thread context. This will fetch the status as well.
	context, errWithCode := m.processor.Status().WebContextGet(ctx, statusID)
	if errWithCode != nil {
		apiutil.WebErrorHandler(c, errWithCode, instanceGet)
		return
	}

	// Ensure status actually belongs to requested account.
	if context.Status.Account.ID != acct.ID {
		err := gtserror.Newf("account %s does not own status %s", requestedUser, statusID)
		apiutil.WebErrorHandler(c, gtserror.NewErrorNotFound(err), instanceGet)
		return
	}

	// Prepare stylesheets for thread.
	stylesheets := make([]string, 0, 6)

	// Basic thread stylesheets.
	stylesheets = append(
		stylesheets,
		[]string{
			cssFA,
			cssStatus,
			cssThread,
		}...,
	)

	// User-selected theme if set.
	if theme := acct.Theme; theme != "" {
		stylesheets = append(
			stylesheets,
			themesPathPrefix+"/"+theme,
		)
	}

	// Custom CSS for this user last in cascade.
	stylesheets = append(
		stylesheets,
		"/@"+acct.Username+"/custom.css",
	)

	page := apiutil.WebPage{
		Template:    "thread.tmpl",
		Instance:    instance,
		OGMeta:      apiutil.OGBase(instance).WithStatus(context.Status),
		Stylesheets: stylesheets,
		Javascript: []apiutil.JavascriptEntry{
			{
				Src:   jsFrontend,
				Async: true,
				Defer: true,
			},
			{
				Bottom: true,
				Src:    jsFrontendPrerender,
			},
		},
		Extra: map[string]any{
			"context": context,
		},
	}

	apiutil.TemplateWebPage(c, page)
}