/*
 * 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 "cache.h"

// We default to the merge behaviour, since that's what most people would
// expect
static int merge_patch = 1;
static const char apply_usage[] = "git-apply <patch>";

/*
 * 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;
static int old_mode, new_mode;
static char *old_name, *new_name, *def_name;
static int is_rename, is_copy, is_new, is_delete;

#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(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]);
}

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

        for (;;) {
                char c = *line;
                if (isspace(c))
                        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.
 */
static int parse_traditional_patch(const char *first, const char *second)
{
        int p_value = 1;
        char *name;

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

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

static int gitdiff_oldname(const char *line)
{
        if (!old_name)
                old_name = find_name(line, NULL, 1);
        return 0;
}

static int gitdiff_newname(const char *line)
{
        if (!new_name)
                new_name = find_name(line, NULL, 1);
        return 0;
}

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

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

static int gitdiff_delete(const char *line)
{
        is_delete = 1;
        return gitdiff_oldmode(line);
}

static int gitdiff_newfile(const char *line)
{
        is_new = 1;
        return gitdiff_newmode(line);
}

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

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

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

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

static int gitdiff_similarity(const char *line)
{
        return 0;
}

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

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

        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 *);
                } 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 from ", gitdiff_renamesrc },
                        { "rename to ", gitdiff_renamedst },
                        { "similarity index ", gitdiff_similarity },
                };
                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) < 0)
                                return offset;
                }
        }

        return offset;
}

static int parse_num(const char *line, int len, int offset, const char *expect, unsigned long *p)
{
        char *ptr;
        int digits, ex;

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

        if (!isdigit(*line))
                return -1;
        *p = strtoul(line, &ptr, 10);

        digits = ptr - line;

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

        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, unsigned long *pos)
{
        int offset;

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

        /* Figure out the number of lines in a fragment */
        offset = parse_num(line, len, 4, ",", pos);
        offset = parse_num(line, len, offset, " +", pos+1);
        offset = parse_num(line, len, offset, ",", pos+2);
        offset = parse_num(line, len, offset, " @@", pos+3);

        return offset;
}

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

        is_rename = is_copy = 0;
        is_new = is_delete = -1;
        old_mode = new_mode = -1;
        def_name = old_name = 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)) {
                        unsigned long pos[4];
                        if (parse_fragment_header(line, len, pos) < 0)
                                continue;
                        error("patch fragment without header at line %d: %.*s", linenr, 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);
                        if (git_hdr_len < 0)
                                continue;

                        *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);
                *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 apply_fragment(char *line, unsigned long size)
{
        int len = linelen(line, size), offset;
        unsigned long pos[4], oldlines, newlines;

        offset = parse_fragment_header(line, len, pos);
        if (offset < 0)
                return -1;
        oldlines = pos[1];
        newlines = pos[3];

        if (is_new < 0 && (pos[0] || oldlines))
                is_new = 0;
        if (is_delete < 0 && (pos[1] || newlines))
                is_delete = 0;

        /* Parse the thing.. */
        line += len;
        size -= len;
        linenr++;
        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 '-':
                        oldlines--;
                        break;
                case '+':
                        newlines--;
                        break;
                }
        }
        return offset;
}

static int apply_single_patch(char *line, unsigned long size)
{
        unsigned long offset = 0;

        while (size > 4 && !memcmp(line, "@@ -", 4)) {
                int len = apply_fragment(line, size);
                if (len <= 0)
                        die("corrupt patch at line %d", linenr);

printf("applying fragment:\n%.*s\n\n", len, line);

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

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

        if (offset < 0)
                return offset;
        header = buffer + offset;

printf("Found header:\n%.*s\n\n", hdrsize, header);
printf("Rename: %d\n", is_rename);
printf("Copy:   %d\n", is_copy);
printf("New:    %d\n", is_new);
printf("Delete: %d\n", is_delete);
printf("Mode:   %o->%o\n", old_mode, new_mode);
printf("Name:   '%s'->'%s'\n", old_name, new_name);

        patch = header + hdrsize;
        patchsize = apply_single_patch(patch, size - offset - hdrsize);

        return offset + hdrsize + patchsize;
}

static int apply_patch(int fd)
{
        unsigned long offset, size;
        char *buffer = read_patch_file(fd, &size);

        if (!buffer)
                return -1;
        offset = 0;
        while (size > 0) {
                int nr = apply_chunk(buffer + offset, size);
                if (nr < 0)
                        break;
                offset += nr;
                size -= nr;
        }
        free(buffer);
        return 0;
}

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

        if (read_cache() < 0)
                die("unable to read index file");

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

                if (!strcmp(arg, "-")) {
                        apply_patch(0);
                        continue;
                }
                if (!strcmp(arg, "--no-merge")) {
                        merge_patch = 0;
                        continue;
                }
                fd = open(arg, O_RDONLY);
                if (fd < 0)
                        usage(apply_usage);
                apply_patch(fd);
                close(fd);
        }
        return 0;
}