Synced resources - proof of concept

src/Contracts/SyncMaster.php

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+<?php
+
+namespace Stancl\Tenancy\Contracts;
+
+use Illuminate\Database\Eloquent\Collection;
+
+// todo rename?
+/**
+ * @property-read Tenant[]|Collection $tenants
+ */
+interface SyncMaster extends Syncable
+{
+    public function tenants(); // Probably should return BelongsToMany
+}

src/Contracts/Syncable.php

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+<?php
+
+namespace Stancl\Tenancy\Contracts;
+
+// todo add comments
+interface Syncable
+{
+    public function getGlobalIdentifierKeyName(): string;
+    public function getGlobalIdentifierKey(): string;
+    public function getCentralModelName(): string;
+    public function getSyncedAttributeNames(): array;
+}

src/Database/Models/Concerns/ResourceSyncing.php

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+<?php
+
+namespace Stancl\Tenancy\Database\Models\Concerns;
+
+use Stancl\Tenancy\Contracts\Syncable;
+use Stancl\Tenancy\Events\SyncedResourceSaved;
+
+trait ResourceSyncing
+{
+    public static function bootResourceSyncing()
+    {
+        static::saving(function (Syncable $model) {
+            event(new SyncedResourceSaved($model, tenant()));
+        });
+    }
+}

src/Events/Listeners/UpdateSyncedResource.php

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+<?php
+
+namespace Stancl\Tenancy\Events\Listeners;
+
+use Illuminate\Database\Eloquent\Model;
+use Stancl\Tenancy\Contracts\SyncMaster;
+use Stancl\Tenancy\Contracts\Tenant;
+use Stancl\Tenancy\Events\SyncedResourceSaved;
+
+class UpdateSyncedResource
+{
+    public function handle(SyncedResourceSaved $event)
+    {
+        $syncedAttributes = $event->model->only($event->model->getSyncedAttributeNames());
+
+        // We update the central record only if the event comes from tenant context.
+        if ($event->tenant) {
+            /** @var Model|SyncMaster $centralModel */
+            $centralModel = $event->model->getCentralModelName()
+                ::where($event->model->getGlobalIdentifierKeyName(), $event->model->getGlobalIdentifierKey())
+                ->first();
+            
+            // We disable events for this call, to avoid triggering this event & listener again.
+            $centralModel->withoutEvents(function () use ($centralModel, $syncedAttributes) {
+                $centralModel->update($syncedAttributes);
+            });
+
+            $tenants = $centralModel->tenants->except($event->tenant->getTenantKey());
+        } else {
+            $centralModel = $event->model;
+            $tenants = $centralModel->tenants;
+        }
+
+        foreach ($tenants as $tenant) {
+            // todo: performance optimization - $tenant->run() does tenancy()->end() after each call.
+            // we dont want that when we want to initialize for the next tenant afterwards rather than for the previous tenant
+            // so we should write a method like run() for running things on multiple tenants efficiently
+
+            $tenant->run(function () use ($event, $syncedAttributes) {
+                // Forget instance state and find the model,
+                // again in the current tenant's context.
+
+                /** @var Tenant|Model $model */                
+                $localModel = $event->model::find($event->model->getKey());
+
+                // Also: We're syncing attributes, not columns, which is
+                // why we're using Eloquent instead of direct DB queries.
+
+                // We disable events for this call, to avoid triggering this event & listener again.
+                $localModel->update($syncedAttributes);
+            });
+        }
+    }
+}

src/Events/SyncedResourceSaved.php

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+<?php
+
+namespace Stancl\Tenancy\Events;
+
+use Illuminate\Database\Eloquent\Model;
+use Stancl\Tenancy\Contracts\Syncable;
+use Stancl\Tenancy\Contracts\Tenant;
+
+class SyncedResourceSaved
+{
+    /** @var Syncable|Model */
+    public $model;
+
+    /** @var Tenant|Model|null */
+    public $tenant;
+
+    public function __construct(Syncable $model, ?Tenant $tenant)
+    {
+        $this->model = $model;
+        $this->tenant = $tenant;
+    }
+}