#!/usr/bin/env bash
# shellcheck disable=2154
#
# shlide - a slide deck presentation tool written in pure bash
# https://github.com/icyphox/shlide
#
# The MIT License (MIT)
#
# Copyright (c) 2020 Anirudh Oppiliappan <x@icyphox.sh>

# Color definitions.
export BLK="\e[30m"
export RED="\e[31m"
export GRN="\e[32m"
export YLW="\e[33m"
export BLU="\e[34m"
export PUR="\e[35m"
export CYN="\e[36m"
export RST="\e[0m"

# Other formatting.
export BLD="\e[1m"
export DIM="\e[2m"
export ITA="\e[3m"
export UND="\e[4m"
export FLS="\e[5m"
export REV="\e[7m"
export INV="\e[8m"
export STR="\e[9m"

lines() {
    mapfile -tn 0 lines < "$1"
    printf '%s\n' "${#lines[@]}"
}

longest_line() {
    max=0 
    local IFS=
    while read -r line; do
        l=$(ansi_filter "$(colorify "$line")")
        if [ "${#l}" -gt "$max" ]; then max="${#l}"; fi
    done < "$1"
    printf '%s\n' "$max"
}

colorify() {
    # 'eval' hack to achieve substitution for colors.
    # Exclude SC2154.
    eval "declare dummy=\"$1\""
    printf '%b' "$dummy"
}

# Filter out color sequences.
ansi_filter() {
    shopt -s extglob
    local IFS=
    printf '%s' "${1//$'\e'[\[(]*([0-9;])[@-n]/}"
    #" A little fix to prevent vim syntax highlighting from breaking.
    shopt -u extglob
}


display() {
    # 1 - slide contents
    # 2 - slide name
    # 3 - current slide nr.
    # 4 - total nr. of slides

    slide_contents="$1"

    # Hide the cursor.
    printf '\e[?25l'

    # Clear the screen.
    printf '\e[2J'

    # Get screen size.
    shopt -s checkwinsize; (:;:)

    # Write slide number at bottom left.
    printf '\e[H'
    printf '\e[%sB%s/%s' "$LINES" "$(($3+1))" "$4"

    # Custom calculations to center text.
    height=$(lines "$2")
    width=$(longest_line "$2")

    # Rough estimates for the true center.
    ((l=LINES/2 - height/2))
    ((c=COLUMNS/2 - width/2))

    printf '\e[%s;%sH' "$l" "$c"

    while IFS= read -r line; do
        reduce=0
        # Print the contents of the slide file, 
        # line by line.
        l=$(colorify "$line")
        printf '%s' "$l"
        case $line in
            "" | "\n")
                ((++reduce));;
        esac
        # Move down and back after each print.
        l=$(ansi_filter "$l")
        printf '\e[%sD\e[B' "$((${#l} - reduce))"
    done <<< "$slide_contents"

}

die() {
    printf '\e[2J'
    printf '\e[?25h'
    exit 0
}

display_end() {
    ((l=LINES/2))
    ((c=COLUMNS/2 - 8))
    printf '\e[2J'
    printf '\e[0;%sH' "$c"
    printf 'END. Press q to quit.'
}

main() {

    slides_dir="${1:-./}"
    slides=("$slides_dir"/[0-9]*.txt)
    total="${#slides[@]}"
    i=0
    while :; do
        # Clear the screen.
        printf '\e[2J'

        # Capture Ctrl+C.
        trap 'die' INT

        # Don't go below 0.
        [[ "$i" -lt 0 ]] && i=0

        # Display END reached prompt, and then exit.
        if [[ "$i" -eq "$total" ]]; then 
            display_end
        else
            display "$(<"${slides[$i]}")" "${slides[$i]}" "$i" "$total"
        fi

        # Navigation
        read -rsn1 input
        case "$input" in
            "j"|"n"|""|";")
                [[ "$i" -eq "$total" ]] && die
                ((++i))
                ;;
            "k"|"p"|""|",")
                ((--i))
                ;;
            "0")
                ((i=0))
                ;;
            "G")
                ((i=total-1))
                ;;
            "q")
                # Return the cursor on exit.
                die
                ;;
            *)
                # Reloads the slide
                ;;
        esac
    done

    # Return the cursor.
    printf '\e[?25h'

}

main "$@"