Support setting foreground/background colors to terminal defaults (#8073)

* Support setting foreground/background colors to terminal defaults

Adds fgDefault to ForegroundColor and bgDefault to BackgroundColor
enums.

For Windows console, the default foreground color is assumed to be
white, and the default background color black.

* Add default fg/bg color caching for Windows Console

1 files changed, 32 insertions, 8 deletions

diff --git a/lib/pure/terminal.nim b/lib/pure/terminal.nim
index 7ad243150..ac41a0aad 100644
--- a/lib/pure/terminal.nim
+++ b/lib/pure/terminal.nim
@@ -542,7 +542,9 @@ type
     fgBlue,                ## blue
     fgMagenta,             ## magenta
     fgCyan,                ## cyan
-    fgWhite                ## white
+    fgWhite,               ## white
+    fg8Bit,                ## 256-color (not supported, see ``enableTrueColors`` instead.)
+    fgDefault              ## default terminal foreground color
 
   BackgroundColor* = enum  ## terminal's background colors
     bgBlack = 40,          ## black
@@ -552,28 +554,40 @@ type
     bgBlue,                ## blue
     bgMagenta,             ## magenta
     bgCyan,                ## cyan
-    bgWhite                ## white
+    bgWhite,               ## white
+    bg8Bit,                ## 256-color (not supported, see ``enableTrueColors`` instead.)
+    bgDefault              ## default terminal background color
 
 {.deprecated: [TForegroundColor: ForegroundColor,
                TBackgroundColor: BackgroundColor].}
 
+when defined(windows):
+  var defaultForegroundColor, defaultBackgroundColor: int16 = 0xFFFF'i16 # Default to an invalid value 0xFFFF
+
 proc setForegroundColor*(f: File, fg: ForegroundColor, bright=false) =
   ## Sets the terminal's foreground color.
   when defined(windows):
     let h = conHandle(f)
     var old = getAttributes(h) and not FOREGROUND_RGB
+    if defaultForegroundColor == 0xFFFF'i16:
+      defaultForegroundColor = old
     old = if bright: old or FOREGROUND_INTENSITY
           else:      old and not(FOREGROUND_INTENSITY)
     const lookup: array[ForegroundColor, int] = [
-      0,
+      0, # ForegroundColor enum with ordinal 30
       (FOREGROUND_RED),
       (FOREGROUND_GREEN),
       (FOREGROUND_RED or FOREGROUND_GREEN),
       (FOREGROUND_BLUE),
       (FOREGROUND_RED or FOREGROUND_BLUE),
       (FOREGROUND_BLUE or FOREGROUND_GREEN),
-      (FOREGROUND_BLUE or FOREGROUND_GREEN or FOREGROUND_RED)]
-    discard setConsoleTextAttribute(h, toU16(old or lookup[fg]))
+      (FOREGROUND_BLUE or FOREGROUND_GREEN or FOREGROUND_RED),
+      0, # fg8Bit not supported, see ``enableTrueColors`` instead.
+      0] # unused
+    if fg == fgDefault:
+      discard setConsoleTextAttribute(h, toU16(old or defaultForegroundColor))
+    else:
+      discard setConsoleTextAttribute(h, toU16(old or lookup[fg]))
   else:
     gFG = ord(fg)
     if bright: inc(gFG, 60)
@@ -584,18 +598,25 @@ proc setBackgroundColor*(f: File, bg: BackgroundColor, bright=false) =
   when defined(windows):
     let h = conHandle(f)
     var old = getAttributes(h) and not BACKGROUND_RGB
+    if defaultBackgroundColor == 0xFFFF'i16:
+      defaultBackgroundColor = old
     old = if bright: old or BACKGROUND_INTENSITY
           else:      old and not(BACKGROUND_INTENSITY)
     const lookup: array[BackgroundColor, int] = [
-      0,
+      0, # BackgroundColor enum with ordinal 40
       (BACKGROUND_RED),
       (BACKGROUND_GREEN),
       (BACKGROUND_RED or BACKGROUND_GREEN),
       (BACKGROUND_BLUE),
       (BACKGROUND_RED or BACKGROUND_BLUE),
       (BACKGROUND_BLUE or BACKGROUND_GREEN),
-      (BACKGROUND_BLUE or BACKGROUND_GREEN or BACKGROUND_RED)]
-    discard setConsoleTextAttribute(h, toU16(old or lookup[bg]))
+      (BACKGROUND_BLUE or BACKGROUND_GREEN or BACKGROUND_RED),
+      0, # bg8Bit not supported, see ``enableTrueColors`` instead.
+      0] # unused
+    if bg == bgDefault:
+      discard setConsoleTextAttribute(h, toU16(old or defaultBackgroundColor))
+    else:
+      discard setConsoleTextAttribute(h, toU16(old or lookup[bg]))
   else:
     gBG = ord(bg)
     if bright: inc(gBG, 60)
@@ -935,3 +956,6 @@ when not defined(testing) and isMainModule:
   stdout.styledWrite(fgGreen, "green text")
   echo ""
   echo "ordinary text"
+  stdout.styledWriteLine(fgRed, "red text ", styleBright, "bold red", fgDefault, " bold text")
+  stdout.styledWriteLine(bgYellow, "text in yellow bg", styleBright, " bold text in yellow bg", bgDefault, " bold text")
+  echo "ordinary text"