/*
 * Copyright (c) 2018 Stefan Sperling <stsp@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/queue.h>
#include <sys/stdint.h>

#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sha1.h>
#include <zlib.h>
#include <ctype.h>

#include "got_error.h"
#include "got_object.h"
#include "got_cancel.h"
#include "got_commit_graph.h"
#include "got_path.h"

#include "got_lib_delta.h"
#include "got_lib_inflate.h"
#include "got_lib_object.h"
#include "got_lib_object_idset.h"

struct got_commit_graph_node {
	struct got_object_id id;
	time_t timestamp;

	/* Used during graph iteration. */
	TAILQ_ENTRY(got_commit_graph_node) entry;
};

TAILQ_HEAD(got_commit_graph_iter_list, got_commit_graph_node);

struct got_commit_graph_branch_tip {
	struct got_object_id *commit_id;
	struct got_commit_object *commit;
	struct got_commit_graph_node *new_node;
	int changed;
	int branch_done;
};

struct got_commit_graph {
	/* The set of all commits we have traversed. */
	struct got_object_idset *node_ids;

	/* The commit at which traversal began (youngest commit in node_ids). */
	struct got_commit_graph_node *head_node;

	int flags;
#define GOT_COMMIT_GRAPH_FIRST_PARENT_TRAVERSAL		0x01

	/*
	 * A set of object IDs of known parent commits which we have not yet
	 * traversed. Each commit ID in this set represents a branch in commit
	 * history: Either the first-parent branch of the head node, or another
	 * branch corresponding to a traversed merge commit for which we have
	 * not traversed a branch point commit yet.
	 *
	 * Whenever we add a commit with a matching ID to the graph, we remove
	 * its corresponding element from this set, and add new elements for
	 * each of that commit's parent commits which were not traversed yet.
	 *
	 * When API users ask us to fetch more commits, we fetch commits from
	 * all currently open branches. This allows API users to process
	 * commits in linear order even though the history contains branches.
	 */
	struct got_object_idset *open_branches;

	/* Array of branch tips for fetch_commits_from_open_branches(). */
	struct got_commit_graph_branch_tip *tips;
	int ntips;

	/* Path of tree entry of interest to the API user. */
	char *path;

	/* The next commit to return when the API user asks for one. */
	struct got_commit_graph_node *iter_node;

	/* The graph iteration list contains all nodes in sorted order. */
	struct got_commit_graph_iter_list iter_list;
};

static struct got_commit_graph *
alloc_graph(const char *path)
{
	struct got_commit_graph *graph;

	graph = calloc(1, sizeof(*graph));
	if (graph == NULL)
		return NULL;

	graph->path = strdup(path);
	if (graph->path == NULL) {
		free(graph);
		return NULL;
	}

	graph->node_ids = got_object_idset_alloc();
	if (graph->node_ids == NULL) {
		free(graph->path);
		free(graph);
		return NULL;
	}

	graph->open_branches = got_object_idset_alloc();
	if (graph->open_branches == NULL) {
		got_object_idset_free(graph->node_ids);
		free(graph->path);
		free(graph);
		return NULL;
	}

	TAILQ_INIT(&graph->iter_list);
	return graph;
}

static const struct got_error *
detect_changed_path(int *changed, struct got_commit_object *commit,
    struct got_object_id *commit_id, const char *path,
    struct got_repository *repo)
{
	const struct got_error *err = NULL;
	struct got_commit_object *pcommit = NULL;
	struct got_tree_object *tree = NULL, *ptree = NULL;
	struct got_object_qid *pid;

	if (got_path_is_root_dir(path)) {
		*changed = 1;
		return NULL;
	}

	*changed = 0;

	pid = SIMPLEQ_FIRST(&commit->parent_ids);
	if (pid == NULL) {
		struct got_object_id *obj_id;
		err = got_object_id_by_path(&obj_id, repo, commit_id, path);
		if (err) {
			if (err->code == GOT_ERR_NO_TREE_ENTRY)
				err = NULL;
		} else
			*changed = 1; /* The path was created in this commit. */
		free(obj_id);
		return err;
	}

	err = got_object_open_as_tree(&tree, repo, commit->tree_id);
	if (err)
		return err;

	err = got_object_open_as_commit(&pcommit, repo, pid->id);
	if (err)
		goto done;

	err = got_object_open_as_tree(&ptree, repo, pcommit->tree_id);
	if (err)
		goto done;

	err = got_object_tree_path_changed(changed, tree, ptree, path, repo);
done:
	if (tree)
		got_object_tree_close(tree);
	if (ptree)
		got_object_tree_close(ptree);
	if (pcommit)
		got_object_commit_close(pcommit);
	return err;
}

static void
add_node_to_iter_list(struct got_commit_graph *graph,
    struct got_commit_graph_node *node,
    struct got_commit_graph_node *child_node)
{
	struct got_commit_graph_node *n, *next;

	if (TAILQ_EMPTY(&graph->iter_list)) {
		TAILQ_INSERT_HEAD(&graph->iter_list, node, entry);
		graph->iter_node = node;
		return;
	}

	n = graph->iter_node;
	/* Ensure that an iteration in progress will see this new commit. */
	while (n) {
		next = TAILQ_NEXT(n, entry);
		if (next && node->timestamp >= next->timestamp) {
			TAILQ_INSERT_BEFORE(next, node, entry);
			return;
		}
		n = next;
	}
	TAILQ_INSERT_TAIL(&graph->iter_list, node, entry);
}

static const struct got_error *
close_branch(struct got_commit_graph *graph, struct got_object_id *commit_id)
{
	const struct got_error *err;

	err = got_object_idset_remove(NULL, graph->open_branches, commit_id);
	if (err && err->code != GOT_ERR_NO_OBJ)
		return err;
	return NULL;
}

static const struct got_error *
advance_branch(struct got_commit_graph *graph,
    struct got_commit_graph_node *node,
    struct got_object_id *commit_id, struct got_commit_object *commit,
    struct got_repository *repo)
{
	const struct got_error *err;
	struct got_object_qid *qid;

	err = close_branch(graph, commit_id);
	if (err)
		return err;

	if (graph->flags & GOT_COMMIT_GRAPH_FIRST_PARENT_TRAVERSAL) {
		qid = SIMPLEQ_FIRST(&commit->parent_ids);
		if (qid == NULL ||
		    got_object_idset_get(graph->open_branches, qid->id))
			return NULL;
		return got_object_idset_add(graph->open_branches,
		    qid->id, node);
	}

	/*
	 * If we are graphing commits for a specific path, skip branches
	 * which do not contribute any content to this path.
	 */
	if (commit->nparents > 1 && !got_path_is_root_dir(graph->path)) {
		struct got_object_id *merged_id, *prev_id = NULL;
		int branches_differ = 0;

		err = got_object_id_by_path(&merged_id, repo, commit_id,
		    graph->path);
		if (err)
			return err;

		SIMPLEQ_FOREACH(qid, &commit->parent_ids, entry) {
			struct got_object_id *id;

			if (got_object_idset_get(graph->open_branches, qid->id))
				continue;

			err = got_object_id_by_path(&id, repo, qid->id,
			    graph->path);
			if (err) {
				if (err->code == GOT_ERR_NO_TREE_ENTRY) {
					branches_differ = 1;
					continue;
				}
				free(merged_id);
				free(prev_id);
				return err;
			}

			if (prev_id) {
				if (!branches_differ &&
				    got_object_id_cmp(id, prev_id) != 0)
					branches_differ = 1;
				free(prev_id);
			}
			prev_id = id;

			/*
			 * If a branch has created the merged content we can
			 * skip any other branches.
			 */
			if (got_object_id_cmp(merged_id, id) == 0) {
				err = got_object_idset_add(graph->open_branches,
				    qid->id, node);
				free(merged_id);
				free(id);
				return err;
			}
		}

		free(prev_id);
		prev_id = NULL;
		free(merged_id);
		merged_id = NULL;

		/*
		 * If the path's content is the same on all branches,
		 * follow the first parent only.
		 */
		if (!branches_differ) {
			qid = SIMPLEQ_FIRST(&commit->parent_ids);
			if (qid == NULL)
				return NULL;
			if (got_object_idset_get(graph->open_branches, qid->id))
				return NULL;
			if (got_object_idset_get(graph->node_ids, qid->id))
				return NULL; /* parent already traversed */
			return got_object_idset_add(graph->open_branches,
			    qid->id, node);
		}
	}

	SIMPLEQ_FOREACH(qid, &commit->parent_ids, entry) {
		if (got_object_idset_get(graph->open_branches, qid->id))
			continue;
		if (got_object_idset_get(graph->node_ids, qid->id))
			continue; /* parent already traversed */
		err = got_object_idset_add(graph->open_branches, qid->id, node);
		if (err)
			return err;
	}

	return NULL;
}

static const struct got_error *
add_node(struct got_commit_graph_node **new_node, int *changed,
    int *branch_done, struct got_commit_graph *graph,
    struct got_object_id *commit_id, struct got_commit_object *commit,
    struct got_commit_graph_node *child_node, struct got_repository *repo)
{
	const struct got_error *err = NULL;
	struct got_commit_graph_node *node;

	*new_node = NULL;
	*changed = 0;
	*branch_done = 0;

	node = calloc(1, sizeof(*node));
	if (node == NULL)
		return got_error_from_errno("calloc");

	memcpy(&node->id, commit_id, sizeof(node->id));
	node->timestamp = commit->committer_time;

	err = got_object_idset_add(graph->node_ids, &node->id, node);
	if (err) {
		free(node);
		return err;
	}

	err = detect_changed_path(changed, commit, commit_id, graph->path,
	    repo);
	if (err) {
		if (err->code == GOT_ERR_NO_OBJ) {
			/*
			 * History of the path stops here on the current
			 * branch. Keep going on other branches.
			 */
			err = NULL;
			*branch_done = 1;
		} else {
			got_object_idset_remove(NULL, graph->node_ids,
			    &node->id);
			free(node);
			return err;
		}
	}

	if (*changed)
		add_node_to_iter_list(graph, node, child_node);
	*new_node = node;
	return NULL;
}

const struct got_error *
got_commit_graph_open(struct got_commit_graph **graph,
    struct got_object_id *commit_id, const char *path,
    int first_parent_traversal, struct got_repository *repo)
{
	const struct got_error *err = NULL;
	struct got_commit_object *commit;
	int changed, branch_done;

	*graph = NULL;

	err = got_object_open_as_commit(&commit, repo, commit_id);
	if (err)
		return err;

	/* The path must exist in our initial commit. */
	if (!got_path_is_root_dir(path)) {
		struct got_object_id *obj_id;
		err = got_object_id_by_path(&obj_id, repo, commit_id, path);
		if (err)
			return err;
		free(obj_id);
	}

	*graph = alloc_graph(path);
	if (*graph == NULL) {
		err = got_error_from_errno("alloc_graph");
		got_object_commit_close(commit);
		return err;
	}

	if (first_parent_traversal)
		(*graph)->flags |= GOT_COMMIT_GRAPH_FIRST_PARENT_TRAVERSAL;

	err = add_node(&(*graph)->head_node, &changed, &branch_done, *graph,
	    commit_id, commit, NULL, repo);
	if (err == NULL) {
		err = advance_branch(*graph, (*graph)->head_node, commit_id,
		    commit, repo);
	}
	got_object_commit_close(commit);
	if (err) {
		got_commit_graph_close(*graph);
		*graph = NULL;
		return err;
	}
	
	return NULL;
}

struct add_branch_tip_arg {
	struct got_commit_graph_branch_tip *tips;
	int ntips;
	struct got_repository *repo;
	struct got_commit_graph *graph;
};

static const struct got_error *
add_branch_tip(struct got_object_id *commit_id, void *data, void *arg)
{
	const struct got_error *err;
	struct got_commit_graph_node *child_node = data;
	struct add_branch_tip_arg *a = arg;
	struct got_commit_graph_node *new_node;
	struct got_commit_object *commit;
	int changed, branch_done;

	err = got_object_open_as_commit(&commit, a->repo, commit_id);
	if (err)
		return err;

	err = add_node(&new_node, &changed, &branch_done, a->graph,
	    commit_id, commit, child_node, a->repo);
	if (err)
		return err;

	a->tips[a->ntips].commit_id = new_node ? &new_node->id : NULL;
	a->tips[a->ntips].commit = commit;
	a->tips[a->ntips].new_node = new_node;
	a->tips[a->ntips].changed = changed;
	a->tips[a->ntips].branch_done = branch_done;
	a->ntips++;

	return NULL;
}

static const struct got_error *
fetch_commits_from_open_branches(int *nfetched,
    struct got_object_id **changed_id, struct got_commit_graph *graph,
    struct got_repository *repo, got_cancel_cb cancel_cb, void *cancel_arg)
{
	const struct got_error *err;
	struct add_branch_tip_arg arg;
	int i, ntips;

	*nfetched = 0;
	if (changed_id)
		*changed_id = NULL;

	ntips = got_object_idset_num_elements(graph->open_branches);
	if (ntips == 0)
		return NULL;

	/* (Re-)allocate branch tips array if necessary. */
	if (graph->ntips < ntips) {
		struct got_commit_graph_branch_tip *tips;
		tips = recallocarray(graph->tips, graph->ntips, ntips,
		    sizeof(*tips));
		if (tips == NULL)
			return got_error_from_errno("recallocarray");
		graph->tips = tips;
		graph->ntips = ntips;
	}
	arg.tips = graph->tips;
	arg.ntips = 0; /* add_branch_tip() will increment */
	arg.repo = repo;
	arg.graph = graph;
	err = got_object_idset_for_each(graph->open_branches, add_branch_tip,
	    &arg);
	if (err)
		goto done;

	for (i = 0; i < arg.ntips; i++) {
		struct got_object_id *commit_id;
		struct got_commit_object *commit;
		struct got_commit_graph_node *new_node;
		int branch_done, changed;

		if (cancel_cb) {
			err = (*cancel_cb)(cancel_arg);
			if (err)
				break;
		}

		commit_id = arg.tips[i].commit_id;
		commit = arg.tips[i].commit;
		new_node = arg.tips[i].new_node;
		branch_done = arg.tips[i].branch_done;
		changed = arg.tips[i].changed;

		if (branch_done)
			err = close_branch(graph, commit_id);
		else
			err = advance_branch(graph, new_node, commit_id,
			    commit, repo);
		if (err)
			break;
		if (changed && changed_id && *changed_id == NULL)
			*changed_id = commit_id;
	}
done:
	for (i = 0; i < arg.ntips; i++)
		got_object_commit_close(arg.tips[i].commit);
	(*nfetched) = arg.ntips;
	return err;
}

const struct got_error *
got_commit_graph_fetch_commits(struct got_commit_graph *graph, int limit,
    struct got_repository *repo, got_cancel_cb cancel_cb, void *cancel_arg)
{
	const struct got_error *err;
	int nfetched = 0, ncommits;
	struct got_object_id *changed_id = NULL;

	while (nfetched < limit) {
		if (cancel_cb) {
			err = (*cancel_cb)(cancel_arg);
			if (err)
				return err;
		}
		err = fetch_commits_from_open_branches(&ncommits,
		    &changed_id, graph, repo, cancel_cb, cancel_arg);
		if (err)
			return err;
		if (ncommits == 0)
			break;
		if (changed_id)
			nfetched += ncommits;
	}

	return NULL;
}

static const struct got_error *
free_node_iter(struct got_object_id *id, void *data, void *arg)
{
	struct got_commit_graph_node *node = data;
	free(node);
	return NULL;
}

void
got_commit_graph_close(struct got_commit_graph *graph)
{
	got_object_idset_free(graph->open_branches);
	got_object_idset_for_each(graph->node_ids, free_node_iter, NULL);
	got_object_idset_free(graph->node_ids);
	free(graph->tips);
	free(graph->path);
	free(graph);
}

const struct got_error *
got_commit_graph_iter_start(struct got_commit_graph *graph,
    struct got_object_id *id, struct got_repository *repo,
    got_cancel_cb cancel_cb, void *cancel_arg)
{
	const struct got_error *err = NULL;
	struct got_commit_graph_node *start_node;
	struct got_commit_object *commit;
	int changed;

	start_node = got_object_idset_get(graph->node_ids, id);
	while (start_node == NULL) {
		int ncommits;
		err = fetch_commits_from_open_branches(&ncommits, NULL, graph,
		    repo, cancel_cb, cancel_arg);
		if (err)
			return err;
		if (ncommits == 0)
			return got_error_no_obj(id);
		start_node = got_object_idset_get(graph->node_ids, id);
	}

	err = got_object_open_as_commit(&commit, repo, &start_node->id);
	if (err)
		return err;

	err = detect_changed_path(&changed, commit, &start_node->id,
	    graph->path, repo);
	if (err) {
		got_object_commit_close(commit);
		return err;
	}

	if (!changed) {
		/* Locate first commit which changed graph->path. */
		struct got_object_id *changed_id = NULL;
		while (changed_id == NULL) {
			int ncommits;
			err = fetch_commits_from_open_branches(&ncommits,
			    &changed_id, graph, repo, cancel_cb, cancel_arg);
			if (err) {
				got_object_commit_close(commit);
				return err;
			}
		}
		start_node = got_object_idset_get(graph->node_ids, changed_id);
	}
	got_object_commit_close(commit);

	graph->iter_node = start_node;
	return NULL;
}

const struct got_error *
got_commit_graph_iter_next(struct got_object_id **id,
    struct got_commit_graph *graph)
{
	*id = NULL;

	if (graph->iter_node == NULL) {
		/* We are done iterating, or iteration was not started. */
		return got_error(GOT_ERR_ITER_COMPLETED);
	}

	if (graph->iter_node ==
	    TAILQ_LAST(&graph->iter_list, got_commit_graph_iter_list) &&
	    got_object_idset_num_elements(graph->open_branches) == 0) {
		/* We are done iterating. */
		*id = &graph->iter_node->id;
		graph->iter_node = NULL;
		return NULL;
	}

	if (TAILQ_NEXT(graph->iter_node, entry) == NULL)
		return got_error(GOT_ERR_ITER_NEED_MORE);

	*id = &graph->iter_node->id;
	graph->iter_node = TAILQ_NEXT(graph->iter_node, entry);
	return NULL;
}

const struct got_error *
got_commit_graph_find_youngest_common_ancestor(struct got_object_id **yca_id,
    struct got_object_id *commit_id, struct got_object_id *commit_id2,
    struct got_repository *repo, got_cancel_cb cancel_cb, void *cancel_arg)
{
	const struct got_error *err = NULL;
	struct got_commit_graph *graph = NULL, *graph2 = NULL;
	int completed = 0, completed2 = 0;
	struct got_object_idset *commit_ids;

	*yca_id = NULL;

	commit_ids = got_object_idset_alloc();
	if (commit_ids == NULL)
		return got_error_from_errno("got_object_idset_alloc");

	err = got_commit_graph_open(&graph, commit_id, "/", 1, repo);
	if (err)
		goto done;

	err = got_commit_graph_open(&graph2, commit_id2, "/", 1, repo);
	if (err)
		goto done;

	err = got_commit_graph_iter_start(graph, commit_id, repo,
	    cancel_cb, cancel_arg);
	if (err)
		goto done;

	err = got_commit_graph_iter_start(graph2, commit_id2, repo,
	    cancel_cb, cancel_arg);
	if (err)
		goto done;

	for (;;) {
		struct got_object_id *id, *id2;

		if (cancel_cb) {
			err = (*cancel_cb)(cancel_arg);
			if (err)
				break;
		}

		if (!completed) {
			err = got_commit_graph_iter_next(&id, graph);
			if (err) {
				if (err->code == GOT_ERR_ITER_COMPLETED)
					completed = 1;
				else if (err->code != GOT_ERR_ITER_NEED_MORE)
					break;
				err = got_commit_graph_fetch_commits(graph, 1,
				    repo, cancel_cb, cancel_arg);
				if (err)
					break;
			}
		}

		if (!completed2) {
			err = got_commit_graph_iter_next(&id2, graph2);
			if (err) {
				if (err->code == GOT_ERR_ITER_COMPLETED)
					completed2 = 1;
				else if (err->code != GOT_ERR_ITER_NEED_MORE)
					break;
				err = got_commit_graph_fetch_commits(graph2, 1,
				    repo, cancel_cb, cancel_arg);
				if (err)
					break;
			}
		}

		if (id) {
			if (got_object_idset_get(commit_ids, id)) {
				*yca_id = got_object_id_dup(id);
				if (*yca_id)
					break;
				err = got_error_from_errno("got_object_id_dup");
				break;

			}
			err = got_object_idset_add(commit_ids, id, id);
			if (err)
				break;
		}
		if (id2) {
			if (got_object_idset_get(commit_ids, id2)) {
				*yca_id = got_object_id_dup(id2);
				if (*yca_id)
					break;
				err = got_error_from_errno("got_object_id_dup");
				break;

			}
			err = got_object_idset_add(commit_ids, id2, id2);
			if (err)
				break;
		}

		if (completed && completed2) {
			err = got_error(GOT_ERR_ANCESTRY);
			break;
		}

	}
done:
	got_object_idset_free(commit_ids);
	if (graph)
		got_commit_graph_close(graph);
	if (graph2)
		got_commit_graph_close(graph2);
	return err;
}