#include "mex.h"

/*
    Differences with matlab built-in findstr:
        - allows to search only the n first occurences of a pattern
        - allows to search only in a substring (given an index of the beginning)
   
    Matlab hack:
        - doesn't use mxGetString to prevent a copy of the string.
        - assumes Matlab stores strings as unsigned short (Unicode 16 bits)
          matrix.h: typedef uint16_T mxChar;
          (that's the case for Matlab 5.* and 6.* but Matlab 4.* stores strings
           as double)
*/

/* Comment the following line to use standard mxGetString (slower) */
#define __HACK_MXCHAR__

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {

    unsigned int i, j, stext, spattern, nbmatch = 0, ind = 1, occur = 0, nboccur = 0;
#ifdef __HACK_MXCHAR__
    unsigned short int *text = NULL, *pattern = NULL;
#else
    char *text = NULL, *pattern = NULL;
#endif
    unsigned int *k = NULL;
    mxArray *out = NULL;
    
	/* Check for proper number of arguments. */
    if ((nrhs == 0) || (nrhs == 1))
	    mexErrMsgTxt("Not enough input arguments.");
    else if (nrhs > 4)
	    mexErrMsgTxt("Too many input arguments.");
    else if (nlhs > 1)
        mexErrMsgTxt("Too many output arguments.");
    
    /* The input TEXT must be a string */
	if (!mxIsChar(prhs[0]))
	    mexErrMsgTxt("Inputs must be character arrays.");
	stext = mxGetM(prhs[0]) * mxGetN(prhs[0]);
#ifdef __HACK_MXCHAR__
	text = mxGetData(prhs[0]);
#else
    text = mxCalloc(stext+1, sizeof(char));
    mxGetString(prhs[0], text, stext+1);
#endif
        
    /* The input PATTERN must be a string */
	if (!mxIsChar(prhs[1]))
		mexErrMsgTxt("Inputs must be character arrays.");
    spattern = mxGetM(prhs[1]) * mxGetN(prhs[1]);
#ifdef __HACK_MXCHAR__
	pattern = mxGetData(prhs[1]);
#else
    pattern = mxCalloc(spattern+1, sizeof(char));
	mxGetString(prhs[1], pattern, spattern+1);
#endif

	/* The input INDEX must be an integer */
	if (nrhs > 2) {
	    if ((!mxIsNumeric(prhs[2]) || (mxGetM(prhs[2]) * mxGetN(prhs[2]) !=  1)))
	        mexErrMsgTxt("Index input must be an integer.");
	    ind = (unsigned int)mxGetScalar(prhs[2]);
	    if (ind < 1)
	        mexErrMsgTxt("Index must be greater than 1.");
	}
	
	/* The input OCCUR must be an integer */
	if (nrhs == 4) {
	    if ((!mxIsNumeric(prhs[3]) || (mxGetM(prhs[3]) * mxGetN(prhs[3]) !=  1)))
	        mexErrMsgTxt("Index input must be an integer.");
	    nboccur = (unsigned int)mxGetScalar(prhs[3]);
	}
	
	/* Find pattern in text */
    for (i=ind-1;i<stext;i++) {
        for (j=0;j<spattern && i+j<stext;j++) {
            if (pattern[j] == text[i+j]) {
                if (j == spattern-1) {
                    nbmatch += 1;
                    k = mxRealloc(k,nbmatch*sizeof(unsigned int));
                    k[nbmatch-1] = i+1;
                    if (++occur == nboccur) i = stext;
                }
            }
            else break;
        }
    }
    
    /* Allocate output */
    out = mxCreateDoubleMatrix((nbmatch) ? 1:0, nbmatch, mxREAL);
    
    /* Copy index array into output */
    for (i=0;i<nbmatch;i++)
        mxGetPr(out)[i] = (double)k[i];
    
    /* Assign pointer to output */
    plhs[0] = out;
    
    /* Free memory */
    if (k) mxFree(k);
}