// 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 media

import (
	"context"
	"fmt"
	"io"
	"net/url"
	"strings"
	"time"

	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
	"github.com/superseriousbusiness/gotosocial/internal/gtscontext"
	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
	"github.com/superseriousbusiness/gotosocial/internal/media"
	"github.com/superseriousbusiness/gotosocial/internal/storage"
	"github.com/superseriousbusiness/gotosocial/internal/uris"
)

// GetFile retrieves a file from storage and streams it back
// to the caller via an io.reader embedded in *apimodel.Content.
func (p *Processor) GetFile(
	ctx context.Context,
	requestingAccount *gtsmodel.Account,
	form *apimodel.GetContentRequestForm,
) (*apimodel.Content, gtserror.WithCode) {
	// parse the form fields
	mediaSize, err := parseSize(form.MediaSize)
	if err != nil {
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("media size %s not valid", form.MediaSize))
	}

	mediaType, err := parseType(form.MediaType)
	if err != nil {
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("media type %s not valid", form.MediaType))
	}

	spl := strings.Split(form.FileName, ".")
	if len(spl) != 2 || spl[0] == "" || spl[1] == "" {
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("file name %s not parseable", form.FileName))
	}
	wantedMediaID := spl[0]
	owningAccountID := form.AccountID

	// get the account that owns the media and make sure it's not suspended
	owningAccount, err := p.state.DB.GetAccountByID(ctx, owningAccountID)
	if err != nil {
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("account with id %s could not be selected from the db: %s", owningAccountID, err))
	}
	if !owningAccount.SuspendedAt.IsZero() {
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("account with id %s is suspended", owningAccountID))
	}

	// make sure the requesting account and the media account don't block each other
	if requestingAccount != nil {
		blocked, err := p.state.DB.IsEitherBlocked(ctx, requestingAccount.ID, owningAccountID)
		if err != nil {
			return nil, gtserror.NewErrorNotFound(fmt.Errorf("block status could not be established between accounts %s and %s: %s", owningAccountID, requestingAccount.ID, err))
		}
		if blocked {
			return nil, gtserror.NewErrorNotFound(fmt.Errorf("block exists between accounts %s and %s", owningAccountID, requestingAccount.ID))
		}
	}

	// the way we store emojis is a little different from the way we store other attachments,
	// so we need to take different steps depending on the media type being requested
	switch mediaType {
	case media.TypeEmoji:
		return p.getEmojiContent(ctx, wantedMediaID, owningAccountID, mediaSize)
	case media.TypeAttachment, media.TypeHeader, media.TypeAvatar:
		return p.getAttachmentContent(ctx, requestingAccount, wantedMediaID, owningAccountID, mediaSize)
	default:
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("media type %s not recognized", mediaType))
	}
}

/*
	UTIL FUNCTIONS
*/

func parseType(s string) (media.Type, error) {
	switch s {
	case string(media.TypeAttachment):
		return media.TypeAttachment, nil
	case string(media.TypeHeader):
		return media.TypeHeader, nil
	case string(media.TypeAvatar):
		return media.TypeAvatar, nil
	case string(media.TypeEmoji):
		return media.TypeEmoji, nil
	}
	return "", fmt.Errorf("%s not a recognized media.Type", s)
}

func parseSize(s string) (media.Size, error) {
	switch s {
	case string(media.SizeSmall):
		return media.SizeSmall, nil
	case string(media.SizeOriginal):
		return media.SizeOriginal, nil
	case string(media.SizeStatic):
		return media.SizeStatic, nil
	}
	return "", fmt.Errorf("%s not a recognized media.Size", s)
}

func (p *Processor) getAttachmentContent(ctx context.Context, requestingAccount *gtsmodel.Account, wantedMediaID string, owningAccountID string, mediaSize media.Size) (*apimodel.Content, gtserror.WithCode) {
	// retrieve attachment from the database and do basic checks on it
	a, err := p.state.DB.GetAttachmentByID(ctx, wantedMediaID)
	if err != nil {
		err = gtserror.Newf("attachment %s could not be taken from the db: %w", wantedMediaID, err)
		return nil, gtserror.NewErrorNotFound(err)
	}

	if a.AccountID != owningAccountID {
		err = gtserror.Newf("attachment %s is not owned by %s", wantedMediaID, owningAccountID)
		return nil, gtserror.NewErrorNotFound(err)
	}

	// If this is an "Unknown" file type, ie., one we
	// tried to process and couldn't, or one we refused
	// to process because it wasn't supported, then we
	// can skip a lot of steps here by simply forwarding
	// the request to the remote URL.
	if a.Type == gtsmodel.FileTypeUnknown {
		remoteURL, err := url.Parse(a.RemoteURL)
		if err != nil {
			err = gtserror.Newf("error parsing remote URL of 'Unknown'-type attachment for redirection: %w", err)
			return nil, gtserror.NewErrorInternalError(err)
		}

		url := &storage.PresignedURL{
			URL: remoteURL,
			// We might manage to cache the media
			// at some point, so set a low-ish expiry.
			Expiry: time.Now().Add(2 * time.Hour),
		}

		return &apimodel.Content{URL: url}, nil
	}

	if !*a.Cached {
		// if we don't have it cached, then we can assume two things:
		// 1. this is remote media, since local media should never be uncached
		// 2. we need to fetch it again using a transport and the media manager
		remoteMediaIRI, err := url.Parse(a.RemoteURL)
		if err != nil {
			return nil, gtserror.NewErrorNotFound(fmt.Errorf("error parsing remote media iri %s: %w", a.RemoteURL, err))
		}

		// use an empty string as requestingUsername to use the instance account, unless the request for this
		// media has been http signed, then use the requesting account to make the request to remote server
		var requestingUsername string
		if requestingAccount != nil {
			requestingUsername = requestingAccount.Username
		}

		// Pour one out for tobi's original streamed recache
		// (streaming data both to the client and storage).
		// Gone and forever missed <3
		//
		// [
		//   the reason it was removed was because a slow
		//   client connection could hold open a storage
		//   recache operation -> holding open a media worker.
		// ]

		dataFn := func(ctx context.Context) (io.ReadCloser, int64, error) {
			t, err := p.transportController.NewTransportForUsername(ctx, requestingUsername)
			if err != nil {
				return nil, 0, err
			}
			return t.DereferenceMedia(gtscontext.SetFastFail(ctx), remoteMediaIRI)
		}

		// Start recaching this media with the prepared data function.
		processingMedia, err := p.mediaManager.PreProcessMediaRecache(ctx, dataFn, wantedMediaID)
		if err != nil {
			return nil, gtserror.NewErrorNotFound(fmt.Errorf("error recaching media: %w", err))
		}

		// Load attachment and block until complete
		a, err = processingMedia.LoadAttachment(ctx)
		if err != nil {
			return nil, gtserror.NewErrorNotFound(fmt.Errorf("error loading recached attachment: %w", err))
		}
	}

	var (
		storagePath       string
		attachmentContent = &apimodel.Content{
			ContentUpdated: a.UpdatedAt,
		}
	)

	// get file information from the attachment depending on the requested media size
	switch mediaSize {
	case media.SizeOriginal:
		attachmentContent.ContentType = a.File.ContentType
		attachmentContent.ContentLength = int64(a.File.FileSize)
		storagePath = a.File.Path
	case media.SizeSmall:
		attachmentContent.ContentType = a.Thumbnail.ContentType
		attachmentContent.ContentLength = int64(a.Thumbnail.FileSize)
		storagePath = a.Thumbnail.Path
	default:
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("media size %s not recognized for attachment", mediaSize))
	}

	// ... so now we can safely return it
	return p.retrieveFromStorage(ctx, storagePath, attachmentContent)
}

func (p *Processor) getEmojiContent(ctx context.Context, fileName string, owningAccountID string, emojiSize media.Size) (*apimodel.Content, gtserror.WithCode) {
	emojiContent := &apimodel.Content{}
	var storagePath string

	// reconstruct the static emoji image url -- reason
	// for using the static URL rather than full size url
	// is that static emojis are always encoded as png,
	// so this is more reliable than using full size url
	imageStaticURL := uris.URIForAttachment(
		owningAccountID,
		string(media.TypeEmoji),
		string(media.SizeStatic),
		fileName,
		"png",
	)

	e, err := p.state.DB.GetEmojiByStaticURL(ctx, imageStaticURL)
	if err != nil {
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("emoji %s could not be taken from the db: %w", fileName, err))
	}

	if *e.Disabled {
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("emoji %s has been disabled", fileName))
	}

	if !*e.Cached {
		// if we don't have it cached, then we can assume two things:
		// 1. this is remote emoji, since local emoji should never be uncached
		// 2. we need to fetch it again using a transport and the media manager
		remoteURL, err := url.Parse(e.ImageRemoteURL)
		if err != nil {
			return nil, gtserror.NewErrorNotFound(fmt.Errorf("error parsing remote emoji iri %s: %w", e.ImageRemoteURL, err))
		}

		dataFn := func(ctx context.Context) (io.ReadCloser, int64, error) {
			t, err := p.transportController.NewTransportForUsername(ctx, "")
			if err != nil {
				return nil, 0, err
			}
			return t.DereferenceMedia(gtscontext.SetFastFail(ctx), remoteURL)
		}

		// Start recaching this emoji with the prepared data function.
		processingEmoji, err := p.mediaManager.PreProcessEmojiRecache(ctx, dataFn, e.ID)
		if err != nil {
			return nil, gtserror.NewErrorNotFound(fmt.Errorf("error recaching emoji: %w", err))
		}

		// Load attachment and block until complete
		e, err = processingEmoji.LoadEmoji(ctx)
		if err != nil {
			return nil, gtserror.NewErrorNotFound(fmt.Errorf("error loading recached emoji: %w", err))
		}
	}

	switch emojiSize {
	case media.SizeOriginal:
		emojiContent.ContentType = e.ImageContentType
		emojiContent.ContentLength = int64(e.ImageFileSize)
		storagePath = e.ImagePath
	case media.SizeStatic:
		emojiContent.ContentType = e.ImageStaticContentType
		emojiContent.ContentLength = int64(e.ImageStaticFileSize)
		storagePath = e.ImageStaticPath
	default:
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("media size %s not recognized for emoji", emojiSize))
	}

	return p.retrieveFromStorage(ctx, storagePath, emojiContent)
}

func (p *Processor) retrieveFromStorage(ctx context.Context, storagePath string, content *apimodel.Content) (*apimodel.Content, gtserror.WithCode) {
	// If running on S3 storage with proxying disabled then
	// just fetch a pre-signed URL instead of serving the content.
	if url := p.state.Storage.URL(ctx, storagePath); url != nil {
		content.URL = url
		return content, nil
	}

	reader, err := p.state.Storage.GetStream(ctx, storagePath)
	if err != nil {
		return nil, gtserror.NewErrorNotFound(fmt.Errorf("error retrieving from storage: %s", err))
	}

	content.Content = reader
	return content, nil
}