#include "postgres.h"
#include "fmgr.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/regexp.h"

PG_MODULE_MAGIC;

Datum regexp_matches(PG_FUNCTION_ARGS);

PG_FUNCTION_INFO_V1(regexp_matches);
Datum
regexp_matches(PG_FUNCTION_ARGS)
{
	text *s = PG_GETARG_TEXT_P(0);
	text *p = PG_GETARG_TEXT_P(1);
	regex_t *cpat;

	cpat = RE_compile_and_cache(p, regex_flavor);
	if (cpat->re_nsub)
	{
		regmatch_t *pmatch = palloc0(sizeof(regmatch_t) * (cpat->re_nsub + 1));
		if (RE_execute(cpat,
					   VARDATA(s),
					   VARSIZE(s) - VARHDRSZ,
					   cpat->re_nsub + 1,
					   pmatch))
		{
			ArrayType *result;
			Datum elems[cpat->re_nsub];
			bool nulls[cpat->re_nsub];
			/* get text type oid, too lazy to do it some other way */
			Oid param_type = get_fn_expr_argtype(fcinfo->flinfo, 0);
			size_t i;
			int ndims = 1;
			int dims[1] = {cpat->re_nsub};
			int lbs[1] = {1};
			int16 typlen;
			bool typbyval;
			char typalign;

			get_typlenbyvalalign(param_type, &typlen, &typbyval, &typalign);

			for (i = 0; i < cpat->re_nsub; ++i)
			{
				int so = pmatch[i+1].rm_so,
				    eo = pmatch[i+1].rm_eo;

				if (so < 0 || eo < 0)
				{
					elems[i] = 0;
					nulls[i] = true;
				}
				else
				{
					elems[i] = DirectFunctionCall3(text_substr,
							PointerGetDatum(s),
							Int32GetDatum(so + 1),
							Int32GetDatum(eo - so));
					nulls[i] = false;
				}
			}

			pfree(pmatch);
			result = construct_md_array(elems, nulls, ndims, dims, lbs,
					param_type, typlen, typbyval, typalign);
			PG_RETURN_ARRAYTYPE_P(result);
		}
		/* if no match, fall through and return null */
	}
	else
	{
		ereport(ERROR,
			(errcode(ERRCODE_INVALID_REGULAR_EXPRESSION),
			 errmsg("regular expression has no match groups")));
	}

	PG_RETURN_NULL();
}