/*
 * libgit2 "merge" example - shows how to perform merges
 *
 * Written by the libgit2 contributors
 *
 * To the extent possible under law, the author(s) have dedicated all copyright
 * and related and neighboring rights to this software to the public domain
 * worldwide. This software is distributed without any warranty.
 *
 * You should have received a copy of the CC0 Public Domain Dedication along
 * with this software. If not, see
 * <http://creativecommons.org/publicdomain/zero/1.0/>.
 */

#include "common.h"
#include <assert.h>

/** The following example demonstrates how to do merges with libgit2.
 *
 * It will merge whatever commit-ish you pass in into the current branch.
 *
 * Recognized options are :
 *  --no-commit: don't actually commit the merge.
 *
 */

typedef struct {
	const char **heads;
	size_t heads_count;

	git_annotated_commit **annotated;
	size_t annotated_count;

	int no_commit : 1;
} merge_options;

static void print_usage(void)
{
	fprintf(stderr, "usage: merge [--no-commit] <commit...>\n");
	exit(1);
}

static void merge_options_init(merge_options *opts)
{
	memset(opts, 0, sizeof(*opts));

	opts->heads = NULL;
	opts->heads_count = 0;
	opts->annotated = NULL;
	opts->annotated_count = 0;
}

static void opts_add_refish(merge_options *opts, const char *refish)
{
	size_t sz;

	assert(opts != NULL);

	sz = ++opts->heads_count * sizeof(opts->heads[0]);
	opts->heads = xrealloc(opts->heads, sz);
	opts->heads[opts->heads_count - 1] = refish;
}

static void parse_options(const char **repo_path, merge_options *opts, int argc, char **argv)
{
	struct args_info args = ARGS_INFO_INIT;

	if (argc <= 1)
		print_usage();

	for (args.pos = 1; args.pos < argc; ++args.pos) {
		const char *curr = argv[args.pos];

		if (curr[0] != '-') {
			opts_add_refish(opts, curr);
		} else if (!strcmp(curr, "--no-commit")) {
			opts->no_commit = 1;
		} else if (match_str_arg(repo_path, &args, "--git-dir")) {
			continue;
		} else {
			print_usage();
		}
	}
}

static int resolve_heads(git_repository *repo, merge_options *opts)
{
	git_annotated_commit **annotated = calloc(opts->heads_count, sizeof(git_annotated_commit *));
	size_t annotated_count = 0, i;
	int err = 0;

	for (i = 0; i < opts->heads_count; i++) {
		err = resolve_refish(&annotated[annotated_count++], repo, opts->heads[i]);
		if (err != 0) {
			fprintf(stderr, "failed to resolve refish %s: %s\n", opts->heads[i], git_error_last()->message);
			annotated_count--;
			continue;
		}
	}

	if (annotated_count != opts->heads_count) {
		fprintf(stderr, "unable to parse some refish\n");
		free(annotated);
		return -1;
	}

	opts->annotated = annotated;
	opts->annotated_count = annotated_count;
	return 0;
}

static int perform_fastforward(git_repository *repo, const git_oid *target_oid, int is_unborn)
{
	git_checkout_options ff_checkout_options = GIT_CHECKOUT_OPTIONS_INIT;
	git_reference *target_ref;
	git_reference *new_target_ref;
	git_object *target = NULL;
	int err = 0;

	if (is_unborn) {
		const char *symbolic_ref;
		git_reference *head_ref;

		/* HEAD reference is unborn, lookup manually so we don't try to resolve it */
		err = git_reference_lookup(&head_ref, repo, "HEAD");
		if (err != 0) {
			fprintf(stderr, "failed to lookup HEAD ref\n");
			return -1;
		}

		/* Grab the reference HEAD should be pointing to */
		symbolic_ref = git_reference_symbolic_target(head_ref);

		/* Create our master reference on the target OID */
		err = git_reference_create(&target_ref, repo, symbolic_ref, target_oid, 0, NULL);
		if (err != 0) {
			fprintf(stderr, "failed to create master reference\n");
			return -1;
		}

		git_reference_free(head_ref);
	} else {
		/* HEAD exists, just lookup and resolve */
		err = git_repository_head(&target_ref, repo);
		if (err != 0) {
			fprintf(stderr, "failed to get HEAD reference\n");
			return -1;
		}
	}

	/* Lookup the target object */
	err = git_object_lookup(&target, repo, target_oid, GIT_OBJECT_COMMIT);
	if (err != 0) {
		fprintf(stderr, "failed to lookup OID %s\n", git_oid_tostr_s(target_oid));
		return -1;
	}

	/* Checkout the result so the workdir is in the expected state */
	ff_checkout_options.checkout_strategy = GIT_CHECKOUT_SAFE;
	err = git_checkout_tree(repo, target, &ff_checkout_options);
	if (err != 0) {
		fprintf(stderr, "failed to checkout HEAD reference\n");
		return -1;
	}

	/* Move the target reference to the target OID */
	err = git_reference_set_target(&new_target_ref, target_ref, target_oid, NULL);
	if (err != 0) {
		fprintf(stderr, "failed to move HEAD reference\n");
		return -1;
	}

	git_reference_free(target_ref);
	git_reference_free(new_target_ref);
	git_object_free(target);

	return 0;
}

static void output_conflicts(git_index *index)
{
	git_index_conflict_iterator *conflicts;
	const git_index_entry *ancestor;
	const git_index_entry *our;
	const git_index_entry *their;
	int err = 0;

	check_lg2(git_index_conflict_iterator_new(&conflicts, index), "failed to create conflict iterator", NULL);

	while ((err = git_index_conflict_next(&ancestor, &our, &their, conflicts)) == 0) {
		fprintf(stderr, "conflict: a:%s o:%s t:%s\n",
		        ancestor ? ancestor->path : "NULL",
		        our->path ? our->path : "NULL",
		        their->path ? their->path : "NULL");
	}

	if (err != GIT_ITEROVER) {
		fprintf(stderr, "error iterating conflicts\n");
	}

	git_index_conflict_iterator_free(conflicts);
}

static int create_merge_commit(git_repository *repo, git_index *index, merge_options *opts)
{
	git_oid tree_oid, commit_oid;
	git_tree *tree;
	git_signature *sign;
	git_reference *merge_ref = NULL;
	git_annotated_commit *merge_commit;
	git_reference *head_ref;
	git_commit **parents = calloc(opts->annotated_count + 1, sizeof(git_commit *));
	const char *msg_target = NULL;
	size_t msglen = 0;
	char *msg;
	size_t i;
	int err;

	/* Grab our needed references */
	check_lg2(git_repository_head(&head_ref, repo), "failed to get repo HEAD", NULL);
	if (resolve_refish(&merge_commit, repo, opts->heads[0])) {
		fprintf(stderr, "failed to resolve refish %s", opts->heads[0]);
		return -1;
	}

	/* Maybe that's a ref, so DWIM it */
	err = git_reference_dwim(&merge_ref, repo, opts->heads[0]);
	check_lg2(err, "failed to DWIM reference", git_error_last()->message);

	/* Grab a signature */
	check_lg2(git_signature_now(&sign, "Me", "me@example.com"), "failed to create signature", NULL);

#define MERGE_COMMIT_MSG "Merge %s '%s'"
	/* Prepare a standard merge commit message */
	if (merge_ref != NULL) {
		check_lg2(git_branch_name(&msg_target, merge_ref), "failed to get branch name of merged ref", NULL);
	} else {
		msg_target = git_oid_tostr_s(git_annotated_commit_id(merge_commit));
	}

	msglen = snprintf(NULL, 0, MERGE_COMMIT_MSG, (merge_ref ? "branch" : "commit"), msg_target);
	if (msglen > 0) msglen++;
	msg = malloc(msglen);
	err = snprintf(msg, msglen, MERGE_COMMIT_MSG, (merge_ref ? "branch" : "commit"), msg_target);

	/* This is only to silence the compiler */
	if (err < 0) goto cleanup;

	/* Setup our parent commits */
	err = git_reference_peel((git_object **)&parents[0], head_ref, GIT_OBJECT_COMMIT);
	check_lg2(err, "failed to peel head reference", NULL);
	for (i = 0; i < opts->annotated_count; i++) {
		git_commit_lookup(&parents[i + 1], repo, git_annotated_commit_id(opts->annotated[i]));
	}

	/* Prepare our commit tree */
	check_lg2(git_index_write_tree(&tree_oid, index), "failed to write merged tree", NULL);
	check_lg2(git_tree_lookup(&tree, repo, &tree_oid), "failed to lookup tree", NULL);

	/* Commit time ! */
	err = git_commit_create(&commit_oid,
	                        repo, git_reference_name(head_ref),
	                        sign, sign,
	                        NULL, msg,
	                        tree,
	                        opts->annotated_count + 1, (const git_commit **)parents);
	check_lg2(err, "failed to create commit", NULL);

	/* We're done merging, cleanup the repository state */
	git_repository_state_cleanup(repo);

cleanup:
	free(parents);
	return err;
}

int lg2_merge(git_repository *repo, int argc, char **argv)
{
	merge_options opts;
	git_index *index;
	git_repository_state_t state;
	git_merge_analysis_t analysis;
	git_merge_preference_t preference;
	const char *path = ".";
	int err = 0;

	merge_options_init(&opts);
	parse_options(&path, &opts, argc, argv);

	state = git_repository_state(repo);
	if (state != GIT_REPOSITORY_STATE_NONE) {
		fprintf(stderr, "repository is in unexpected state %d\n", state);
		goto cleanup;
	}

	err = resolve_heads(repo, &opts);
	if (err != 0)
		goto cleanup;

	err = git_merge_analysis(&analysis, &preference,
	                         repo,
	                         (const git_annotated_commit **)opts.annotated,
	                         opts.annotated_count);
	check_lg2(err, "merge analysis failed", NULL);

	if (analysis & GIT_MERGE_ANALYSIS_UP_TO_DATE) {
		printf("Already up-to-date\n");
		return 0;
	} else if (analysis & GIT_MERGE_ANALYSIS_UNBORN ||
	          (analysis & GIT_MERGE_ANALYSIS_FASTFORWARD &&
	          !(preference & GIT_MERGE_PREFERENCE_NO_FASTFORWARD))) {
		const git_oid *target_oid;
		if (analysis & GIT_MERGE_ANALYSIS_UNBORN) {
			printf("Unborn\n");
		} else {
			printf("Fast-forward\n");
		}

		/* Since this is a fast-forward, there can be only one merge head */
		target_oid = git_annotated_commit_id(opts.annotated[0]);
		assert(opts.annotated_count == 1);

		return perform_fastforward(repo, target_oid, (analysis & GIT_MERGE_ANALYSIS_UNBORN));
	} else if (analysis & GIT_MERGE_ANALYSIS_NORMAL) {
		git_merge_options merge_opts = GIT_MERGE_OPTIONS_INIT;
		git_checkout_options checkout_opts = GIT_CHECKOUT_OPTIONS_INIT;

		merge_opts.flags = 0;
		merge_opts.file_flags = GIT_MERGE_FILE_STYLE_DIFF3;

		checkout_opts.checkout_strategy = GIT_CHECKOUT_FORCE|GIT_CHECKOUT_ALLOW_CONFLICTS;

		if (preference & GIT_MERGE_PREFERENCE_FASTFORWARD_ONLY) {
			printf("Fast-forward is preferred, but only a merge is possible\n");
			return -1;
		}

		err = git_merge(repo,
		                (const git_annotated_commit **)opts.annotated, opts.annotated_count,
		                &merge_opts, &checkout_opts);
		check_lg2(err, "merge failed", NULL);
	}

	/* If we get here, we actually performed the merge above */

	check_lg2(git_repository_index(&index, repo), "failed to get repository index", NULL);

	if (git_index_has_conflicts(index)) {
		/* Handle conflicts */
		output_conflicts(index);
	} else if (!opts.no_commit) {
		create_merge_commit(repo, index, &opts);
		printf("Merge made\n");
	}

cleanup:
	free(opts.heads);
	free(opts.annotated);

	return 0;
}
