/*
 * GIT - The information manager from hell
 *
 * Copyright (C) Linus Torvalds, 2005
 *
 * This handles basic git sha1 object files - packing, unpacking,
 * creation etc.
 */
#include "cache.h"
#include "delta.h"

#ifndef O_NOATIME
#if defined(__linux__) && (defined(__i386__) || defined(__PPC__))
#define O_NOATIME 01000000
#else
#define O_NOATIME 0
#endif
#endif

static unsigned int sha1_file_open_flag = O_NOATIME;

static unsigned hexval(char c)
{
        if (c >= '0' && c <= '9')
                return c - '0';
        if (c >= 'a' && c <= 'f')
                return c - 'a' + 10;
        if (c >= 'A' && c <= 'F')
                return c - 'A' + 10;
        return ~0;
}

int get_sha1_hex(const char *hex, unsigned char *sha1)
{
        int i;
        for (i = 0; i < 20; i++) {
                unsigned int val = (hexval(hex[0]) << 4) | hexval(hex[1]);
                if (val & ~0xff)
                        return -1;
                *sha1++ = val;
                hex += 2;
        }
        return 0;
}

static int get_sha1_file(const char *path, unsigned char *result)
{
        char buffer[60];
        int fd = open(path, O_RDONLY);
        int len;

        if (fd < 0)
                return -1;
        len = read(fd, buffer, sizeof(buffer));
        close(fd);
        if (len < 40)
                return -1;
        return get_sha1_hex(buffer, result);
}

static char *git_dir, *git_object_dir, *git_index_file, *git_refs_dir;
static void setup_git_env(void)
{
        git_dir = gitenv(GIT_DIR_ENVIRONMENT);
        if (!git_dir)
                git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
        git_object_dir = gitenv(DB_ENVIRONMENT);
        if (!git_object_dir) {
                git_object_dir = xmalloc(strlen(git_dir) + 9);
                sprintf(git_object_dir, "%s/objects", git_dir);
        }
        git_refs_dir = xmalloc(strlen(git_dir) + 6);
        sprintf(git_refs_dir, "%s/refs", git_dir);
        git_index_file = gitenv(INDEX_ENVIRONMENT);
        if (!git_index_file) {
                git_index_file = xmalloc(strlen(git_dir) + 7);
                sprintf(git_index_file, "%s/index", git_dir);
        }
}

char *get_object_directory(void)
{
        if (!git_object_dir)
                setup_git_env();
        return git_object_dir;
}

char *get_refs_directory(void)
{
        if (!git_refs_dir)
                setup_git_env();
        return git_refs_dir;
}

char *get_index_file(void)
{
        if (!git_index_file)
                setup_git_env();
        return git_index_file;
}

int get_sha1(const char *str, unsigned char *sha1)
{
        static char pathname[PATH_MAX];
        static const char *prefix[] = {
                "",
                "refs",
                "refs/tags",
                "refs/heads",
                "refs/snap",
                NULL
        };
        const char **p;

        if (!get_sha1_hex(str, sha1))
                return 0;

        if (!git_dir)
                setup_git_env();
        for (p = prefix; *p; p++) {
                snprintf(pathname, sizeof(pathname), "%s/%s/%s",
                         git_dir, *p, str);
                if (!get_sha1_file(pathname, sha1))
                        return 0;
        }

        return -1;
}

char * sha1_to_hex(const unsigned char *sha1)
{
        static char buffer[50];
        static const char hex[] = "0123456789abcdef";
        char *buf = buffer;
        int i;

        for (i = 0; i < 20; i++) {
                unsigned int val = *sha1++;
                *buf++ = hex[val >> 4];
                *buf++ = hex[val & 0xf];
        }
        return buffer;
}

static void fill_sha1_path(char *pathbuf, const unsigned char *sha1)
{
        int i;
        for (i = 0; i < 20; i++) {
                static char hex[] = "0123456789abcdef";
                unsigned int val = sha1[i];
                char *pos = pathbuf + i*2 + (i > 0);
                *pos++ = hex[val >> 4];
                *pos = hex[val & 0xf];
        }
}

/*
 * NOTE! This returns a statically allocated buffer, so you have to be
 * careful about using it. Do a "strdup()" if you need to save the
 * filename.
 *
 * Also note that this returns the location for creating.  Reading
 * SHA1 file can happen from any alternate directory listed in the
 * DB_ENVIRONMENT environment variable if it is not found in
 * the primary object database.
 */
char *sha1_file_name(const unsigned char *sha1)
{
        static char *name, *base;

        if (!base) {
                const char *sha1_file_directory = get_object_directory();
                int len = strlen(sha1_file_directory);
                base = xmalloc(len + 60);
                memcpy(base, sha1_file_directory, len);
                memset(base+len, 0, 60);
                base[len] = '/';
                base[len+3] = '/';
                name = base + len + 1;
        }
        fill_sha1_path(name, sha1);
        return base;
}

static struct alternate_object_database {
        char *base;
        char *name;
} *alt_odb;

/*
 * Prepare alternate object database registry.
 * alt_odb points at an array of struct alternate_object_database.
 * This array is terminated with an element that has both its base
 * and name set to NULL.  alt_odb[n] comes from n'th non-empty
 * element from colon separated ALTERNATE_DB_ENVIRONMENT environment
 * variable, and its base points at a statically allocated buffer
 * that contains "/the/directory/corresponding/to/.git/objects/...",
 * while its name points just after the slash at the end of
 * ".git/objects/" in the example above, and has enough space to hold
 * 40-byte hex SHA1, an extra slash for the first level indirection,
 * and the terminating NUL.
 * This function allocates the alt_odb array and all the strings
 * pointed by base fields of the array elements with one xmalloc();
 * the string pool immediately follows the array.
 */
static void prepare_alt_odb(void)
{
        int pass, totlen, i;
        const char *cp, *last;
        char *op = NULL;
        const char *alt = gitenv(ALTERNATE_DB_ENVIRONMENT) ? : "";

        /* The first pass counts how large an area to allocate to
         * hold the entire alt_odb structure, including array of
         * structs and path buffers for them.  The second pass fills
         * the structure and prepares the path buffers for use by
         * fill_sha1_path().
         */
        for (totlen = pass = 0; pass < 2; pass++) {
                last = alt;
                i = 0;
                do {
                        cp = strchr(last, ':') ? : last + strlen(last);
                        if (last != cp) {
                                /* 43 = 40-byte + 2 '/' + terminating NUL */
                                int pfxlen = cp - last;
                                int entlen = pfxlen + 43;
                                if (pass == 0)
                                        totlen += entlen;
                                else {
                                        alt_odb[i].base = op;
                                        alt_odb[i].name = op + pfxlen + 1;
                                        memcpy(op, last, pfxlen);
                                        op[pfxlen] = op[pfxlen + 3] = '/';
                                        op[entlen-1] = 0;
                                        op += entlen;
                                }
                                i++;
                        }
                        while (*cp && *cp == ':')
                                cp++;
                        last = cp;
                } while (*cp);
                if (pass)
                        break;
                alt_odb = xmalloc(sizeof(*alt_odb) * (i + 1) + totlen);
                alt_odb[i].base = alt_odb[i].name = NULL;
                op = (char*)(&alt_odb[i+1]);
        }
}

static char *find_sha1_file(const unsigned char *sha1, struct stat *st)
{
        int i;
        char *name = sha1_file_name(sha1);

        if (!stat(name, st))
                return name;
        if (!alt_odb)
                prepare_alt_odb();
        for (i = 0; (name = alt_odb[i].name) != NULL; i++) {
                fill_sha1_path(name, sha1);
                if (!stat(alt_odb[i].base, st))
                        return alt_odb[i].base;
        }
        return NULL;
}

int check_sha1_signature(const unsigned char *sha1, void *map, unsigned long size, const char *type)
{
        char header[100];
        unsigned char real_sha1[20];
        SHA_CTX c;

        SHA1_Init(&c);
        SHA1_Update(&c, header, 1+sprintf(header, "%s %lu", type, size));
        SHA1_Update(&c, map, size);
        SHA1_Final(real_sha1, &c);
        return memcmp(sha1, real_sha1, 20) ? -1 : 0;
}

void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
{
        struct stat st;
        void *map;
        int fd;
        char *filename = find_sha1_file(sha1, &st);

        if (!filename) {
                error("cannot map sha1 file %s", sha1_to_hex(sha1));
                return NULL;
        }

        fd = open(filename, O_RDONLY | sha1_file_open_flag);
        if (fd < 0) {
                /* See if it works without O_NOATIME */
                switch (sha1_file_open_flag) {
                default:
                        fd = open(filename, O_RDONLY);
                        if (fd >= 0)
                                break;
                /* Fallthrough */
                case 0:
                        perror(filename);
                        return NULL;
                }

                /* If it failed once, it will probably fail again. Stop using O_NOATIME */
                sha1_file_open_flag = 0;
        }
        map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
        close(fd);
        if (-1 == (int)(long)map)
                return NULL;
        *size = st.st_size;
        return map;
}

int unpack_sha1_header(z_stream *stream, void *map, unsigned long mapsize, void *buffer, unsigned long size)
{
        /* Get the data stream */
        memset(stream, 0, sizeof(*stream));
        stream->next_in = map;
        stream->avail_in = mapsize;
        stream->next_out = buffer;
        stream->avail_out = size;

        inflateInit(stream);
        return inflate(stream, 0);
}

void *unpack_sha1_rest(z_stream *stream, void *buffer, unsigned long size)
{
        int bytes = strlen(buffer) + 1;
        char *buf = xmalloc(1+size);

        memcpy(buf, buffer + bytes, stream->total_out - bytes);
        bytes = stream->total_out - bytes;
        if (bytes < size) {
                stream->next_out = buf + bytes;
                stream->avail_out = size - bytes;
                while (inflate(stream, Z_FINISH) == Z_OK)
                        /* nothing */;
        }
        buf[size] = 0;
        inflateEnd(stream);
        return buf;
}

/*
 * We used to just use "sscanf()", but that's actually way
 * too permissive for what we want to check. So do an anal
 * object header parse by hand.
 */
int parse_sha1_header(char *hdr, char *type, unsigned long *sizep)
{
        int i;
        unsigned long size;

        /*
         * The type can be at most ten bytes (including the 
         * terminating '\0' that we add), and is followed by
         * a space. 
         */
        i = 10;
        for (;;) {
                char c = *hdr++;
                if (c == ' ')
                        break;
                if (!--i)
                        return -1;
                *type++ = c;
        }
        *type = 0;

        /*
         * The length must follow immediately, and be in canonical
         * decimal format (ie "010" is not valid).
         */
        size = *hdr++ - '0';
        if (size > 9)
                return -1;
        if (size) {
                for (;;) {
                        unsigned long c = *hdr - '0';
                        if (c > 9)
                                break;
                        hdr++;
                        size = size * 10 + c;
                }
        }
        *sizep = size;

        /*
         * The length must be followed by a zero byte
         */
        return *hdr ? -1 : 0;
}

void * unpack_sha1_file(void *map, unsigned long mapsize, char *type, unsigned long *size)
{
        int ret;
        z_stream stream;
        char hdr[8192];

        ret = unpack_sha1_header(&stream, map, mapsize, hdr, sizeof(hdr));
        if (ret < Z_OK || parse_sha1_header(hdr, type, size) < 0)
                return NULL;

        return unpack_sha1_rest(&stream, hdr, *size);
}

int sha1_delta_base(const unsigned char *sha1, unsigned char *base_sha1)
{
        int ret;
        unsigned long mapsize, size;
        void *map;
        z_stream stream;
        char hdr[64], type[20];
        void *delta_data_head;

        map = map_sha1_file(sha1, &mapsize);
        if (!map)
                return -1;
        ret = unpack_sha1_header(&stream, map, mapsize, hdr, sizeof(hdr));
        if (ret < Z_OK || parse_sha1_header(hdr, type, &size) < 0) {
                ret = -1;
                goto out;
        }
        if (strcmp(type, "delta")) {
                ret = 0;
                goto out;
        }

        delta_data_head = hdr + strlen(hdr) + 1;
        ret = 1;
        memcpy(base_sha1, delta_data_head, 20);
 out:
        inflateEnd(&stream);
        munmap(map, mapsize);
        return ret;
}

int sha1_file_size(const unsigned char *sha1, unsigned long *sizep)
{
        int ret, status;
        unsigned long mapsize, size;
        void *map;
        z_stream stream;
        char hdr[64], type[20];
        const unsigned char *data;
        unsigned char cmd;
        int i;

        map = map_sha1_file(sha1, &mapsize);
        if (!map)
                return -1;
        ret = unpack_sha1_header(&stream, map, mapsize, hdr, sizeof(hdr));
        status = -1;
        if (ret < Z_OK || parse_sha1_header(hdr, type, &size) < 0)
                goto out;
        if (strcmp(type, "delta")) {
                *sizep = size;
                status = 0;
                goto out;
        }

        /* We are dealing with a delta object.  Inflated, the first
         * 20 bytes hold the base object SHA1, and delta data follows
         * immediately after it.
         *
         * The initial part of the delta starts at delta_data_head +
         * 20.  Borrow code from patch-delta to read the result size.
         */
        data = hdr + strlen(hdr) + 1 + 20;

        /* Skip over the source size; we are not interested in
         * it and we cannot verify it because we do not want
         * to read the base object.
         */
        cmd = *data++;
        while (cmd) {
                if (cmd & 1)
                        data++;
                cmd >>= 1;
        }
        /* Read the result size */
        size = i = 0;
        cmd = *data++;
        while (cmd) {
                if (cmd & 1)
                        size |= *data++ << i;
                i += 8;
                cmd >>= 1;
        }
        *sizep = size;
        status = 0;
 out:
        inflateEnd(&stream);
        munmap(map, mapsize);
        return status;
}

void * read_sha1_file(const unsigned char *sha1, char *type, unsigned long *size)
{
        unsigned long mapsize;
        void *map, *buf;

        map = map_sha1_file(sha1, &mapsize);
        if (map) {
                buf = unpack_sha1_file(map, mapsize, type, size);
                munmap(map, mapsize);
                if (buf && !strcmp(type, "delta")) {
                        void *ref = NULL, *delta = buf;
                        unsigned long ref_size, delta_size = *size;
                        buf = NULL;
                        if (delta_size > 20)
                                ref = read_sha1_file(delta, type, &ref_size);
                        if (ref)
                                buf = patch_delta(ref, ref_size,
                                                  delta+20, delta_size-20, 
                                                  size);
                        free(delta);
                        free(ref);
                }
                return buf;
        }
        return NULL;
}

void *read_object_with_reference(const unsigned char *sha1,
                                 const char *required_type,
                                 unsigned long *size,
                                 unsigned char *actual_sha1_return)
{
        char type[20];
        void *buffer;
        unsigned long isize;
        unsigned char actual_sha1[20];

        memcpy(actual_sha1, sha1, 20);
        while (1) {
                int ref_length = -1;
                const char *ref_type = NULL;

                buffer = read_sha1_file(actual_sha1, type, &isize);
                if (!buffer)
                        return NULL;
                if (!strcmp(type, required_type)) {
                        *size = isize;
                        if (actual_sha1_return)
                                memcpy(actual_sha1_return, actual_sha1, 20);
                        return buffer;
                }
                /* Handle references */
                else if (!strcmp(type, "commit"))
                        ref_type = "tree ";
                else if (!strcmp(type, "tag"))
                        ref_type = "object ";
                else {
                        free(buffer);
                        return NULL;
                }
                ref_length = strlen(ref_type);

                if (memcmp(buffer, ref_type, ref_length) ||
                    get_sha1_hex(buffer + ref_length, actual_sha1)) {
                        free(buffer);
                        return NULL;
                }
                /* Now we have the ID of the referred-to object in
                 * actual_sha1.  Check again. */
        }
}

int write_sha1_file(void *buf, unsigned long len, const char *type, unsigned char *returnsha1)
{
        int size;
        unsigned char *compressed;
        z_stream stream;
        unsigned char sha1[20];
        SHA_CTX c;
        char *filename;
        static char tmpfile[PATH_MAX];
        unsigned char hdr[50];
        int fd, hdrlen, ret;

        /* Generate the header */
        hdrlen = sprintf((char *)hdr, "%s %lu", type, len)+1;

        /* Sha1.. */
        SHA1_Init(&c);
        SHA1_Update(&c, hdr, hdrlen);
        SHA1_Update(&c, buf, len);
        SHA1_Final(sha1, &c);

        if (returnsha1)
                memcpy(returnsha1, sha1, 20);

        filename = sha1_file_name(sha1);
        fd = open(filename, O_RDONLY);
        if (fd >= 0) {
                /*
                 * FIXME!!! We might do collision checking here, but we'd
                 * need to uncompress the old file and check it. Later.
                 */
                close(fd);
                return 0;
        }

        if (errno != ENOENT) {
                fprintf(stderr, "sha1 file %s: %s", filename, strerror(errno));
                return -1;
        }

        snprintf(tmpfile, sizeof(tmpfile), "%s/obj_XXXXXX", get_object_directory());

        fd = mkstemp(tmpfile);
        if (fd < 0) {
                fprintf(stderr, "unable to create temporary sha1 filename %s: %s", tmpfile, strerror(errno));
                return -1;
        }

        /* Set it up */
        memset(&stream, 0, sizeof(stream));
        deflateInit(&stream, Z_BEST_COMPRESSION);
        size = deflateBound(&stream, len+hdrlen);
        compressed = xmalloc(size);

        /* Compress it */
        stream.next_out = compressed;
        stream.avail_out = size;

        /* First header.. */
        stream.next_in = hdr;
        stream.avail_in = hdrlen;
        while (deflate(&stream, 0) == Z_OK)
                /* nothing */;

        /* Then the data itself.. */
        stream.next_in = buf;
        stream.avail_in = len;
        while (deflate(&stream, Z_FINISH) == Z_OK)
                /* nothing */;
        deflateEnd(&stream);
        size = stream.total_out;

        if (write(fd, compressed, size) != size)
                die("unable to write file");
        fchmod(fd, 0444);
        close(fd);
        free(compressed);

        ret = link(tmpfile, filename);
        if (ret < 0) {
                ret = errno;

                /*
                 * Coda hack - coda doesn't like cross-directory links,
                 * so we fall back to a rename, which will mean that it
                 * won't be able to check collisions, but that's not a
                 * big deal.
                 *
                 * When this succeeds, we just return 0. We have nothing
                 * left to unlink.
                 */
                if (ret == EXDEV && !rename(tmpfile, filename))
                        return 0;
        }
        unlink(tmpfile);
        if (ret) {
                if (ret != EEXIST) {
                        fprintf(stderr, "unable to write sha1 filename %s: %s", filename, strerror(ret));
                        return -1;
                }
                /* FIXME!!! Collision check here ? */
        }

        return 0;
}

int write_sha1_from_fd(const unsigned char *sha1, int fd)
{
        char *filename = sha1_file_name(sha1);

        int local;
        z_stream stream;
        unsigned char real_sha1[20];
        unsigned char buf[4096];
        unsigned char discard[4096];
        int ret;
        SHA_CTX c;

        local = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0666);

        if (local < 0)
                return error("Couldn't open %s\n", filename);

        memset(&stream, 0, sizeof(stream));

        inflateInit(&stream);

        SHA1_Init(&c);

        do {
                ssize_t size;
                size = read(fd, buf, 4096);
                if (size <= 0) {
                        close(local);
                        unlink(filename);
                        if (!size)
                                return error("Connection closed?");
                        perror("Reading from connection");
                        return -1;
                }
                write(local, buf, size);
                stream.avail_in = size;
                stream.next_in = buf;
                do {
                        stream.next_out = discard;
                        stream.avail_out = sizeof(discard);
                        ret = inflate(&stream, Z_SYNC_FLUSH);
                        SHA1_Update(&c, discard, sizeof(discard) -
                                    stream.avail_out);
                } while (stream.avail_in && ret == Z_OK);
                
        } while (ret == Z_OK);
        inflateEnd(&stream);

        close(local);
        SHA1_Final(real_sha1, &c);
        if (ret != Z_STREAM_END) {
                unlink(filename);
                return error("File %s corrupted", sha1_to_hex(sha1));
        }
        if (memcmp(sha1, real_sha1, 20)) {
                unlink(filename);
                return error("File %s has bad hash\n", sha1_to_hex(sha1));
        }
        
        return 0;
}

int has_sha1_file(const unsigned char *sha1)
{
        struct stat st;
        return !!find_sha1_file(sha1, &st);
}

int index_fd(unsigned char *sha1, int fd, struct stat *st)
{
        unsigned long size = st->st_size;
        void *buf;
        int ret;

        buf = "";
        if (size)
                buf = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
        close(fd);
        if ((int)(long)buf == -1)
                return -1;

        ret = write_sha1_file(buf, size, "blob", sha1);
        if (size)
                munmap(buf, size);
        return ret;
}