/*
 * The patch page, which serves a commit or a range of commits as plain text
 * in the mail format git format-patch writes, so that a change read in cgit
 * can be fed straight to git am. A merge carries no single patch and drops
 * out of a range, and max-patch-count bounds how many commits one request
 * may emit.
 */

#define USE_THE_REPOSITORY_VARIABLE

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

// Room for two hex object ids, the two dots between them, and the null byte.
#define REV_RANGE_LEN (2 * GIT_MAX_HEXSZ + 3)

void cgit_print_patch(const char *new_rev, const char *old_rev, const char *prefix)
{
	struct rev_info rev;
	struct commit *commit;
	struct object_id new_oid, old_oid;
	struct strvec rev_argv = STRVEC_INIT;
	char rev_range[REV_RANGE_LEN];
	const char *version;

	if (!new_rev)
		new_rev = ctx.qry.head;

	// A leading colon makes git read the path as a pathspec with magic,
	// which can end the request inside git after the headers are out.
	if (prefix && prefix[0] == ':') {
		cgit_print_error_page(400, "Bad Request", "Invalid path");
		return;
	}

	commit = cgit_get_commit(new_rev, &new_oid);
	if (!commit || cgit_get_old_oid(old_rev, commit, &old_oid))
		return;

	if (is_null_oid(&old_oid)) {
		oid_to_hex_r(rev_range, &new_oid);
	} else {
		xsnprintf(rev_range, sizeof(rev_range), "%s..%s", oid_to_hex(&old_oid), oid_to_hex(&new_oid));
	}

	strvec_pushl(&rev_argv, "patch", "--reverse", NULL);
	if (ctx.cfg.enable_plain_email)
		strvec_push(&rev_argv, "--format=email");
	else
		strvec_push(&rev_argv, "--format=format:From %H Mon Sep 17 00:00:00 2001%n"
			"From: %an%nDate: %aD%n%w(78,0,1)Subject: %s%n%n%w(0)%b");
	strvec_pushl(&rev_argv, rev_range, "--", NULL);
	if (prefix)
		strvec_push(&rev_argv, prefix);

	// Git inlines a blob up to its own big-file threshold, far past what
	// any other view inflates, so max-blob-size is applied through it.
	if (ctx.cfg.max_blob_size)
		repo_settings_set_big_file_threshold(the_repository, (unsigned long)ctx.cfg.max_blob_size * 1024);
	repo_init_revisions(the_repository, &rev, NULL);
	rev.verbose_header = 1;
	rev.diff = 1;
	rev.show_root_diff = 1;
	rev.max_parents = 1;
	rev.diffopt.output_format |= DIFF_FORMAT_DIFFSTAT | DIFF_FORMAT_PATCH | DIFF_FORMAT_SUMMARY;
	// Allocated rather than formatted into cgit_fmt's fixed buffer, because
	// the path comes from the request and a long one would abort the
	// process.
	if (prefix)
		rev.diffopt.stat_sep = xstrfmt("(limited to '%s')\n\n", prefix);
	setup_revisions(rev_argv.nr, rev_argv.v, &rev, NULL);
	// A single commit resolves to a range starting at its parent, so this
	// only ever cuts an explicit range short and keeps one request from
	// emitting a patch for the whole history.
	if (ctx.cfg.max_patch_count > 0)
		rev.max_count = ctx.cfg.max_patch_count;
	// The headers wait until the walk has started.
	if (cgit_prepare_walk(&rev)) {
		strvec_clear(&rev_argv);
		return;
	}

	ctx.page.mimetype = "text/plain";
	ctx.page.filename = cgit_fmt("%s.patch", rev_range);
	cgit_print_http_headers();

	// git format-patch signs with its bare version number, so the v that
	// cgit's tags carry is left off to read the same way.
	if (!skip_prefix(cgit_version, "v", &version))
		version = cgit_version;

	while ((commit = get_revision(&rev))) {
		log_tree_commit(&rev, commit);
		// Two dashes and a space is the mail signature separator, so
		// git am and mail readers drop the version note below rather
		// than carrying it into the commit message.
		if (ctx.cfg.enable_version_info)
			printf("-- \ncgit %s\n\n", version);
		else
			printf("-- \ncgit\n\n");
	}
	strvec_clear(&rev_argv);
}