#!/bin/sh
#shellcheck disable=SC2039

#
# mdfmt - Markdown formatted output from your shell scripts
#
# These functions allow you to easily output a valid Markdown
# from your script.
#

#
# Default text width
#
# Most paragraph text will be re-formatted to not exceed this width.
#
MDFMT_WIDTH=${MDFMT_WIDTH:-75}

_mdfmt__fmttype() {
    #
    # Format fragments $@ as type $Elem
    #
    case $Elem in
        h1)
            local hdr
            hdr=$(_mdfmt__join "$@")
            echo
            echo
            echo "$hdr"
            echo "$hdr" | tr -c '\n' =
            ;;
        h2)
            local hdr
            hdr=$(_mdfmt__join "$@")
            echo
            echo
            echo "$hdr"
            echo "$hdr" | tr -c '\n' -
            ;;
        h3)
            local hdr
            hdr=$(_mdfmt__join "$@")
            echo
            echo
            echo "### $hdr ###"
            ;;
        p)
            echo
            _mdfmt__join "$@" \
              | fmt -w "$(_mdfmt__width)"
            ;;
        ul)
            printf '\n *  '
            _mdfmt__join "$@" \
              | fmt -t -w "$(_mdfmt__width)" \
              | sed -e 's/^   /    /'
            ;;
        ol)
            printf '\n 1. '
            _mdfmt__join "$@" \
              | fmt -t -w "$(_mdfmt__width)" \
              | sed -e 's/^   /    /'
            ;;
        pre)
            echo
            _mdfmt__join "$@" \
              | sed -e 's/^/    /'
            ;;
    esac
}

_mdfmt__indent() {
    #
    # Indent as many spaces as needed
    #
    local pfx
    test "$Nest" -eq 0 && { cat; return; }
    test "$Elem" == h1 && { cat; return; }
    test "$Elem" == h2 && { cat; return; }
    test "$Elem" == h3 && { cat; return; }
    pfx=$(
        #shellcheck disable=SC2034
        for n in $(seq 1 "$Nest"); do
            printf '    '
        done
    )
    sed "s/^/$pfx/"
}

_mdfmt__join() {
    #
    # Properly join text fragments $@
    #
    case $Elem in
        pre)  printf '%s\n' "$@" ;;
        h*)   echo "$1"          ;;
        *)    echo "$@"          ;;
    esac
}

_mdfmt__quote() {
    #
    # Quote if needed
    #
    local pfx
    $Quoted || { cat; return; }
    test "$Elem" == h1 && { cat; return; }
    test "$Elem" == h2 && { cat; return; }
    test "$Elem" == h3 && { cat; return; }
    sed 's/^/> /'
}

_mdfmt__width() {
    #
    # Calculate width
    #
    echo "$((MDFMT_WIDTH - Nest * 4))"
}

mdfmt() {
    #
    # Format text as Markdown element $1
    #
    # Usage:
    #     mdfmt [-n|--nest LEVEL] [-q|--quote] ELEM FRAG [FRAG..]
    #
    # Take text passed as one or more FRAGs and output it formatted in
    # Markdown as ELEM.  Passing higher LEVEL than previous item causes
    # items to nest.
    #
    # When multiple FRAGs are provided, the text is simply joined together
    # (and in most cases re-formatted to fit $MDFMT_WIDTH).  This allows
    # you to pass long texts and keep your code tidy by breaking the text
    # into several pieces and using line continuation character `\`.
    #
    # Additional character-level formatting is achieved using standard
    # Markdown motation, i.e. asterisk for emphasis, double asterisk
    # for strong emphasis and backtick for verbatim text.
    #
    # Options:
    #
    #   * `-n LEVEL`, `--nest LEVEL`  Causes item to be indented so that
    #     it will be nested into the previous item, if the LEVEL is higher
    #     than the previous one.  Default value is zero.
    #
    #     This can be used to e.g. include unordered items or code examples
    #     inside ordered items, or multiple paragraphs per (un)ordered
    #     item.
    #
    #   * `-q`, `--quote`  Causes item to appear blockquoted.
    #
    # Following values are available for ELEM (names are inspired by
    # HTML elements):
    #
    #  *  `h1`, `h2`, `h3`  - headings of respective weight. Ignores
    #     nesting.   Accepts only single FRAG.
    #
    #  *  `p` - a paragraph.
    #
    #  *  `ul`, `ol` - unordered list item (bullet) or ordered (numbered)
    #     list item.
    #
    #  *  `pre` - pre-formatted code.  Multiple FRAGs are treated as lines
    #     and spaces are preserved.
    #
    # Examples:
    #
    #     mdfmt h1 "how to boil an egg"
    #
    #     mdfmt p  "this tutorial shows you how to boil an egg" \
    #              "the best way possible"
    #
    #     mdfmt h2 "variant 1"
    #
    #     mdfmt ol "take egg"
    #     mdfmt ol "put it in a pot full of water"
    #     mdfmt ol "place pot onto stove"
    #     mdfmt ol "turn on stove"
    #     mdfmt ol "wait"
    #     mdfmt --nest 1 ul "for hard-boiled, wait 10 minutes"
    #     mdfmt --nest 1 ul "for soft-boiled, wait 3 minutes"
    #     mdfmt ol "turn off the stove"
    #     mdfmt ol "replace water with cold water "
    #     mdfmt ol "break and replace shell from the egg"
    #
    #     mdfmt h2 "variant 1"
    #
    #     mdfmt ol "start your favorite browser"
    #     mdfmt ol "open youtube:"
    #     mdfmt --nest 1 pre "https://www.youtube.com/"
    #     mdfmt ol "enter following text in Search box:"
    #     mdfmt --nest 1 pre "how to boil an egg"
    #     mdfmt ol "watch at least 5 videos"
    #     mdfmt ol "go to the closest restaurant and ask for" \
    #               "a boiled egg"
    #
    #     mdfmt h2 "conclusion"
    #
    #     mdfmt p  "We hope you enjoy the egg. Seriously."
    #
    local Nest=0
    local Elem
    local Quoted=false
    local usage="usage: mdfmt [-n|--nest LVL] ELEM FRAG [FRAG..]"
    while true; do case $1 in
        -n|--nest)
            Nest=$2
            shift 2 || {
                echo "$usage" >&2
                return 2
            }
            ;;
        -q|--quote)
            Quoted=true
            shift
            ;;
        -*)
            echo "$usage" >&2
            return 2
            ;;
        *)
            break
            ;;
    esac done
    Elem=$1; shift
    case $Elem in
        h1|h2|h3|p|ol|ul|pre)
            true
            ;;
        *)
            echo "$usage" >&2
            return 2
            ;;
    esac
    _mdfmt__fmttype "$@" \
      | _mdfmt__quote \
      | _mdfmt__indent
}