'use strict'

var bsearch = require('binary-search-bounds')

module.exports = createTriangulation

function Triangulation(stars, edges) {
  this.stars = stars
  this.edges = edges
}

var proto = Triangulation.prototype

function removePair(list, j, k) {
  for(var i=1, n=list.length; i<n; i+=2) {
    if(list[i-1] === j && list[i] === k) {
      list[i-1] = list[n-2]
      list[i] = list[n-1]
      list.length = n - 2
      return
    }
  }
}

proto.isConstraint = (function() {
  var e = [0,0]
  function compareLex(a, b) {
    return a[0] - b[0] || a[1] - b[1]
  }
  return function(i, j) {
    e[0] = Math.min(i,j)
    e[1] = Math.max(i,j)
    return bsearch.eq(this.edges, e, compareLex) >= 0
  }
})()

proto.removeTriangle = function(i, j, k) {
  var stars = this.stars
  removePair(stars[i], j, k)
  removePair(stars[j], k, i)
  removePair(stars[k], i, j)
}

proto.addTriangle = function(i, j, k) {
  var stars = this.stars
  stars[i].push(j, k)
  stars[j].push(k, i)
  stars[k].push(i, j)
}

proto.opposite = function(j, i) {
  var list = this.stars[i]
  for(var k=1, n=list.length; k<n; k+=2) {
    if(list[k] === j) {
      return list[k-1]
    }
  }
  return -1
}

proto.flip = function(i, j) {
  var a = this.opposite(i, j)
  var b = this.opposite(j, i)
  this.removeTriangle(i, j, a)
  this.removeTriangle(j, i, b)
  this.addTriangle(i, b, a)
  this.addTriangle(j, a, b)
}

proto.edges = function() {
  var stars = this.stars
  var result = []
  for(var i=0, n=stars.length; i<n; ++i) {
    var list = stars[i]
    for(var j=0, m=list.length; j<m; j+=2) {
      result.push([list[j], list[j+1]])
    }
  }
  return result
}

proto.cells = function() {
  var stars = this.stars
  var result = []
  for(var i=0, n=stars.length; i<n; ++i) {
    var list = stars[i]
    for(var j=0, m=list.length; j<m; j+=2) {
      var s = list[j]
      var t = list[j+1]
      if(i < Math.min(s, t)) {
        result.push([i, s, t])
      }
    }
  }
  return result
}

function createTriangulation(numVerts, edges) {
  var stars = new Array(numVerts)
  for(var i=0; i<numVerts; ++i) {
    stars[i] = []
  }
  return new Triangulation(stars, edges)
}