#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 11 January 2021
# Edit: 16 September 2023
# https://github.com/trizen

# Check and use formulas defined in terms of OEIS sequences.

var aliases = Hash(
    arccos => 'acos',
    arcsin => 'asin',
    arctan => 'atan',
    arccsc => 'acsc',
    arcsec => 'asec',
    arccot => 'acot',

    arccosh => 'acosh',
    arcsinh => 'asinh',
    arctanh => 'atanh',
    arccsch => 'acsch',
    arcsech => 'asech',
    arccoth => 'acoth',

    BernoulliB => 'bernoulli',
)

aliases.each {|k,v|
    Number.alias_method(v, k)
}

var main_dir   = File(__FILE__).rel2abs.dirname
var bfiles_dir = (main_dir + 'bfiles')

if (!bfiles_dir.exists) {
    bfiles_dir.mkdir || die "Can't create dir <<#{bfiles_dir}>>: #{$!}\n"
}

func mirror_url(url, file) {

    static HAS_HTTPS_SUPPORT = try {
        require('LWP::UserAgent')
        require('LWP::Protocol::https')
    }

    if (!HAS_HTTPS_SUPPORT) {   # no https:// support
        url.sub!('https://', 'http://')

        static http_tiny = do {
            require('HTTP::Tiny')
            %O<HTTP::Tiny>.new(
                agent => "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Firefox/91.0",
            )
        }

        return http_tiny.mirror(url, file)
    }

    static lwp = do {
        %O<LWP::UserAgent>.new(
           timeout       => 60,
           show_progress => 1,
           agent         => "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Firefox/91.0",
           ssl_opts      => Hash(verify_hostname => 1, SSL_version => 'TLSv1_3'),
        )
    }

    lwp.mirror(url, file)
}

func parse_bfile (bfile) {

    var fh = bfile.open_r || die "Can't open <<#{bfile}>>: #{$!}\n"

    var (n,k)
    var data = Hash()

    fh.each {|line|

        line.begins_with('#') && next

        (n,k)   = line.words...
        data{n} = Number(k) if defined(k)
    }

    fh.close
    data
}

func download_sequence(id) is cached {

    var url   = sprintf("https://oeis.org/A%s/b%s.txt", id, id)
    var bfile = (bfiles_dir + File("#{id}.txt"))

    if (!bfile.exists) {
        mirror_url(url, bfile)
    }

    parse_bfile(bfile)
}

class Number {
    method AUTOLOAD(_, name, k=nil) {

        var match = (name =~ /^A([0-9]+)\z/)
        match || die "unknown method: #{name}\n"

        var oeis_id = match[0]
        var len     = oeis_id.len

        if (len > 6) {
            die "Invalid OEIS ID: A#{oeis_id}\n"
        }

        if (len < 6) {
            oeis_id = ("%06s" % oeis_id)
        }

        var n = self
        var data = download_sequence(oeis_id)

        # Support for tables
        if (defined(k)) {
            n = (n*(n+1)/2 + k)
        }

        if (!data.has(n)) {
            die "A#{oeis_id}(#{n}) does not exist in the b-file...\n"
        }

        data{n}
    }
}