Simplify file creation branch of process_rule.zig

Still not quite where I want it, but definitely better than what it was

src/app/jobs/process_rule.zig

@@ -20,18 +20,25 @@ pub fn run(allocator: std.mem.Allocator, params: *jetzig.data.Value, env: jetzig
     };
 
     const Rules = struct {
-        rules: []Rule,
+        rules: []const Rule,
     };
 
     const rule = try std.json.parseFromSliceLeaky(Rule, allocator, try params.toJson(), .{ .ignore_unknown_fields = true });
 
     const file_read: std.fs.File = std.fs.cwd().openFile("rules.json", .{}) catch |read_err| switch (read_err) {
-        error.FileNotFound => std.fs.cwd().createFile("rules.json", .{ .read = true, .exclusive = true }) catch |write_err| switch (write_err) {
-            error.PathAlreadyExists => unreachable,
-            else => {
-                std.log.debug("{any} while writing file", .{write_err});
-                return;
-            },
+        error.FileNotFound => {
+            const file = std.fs.cwd().createFile("rules.json", .{ .read = true, .exclusive = true }) catch |write_err| switch (write_err) {
+                error.PathAlreadyExists => unreachable,
+                else => {
+                    std.log.debug("{any} while writing file", .{write_err});
+                    return;
+                },
+            };
+            const out_rules = Rules{ .rules = &[_]Rule{rule} };
+            const out = try std.json.stringifyAlloc(allocator, out_rules, .{});
+            try file.writeAll(out);
+            file.close();
+            return;
         },
         else => {
             std.log.debug("{any} while reading file", .{read_err});
@@ -40,16 +47,19 @@ pub fn run(allocator: std.mem.Allocator, params: *jetzig.data.Value, env: jetzig
     };
 
     var rules = std.ArrayList(Rule).init(allocator);
+    defer rules.deinit();
+
     const file_content = try file_read.readToEndAlloc(allocator, 16_000_000);
-    if (file_content.len != 0) {
-        const content: Rules = try std.json.parseFromSliceLeaky(Rules, allocator, file_content, .{});
-        try rules.appendSlice(content.rules);
-    }
+    const content: Rules = try std.json.parseFromSliceLeaky(Rules, allocator, file_content, .{});
+    try rules.appendSlice(content.rules);
     try rules.append(rule);
     file_read.close();
 
     const file_write: std.fs.File = try std.fs.cwd().openFile("rules.json", .{ .mode = .write_only });
     const out_rules = Rules{ .rules = rules.items };
     const out = try std.json.stringifyAlloc(allocator, out_rules, .{});
+
     try file_write.writeAll(out);
+    file_write.close();
+    return;
 }