// Rosetta Code problem: http://rosettacode.org/wiki/Sequence_mutation
// by Galileo, 07/2022

r = int(ran(300))

for i = 1 to 200 + r : dna$ = dna$ + mid$("ACGT", int(ran(4))+1, 1) : next

sub show()
    local acgt(4), i, j, x, total

    for i = 1 to len(dna$)
        x = instr("ACGT", mid$(dna$, i, 1))
        acgt(x) = acgt(x) + 1
    next

    for i = 1 to 4 : total = total + acgt(i) : next

    for i = 1 to len(dna$) step 50
        print i, ":\t";
        for j = 0 to 49 step 10
            print mid$(dna$, i+j, 10), " ";
        next
        print
    next
    print "\nBase counts: A: ", acgt(1), ", C: ", acgt(2), ", G: ", acgt(3), ", T: ", acgt(4), ", total: ", total
end sub


sub mutate()
    local i, p, sdi$, rep$, was$

    print

    for i = 1 to 10
        p = int(ran(len(dna$))) + 1
        sdi$ = mid$("SDI", int(ran(3)) + 1, 1)
        rep$ = mid$("ACGT", int(ran(4)) + 1, 1)
        was$ = mid$(dna$, p, 1)
        switch sdi$
            case "S": mid$(dna$, p, 1) = rep$
                      print "swapped ", was$, " at ", p, " for ", rep$ : break
            case "D": dna$ = left$(dna$, p - 1) + right$(dna$, len(dna$) - p)
                      print "deleted ", was$, " at ", p : break
            case "I": dna$ = left$(dna$, p - 1) + rep$ + right$(dna$, (len(dna$) - p + 1))
                      print "inserted ", rep$, " at ", p, ", before ", was$ : break
        end switch
    next
    print
end sub

show()
mutate()
show()