Parsing HTML (modifying a siterip)

#!/bin/bash
# This script is meant to fix the links in the HTML files of my BetaArchive
# forum siterip (done with wget).

# This is the command I used to make a local mirror of a forum thread:

# page=0; for n in {1..45}; do wget -EHkp -e robots=off --waitretry=10 --tries=10 --user-agent='Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.105 Safari/537.36' "www.betaarchive.com/forum/viewtopic.php?f=61&t=33250&start=${page}"; (( page = page + 25 )); done

dir="${HOME}/betaarchive"

if [[ ! -d "$dir" ]]; then
    exit
fi

cd "$dir"

mapfile -t files < <(find "${dir}/www.betaarchive.com/forum" -maxdepth 1 -type f -iname "*.html" | sort)

image_regex='<a href=\"https{0,1}://www\.betaarchive\.com/.*\.(png|jpe{0,1}g|gif)\" class=\"postlink\"'
page_regex='href=\"https{0,1}://www\.betaarchive\.com/forum/viewtopic\.php'
page_regex2='\?f=[0-9]+\&amp\;t=[0-9]+\&amp\;sid=[[:alnum:]]+\&amp\;start=[0-9]+\"'
page_regex3='\"\.\&\#x2F\;viewtopic\.php\&\#x3F\;f\&\#x3D\;[0-9]+\&amp\;amp\&\#x3B\;t\&\#x3D\;[0-9]+\&amp\;amp\&\#x3B\;sid\&\#x3D\;[[:alnum:]]+\"'
page_regex4='href=\"viewtopic\.php\%3Ff=[0-9]+\&amp\;t=[0-9]+\&amp\;start=[0-9]+\.html\#([a-z]+){0,1}\"'
page_regex5='\"viewtopic\.php\?f=[0-9]+\&amp\;t=[0-9]+\&amp\;sid=[[:alnum:]]+\"'
page_regex6='href=\"viewtopic\.php\?p=[0-9]+\&amp\;sid=[[:alnum:]]+\#p[0-9]+\"'
page_regex7='\"viewtopic\.php\?f=[0-9]+\&amp\;t=[0-9]+\&amp\;start=[0-9]+\&amp\;sid=[[:alnum:]]+\"'
#<a href="viewtopic.php?f=61&amp;t=33250&amp;start=25&amp;sid=3e8af540222e2e1ce3a623dc88c577c5">Windows NT 4 Source Compiled! version 2</a>

for (( i = 0; i < ${#files[@]}; i++ )); do
    f="${files[${i}]}"
    f_dn=$(dirname "$f")

    num=$(sed -E "s|.*viewtopic\.php.*start=([0-9]+).html$|\1|" <<<"$f")
    new_f=$(sed -E "s|viewtopic\.php.*start=([0-9]+).html$|page\1\.html|" <<<"$f")

    mapfile -t html <"$f"

    for (( j = 0; j < ${#html[@]}; j++ )); do
        line="${html[${j}]}"

        if [[ $line =~ $image_regex ]]; then
            get_html=$(sed -E 's/^.*(https{0,1}:\/\/www\.betaarchive\.com\/.*(\.png|jpe{0,1}g|gif))\" class=\"postlink\".*$/\1/I' <<<"$line")
            html[${j}]=$(sed -E 's/https{0,1}:\/\/www\.betaarchive\.com(\/.*(\.png|jpe{0,1}g|gif))/\.\.\1/I' <<<"$line")
#           wget -x -e robots=off --waitretry=10 --tries=10 --user-agent='Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.105 Safari/537.36' "$get_html"
            echo "${html[${j}]}"
        fi

        if [[ $line =~ $page_regex ]]; then
            html[${j}]=$(sed -E 's|(.*)https{0,1}:\/\/www\.betaarchive\.com\/forum\/(.*)|\1\2|' <<<"$line")

            if [[ $line =~ $page_regex2 ]]; then
                page_tmp=$(sed -E "s|.*viewtopic\.php\?f=[0-9]+\&.*t=[0-9]+\&.*start=([0-9]+).*|\1|" <<<"${html[${j}]}")
                html[${j}]=$(sed -E "s|viewtopic\.php(\?f=[0-9]+\&.*t=[0-9]+\&.*start=[0-9]+)|page${page_tmp}\.html\1|" <<<"${html[${j}]}")
            fi

            if [[ ${html[${j}]} =~ $page_regex6 ]]; then
                html[${j}]=$(sed -E "s|\"viewtopic\.php(\?p=[0-9]+\&amp\;sid=[[:alnum:]]+\#p[0-9]+)\"|\"page${num}\.html\1\"|" <<<"${html[${j}]}")
            fi

            if [[ ${html[${j}]} =~ $page_regex7 ]]; then
                html[${j}]=$(sed -E "s|\"viewtopic\.php(\?f=[0-9]+\&amp\;t=[0-9]+\&amp\;start=[0-9]+\&amp\;sid=[[:alnum:]]+)\"|\"page${num}\.html\1\"|" <<<"${html[${j}]}")
            fi

            echo "${html[${j}]}"
        fi

#       if [[ $line =~ $page_regex3 ]]; then
#           html[${j}]=$(sed -E "s|\.\&\#x2F\;viewtopic\.php(\&\#x3F\;f\&\#x3D\;[0-9]+\&amp\;amp\&\#x3B\;t\&\#x3D\;[0-9]+\&amp\;amp\&\#x3B\;sid\&\#x3D\;[[:alnum:]]+)|page${num}\.html\1|" <<<"${html[${j}]}")
#           echo "${html[${j}]}"
#       fi

        if [[ ${html[${j}]} =~ $page_regex4 ]]; then
            html[${j}]=$(sed -E "s|viewtopic\.php\%3Ff=[0-9]+\&.*t=[0-9]+\&.*start=([0-9]+).html(\#([a-z]+){0,1})|page\1\.html\2|" <<<"${html[${j}]}")
            echo "${html[${j}]}"
        fi

        if [[ ${html[${j}]} =~ $page_regex5 ]]; then
            html[${j}]=$(sed -E "s|\"viewtopic\.php(\?f=[0-9]+\&amp\;t=[0-9]+\&amp\;sid=[[:alnum:]]+)\"|\"page0\.html\1\"|" <<<"${html[${j}]}")
            echo "${html[${j}]}"
        fi
    done

    rm "$f" || exit

    if [[ -f $new_f ]]; then
        exit
    fi

    touch "$new_f" || exit

    for (( j = 0; j < ${#html[@]}; j++ )); do
        echo "${html[${j}]}" >> "$new_f"
    done
done