/*
 * Copyright (c) 2011, Google Inc.
 */
#include "cache.h"
#include "streaming.h"

enum input_source {
        stream_error = -1,
        incore = 0,
        loose = 1,
        pack_non_delta = 2
};

typedef int (*open_istream_fn)(struct git_istream *,
                               struct object_info *,
                               const unsigned char *,
                               enum object_type *);
typedef int (*close_istream_fn)(struct git_istream *);
typedef ssize_t (*read_istream_fn)(struct git_istream *, char *, size_t);

struct stream_vtbl {
        close_istream_fn close;
        read_istream_fn read;
};

#define open_method_decl(name) \
        int open_istream_ ##name \
        (struct git_istream *st, struct object_info *oi, \
         const unsigned char *sha1, \
         enum object_type *type)

#define close_method_decl(name) \
        int close_istream_ ##name \
        (struct git_istream *st)

#define read_method_decl(name) \
        ssize_t read_istream_ ##name \
        (struct git_istream *st, char *buf, size_t sz)

/* forward declaration */
static open_method_decl(incore);
static open_method_decl(loose);
static open_method_decl(pack_non_delta);

static open_istream_fn open_istream_tbl[] = {
        open_istream_incore,
        open_istream_loose,
        open_istream_pack_non_delta,
};

struct git_istream {
        const struct stream_vtbl *vtbl;
        unsigned long size; /* inflated size of full object */
        z_stream z;
        enum { z_unused, z_used, z_done, z_error } z_state;

        union {
                struct {
                        char *buf; /* from read_object() */
                        unsigned long read_ptr;
                } incore;

                struct {
                        int fd; /* open for reading */
                        /* NEEDSWORK: what else? */
                } loose;

                struct {
                        struct packed_git *pack;
                        off_t pos;
                } in_pack;
        } u;
};

int close_istream(struct git_istream *st)
{
        return st->vtbl->close(st);
}

ssize_t read_istream(struct git_istream *st, char *buf, size_t sz)
{
        return st->vtbl->read(st, buf, sz);
}

static enum input_source istream_source(const unsigned char *sha1,
                                        enum object_type *type,
                                        struct object_info *oi)
{
        unsigned long size;
        int status;

        oi->sizep = &size;
        status = sha1_object_info_extended(sha1, oi);
        if (status < 0)
                return stream_error;
        *type = status;

        switch (oi->whence) {
        case OI_LOOSE:
                return loose;
        case OI_PACKED:
                if (!oi->u.packed.is_delta && big_file_threshold <= size)
                        return pack_non_delta;
                /* fallthru */
        default:
                return incore;
        }
}

struct git_istream *open_istream(const unsigned char *sha1,
                                 enum object_type *type,
                                 unsigned long *size)
{
        struct git_istream *st;
        struct object_info oi;
        const unsigned char *real = lookup_replace_object(sha1);
        enum input_source src = istream_source(real, type, &oi);

        if (src < 0)
                return NULL;

        st = xmalloc(sizeof(*st));
        if (open_istream_tbl[src](st, &oi, real, type)) {
                if (open_istream_incore(st, &oi, real, type)) {
                        free(st);
                        return NULL;
                }
        }
        *size = st->size;
        return st;
}


/*****************************************************************
 *
 * Common helpers
 *
 *****************************************************************/

static void close_deflated_stream(struct git_istream *st)
{
        if (st->z_state == z_used)
                git_inflate_end(&st->z);
}


/*****************************************************************
 *
 * Loose object stream
 *
 *****************************************************************/

static open_method_decl(loose)
{
        return -1; /* for now */
}


/*****************************************************************
 *
 * Non-delta packed object stream
 *
 *****************************************************************/

static read_method_decl(pack_non_delta)
{
        size_t total_read = 0;

        switch (st->z_state) {
        case z_unused:
                memset(&st->z, 0, sizeof(st->z));
                git_inflate_init(&st->z);
                st->z_state = z_used;
                break;
        case z_done:
                return 0;
        case z_error:
                return -1;
        case z_used:
                break;
        }

        while (total_read < sz) {
                int status;
                struct pack_window *window = NULL;
                unsigned char *mapped;

                mapped = use_pack(st->u.in_pack.pack, &window,
                                  st->u.in_pack.pos, &st->z.avail_in);

                st->z.next_out = (unsigned char *)buf + total_read;
                st->z.avail_out = sz - total_read;
                st->z.next_in = mapped;
                status = git_inflate(&st->z, Z_FINISH);

                st->u.in_pack.pos += st->z.next_in - mapped;
                total_read = st->z.next_out - (unsigned char *)buf;
                unuse_pack(&window);

                if (status == Z_STREAM_END) {
                        git_inflate_end(&st->z);
                        st->z_state = z_done;
                        break;
                }
                if (status != Z_OK && status != Z_BUF_ERROR) {
                        git_inflate_end(&st->z);
                        st->z_state = z_error;
                        return -1;
                }
        }
        return total_read;
}

static close_method_decl(pack_non_delta)
{
        close_deflated_stream(st);
        return 0;
}

static struct stream_vtbl pack_non_delta_vtbl = {
        close_istream_pack_non_delta,
        read_istream_pack_non_delta,
};

static open_method_decl(pack_non_delta)
{
        struct pack_window *window;
        enum object_type in_pack_type;

        st->u.in_pack.pack = oi->u.packed.pack;
        st->u.in_pack.pos = oi->u.packed.offset;
        window = NULL;

        in_pack_type = unpack_object_header(st->u.in_pack.pack,
                                            &window,
                                            &st->u.in_pack.pos,
                                            &st->size);
        unuse_pack(&window);
        switch (in_pack_type) {
        default:
                return -1; /* we do not do deltas for now */
        case OBJ_COMMIT:
        case OBJ_TREE:
        case OBJ_BLOB:
        case OBJ_TAG:
                break;
        }
        st->z_state = z_unused;
        st->vtbl = &pack_non_delta_vtbl;
        return 0;
}


/*****************************************************************
 *
 * In-core stream
 *
 *****************************************************************/

static close_method_decl(incore)
{
        free(st->u.incore.buf);
        return 0;
}

static read_method_decl(incore)
{
        size_t read_size = sz;
        size_t remainder = st->size - st->u.incore.read_ptr;

        if (remainder <= read_size)
                read_size = remainder;
        if (read_size) {
                memcpy(buf, st->u.incore.buf + st->u.incore.read_ptr, read_size);
                st->u.incore.read_ptr += read_size;
        }
        return read_size;
}

static struct stream_vtbl incore_vtbl = {
        close_istream_incore,
        read_istream_incore,
};

static open_method_decl(incore)
{
        st->u.incore.buf = read_sha1_file_extended(sha1, type, &st->size, 0);
        st->u.incore.read_ptr = 0;
        st->vtbl = &incore_vtbl;

        return st->u.incore.buf ? 0 : -1;
}