(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
    typeof define === 'function' && define.amd ? define(factory) :
    (global.OceanLayers = factory());
}(this, (function () { 'use strict';

  let cells, vertices, pointsN, used;

  var OceanLayers = function OceanLayers() {
    const outline = outlineLayersInput.value;
    if (outline === "none") return;
    console.time("drawOceanLayers");

    cells = grid.cells, pointsN = grid.cells.i.length, vertices = grid.vertices;
    const limits = outline === "random" ? randomizeOutline() : outline.split(",").map(s => +s);
    markupOcean(limits);

    const chains = [];
    const opacity = rn(0.4 / limits.length, 2);
    used = new Uint8Array(pointsN); // to detect already passed cells

    for (const i of cells.i) {
      const t = cells.t[i];
      if (used[i] || !limits.includes(t)) continue;
      const start = findStart(i, t);
      if (!start) continue;
      used[i] = 1;
      //debug.append("circle").attr("r", 3).attr("cx", vertices.p[start.c][0]).attr("cy", vertices.p[start.c][1]).attr("fill", "red").attr("stroke", "black").attr("stroke-width", .3);

      const chain = connectVertices(start, t); // vertices chain to form a path
      const relaxation = 1 + t * -2; // select only n-th point
      const relaxed = chain.filter((v, i) => i % relaxation === 0 || vertices.c[v].some(c => c >= pointsN));
      if (relaxed.length >= 3) chains.push([t, relaxed.map(v => vertices.p[v])]);
    }
    //debug.selectAll("text").data(cells.i).enter().append("text").attr("font-size", 2).attr("x", d => grid.points[d][0]).attr("y", d => grid.points[d][1]).text(d => cells.t[d]+","+used[d]);

    for (const t of limits) {
      const path = chains.filter(c => c[0] === t).map(c => round(lineGen(c[1]))).join();
      if (path) oceanLayers.append("path").attr("d", path).attr("fill", "#ecf2f9").style("opacity", opacity);
      // For each layer there should outer ring. If no, layer will be upside down. Need to fix it in the future
    }

    // find eligible cell vertex to start path detection
    function findStart(i, t) {
      if (cells.b[i]) return cells.v[i].find(v => vertices.c[v].some(c => c >= pointsN)); // map border cell
      return cells.v[i][cells.c[i].findIndex(c => cells.t[c] < t || !cells.t[c])];
    }

    console.timeEnd("drawOceanLayers");
  }

  function randomizeOutline() {
    const limits = [];
    let odd = 0.2
    for (let l = -9; l < 0; l++) {
      if (Math.random() < odd) {odd = 0.2; limits.push(l);}
      else {odd *= 2;}
    }
    return limits;
  }

  function markupOcean(limits) {
    // Define ocean cells type based on distance form land
    for (let t = -2; t >= limits[0]-1; t--) {
      for (let i = 0; i < pointsN; i++) {
        if (cells.t[i] !== t+1) continue;
        cells.c[i].forEach(function(e) {if (!cells.t[e]) cells.t[e] = t;});
      }
    }
  }

  // connect vertices to chain
  function connectVertices(start, t) {
    const chain = []; // vertices chain to form a path
    for (let i=0, current = start; i === 0 || current !== start && i < 10000; i++) {
      const prev = chain[chain.length - 1]; // previous vertex in chain
      chain.push(current); // add current vertex to sequence
      const c = vertices.c[current]; // cells adjacent to vertex
      c.filter(c => cells.t[c] === t).forEach(c => used[c] = 1);
      const v = vertices.v[current]; // neighboring vertices
      const c0 = !cells.t[c[0]] || cells.t[c[0]] === t-1;
      const c1 = !cells.t[c[1]] || cells.t[c[1]] === t-1;
      const c2 = !cells.t[c[2]] || cells.t[c[2]] === t-1;
      if (v[0] !== undefined && v[0] !== prev && c0 !== c1) current = v[0];
      else if (v[1] !== undefined && v[1] !== prev && c1 !== c2) current = v[1];
      else if (v[2] !== undefined && v[2] !== prev && c0 !== c2) current = v[2];
      if (current === chain[chain.length - 1]) {console.error("Next vertex is not found"); break;}
    }
    chain.push(chain[0]); // push first vertex as the last one
    return chain;
  }
  
  return OceanLayers;

})));