overleaf/services/document-updater/app/js/sharejs/text.js

/* eslint-disable
    camelcase,
    no-return-assign,
    no-undef,
*/
// TODO: This file was created by bulk-decaffeinate.
// Fix any style issues and re-enable lint.
/*
 * decaffeinate suggestions:
 * DS101: Remove unnecessary use of Array.from
 * DS102: Remove unnecessary code created because of implicit returns
 * DS207: Consider shorter variations of null checks
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
 */
// A simple text implementation
//
// Operations are lists of components.
// Each component either inserts or deletes at a specified position in the document.
//
// Components are either:
//  {i:'str', p:100}: Insert 'str' at position 100 in the document
//  {d:'str', p:100}: Delete 'str' at position 100 in the document
//
// Components in an operation are executed sequentially, so the position of components
// assumes previous components have already executed.
//
// Eg: This op:
//   [{i:'abc', p:0}]
// is equivalent to this op:
//   [{i:'a', p:0}, {i:'b', p:1}, {i:'c', p:2}]

// NOTE: The global scope here is shared with other sharejs files when built with closure.
// Be careful what ends up in your namespace.

let append, transformComponent
const text = {}

text.name = 'text'

text.create = () => ''

const strInject = (s1, pos, s2) => s1.slice(0, pos) + s2 + s1.slice(pos)

const checkValidComponent = function (c) {
  if (typeof c.p !== 'number') {
    throw new Error('component missing position field')
  }

  const i_type = typeof c.i
  const d_type = typeof c.d
  if (!((i_type === 'string') ^ (d_type === 'string'))) {
    throw new Error('component needs an i or d field')
  }

  if (!(c.p >= 0)) {
    throw new Error('position cannot be negative')
  }
}

const checkValidOp = function (op) {
  for (const c of Array.from(op)) {
    checkValidComponent(c)
  }
  return true
}

text.apply = function (snapshot, op) {
  checkValidOp(op)
  for (const component of Array.from(op)) {
    if (component.i != null) {
      snapshot = strInject(snapshot, component.p, component.i)
    } else {
      const deleted = snapshot.slice(
        component.p,
        component.p + component.d.length
      )
      if (component.d !== deleted) {
        throw new Error(
          `Delete component '${component.d}' does not match deleted text '${deleted}'`
        )
      }
      snapshot =
        snapshot.slice(0, component.p) +
        snapshot.slice(component.p + component.d.length)
    }
  }

  return snapshot
}

// Exported for use by the random op generator.
//
// For simplicity, this version of append does not compress adjacent inserts and deletes of
// the same text. It would be nice to change that at some stage.
text._append = append = function (newOp, c) {
  if (c.i === '' || c.d === '') {
    return
  }
  if (newOp.length === 0) {
    return newOp.push(c)
  } else {
    const last = newOp[newOp.length - 1]

    // Compose the insert into the previous insert if possible
    if (
      last.i != null &&
      c.i != null &&
      last.p <= c.p &&
      c.p <= last.p + last.i.length
    ) {
      return (newOp[newOp.length - 1] = {
        i: strInject(last.i, c.p - last.p, c.i),
        p: last.p,
      })
    } else if (
      last.d != null &&
      c.d != null &&
      c.p <= last.p &&
      last.p <= c.p + c.d.length
    ) {
      return (newOp[newOp.length - 1] = {
        d: strInject(c.d, last.p - c.p, last.d),
        p: c.p,
      })
    } else {
      return newOp.push(c)
    }
  }
}

text.compose = function (op1, op2) {
  checkValidOp(op1)
  checkValidOp(op2)

  const newOp = op1.slice()
  for (const c of Array.from(op2)) {
    append(newOp, c)
  }

  return newOp
}

// Attempt to compress the op components together 'as much as possible'.
// This implementation preserves order and preserves create/delete pairs.
text.compress = op => text.compose([], op)

text.normalize = function (op) {
  const newOp = []

  // Normalize should allow ops which are a single (unwrapped) component:
  // {i:'asdf', p:23}.
  // There's no good way to test if something is an array:
  // http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/
  // so this is probably the least bad solution.
  if (op.i != null || op.p != null) {
    op = [op]
  }

  for (const c of Array.from(op)) {
    if (c.p == null) {
      c.p = 0
    }
    append(newOp, c)
  }

  return newOp
}

// This helper method transforms a position by an op component.
//
// If c is an insert, insertAfter specifies whether the transform
// is pushed after the insert (true) or before it (false).
//
// insertAfter is optional for deletes.
const transformPosition = function (pos, c, insertAfter) {
  if (c.i != null) {
    if (c.p < pos || (c.p === pos && insertAfter)) {
      return pos + c.i.length
    } else {
      return pos
    }
  } else {
    // I think this could also be written as: Math.min(c.p, Math.min(c.p - otherC.p, otherC.d.length))
    // but I think its harder to read that way, and it compiles using ternary operators anyway
    // so its no slower written like this.
    if (pos <= c.p) {
      return pos
    } else if (pos <= c.p + c.d.length) {
      return c.p
    } else {
      return pos - c.d.length
    }
  }
}

// Helper method to transform a cursor position as a result of an op.
//
// Like transformPosition above, if c is an insert, insertAfter specifies whether the cursor position
// is pushed after an insert (true) or before it (false).
text.transformCursor = function (position, op, side) {
  const insertAfter = side === 'right'
  for (const c of Array.from(op)) {
    position = transformPosition(position, c, insertAfter)
  }
  return position
}

// Transform an op component by another op component. Asymmetric.
// The result will be appended to destination.
//
// exported for use in JSON type
text._tc = transformComponent = function (dest, c, otherC, side) {
  checkValidOp([c])
  checkValidOp([otherC])

  if (c.i != null) {
    append(dest, {
      i: c.i,
      p: transformPosition(c.p, otherC, side === 'right'),
    })
  } else {
    // Delete
    if (otherC.i != null) {
      // delete vs insert
      let s = c.d
      if (c.p < otherC.p) {
        append(dest, { d: s.slice(0, otherC.p - c.p), p: c.p })
        s = s.slice(otherC.p - c.p)
      }
      if (s !== '') {
        append(dest, { d: s, p: c.p + otherC.i.length })
      }
    } else {
      // Delete vs delete
      if (c.p >= otherC.p + otherC.d.length) {
        append(dest, { d: c.d, p: c.p - otherC.d.length })
      } else if (c.p + c.d.length <= otherC.p) {
        append(dest, c)
      } else {
        // They overlap somewhere.
        const newC = { d: '', p: c.p }
        if (c.p < otherC.p) {
          newC.d = c.d.slice(0, otherC.p - c.p)
        }
        if (c.p + c.d.length > otherC.p + otherC.d.length) {
          newC.d += c.d.slice(otherC.p + otherC.d.length - c.p)
        }

        // This is entirely optional - just for a check that the deleted
        // text in the two ops matches
        const intersectStart = Math.max(c.p, otherC.p)
        const intersectEnd = Math.min(
          c.p + c.d.length,
          otherC.p + otherC.d.length
        )
        const cIntersect = c.d.slice(intersectStart - c.p, intersectEnd - c.p)
        const otherIntersect = otherC.d.slice(
          intersectStart - otherC.p,
          intersectEnd - otherC.p
        )
        if (cIntersect !== otherIntersect) {
          throw new Error(
            'Delete ops delete different text in the same region of the document'
          )
        }

        if (newC.d !== '') {
          // This could be rewritten similarly to insert v delete, above.
          newC.p = transformPosition(newC.p, otherC)
          append(dest, newC)
        }
      }
    }
  }

  return dest
}

const invertComponent = function (c) {
  if (c.i != null) {
    return { d: c.i, p: c.p }
  } else {
    return { i: c.d, p: c.p }
  }
}

// No need to use append for invert, because the components won't be able to
// cancel with one another.
text.invert = op =>
  Array.from(op.slice().reverse()).map(c => invertComponent(c))

if (typeof WEB !== 'undefined' && WEB !== null) {
  if (!exports.types) {
    exports.types = {}
  }

  // This is kind of awful - come up with a better way to hook this helper code up.
  bootstrapTransform(text, transformComponent, checkValidOp, append)

  // [] is used to prevent closure from renaming types.text
  exports.types.text = text
} else {
  module.exports = text

  // The text type really shouldn't need this - it should be possible to define
  // an efficient transform function by making a sort of transform map and passing each
  // op component through it.
  require('./helpers').bootstrapTransform(
    text,
    transformComponent,
    checkValidOp,
    append
  )
}