// a tree representing the difference between two trees
// A Diff node's parent is not necessarily the parent of
// the node location it refers to, but rather the highest level
// node that needs to be either changed or removed.
// Thus, the root Diff node is the shallowest change required
// for a given branch of the tree being mutated.

const {depth} = require('treeverse')
const {existsSync} = require('fs')

const ssri = require('ssri')

class Diff {
  constructor ({actual, ideal, filterSet, shrinkwrapInflated}) {
    this.filterSet = filterSet
    this.shrinkwrapInflated = shrinkwrapInflated
    this.children = []
    this.actual = actual
    this.ideal = ideal
    if (this.ideal) {
      this.resolved = this.ideal.resolved
      this.integrity = this.ideal.integrity
    }
    this.action = getAction(this)
    this.parent = null
    // the set of leaf nodes that we rake up to the top level
    this.leaves = []
    // the set of nodes that don't change in this branch of the tree
    this.unchanged = []
    // the set of nodes that will be removed in this branch of the tree
    this.removed = []
  }

  static calculate ({actual, ideal, filterNodes = [], shrinkwrapInflated = new Set()}) {
    // if there's a filterNode, then:
    // - get the path from the root to the filterNode.  The root or
    //   root.target should have an edge either to the filterNode or
    //   a link to the filterNode.  If not, abort.  Add the path to the
    //   filterSet.
    // - Add set of Nodes depended on by the filterNode to filterSet.
    // - Anything outside of that set should be ignored by getChildren
    const filterSet = new Set()
    const extraneous = new Set()
    for (const filterNode of filterNodes) {
      const { root } = filterNode
      if (root !== ideal && root !== actual)
        throw new Error('invalid filterNode: outside idealTree/actualTree')
      const { target } = root
      const rootTarget = target || root
      const edge = [...rootTarget.edgesOut.values()].filter(e => {
        return e.to && (e.to === filterNode || e.to.target === filterNode)
      })[0]
      filterSet.add(root)
      filterSet.add(rootTarget)
      filterSet.add(ideal)
      filterSet.add(actual)
      if (edge && edge.to) {
        filterSet.add(edge.to)
        if (edge.to.target)
          filterSet.add(edge.to.target)
      }
      filterSet.add(filterNode)

      depth({
        tree: filterNode,
        visit: node => filterSet.add(node),
        getChildren: node => {
          node = node.target || node
          const loc = node.location
          const idealNode = ideal.inventory.get(loc)
          const ideals = !idealNode ? []
            : [...idealNode.edgesOut.values()].filter(e => e.to).map(e => e.to)
          const actualNode = actual.inventory.get(loc)
          const actuals = !actualNode ? []
            : [...actualNode.edgesOut.values()].filter(e => e.to).map(e => e.to)
          if (actualNode) {
            for (const child of actualNode.children.values()) {
              if (child.extraneous)
                extraneous.add(child)
            }
          }

          return ideals.concat(actuals)
        },
      })
    }
    for (const extra of extraneous)
      filterSet.add(extra)

    return depth({
      tree: new Diff({actual, ideal, filterSet, shrinkwrapInflated}),
      getChildren,
      leave,
    })
  }
}

const getAction = ({actual, ideal}) => {
  if (!ideal)
    return 'REMOVE'

  // bundled meta-deps are copied over to the ideal tree when we visit it,
  // so they'll appear to be missing here.  There's no need to handle them
  // in the diff, though, because they'll be replaced at reify time anyway
  // Otherwise, add the missing node.
  if (!actual)
    return ideal.inDepBundle ? null : 'ADD'

  // always ignore the root node
  if (ideal.isRoot && actual.isRoot)
    return null

  // if the versions don't match, it's a change no matter what
  if (ideal.version !== actual.version)
    return 'CHANGE'

  const binsExist = ideal.binPaths.every((path) => existsSync(path))

  // top nodes, links, and git deps won't have integrity, but do have resolved
  // if neither node has integrity, the bins exist, and either (a) neither
  // node has a resolved value or (b) they both do and match, then we can
  // leave this one alone since we already know the versions match due to
  // the condition above.  The "neither has resolved" case (a) cannot be
  // treated as a 'mark CHANGE and refetch', because shrinkwraps, bundles,
  // and link deps may lack this information, and we don't want to try to
  // go to the registry for something that isn't there.
  const noIntegrity = !ideal.integrity && !actual.integrity
  const noResolved = !ideal.resolved && !actual.resolved
  const resolvedMatch = ideal.resolved && ideal.resolved === actual.resolved
  if (noIntegrity && binsExist && (resolvedMatch || noResolved))
    return null

  // otherwise, verify that it's the same bits
  // note that if ideal has integrity, and resolved doesn't, we treat
  // that as a 'change', so that it gets re-fetched and locked down.
  const integrityMismatch = !ideal.integrity || !actual.integrity ||
    !ssri.parse(ideal.integrity).match(actual.integrity)
  if (integrityMismatch || !binsExist)
    return 'CHANGE'

  return null
}

const allChildren = node => {
  if (!node)
    return new Map()

  // if the node is root, and also a link, then what we really
  // want is to traverse the target's children
  if (node.isRoot && node.isLink)
    return allChildren(node.target)

  const kids = new Map()
  for (const n of [node, ...node.fsChildren]) {
    for (const kid of n.children.values())
      kids.set(kid.path, kid)
  }
  return kids
}

// functions for the walk options when we traverse the trees
// to create the diff tree
const getChildren = diff => {
  const children = []
  const {actual, ideal, unchanged, removed, filterSet, shrinkwrapInflated} = diff

  // Note: we DON'T diff fsChildren themselves, because they are either
  // included in the package contents, or part of some other project, and
  // will never appear in legacy shrinkwraps anyway.  but we _do_ include the
  // child nodes of fsChildren, because those are nodes that we are typically
  // responsible for installing.
  const actualKids = allChildren(actual)
  const idealKids = allChildren(ideal)

  if (ideal && ideal.hasShrinkwrap && !shrinkwrapInflated.has(ideal)) {
    // Guaranteed to get a diff.leaves here, because we always
    // be called with a proper Diff object when ideal has a shrinkwrap
    // that has not been inflated.
    diff.leaves.push(diff)
    return children
  }

  const paths = new Set([...actualKids.keys(), ...idealKids.keys()])
  for (const path of paths) {
    const actual = actualKids.get(path)
    const ideal = idealKids.get(path)
    diffNode(actual, ideal, children, unchanged, removed, filterSet, shrinkwrapInflated)
  }

  if (diff.leaves && !children.length)
    diff.leaves.push(diff)

  return children
}

const diffNode = (actual, ideal, children, unchanged, removed, filterSet, shrinkwrapInflated) => {
  if (filterSet.size && !(filterSet.has(ideal) || filterSet.has(actual)))
    return

  const action = getAction({actual, ideal})

  // if it's a match, then get its children
  // otherwise, this is the child diff node
  if (action || (!shrinkwrapInflated.has(ideal) && ideal.hasShrinkwrap)) {
    if (action === 'REMOVE')
      removed.push(actual)
    children.push(new Diff({actual, ideal, filterSet, shrinkwrapInflated}))
  } else {
    unchanged.push(ideal)
    // !*! Weird dirty hack warning !*!
    //
    // Bundled deps aren't loaded in the ideal tree, because we don't know
    // what they are going to be without unpacking.  Swap them over now if
    // the bundling node isn't changing, so we don't prune them later.
    //
    // It's a little bit dirty to be doing this here, since it means that
    // diffing trees can mutate them, but otherwise we have to walk over
    // all unchanging bundlers and correct the diff later, so it's more
    // efficient to just fix it while we're passing through already.
    //
    // Note that moving over a bundled dep will break the links to other
    // deps under this parent, which may have been transitively bundled.
    // Breaking those links means that we'll no longer see the transitive
    // dependency, meaning that it won't appear as bundled any longer!
    // In order to not end up dropping transitively bundled deps, we have
    // to get the list of nodes to move, then move them all at once, rather
    // than moving them one at a time in the first loop.
    const bd = ideal.package.bundleDependencies
    if (actual && bd && bd.length) {
      const bundledChildren = []
      for (const node of actual.children.values()) {
        if (node.inBundle)
          bundledChildren.push(node)
      }
      for (const node of bundledChildren)
        node.parent = ideal
    }
    children.push(...getChildren({actual, ideal, unchanged, removed, filterSet, shrinkwrapInflated}))
  }
}

// set the parentage in the leave step so that we aren't attaching
// child nodes only to remove them later.  also bubble up the unchanged
// nodes so that we can move them out of staging in the reification step.
const leave = (diff, children) => {
  children.forEach(kid => {
    kid.parent = diff
    diff.leaves.push(...kid.leaves)
    diff.unchanged.push(...kid.unchanged)
    diff.removed.push(...kid.removed)
  })
  diff.children = children
  return diff
}

module.exports = Diff
