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

#define steq(x,y) (!strcmp((x),(y)))
#define FALSE 0
#define TRUE 1

static char *Argv0;

static int Entab = FALSE;
static int EntabMargin = 2;
static int ReplaceFiles = FALSE;
static int TabStop = 8;
static const char *CopyName = "cp";
static int IndentOnly = FALSE;
static int FinishNewline = FALSE;


void detab(FILE *in, FILE *out);
void do_error(const char *fmat, ...);
void do_help(int man);

int main(int argc, char *argv[])
{
    int i, j;

    Argv0 = argv[0];

    for (i=1; i < argc; i++)
    {
        char *tmp;
        int newTabStop;

        if (argv[i][0] != '-') break;
        if (argv[i][1] == '\0') break;

        if (steq(argv[i]+1, "-")) { ++i; break; }
        else if (steq(argv[i]+1, "-help") ||
                 steq(argv[i]+1, "?") || steq(argv[i]+1, "h"))
           do_help(0);
        else if (steq(argv[i]+1, "-man")) do_help(1);
        else if (steq(argv[i], "-c") || steq(argv[i], "-C")) {
            if (i >= argc-1) {
                do_error("Need command with option -c");
            }
            CopyName = argv[++i];
        }
        else if ((newTabStop = strtol(argv[i]+1, &tmp, 10)), (*tmp==0)) {
            TabStop = newTabStop;
            if (TabStop <= EntabMargin)
              EntabMargin = TabStop - 1;
        }
        else {
            for (j=1; argv[i][j]; ++j) {
                if (argv[i][j] == 'r' || argv[i][j] == 'R')  
                  ReplaceFiles = TRUE;
                else if (argv[i][j] == 'n' || argv[i][j] == 'N')  
                  FinishNewline = TRUE;
                else if (argv[i][j] == 'i' || argv[i][j] == 'I')  
                  IndentOnly = TRUE;
                else if (argv[i][j] == 'e' || argv[i][j] == 'E') {
                    Entab = TRUE;
                    if (isdigit(argv[i][j+1])) {
                        EntabMargin = 0;
                        for ( ; isdigit(argv[i][j+1]); ++j)
                          EntabMargin = 10*EntabMargin+argv[i][j+1]-'0';
                    }
                }
                else do_error("Unrecognized option(s) %s; -h for help",
                              argv[i]);
            }
        }
    }

    if (i == argc) do_error("No files to process");

    for (; i < argc; i++)
    {
        FILE *fp;

        if (steq(argv[i], "-")) {
            fp = stdin;
        }
        else if (0 == (fp = fopen(argv[i], "r"))) {
            do_error("File does not exist: %s", argv[i]);
        }

        if (ReplaceFiles) {
            FILE *ftmp;
            char nam[L_tmpnam];
            char buf[100+L_tmpnam];
            if (0 == (ftmp = fopen(tmpnam(nam), "w"))) {
                do_error("Could not open temporary file %s for writing",
                         nam);
            }
            detab(fp, ftmp);
            fclose(ftmp);
            fclose(fp);
            sprintf(buf, "%s %s %s", CopyName, nam, argv[i]);
            system(buf);
        }
        else {
            detab(fp, stdout);
            fclose(fp);
        }
    }

    return EXIT_SUCCESS;
}


void detab(FILE *in, FILE *out)
{
    int cstart = 0;       /* the first space, mod TabStop */
    int cstop = 0;        /* the current char, mod TabStop */
    int spacecount = 0;   /* the length of whitespace */
    int new_line = TRUE;  /* are we still indenting? */
    int ch;

    while ((ch = fgetc(in)) != EOF) {
        if (ch == '\n') {
            putc('\n', out);
            cstart = 0;
            cstop = 0;
            spacecount = 0;
            new_line = TRUE;
        }
        else if (ch == '\t') {
            if (IndentOnly && !new_line)
              putc('\t', out);
            else
              spacecount += (TabStop - (cstop % TabStop));
            cstop = TabStop;
        }
        else if (ch == ' ') {
            if (IndentOnly && !new_line)
              putc(' ', out);
            else
              ++spacecount;
            ++cstop;
        }
        else {
            if (spacecount) {
                if (Entab && (spacecount > EntabMargin))
                {
                    /* use tabs, then spaces */
                    int offset = TabStop - (cstart % TabStop);
                    while (spacecount >= offset) {
                        putc('\t', out);
                        spacecount -= offset;
                        offset = TabStop;
                    }
                    for ( ; spacecount; --spacecount)
                      putc(' ', out);
                }
                else {
                    /* use only spaces */
                    for ( ; spacecount; --spacecount)
                      putc(' ', out);
                }
            }
            putc(ch, out);
            cstart = cstop+1;
            ++cstop;
            new_line = FALSE;
        }
    }

    if (FinishNewline && cstop != 0)
      putc('\n', out);
}


void do_error(const char *fmat, ...)
{
    va_list ap;
    printf("%s: ", Argv0);
    va_start(ap, fmat);
    vprintf(fmat, ap);
    printf("\n");
    va_end(ap);
    exit(EXIT_FAILURE);
}


void do_help(int man)
{
    if (man) goto man;
  man:
    puts("detab [-?h] [-Ee[#]IiNnRr] [-c cmd] [tabstop] filenames");
    puts("Removes tab characters from a text file, replacing them"
           " with spaces.");
    puts("  -E: entab files (replacing multiple spaces with tabs)");
    puts("  -En (e.g., -e2): do not entab on n or fewer spaces");
    puts("  -I: detab/entab only at start of line (indent)");
    puts("  -N: make sure each file ends with a newline");
    puts("  -R: replace named files with detabbed versions");
    puts("  tabstop (e.g., -4, -20): tabstop every n characters");
    puts("  -c <cmd>: specify equivalent of Unix 'cp' (for use with -R)");
    puts("  --help: show this message");
    puts("  --man: show complete help text");
    exit(0);
}