Cast empty Collections to null, Cast strings to zstd compressed strings, add msg_src to echomails processed, fix duplicate seenbys

app/Casts/CompressedString.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace App\Casts;
+
+use Illuminate\Contracts\Database\Eloquent\CastsAttributes;
+use Illuminate\Database\Eloquent\Model;
+
+class CompressedString implements CastsAttributes
+{
+	/**
+	 * Cast the given value.
+	 *
+	 * @param  \Illuminate\Database\Eloquent\Model  $model
+	 * @param  string  $key
+	 * @param  mixed  $value
+	 * @param  array  $attributes
+	 * @return string
+	 */
+	public function get($model, string $key, $value, array $attributes): string
+	{
+		return zstd_uncompress(base64_decode($value));
+	}
+
+	/**
+	 * Prepare the given value for storage.
+	 *
+	 * @param Model $model
+	 * @param string $key
+	 * @param mixed $value
+	 * @param array $attributes
+	 * @return string|null
+	 */
+	public function set($model, string $key, $value, array $attributes): ?string
+	{
+		return $value ? base64_encode(zstd_compress($value)) : NULL;
+	}
+}