/* eslint-disable require-jsdoc */

import attributeDiff from "src/decidim/editor/attribute_diff"

const Delta = Quill.import("delta");

const previousChar = (quill, range) => {
  return quill.getText(range.index - 1, 1);
}

const beforePreviousChar = (quill, range) => {
  return quill.getText(range.index - 2, 1);
}

const nextChar = (quill, range) => {
  return quill.getText(range.index, 1);
}

const handleListSelection = (quill, range) => {
  const lastCharacterOfPreviousLine = quill.getText(range.index - 3, 1);
  if (nextChar(quill, range) === "\n" || lastCharacterOfPreviousLine !== "\n") {
    quill.setSelection(range.index - 1, Quill.sources.SILENT);
  } else {
    quill.setSelection(range.index - 3, Quill.sources.SILENT);
  }
}

const moveSelectionToPreviousLine = (quill, range) => {
  const lastCharacterOfPreviousLine = quill.getText(range.index - 3, 1);
  if (nextChar(quill, range) === "\n" || lastCharacterOfPreviousLine !== "\n") {
    quill.setSelection(range.index - 1, Quill.sources.SILENT);
  } else {
    quill.setSelection(range.index - 3, Quill.sources.SILENT);
  }
}

export default function backspaceBindings(quill) {
  quill.keyboard.addBinding({ key: 8, offset: 1, collapsed: true }, (range, context) => {
    let length = 1
    if ((/[\uD800-\uDBFF][\uDC00-\uDFFF]$/).test(context.prefix)) {
      length = 2;
    }

    if (range.index === 0 || quill.getLength() <= 1) {
      return;
    }
    let formats = {};
    const [line] = quill.getLine(range.index);
    let delta = new Delta().retain(range.index - length).delete(length);
    if (context.offset === 1 && previousChar(quill, range) === "\n") {
      const [prev] = quill.getLine(range.index - 2);
      if (prev && prev.statics.blotName === "list-item") {
        formats = handleListSelection(quill, range);
        if (prev !== null && prev.length() > 1) {
          let curFormats = line.formats();
          let prevFormats = quill.getFormat(range.index - 2, 1);
          formats = attributeDiff(curFormats, prevFormats) || {};
          length += 1;
        }
        delta = new Delta().retain(range.index - 2).delete(2);
        moveSelectionToPreviousLine(quill, range);
      } else {
        delta = new Delta().retain(range.index - 1).delete(1);
        if (range.index < 2) {
          delta = new Delta().delete(1).retain(range.index + line.length() - 1);
        } else if (previousChar(quill, range) === "\n" && beforePreviousChar(quill, range) === "\n") {
          delta = new Delta().retain(range.index - 2).delete(2);
        }
      }
    } else {
      const [prev] = quill.getLine(range.index - 1);
      if (prev) {
        const isPrevLineEmpty =
          prev.statics.blotName === "block" && prev.length() <= 1;
        if (!isPrevLineEmpty) {
          const curFormats = line.formats();
          const prevFormats = quill.getFormat(range.index - 1, 1);
          formats = attributeDiff(curFormats, prevFormats) || {};
          if (Object.keys(formats).length > 0) {
            // line.length() - 1 targets \n in line, another -1 for newline being deleted
            const formatDelta = new Delta().retain(range.index + line.length() - 2).retain(1, formats);
            delta = delta.compose(formatDelta);
          }
        }
      }
    }
    quill.updateContents(delta, Quill.sources.USER);
    if (Object.keys(formats).length > 0) {
      quill.formatLine(range.index - length, length, formats, Quill.sources.USER);
    }
    quill.focus();
  });

  // Put this backspace binding to second
  quill.keyboard.bindings[8].splice(1, 0, quill.keyboard.bindings[8].pop());
}