fix: ImportPostcodes streams into staging, swaps on success

Audit item #13. The command truncated postcodes + outcodes immediately
and then chunk-inserted from the CSV. A mid-stream failure (network
drive disconnect, malformed row) left the production tables empty
until a successful re-run.

Now streams into a postcodes_staging table created via Schema::create
(works on both MySQL and SQLite) and only swaps into the live tables
once the full CSV has been consumed. A try/finally ensures the file
handle and staging table are cleaned up on any path. Live data is now
preserved on partial failures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Console/Commands/ImportPostcodes.php

@@ -5,7 +5,10 @@ namespace App\Console\Commands;
 use Illuminate\Console\Attributes\Description;
 use Illuminate\Console\Attributes\Signature;
 use Illuminate\Console\Command;
+use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+use Throwable;
 
 #[Signature('postcodes:import {--file= : Path to ONSPD CSV file}')]
 #[Description('Import UK postcodes (ONSPD) into the local postcodes and outcodes tables')]
@@ -79,12 +82,21 @@ final class ImportPostcodes extends Command
 
         $hasDoterm = isset($columns['doterm']);
 
-        DB::table('postcodes')->truncate();
+        // Stream into a staging table first. Only swap into the live
-        DB::table('outcodes')->truncate();
+        // postcodes / outcodes tables once the full CSV has been consumed —
+        // a mid-stream failure leaves production data untouched.
+        Schema::dropIfExists('postcodes_staging');
+        Schema::create('postcodes_staging', function (Blueprint $table): void {
+            $table->string('postcode', 7);
+            $table->string('outcode', 4);
+            $table->decimal('lat', 10, 7);
+            $table->decimal('lng', 10, 7);
+        });
 
         $buffer = [];
         $imported = 0;
 
+        try {
             while (($row = fgetcsv($handle)) !== false) {
                 if ($hasDoterm && trim((string) ($row[$columns['doterm']] ?? '')) !== '') {
                     continue;
@@ -111,23 +123,36 @@ final class ImportPostcodes extends Command
                 ];
 
                 if (count($buffer) >= self::CHUNK_SIZE) {
-                DB::table('postcodes')->insert($buffer);
+                    DB::table('postcodes_staging')->insert($buffer);
                     $imported += count($buffer);
                     $buffer = [];
                 }
             }
 
             if ($buffer !== []) {
-            DB::table('postcodes')->insert($buffer);
+                DB::table('postcodes_staging')->insert($buffer);
                 $imported += count($buffer);
             }
 
-        fclose($handle);
+            // Swap: empty live tables, copy from staging, derive outcodes.
-
+            DB::table('outcodes')->truncate();
+            DB::table('postcodes')->truncate();
+            DB::statement(
+                'INSERT INTO postcodes (postcode, outcode, lat, lng)
+                 SELECT postcode, outcode, lat, lng FROM postcodes_staging'
+            );
             DB::statement(
                 'INSERT INTO outcodes (outcode, lat, lng)
                  SELECT outcode, AVG(lat), AVG(lng) FROM postcodes GROUP BY outcode'
             );
+        } catch (Throwable $e) {
+            $this->error('Import failed — live tables left untouched: '.$e->getMessage());
+
+            return self::FAILURE;
+        } finally {
+            fclose($handle);
+            Schema::dropIfExists('postcodes_staging');
+        }
 
         $this->info("Imported {$imported} postcodes.");
         $this->info('Derived '.DB::table('outcodes')->count().' outcode centroids.');