import {Node} from "prosemirror-model"
import {StepMap} from "prosemirror-transform"
import {computeDiff} from "./diff"
import {Change, Span} from "./change"
export {Change, Span}
export {simplifyChanges} from "./simplify"

/// A change set tracks the changes to a document from a given point
/// in the past. It condenses a number of step maps down to a flat
/// sequence of replacements, and simplifies replacments that
/// partially undo themselves by comparing their content.
export class ChangeSet<Data = any> {
  /// @internal
  constructor(
    /// @internal
    readonly config: {doc: Node, combine: (dataA: Data, dataB: Data) => Data},
    /// Replaced regions.
    readonly changes: readonly Change<Data>[]
  ) {}

  /// Computes a new changeset by adding the given step maps and
  /// metadata (either as an array, per-map, or as a single value to be
  /// associated with all maps) to the current set. Will not mutate the
  /// old set.
  ///
  /// Note that due to simplification that happens after each add,
  /// incrementally adding steps might create a different final set
  /// than adding all those changes at once, since different document
  /// tokens might be matched during simplification depending on the
  /// boundaries of the current changed ranges.
  addSteps(newDoc: Node, maps: readonly StepMap[], data: Data | readonly Data[]): ChangeSet<Data> {
    // This works by inspecting the position maps for the changes,
    // which indicate what parts of the document were replaced by new
    // content, and the size of that new content. It uses these to
    // build up Change objects.
    //
    // These change objects are put in sets and merged together using
    // Change.merge, giving us the changes created by the new steps.
    // Those changes can then be merged with the existing set of
    // changes.
    //
    // For each change that was touched by the new steps, we recompute
    // a diff to try to minimize the change by dropping matching
    // pieces of the old and new document from the change.

    let stepChanges: Change<Data>[] = []
    // Add spans for new steps.
    for (let i = 0; i < maps.length; i++) {
      let d = Array.isArray(data) ? data[i] : data
      let off = 0
      maps[i].forEach((fromA, toA, fromB, toB) => {

        stepChanges.push(new Change(fromA + off, toA + off, fromB, toB,
                                    fromA == toA ? Span.none : [new Span(toA - fromA, d)],
                                    fromB == toB ? Span.none : [new Span(toB - fromB, d)]))

        off = (toB - fromB) - (toA - fromA)
      })
    }
    if (stepChanges.length == 0) return this

    let newChanges = mergeAll(stepChanges, this.config.combine)
    let changes = Change.merge(this.changes, newChanges, this.config.combine)
    let updated: Change<Data>[] = changes as Change<Data>[]

    // Minimize changes when possible
    for (let i = 0; i < updated.length; i++) {
      let change = updated[i]
      if (change.fromA == change.toA || change.fromB == change.toB ||
          // Only look at changes that touch newly added changed ranges
          !newChanges.some(r => r.toB > change.fromB && r.fromB < change.toB)) continue
      let diff = computeDiff(this.config.doc.content, newDoc.content, change)

      // Fast path: If they are completely different, don't do anything
      if (diff.length == 1 && diff[0].fromB == 0 && diff[0].toB == change.toB - change.fromB)
        continue

      if (updated == changes) updated = changes.slice()
      if (diff.length == 1) {
        updated[i] = diff[0]
      } else {
        updated.splice(i, 1, ...diff)
        i += diff.length - 1
      }
    }

    return new ChangeSet(this.config, updated)
  }

  /// The starting document of the change set.
  get startDoc(): Node { return this.config.doc }

  /// Map the span's data values in the given set through a function
  /// and construct a new set with the resulting data.
  map(f: (range: Span<Data>) => Data): ChangeSet<Data> {
    let mapSpan = (span: Span<Data>) => {
      let newData = f(span)
      return newData === span.data ? span : new Span(span.length, newData)
    }
    return new ChangeSet(this.config, this.changes.map((ch: Change<Data>) => {
      return new Change(ch.fromA, ch.toA, ch.fromB, ch.toB, ch.deleted.map(mapSpan), ch.inserted.map(mapSpan))
    }))
  }

  /// Compare two changesets and return the range in which they are
  /// changed, if any. If the document changed between the maps, pass
  /// the maps for the steps that changed it as second argument, and
  /// make sure the method is called on the old set and passed the new
  /// set. The returned positions will be in new document coordinates.
  changedRange(b: ChangeSet, maps?: readonly StepMap[]): {from: number, to: number} | null {
    if (b == this) return null
    let touched = maps && touchedRange(maps)
    let moved = touched ? (touched.toB - touched.fromB) - (touched.toA - touched.fromA) : 0
    function map(p: number) {
      return !touched || p <= touched.fromA ? p : p + moved
    }

    let from = touched ? touched.fromB : 2e8, to = touched ? touched.toB : -2e8
    function add(start: number, end = start) {
      from = Math.min(start, from); to = Math.max(end, to)
    }

    let rA = this.changes, rB = b.changes
    for (let iA = 0, iB = 0; iA < rA.length && iB < rB.length;) {
      let rangeA = rA[iA], rangeB = rB[iB]
      if (rangeA && rangeB && sameRanges(rangeA, rangeB, map)) { iA++; iB++ }
      else if (rangeB && (!rangeA || map(rangeA.fromB) >= rangeB.fromB)) { add(rangeB.fromB, rangeB.toB); iB++ }
      else { add(map(rangeA.fromB), map(rangeA.toB)); iA++ }
    }

    return from <= to ? {from, to} : null
  }

  /// Create a changeset with the given base object and configuration.
  /// The `combine` function is used to compare and combine metadata—it
  /// should return null when metadata isn't compatible, and a combined
  /// version for a merged range when it is.
  static create<Data = any>(doc: Node, combine: (dataA: Data, dataB: Data) => Data = (a, b) => a === b ? a : null as any) {
    return new ChangeSet({combine, doc}, [])
  }

  /// Exported for testing @internal
  static computeDiff = computeDiff
}

// Divide-and-conquer approach to merging a series of ranges.
function mergeAll<Data>(
  ranges: readonly Change<Data>[],
  combine: (dA: Data, dB: Data) => Data,
  start = 0, end = ranges.length
): readonly Change<Data>[] {
  if (end == start + 1) return [ranges[start]]
  let mid = (start + end) >> 1
  return Change.merge(mergeAll(ranges, combine, start, mid),
                      mergeAll(ranges, combine, mid, end), combine)
}

function endRange(maps: readonly StepMap[]) {
  let from = 2e8, to = -2e8
  for (let i = 0; i < maps.length; i++) {
    let map = maps[i]
    if (from != 2e8) {
      from = map.map(from, -1)
      to = map.map(to, 1)
    }
    map.forEach((_s, _e, start, end) => {
      from = Math.min(from, start)
      to = Math.max(to, end)
    })
  }
  return from == 2e8 ? null : {from, to}
}

function touchedRange(maps: readonly StepMap[]) {
  let b = endRange(maps)
  if (!b) return null
  let a = endRange(maps.map(m => m.invert()).reverse())!
  return {fromA: a.from, toA: a.to, fromB: b.from, toB: b.to}
}

function sameRanges<Data>(a: Change<Data>, b: Change<Data>, map: (pos: number) => number) {
  return map(a.fromB) == b.fromB && map(a.toB) == b.toB &&
    sameSpans(a.deleted, b.deleted) && sameSpans(a.inserted, b.inserted)
}

function sameSpans<Data>(a: readonly Span<Data>[], b: readonly Span<Data>[]) {
  if (a.length != b.length) return false
  for (let i = 0; i < a.length; i++)
    if (a[i].length != b[i].length || a[i].data !== b[i].data) return false
  return true
}