#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# Date: 11 January 2021
# Edit: 07 June 2022
# https://github.com/trizen

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

# usage:
#   sidef oeis.isf 'formula' [from=1] [to=10]

# Examples:
#   sidef oeis.sf 'A033676(n)^2 + A033677(n)^2'              # first 10 terms
#   sidef oeis.sf 'A033676(n)^2 + A033677(n)^2' 5            # 5-th term
#   sidef oeis.sf 'A033676(n)^2 + A033677(n)^2' 5 20         # terms 5..20

# Sum example:
#   sidef oeis.sf 'sum(0..n, {|k| A048994(n, k) * A048993(n+k, n) })'

local Num!PREC = 4096

include OEIS

func eval_formula(formula, n = nil) {
    Sidef.new.execute_code((defined(n) ? "var n = #{n};" : "") + formula)
}

func process_input(formula, indices) {

    formula.gsub!(/\^/, '**') \
           .gsub!(/\b\d+\Kn\b/, '*n') \
           .gsub!(/\xC2/, '') \
           .gsub!(/\bxor\b/i, '^') \
           .gsub!(/\bor\b/i,  '|') \
           .gsub!(/\band\b/i, '&') \
           .gsub!(/\bnot\b/i, '~') \
           .gsub!(/ = /, ' == ')

    if (formula =~ /\bn\b/) {

        var terms = []

        for n in (indices) {
            terms << (eval_formula(formula, n) \\ do { say $@; break })
        }

        say terms.join(", ")
        return true
    }

    say eval_formula(formula)
    return true
}

ARGV || do {
    STDERR << "usage: #{File(__MAIN__).basename} [formula] [from=1] [to=10]\n"
    Sys.exit(1)
}

var formula = ARGV[0]
var indices = 1..10

if (ARGV.len == 2) {
    indices = [Num(ARGV[1])]
}
elsif (ARGV.len == 3) {
    indices = Num(ARGV[1])..Num(ARGV[2])
}
elsif (ARGV.len > 3) {
    indices = ARGV.ft(1).map{ Num(.gsub(/,/, '')) }
}

process_input(formula, indices)