// Copyright (c) 2006-2024, Timothy A. Davis, All Rights Reserved.
// SPDX-License-Identifier: LGPL-2.1+
// https://github.com/DrTimothyAldenDavis/SuiteSparse/tree/dev/CSparse/Source
import { csMark } from './csMark.js';
import { csMarked } from './csMarked.js';

/**
 * Find nonzero pattern of Cholesky L(k,1:k-1) using etree and triu(A(:,k))
 *
 * @param {Matrix}  a               The A matrix
 * @param {Number}  k               The kth column in A
 * @param {Array}   parent          The parent vector from the symbolic analysis result
 * @param {Array}   w               The nonzero pattern xi[top] .. xi[n - 1], an array of size = 2 * n
 *                                  The first n entries is the nonzero pattern, the last n entries is the stack
 *
 * @return {Number}                 The index for the nonzero pattern
 */
export function csEreach(a, k, parent, w) {
  // a arrays
  var aindex = a._index;
  var aptr = a._ptr;
  var asize = a._size;
  // columns
  var n = asize[1];
  // initialize top
  var top = n;
  // vars
  var p, p0, p1, len;
  // mark node k as visited
  csMark(w, k);
  // loop values & index for column k
  for (p0 = aptr[k], p1 = aptr[k + 1], p = p0; p < p1; p++) {
    // A(i,k) is nonzero
    var i = aindex[p];
    // only use upper triangular part of A
    if (i > k) {
      continue;
    }
    // traverse up etree
    for (len = 0; !csMarked(w, i); i = parent[i]) {
      // L(k,i) is nonzero, last n entries in w
      w[n + len++] = i;
      // mark i as visited
      csMark(w, i);
    }
    while (len > 0) {
      // decrement top & len
      --top;
      --len;
      // push path onto stack, last n entries in w
      w[n + top] = w[n + len];
    }
  }
  // unmark all nodes
  for (p = top; p < n; p++) {
    // use stack value, last n entries in w
    csMark(w, w[n + p]);
  }
  // unmark node k
  csMark(w, k);
  // s[top..n-1] contains pattern of L(k,:)
  return top;
}