merge trails function added (#627)

* merge trails function added

* fix conflict resolve issues

* avoid incorrect authorship when merging trail comments

* require edit access for all selected trails before merge

* fix likes checkbox binding in trail merge modal

* improve error handling

* require editable target and deletable sources for merge

* avoid duplicate trail fetch during merge

* prevent duplicate likes when merging trails

* check photo download responses during trail merge

* add merge completion toast notifications

* cleanup

* small fixes

* move merge code to backend, option to merge single trail selection with similar one, automatic merge for integrations add as option, maintenance page to find and merge similar trails added

* fix build error

* fix

* docu, beautifying, refactoring

---------

Co-authored-by: Flomp <Flomp@users.noreply.github.com>

db/util/trail_external_reference.go

@@ -0,0 +1,130 @@
+package util
+
+import (
+	"fmt"
+
+	"github.com/pocketbase/dbx"
+	"github.com/pocketbase/pocketbase/core"
+)
+
+func FindTrailByExternalReference(app core.App, provider string, externalID string) (*core.Record, error) {
+	if provider == "" || externalID == "" {
+		return nil, nil
+	}
+
+	refs, err := app.FindRecordsByFilter(
+		"trail_external_reference",
+		"provider={:provider} && external_id={:external_id}",
+		"+created",
+		1,
+		0,
+		dbx.Params{
+			"provider":    provider,
+			"external_id": externalID,
+		},
+	)
+	if err != nil || len(refs) == 0 {
+		return nil, err
+	}
+
+	trailID := refs[0].GetString("trail")
+	if trailID == "" {
+		return nil, nil
+	}
+
+	return app.FindRecordById("trails", trailID)
+}
+
+func EnsureTrailExternalReference(app core.App, trailID string, provider string, externalID string) error {
+	if trailID == "" || provider == "" || externalID == "" {
+		return nil
+	}
+
+	refs, err := app.FindRecordsByFilter(
+		"trail_external_reference",
+		"provider={:provider} && external_id={:external_id}",
+		"",
+		1,
+		0,
+		dbx.Params{
+			"provider":    provider,
+			"external_id": externalID,
+		},
+	)
+	if err != nil {
+		return err
+	}
+	if len(refs) > 0 {
+		if refs[0].GetString("trail") == trailID {
+			return nil
+		}
+		return fmt.Errorf("trail external reference already exists for another trail")
+	}
+
+	collection, err := app.FindCollectionByNameOrId("trail_external_reference")
+	if err != nil {
+		return err
+	}
+
+	record := core.NewRecord(collection)
+	record.Load(map[string]any{
+		"trail":       trailID,
+		"provider":    provider,
+		"external_id": externalID,
+	})
+
+	return app.Save(record)
+}
+
+func ReassignTrailExternalReferences(app core.App, sourceTrailID string, targetTrailID string) error {
+	if sourceTrailID == "" || targetTrailID == "" || sourceTrailID == targetTrailID {
+		return nil
+	}
+
+	refs, err := app.FindRecordsByFilter(
+		"trail_external_reference",
+		"trail={:trail}",
+		"",
+		-1,
+		0,
+		dbx.Params{"trail": sourceTrailID},
+	)
+	if err != nil {
+		return err
+	}
+
+	for _, ref := range refs {
+		provider := ref.GetString("provider")
+		externalID := ref.GetString("external_id")
+
+		existing, err := app.FindRecordsByFilter(
+			"trail_external_reference",
+			"trail={:trail} && provider={:provider} && external_id={:external_id}",
+			"",
+			1,
+			0,
+			dbx.Params{
+				"trail":       targetTrailID,
+				"provider":    provider,
+				"external_id": externalID,
+			},
+		)
+		if err != nil {
+			return err
+		}
+
+		if len(existing) > 0 {
+			if err := app.Delete(ref); err != nil {
+				return err
+			}
+			continue
+		}
+
+		ref.Set("trail", targetTrailID)
+		if err := app.Save(ref); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}