/// There are several things that positions can be mapped through.
/// Such objects conform to this interface.
export interface Mappable {
  /// Map a position through this object. When given, `assoc` (should
  /// be -1 or 1, defaults to 1) determines with which side the
  /// position is associated, which determines in which direction to
  /// move when a chunk of content is inserted at the mapped position.
  map: (pos: number, assoc?: number) => number

  /// Map a position, and return an object containing additional
  /// information about the mapping. The result's `deleted` field tells
  /// you whether the position was deleted (completely enclosed in a
  /// replaced range) during the mapping. When content on only one side
  /// is deleted, the position itself is only considered deleted when
  /// `assoc` points in the direction of the deleted content.
  mapResult: (pos: number, assoc?: number) => MapResult
}

// Recovery values encode a range index and an offset. They are
// represented as numbers, because tons of them will be created when
// mapping, for example, a large number of decorations. The number's
// lower 16 bits provide the index, the remaining bits the offset.
//
// Note: We intentionally don't use bit shift operators to en- and
// decode these, since those clip to 32 bits, which we might in rare
// cases want to overflow. A 64-bit float can represent 48-bit
// integers precisely.

const lower16 = 0xffff
const factor16 = Math.pow(2, 16)

function makeRecover(index: number, offset: number) { return index + offset * factor16 }
function recoverIndex(value: number) { return value & lower16 }
function recoverOffset(value: number) { return (value - (value & lower16)) / factor16 }

const DEL_BEFORE = 1, DEL_AFTER = 2, DEL_ACROSS = 4, DEL_SIDE = 8

/// An object representing a mapped position with extra
/// information.
export class MapResult {
  /// @internal
  constructor(
    /// The mapped version of the position.
    readonly pos: number,
    /// @internal
    readonly delInfo: number,
    /// @internal
    readonly recover: number | null
  ) {}

  /// Tells you whether the position was deleted, that is, whether the
  /// step removed the token on the side queried (via the `assoc`)
  /// argument from the document.
  get deleted() { return (this.delInfo & DEL_SIDE) > 0 }

  /// Tells you whether the token before the mapped position was deleted.
  get deletedBefore() { return (this.delInfo & (DEL_BEFORE | DEL_ACROSS)) > 0 }

  /// True when the token after the mapped position was deleted.
  get deletedAfter() { return (this.delInfo & (DEL_AFTER | DEL_ACROSS)) > 0 }

  /// Tells whether any of the steps mapped through deletes across the
  /// position (including both the token before and after the
  /// position).
  get deletedAcross() { return (this.delInfo & DEL_ACROSS) > 0 }
}

/// A map describing the deletions and insertions made by a step, which
/// can be used to find the correspondence between positions in the
/// pre-step version of a document and the same position in the
/// post-step version.
export class StepMap implements Mappable {
  /// Create a position map. The modifications to the document are
  /// represented as an array of numbers, in which each group of three
  /// represents a modified chunk as `[start, oldSize, newSize]`.
  constructor(
    /// @internal
    readonly ranges: readonly number[],
    /// @internal
    readonly inverted = false
  ) {
    if (!ranges.length && StepMap.empty) return StepMap.empty
  }

  /// @internal
  recover(value: number) {
    let diff = 0, index = recoverIndex(value)
    if (!this.inverted) for (let i = 0; i < index; i++)
      diff += this.ranges[i * 3 + 2] - this.ranges[i * 3 + 1]
    return this.ranges[index * 3] + diff + recoverOffset(value)
  }

  mapResult(pos: number, assoc = 1): MapResult { return this._map(pos, assoc, false) as MapResult }

  map(pos: number, assoc = 1): number { return this._map(pos, assoc, true) as number }

  /// @internal
  _map(pos: number, assoc: number, simple: boolean) {
    let diff = 0, oldIndex = this.inverted ? 2 : 1, newIndex = this.inverted ? 1 : 2
    for (let i = 0; i < this.ranges.length; i += 3) {
      let start = this.ranges[i] - (this.inverted ? diff : 0)
      if (start > pos) break
      let oldSize = this.ranges[i + oldIndex], newSize = this.ranges[i + newIndex], end = start + oldSize
      if (pos <= end) {
        let side = !oldSize ? assoc : pos == start ? -1 : pos == end ? 1 : assoc
        let result = start + diff + (side < 0 ? 0 : newSize)
        if (simple) return result
        let recover = pos == (assoc < 0 ? start : end) ? null : makeRecover(i / 3, pos - start)
        let del = pos == start ? DEL_AFTER : pos == end ? DEL_BEFORE : DEL_ACROSS
        if (assoc < 0 ? pos != start : pos != end) del |= DEL_SIDE
        return new MapResult(result, del, recover)
      }
      diff += newSize - oldSize
    }
    return simple ? pos + diff : new MapResult(pos + diff, 0, null)
  }

  /// @internal
  touches(pos: number, recover: number) {
    let diff = 0, index = recoverIndex(recover)
    let oldIndex = this.inverted ? 2 : 1, newIndex = this.inverted ? 1 : 2
    for (let i = 0; i < this.ranges.length; i += 3) {
      let start = this.ranges[i] - (this.inverted ? diff : 0)
      if (start > pos) break
      let oldSize = this.ranges[i + oldIndex], end = start + oldSize
      if (pos <= end && i == index * 3) return true
      diff += this.ranges[i + newIndex] - oldSize
    }
    return false
  }

  /// Calls the given function on each of the changed ranges included in
  /// this map.
  forEach(f: (oldStart: number, oldEnd: number, newStart: number, newEnd: number) => void) {
    let oldIndex = this.inverted ? 2 : 1, newIndex = this.inverted ? 1 : 2
    for (let i = 0, diff = 0; i < this.ranges.length; i += 3) {
      let start = this.ranges[i], oldStart = start - (this.inverted ? diff : 0), newStart = start + (this.inverted ? 0 : diff)
      let oldSize = this.ranges[i + oldIndex], newSize = this.ranges[i + newIndex]
      f(oldStart, oldStart + oldSize, newStart, newStart + newSize)
      diff += newSize - oldSize
    }
  }

  /// Create an inverted version of this map. The result can be used to
  /// map positions in the post-step document to the pre-step document.
  invert() {
    return new StepMap(this.ranges, !this.inverted)
  }

  /// @internal
  toString() {
    return (this.inverted ? "-" : "") + JSON.stringify(this.ranges)
  }

  /// Create a map that moves all positions by offset `n` (which may be
  /// negative). This can be useful when applying steps meant for a
  /// sub-document to a larger document, or vice-versa.
  static offset(n: number) {
    return n == 0 ? StepMap.empty : new StepMap(n < 0 ? [0, -n, 0] : [0, 0, n])
  }

  /// A StepMap that contains no changed ranges.
  static empty = new StepMap([])
}

/// A mapping represents a pipeline of zero or more [step
/// maps](#transform.StepMap). It has special provisions for losslessly
/// handling mapping positions through a series of steps in which some
/// steps are inverted versions of earlier steps. (This comes up when
/// ‘[rebasing](/docs/guide/#transform.rebasing)’ steps for
/// collaboration or history management.)
export class Mapping implements Mappable {
  /// Create a new mapping with the given position maps.
  constructor(
    /// The step maps in this mapping.
    readonly maps: StepMap[] = [],
    /// @internal
    public mirror?: number[],
    /// The starting position in the `maps` array, used when `map` or
    /// `mapResult` is called.
    public from = 0,
    /// The end position in the `maps` array.
    public to = maps.length
  ) {}

  /// Create a mapping that maps only through a part of this one.
  slice(from = 0, to = this.maps.length) {
    return new Mapping(this.maps, this.mirror, from, to)
  }

  /// @internal
  copy() {
    return new Mapping(this.maps.slice(), this.mirror && this.mirror.slice(), this.from, this.to)
  }

  /// Add a step map to the end of this mapping. If `mirrors` is
  /// given, it should be the index of the step map that is the mirror
  /// image of this one.
  appendMap(map: StepMap, mirrors?: number) {
    this.to = this.maps.push(map)
    if (mirrors != null) this.setMirror(this.maps.length - 1, mirrors)
  }

  /// Add all the step maps in a given mapping to this one (preserving
  /// mirroring information).
  appendMapping(mapping: Mapping) {
    for (let i = 0, startSize = this.maps.length; i < mapping.maps.length; i++) {
      let mirr = mapping.getMirror(i)
      this.appendMap(mapping.maps[i], mirr != null && mirr < i ? startSize + mirr : undefined)
    }
  }

  /// Finds the offset of the step map that mirrors the map at the
  /// given offset, in this mapping (as per the second argument to
  /// `appendMap`).
  getMirror(n: number): number | undefined {
    if (this.mirror) for (let i = 0; i < this.mirror.length; i++)
      if (this.mirror[i] == n) return this.mirror[i + (i % 2 ? -1 : 1)]
  }

  /// @internal
  setMirror(n: number, m: number) {
    if (!this.mirror) this.mirror = []
    this.mirror.push(n, m)
  }

  /// Append the inverse of the given mapping to this one.
  appendMappingInverted(mapping: Mapping) {
    for (let i = mapping.maps.length - 1, totalSize = this.maps.length + mapping.maps.length; i >= 0; i--) {
      let mirr = mapping.getMirror(i)
      this.appendMap(mapping.maps[i].invert(), mirr != null && mirr > i ? totalSize - mirr - 1 : undefined)
    }
  }

  /// Create an inverted version of this mapping.
  invert() {
    let inverse = new Mapping
    inverse.appendMappingInverted(this)
    return inverse
  }

  /// Map a position through this mapping.
  map(pos: number, assoc = 1) {
    if (this.mirror) return this._map(pos, assoc, true) as number
    for (let i = this.from; i < this.to; i++)
      pos = this.maps[i].map(pos, assoc)
    return pos
  }

  /// Map a position through this mapping, returning a mapping
  /// result.
  mapResult(pos: number, assoc = 1) { return this._map(pos, assoc, false) as MapResult }

  /// @internal
  _map(pos: number, assoc: number, simple: boolean) {
    let delInfo = 0

    for (let i = this.from; i < this.to; i++) {
      let map = this.maps[i], result = map.mapResult(pos, assoc)
      if (result.recover != null) {
        let corr = this.getMirror(i)
        if (corr != null && corr > i && corr < this.to) {
          i = corr
          pos = this.maps[corr].recover(result.recover)
          continue
        }
      }

      delInfo |= result.delInfo
      pos = result.pos
    }

    return simple ? pos : new MapResult(pos, delInfo, null)
  }
}