/*
 * ***** BEGIN GPL LICENSE BLOCK *****
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * The Original Code is Copyright (C) 2004 by Blender Foundation.
 * All rights reserved.
 *
 * The Original Code is: all of this file.
 *
 * Contributor(s): Joseph Eagar
 *
 * ***** END GPL LICENSE BLOCK *****
 */

/** \file blender/editors/mesh/editmesh_rip.c
 *  \ingroup edmesh
 */

#include "MEM_guardedalloc.h"

#include "DNA_object_types.h"

#include "BLI_math.h"
#include "BLI_array.h"

#include "BKE_context.h"
#include "BKE_report.h"
#include "BKE_editmesh.h"

#include "RNA_define.h"
#include "RNA_access.h"

#include "WM_types.h"

#include "ED_mesh.h"
#include "ED_screen.h"
#include "ED_transform.h"
#include "ED_view3d.h"

#include "bmesh.h"
#include "bmesh_tools.h"

#include "mesh_intern.h"  /* own include */

/**
 * helper to find edge for edge_rip,
 *
 * \param inset is used so we get some useful distance
 * when comparing multiple edges that meet at the same
 * point and would result in the same distance.
 */
#define INSET_DEFAULT 0.00001f
static float edbm_rip_edgedist_squared(
        ARegion *ar, float mat[4][4],
        const float co1[3], const float co2[3], const float mvalf[2],
        const float inset)
{
	float vec1[2], vec2[2], dist_sq;

	ED_view3d_project_float_v2_m4(ar, co1, vec1, mat);
	ED_view3d_project_float_v2_m4(ar, co2, vec2, mat);

	if (inset != 0.0f) {
		const float dist_2d = len_v2v2(vec1, vec2);
		if (dist_2d > FLT_EPSILON) {
			const float dist = inset / dist_2d;
			BLI_assert(isfinite(dist));
			interp_v2_v2v2(vec1, vec1, vec2, dist);
			interp_v2_v2v2(vec2, vec2, vec1, dist);
		}
	}

	dist_sq = dist_squared_to_line_segment_v2(mvalf, vec1, vec2);
	BLI_assert(isfinite(dist_sq));

	return dist_sq;
}

#if 0
static float edbm_rip_linedist(
        ARegion *ar, float mat[4][4],
        const float co1[3], const float co2[3], const float mvalf[2])
{
	float vec1[2], vec2[2];

	ED_view3d_project_float_v2_m4(ar, co1, vec1, mat);
	ED_view3d_project_float_v2_m4(ar, co2, vec2, mat);

	return dist_to_line_v2(mvalf, vec1, vec2);
}
#endif

/* calculaters a point along the loop tangent which can be used to measure against edges */
static void edbm_calc_loop_co(BMLoop *l, float l_mid_co[3])
{
	BM_loop_calc_face_tangent(l, l_mid_co);

	/* scale to average of surrounding edge size, only needs to be approx, but should
	 * be roughly equivalent to the check below which uses the middle of the edge. */
	mul_v3_fl(l_mid_co, (BM_edge_calc_length(l->e) + BM_edge_calc_length(l->prev->e)) / 2.0f);

	add_v3_v3(l_mid_co, l->v->co);
}


static float edbm_rip_edge_side_measure(
        BMEdge *e, BMLoop *e_l,
        ARegion *ar,
        float projectMat[4][4], const float fmval[2])
{
	float cent[3] = {0, 0, 0}, mid[3];

	float vec[2];
	float fmval_tweak[2];
	float e_v1_co[2], e_v2_co[2];
	float score;

	BMVert *v1_other;
	BMVert *v2_other;

	BLI_assert(BM_vert_in_edge(e, e_l->v));

	/* method for calculating distance:
	 *
	 * for each edge: calculate face center, then made a vector
	 * from edge midpoint to face center.  offset edge midpoint
	 * by a small amount along this vector. */

	/* rather then the face center, get the middle of
	 * both edge verts connected to this one */
	v1_other = BM_face_other_vert_loop(e_l->f, e->v2, e->v1)->v;
	v2_other = BM_face_other_vert_loop(e_l->f, e->v1, e->v2)->v;
	mid_v3_v3v3(cent, v1_other->co, v2_other->co);
	mid_v3_v3v3(mid, e->v1->co, e->v2->co);

	ED_view3d_project_float_v2_m4(ar, cent, cent, projectMat);
	ED_view3d_project_float_v2_m4(ar, mid, mid, projectMat);

	ED_view3d_project_float_v2_m4(ar, e->v1->co, e_v1_co, projectMat);
	ED_view3d_project_float_v2_m4(ar, e->v2->co, e_v2_co, projectMat);

	sub_v2_v2v2(vec, cent, mid);
	normalize_v2_length(vec, 0.01f);

	/* rather then adding to both verts, subtract from the mouse */
	sub_v2_v2v2(fmval_tweak, fmval, vec);

	score = len_v2v2(e_v1_co, e_v2_co);

	if (dist_squared_to_line_segment_v2(fmval_tweak, e_v1_co, e_v2_co) >
	    dist_squared_to_line_segment_v2(fmval,       e_v1_co, e_v2_co))
	{
		return score;
	}
	else {
		return -score;
	}
}


/* - Advanced selection handling 'ripsel' functions ----- */

/**
 * How rip selection works
 *
 * Firstly - rip is basically edge split with side-selection & grab.
 * Things would be much more simple if we didn't have to worry about side selection
 *
 * The method used for checking the side of selection is as follows...
 * - First tag all rip-able edges.
 * - Build a contiguous edge list by looping over tagged edges and following each ones tagged siblings in both
 *   directions.
 *   - The loops are not stored in an array, Instead both loops on either side of each edge has its index values set
 *     to count down from the last edge, this way, once we have the 'last' edge its very easy to walk down the
 *     connected edge loops.
 *     The reason for using loops like this is because when the edges are split we don't which face user gets the newly
 *     created edge (its as good as random so we cant assume new edges will be on once side).
 *     After splitting, its very simple to walk along boundary loops since each only has one edge from a single side.
 * - The end loop pairs are stored in an array however to support multiple edge-selection-islands, so you can rip
 *   multiple selections at once.
 * - * Execute the split *
 * - For each #EdgeLoopPair walk down both sides of the split using the loops and measure which is facing the mouse.
 * - Deselect the edge loop facing away.
 *
 * Limitation!
 * This currently works very poorly with intersecting edge islands (verts with more than 2 tagged edges)
 * This is nice to but for now not essential.
 *
 * - campbell.
 */


#define IS_VISIT_POSSIBLE(e)   (BM_edge_is_manifold(e) && BM_elem_flag_test(e, BM_ELEM_TAG))
#define IS_VISIT_DONE(e) ((e)->l && (BM_elem_index_get((e)->l) != INVALID_UID))
#define INVALID_UID INT_MIN

/* mark, assign uid and step */
static BMEdge *edbm_ripsel_edge_mark_step(BMVert *v, const int uid)
{
	BMIter iter;
	BMEdge *e;
	BM_ITER_ELEM (e, &iter, v, BM_EDGES_OF_VERT) {
		if (IS_VISIT_POSSIBLE(e) && !IS_VISIT_DONE(e)) {
			BMLoop *l_a, *l_b;

			BM_edge_loop_pair(e, &l_a, &l_b); /* no need to check, we know this will be true */

			/* so (IS_VISIT_DONE == true) */
			BM_elem_index_set(l_a, uid);  /* set_dirty */
			BM_elem_index_set(l_b, uid);  /* set_dirty */

			return e;
		}
	}
	return NULL;
}

typedef struct EdgeLoopPair {
	BMLoop *l_a;
	BMLoop *l_b;
} EdgeLoopPair;

static EdgeLoopPair *edbm_ripsel_looptag_helper(BMesh *bm)
{
	BMIter fiter;
	BMIter liter;

	BMFace *f;
	BMLoop *l;

	int uid_start;
	int uid_end;
	int uid = bm->totedge; /* can start anywhere */

	EdgeLoopPair *eloop_pairs = NULL;
	BLI_array_declare(eloop_pairs);
	EdgeLoopPair *lp;

	/* initialize loops with dummy invalid index values */
	BM_ITER_MESH (f, &fiter, bm, BM_FACES_OF_MESH) {
		BM_ITER_ELEM (l, &liter, f, BM_LOOPS_OF_FACE) {
			BM_elem_index_set(l, INVALID_UID);  /* set_dirty */
		}
	}
	bm->elem_index_dirty |= BM_LOOP;

	/* set contiguous loops ordered 'uid' values for walking after split */
	while (true) {
		int tot = 0;
		BMIter eiter;
		BMEdge *e_step;
		BMVert *v_step;
		BMEdge *e;
		BMEdge *e_first;
		BMEdge *e_last;

		e_first = NULL;
		BM_ITER_MESH (e, &eiter, bm, BM_EDGES_OF_MESH) {
			if (IS_VISIT_POSSIBLE(e) && !IS_VISIT_DONE(e)) {
				e_first = e;
				break;
			}
		}

		if (e_first == NULL) {
			break;
		}

		/* initialize  */
		e_first = e;
		v_step = e_first->v1;
		e_step = NULL; /* quiet warning, will never remain this value */

		uid_start = uid;
		while ((e = edbm_ripsel_edge_mark_step(v_step, uid))) {
			v_step = BM_edge_other_vert((e_step = e), v_step);
			uid++; /* only different line */
			tot++;
		}

		/* this edges loops have the highest uid's, store this to walk down later */
		e_last = e_step;

		/* always store the highest 'uid' edge for the stride */
		uid_end = uid - 1;
		uid = uid_start - 1;

		/* initialize */
		v_step = e_first->v1;

		while ((e = edbm_ripsel_edge_mark_step(v_step, uid))) {
			v_step = BM_edge_other_vert((e_step = e), v_step);
			uid--; /* only different line */
			tot++;
		}

		/* stride far enough not to _ever_ overlap range */
		uid_start = uid;
		uid = uid_end + bm->totedge;

		lp = BLI_array_append_ret(eloop_pairs);
		BM_edge_loop_pair(e_last, &lp->l_a, &lp->l_b); /* no need to check, we know this will be true */


		BLI_assert(tot == uid_end - uid_start);

#if 0
		printf("%s: found contiguous edge loop of (%d)\n", __func__, uid_end - uid_start);
#endif

	}

	/* null terminate */
	lp = BLI_array_append_ret(eloop_pairs);
	lp->l_a = lp->l_b = NULL;

	return eloop_pairs;
}


/* - De-Select the worst rip-edge side -------------------------------- */


static BMEdge *edbm_ripsel_edge_uid_step(BMEdge *e_orig, BMVert **v_prev)
{
	BMIter eiter;
	BMEdge *e;
	BMVert *v = BM_edge_other_vert(e_orig, *v_prev);
	const int uid_cmp = BM_elem_index_get(e_orig->l) - 1;

	BM_ITER_ELEM (e, &eiter, v, BM_EDGES_OF_VERT) {
		if (BM_elem_index_get(e->l) == uid_cmp) {
			*v_prev = v;
			return e;
		}
	}
	return NULL;
}

static BMVert *edbm_ripsel_edloop_pair_start_vert(BMEdge *e)
{
	/* try step in a direction, if it fails we know do go the other way */
	BMVert *v_test = e->v1;
	return (edbm_ripsel_edge_uid_step(e, &v_test)) ? e->v1 : e->v2;
}

static void edbm_ripsel_deselect_helper(BMesh *bm, EdgeLoopPair *eloop_pairs,
                                        ARegion *ar, float projectMat[4][4], float fmval[2])
{
	EdgeLoopPair *lp;

	for (lp = eloop_pairs; lp->l_a; lp++) {
		BMEdge *e;
		BMVert *v_prev;

		float score_a = 0.0f;
		float score_b = 0.0f;

		e = lp->l_a->e;
		v_prev = edbm_ripsel_edloop_pair_start_vert(e);
		for (; e; e = edbm_ripsel_edge_uid_step(e, &v_prev)) {
			score_a += edbm_rip_edge_side_measure(e, e->l, ar, projectMat, fmval);
		}
		e = lp->l_b->e;
		v_prev = edbm_ripsel_edloop_pair_start_vert(e);
		for (; e; e = edbm_ripsel_edge_uid_step(e, &v_prev)) {
			score_b += edbm_rip_edge_side_measure(e, e->l, ar, projectMat, fmval);
		}

		e = (score_a > score_b) ? lp->l_a->e : lp->l_b->e;
		v_prev = edbm_ripsel_edloop_pair_start_vert(e);
		for (; e; e = edbm_ripsel_edge_uid_step(e, &v_prev)) {
			BM_edge_select_set(bm, e, false);
		}
	}
}
/* --- end 'ripsel' selection handling code --- */


/* --- face-fill code --- */
/**
 * return an un-ordered array of loop pairs
 * use for rebuilding face-fill
 *
 * \note the method currently used fails for edges with 3+ face users and gives
 *       nasty holes in the mesh, there isnt a good way of knowing ahead of time
 *       which loops will be split apart (its possible to figure out but quite involved).
 *       So for now this is a known limitation of current rip-fill option.
 */

typedef struct UnorderedLoopPair {
	BMLoop *l_pair[2];
	char    flag;
} UnorderedLoopPair;
enum {
	ULP_FLIP_0 = (1 << 0),
	ULP_FLIP_1 = (1 << 1)
};

static UnorderedLoopPair *edbm_tagged_loop_pairs_to_fill(BMesh *bm)
{
	BMIter iter;
	BMEdge *e;

	unsigned int total_tag = 0;
	/* count tags, could be pre-calculated */
	BM_ITER_MESH (e, &iter, bm, BM_EDGES_OF_MESH) {
		if (BM_elem_flag_test(e, BM_ELEM_TAG)) {
			total_tag++;
		}
	}

	if (total_tag) {
		UnorderedLoopPair *uloop_pairs = MEM_mallocN(total_tag * sizeof(UnorderedLoopPair), __func__);
		UnorderedLoopPair *ulp = uloop_pairs;

		BM_ITER_MESH (e, &iter, bm, BM_EDGES_OF_MESH) {
			if (BM_elem_flag_test(e, BM_ELEM_TAG)) {
				BMLoop *l1, *l2;
				if (BM_edge_loop_pair(e, &l1, &l2)) {
					BMVert *v_cmp = l1->e->v1;
					ulp->flag = (((l1->v != v_cmp) ? ULP_FLIP_0 : 0) |
					             ((l2->v == v_cmp) ? ULP_FLIP_1 : 0));
				}
				else {
					ulp->flag = 0;
				}
				ulp->l_pair[0] = l1;
				ulp->l_pair[1] = l2;

				ulp++;
			}
		}

		return uloop_pairs;
	}
	else {
		return NULL;
	}
}

static void edbm_tagged_loop_pairs_do_fill_faces(BMesh *bm, UnorderedLoopPair *uloop_pairs)
{
	UnorderedLoopPair *ulp;
	unsigned int total_tag = MEM_allocN_len(uloop_pairs) / sizeof(UnorderedLoopPair);
	unsigned int i;

	for (i = 0, ulp = uloop_pairs; i < total_tag; i++, ulp++) {
		if ((ulp->l_pair[0]    && ulp->l_pair[1]) &&
		    (ulp->l_pair[0]->e != ulp->l_pair[1]->e))
		{
			/* time has come to make a face! */
			BMVert *v_shared = BM_edge_share_vert(ulp->l_pair[0]->e, ulp->l_pair[1]->e);
			BMFace *f, *f_example = ulp->l_pair[0]->f;
			BMLoop *l_iter;
			BMVert *f_verts[4];

			if (v_shared == NULL) {
				/* quad */
				f_verts[0] = ulp->l_pair[0]->e->v1;
				f_verts[1] = ulp->l_pair[1]->e->v1;
				f_verts[2] = ulp->l_pair[1]->e->v2;
				f_verts[3] = ulp->l_pair[0]->e->v2;

				if (ulp->flag & ULP_FLIP_0) {
					SWAP(BMVert *, f_verts[0], f_verts[3]);
				}
				if (ulp->flag & ULP_FLIP_1) {
					SWAP(BMVert *, f_verts[1], f_verts[2]);
				}
			}
			else {
				/* tri */
				f_verts[0] = v_shared;
				f_verts[1] = BM_edge_other_vert(ulp->l_pair[0]->e, v_shared);
				f_verts[2] = BM_edge_other_vert(ulp->l_pair[1]->e, v_shared);
				f_verts[3] = NULL;

				/* don't use the flip flags */
				if (v_shared == ulp->l_pair[0]->v) {
					SWAP(BMVert *, f_verts[0], f_verts[1]);
				}
			}

			/* face should never exist */
			BLI_assert(!BM_face_exists(f_verts, f_verts[3] ? 4 : 3));

			f = BM_face_create_verts(bm, f_verts, f_verts[3] ? 4 : 3, f_example, BM_CREATE_NOP, true);

			l_iter = BM_FACE_FIRST_LOOP(f);

			if (f_verts[3]) {
				BM_elem_attrs_copy(bm, bm, BM_edge_other_loop(ulp->l_pair[0]->e, l_iter), l_iter); l_iter = l_iter->next;
				BM_elem_attrs_copy(bm, bm, BM_edge_other_loop(ulp->l_pair[1]->e, l_iter), l_iter); l_iter = l_iter->next;
				BM_elem_attrs_copy(bm, bm, BM_edge_other_loop(ulp->l_pair[1]->e, l_iter), l_iter); l_iter = l_iter->next;
				BM_elem_attrs_copy(bm, bm, BM_edge_other_loop(ulp->l_pair[0]->e, l_iter), l_iter);
			}
			else {
				BM_elem_attrs_copy(bm, bm, BM_edge_other_loop(ulp->l_pair[0]->e, l_iter), l_iter); l_iter = l_iter->next;
				BM_elem_attrs_copy(bm, bm, BM_edge_other_loop(ulp->l_pair[0]->e, l_iter), l_iter); l_iter = l_iter->next;
				BM_elem_attrs_copy(bm, bm, BM_edge_other_loop(ulp->l_pair[1]->e, l_iter), l_iter);
			}

		}
	}
}

/* --- end 'face-fill' code --- */

/**
 * This is the main vert ripping function (rip when one vertex is selected)
 */
static int edbm_rip_invoke__vert(bContext *C, wmOperator *op, const wmEvent *event)
{
	const bool do_fill = RNA_boolean_get(op->ptr, "use_fill");
	UnorderedLoopPair *fill_uloop_pairs = NULL;
	Object *obedit = CTX_data_edit_object(C);
	ARegion *ar = CTX_wm_region(C);
	RegionView3D *rv3d = CTX_wm_region_view3d(C);
	BMEditMesh *em = BKE_editmesh_from_object(obedit);
	BMesh *bm = em->bm;
	BMIter iter, liter;
	BMLoop *l;
	BMEdge *e_best;
	BMVert *v;
	const int totvert_orig = bm->totvert;
	int i;
	float projectMat[4][4], fmval[3] = {event->mval[0], event->mval[1]};
	float dist_sq = FLT_MAX;
	float d;
	bool is_wire, is_manifold_region;

	BMEditSelection ese;
	int totboundary_edge = 0;

	ED_view3d_ob_project_mat_get(rv3d, obedit, projectMat);

	/* find selected vert - same some time and check history first */
	if (BM_select_history_active_get(bm, &ese) && ese.htype == BM_VERT) {
		v = (BMVert *)ese.ele;
	}
	else {
		ese.ele = NULL;

		BM_ITER_MESH (v, &iter, bm, BM_VERTS_OF_MESH) {
			if (BM_elem_flag_test(v, BM_ELEM_SELECT))
				break;
		}
	}

	/* (v == NULL) should be impossible */
	if ((v == NULL) || (v->e == NULL)) {
		return OPERATOR_CANCELLED;
	}

	is_wire = BM_vert_is_wire(v);
	is_manifold_region = BM_vert_is_manifold_region(v);

	e_best = NULL;

	{
		BMEdge *e;
		/* find closest edge to mouse cursor */
		BM_ITER_ELEM (e, &iter, v, BM_EDGES_OF_VERT) {
			/* consider wire as boundary for this purpose,
			 * otherwise we can't a face away from a wire edge */
			totboundary_edge += (BM_edge_is_boundary(e) || BM_edge_is_wire(e));
			if (!BM_elem_flag_test(e, BM_ELEM_HIDDEN)) {
				if ((is_manifold_region == false) || BM_edge_is_manifold(e)) {
					d = edbm_rip_edgedist_squared(ar, projectMat, e->v1->co, e->v2->co, fmval, INSET_DEFAULT);
					if ((e_best == NULL) || (d < dist_sq)) {
						dist_sq = d;
						e_best = e;
					}
				}
			}
		}
	}

	if (e_best && e_best->l && (is_manifold_region == false)) {
		/* Try to split off a non-manifold fan (when we have multiple disconnected fans) */
		BMLoop *l_sep = e_best->l->v == v ? e_best->l : e_best->l->next;
		BMVert *v_new;

		BLI_assert(l_sep->v == v);
		v_new = BM_face_loop_separate_multi_isolated(bm, l_sep);
		BLI_assert(BM_vert_find_first_loop(v));

		BM_vert_select_set(bm, v, false);
		BM_select_history_remove(bm, v);

		BM_vert_select_set(bm, v_new, true);
		if (ese.ele) {
			BM_select_history_store(bm, v_new);
		}

		if (do_fill) {
			BM_edge_create(bm, v, v_new, NULL, BM_CREATE_NOP);
		}

		return OPERATOR_FINISHED;
	}

	/* if we are ripping a single vertex from 3 faces,
	 * then measure the distance to the face corner as well as the edge */
	if (BM_vert_face_count_is_equal(v, 3) &&
	    BM_vert_edge_count_is_equal(v, 3))
	{
		BMEdge *e_all[3];
		BMLoop *l_all[3];
		int i1, i2;

		BM_iter_as_array(bm, BM_EDGES_OF_VERT, v, (void **)e_all, 3);
		BM_iter_as_array(bm, BM_LOOPS_OF_VERT, v, (void **)l_all, 3);

		/* not do a loop similar to the one above, but test against loops */
		for (i1 = 0; i1 < 3; i1++) {
			/* consider wire as boundary for this purpose,
			 * otherwise we can't a face away from a wire edge */
			float l_mid_co[3];
			l = l_all[i1];
			edbm_calc_loop_co(l, l_mid_co);
			d = edbm_rip_edgedist_squared(ar, projectMat, l->v->co, l_mid_co, fmval, INSET_DEFAULT);
			if ((e_best == NULL) || (d < dist_sq)) {
				dist_sq = d;

				/* find the edge that is not in this loop */
				e_best = NULL;
				for (i2 = 0; i2 < 3; i2++) {
					if (!BM_edge_in_loop(e_all[i2], l)) {
						e_best = e_all[i2];
						break;
					}
				}
				BLI_assert(e_best != NULL);
			}
		}
	}

	/* should we go ahead with edge rip or do we need to do special case, split off vertex?:
	 * split off vertex if...
	 * - we cant find an edge - this means we are ripping a faces vert that is connected to other
	 *   geometry only at the vertex.
	 * - the boundary edge total is greater than 2,
	 *   in this case edge split _can_ work but we get far nicer results if we use this special case.
	 * - there are only 2 edges but we are a wire vert. */
	if ((is_wire == false && totboundary_edge > 2) ||
	    (is_wire == true  && totboundary_edge > 1))
	{
		BMVert **vout;
		int vout_len;

		BM_vert_select_set(bm, v, false);

		bmesh_kernel_vert_separate(bm, v, &vout, &vout_len, true);

		if (vout_len < 2) {
			MEM_freeN(vout);
			/* set selection back to avoid active-unselected vertex */
			BM_vert_select_set(bm, v, true);
			/* should never happen */
			BKE_report(op->reports, RPT_ERROR, "Error ripping vertex from faces");
			return OPERATOR_CANCELLED;
		}
		else {
			int vi_best = 0;

			if (ese.ele) {
				BM_select_history_remove(bm, ese.ele);
			}

			dist_sq = FLT_MAX;

			/* in the loop below we find the best vertex to drag based on its connected geometry,
			 * either by its face corner, or connected edge (when no faces are attached) */
			for (i = 0; i < vout_len; i++) {

				if (BM_vert_is_wire(vout[i]) == false) {
					/* find the best face corner */
					BM_ITER_ELEM (l, &iter, vout[i], BM_LOOPS_OF_VERT) {
						if (!BM_elem_flag_test(l->f, BM_ELEM_HIDDEN)) {
							float l_mid_co[3];

							edbm_calc_loop_co(l, l_mid_co);
							d = edbm_rip_edgedist_squared(ar, projectMat, v->co, l_mid_co, fmval, INSET_DEFAULT);

							if (d < dist_sq) {
								dist_sq = d;
								vi_best = i;
							}
						}
					}
				}
				else {
					BMEdge *e;
					/* a wire vert, find the best edge */
					BM_ITER_ELEM (e, &iter, vout[i], BM_EDGES_OF_VERT) {
						if (!BM_elem_flag_test(e, BM_ELEM_HIDDEN)) {
							float e_mid_co[3];

							mid_v3_v3v3(e_mid_co, e->v1->co, e->v2->co);
							d = edbm_rip_edgedist_squared(ar, projectMat, v->co, e_mid_co, fmval, INSET_DEFAULT);

							if (d < dist_sq) {
								dist_sq = d;
								vi_best = i;
							}
						}
					}
				}
			}

			/* vout[0]  == best
			 * vout[1]  == glue
			 * vout[2+] == splice with glue (when vout_len > 2)
			 */
			if (vi_best != 0) {
				SWAP(BMVert *, vout[0], vout[vi_best]);
				vi_best = 0;
			}

			/* select the vert from the best region */
			v = vout[vi_best];
			BM_vert_select_set(bm, v, true);

			if (ese.ele) {
				BM_select_history_store(bm, v);
			}

			/* splice all others back together */
			if (vout_len > 2) {
				for (i = 2; i < vout_len; i++) {
					BM_vert_splice(bm, vout[1], vout[i]);
				}
			}

			if (do_fill) {
				/* match extrude vert-order */
				BM_edge_create(bm, vout[1], vout[0], NULL, BM_CREATE_NOP);
			}

			MEM_freeN(vout);

			return OPERATOR_FINISHED;
		}
	}

	if (!e_best) {
		BKE_report(op->reports, RPT_ERROR, "Selected vertex has no edge/face pairs attached");
		return OPERATOR_CANCELLED;
	}

	/* *** Execute the split! *** */
	/* unlike edge split, for single vertex split we only use the operator in one of the cases
	 * but both allocate fill */

	{
		BMVert *v_rip;
		BMLoop *larr[2];
		int larr_len = 0;

		/* rip two adjacent edges */
		if (BM_edge_is_boundary(e_best) || BM_vert_face_count_is_equal(v, 2)) {
			/* Don't run the edge split operator in this case */

			l = BM_edge_vert_share_loop(e_best->l, v);
			larr[larr_len] = l;
			larr_len++;

			/* only tag for face-fill (we don't call the operator) */
			if (BM_edge_is_boundary(e_best)) {
				BM_elem_flag_enable(e_best, BM_ELEM_TAG);
			}
			else {
				BM_elem_flag_enable(l->e, BM_ELEM_TAG);
				BM_elem_flag_enable(l->prev->e, BM_ELEM_TAG);
			}
		}
		else {
			if (BM_edge_is_manifold(e_best)) {
				BMLoop *l_iter, *l_first;
				l_iter = l_first = e_best->l;
				do {
					larr[larr_len] = BM_edge_vert_share_loop(l_iter, v);

					if (do_fill) {
						/* Only needed when filling...
						 * Also, we never want to tag best edge, that one won't change during split. See T44618. */
						if (larr[larr_len]->e == e_best) {
							BM_elem_flag_enable(larr[larr_len]->prev->e, BM_ELEM_TAG);
						}
						else {
							BM_elem_flag_enable(larr[larr_len]->e, BM_ELEM_TAG);
						}
					}
					larr_len++;
				} while ((l_iter = l_iter->radial_next) != l_first);
			}
			else {
				/* looks like there are no split edges, we could just return/report-error? - Campbell */
			}
		}

		/* keep directly before edgesplit */
		if (do_fill) {
			fill_uloop_pairs = edbm_tagged_loop_pairs_to_fill(bm);
		}

		if (larr_len) {
			v_rip = BM_face_loop_separate_multi(bm, larr, larr_len);
		}
		else {
			v_rip = NULL;
		}

		if (v_rip) {
			BM_vert_select_set(bm, v_rip, true);
		}
		else {
			if (fill_uloop_pairs) MEM_freeN(fill_uloop_pairs);
			return OPERATOR_CANCELLED;
		}
	}

	{
		/* --- select which vert --- */
		BMVert *v_best = NULL;
		float l_corner_co[3];

		dist_sq = FLT_MAX;
		BM_ITER_MESH (v, &iter, bm, BM_VERTS_OF_MESH) {
			if (BM_elem_flag_test(v, BM_ELEM_SELECT)) {
				/* disable by default, re-enable winner at end */
				BM_vert_select_set(bm, v, false);
				BM_select_history_remove(bm, v);

				BM_ITER_ELEM (l, &liter, v, BM_LOOPS_OF_VERT) {

					/* check if v_best is null in the _rare_ case there are numeric issues */
					edbm_calc_loop_co(l, l_corner_co);
					d = edbm_rip_edgedist_squared(ar, projectMat, l->v->co, l_corner_co, fmval, INSET_DEFAULT);
					if ((v_best == NULL) || (d < dist_sq)) {
						v_best = v;
						dist_sq = d;
					}
				}
			}
		}

		if (v_best) {
			BM_vert_select_set(bm, v_best, true);
			if (ese.ele) {
				BM_select_history_store(bm, v_best);
			}
		}
	}

	if (do_fill && fill_uloop_pairs) {
		edbm_tagged_loop_pairs_do_fill_faces(bm, fill_uloop_pairs);
		MEM_freeN(fill_uloop_pairs);
	}


	if (totvert_orig == bm->totvert) {
		BKE_report(op->reports, RPT_ERROR, "No vertices could be ripped");
		return OPERATOR_CANCELLED;
	}

	return OPERATOR_FINISHED;
}

/**
 * This is the main edge ripping function
 */
static int edbm_rip_invoke__edge(bContext *C, wmOperator *op, const wmEvent *event)
{
	const bool do_fill = RNA_boolean_get(op->ptr, "use_fill");
	UnorderedLoopPair *fill_uloop_pairs = NULL;
	Object *obedit = CTX_data_edit_object(C);
	ARegion *ar = CTX_wm_region(C);
	RegionView3D *rv3d = CTX_wm_region_view3d(C);
	BMEditMesh *em = BKE_editmesh_from_object(obedit);
	BMesh *bm = em->bm;
	BMIter iter, eiter;
	BMLoop *l;
	BMEdge *e_best;
	BMVert *v;
	const int totedge_orig = bm->totedge;
	float projectMat[4][4], fmval[3] = {event->mval[0], event->mval[1]};

	EdgeLoopPair *eloop_pairs;

	ED_view3d_ob_project_mat_get(rv3d, obedit, projectMat);

	/* important this runs on the original selection, before tampering with tagging */
	eloop_pairs = edbm_ripsel_looptag_helper(bm);

	/* expand edge selection */
	BM_ITER_MESH (v, &iter, bm, BM_VERTS_OF_MESH) {
		BMEdge *e;
		bool all_manifold;
		int totedge_manifold;  /* manifold, visible edges */
		int i;

		e_best = NULL;
		i = 0;
		totedge_manifold = 0;
		all_manifold = true;
		BM_ITER_ELEM (e, &eiter, v, BM_EDGES_OF_VERT) {

			if (!BM_edge_is_wire(e) &&
			    !BM_elem_flag_test(e, BM_ELEM_HIDDEN))
			{
				/* important to check selection rather then tag here
				 * else we get feedback loop */
				if (BM_elem_flag_test(e, BM_ELEM_SELECT)) {
					e_best = e;
					i++;
				}
				totedge_manifold++;
			}

			/** #BM_vert_other_disk_edge has no hidden checks so don't check hidden here */
			if ((all_manifold == true) && (BM_edge_is_manifold(e) == false)) {
				all_manifold = false;
			}
		}

		/* single edge, extend */
		if (i == 1 && e_best->l) {
			/* note: if the case of 3 edges has one change in loop stepping,
			 * if this becomes more involved we may be better off splitting
			 * the 3 edge case into its own else-if branch */
			if ((totedge_manifold == 4 || totedge_manifold == 3) || (all_manifold == false)) {
				BMLoop *l_a = e_best->l;
				BMLoop *l_b = l_a->radial_next;

				/* find the best face to follow, this way the edge won't point away from
				 * the mouse when there are more than 4 (takes the shortest face fan around) */
				l = (edbm_rip_edge_side_measure(e_best, l_a, ar, projectMat, fmval) <
				     edbm_rip_edge_side_measure(e_best, l_b, ar, projectMat, fmval)) ? l_a : l_b;

				l = BM_loop_other_edge_loop(l, v);
				/* important edge is manifold else we can be attempting to split off a fan that don't budge,
				 * not crashing but adds duplicate edge. */
				if (BM_edge_is_manifold(l->e)) {
					l = l->radial_next;

					if (totedge_manifold != 3)
						l = BM_loop_other_edge_loop(l, v);

					if (l) {
						BLI_assert(!BM_elem_flag_test(l->e, BM_ELEM_TAG));
						BM_elem_flag_enable(l->e, BM_ELEM_TAG);
					}
				}
			}
			else {
				e = BM_vert_other_disk_edge(v, e_best);

				if (e) {
					BLI_assert(!BM_elem_flag_test(e, BM_ELEM_TAG));
					BM_elem_flag_enable(e, BM_ELEM_TAG);
				}
			}
		}
	}

	/* keep directly before edgesplit */
	if (do_fill) {
		fill_uloop_pairs = edbm_tagged_loop_pairs_to_fill(bm);
	}

	BM_mesh_edgesplit(em->bm, true, true, true);

	/* note: the output of the bmesh operator is ignored, since we built
	 * the contiguous loop pairs to split already, its possible that some
	 * edge did not split even though it was tagged which would not work
	 * as expected (but not crash), however there are checks to ensure
	 * tagged edges will split. So far its not been an issue. */
	edbm_ripsel_deselect_helper(bm, eloop_pairs,
	                            ar, projectMat, fmval);
	MEM_freeN(eloop_pairs);

	/* deselect loose verts */
	BM_mesh_select_mode_clean_ex(bm, SCE_SELECT_EDGE);

	if (do_fill && fill_uloop_pairs) {
		edbm_tagged_loop_pairs_do_fill_faces(bm, fill_uloop_pairs);
		MEM_freeN(fill_uloop_pairs);
	}

	if (totedge_orig == bm->totedge) {
		BKE_report(op->reports, RPT_ERROR, "No edges could be ripped");
		return OPERATOR_CANCELLED;
	}

	BM_select_history_validate(bm);

	return OPERATOR_FINISHED;
}

/* based on mouse cursor position, it defines how is being ripped */
static int edbm_rip_invoke(bContext *C, wmOperator *op, const wmEvent *event)
{
	Object *obedit = CTX_data_edit_object(C);
	BMEditMesh *em = BKE_editmesh_from_object(obedit);
	BMesh *bm = em->bm;
	BMIter iter;
	BMEdge *e;
	const bool singlesel = (bm->totvertsel == 1 && bm->totedgesel == 0 && bm->totfacesel == 0);
	int ret;

	/* running in face mode hardly makes sense, so convert to region loop and rip */
	if (bm->totfacesel) {
		/* highly nifty but hard to support since the operator can fail and we're left
		 * with modified selection */
		// WM_operator_name_call(C, "MESH_OT_region_to_loop", WM_OP_INVOKE_DEFAULT, NULL);

		BKE_report(op->reports, RPT_ERROR, "Cannot rip selected faces");
		return OPERATOR_CANCELLED;
	}

	/* we could support this, but not for now */
	if ((bm->totvertsel > 1) && (bm->totedgesel == 0)) {
		BKE_report(op->reports, RPT_ERROR, "Cannot rip multiple disconnected vertices");
		return OPERATOR_CANCELLED;
	}

	/* note on selection:
	 * When calling edge split we operate on tagged edges rather then selected
	 * this is important because the edges to operate on are extended by one,
	 * but the selection is left alone.
	 *
	 * After calling edge split - the duplicated edges have the same selection state as the
	 * original, so all we do is de-select the far side from the mouse and we have a
	 * useful selection for grabbing.
	 */

	/* BM_ELEM_SELECT --> BM_ELEM_TAG */
	BM_ITER_MESH (e, &iter, bm, BM_EDGES_OF_MESH) {
		BM_elem_flag_set(e, BM_ELEM_TAG, BM_elem_flag_test(e, BM_ELEM_SELECT));
	}

	/* split 2 main parts of this operator out into vertex and edge ripping */
	if (singlesel) {
		ret = edbm_rip_invoke__vert(C, op, event);
	}
	else {
		ret = edbm_rip_invoke__edge(C, op, event);
	}

	if (ret == OPERATOR_CANCELLED) {
		return OPERATOR_CANCELLED;
	}

	BLI_assert(singlesel ? (bm->totvertsel > 0) : (bm->totedgesel > 0));

	if (bm->totvertsel == 0) {
		return OPERATOR_CANCELLED;
	}

	EDBM_update_generic(em, true, true);

	return OPERATOR_FINISHED;
}


void MESH_OT_rip(wmOperatorType *ot)
{
	/* identifiers */
	ot->name = "Rip";
	ot->idname = "MESH_OT_rip";
	ot->description = "Disconnect vertex or edges from connected geometry";

	/* api callbacks */
	ot->invoke = edbm_rip_invoke;
	ot->poll = EDBM_view3d_poll;

	/* flags */
	ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;

	/* to give to transform */
	Transform_Properties(ot, P_PROPORTIONAL | P_MIRROR_DUMMY);
	RNA_def_boolean(ot->srna, "use_fill", false, "Fill", "Fill the ripped region");
}
