/* vi: set sw=4 ts=4:
 *
 * Apply a "universal" diff.
 * Adapted from toybox's patch implementation.
 *
 * Copyright 2007 Rob Landley <rob@landley.net>
 *
 * see http://www.opengroup.org/onlinepubs/009695399/utilities/patch.html
 * (But only does -u, because who still cares about "ed"?)
 *
 * TODO:
 * -b backup
 * -l treat all whitespace as a single space
 * -d chdir first
 * -D define wrap #ifdef and #ifndef around changes
 * -o outfile output here instead of in place
 * -r rejectfile write rejected hunks to this file
 * --dry-run (regression!)
 *
 * -f force (no questions asked)
 * -F fuzz (number, default 2)
 * [file] which file to patch
 */

//config:config PATCH
//config:       bool "patch"
//config:       default y
//config:       help
//config:         Apply a unified diff formatted patch.

//applet:IF_PATCH(APPLET(patch, BB_DIR_USR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_PATCH) += patch.o

//usage:#define patch_trivial_usage
//usage:       "[OPTIONS] [ORIGFILE [PATCHFILE]]"
//usage:#define patch_full_usage "\n\n"
//usage:        IF_LONG_OPTS(
//usage:       "        -p,--strip N            Strip N leading components from file names"
//usage:     "\n        -i,--input DIFF         Read DIFF instead of stdin"
//usage:     "\n        -R,--reverse            Reverse patch"
//usage:     "\n        -N,--forward            Ignore already applied patches"
/*usage:     "\n        --dry-run               Don't actually change files" - TODO */
//usage:     "\n        -E,--remove-empty-files Remove output files if they become empty"
//usage:        )
//usage:        IF_NOT_LONG_OPTS(
//usage:       "        -p N    Strip N leading components from file names"
//usage:     "\n        -i DIFF Read DIFF instead of stdin"
//usage:     "\n        -R      Reverse patch"
//usage:     "\n        -N      Ignore already applied patches"
//usage:     "\n        -E      Remove output files if they become empty"
//usage:        )
/* -u "interpret as unified diff" is supported but not documented: this info is not useful for --help */
/* -x "debug" is supported but does nothing */
//usage:
//usage:#define patch_example_usage
//usage:       "$ patch -p1 < example.diff\n"
//usage:       "$ patch -p0 -i example.diff"

#include "libbb.h"


// libbb candidate?

struct double_list {
        struct double_list *next;
        struct double_list *prev;
        char *data;
};

// Free all the elements of a linked list
// Call freeit() on each element before freeing it.
static void dlist_free(struct double_list *list, void (*freeit)(void *data))
{
        while (list) {
                void *pop = list;
                list = list->next;
                freeit(pop);
                // Bail out also if list is circular.
                if (list == pop) break;
        }
}

// Add an entry before "list" element in (circular) doubly linked list
static struct double_list *dlist_add(struct double_list **list, char *data)
{
        struct double_list *llist;
        struct double_list *line = xmalloc(sizeof(*line));

        line->data = data;
        llist = *list;
        if (llist) {
                struct double_list *p;
                line->next = llist;
                p = line->prev = llist->prev;
                // (list is circular, we assume p is never NULL)
                p->next = line;
                llist->prev = line;
        } else
                *list = line->next = line->prev = line;

        return line;
}


struct globals {
        char *infile;
        long prefix;

        struct double_list *current_hunk;

        long oldline, oldlen, newline, newlen;
        long linenum;
        int context, state, hunknum;
        int filein, fileout;
        char *tempname;

        int exitval;
};
#define TT (*ptr_to_globals)
#define INIT_TT() do { \
        SET_PTR_TO_GLOBALS(xzalloc(sizeof(TT))); \
} while (0)


#define FLAG_STR "Rup:i:NEx"
/* FLAG_REVERSE must be == 1! Code uses this fact. */
#define FLAG_REVERSE (1 << 0)
#define FLAG_u       (1 << 1)
#define FLAG_PATHLEN (1 << 2)
#define FLAG_INPUT   (1 << 3)
#define FLAG_IGNORE  (1 << 4)
#define FLAG_RMEMPTY (1 << 5)
/* Enable this bit and use -x for debug output: */
#define FLAG_DEBUG   (0 << 6)

// Dispose of a line of input, either by writing it out or discarding it.

// state < 2: just free
// state = 2: write whole line to stderr
// state = 3: write whole line to fileout
// state > 3: write line+1 to fileout when *line != state

#define PATCH_DEBUG (option_mask32 & FLAG_DEBUG)

static void do_line(void *data)
{
        struct double_list *dlist = data;

        if (TT.state>1 && *dlist->data != TT.state)
                fdprintf(TT.state == 2 ? 2 : TT.fileout,
                        "%s\n", dlist->data+(TT.state>3 ? 1 : 0));

        if (PATCH_DEBUG) fdprintf(2, "DO %d: %s\n", TT.state, dlist->data);

        free(dlist->data);
        free(dlist);
}

static void finish_oldfile(void)
{
        if (TT.tempname) {
                // Copy the rest of the data and replace the original with the copy.
                char *temp;

                if (TT.filein != -1) {
                        bb_copyfd_eof(TT.filein, TT.fileout);
                        xclose(TT.filein);
                }
                xclose(TT.fileout);

                temp = xstrdup(TT.tempname);
                temp[strlen(temp) - 6] = '\0';
                rename(TT.tempname, temp);
                free(temp);

                free(TT.tempname);
                TT.tempname = NULL;
        }
        TT.fileout = TT.filein = -1;
}

static void fail_hunk(void)
{
        if (!TT.current_hunk) return;

        fdprintf(2, "Hunk %d FAILED %ld/%ld.\n", TT.hunknum, TT.oldline, TT.newline);
        TT.exitval = 1;

        // If we got to this point, we've seeked to the end.  Discard changes to
        // this file and advance to next file.

        TT.state = 2;
        TT.current_hunk->prev->next = NULL;
        dlist_free(TT.current_hunk, do_line);
        TT.current_hunk = NULL;

        // Abort the copy and delete the temporary file.
        close(TT.filein);
        close(TT.fileout);
        unlink(TT.tempname);
        free(TT.tempname);
        TT.tempname = NULL;

        TT.state = 0;
}

// Given a hunk of a unified diff, make the appropriate change to the file.
// This does not use the location information, but instead treats a hunk
// as a sort of regex.  Copies data from input to output until it finds
// the change to be made, then outputs the changed data and returns.
// (Finding EOF first is an error.)  This is a single pass operation, so
// multiple hunks must occur in order in the file.

static int apply_one_hunk(void)
{
        struct double_list *plist, *buf = NULL, *check;
        int matcheof = 0, reverse = option_mask32 & FLAG_REVERSE, backwarn = 0;
        /* Do we try "dummy" revert to check whether
         * to silently skip this hunk? Used to implement -N.
         */
        int dummy_revert = 0;

        // Break doubly linked list so we can use singly linked traversal function.
        TT.current_hunk->prev->next = NULL;

        // Match EOF if there aren't as many ending context lines as beginning
        for (plist = TT.current_hunk; plist; plist = plist->next) {
                if (plist->data[0]==' ') matcheof++;
                else matcheof = 0;
                if (PATCH_DEBUG) fdprintf(2, "HUNK:%s\n", plist->data);
        }
        matcheof = !matcheof || matcheof < TT.context;

        if (PATCH_DEBUG) fdprintf(2,"MATCHEOF=%c\n", matcheof ? 'Y' : 'N');

        // Loop through input data searching for this hunk.  Match all context
        // lines and all lines to be removed until we've found the end of a
        // complete hunk.
        plist = TT.current_hunk;
        buf = NULL;
        if (reverse ? TT.oldlen : TT.newlen) for (;;) {
                char *data = xmalloc_reads(TT.filein, NULL);

                TT.linenum++;

                // Figure out which line of hunk to compare with next.  (Skip lines
                // of the hunk we'd be adding.)
                while (plist && *plist->data == "+-"[reverse]) {
                        if (data && !strcmp(data, plist->data+1)) {
                                if (!backwarn) {
                                        backwarn = TT.linenum;
                                        if (option_mask32 & FLAG_IGNORE) {
                                                dummy_revert = 1;
                                                reverse ^= 1;
                                                continue;
                                        }
                                }
                        }
                        plist = plist->next;
                }

                // Is this EOF?
                if (!data) {
                        if (PATCH_DEBUG) fdprintf(2, "INEOF\n");

                        // Does this hunk need to match EOF?
                        if (!plist && matcheof) break;

                        if (backwarn)
                                fdprintf(2,"Possibly reversed hunk %d at %ld\n",
                                        TT.hunknum, TT.linenum);

                        // File ended before we found a place for this hunk.
                        fail_hunk();
                        goto done;
                }

                if (PATCH_DEBUG) fdprintf(2, "IN: %s\n", data);
                check = dlist_add(&buf, data);

                // Compare this line with next expected line of hunk.
                // todo: teach the strcmp() to ignore whitespace.

                // A match can fail because the next line doesn't match, or because
                // we hit the end of a hunk that needed EOF, and this isn't EOF.

                // If match failed, flush first line of buffered data and
                // recheck buffered data for a new match until we find one or run
                // out of buffer.

                for (;;) {
                        if (!plist || strcmp(check->data, plist->data+1)) {
                                // Match failed.  Write out first line of buffered data and
                                // recheck remaining buffered data for a new match.

                                if (PATCH_DEBUG)
                                        fdprintf(2, "NOT: %s\n", plist->data);

                                TT.state = 3;
                                check = buf;
                                buf = buf->next;
                                check->prev->next = buf;
                                buf->prev = check->prev;
                                do_line(check);
                                plist = TT.current_hunk;

                                // If we've reached the end of the buffer without confirming a
                                // match, read more lines.
                                if (check == buf) {
                                        buf = NULL;
                                        break;
                                }
                                check = buf;
                        } else {
                                if (PATCH_DEBUG)
                                        fdprintf(2, "MAYBE: %s\n", plist->data);
                                // This line matches.  Advance plist, detect successful match.
                                plist = plist->next;
                                if (!plist && !matcheof) goto out;
                                check = check->next;
                                if (check == buf) break;
                        }
                }
        }
out:
        // We have a match.  Emit changed data.
        TT.state = "-+"[reverse ^ dummy_revert];
        dlist_free(TT.current_hunk, do_line);
        TT.current_hunk = NULL;
        TT.state = 1;
done:
        if (buf) {
                buf->prev->next = NULL;
                dlist_free(buf, do_line);
        }

        return TT.state;
}

// Read a patch file and find hunks, opening/creating/deleting files.
// Call apply_one_hunk() on each hunk.

// state 0: Not in a hunk, look for +++.
// state 1: Found +++ file indicator, look for @@
// state 2: In hunk: counting initial context lines
// state 3: In hunk: getting body
// Like GNU patch, we don't require a --- line before the +++, and
// also allow the --- after the +++ line.

int patch_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int patch_main(int argc UNUSED_PARAM, char **argv)
{
        int opts;
        int reverse, state = 0;
        char *oldname = NULL, *newname = NULL;
        char *opt_p, *opt_i;
        long oldlen = oldlen; /* for compiler */
        long newlen = newlen; /* for compiler */

        INIT_TT();

        opts = getopt32(argv, FLAG_STR, &opt_p, &opt_i);
        argv += optind;
        reverse = opts & FLAG_REVERSE;
        TT.prefix = (opts & FLAG_PATHLEN) ? xatoi(opt_p) : 0; // can be negative!
        TT.filein = TT.fileout = -1;
        if (opts & FLAG_INPUT) {
                xmove_fd(xopen_stdin(opt_i), STDIN_FILENO);
        } else {
                if (argv[0] && argv[1]) {
                        xmove_fd(xopen_stdin(argv[1]), STDIN_FILENO);
                }
        }

        // Loop through the lines in the patch
        for(;;) {
                char *patchline;

                patchline = xmalloc_fgetline(stdin);
                if (!patchline) break;

                // Other versions of patch accept damaged patches,
                // so we need to also.
                if (!*patchline) {
                        free(patchline);
                        patchline = xstrdup(" ");
                }

                // Are we assembling a hunk?
                if (state >= 2) {
                        if (*patchline==' ' || *patchline=='+' || *patchline=='-') {
                                dlist_add(&TT.current_hunk, patchline);

                                if (*patchline != '+') oldlen--;
                                if (*patchline != '-') newlen--;

                                // Context line?
                                if (*patchline==' ' && state==2) TT.context++;
                                else state=3;

                                // If we've consumed all expected hunk lines, apply the hunk.

                                if (!oldlen && !newlen) state = apply_one_hunk();
                                continue;
                        }
                        fail_hunk();
                        state = 0;
                        continue;
                }

                // Open a new file?
                if (is_prefixed_with(patchline, "--- ") || is_prefixed_with(patchline, "+++ ")) {
                        char *s, **name = reverse ? &newname : &oldname;
                        int i;

                        if (*patchline == '+') {
                                name = reverse ? &oldname : &newname;
                                state = 1;
                        }

                        finish_oldfile();

                        if (!argv[0]) {
                                free(*name);
                                // Trim date from end of filename (if any).  We don't care.
                                for (s = patchline+4; *s && *s!='\t'; s++)
                                        if (*s=='\\' && s[1]) s++;
                                i = atoi(s);
                                if (i>1900 && i<=1970)
                                        *name = xstrdup("/dev/null");
                                else {
                                        *s = 0;
                                        *name = xstrdup(patchline+4);
                                }
                        }

                        // We defer actually opening the file because svn produces broken
                        // patches that don't signal they want to create a new file the
                        // way the patch man page says, so you have to read the first hunk
                        // and _guess_.

                // Start a new hunk?  Usually @@ -oldline,oldlen +newline,newlen @@
                // but a missing ,value means the value is 1.
                } else if (state == 1 && is_prefixed_with(patchline, "@@ -")) {
                        int i;
                        char *s = patchline+4;

                        // Read oldline[,oldlen] +newline[,newlen]

                        TT.oldlen = oldlen = TT.newlen = newlen = 1;
                        TT.oldline = strtol(s, &s, 10);
                        if (*s == ',') TT.oldlen = oldlen = strtol(s+1, &s, 10);
                        TT.newline = strtol(s+2, &s, 10);
                        if (*s == ',') TT.newlen = newlen = strtol(s+1, &s, 10);

                        if (oldlen < 1 && newlen < 1)
                                bb_error_msg_and_die("Really? %s", patchline);

                        TT.context = 0;
                        state = 2;

                        // If the --- line is missing or malformed, either oldname
                        // or (for -R) newname could be NULL -- but not both.  Like
                        // GNU patch, proceed based on the +++ line, and avoid SEGVs.
                        if (!oldname)
                                oldname = xstrdup("MISSING_FILENAME");
                        if (!newname)
                                newname = xstrdup("MISSING_FILENAME");

                        // If this is the first hunk, open the file.
                        if (TT.filein == -1) {
                                int oldsum, newsum, empty = 0;
                                char *name;

                                oldsum = TT.oldline + oldlen;
                                newsum = TT.newline + newlen;

                                name = reverse ? oldname : newname;

                                // We're deleting oldname if new file is /dev/null (before -p)
                                // or if new hunk is empty (zero context) after patching
                                if (!strcmp(name, "/dev/null") || !(reverse ? oldsum : newsum)) {
                                        name = reverse ? newname : oldname;
                                        empty = 1;
                                }

                                // Handle -p path truncation.
                                for (i = 0, s = name; *s;) {
                                        if ((option_mask32 & FLAG_PATHLEN) && TT.prefix == i)
                                                break;
                                        if (*s++ != '/')
                                                continue;
                                        while (*s == '/')
                                                s++;
                                        i++;
                                        name = s;
                                }
                                // If "patch FILE_TO_PATCH", completely ignore name from patch
                                if (argv[0])
                                        name = argv[0];

                                if (empty) {
                                        // File is empty after the patches have been applied
                                        state = 0;
                                        if (option_mask32 & FLAG_RMEMPTY) {
                                                // If flag -E or --remove-empty-files is set
                                                printf("removing %s\n", name);
                                                xunlink(name);
                                        } else {
                                                printf("patching file %s\n", name);
                                                xclose(xopen(name, O_WRONLY | O_TRUNC));
                                        }
                                // If we've got a file to open, do so.
                                } else if (!(option_mask32 & FLAG_PATHLEN) || i <= TT.prefix) {
                                        struct stat statbuf;

                                        // If the old file was null, we're creating a new one.
                                        if (!strcmp(oldname, "/dev/null") || !oldsum) {
                                                printf("creating %s\n", name);
                                                s = strrchr(name, '/');
                                                if (s) {
                                                        *s = 0;
                                                        bb_make_directory(name, -1, FILEUTILS_RECUR);
                                                        *s = '/';
                                                }
                                                TT.filein = xopen(name, O_CREAT|O_EXCL|O_RDWR);
                                        } else {
                                                printf("patching file %s\n", name);
                                                TT.filein = xopen(name, O_RDONLY);
                                        }

                                        TT.tempname = xasprintf("%sXXXXXX", name);
                                        TT.fileout = xmkstemp(TT.tempname);
                                        // Set permissions of output file
                                        fstat(TT.filein, &statbuf);
                                        fchmod(TT.fileout, statbuf.st_mode);

                                        TT.linenum = 0;
                                        TT.hunknum = 0;
                                }
                        }

                        TT.hunknum++;

                        continue;
                }

                // If we didn't continue above, discard this line.
                free(patchline);
        }

        finish_oldfile();

        if (ENABLE_FEATURE_CLEAN_UP) {
                free(oldname);
                free(newname);
        }

        return TT.exitval;
}