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#include "builtin.h"
#include "tree-walk.h"
#include "xdiff-interface.h"
#include "blob.h"
#include "exec_cmd.h"
#include "merge-file.h"

static const char merge_tree_usage[] = "git merge-tree <base-tree> <branch1> <branch2>";
static int resolve_directories = 1;

struct merge_list {
struct merge_list *next;
struct merge_list *link; /* other stages for this object */

unsigned int stage : 2,
flags : 30;
unsigned int mode;
const char *path;
struct blob *blob;
};

static struct merge_list *merge_result, **merge_result_end = &merge_result;

static void add_merge_entry(struct merge_list *entry)
{
*merge_result_end = entry;
merge_result_end = &entry->next;
}

static void merge_trees(struct tree_desc t[3], const char *base);

static const char *explanation(struct merge_list *entry)
{
switch (entry->stage) {
case 0:
return "merged";
case 3:
return "added in remote";
case 2:
if (entry->link)
return "added in both";
return "added in local";
}

/* Existed in base */
entry = entry->link;
if (!entry)
return "removed in both";

if (entry->link)
return "changed in both";

if (entry->stage == 3)
return "removed in local";
return "removed in remote";
}

static void *result(struct merge_list *entry, unsigned long *size)
{
enum object_type type;
struct blob *base, *our, *their;
const char *path = entry->path;

if (!entry->stage)
return read_sha1_file(entry->blob->object.sha1, &type, size);
base = NULL;
if (entry->stage == 1) {
base = entry->blob;
entry = entry->link;
}
our = NULL;
if (entry && entry->stage == 2) {
our = entry->blob;
entry = entry->link;
}
their = NULL;
if (entry)
their = entry->blob;
return merge_file(path, base, our, their, size);
}

static void *origin(struct merge_list *entry, unsigned long *size)
{
enum object_type type;
while (entry) {
if (entry->stage == 2)
return read_sha1_file(entry->blob->object.sha1, &type, size);
entry = entry->link;
}
return NULL;
}

static int show_outf(void *priv_, mmbuffer_t *mb, int nbuf)
{
int i;
for (i = 0; i < nbuf; i++)
printf("%.*s", (int) mb[i].size, mb[i].ptr);
return 0;
}

static void show_diff(struct merge_list *entry)
{
unsigned long size;
mmfile_t src, dst;
xpparam_t xpp;
xdemitconf_t xecfg;
xdemitcb_t ecb;

xpp.flags = 0;
memset(&xecfg, 0, sizeof(xecfg));
xecfg.ctxlen = 3;
ecb.outf = show_outf;
ecb.priv = NULL;

src.ptr = origin(entry, &size);
if (!src.ptr)
size = 0;
src.size = size;
dst.ptr = result(entry, &size);
if (!dst.ptr)
size = 0;
dst.size = size;
xdi_diff(&src, &dst, &xpp, &xecfg, &ecb);
free(src.ptr);
free(dst.ptr);
}

static void show_result_list(struct merge_list *entry)
{
printf("%s\n", explanation(entry));
do {
struct merge_list *link = entry->link;
static const char *desc[4] = { "result", "base", "our", "their" };
printf(" %-6s %o %s %s\n", desc[entry->stage], entry->mode, sha1_to_hex(entry->blob->object.sha1), entry->path);
entry = link;
} while (entry);
}

static void show_result(void)
{
struct merge_list *walk;

walk = merge_result;
while (walk) {
show_result_list(walk);
show_diff(walk);
walk = walk->next;
}
}

/* An empty entry never compares same, not even to another empty entry */
static int same_entry(struct name_entry *a, struct name_entry *b)
{
return a->sha1 &&
b->sha1 &&
!hashcmp(a->sha1, b->sha1) &&
a->mode == b->mode;
}

static struct merge_list *create_entry(unsigned stage, unsigned mode, const unsigned char *sha1, const char *path)
{
struct merge_list *res = xcalloc(1, sizeof(*res));

res->stage = stage;
res->path = path;
res->mode = mode;
res->blob = lookup_blob(sha1);
return res;
}

static char *traverse_path(const struct traverse_info *info, const struct name_entry *n)
{
char *path = xmalloc(traverse_path_len(info, n) + 1);
return make_traverse_path(path, info, n);
}

static void resolve(const struct traverse_info *info, struct name_entry *branch1, struct name_entry *result)
{
struct merge_list *orig, *final;
const char *path;

/* If it's already branch1, don't bother showing it */
if (!branch1)
return;

path = traverse_path(info, result);
orig = create_entry(2, branch1->mode, branch1->sha1, path);
final = create_entry(0, result->mode, result->sha1, path);

final->link = orig;

add_merge_entry(final);
}

static int unresolved_directory(const struct traverse_info *info, struct name_entry n[3])
{
char *newbase;
struct name_entry *p;
struct tree_desc t[3];
void *buf0, *buf1, *buf2;

if (!resolve_directories)
return 0;
p = n;
if (!p->mode) {
p++;
if (!p->mode)
p++;
}
if (!S_ISDIR(p->mode))
return 0;
newbase = traverse_path(info, p);
buf0 = fill_tree_descriptor(t+0, n[0].sha1);
buf1 = fill_tree_descriptor(t+1, n[1].sha1);
buf2 = fill_tree_descriptor(t+2, n[2].sha1);
merge_trees(t, newbase);

free(buf0);
free(buf1);
free(buf2);
free(newbase);
return 1;
}


static struct merge_list *link_entry(unsigned stage, const struct traverse_info *info, struct name_entry *n, struct merge_list *entry)
{
const char *path;
struct merge_list *link;

if (!n->mode)
return entry;
if (entry)
path = entry->path;
else
path = traverse_path(info, n);
link = create_entry(stage, n->mode, n->sha1, path);
link->link = entry;
return link;
}

static void unresolved(const struct traverse_info *info, struct name_entry n[3])
{
struct merge_list *entry = NULL;

if (unresolved_directory(info, n))
return;

/*
* Do them in reverse order so that the resulting link
* list has the stages in order - link_entry adds new
* links at the front.
*/
entry = link_entry(3, info, n + 2, entry);
entry = link_entry(2, info, n + 1, entry);
entry = link_entry(1, info, n + 0, entry);

add_merge_entry(entry);
}

/*
* Merge two trees together (t[1] and t[2]), using a common base (t[0])
* as the origin.
*
* This walks the (sorted) trees in lock-step, checking every possible
* name. Note that directories automatically sort differently from other
* files (see "base_name_compare"), so you'll never see file/directory
* conflicts, because they won't ever compare the same.
*
* IOW, if a directory changes to a filename, it will automatically be
* seen as the directory going away, and the filename being created.
*
* Think of this as a three-way diff.
*
* The output will be either:
* - successful merge
* "0 mode sha1 filename"
* NOTE NOTE NOTE! FIXME! We really really need to walk the index
* in parallel with this too!
*
* - conflict:
* "1 mode sha1 filename"
* "2 mode sha1 filename"
* "3 mode sha1 filename"
* where not all of the 1/2/3 lines may exist, of course.
*
* The successful merge rules are the same as for the three-way merge
* in git-read-tree.
*/
static int threeway_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *entry, struct traverse_info *info)
{
/* Same in both? */
if (same_entry(entry+1, entry+2)) {
if (entry[0].sha1) {
resolve(info, NULL, entry+1);
return mask;
}
}

if (same_entry(entry+0, entry+1)) {
if (entry[2].sha1 && !S_ISDIR(entry[2].mode)) {
resolve(info, entry+1, entry+2);
return mask;
}
}

if (same_entry(entry+0, entry+2)) {
if (entry[1].sha1 && !S_ISDIR(entry[1].mode)) {
resolve(info, NULL, entry+1);
return mask;
}
}

unresolved(info, entry);
return mask;
}

static void merge_trees(struct tree_desc t[3], const char *base)
{
struct traverse_info info;

setup_traverse_info(&info, base);
info.fn = threeway_callback;
traverse_trees(3, t, &info);
}

static void *get_tree_descriptor(struct tree_desc *desc, const char *rev)
{
unsigned char sha1[20];
void *buf;

if (get_sha1(rev, sha1))
die("unknown rev %s", rev);
buf = fill_tree_descriptor(desc, sha1);
if (!buf)
die("%s is not a tree", rev);
return buf;
}

int cmd_merge_tree(int argc, const char **argv, const char *prefix)
{
struct tree_desc t[3];
void *buf1, *buf2, *buf3;

if (argc != 4)
usage(merge_tree_usage);

buf1 = get_tree_descriptor(t+0, argv[1]);
buf2 = get_tree_descriptor(t+1, argv[2]);
buf3 = get_tree_descriptor(t+2, argv[3]);
merge_trees(t, "");
free(buf1);
free(buf2);
free(buf3);

show_result();
return 0;
}
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