/*
 * apply.c
 *
 * Copyright (C) Linus Torvalds, 2005
 *
 * This applies patches on top of some (arbitrary) version of the SCM.
 *
 * NOTE! It does all its work in the index file, and only cares about
 * the files in the working directory if you tell it to "merge" the
 * patch apply.
 *
 * Even when merging it always takes the source from the index, and
 * uses the working tree as a "branch" for a 3-way merge.
 */
#include <ctype.h>
#include <fnmatch.h>
#include "cache.h"

// We default to the merge behaviour, since that's what most people would
// expect.
//
//  --check turns on checking that the working tree matches the
//    files that are being modified, but doesn't apply the patch
//  --stat does just a diffstat, and doesn't actually apply
//  --show-files shows the directory changes
//
static int merge_patch = 1;
static int check_index = 0;
static int write_index = 0;
static int diffstat = 0;
static int summary = 0;
static int check = 0;
static int apply = 1;
static int show_files = 0;
static const char apply_usage[] =
"git-apply [--no-merge] [--stat] [--summary] [--check] [--index] [--apply] [--show-files] <patch>...";

/*
 * For "diff-stat" like behaviour, we keep track of the biggest change
 * we've seen, and the longest filename. That allows us to do simple
 * scaling.
 */
static int max_change, max_len;

/*
 * Various "current state", notably line numbers and what
 * file (and how) we're patching right now.. The "is_xxxx"
 * things are flags, where -1 means "don't know yet".
 */
static int linenr = 1;

struct fragment {
        unsigned long oldpos, oldlines;
        unsigned long newpos, newlines;
        const char *patch;
        int size;
        struct fragment *next;
};

struct patch {
        char *new_name, *old_name, *def_name;
        unsigned int old_mode, new_mode;
        int is_rename, is_copy, is_new, is_delete;
        int lines_added, lines_deleted;
        int score;
        struct fragment *fragments;
        char *result;
        unsigned long resultsize;
        struct patch *next;
};

#define CHUNKSIZE (8192)
#define SLOP (16)

static void *read_patch_file(int fd, unsigned long *sizep)
{
        unsigned long size = 0, alloc = CHUNKSIZE;
        void *buffer = xmalloc(alloc);

        for (;;) {
                int nr = alloc - size;
                if (nr < 1024) {
                        alloc += CHUNKSIZE;
                        buffer = xrealloc(buffer, alloc);
                        nr = alloc - size;
                }
                nr = read(fd, buffer + size, nr);
                if (!nr)
                        break;
                if (nr < 0) {
                        if (errno == EAGAIN)
                                continue;
                        die("git-apply: read returned %s", strerror(errno));
                }
                size += nr;
        }
        *sizep = size;

        /*
         * Make sure that we have some slop in the buffer
         * so that we can do speculative "memcmp" etc, and
         * see to it that it is NUL-filled.
         */
        if (alloc < size + SLOP)
                buffer = xrealloc(buffer, size + SLOP);
        memset(buffer + size, 0, SLOP);
        return buffer;
}

static unsigned long linelen(const char *buffer, unsigned long size)
{
        unsigned long len = 0;
        while (size--) {
                len++;
                if (*buffer++ == '\n')
                        break;
        }
        return len;
}

static int is_dev_null(const char *str)
{
        return !memcmp("/dev/null", str, 9) && isspace(str[9]);
}

#define TERM_SPACE      1
#define TERM_TAB        2

static int name_terminate(const char *name, int namelen, int c, int terminate)
{
        if (c == ' ' && !(terminate & TERM_SPACE))
                return 0;
        if (c == '\t' && !(terminate & TERM_TAB))
                return 0;

        return 1;
}

static char * find_name(const char *line, char *def, int p_value, int terminate)
{
        int len;
        const char *start = line;
        char *name;

        for (;;) {
                char c = *line;

                if (isspace(c)) {
                        if (c == '\n')
                                break;
                        if (name_terminate(start, line-start, c, terminate))
                                break;
                }
                line++;
                if (c == '/' && !--p_value)
                        start = line;
        }
        if (!start)
                return def;
        len = line - start;
        if (!len)
                return def;

        /*
         * Generally we prefer the shorter name, especially
         * if the other one is just a variation of that with
         * something else tacked on to the end (ie "file.orig"
         * or "file~").
         */
        if (def) {
                int deflen = strlen(def);
                if (deflen < len && !strncmp(start, def, deflen))
                        return def;
        }

        name = xmalloc(len + 1);
        memcpy(name, start, len);
        name[len] = 0;
        free(def);
        return name;
}

/*
 * Get the name etc info from the --/+++ lines of a traditional patch header
 *
 * NOTE! This hardcodes "-p1" behaviour in filename detection.
 *
 * FIXME! The end-of-filename heuristics are kind of screwy. For existing
 * files, we can happily check the index for a match, but for creating a
 * new file we should try to match whatever "patch" does. I have no idea.
 */
static void parse_traditional_patch(const char *first, const char *second, struct patch *patch)
{
        int p_value = 1;
        char *name;

        first += 4;     // skip "--- "
        second += 4;    // skip "+++ "
        if (is_dev_null(first)) {
                patch->is_new = 1;
                patch->is_delete = 0;
                name = find_name(second, NULL, p_value, TERM_SPACE | TERM_TAB);
                patch->new_name = name;
        } else if (is_dev_null(second)) {
                patch->is_new = 0;
                patch->is_delete = 1;
                name = find_name(first, NULL, p_value, TERM_SPACE | TERM_TAB);
                patch->old_name = name;
        } else {
                name = find_name(first, NULL, p_value, TERM_SPACE | TERM_TAB);
                name = find_name(second, name, p_value, TERM_SPACE | TERM_TAB);
                patch->old_name = patch->new_name = name;
        }
        if (!name)
                die("unable to find filename in patch at line %d", linenr);
}

static int gitdiff_hdrend(const char *line, struct patch *patch)
{
        return -1;
}

/*
 * We're anal about diff header consistency, to make
 * sure that we don't end up having strange ambiguous
 * patches floating around.
 *
 * As a result, gitdiff_{old|new}name() will check
 * their names against any previous information, just
 * to make sure..
 */
static char *gitdiff_verify_name(const char *line, int isnull, char *orig_name, const char *oldnew)
{
        int len;
        const char *name;

        if (!orig_name && !isnull)
                return find_name(line, NULL, 1, 0);

        name = "/dev/null";
        len = 9;
        if (orig_name) {
                name = orig_name;
                len = strlen(name);
                if (isnull)
                        die("git-apply: bad git-diff - expected /dev/null, got %s on line %d", name, linenr);
        }

        if (*name == '/')
                goto absolute_path;

        for (;;) {
                char c = *line++;
                if (c == '\n')
                        break;
                if (c != '/')
                        continue;
absolute_path:
                if (memcmp(line, name, len) || line[len] != '\n')
                        break;
                return orig_name;
        }
        die("git-apply: bad git-diff - inconsistent %s filename on line %d", oldnew, linenr);
        return NULL;
}

static int gitdiff_oldname(const char *line, struct patch *patch)
{
        patch->old_name = gitdiff_verify_name(line, patch->is_new, patch->old_name, "old");
        return 0;
}

static int gitdiff_newname(const char *line, struct patch *patch)
{
        patch->new_name = gitdiff_verify_name(line, patch->is_delete, patch->new_name, "new");
        return 0;
}

static int gitdiff_oldmode(const char *line, struct patch *patch)
{
        patch->old_mode = strtoul(line, NULL, 8);
        return 0;
}

static int gitdiff_newmode(const char *line, struct patch *patch)
{
        patch->new_mode = strtoul(line, NULL, 8);
        return 0;
}

static int gitdiff_delete(const char *line, struct patch *patch)
{
        patch->is_delete = 1;
        patch->old_name = patch->def_name;
        return gitdiff_oldmode(line, patch);
}

static int gitdiff_newfile(const char *line, struct patch *patch)
{
        patch->is_new = 1;
        patch->new_name = patch->def_name;
        return gitdiff_newmode(line, patch);
}

static int gitdiff_copysrc(const char *line, struct patch *patch)
{
        patch->is_copy = 1;
        patch->old_name = find_name(line, NULL, 0, 0);
        return 0;
}

static int gitdiff_copydst(const char *line, struct patch *patch)
{
        patch->is_copy = 1;
        patch->new_name = find_name(line, NULL, 0, 0);
        return 0;
}

static int gitdiff_renamesrc(const char *line, struct patch *patch)
{
        patch->is_rename = 1;
        patch->old_name = find_name(line, NULL, 0, 0);
        return 0;
}

static int gitdiff_renamedst(const char *line, struct patch *patch)
{
        patch->is_rename = 1;
        patch->new_name = find_name(line, NULL, 0, 0);
        return 0;
}

static int gitdiff_similarity(const char *line, struct patch *patch)
{
        if ((patch->score = strtoul(line, NULL, 10)) == ULONG_MAX)
                patch->score = 0;
        return 0;
}

static int gitdiff_dissimilarity(const char *line, struct patch *patch)
{
        if ((patch->score = strtoul(line, NULL, 10)) == ULONG_MAX)
                patch->score = 0;
        return 0;
}

/*
 * This is normal for a diff that doesn't change anything: we'll fall through
 * into the next diff. Tell the parser to break out.
 */
static int gitdiff_unrecognized(const char *line, struct patch *patch)
{
        return -1;
}

static char *git_header_name(char *line)
{
        int len;
        char *name, *second;

        /*
         * Find the first '/'
         */
        name = line;
        for (;;) {
                char c = *name++;
                if (c == '\n')
                        return NULL;
                if (c == '/')
                        break;
        }

        /*
         * We don't accept absolute paths (/dev/null) as possibly valid
         */
        if (name == line+1)
                return NULL;

        /*
         * Accept a name only if it shows up twice, exactly the same
         * form.
         */
        for (len = 0 ; ; len++) {
                char c = name[len];

                switch (c) {
                default:
                        continue;
                case '\n':
                        break;
                case '\t': case ' ':
                        second = name+len;
                        for (;;) {
                                char c = *second++;
                                if (c == '\n')
                                        return NULL;
                                if (c == '/')
                                        break;
                        }
                        if (second[len] == '\n' && !memcmp(name, second, len)) {
                                char *ret = xmalloc(len + 1);
                                memcpy(ret, name, len);
                                ret[len] = 0;
                                return ret;
                        }
                }
        }
        return NULL;
}

/* Verify that we recognize the lines following a git header */
static int parse_git_header(char *line, int len, unsigned int size, struct patch *patch)
{
        unsigned long offset;

        /* A git diff has explicit new/delete information, so we don't guess */
        patch->is_new = 0;
        patch->is_delete = 0;

        /*
         * Some things may not have the old name in the
         * rest of the headers anywhere (pure mode changes,
         * or removing or adding empty files), so we get
         * the default name from the header.
         */
        patch->def_name = git_header_name(line + strlen("diff --git "));

        line += len;
        size -= len;
        linenr++;
        for (offset = len ; size > 0 ; offset += len, size -= len, line += len, linenr++) {
                static const struct opentry {
                        const char *str;
                        int (*fn)(const char *, struct patch *);
                } optable[] = {
                        { "@@ -", gitdiff_hdrend },
                        { "--- ", gitdiff_oldname },
                        { "+++ ", gitdiff_newname },
                        { "old mode ", gitdiff_oldmode },
                        { "new mode ", gitdiff_newmode },
                        { "deleted file mode ", gitdiff_delete },
                        { "new file mode ", gitdiff_newfile },
                        { "copy from ", gitdiff_copysrc },
                        { "copy to ", gitdiff_copydst },
                        { "rename old ", gitdiff_renamesrc },
                        { "rename new ", gitdiff_renamedst },
                        { "rename from ", gitdiff_renamesrc },
                        { "rename to ", gitdiff_renamedst },
                        { "similarity index ", gitdiff_similarity },
                        { "dissimilarity index ", gitdiff_dissimilarity },
                        { "", gitdiff_unrecognized },
                };
                int i;

                len = linelen(line, size);
                if (!len || line[len-1] != '\n')
                        break;
                for (i = 0; i < sizeof(optable) / sizeof(optable[0]); i++) {
                        const struct opentry *p = optable + i;
                        int oplen = strlen(p->str);
                        if (len < oplen || memcmp(p->str, line, oplen))
                                continue;
                        if (p->fn(line + oplen, patch) < 0)
                                return offset;
                        break;
                }
        }

        return offset;
}

static int parse_num(const char *line, unsigned long *p)
{
        char *ptr;

        if (!isdigit(*line))
                return 0;
        *p = strtoul(line, &ptr, 10);
        return ptr - line;
}

static int parse_range(const char *line, int len, int offset, const char *expect,
                        unsigned long *p1, unsigned long *p2)
{
        int digits, ex;

        if (offset < 0 || offset >= len)
                return -1;
        line += offset;
        len -= offset;

        digits = parse_num(line, p1);
        if (!digits)
                return -1;

        offset += digits;
        line += digits;
        len -= digits;

        *p2 = *p1;
        if (*line == ',') {
                digits = parse_num(line+1, p2);
                if (!digits)
                        return -1;

                offset += digits+1;
                line += digits+1;
                len -= digits+1;
        }

        ex = strlen(expect);
        if (ex > len)
                return -1;
        if (memcmp(line, expect, ex))
                return -1;

        return offset + ex;
}

/*
 * Parse a unified diff fragment header of the
 * form "@@ -a,b +c,d @@"
 */
static int parse_fragment_header(char *line, int len, struct fragment *fragment)
{
        int offset;

        if (!len || line[len-1] != '\n')
                return -1;

        /* Figure out the number of lines in a fragment */
        offset = parse_range(line, len, 4, " +", &fragment->oldpos, &fragment->oldlines);
        offset = parse_range(line, len, offset, " @@", &fragment->newpos, &fragment->newlines);

        return offset;
}

static int find_header(char *line, unsigned long size, int *hdrsize, struct patch *patch)
{
        unsigned long offset, len;

        patch->is_rename = patch->is_copy = 0;
        patch->is_new = patch->is_delete = -1;
        patch->old_mode = patch->new_mode = 0;
        patch->old_name = patch->new_name = NULL;
        for (offset = 0; size > 0; offset += len, size -= len, line += len, linenr++) {
                unsigned long nextlen;

                len = linelen(line, size);
                if (!len)
                        break;

                /* Testing this early allows us to take a few shortcuts.. */
                if (len < 6)
                        continue;

                /*
                 * Make sure we don't find any unconnected patch fragmants.
                 * That's a sign that we didn't find a header, and that a
                 * patch has become corrupted/broken up.
                 */
                if (!memcmp("@@ -", line, 4)) {
                        struct fragment dummy;
                        if (parse_fragment_header(line, len, &dummy) < 0)
                                continue;
                        error("patch fragment without header at line %d: %.*s", linenr, (int)len-1, line);
                }

                if (size < len + 6)
                        break;

                /*
                 * Git patch? It might not have a real patch, just a rename
                 * or mode change, so we handle that specially
                 */
                if (!memcmp("diff --git ", line, 11)) {
                        int git_hdr_len = parse_git_header(line, len, size, patch);
                        if (git_hdr_len <= len)
                                continue;
                        if (!patch->old_name && !patch->new_name) {
                                if (!patch->def_name)
                                        die("git diff header lacks filename information (line %d)", linenr);
                                patch->old_name = patch->new_name = patch->def_name;
                        }
                        *hdrsize = git_hdr_len;
                        return offset;
                }

                /** --- followed by +++ ? */
                if (memcmp("--- ", line,  4) || memcmp("+++ ", line + len, 4))
                        continue;

                /*
                 * We only accept unified patches, so we want it to
                 * at least have "@@ -a,b +c,d @@\n", which is 14 chars
                 * minimum
                 */
                nextlen = linelen(line + len, size - len);
                if (size < nextlen + 14 || memcmp("@@ -", line + len + nextlen, 4))
                        continue;

                /* Ok, we'll consider it a patch */
                parse_traditional_patch(line, line+len, patch);
                *hdrsize = len + nextlen;
                linenr += 2;
                return offset;
        }
        return -1;
}

/*
 * Parse a unified diff. Note that this really needs
 * to parse each fragment separately, since the only
 * way to know the difference between a "---" that is
 * part of a patch, and a "---" that starts the next
 * patch is to look at the line counts..
 */
static int parse_fragment(char *line, unsigned long size, struct patch *patch, struct fragment *fragment)
{
        int added, deleted;
        int len = linelen(line, size), offset;
        unsigned long oldlines, newlines;

        offset = parse_fragment_header(line, len, fragment);
        if (offset < 0)
                return -1;
        oldlines = fragment->oldlines;
        newlines = fragment->newlines;

        if (patch->is_new < 0) {
                patch->is_new =  !oldlines;
                if (!oldlines)
                        patch->old_name = NULL;
        }
        if (patch->is_delete < 0) {
                patch->is_delete = !newlines;
                if (!newlines)
                        patch->new_name = NULL;
        }

        if (patch->is_new != !oldlines)
                return error("new file depends on old contents");
        if (patch->is_delete != !newlines) {
                if (newlines)
                        return error("deleted file still has contents");
                fprintf(stderr, "** warning: file %s becomes empty but is not deleted\n", patch->new_name);
        }

        /* Parse the thing.. */
        line += len;
        size -= len;
        linenr++;
        added = deleted = 0;
        for (offset = len; size > 0; offset += len, size -= len, line += len, linenr++) {
                if (!oldlines && !newlines)
                        break;
                len = linelen(line, size);
                if (!len || line[len-1] != '\n')
                        return -1;
                switch (*line) {
                default:
                        return -1;
                case ' ':
                        oldlines--;
                        newlines--;
                        break;
                case '-':
                        deleted++;
                        oldlines--;
                        break;
                case '+':
                        added++;
                        newlines--;
                        break;
                /* We allow "\ No newline at end of file" */
                case '\\':
                        if (len < 12 || memcmp(line, "\\ No newline", 12))
                                return -1;
                        break;
                }
        }
        /* If a fragment ends with an incomplete line, we failed to include
         * it in the above loop because we hit oldlines == newlines == 0
         * before seeing it.
         */
        if (12 < size && !memcmp(line, "\\ No newline", 12))
                offset += linelen(line, size);

        patch->lines_added += added;
        patch->lines_deleted += deleted;
        return offset;
}

static int parse_single_patch(char *line, unsigned long size, struct patch *patch)
{
        unsigned long offset = 0;
        struct fragment **fragp = &patch->fragments;

        while (size > 4 && !memcmp(line, "@@ -", 4)) {
                struct fragment *fragment;
                int len;

                fragment = xmalloc(sizeof(*fragment));
                memset(fragment, 0, sizeof(*fragment));
                len = parse_fragment(line, size, patch, fragment);
                if (len <= 0)
                        die("corrupt patch at line %d", linenr);

                fragment->patch = line;
                fragment->size = len;

                *fragp = fragment;
                fragp = &fragment->next;

                offset += len;
                line += len;
                size -= len;
        }
        return offset;
}

static int parse_chunk(char *buffer, unsigned long size, struct patch *patch)
{
        int hdrsize, patchsize;
        int offset = find_header(buffer, size, &hdrsize, patch);

        if (offset < 0)
                return offset;

        patchsize = parse_single_patch(buffer + offset + hdrsize, size - offset - hdrsize, patch);

        return offset + hdrsize + patchsize;
}

static const char pluses[] = "++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++";
static const char minuses[]= "----------------------------------------------------------------------";

static void show_stats(struct patch *patch)
{
        const char *prefix = "";
        char *name = patch->new_name;
        int len, max, add, del, total;

        if (!name)
                name = patch->old_name;

        /*
         * "scale" the filename
         */
        len = strlen(name);
        max = max_len;
        if (max > 50)
                max = 50;
        if (len > max) {
                char *slash;
                prefix = "...";
                max -= 3;
                name += len - max;
                slash = strchr(name, '/');
                if (slash)
                        name = slash;
        }
        len = max;

        /*
         * scale the add/delete
         */
        max = max_change;
        if (max + len > 70)
                max = 70 - len;

        add = patch->lines_added;
        del = patch->lines_deleted;
        total = add + del;

        if (max_change > 0) {
                total = (total * max + max_change / 2) / max_change;
                add = (add * max + max_change / 2) / max_change;
                del = total - add;
        }
        printf(" %s%-*s |%5d %.*s%.*s\n", prefix,
                len, name, patch->lines_added + patch->lines_deleted,
                add, pluses, del, minuses);
}

static int read_old_data(struct stat *st, const char *path, void *buf, unsigned long size)
{
        int fd;
        unsigned long got;

        switch (st->st_mode & S_IFMT) {
        case S_IFLNK:
                return readlink(path, buf, size);
        case S_IFREG:
                fd = open(path, O_RDONLY);
                if (fd < 0)
                        return error("unable to open %s", path);
                got = 0;
                for (;;) {
                        int ret = read(fd, buf + got, size - got);
                        if (ret < 0) {
                                if (errno == EAGAIN)
                                        continue;
                                break;
                        }
                        if (!ret)
                                break;
                        got += ret;
                }
                close(fd);
                return got;

        default:
                return -1;
        }
}

static int find_offset(const char *buf, unsigned long size, const char *fragment, unsigned long fragsize, int line)
{
        int i;
        unsigned long start, backwards, forwards;

        if (fragsize > size)
                return -1;

        start = 0;
        if (line > 1) {
                unsigned long offset = 0;
                i = line-1;
                while (offset + fragsize <= size) {
                        if (buf[offset++] == '\n') {
                                start = offset;
                                if (!--i)
                                        break;
                        }
                }
        }

        /* Exact line number? */
        if (!memcmp(buf + start, fragment, fragsize))
                return start;

        /*
         * There's probably some smart way to do this, but I'll leave
         * that to the smart and beautiful people. I'm simple and stupid.
         */
        backwards = start;
        forwards = start;
        for (i = 0; ; i++) {
                unsigned long try;
                int n;

                /* "backward" */
                if (i & 1) {
                        if (!backwards) {
                                if (forwards + fragsize > size)
                                        break;
                                continue;
                        }
                        do {
                                --backwards;
                        } while (backwards && buf[backwards-1] != '\n');
                        try = backwards;
                } else {
                        while (forwards + fragsize <= size) {
                                if (buf[forwards++] == '\n')
                                        break;
                        }
                        try = forwards;
                }

                if (try + fragsize > size)
                        continue;
                if (memcmp(buf + try, fragment, fragsize))
                        continue;
                n = (i >> 1)+1;
                if (i & 1)
                        n = -n;
                return try;
        }

        /*
         * We should start searching forward and backward.
         */
        return -1;
}

struct buffer_desc {
        char *buffer;
        unsigned long size;
        unsigned long alloc;
};

static int apply_one_fragment(struct buffer_desc *desc, struct fragment *frag)
{
        char *buf = desc->buffer;
        const char *patch = frag->patch;
        int offset, size = frag->size;
        char *old = xmalloc(size);
        char *new = xmalloc(size);
        int oldsize = 0, newsize = 0;

        while (size > 0) {
                int len = linelen(patch, size);
                int plen;

                if (!len)
                        break;

                /*
                 * "plen" is how much of the line we should use for
                 * the actual patch data. Normally we just remove the
                 * first character on the line, but if the line is
                 * followed by "\ No newline", then we also remove the
                 * last one (which is the newline, of course).
                 */
                plen = len-1;
                if (len < size && patch[len] == '\\')
                        plen--;
                switch (*patch) {
                case ' ':
                case '-':
                        memcpy(old + oldsize, patch + 1, plen);
                        oldsize += plen;
                        if (*patch == '-')
                                break;
                /* Fall-through for ' ' */
                case '+':
                        memcpy(new + newsize, patch + 1, plen);
                        newsize += plen;
                        break;
                case '@': case '\\':
                        /* Ignore it, we already handled it */
                        break;
                default:
                        return -1;
                }
                patch += len;
                size -= len;
        }

        offset = find_offset(buf, desc->size, old, oldsize, frag->newpos);
        if (offset >= 0) {
                int diff = newsize - oldsize;
                unsigned long size = desc->size + diff;
                unsigned long alloc = desc->alloc;

                if (size > alloc) {
                        alloc = size + 8192;
                        desc->alloc = alloc;
                        buf = xrealloc(buf, alloc);
                        desc->buffer = buf;
                }
                desc->size = size;
                memmove(buf + offset + newsize, buf + offset + oldsize, size - offset - newsize);
                memcpy(buf + offset, new, newsize);
                offset = 0;
        }

        free(old);
        free(new);
        return offset;
}

static int apply_fragments(struct buffer_desc *desc, struct patch *patch)
{
        struct fragment *frag = patch->fragments;

        while (frag) {
                if (apply_one_fragment(desc, frag) < 0)
                        return error("patch failed: %s:%ld", patch->old_name, frag->oldpos);
                frag = frag->next;
        }
        return 0;
}

static int apply_data(struct patch *patch, struct stat *st)
{
        char *buf;
        unsigned long size, alloc;
        struct buffer_desc desc;

        size = 0;
        alloc = 0;
        buf = NULL;
        if (patch->old_name) {
                size = st->st_size;
                alloc = size + 8192;
                buf = xmalloc(alloc);
                if (read_old_data(st, patch->old_name, buf, alloc) != size)
                        return error("read of %s failed", patch->old_name);
        }

        desc.size = size;
        desc.alloc = alloc;
        desc.buffer = buf;
        if (apply_fragments(&desc, patch) < 0)
                return -1;
        patch->result = desc.buffer;
        patch->resultsize = desc.size;

        if (patch->is_delete && patch->resultsize)
                return error("removal patch leaves file contents");

        return 0;
}

static int check_patch(struct patch *patch)
{
        struct stat st;
        const char *old_name = patch->old_name;
        const char *new_name = patch->new_name;

        if (old_name) {
                int changed;

                if (lstat(old_name, &st) < 0)
                        return error("%s: %s", old_name, strerror(errno));
                if (check_index) {
                        int pos = cache_name_pos(old_name, strlen(old_name));
                        if (pos < 0)
                                return error("%s: does not exist in index", old_name);
                        changed = ce_match_stat(active_cache[pos], &st);
                        if (changed)
                                return error("%s: does not match index", old_name);
                }
                if (patch->is_new < 0)
                        patch->is_new = 0;
                st.st_mode = ntohl(create_ce_mode(st.st_mode));
                if (!patch->old_mode)
                        patch->old_mode = st.st_mode;
                if ((st.st_mode ^ patch->old_mode) & S_IFMT)
                        return error("%s: wrong type", old_name);
                if (st.st_mode != patch->old_mode)
                        fprintf(stderr, "warning: %s has type %o, expected %o\n",
                                old_name, st.st_mode, patch->old_mode);
        }

        if (new_name && (patch->is_new | patch->is_rename | patch->is_copy)) {
                if (check_index && cache_name_pos(new_name, strlen(new_name)) >= 0)
                        return error("%s: already exists in index", new_name);
                if (!lstat(new_name, &st))
                        return error("%s: already exists in working directory", new_name);
                if (errno != ENOENT)
                        return error("%s: %s", new_name, strerror(errno));
                if (!patch->new_mode)
                        patch->new_mode = S_IFREG | 0644;
        }

        if (new_name && old_name) {
                int same = !strcmp(old_name, new_name);
                if (!patch->new_mode)
                        patch->new_mode = patch->old_mode;
                if ((patch->old_mode ^ patch->new_mode) & S_IFMT)
                        return error("new mode (%o) of %s does not match old mode (%o)%s%s",
                                patch->new_mode, new_name, patch->old_mode,
                                same ? "" : " of ", same ? "" : old_name);
        }       

        if (apply_data(patch, &st) < 0)
                return error("%s: patch does not apply", old_name);
        return 0;
}

static int check_patch_list(struct patch *patch)
{
        int error = 0;

        for (;patch ; patch = patch->next)
                error |= check_patch(patch);
        return error;
}

static void show_file(int c, unsigned int mode, const char *name)
{
        printf("%c %o %s\n", c, mode, name);
}

static void show_file_list(struct patch *patch)
{
        for (;patch ; patch = patch->next) {
                if (patch->is_rename) {
                        show_file('-', patch->old_mode, patch->old_name);
                        show_file('+', patch->new_mode, patch->new_name);
                        continue;
                }
                if (patch->is_copy || patch->is_new) {
                        show_file('+', patch->new_mode, patch->new_name);
                        continue;
                }
                if (patch->is_delete) {
                        show_file('-', patch->old_mode, patch->old_name);
                        continue;
                }
                if (patch->old_mode && patch->new_mode && patch->old_mode != patch->new_mode) {
                        printf("M %o:%o %s\n", patch->old_mode, patch->new_mode, patch->old_name);
                        continue;
                }
                printf("M %o %s\n", patch->old_mode, patch->old_name);
        }
}

static void stat_patch_list(struct patch *patch)
{
        int files, adds, dels;

        for (files = adds = dels = 0 ; patch ; patch = patch->next) {
                files++;
                adds += patch->lines_added;
                dels += patch->lines_deleted;
                show_stats(patch);
        }

        printf(" %d files changed, %d insertions(+), %d deletions(-)\n", files, adds, dels);
}

static void show_file_mode_name(const char *newdelete, unsigned int mode, const char *name)
{
        if (mode)
                printf(" %s mode %06o %s\n", newdelete, mode, name);
        else
                printf(" %s %s\n", newdelete, name);
}

static void show_mode_change(struct patch *p, int show_name)
{
        if (p->old_mode && p->new_mode && p->old_mode != p->new_mode) {
                if (show_name)
                        printf(" mode change %06o => %06o %s\n",
                               p->old_mode, p->new_mode, p->new_name);
                else
                        printf(" mode change %06o => %06o\n",
                               p->old_mode, p->new_mode);
        }
}

static void show_rename_copy(struct patch *p)
{
        const char *renamecopy = p->is_rename ? "rename" : "copy";
        const char *old, *new;

        /* Find common prefix */
        old = p->old_name;
        new = p->new_name;
        while (1) {
                const char *slash_old, *slash_new;
                slash_old = strchr(old, '/');
                slash_new = strchr(new, '/');
                if (!slash_old ||
                    !slash_new ||
                    slash_old - old != slash_new - new ||
                    memcmp(old, new, slash_new - new))
                        break;
                old = slash_old + 1;
                new = slash_new + 1;
        }
        /* p->old_name thru old is the common prefix, and old and new
         * through the end of names are renames
         */
        if (old != p->old_name)
                printf(" %s %.*s{%s => %s} (%d%%)\n", renamecopy,
                       (int)(old - p->old_name), p->old_name,
                       old, new, p->score);
        else
                printf(" %s %s => %s (%d%%)\n", renamecopy,
                       p->old_name, p->new_name, p->score);
        show_mode_change(p, 0);
}

static void summary_patch_list(struct patch *patch)
{
        struct patch *p;

        for (p = patch; p; p = p->next) {
                if (p->is_new)
                        show_file_mode_name("create", p->new_mode, p->new_name);
                else if (p->is_delete)
                        show_file_mode_name("delete", p->old_mode, p->old_name);
                else {
                        if (p->is_rename || p->is_copy)
                                show_rename_copy(p);
                        else {
                                if (p->score) {
                                        printf(" rewrite %s (%d%%)\n",
                                               p->new_name, p->score);
                                        show_mode_change(p, 0);
                                }
                                else
                                        show_mode_change(p, 1);
                        }
                }
        }
}

static void patch_stats(struct patch *patch)
{
        int lines = patch->lines_added + patch->lines_deleted;

        if (lines > max_change)
                max_change = lines;
        if (patch->old_name) {
                int len = strlen(patch->old_name);
                if (len > max_len)
                        max_len = len;
        }
        if (patch->new_name) {
                int len = strlen(patch->new_name);
                if (len > max_len)
                        max_len = len;
        }
}

static void remove_file(struct patch *patch)
{
        if (write_index) {
                if (remove_file_from_cache(patch->old_name) < 0)
                        die("unable to remove %s from index", patch->old_name);
        }
        unlink(patch->old_name);
}

static void add_index_file(const char *path, unsigned mode, void *buf, unsigned long size)
{
        struct stat st;
        struct cache_entry *ce;
        int namelen = strlen(path);
        unsigned ce_size = cache_entry_size(namelen);

        if (!write_index)
                return;

        ce = xmalloc(ce_size);
        memset(ce, 0, ce_size);
        memcpy(ce->name, path, namelen);
        ce->ce_mode = create_ce_mode(mode);
        ce->ce_flags = htons(namelen);
        if (lstat(path, &st) < 0)
                die("unable to stat newly created file %s", path);
        fill_stat_cache_info(ce, &st);
        if (write_sha1_file(buf, size, "blob", ce->sha1) < 0)
                die("unable to create backing store for newly created file %s", path);
        if (add_cache_entry(ce, ADD_CACHE_OK_TO_ADD) < 0)
                die("unable to add cache entry for %s", path);
}

static void create_subdirectories(const char *path)
{
        int len = strlen(path);
        char *buf = xmalloc(len + 1);
        const char *slash = path;

        while ((slash = strchr(slash+1, '/')) != NULL) {
                len = slash - path;
                memcpy(buf, path, len);
                buf[len] = 0;
                if (mkdir(buf, 0777) < 0) {
                        if (errno != EEXIST)
                                break;
                }
        }
        free(buf);
}

static int try_create_file(const char *path, unsigned int mode, const char *buf, unsigned long size)
{
        int fd;

        if (S_ISLNK(mode))
                return symlink(buf, path);
        fd = open(path, O_CREAT | O_EXCL | O_WRONLY | O_TRUNC, (mode & 0100) ? 0777 : 0666);
        if (fd < 0)
                return -1;
        while (size) {
                int written = write(fd, buf, size);
                if (written < 0) {
                        if (errno == EINTR || errno == EAGAIN)
                                continue;
                        die("writing file %s: %s", path, strerror(errno));
                }
                if (!written)
                        die("out of space writing file %s", path);
                buf += written;
                size -= written;
        }
        if (close(fd) < 0)
                die("closing file %s: %s", path, strerror(errno));
        return 0;
}

/*
 * We optimistically assume that the directories exist,
 * which is true 99% of the time anyway. If they don't,
 * we create them and try again.
 */
static void create_one_file(const char *path, unsigned mode, const char *buf, unsigned long size)
{
        if (!try_create_file(path, mode, buf, size))
                return;

        if (errno == ENOENT) {
                create_subdirectories(path);
                if (!try_create_file(path, mode, buf, size))
                        return;
        }

        if (errno == EEXIST) {
                unsigned int nr = getpid();

                for (;;) {
                        const char *newpath;
                        newpath = mkpath("%s~%u", path, nr);
                        if (!try_create_file(newpath, mode, buf, size)) {
                                if (!rename(newpath, path))
                                        return;
                                unlink(newpath);
                                break;
                        }
                        if (errno != EEXIST)
                                break;
                }                       
        }
        die("unable to write file %s mode %o", path, mode);
}

static void create_file(struct patch *patch)
{
        const char *path = patch->new_name;
        unsigned mode = patch->new_mode;
        unsigned long size = patch->resultsize;
        char *buf = patch->result;

        if (!mode)
                mode = S_IFREG | 0644;
        create_one_file(path, mode, buf, size); 
        add_index_file(path, mode, buf, size);
}

static void write_out_one_result(struct patch *patch)
{
        if (patch->is_delete > 0) {
                remove_file(patch);
                return;
        }
        if (patch->is_new > 0 || patch->is_copy) {
                create_file(patch);
                return;
        }
        /*
         * Rename or modification boils down to the same
         * thing: remove the old, write the new
         */
        remove_file(patch);
        create_file(patch);
}

static void write_out_results(struct patch *list, int skipped_patch)
{
        if (!list && !skipped_patch)
                die("No changes");

        while (list) {
                write_out_one_result(list);
                list = list->next;
        }
}

static struct cache_file cache_file;

static struct excludes {
        struct excludes *next;
        const char *path;
} *excludes;

static int use_patch(struct patch *p)
{
        const char *pathname = p->new_name ? : p->old_name;
        struct excludes *x = excludes;
        while (x) {
                if (fnmatch(x->path, pathname, 0) == 0)
                        return 0;
                x = x->next;
        }
        return 1;
}

static int apply_patch(int fd)
{
        int newfd;
        unsigned long offset, size;
        char *buffer = read_patch_file(fd, &size);
        struct patch *list = NULL, **listp = &list;
        int skipped_patch = 0;

        if (!buffer)
                return -1;
        offset = 0;
        while (size > 0) {
                struct patch *patch;
                int nr;

                patch = xmalloc(sizeof(*patch));
                memset(patch, 0, sizeof(*patch));
                nr = parse_chunk(buffer + offset, size, patch);
                if (nr < 0)
                        break;
                if (use_patch(patch)) {
                        patch_stats(patch);
                        *listp = patch;
                        listp = &patch->next;
                } else {
                        /* perhaps free it a bit better? */
                        free(patch);
                        skipped_patch++;
                }
                offset += nr;
                size -= nr;
        }

        newfd = -1;
        write_index = check_index && apply;
        if (write_index)
                newfd = hold_index_file_for_update(&cache_file, get_index_file());
        if (check_index) {
                if (read_cache() < 0)
                        die("unable to read index file");
        }

        if ((check || apply) && check_patch_list(list) < 0)
                exit(1);

        if (apply)
                write_out_results(list, skipped_patch);

        if (write_index) {
                if (write_cache(newfd, active_cache, active_nr) ||
                    commit_index_file(&cache_file))
                        die("Unable to write new cachefile");
        }

        if (show_files)
                show_file_list(list);

        if (diffstat)
                stat_patch_list(list);

        if (summary)
                summary_patch_list(list);

        free(buffer);
        return 0;
}

int main(int argc, char **argv)
{
        int i;
        int read_stdin = 1;

        for (i = 1; i < argc; i++) {
                const char *arg = argv[i];
                int fd;

                if (!strcmp(arg, "-")) {
                        apply_patch(0);
                        read_stdin = 0;
                        continue;
                }
                if (!strncmp(arg, "--exclude=", 10)) {
                        struct excludes *x = xmalloc(sizeof(*x));
                        x->path = arg + 10;
                        x->next = excludes;
                        excludes = x;
                        continue;
                }
                /* NEEDSWORK: this does not do anything at this moment. */
                if (!strcmp(arg, "--no-merge")) {
                        merge_patch = 0;
                        continue;
                }
                if (!strcmp(arg, "--stat")) {
                        apply = 0;
                        diffstat = 1;
                        continue;
                }
                if (!strcmp(arg, "--summary")) {
                        apply = 0;
                        summary = 1;
                        continue;
                }
                if (!strcmp(arg, "--check")) {
                        apply = 0;
                        check = 1;
                        continue;
                }
                if (!strcmp(arg, "--index")) {
                        check_index = 1;
                        continue;
                }
                if (!strcmp(arg, "--apply")) {
                        apply = 1;
                        continue;
                }
                if (!strcmp(arg, "--show-files")) {
                        show_files = 1;
                        continue;
                }
                fd = open(arg, O_RDONLY);
                if (fd < 0)
                        usage(apply_usage);
                read_stdin = 0;
                apply_patch(fd);
                close(fd);
        }
        if (read_stdin)
                apply_patch(0);
        return 0;
}