#!/bin/sh
DOCUMENTATION=$(cat <<END_OF_DOCUMENTATION
format.sh 1.3

Read an HTML file via STDIN, template it if it starts with a meta
block, and output that to STDOUT.

A meta block is deemed started if the first line of the HTML file
consists of exactly '<div class="meta">'.  The meta block is
deemed ended on the first line consisting of exactly '</div>'.

Each line of the meta block specifies an option, followed by an '='
and then the value.  The value may contain whitespace, but there may
not be whitespace between the option and the '='.

Valid options are:
  language       - Page language in ISO format. Eg. 'en' for English.
  title          - Self explanatory.
  subtitle       - Goes underneath the title.
  description    - The description to be used for social media
                   embeds.
  image          - The image to be used for social media embeds.
                   (Should be a URL.)
  date-published - Self explanatory.
  date-updated   - Self explanatory.
  has            - Optional components to be loaded.
  redirect-to    - Optional, contains a path for a redirect.
                   If present no page content will be shown.

Sample meta block:
<div class="meta">
  title=Why HTML is Better Than Markdown
  date-published=5 February 2020
  date-updated=2 March 2021
  has=code latex
</div>

USAGE: format.sh [OPTIONS]

Where the OPTIONS are:
  --help
    Outputs this manual-style help message and immediately exits.

  --location LOCATION
    Set the location to LOCATION, which is assumed to be relative
    to the base url.  Used mainly for meta tags.  It should
    include a leading '/'.

  --version
    Outputs the script name along with its version number.

The program will exit with one of four exit codes:
  0 - if the program has been templated successfully,
  1 - catastrophic failure,
  2 - if no meta block has been found, and so this program
      effectively acted the same as the 'cat' command,
  3 - if the meta block is badly formed (likely because the div
      was never ended, and
  4 - if an invalid meta block option was encountered.

Requirements: As far as I can tell, this script uses only features
required in a POSIX compliant shell.

Hacking hint: most of the modifications to this system will be
done to this file, specifically in the 'Templates' section.

SPDX-FileCopyrightText: Copyright (c) 2022, Theodore Preduta.
SPDX-License-Identifier: BSD-2-Clause
END_OF_DOCUMENTATION
)

usage() {
  [ -n "$1" ] && echo "$1" && echo

  echo "Usage: format.sh [OPTIONS]"
  echo "Try running with --help for more information."

  exit 1
}

location="/404/"

while [ ! "$*" = "" ]; do
  case "$1" in
    --help)
      echo "$DOCUMENTATION"
      exit 0;;
    --location)
      location="$2"
      shift 2;;
    --version)
      echo "$DOCUMENTATION" | head -n 1
      exit 0;;
    *)
      usage "Unkown argument: $1";;
  esac
done

has() {
  if test "${has_line#*$1}" != "$has_line"
  then
    return 0
  else
    return 1
  fi
}

#######################
# (Default) Variables #
#######################
base_url="https://www.pta.gg"
language="en"
title="<span class=\"error\">Unset Title</span>"
subtitle=""
description=""
image=""
date_published=""
date_updated=""
has_line=""
redirect_to=""

#############
# Templates #
#############
head() {
  cat <<EOF
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="apple-touch-icon" sizes="180x180" href="/assets/images/apple-touch-icon.png">
<link rel="icon" type="image/png" sizes="512x512" href="/assets/images/favicon512.png">
<link rel="icon" type="image/png" sizes="192x192" href="/assets/images/favicon192.png">
<link rel="icon" type="image/png" sizes="32x32" href="/assets/images/favicon32.png">
<link rel="icon" type="image/png" sizes="16x16" href="/assets/images/favicon16.png">
<link rel="shortcut icon" href="/assets/images/favicon.ico">
<link rel="stylesheet" href="/assets/css/style.css">
<link rel="stylesheet" href="/assets/css/fonts.css">
EOF

  has "code" && cat <<EOF
<link rel="stylesheet" href="/assets/css/prism.min.css">
EOF

  has "latex" && cat <<EOF
<link rel="stylesheet" href="/assets/css/katex.min.css">
EOF

  cat <<EOF
<meta property="og:type" content="website">
<meta property="og:url" content="$base_url$location">
<title>$title</title>
<meta property="og:title" content="$title">
EOF

  [ -n "$description" ] && cat <<EOF
<meta name="description" content="$description">
<meta property="og:description" content="$description">
EOF

  # TODO do this only if image is actually provided as an absolute
  # link.
  [ -n "$image" ] && cat <<EOF
<meta property="og:image" content="$base_url$image">
EOF
}

header() {
  echo "<h1>$title</h1>"

  if [ -n "$subtitle" ]; then
    echo "<h2>$subtitle</h2>"
  fi

  cat <<EOF
<nav>
  <a href="#main" class="skip-navigation">Skip Navigation</a>
  <a href="/">Home</a>
  <a href="/about/">About</a>
  <a href="/projects/">Projects</a>
  <a href="/articles/" hidden>Blog</a>
</nav>
EOF
}

prebody() {
  if [ -n "$date_published" ] || [ -n "$date_updated" ]; then

    printf "<p class=\"date-block\">"

    if [ -n "$date_published" ]; then
      printf "Published %s" "$date_published"

      if [ -n "$date_updated" ]; then
        printf "; "
      fi
    fi

    if [ -n "$date_updated" ]; then
      printf "Updated %s" "$date_updated"
    fi

    echo ".</p>"
  fi
}

postbody() {
  true # Unused
}

footer() {
  cat <<EOF
<nav>
  <a href="https://www.pta.gg/">Main Site</a>
  <a href="https://vcs.pta.gg/">Version Control</a>
  <a href="https://www.pta.gg/licenses/">Licenses</a>
  <a href="#" id="chaos-button">Enable Chaos</a>
</nav>

<p>&#169; 2021-2024, Theodore Preduta. All rights reserved.</p>
EOF
}

foot() {
  cat <<EOF
<script defer src="/assets/js/chaos.js"></script>
EOF

  has "code" && cat <<EOF
<script defer src="/assets/js/prism.min.js"></script>
EOF

  has "latex" && cat <<EOF
<script defer src="/assets/js/katex.min.js"></script>
<script defer src="/assets/js/katex-auto-render.min.js" onload="renderMathInElement(document.body);"></script>
EOF
}

###############
# Main render #
###############
read -r line

# If the first line is not opening a meta block, we assume the
# input is a standalone webpage and just vomit it back out.
if [ ! "$line" = "<div class=\"meta\">" ]; then
   echo "$line"
   cat
   exit 2
fi

# Attempt to parse the meta block.
while read -r line
do
  if [ "$line" = "</div>" ]; then break; fi
  if [ "$line" = "" ]; then continue; fi

  var_part="${line%%=*}"
  val_part="${line#*=}"

  case "$var_part" in
    language)       language="$val_part" ;;
    title)          title="$val_part" ;;
    subtitle)       subtitle="$val_part" ;;
    description)    description="$val_part" ;;
    image)          image="$val_part" ;;
    date-published) date_published="$val_part" ;;
    date-updated)   date_updated="$val_part" ;;
    has)            has_line="$val_part" ;;
    redirect-to)    redirect_to="$val_part" ;;
    *)              exit 3;; # Unknown option
  esac
done

# The meta block has not been fully read.
if [ ! "$line" = "</div>" ]; then exit 3; fi

# Handle redirects.
if [ ! "$redirect_to" = "" ]; then
  echo "<!DOCTYPE html>"
  echo "<html lang=\"en\">"
  echo "<head>"
  echo "<meta charset=\"utf-8\">"
  echo "<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">"
  echo "<meta http-equiv=\"refresh\" content=\"0; url=$redirect_to\">"
  echo "<title>Redirect</title>"
  echo "</head>"
  echo "<body>"
  echo "<p>Redirecting <a href=\"$redirect_to\">here</a>...</p>"
  echo "</body>"
  echo "</html>"
  exit 0
fi

# Template the rest.  Failures past this line needs to be debugged
# with a browser.  Hopefully(tm) there is an obvious visual error.
echo "<!DOCTYPE html>"
echo "<html lang=\"$language\">"
echo "<head>"
head
echo "</head>"
echo "<body>"
echo "<header>"
header
echo "</header>"
echo "<main id=\"main\">"
prebody
cat # Body
postbody
echo "</main>"
echo "<footer>"
footer
echo "</footer>"
foot
echo "</body>"
echo "</html>"