f1ad2033144e

--- a/src/main.lisp	Tue Nov 28 18:48:55 2017 -0500
+++ b/src/main.lisp	Tue Nov 28 20:43:25 2017 -0500
@@ -1,1 +1,125 @@
 (in-package :trivial-ppm)
+
+;;;; Utils --------------------------------------------------------------------
+(defun skip-comment (stream)
+  (peek-char #\newline stream nil nil)
+  (read-char stream nil nil))
+
+(defun skip-whitespace (stream)
+  (when (eql #\# (peek-char t stream nil nil))
+    (skip-comment stream)))
+
+(defun peek (stream)
+  (peek-char nil stream nil nil))
+
+
+(defun read-number (stream)
+  (skip-whitespace stream)
+  (loop :with i = 0
+        :for ch = (peek stream)
+        :while ch
+        :for digit = (digit-char-p ch)
+        :while digit
+        :do (read-char stream)
+        :do (setf i (+ (* i 10) digit))
+        :finally (return i)))
+
+(defun read-magic-byte (stream)
+  (assert (eql (read-char stream) #\P))
+  (read-char stream))
+
+(defun read-header (stream)
+  (values (read-number stream)
+          (read-number stream)
+          (read-number stream)))
+
+
+(defun file-format (magic-byte)
+  (ecase magic-byte
+    (#\1 :pbm-ascii)
+    (#\2 :pgm-ascii)
+    (#\3 :ppm-ascii)
+    (#\4 :pbm-binary)
+    (#\5 :pgm-binary)
+    (#\6 :ppm-binary)))
+
+(defun magic-byte (file-format)
+  (ecase file-format
+    (:pbm-ascii #\1)
+    (:pgm-ascii #\2)
+    (:ppm-ascii #\3)
+    (:pbm-binary #\4)
+    (:pgm-binary #\5)
+    (:ppm-binary #\6)))
+
+
+;;;; PPM ----------------------------------------------------------------------
+(declaim (inline read-ppm-from-stream))
+
+(defun read-ppm-from-stream (reader stream binary?)
+  (multiple-value-bind (width height bit-depth)
+      (read-header stream)
+    (let ((data (make-array (list height width)
+                  :element-type `(simple-array (integer 0 ,bit-depth) (3)))))
+      (when binary?
+        (read-char stream)) ; chomp last newline before bytes
+      (dotimes (y height)
+        (dotimes (x width)
+          (setf (aref data y x)
+                (make-array 3 :initial-contents (list (funcall reader stream)
+                                                      (funcall reader stream)
+                                                      (funcall reader stream))
+                  :element-type 'fixnum))))
+      data)))
+
+
+(defun read-ppm-ascii-from-stream (stream)
+  (read-ppm-from-stream #'read-number stream nil))
+
+(defun read-ppm-binary-from-stream (stream)
+  (read-ppm-from-stream #'read-byte stream t))
+
+
+(defun write-pixel-ascii (stream pixel)
+  (format stream "~D ~D ~D "
+          (aref pixel 0)
+          (aref pixel 1)
+          (aref pixel 2)))
+
+(defun write-pixel-binary (stream pixel)
+  (write-byte (aref pixel 0) stream)
+  (write-byte (aref pixel 1) stream)
+  (write-byte (aref pixel 2) stream))
+
+
+(declaim (inline write-ppm-to-stream))
+
+(defun write-ppm-to-stream (file-format data stream maximum-value writer)
+  (let ((stream (flexi-streams:make-flexi-stream stream :external-format :ascii)))
+    (destructuring-bind (height width) (array-dimensions data)
+      (format stream "P~D~%~D ~D~%~D~%"
+              (magic-byte file-format) width height maximum-value)
+      (dotimes (row height)
+        (dotimes (col width)
+          (funcall writer stream (aref data row col)))))))
+
+(defun write-ppm-ascii-to-stream (data stream maximum-value)
+  (write-ppm-to-stream :ppm-ascii data stream maximum-value #'write-pixel-ascii))
+
+(defun write-ppm-binary-to-stream (data stream maximum-value)
+  (write-ppm-to-stream :ppm-binary data stream maximum-value #'write-pixel-binary))
+
+
+;;;; API ----------------------------------------------------------------------
+(defun read-from-stream (stream)
+  (let ((stream (flexi-streams:make-flexi-stream stream :external-format :ascii)))
+    (ecase (file-format (read-magic-byte stream))
+      (:ppm-ascii (read-ppm-ascii-from-stream stream))
+      (:ppm-binary (read-ppm-binary-from-stream stream)))))
+
+(defun write-to-stream (stream data &key
+                        (maximum-value 255)
+                        (format :binary))
+  (ccase format
+    (:ascii (write-ppm-ascii-to-stream data stream maximum-value))
+    (:binary (write-ppm-binary-to-stream data stream maximum-value))))

--- a/trivial-ppm.asd	Tue Nov 28 18:48:55 2017 -0500
+++ b/trivial-ppm.asd	Tue Nov 28 20:43:25 2017 -0500
@@ -6,7 +6,7 @@
 
   :license "MIT/X11"
 
-  :depends-on ()
+  :depends-on (:flexi-streams)
 
   :serial t
   :components ((:module "vendor" :serial t