From 61eed33ee7a89b8db304ff33e0b7b08aad321f0d Mon Sep 17 00:00:00 2001
From: Case Duckworth
Date: Wed, 8 Mar 2023 09:10:24 -0600
Subject: Initial commit

---
 vellum | 170 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 170 insertions(+)
 create mode 100755 vellum

diff --git a/vellum b/vellum
new file mode 100755
index 0000000..b436b6c
--- /dev/null
+++ b/vellum
@@ -0,0 +1,170 @@
+#!/bin/sh
+
+# https://unix.stackexchange.com/a/464963
+readc() { # arg: <variable-name>
+	if [ -t 0 ]; then
+		# if stdin is a tty device, put it out of icanon, set min and
+		# time to sane value, but don't otherwise touch other input or
+		# or local settings (echo, isig, icrnl...). Take a backup of the
+		# previous settings beforehand.
+		saved_tty_settings=$(stty -g)
+		stty -icanon min 1 time 0
+	fi
+	eval "$1="
+	while
+		# read one byte, using a work around for the fact that command
+		# substitution strips the last character.
+		c=$(dd bs=1 count=1 2> /dev/null; echo .)
+		c=${c%.}
+
+		# break out of the loop on empty input (eof) or if a full character
+		# has been accumulated in the output variable (using "wc -m" to count
+		# the number of characters).
+		[ -n "$c" ] &&
+			eval "$1=\${$1}"'$c
+	  [ "$(($(printf %s "${'"$1"'}" | wc -m)))" -eq 0 ]'; do
+		continue
+	done
+	if [ -t 0 ]; then
+		# restore settings saved earlier if stdin is a tty device.
+		stty "$saved_tty_settings"
+	fi
+}
+
+setup_terminal() {
+	# Setup the terminal for the TUI.
+	# '\e[?1049h': Use alternative screen buffer.
+	# '\e[?7l':    Disable line wrapping.
+	# '\e[?25l':   Hide the cursor.
+	# '\e[2J':     Clear the screen.
+	# '\e[1;Nr':   Limit scrolling to scrolling area.
+	#              Also sets cursor to (0,0).
+	printf '\e[?1049h\e[?7l\e[2J\e[1;%sr' "$((LINES - 1))"
+
+	# Hide echoing of user input
+	stty -echo
+}
+
+reset_terminal() {
+	# Reset the terminal to a useable state (undo all changes).
+	# '\e[?7h':   Re-enable line wrapping.
+	# '\e[?25h':  Unhide the cursor.
+	# '\e[2J':    Clear the terminal.
+	# '\e[;r':    Set the scroll region to its default value.
+	#             Also sets cursor to (0,0).
+	# '\e[?1049l: Restore main screen buffer.
+	printf '\e[?7h\e[?25h\e[2J\e[;r\e[?1049l'
+
+	# Show user input.
+	stty echo
+}
+
+printlines() { # printlines file min max
+	if test -n "$DEBUG"; then
+		echo --- >&2
+	else
+		clear
+	fi
+	sed -n "$2,$3p" "$1"
+	notify_flush
+}
+
+notify() { # notify STRING
+	notification="$notification$1"
+}
+
+notify_flush() { # notify_flush
+	winch
+	printf '\e[s\e[%s;%sH' 0 "$c"
+	printf '%s' "$notification"
+	printf '\e[u'
+	notification=
+}
+
+scroll() { # scroll nlines -- MUTATES GLOBAL STATE
+	case "${1:-0}" in
+		\+*|\-*) n=$((n+$1)) ;;
+		0) ;;
+		*) n=$1 ;;
+	esac
+
+	if test $n -gt $((max - l))
+	then
+		n=$((max - l))
+		notify '_'
+	fi
+
+	if test $n -lt $min
+	then
+		notify '^'
+		n=$min
+	fi
+
+	m=$((n+l))
+	if $m -ge $max
+	then
+		m=$max
+	fi
+	# echo "min:$min max:$max n:$n m:$m l:$l" >&2
+}
+
+ctty() { # ctty
+	## Get the controlling TTY interface.
+	tty <&2 || # only works if not redirecting stderr
+		echo /proc/self/fd/1 # probably only works on linux
+}
+
+winch() {
+	stty size > "$wf"
+	read -r l c < "$wf"
+	# echo l:$l c:$c >&2
+	l=$((l-2)) # last line
+}
+
+cleanup() {
+	rm "$bf" "$wf"
+	reset_terminal
+	exit
+}
+
+vellum() { # vellum [-n NUM] < INPUT
+	# Set up buffer
+	bf="$(mktemp)" # buffer
+	cat "${@:--}" > "$bf"
+	# Redirect input to the controlling terminal
+	## XXX: This assumes that you haven't redirected stderr.
+	exec < "$(ctty)"
+	max=$(wc -l < "$bf")
+	min=1 # min = minimum accessible line num.
+	n=$min # n = num. first line to show
+
+	# Set up terminal
+	setup_terminal
+	wf="$(mktemp)" # winch file
+	winch; trap winch WINCH
+	m=$((n+l)) # m = num. last line to show
+
+	trap cleanup EXIT INT QUIT
+
+	# Main loop
+	while :; do
+		scroll
+		printlines "$bf" $n $m
+
+		readc key >/dev/null 2>&1
+		case "$key" in
+			' ') scroll +$l ;;
+			'') scroll -$l ;;
+			j) scroll +1 ;;
+			k) scroll -1 ;;
+			g) scroll $min ;;
+			G) scroll $max ;;
+			q) break ;;
+		esac
+	done
+	break
+	echo
+}
+
+test -n "$DEBUG" && { set -x; exec 2> /tmp/vellum.log; }
+test -z "$SOURCE" && vellum "$@"
-- 
cgit 1.4.1-21-gabe81