1 files changed, 91 insertions, 0 deletions
diff --git a/prefabs.scm b/prefabs.scm
new file mode 100644
index 0000000..56bc60a
--- /dev/null
+++ b/prefabs.scm
@@ -0,0 +1,91 @@
+(module downstroke-prefabs *
+  (import scheme
+          (chicken base)
+          (chicken keyword)
+          (chicken port)
+          defstruct
+          downstroke-entity
+          downstroke-ai)
+
+  ;; Registry struct to hold prefab data
+  (defstruct prefab-registry
+    prefabs file engine-mixin-table user-hooks hook-table)
+
+  ;; Return engine's built-in mixin table
+  (define (engine-mixins)
+    '((physics-body #:vx 0 #:vy 0 #:ay 0 #:gravity? #t #:solid? #t #:on-ground? #f)
+      (has-facing   #:facing 1)
+      (animated     #:anim-name idle #:anim-frame 0 #:anim-tick 0 #:tile-id 0)
+      (ai-body      #:ai-facing 1 #:ai-machine #f #:chase-origin-x 0 #:disabled #f)))
+
+  ;; Compose a prefab entry with mixin table
+  ;; Returns (name . merged-plist)
+  (define (compose-prefab entry mixin-table)
+    (let* ((name (car entry))
+           (rest (cdr entry))
+           (split (let loop ((lst rest) (mixins '()))
+                    (if (or (null? lst) (keyword? (car lst)))
+                        (cons (reverse mixins) lst)
+                        (loop (cdr lst) (cons (car lst) mixins)))))
+           (mixin-names  (car split))
+           (inline-fields (cdr split))
+           (mixin-plists
+             (map (lambda (mname)
+                    (let ((m (assq mname mixin-table)))
+                      (if m (cdr m) (error "Unknown mixin" mname))))
+                  mixin-names))
+           ;; inline-fields prepended → first-match semantics give them highest priority
+           (merged (apply append inline-fields mixin-plists)))
+      (cons name merged)))
+
+  ;; Engine-level hooks
+  (define *engine-hooks*
+    `((init-enemy-ai . ,(lambda (e) (entity-set e #:ai-machine (make-enemy-ai-machine))))))
+
+  ;; Lookup a hook symbol in the hook table
+  (define (lookup-hook hook-table hook-sym)
+    (let ((entry (assq hook-sym hook-table)))
+      (if entry
+          (cdr entry)
+          (error "Unknown prefab hook" hook-sym))))
+
+  (define (load-prefabs file engine-mixin-table user-hooks)
+    (let* ((data (with-input-from-file file read))
+           (mixin-section  (cdr (assq 'mixins data)))
+           (prefab-section (cdr (assq 'prefabs data)))
+           ;; user mixins first → user wins on assq lookup (overrides engine mixin by name)
+           (user-mixin-table (map (lambda (m) (cons (car m) (cdr m))) mixin-section))
+           (merged-mixin-table (append user-mixin-table engine-mixin-table))
+           ;; user-hooks first → user wins on assq lookup (overrides engine hooks by name)
+           (hook-table (append user-hooks *engine-hooks*))
+           (prefab-table (map (lambda (entry) (compose-prefab entry merged-mixin-table))
+                              prefab-section)))
+      (make-prefab-registry
+        prefabs:            prefab-table
+        file:               file
+        engine-mixin-table: engine-mixin-table
+        user-hooks:         user-hooks
+        hook-table:         hook-table)))
+
+  (define (reload-prefabs! registry)
+    (load-prefabs (prefab-registry-file               registry)
+                  (prefab-registry-engine-mixin-table registry)
+                  (prefab-registry-user-hooks         registry)))
+
+  (define (instantiate-prefab registry type x y w h)
+    (if (not registry)
+        #f
+        (let ((entry (assq type (prefab-registry-prefabs registry))))
+          (if (not entry)
+              #f
+              ;; instance fields prepended → highest priority
+              (let* ((base (append (list #:x x #:y y #:width w #:height h)
+                                   (cdr entry)))
+                     (hook-val (entity-ref base #:on-instantiate #f))
+                     (handler
+                       (cond
+                         ((procedure? hook-val) hook-val)
+                         ((symbol?    hook-val)
+                          (lookup-hook (prefab-registry-hook-table registry) hook-val))
+                         (else #f))))
+                (if handler (handler base) base)))))))