[chore] media and emoji refactoring (#3000)

* start updating media manager interface ready for storing attachments / emoji right away

* store emoji and media as uncached immediately, then (re-)cache on Processing{}.Load()

* remove now unused media workers

* fix tests and issues

* fix another test!

* fix emoji activitypub uri setting behaviour, fix remainder of test compilation issues

* fix more tests

* fix (most of) remaining tests, add debouncing to repeatedly failing media / emojis

* whoops, rebase issue

* remove kim's whacky experiments

* do some reshuffling, ensure emoji uri gets set

* ensure marked as not cached on cleanup

* tweaks to media / emoji processing to handle context canceled better

* ensure newly fetched emojis actually get set in returned slice

* use different varnames to be a bit more obvious

* move emoji refresh rate limiting to dereferencer

* add exported dereferencer functions for remote media, use these for recaching in processor

* add check for nil attachment in updateAttachment()

* remove unused emoji and media fields + columns

* see previous commit

* fix old migrations expecting image_updated_at to exists (from copies of old models)

* remove freshness checking code (seems to be broken...)

* fix error arg causing nil ptr exception

* finish documentating functions with comments, slight tweaks to media / emoji deref error logic

* remove some extra unneeded boolean checking

* finish writing documentation (code comments) for exported media manager methods

* undo changes to migration snapshot gtsmodels, updated failing migration to have its own snapshot

* move doesColumnExist() to util.go in migrations package

1 files changed, 20 insertions, 104 deletions

diff --git a/internal/federation/dereferencing/util.go b/internal/federation/dereferencing/util.go
index 5cb7a0106..297e90adc 100644
--- a/internal/federation/dereferencing/util.go
+++ b/internal/federation/dereferencing/util.go
@@ -18,120 +18,36 @@
 package dereferencing
 
 import (
-	"context"
-	"io"
-	"net/url"
 	"slices"
 
-	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
-	"github.com/superseriousbusiness/gotosocial/internal/media"
-	"github.com/superseriousbusiness/gotosocial/internal/transport"
-	"github.com/superseriousbusiness/gotosocial/internal/util"
 )
 
-// loadAttachment handles the case of a new media attachment
-// that requires loading. it stores and caches from given data.
-func (d *Dereferencer) loadAttachment(
-	ctx context.Context,
-	tsport transport.Transport,
-	accountID string, // media account owner
-	remoteURL string,
-	info *media.AdditionalMediaInfo,
+// getEmojiByShortcodeDomain searches input slice
+// for emoji with given shortcode and domain.
+func getEmojiByShortcodeDomain(
+	emojis []*gtsmodel.Emoji,
+	shortcode string,
+	domain string,
 ) (
-	*gtsmodel.MediaAttachment,
-	error,
+	*gtsmodel.Emoji,
+	bool,
 ) {
-	// Parse str as valid URL object.
-	url, err := url.Parse(remoteURL)
-	if err != nil {
-		return nil, gtserror.Newf("invalid remote media url %q: %v", remoteURL, err)
-	}
-
-	// Start pre-processing remote media at remote URL.
-	processing := d.mediaManager.PreProcessMedia(
-		func(ctx context.Context) (io.ReadCloser, int64, error) {
-			return tsport.DereferenceMedia(ctx, url)
-		},
-		accountID,
-		info,
-	)
-
-	// Force attachment loading *right now*.
-	return processing.LoadAttachment(ctx)
-}
-
-// updateAttachment handles the case of an existing media attachment
-// that *may* have changes or need recaching. it checks for changed
-// fields, updating in the database if so, and recaches uncached media.
-func (d *Dereferencer) updateAttachment(
-	ctx context.Context,
-	tsport transport.Transport,
-	existing *gtsmodel.MediaAttachment, // existing attachment
-	media *gtsmodel.MediaAttachment, // (optional) changed media
-) (
-	*gtsmodel.MediaAttachment, // always set
-	error,
-) {
-	if media != nil {
-		// Possible changed media columns.
-		changed := make([]string, 0, 3)
-
-		// Check if attachment description has changed.
-		if existing.Description != media.Description {
-			changed = append(changed, "description")
-			existing.Description = media.Description
+	for _, emoji := range emojis {
+		if emoji.Shortcode == shortcode &&
+			emoji.Domain == domain {
+			return emoji, true
 		}
-
-		// Check if attachment blurhash has changed (i.e. content change).
-		if existing.Blurhash != media.Blurhash && media.Blurhash != "" {
-			changed = append(changed, "blurhash", "cached")
-			existing.Blurhash = media.Blurhash
-			existing.Cached = util.Ptr(false)
-		}
-
-		if len(changed) > 0 {
-			// Update the existing attachment model in the database.
-			err := d.state.DB.UpdateAttachment(ctx, existing, changed...)
-			if err != nil {
-				return media, gtserror.Newf("error updating media: %w", err)
-			}
-		}
-	}
-
-	// Check if cached.
-	if *existing.Cached {
-		return existing, nil
-	}
-
-	// Parse str as valid URL object.
-	url, err := url.Parse(existing.RemoteURL)
-	if err != nil {
-		return nil, gtserror.Newf("invalid remote media url %q: %v", media.RemoteURL, err)
 	}
+	return nil, false
+}
 
-	// Start pre-processing remote media recaching from remote.
-	processing, err := d.mediaManager.PreProcessMediaRecache(
-		ctx,
-		func(ctx context.Context) (io.ReadCloser, int64, error) {
-			return tsport.DereferenceMedia(ctx, url)
-		},
-		existing.ID,
-	)
-	if err != nil {
-		return nil, gtserror.Newf("error processing recache: %w", err)
-	}
-
-	// Force load attachment recache *right now*.
-	recached, err := processing.LoadAttachment(ctx)
-
-	// Always return the error we
-	// receive, but ensure we return
-	// most up-to-date media file.
-	if recached != nil {
-		return recached, err
-	}
-	return existing, err
+// emojiChanged returns whether an emoji has changed in a way
+// that indicates that it should be refetched and refreshed.
+func emojiChanged(existing, latest *gtsmodel.Emoji) bool {
+	return existing.URI != latest.URI ||
+		existing.ImageRemoteURL != latest.ImageRemoteURL ||
+		existing.ImageStaticRemoteURL != latest.ImageStaticRemoteURL
 }
 
 // pollChanged returns whether a poll has changed in way that