#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define RNACOMP(x0, x1) (rna[i + 2] == x0 || rna[i + 2] == x1)

char *dna_to_rna(char *dna)
{
	size_t sz = strlen(dna);
	unsigned i;

	char *rna = malloc(sz);

	if (!rna) {
		fprintf(stderr, "cannot allocate memory for rna strand\n");
		return NULL;
	}

	for (i = 0; i < sz; i++) {
		switch (dna[i]) {
		case 'A':
			rna[i] = 'U';
			break;
		case 'U':
			rna[i] = 'A';
			break;
		case 'T':
			rna[i] = 'A';
			break;
		case 'G':
			rna[i] = 'C';
			break;
		case 'C':
			rna[i] = 'G';
			break;
		default:
			fprintf(stderr, "%c is not a valid base!\n", dna[i]);
			break;
		}
	}

	return rna;
}

char *rna_to_trna(char *rna)
{
	return dna_to_rna(rna);
}

char *rna_to_aminoacid(char *rna)
{
	size_t sz = strlen(rna);
	unsigned i;

	char *polypeptide = malloc(sz);

	if (sz % 3) {
		fprintf(stderr, "length of RNA is not multiple of 3\n");
		free(polypeptide);
		return NULL;
	}

	for (i = 0; i < sz; i+=3) {
		switch (rna[i]) {
		case 'U':
			switch (rna[i + 1]) {
			case 'U':
				if (RNACOMP('U', 'C'))
					strcat(polypeptide, "phe"); /* UUU UUC */
				else
					strcat(polypeptide, "leu"); /* UUA UUG */
				break;
			case 'A':
				if (RNACOMP('U', 'C'))
					strcat(polypeptide, "tyr");
				else
					strcat(polypeptide, "end");
				break;
			case 'C':
				strcat(polypeptide, "ser");
				break;
			case 'G':
				if (RNACOMP('U', 'C'))
					strcat(polypeptide, "cys");
				else if (rna[i + 2] == 'A')
					strcat(polypeptide, "end");
				else
					strcat(polypeptide, "trp");
				break;
			default:
				break;
			}
			break;
		case 'A':
			switch (rna[i + 1]) {
			case 'U':
				if (rna[i + 2] == 'G')
					strcat(polypeptide, "met");
				else
					strcat(polypeptide, "ile");
				break;
			case 'A':
				if (RNACOMP('U', 'C'))
					strcat(polypeptide, "asn");
				else
					strcat(polypeptide, "lys");
				break;
			case 'C':
				strcat(polypeptide, "thr");
				break;
			case 'G':
				if (RNACOMP('U', 'C'))
					strcat(polypeptide, "ser");
				else
					strcat(polypeptide, "arg");
				break;
			default:
				break;
			}
			break;
		case 'C':
			switch (rna[i + 1]) {
			case 'U':
				strcat(polypeptide, "leu");
				break;
			case 'A':
				if (RNACOMP('U', 'C'))
					strcat(polypeptide, "his");
				else
					strcat(polypeptide, "gln");
				break;
			case 'C':
				strcat(polypeptide, "pro");
				break;
			case 'G':
				strcat(polypeptide, "arg");
				break;
			default:
				break;
			}
			break;
		case 'G':
			switch (rna[i + 1]) {
			case 'U':
				strcat(polypeptide, "val");
				break;
			case 'A':
				if (RNACOMP('U', 'C'))
					strcat(polypeptide, "asp");
				else
					strcat(polypeptide, "glu");
				break;
			case 'C':
				strcat(polypeptide, "ala");
				break;
			case 'G':
				strcat(polypeptide, "gly");
				break;
			default:
				break;
			}
			break;
		default:
			break;
		}
	}

	return polypeptide;
}

int main(int argc, char **argv)
{
	char *rna;
	char *trna;
	char *polypeptide;

	if (argc != 2) {
		fprintf(stderr, "Usage: %s [dna here]\n", argv[0]);
		return 0;
	}

	rna = dna_to_rna(argv[1]);
	trna = rna_to_trna(rna);
	polypeptide = rna_to_aminoacid(rna);

	printf("RNA: %s\ntRNA: %s\nPolypeptide: %s\n", rna, trna, polypeptide);

	free(rna);
	free(trna);
	free(polypeptide);

	return 0;
}