/*
 * The dumb HTTP transport, which lets a client clone by fetching plain files
 * rather than by talking to a server side helper. It answers the requests
 * such a client makes, the ref listing under info, the loose objects and pack
 * files under objects, and HEAD, each written as raw bytes rather than as a
 * page. The two listings a clone starts from are built per request, so a
 * repository serves without anyone having run git update-server-info over it.
 */

#define USE_THE_REPOSITORY_VARIABLE

#include "cgit.h"
#include "html.h"
#include "ui-clone.h"
#include "ui-shared.h"

/*
 * A client reading this listing expects an annotated tag to be followed by a
 * second line, marked with ^{}, naming the object the tag peels to, the
 * format git update-server-info writes into info/refs.
 */
static int print_ref(const struct reference *ref, void *cb_data UNUSED)
{
	struct object *obj;

	obj = parse_object(the_repository, ref->oid);
	if (!obj)
		return 0;

	htmlf("%s\t%s\n", oid_to_hex(ref->oid), ref->name);
	if (obj->type == OBJ_TAG) {
		obj = deref_tag(the_repository, obj, ref->name, 0);
		if (!obj)
			return 0;
		htmlf("%s\t%s^{}\n", oid_to_hex(&obj->oid), ref->name);
	}
	return 0;
}

/*
 * A path ending in a slash is handed back whole, where git's own
 * pack_basename would return the empty string.
 */
static const char *last_path_component(const char *path)
{
	const char *slash = strrchr(path, '/');

	if (slash && slash[1] != '\0')
		return slash + 1;
	return path;
}

/*
 * Only the packs this repository holds itself are listed, because one
 * borrowed from an alternate is not reachable below this URL and a client
 * told about it would come back for a file that is not there.
 */
static void print_pack_info(void)
{
	struct odb_source *source;

	ctx.page.mimetype = "text/plain";
	ctx.page.filename = "objects/info/packs";
	cgit_print_http_headers();
	odb_reprepare(the_repository->objects);
	for (source = the_repository->objects->sources; source; source = source->next) {
		struct odb_source_files *files = odb_source_files_downcast(source);
		struct packfile_list_entry *entry;
		// Asked for through the accessor rather than read off the list,
		// because a pack the multi-pack-index already covers joins that
		// list only when the accessor loads it, and reading the field
		// directly leaves those packs unfindable.
		for (entry = packfile_store_get_packs(files->packed); entry; entry = entry->next) {
			struct packed_git *pack = entry->pack;

			if (pack->pack_local)
				htmlf("P %s\n", last_path_component(pack->pack_name));
		}
	}
}

static size_t hex_span(const char *s)
{
	return strspn(s, "0123456789abcdef");
}

/*
 * A dumb client asks for three shapes of file below objects: a loose object
 * at xx/rest-of-hex, a pack or its index at pack/pack-hex.pack or .idx, and
 * info/http-alternates. Nothing else is served, so no spelling of a path can
 * reach a file outside those, the alternates file among them.
 */
static int object_path_is_served(const char *path)
{
	const size_t hexsz = the_hash_algo->hexsz;
	const char *rest;

	if (!strcmp(path, "info/http-alternates"))
		return 1;
	if (skip_prefix(path, "pack/pack-", &rest)) {
		size_t n = hex_span(rest);

		return n == hexsz && (!strcmp(rest + n, ".pack") || !strcmp(rest + n, ".idx"));
	}
	return hex_span(path) == 2 && path[2] == '/' && hex_span(path + 3) == hexsz - 2 &&
		path[hexsz + 1] == '\0';
}

/*
 * The file is read in batches the size of the output buffer, so each one
 * goes to the client in a single write, and its size is sent ahead so the
 * client can tell a cut-off transfer from a complete one.
 */
static void send_file(const char *path)
{
	static char buf[HTML_BATCH];
	struct stat st;
	ssize_t got;
	int fd;

	fd = open(path, O_RDONLY);
	if (fd < 0) {
		switch (errno) {
		case ENOENT:
			cgit_print_error_page(404, "Not Found", "Not found");
			break;
		case EACCES:
			cgit_print_error_page(403, "Forbidden", "Forbidden");
			break;
		default:
			cgit_print_error_page(400, "Bad Request", "Bad request");
		}
		return;
	}
	// open succeeds on a directory on most systems and reads nothing from
	// it.
	if (fstat(fd, &st) || !S_ISREG(st.st_mode)) {
		close(fd);
		cgit_print_error_page(404, "Not Found", "Not found");
		return;
	}
	ctx.page.mimetype = "application/octet-stream";
	// Offer the file under its path inside the repository, so the layout
	// of the server's disk stays out of the download name.
	ctx.page.filename = path;
	skip_prefix(path, ctx.repo->path, &ctx.page.filename);
	skip_prefix(ctx.page.filename, "/", &ctx.page.filename);
	ctx.page.size = st.st_size;
	cgit_print_http_headers();
	while ((got = xread(fd, buf, sizeof(buf))) > 0)
		html_raw(buf, got);
	close(fd);
}

void cgit_clone_info(void)
{
	if (!ctx.qry.path || strcmp(ctx.qry.path, "refs")) {
		cgit_print_error_page(400, "Bad Request", "Bad request");
		return;
	}

	ctx.page.mimetype = "text/plain";
	ctx.page.filename = "info/refs";
	cgit_print_http_headers();
	refs_for_each_ref(get_main_ref_store(the_repository), print_ref, NULL);
}

void cgit_clone_objects(void)
{
	char *path;

	if (!ctx.qry.path)
		goto err;

	if (!strcmp(ctx.qry.path, "info/packs")) {
		print_pack_info();
		return;
	}

	if (!object_path_is_served(ctx.qry.path)) {
		cgit_print_error_page(404, "Not Found", "Not found");
		return;
	}

	path = repo_git_path(the_repository, "objects/%s", ctx.qry.path);
	send_file(path);
	free(path);
	return;

err:
	cgit_print_error_page(400, "Bad Request", "Bad request");
}

/*
 * HEAD is answered from the ref store, the way git's own http-backend answers
 * it, rather than read off the disk, where a reftable repository keeps only a
 * placeholder. The target need not exist yet, so an empty repository still
 * names the branch a first push will create.
 */
void cgit_clone_head(void)
{
	struct strbuf head = STRBUF_INIT;
	struct object_id oid;
	const char *target;
	int flags;

	target = refs_resolve_ref_unsafe(get_main_ref_store(the_repository), "HEAD", 0, &oid,
		&flags);
	if (!target) {
		cgit_print_error_page(404, "Not Found", "Not found");
		return;
	}
	if (flags & REF_ISSYMREF)
		strbuf_addf(&head, "ref: %s\n", target);
	else
		strbuf_addf(&head, "%s\n", oid_to_hex(&oid));
	ctx.page.mimetype = "text/plain";
	ctx.page.filename = "HEAD";
	ctx.page.size = head.len;
	cgit_print_http_headers();
	html_raw(head.buf, head.len);
	strbuf_release(&head);
}