#!/bin/sh
#
## _This documentation file was extracted from `dddoc.sh` using the following
## command:_
##
##     ./dddoc.sh -d . dddoc.sh && mv dddoc.sh.md README.md
##
## dddoc -- Double-Dièse Documentation extractor
## =============================================
##
## This script is designed to extract inline documentation from shell scripts
## or libraries, or any other language using the sharp (#) as a comment mark.
## It follows the tradition of POD (Plain Old Documentation), but permits an
## easier-to-read syntax, allowing you to use the markup language that suits
## you (such as MarkDown, txt2tags, etc.).
##
## The only pre-requisite is that the comment lines to be extracted start with
## two sharps (##), hence the name of this script ("dièse" stands for "sharp"
## in French). The two sharps must be followed by at least one space or an end
## of line for the line to be extracted; for instance, lines starting with
## three sharps won't be extracted. Both sharps starting the line, and exactly
## one space (if any) will be stripped.
##
## Each output file bares the name of the corresponding input file, with a
## user-defined suffix (`-s` switch), that defaults to "md".
##
## The input file hierarchy is respected, and this script is best used along
## with `find` and `xargs`, for instance:
##
##     cd /project/path
##     find * -type f -print0 | xargs -0 dddoc /path/to/destdir
##
## The destination directory could be a clone of a GitLab wiki (or Gitea, or
## GitHub...), which will allow you to easily publish a nice-looking set of
## docs.
##
## License
## =======
##
## Copyright 2018 Matteo Cypriani <mcy@lm7.fr>
##
## This program is free software. It comes without any warranty, to the extent
## permitted by applicable law. You can redistribute it and/or modify it under
## the terms of the Do What The Fuck You Want To Public License, Version 2, as
## published by Sam Hocevar. See http://sam.zoy.org/wtfpl/COPYING for more
## details.

set -e
#set -x

##
## Globals
## =======
##
## This section and the followings document `dddoc.sh`; they are not
## particularly interesting, but are meant as a demonstration and documenting
## guide.
##

## - `PROGNAME`: this script's name
PROGNAME="$(basename "$0")"

## - `DESTDIR`: output directory
DESTDIR=

## - `VERBOSE`: verbose level
VERBOSE=1

## - `SUFFIX`: suffix (extension) of output files
SUFFIX=".md"

## - `REGEX`: the regular expression that determines which lines will be
##   extracted from input files
REGEX='^##( |$)'

##
## Functions
## =========
##

## print_usage()
## -------------
## Prints the usage message.
##
print_usage()
{
    cat <<EOF
Usage:
    $PROGNAME [-h]
    $PROGNAME -d <output_dir> [-s <suffix>] [-v] <file1> [file2 ...]
Options:
    -h: display this help and exit
    -d: output files' destination directory
    -s: output files' suffix (default: "$SUFFIX")
    -q: set verbose level to 0
    -v: increment verbose level; this option can be provided several times
Verbose levels (default is $VERBOSE):
    0 = silent
    1 = display global options
    2 = print a message for each generated files
    3 = print a message for skipped files as well
EOF
}

## bad_usage()
## -----------
## Prints the usage message to the standard error and exits with an error code.
##
bad_usage()
{
    print_usage >&2
    exit 127
}


###
### Main program
### ============
### (Note that these triple-dashed comments won't be extracted by this script.)
###

# Parse CLI options
while getopts d:hqs:v option ; do
    case $option in
        h)  print_usage
            exit 0
            ;;
        d)  DESTDIR="$OPTARG" ;;
        q)  VERBOSE=0 ;;
        s)  SUFFIX=".$OPTARG" ;;
        v)  VERBOSE=$((VERBOSE + 1)) ;;
        *)  bad_usage
    esac
done
shift $((OPTIND - 1))

# Check CLI options
if [ -z "$DESTDIR" ] || [ $# -lt 1 ] ; then
    bad_usage
fi

if [ $VERBOSE -ge 1 ] ; then
    printf 'Verbose level: %d\n' "$VERBOSE"
    printf 'Will use "%s" as the destination directory.\n' "$DESTDIR"
    printf 'Will use "%s" as a suffix for output files.\n' "$SUFFIX"
fi

while [ -n "$1" ] ; do
    src="$1"
    shift
    srcdir="$(dirname "$src")"
    destdir="$DESTDIR/$srcdir"
    dest="$destdir/$(basename "$src")$SUFFIX"

    if ! grep -Eq "$REGEX" "$src" ; then
        [ $VERBOSE -ge 3 ] && printf \
            "\"%s\" doesn't seem to contain any double-sharp comments. Skipping.\\n" \
            "$src"
        continue
    fi

    [ $VERBOSE -ge 2 ] && \
        printf 'Extracting doc from "%s" to "%s"...\n' "$src" "$dest"

    mkdir -p "$destdir"
    sed -rn "s/$REGEX//p" "$src" >"$dest"
done

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