import type { ChangeSpec, Line, Text } from '@codemirror/state';
import type { EditorView } from '@codemirror/view';

// https://regex101.com/r/5ILXUX/1
const LEADING_SPACES = /^\s*/;
// https://regex101.com/r/ScAXzy/1
const createPrefixPattern = (prefix: string) =>
  new RegExp(`^\\s*(${prefix}+)\\s*`);

const removePrefix = (text: string, prefix: string): string => {
  if (text.startsWith(prefix)) {
    return text.slice(prefix.length).trimStart();
  }
  return text;
};

const allLinesEmpty = (doc: Text, startLine: Line, endLine: Line): boolean => {
  for (let i = startLine.number; i <= endLine.number; i++) {
    const line = doc.line(i);
    if (line.text.trim() !== '') {
      return false;
    }
  }
  return true;
};

const allLinesHavePrefix = (
  doc: Text,
  startLine: Line,
  endLine: Line,
  prefix: string,
): boolean => {
  let hasNonEmptyLine = false;

  for (let i = startLine.number; i <= endLine.number; i++) {
    const line = doc.line(i);
    const trimmedLine = line.text.trim();

    if (trimmedLine !== '') {
      hasNonEmptyLine = true;
      if (!trimmedLine.startsWith(prefix)) {
        return false;
      }
    }
  }

  return hasNonEmptyLine;
};

/**
 * Insert or toggle a prefix at the beginning of the current line(s).
 * Handles multi-line selections. Removes prefix if all lines already have it.
 */
export const insertLinePrefix = (
  view: EditorView,
  prefix: string,
  noSpaceIfPrefixExists = false,
): void => {
  const { from, to } = view.state.selection.main;
  const doc = view.state.doc;
  const startLine = doc.lineAt(from);
  const endLine = doc.lineAt(to);

  const changes: ChangeSpec[] = [];
  let totalLengthChange = 0;

  const isPrefixRemoval = allLinesHavePrefix(doc, startLine, endLine, prefix);

  if (allLinesEmpty(doc, startLine, endLine)) {
    for (let i = startLine.number; i <= endLine.number; i++) {
      const line = view.state.doc.line(i);
      const leadingSpaces = line.text.match(LEADING_SPACES)?.[0] || '';
      const insertText = `${leadingSpaces}${prefix} `;

      const change = {
        from: line.from,
        to: line.to,
        insert: insertText,
      };

      changes.push(change);
      totalLengthChange += insertText.length - (line.to - line.from);
    }

    view.dispatch({ changes });
    view.dispatch({
      selection: {
        anchor: from + totalLengthChange,
        head: to + totalLengthChange,
      },
    });
    view.focus();
    return;
  }

  for (let i = startLine.number; i <= endLine.number; i++) {
    const line = view.state.doc.line(i);
    const trimmedLine = line.text.trim();
    const leadingSpaces = line.text.match(LEADING_SPACES)?.[0] || '';
    const contentTrimmed = line.text.trimStart();

    if (trimmedLine === '') {
      continue;
    }

    let newLine = '';
    let lengthChange = 0;

    if (isPrefixRemoval) {
      const prefixPattern = createPrefixPattern(prefix);
      const contentStartMatch = line.text.match(prefixPattern);

      if (contentStartMatch) {
        if (noSpaceIfPrefixExists) {
          const existingPrefixes = contentStartMatch[1];
          const indentLevel = Math.floor(leadingSpaces.length / 2) * 2;
          const newIndent = ' '.repeat(indentLevel);
          newLine = `${newIndent}${existingPrefixes}${prefix} ${line.text.slice(contentStartMatch[0].length)}`;
        } else {
          const indentLevel = Math.floor(leadingSpaces.length / 2) * 2;
          const newIndent = ' '.repeat(indentLevel);
          const prefixRemovedText = removePrefix(contentTrimmed, prefix);
          newLine = `${newIndent}${prefixRemovedText}`;
        }

        lengthChange = newLine.length - (line.to - line.from);

        changes.push({
          from: line.from,
          to: line.to,
          insert: newLine,
        });
      }
    } else {
      if (noSpaceIfPrefixExists && contentTrimmed.startsWith(prefix)) {
        newLine = `${leadingSpaces}${prefix}${contentTrimmed}`;
      } else {
        newLine = `${leadingSpaces}${prefix} ${contentTrimmed}`;
      }

      lengthChange = newLine.length - (line.to - line.from);

      changes.push({
        from: line.from,
        to: line.to,
        insert: newLine,
      });
    }

    totalLengthChange += lengthChange;
  }

  if (changes.length > 0) {
    view.dispatch({ changes });

    view.dispatch({
      selection: {
        anchor: from,
        head: to + totalLengthChange,
      },
    });
    view.focus();
  }
};