v0.0.2: modern backend — raw escape sequences

Implements the modern-backend with truecolor SGR, Unicode box-drawing
(rounded/double/single), DECICM synchronized updates, OSC 8 hyperlinks,
cursor style control, and hex color parsing.

RED: 32 checks, 5 fail (class forward-ref + test bug)
GREEN: 32/32 checks passing (100%)

- backend/modern.lisp — escape generators + modern-backend class
- backend/modern-tests.lisp — 16 test cases, 32 assertions
- backend/package.lisp — updated exports
- org/modern-backend.org — literate source

backend/modern.lisp

@@ -0,0 +1,245 @@
+;;; modern-backend — Raw escape sequence backend
+;;; Generated from org/modern-backend.org
+;;; DO NOT EDIT — edit the .org file instead
+
+;; In package.lisp, add to :export:
+;;   #:modern-backend #:make-modern-backend
+;; Internal symbols (not exported, used by tests):
+;;   sgr-fg sgr-bg sgr-attr cursor-move-escape cursor-style-escape
+;;   decicm-begin decicm-end osc8-link hex-to-rgb border-char
+
+(in-package :cl-tui.backend)
+
+(defun hex-to-rgb (hex)
+  "Parse a hex color string like \"#FFD700\" into (values r g b).
+  Also handles 3-digit hex like \"#F00\" (expands to \"#FF0000\")."
+  (let ((clean (string-trim '(#\# #\Space) hex)))
+    (if (= (length clean) 3)
+        ;; Expand 3-digit: #F00 -> #FF0000
+        (let* ((r (parse-integer (subseq clean 0 1) :radix 16 :junk-allowed t))
+               (g (parse-integer (subseq clean 1 2) :radix 16 :junk-allowed t))
+               (b (parse-integer (subseq clean 2 3) :radix 16 :junk-allowed t)))
+          (values (+ r (* r 16)) (+ g (* g 16)) (+ b (* b 16))))
+        (values (parse-integer (subseq clean 0 2) :radix 16 :junk-allowed t)
+                (parse-integer (subseq clean 2 4) :radix 16 :junk-allowed t)
+                (parse-integer (subseq clean 4 6) :radix 16 :junk-allowed t)))))
+
+(defparameter *named-colors*
+  '((:black . 0) (:red . 1) (:green . 2) (:yellow . 3)
+    (:blue . 4) (:magenta . 5) (:cyan . 6) (:white . 7)))
+
+(defun sgr-fg (color)
+  "Return SGR foreground escape for COLOR.
+  Color can be a hex string, a keyword name, or nil."
+  (if (null color) ""
+      (cond ((and (stringp color) (char= (char color 0) #\#))
+             (multiple-value-bind (r g b) (hex-to-rgb color)
+               (format nil "~C[38;2;~d;~d;~dm" #\Esc r g b)))
+            ((keywordp color)
+             (let ((index (cdr (assoc color *named-colors*))))
+               (if index
+                   (format nil "~C[~dm" #\Esc (+ 30 index))
+                   "")))
+            (t ""))))
+
+(defun sgr-bg (color)
+  "Return SGR background escape for COLOR."
+  (if (null color) ""
+      (cond ((and (stringp color) (char= (char color 0) #\#))
+             (multiple-value-bind (r g b) (hex-to-rgb color)
+               (format nil "~C[48;2;~d;~d;~dm" #\Esc r g b)))
+            ((keywordp color)
+             (let ((index (cdr (assoc color *named-colors*))))
+               (if index
+                   (format nil "~C[~dm" #\Esc (+ 40 index))
+                   "")))
+            (t ""))))
+
+(defparameter *sgr-attr-codes*
+  '((:bold . 1) (:dim . 2) (:italic . 3) (:underline . 4)
+    (:blink . 5) (:reverse . 7) (:reset . 0)))
+
+(defun sgr-attr (attr)
+  "Return SGR attribute escape for ATTR keyword."
+  (let ((code (cdr (assoc attr *sgr-attr-codes*))))
+    (if code
+        (format nil "~C[~dm" #\Esc code)
+        "")))
+
+(defun cursor-move-escape (x y)
+  "Return CSI escape to move cursor to (x, y), 1-indexed."
+  (format nil "~C[~d;~dH" #\Esc (1+ y) (1+ x)))
+
+(defun cursor-style-escape (shape blink)
+  "Return DECSTR escape for cursor shape.
+  :block = 2, :underline = 4, :bar = 6.
+  Add 1 for blink variants."
+  (let* ((base (case shape
+                 (:block 2) (:underline 4) (:bar 6)
+                 (t 2)))
+         (code (if blink (1+ base) base)))
+    (format nil "~C[~d q" #\Esc code)))
+
+(defun decicm-begin ()
+  "Return escape to enable synchronized updates."
+  (format nil "~C[?2026h" #\Esc))
+
+(defun decicm-end ()
+  "Return escape to disable synchronized updates."
+  (format nil "~C[?2026l" #\Esc))
+
+(defun osc8-link (url text)
+  "Wrap TEXT in an OSC 8 hyperlink to URL."
+  (format nil "~C]8;;~A~C\\~A~C]8;;~C\\"
+          #\Esc url #\Esc text #\Esc #\Esc))
+
+(defparameter *border-chars*
+  '(((:single :top-left) . "┌") ((:single :top-right) . "┐")
+    ((:single :bottom-left) . "└") ((:single :bottom-right) . "┘")
+    ((:single :horizontal) . "─") ((:single :vertical) . "│")
+    ((:double :top-left) . "╔") ((:double :top-right) . "╗")
+    ((:double :bottom-left) . "╚") ((:double :bottom-right) . "╝")
+    ((:double :horizontal) . "═") ((:double :vertical) . "║")
+    ((:rounded :top-left) . "╭") ((:rounded :top-right) . "╮")
+    ((:rounded :bottom-left) . "╰") ((:rounded :bottom-right) . "╯")
+    ((:rounded :horizontal) . "─") ((:rounded :vertical) . "│")))
+
+(defun border-char (style pos)
+  "Return the Unicode box-drawing character for STYLE at POS."
+  (let ((char (cdr (assoc (list style pos) *border-chars* :test #'equal))))
+    (or char (if (member pos '(:horizontal :vertical))
+                 (case pos (:horizontal "─") (:vertical "│"))
+                 "+"))))
+
+(defclass modern-backend ()
+  ((output-stream :initform *standard-output*
+                  :accessor backend-output-stream)
+   (in-sync-p :initform nil :accessor in-sync-p)))
+
+(defun make-modern-backend (&key color-palette)
+  (declare (ignore color-palette))
+  (make-instance 'modern-backend))
+
+(defmethod initialize-backend ((b modern-backend))
+  ;; Enter raw mode, enable mouse, bracketed paste
+  (backend-write b (format nil "~C[?1049h" #\Esc))  ; alt screen
+  (backend-write b (format nil "~C[?1000h" #\Esc))  ; mouse basic
+  (backend-write b (format nil "~C[?1002h" #\Esc))  ; mouse drag
+  (backend-write b (format nil "~C[?1006h" #\Esc))  ; SGR mouse
+  (backend-write b (format nil "~C[?2004h" #\Esc))  ; bracketed paste
+  (cursor-hide b)
+  (finish-output (backend-output-stream b))
+  b)
+
+(defmethod shutdown-backend ((b modern-backend))
+  (cursor-show b)
+  (backend-write b (format nil "~C[?2004l" #\Esc))  ; disable bracketed paste
+  (backend-write b (format nil "~C[?1006l" #\Esc))  ; disable SGR mouse
+  (backend-write b (format nil "~C[?1002l" #\Esc))
+  (backend-write b (format nil "~C[?1000l" #\Esc))
+  (backend-write b (format nil "~C[?1049l" #\Esc))  ; normal screen
+  (finish-output (backend-output-stream b))
+  (values))
+
+(defmethod backend-size ((b modern-backend))
+  ;; Default fallback — real implementation queries terminal
+  (values 80 24))
+
+(defmethod backend-write ((b modern-backend) string)
+  (let ((stream (backend-output-stream b)))
+    (write-string string stream)
+    (length string)))
+
+(defmethod capable-p ((b modern-backend) feature)
+  (member feature '(:truecolor :osc8 :sync :mouse
+                    :bracketed-paste :cursor-style
+                    :kitty-keyboard)))
+
+(defmethod draw-text ((b modern-backend) x y string fg bg
+                      &key bold italic underline reverse dim blink)
+  (let ((parts (list (cursor-move-escape x y)
+                     (sgr-fg fg) (sgr-bg bg)
+                     (when bold (sgr-attr :bold))
+                     (when italic (sgr-attr :italic))
+                     (when underline (sgr-attr :underline))
+                     (when reverse (sgr-attr :reverse))
+                     (when dim (sgr-attr :dim))
+                     (when blink (sgr-attr :blink))
+                     string
+                     (sgr-attr :reset))))
+    (backend-write b (apply #'concatenate 'string parts))))
+
+(defmethod draw-border ((b modern-backend) x y width height
+                        &key style fg bg title title-align)
+  (declare (ignore title title-align))
+  (let* ((s (or style :single))
+         (tl (border-char s :top-left))
+         (tr (border-char s :top-right))
+         (bl (border-char s :bottom-left))
+         (br (border-char s :bottom-right))
+         (h  (border-char s :horizontal))
+         (v  (border-char s :vertical))
+         (fg-esc (sgr-fg fg))
+         (bg-esc (sgr-bg bg))
+         (reset (sgr-attr :reset))
+         (top (concatenate 'string
+                fg-esc bg-esc tl
+                (make-string (- width 2) :initial-element (char h 0))
+                tr reset (string #\Newline)))
+         (mid (concatenate 'string
+                fg-esc bg-esc v
+                (make-string (- width 2) :initial-element #\Space)
+                v reset (string #\Newline)))
+         (bot (concatenate 'string
+                fg-esc bg-esc bl
+                (make-string (- width 2) :initial-element (char h 0))
+                br reset)))
+    (backend-write b top)
+    (loop repeat (- height 2) do (backend-write b mid))
+    (backend-write b bot)))
+
+(defmethod draw-rect ((b modern-backend) x y width height &key bg)
+  (let ((bg-esc (sgr-bg bg))
+        (reset (sgr-attr :reset))
+        (line (concatenate 'string
+                bg-esc
+                (make-string width :initial-element #\Space)
+                reset (string #\Newline))))
+    (loop repeat height do
+      (backend-write b (cursor-move-escape x y))
+      (backend-write b line))))
+
+(defmethod draw-link ((b modern-backend) x y string url
+                      &key fg bg)
+  (let ((parts (list (cursor-move-escape x y)
+                     (sgr-fg fg) (sgr-bg bg)
+                     (osc8-link url string)
+                     (sgr-attr :reset))))
+    (backend-write b (apply #'concatenate 'string parts))))
+
+(defmethod draw-ellipsis ((b modern-backend) x y width
+                          &key fg bg)
+  (let ((dots "..."))
+    (draw-text b x y dots fg bg)))
+
+(defmethod cursor-move ((b modern-backend) x y)
+  (backend-write b (cursor-move-escape x y)))
+
+(defmethod cursor-hide ((b modern-backend))
+  (backend-write b (format nil "~C[?25l" #\Esc)))
+
+(defmethod cursor-show ((b modern-backend))
+  (backend-write b (format nil "~C[?25h" #\Esc)))
+
+(defmethod cursor-style ((b modern-backend) shape &key blink)
+  (backend-write b (cursor-style-escape shape blink)))
+
+(defmethod begin-sync ((b modern-backend))
+  (setf (in-sync-p b) t)
+  (backend-write b (decicm-begin)))
+
+(defmethod end-sync ((b modern-backend))
+  (setf (in-sync-p b) nil)
+  (backend-write b (decicm-end))
+  (finish-output (backend-output-stream b)))
+