1#!/usr/bin/env bash
  2# 
  3# Usage: shlide path/to/slides/
  4# Each slide is a textfile under path/to/slides
  5
  6# Color definitions
  7
  8BLK="\e[30m"
  9RED="\e[31m"
 10GRN="\e[32m"
 11YLW="\e[33m"
 12BLU="\e[34m"
 13PUR="\e[35m"
 14CYN="\e[36m"
 15RST="\e[0m"
 16
 17lines() {
 18    mapfile -tn 0 lines < "$1"
 19    printf '%s\n' "${#lines[@]}"
 20}
 21
 22longest_line() {
 23    max=0 IFS=
 24    while read -r line; do
 25        if [ "${#line}" -gt "$max" ]; then max="${#line}"; fi
 26    done < "$1"
 27    printf '%s\n' "$max"
 28}
 29
 30display() {
 31    # 1 - slide contents
 32    # 2 - slide name
 33
 34    slide_contents="$1"
 35
 36    # Hides the cursor.
 37    printf '\e[?25l'
 38
 39    # Clear the screen.
 40    printf '\e[2J'
 41
 42    # Move the cursor to the center.
 43    read -r LINES COLUMNS < <(stty -F /dev/tty size)
 44    height=$(lines "$2")
 45    width=$(longest_line "$2")
 46
 47    # Rough estimates for the true center.
 48    ((l=$LINES/2 - $height/2))
 49    ((c=$COLUMNS/2 - $width/2))
 50
 51    printf '\e[%s;%sH' "$l" "$c"
 52
 53    while IFS= read -r line; do
 54        # Print the contents of the slide file, 
 55        # line by line.
 56        printf "%s" "$line"
 57        # Move down and back after each print.
 58        printf '\e[%sD\e[B' "${#line}"
 59    done <<< "$slide_contents"
 60
 61}
 62
 63main() {
 64
 65    slides_dir="${1:-./}"
 66    slides=("$slides_dir"/[0-9]*.txt)
 67    i=0
 68    while true; do
 69
 70        # Exit after last slide.
 71        [[ "$i" -gt "$((${#slides[@]} - 1))" ]] && {
 72            printf '\e[?25h'
 73            exit
 74        }
 75
 76        # Don't go below 0.
 77        [[ "$i" -lt 0 ]] && i=0
 78
 79        # Navigate on j/k/n/p and quit on q.
 80        display "$(<${slides[$i]})" "${slides[$i]}"
 81        read -rsn1 input
 82        case "$input" in 
 83            "j"|"n")
 84                ((++i))
 85                ;;
 86            "k"|"p")
 87                ((--i))
 88                ;;
 89            "q")
 90                # Return the cursor on exit.
 91                printf '\e[?25h'
 92                exit
 93                ;;
 94        esac
 95    done
 96
 97    # Return the cursor.
 98    printf '\e[?25h'
 99
100}
101
102main "$@"