export default class DAG {
  #nodes = new Map()

  #edges = new Set()

  #layers = []

  constructor(nodes) {
    this.#nodes = new Map(nodes.map((node) => [node._id, node]))
    this.#edges = new Set()
    this.#nodes.forEach((_, id) => {
      this.#setLayer(id)
      this.#addEdges(id)
    })
  }

  getNode(id) {
    return this.#nodes.get(id)
  }

  getNodes() {
    return Array.from(this.#nodes.values())
  }

  getEdges() {
    return this.#edges
  }

  getEdgesArray() {
    return Array.from(this.#edges.values())
  }

  getLayers() {
    return this.#layers
  }

  getLayer(id) {
    const node = this.getNode(id)
    if (!node) {
      throw new Error(`Node ${id} not found`)
    }
    return this.#layers[node.layer - 1]
  }

  #setLayer(id) {
    const node = this.getNode(id)
    if (!node) {
      throw new Error(`Node ${id} not found`)
    }
    if (node.layer !== undefined) {
      return node.layer
    }
    const previousLayer = node.requirements.map((rId) => this.#setLayer(rId))
    node.layer = Math.max(...previousLayer, 0) + 1
    if (this.#layers.length < node.layer) {
      this.#layers.push(1)
    } else {
      this.#layers[node.layer - 1] += 1
    }
    node.index = this.#layers[node.layer - 1]
    return node.layer
  }

  #addEdges(id) {
    const node = this.getNode(id)
    if (!node) {
      throw new Error(`Node ${id} not found`)
    }
    node.requirements.forEach((rId) => {
      this.#edges.add([rId, id])
    })
  }
}