How to use fast-diff - 10 common examples

export function getTextRangeChanges(
  before: string,
  after: string,
): Promise {
  const newRanges: TextEdit[] = [];
  let lineNumber = 0;
  let column = 0;

  const parts = diff(before, after);

  // Loop over every part, keeping track of:
  // 1. The current line no. and column in the `after` string
  // 2. Character ranges for all "added" parts in the `after` string
  parts.forEach(part => {
    const startLineNumber = lineNumber;
    const startColumn = column;
    if (part[0] === 0 || part[0] === -1) {
      // Split the part into lines. Loop through these lines to find
      // the line no. and column at the end of this part.
      const substring = part[1];
      const lines = substring.split("\n");
      lines.forEach((line, lineIndex) => {
        // The first `line` is actually just a continuation of the last line
        if (lineIndex === 0) {
          column += line.length;

const onTitleEditorChanged = () => {
    if (!titleCollab) {
      return
    }

    const oldTitle = titleCollab.shared.value().join('')
    const newTitle = titleEditor.value

    const diffs = Diff(oldTitle, newTitle)

    let pos = 0
    diffs.forEach((d) => {
      if (d[0] === 0) { // EQUAL
        pos += d[1].length
      } else if (d[0] === -1) { // DELETE
        const delText = d[1]
        for (let i = delText.length - 1; i >= 0; i--) {
          try {
            titleCollab.shared.removeAt(pos + i)
          } catch (err) {
            console.error(err)
            onStateChanged()
          }
        }
      } else { // INSERT

applyChanges (target, newText) {
    const { collaboration } = this.props
    const oldText = this.state.value
    const diffs = Diff(oldText, newText)
    let pos = 0
    diffs.forEach((d) => {
      if (d[0] === 0) { // EQUAL
        pos += d[1].length
      } else if (d[0] === -1) { // DELETE
        const delText = d[1]
        for (let i = delText.length - 1; i >= 0; i--) {
          collaboration.shared.removeAt(pos + i)
        }
      } else { // INSERT
        d[1].split('').forEach((c) => {
          collaboration.shared.insertAt(pos, d[1])
        })
        pos += d[1].length
      }
    })

onRemoteChange (oldText, newText) {
    console.log('onValueChanged', oldText, newText)
    const textArea = this.refs.collaborativeTextArea
    if (textArea.value === newText) {
      console.log('value is the same', textArea.value)
      return
    }
    const cursor = {
      start: textArea.selectionStart,
      end: textArea.selectionEnd
    }

    const diffs = Diff(oldText, newText)

    let pos = 0
    diffs.forEach((d) => {
      if (d[0] === 0) { // EQUAL
        pos += d[1].length
      } else if (d[0] === -1) { // DELETE
        const delText = d[1]
        if (pos < cursor.start) {
          cursor.start -= delText.length
        }
        if (pos < cursor.end) {
          cursor.end -= delText.length
        }
      } else { // INSERT
        const insertText = d[1]
        if (pos < cursor.start) {

private async applyComposedEdit(original: string, edit: TextEdit): Promise {
    // check complex edit
    let { range, newText } = edit
    let { nvim, ranges } = this
    let doc = TextDocument.create('file:///1', '', 0, original)
    let edits: TextEdit[] = []
    let diffs = fastDiff(original, newText)
    let offset = 0
    for (let i = 0; i < diffs.length; i++) {
      let diff = diffs[i]
      let pos = adjustPosition(range.start, doc.positionAt(offset))
      if (diff[0] == fastDiff.EQUAL) {
        offset = offset + diff[1].length
      } else if (diff[0] == fastDiff.DELETE) {
        let end = adjustPosition(range.start, doc.positionAt(offset + diff[1].length))
        if (diffs[i + 1] && diffs[i + 1][0] == fastDiff.INSERT) {
          // change
          edits.push({ range: Range.create(pos, end), newText: diffs[i + 1][1] })
          i = i + 1
        } else {
          // delete
          edits.push({ range: Range.create(pos, end), newText: '' })
        }

private async applyComposedEdit(original: string, edit: TextEdit): Promise {
    // check complex edit
    let { range, newText } = edit
    let { nvim, ranges } = this
    let doc = TextDocument.create('file:///1', '', 0, original)
    let edits: TextEdit[] = []
    let diffs = fastDiff(original, newText)
    let offset = 0
    for (let i = 0; i < diffs.length; i++) {
      let diff = diffs[i]
      let pos = adjustPosition(range.start, doc.positionAt(offset))
      if (diff[0] == fastDiff.EQUAL) {
        offset = offset + diff[1].length
      } else if (diff[0] == fastDiff.DELETE) {
        let end = adjustPosition(range.start, doc.positionAt(offset + diff[1].length))
        if (diffs[i + 1] && diffs[i + 1][0] == fastDiff.INSERT) {
          // change
          edits.push({ range: Range.create(pos, end), newText: diffs[i + 1][1] })
          i = i + 1
        } else {
          // delete
          edits.push({ range: Range.create(pos, end), newText: '' })
        }
        offset = offset + diff[1].length
      } else if (diff[0] == fastDiff.INSERT) {
        edits.push({ range: Range.create(pos, pos), newText: diff[1] })
      }
    }
    if (edits.some(edit => edit.newText.indexOf('\n') != -1 || edit.range.start.line != edit.range.end.line)) {
      this.cancel()

let diff = diffs[i]
        let pos = orig.positionAt(offset)
        if (diff[0] == fastDiff.EQUAL) {
          offset = offset + diff[1].length
        } else if (diff[0] == fastDiff.DELETE) {
          let end = orig.positionAt(offset + diff[1].length)
          if (diffs[i + 1] && diffs[i + 1][0] == fastDiff.INSERT) {
            let delta = diffs[i + 1][1].split('\n').length - (end.line - pos.line) - 1
            if (delta != 0) lineChanges.push({ delta, lnum: pos.line + startLine })
            i = i + 1
          } else {
            let delta = - (end.line - pos.line)
            if (delta != 0) lineChanges.push({ delta, lnum: pos.line + startLine })
          }
          offset = offset + diff[1].length
        } else if (diff[0] == fastDiff.INSERT) {
          let delta = diff[1].split('\n').length - 1
          if (delta != 0) lineChanges.push({ delta, lnum: pos.line + startLine })
        }
      }
    } else {
      lineChanges = [{ delta: lineChange, lnum: range.start.line }]
    }
    let changed = false
    // adjust LineNr highlights
    for (let item of fileItems) {
      for (let range of item.ranges) {
        let arr = lineChanges.filter(o => o.lnum < range.lnum - 1)
        if (arr.length) {
          let total = arr.reduce((p, c) => p + c.delta, 0)
          range.lnum = range.lnum + total
          changed = true

private async applyComposedEdit(original: string, edit: TextEdit): Promise {
    // check complex edit
    let { range, newText } = edit
    let { nvim, ranges } = this
    let doc = TextDocument.create('file:///1', '', 0, original)
    let edits: TextEdit[] = []
    let diffs = fastDiff(original, newText)
    let offset = 0
    for (let i = 0; i < diffs.length; i++) {
      let diff = diffs[i]
      let pos = adjustPosition(range.start, doc.positionAt(offset))
      if (diff[0] == fastDiff.EQUAL) {
        offset = offset + diff[1].length
      } else if (diff[0] == fastDiff.DELETE) {
        let end = adjustPosition(range.start, doc.positionAt(offset + diff[1].length))
        if (diffs[i + 1] && diffs[i + 1][0] == fastDiff.INSERT) {
          // change
          edits.push({ range: Range.create(pos, end), newText: diffs[i + 1][1] })
          i = i + 1
        } else {
          // delete
          edits.push({ range: Range.create(pos, end), newText: '' })
        }
        offset = offset + diff[1].length
      } else if (diff[0] == fastDiff.INSERT) {
        edits.push({ range: Range.create(pos, pos), newText: diff[1] })
      }
    }
    if (edits.some(edit => edit.newText.indexOf('\n') != -1 || edit.range.start.line != edit.range.end.line)) {
      this.cancel()
      return
    }

function diffLine (theme, actual, expected) {
  const outcome = fastDiff(actual, expected)

  // TODO: Compute when line is mostly unequal (80%? 90%?) and treat it as being
  // completely unequal.
  const isPartiallyEqual = !(
    (outcome.length === 2 && outcome[0][1] === actual && outcome[1][1] === expected) ||
    // Discount line ending control pictures, which will be equal even when the
    // rest of the line isn't.
    (
      outcome.length === 3 &&
      outcome[2][0] === fastDiff.EQUAL &&
      MATCH_CONTROL_PICTURES.test(outcome[2][1]) &&
      outcome[0][1] + outcome[2][1] === actual &&
      outcome[1][1] + outcome[2][1] === expected
    )
  )

  let stringActual = ''
  let stringExpected = ''

  const noopWrap = { open: '', close: '' }
  const deleteWrap = isPartiallyEqual ? theme.string.diff.delete : noopWrap
  const insertWrap = isPartiallyEqual ? theme.string.diff.insert : noopWrap
  const equalWrap = isPartiallyEqual ? theme.string.diff.equal : noopWrap
  for (const diff of outcome) {
    if (diff[0] === fastDiff.DELETE) {
      stringActual += formatUtils.wrap(deleteWrap, diff[1])

private async applyComposedEdit(original: string, edit: TextEdit): Promise {
    // check complex edit
    let { range, newText } = edit
    let { nvim, ranges } = this
    let doc = TextDocument.create('file:///1', '', 0, original)
    let edits: TextEdit[] = []
    let diffs = fastDiff(original, newText)
    let offset = 0
    for (let i = 0; i < diffs.length; i++) {
      let diff = diffs[i]
      let pos = adjustPosition(range.start, doc.positionAt(offset))
      if (diff[0] == fastDiff.EQUAL) {
        offset = offset + diff[1].length
      } else if (diff[0] == fastDiff.DELETE) {
        let end = adjustPosition(range.start, doc.positionAt(offset + diff[1].length))
        if (diffs[i + 1] && diffs[i + 1][0] == fastDiff.INSERT) {
          // change
          edits.push({ range: Range.create(pos, end), newText: diffs[i + 1][1] })
          i = i + 1
        } else {
          // delete
          edits.push({ range: Range.create(pos, end), newText: '' })
        }
        offset = offset + diff[1].length
      } else if (diff[0] == fastDiff.INSERT) {
        edits.push({ range: Range.create(pos, pos), newText: diff[1] })
      }
    }