Add sectioning and a table of contents to a markdown file

mdmaketoc.awk

#!/usr/bin/env -S gawk -f

$1~/^##+$/ && $0!~/Table of Contents$/{
    intoc = 0
    if (l > length($1)) for (k in num) if (k > length($1)) delete num[k]
    l = length($1)
    num[l] += 1
    r = q = substr($0, l + 2)

    gsub(" ", "-", q);
    toc = toc sprintf("%" ((l - 2) * 4 + 2) "s[%s](#%s)\n", "* ", r, q)

    p = ""; for (i in num) p = p num[i] "."
    if (length(num) > 1) p = substr(p, 0, length(p) - 1)
    gsub("^[0-9.]+ ", "", r)
    result = result sprintf("%s %s %s", $1, p, r) ORS
    next
}

!intoc{result = result $0 ORS}

$1~/^##+$/ && $0~/Table of Contents$/{
    intoc = 1
    tocindex = length(result)
    result = result ORS
}

END{
    printf "%s", substr(result, 0, tocindex) toc substr(result, tocindex + 1)
}