import {
  StateCommand,
  Text,
  EditorSelection,
  ChangeSpec,
} from "@codemirror/state";
import { syntaxTree } from "@codemirror/language";
import { SyntaxNode, Tree } from "@lezer/common";
import { markdownLanguage } from "./markdown";

function nodeStart(node: SyntaxNode, doc: Text) {
  return doc.sliceString(node.from, node.from + 50);
}

class Context {
  constructor(
    readonly node: SyntaxNode,
    readonly from: number,
    readonly to: number,
    readonly spaceBefore: string,
    readonly spaceAfter: string,
    readonly type: string,
    readonly item: SyntaxNode | null
  ) {}

  blank(trailing: boolean = true) {
    let result = this.spaceBefore;
    if (this.node.name == "Blockquote") result += ">";
    else
      for (
        let i = this.to - this.from - result.length - this.spaceAfter.length;
        i > 0;
        i--
      )
        result += " ";
    return result + (trailing ? this.spaceAfter : "");
  }

  marker(doc: Text, add: number) {
    let number =
      this.node.name == "OrderedList"
        ? String(+itemNumber(this.item!, doc)[2] + add)
        : "";
    return this.spaceBefore + number + this.type + this.spaceAfter;
  }
}

function getContext(node: SyntaxNode, line: string, doc: Text) {
  let nodes = [];
  for (
    let cur: SyntaxNode | null = node;
    cur && cur.name != "Document";
    cur = cur.parent
  ) {
    if (cur.name == "ListItem" || cur.name == "Blockquote") nodes.push(cur);
  }
  let context = [],
    pos = 0;
  for (let i = nodes.length - 1; i >= 0; i--) {
    let node = nodes[i],
      match,
      start = pos;
    if (
      node.name == "Blockquote" &&
      (match = /^[ \t]*>( ?)/.exec(line.slice(pos)))
    ) {
      pos += match[0].length;
      context.push(new Context(node, start, pos, "", match[1], ">", null));
    } else if (
      node.name == "ListItem" &&
      node.parent!.name == "OrderedList" &&
      (match = /^([ \t]*)\d+([.)])([ \t]*)/.exec(nodeStart(node, doc)))
    ) {
      let after = match[3],
        len = match[0].length;
      if (after.length >= 4) {
        after = after.slice(0, after.length - 4);
        len -= 4;
      }
      pos += len;
      context.push(
        new Context(node.parent!, start, pos, match[1], after, match[2], node)
      );
    } else if (
      node.name == "ListItem" &&
      node.parent!.name == "BulletList" &&
      (match = /^([ \t]*)([-+*])([ \t]{1,4}\[[ xX]\])?([ \t]+)/.exec(
        nodeStart(node, doc)
      ))
    ) {
      let after = match[4],
        len = match[0].length;
      if (after.length > 4) {
        after = after.slice(0, after.length - 4);
        len -= 4;
      }
      let type = match[2];
      if (match[3]) type += match[3].replace(/[xX]/, " ");
      pos += len;
      context.push(
        new Context(node.parent!, start, pos, match[1], after, type, node)
      );
    }
  }
  return context;
}

function itemNumber(item: SyntaxNode, doc: Text) {
  return /^(\s*)(\d+)(?=[.)])/.exec(
    doc.sliceString(item.from, item.from + 10)
  )!;
}

function renumberList(
  after: SyntaxNode,
  doc: Text,
  changes: ChangeSpec[],
  offset = 0
) {
  for (let prev = -1, node = after; ; ) {
    if (node.name == "ListItem") {
      let m = itemNumber(node, doc);
      let number = +m[2];
      if (prev >= 0) {
        if (number != prev + 1) return;
        changes.push({
          from: node.from + m[1].length,
          to: node.from + m[0].length,
          insert: String(prev + 2 + offset),
        });
      }
      prev = number;
    }
    let next = node.nextSibling;
    if (!next) break;
    node = next;
  }
}

/// This command, when invoked in Markdown context with cursor
/// selection(s), will create a new line with the markup for
/// blockquotes and lists that were active on the old line. If the
/// cursor was directly after the end of the markup for the old line,
/// trailing whitespace and list markers are removed from that line.
///
/// The command does nothing in non-Markdown context, so it should
/// not be used as the only binding for Enter (even in a Markdown
/// document, HTML and code regions might use a different language).
export const insertNewlineContinueMarkup: StateCommand = ({
  state,
  dispatch,
}) => {
  let tree = syntaxTree(state),
    { doc } = state;
  let dont = null,
    changes = state.changeByRange((range) => {
      if (!range.empty || !markdownLanguage.isActiveAt(state, range.from))
        return (dont = { range });
      let pos = range.from,
        line = doc.lineAt(pos);
      let context = getContext(tree.resolveInner(pos, -1), line.text, doc);
      while (
        context.length &&
        context[context.length - 1].from > pos - line.from
      )
        context.pop();
      if (!context.length) return (dont = { range });
      let inner = context[context.length - 1];
      if (inner.to - inner.spaceAfter.length > pos - line.from)
        return (dont = { range });

      let emptyLine =
        pos >= inner.to - inner.spaceAfter.length &&
        !/\S/.test(line.text.slice(inner.to));
      // Empty line in list
      if (inner.item && emptyLine) {
        // First list item or blank line before: delete a level of markup
        if (
          inner.node.firstChild!.to >= pos ||
          (line.from > 0 && !/[^\s>]/.test(doc.lineAt(line.from - 1).text))
        ) {
          let next = context.length > 1 ? context[context.length - 2] : null;
          let delTo,
            insert = "";
          if (next && next.item) {
            // Re-add marker for the list at the next level
            delTo = line.from + next.from;
            insert = next.marker(doc, 1);
          } else {
            delTo = line.from + (next ? next.to : 0);
          }
          let changes: ChangeSpec[] = [{ from: delTo, to: pos, insert }];
          if (inner.node.name == "OrderedList")
            renumberList(inner.item!, doc, changes, -2);
          if (next && next.node.name == "OrderedList")
            renumberList(next.item!, doc, changes);
          return {
            range: EditorSelection.cursor(delTo + insert.length),
            changes,
          };
        } else {
          // Move this line down
          let insert = "";
          for (let i = 0, e = context.length - 2; i <= e; i++)
            insert += context[i].blank(i < e);
          insert += state.lineBreak;
          return {
            range: EditorSelection.cursor(pos + insert.length),
            changes: { from: line.from, insert },
          };
        }
      }

      if (inner.node.name == "Blockquote" && emptyLine && line.from) {
        let prevLine = doc.lineAt(line.from - 1),
          quoted = />\s*$/.exec(prevLine.text);
        // Two aligned empty quoted lines in a row
        if (quoted && quoted.index == inner.from) {
          let changes = state.changes([
            { from: prevLine.from + quoted.index, to: prevLine.to },
            { from: line.from + inner.from, to: line.to },
          ]);
          return { range: range.map(changes), changes };
        }
      }

      let changes: ChangeSpec[] = [];
      if (inner.node.name == "OrderedList")
        renumberList(inner.item!, doc, changes);
      let insert = state.lineBreak;
      let continued = inner.item && inner.item.from < line.from;
      // If not dedented
      if (
        !continued ||
        /^[\s\d.)\-+*>]*/.exec(line.text)![0].length >= inner.to
      ) {
        for (let i = 0, e = context.length - 1; i <= e; i++)
          insert +=
            i == e && !continued
              ? context[i].marker(doc, 1)
              : context[i].blank();
      }
      let from = pos;
      while (
        from > line.from &&
        /\s/.test(line.text.charAt(from - line.from - 1))
      )
        from--;
      changes.push({ from, to: pos, insert });
      return { range: EditorSelection.cursor(from + insert.length), changes };
    });
  if (dont) return false;
  dispatch(state.update(changes, { scrollIntoView: true, userEvent: "input" }));
  return true;
};

function isMark(node: SyntaxNode) {
  return node.name == "QuoteMark" || node.name == "ListMark";
}

function contextNodeForDelete(tree: Tree, pos: number) {
  let node = tree.resolveInner(pos, -1),
    scan = pos;
  if (isMark(node)) {
    scan = node.from;
    node = node.parent!;
  }
  for (let prev; (prev = node.childBefore(scan)); ) {
    if (isMark(prev)) {
      scan = prev.from;
    } else if (prev.name == "OrderedList" || prev.name == "BulletList") {
      node = prev.lastChild!;
      scan = node.to;
    } else {
      break;
    }
  }
  return node;
}

/// This command will, when invoked in a Markdown context with the
/// cursor directly after list or blockquote markup, delete one level
/// of markup. When the markup is for a list, it will be replaced by
/// spaces on the first invocation (a further invocation will delete
/// the spaces), to make it easy to continue a list.
///
/// When not after Markdown block markup, this command will return
/// false, so it is intended to be bound alongside other deletion
/// commands, with a higher precedence than the more generic commands.
export const deleteMarkupBackward: StateCommand = ({ state, dispatch }) => {
  let tree = syntaxTree(state);
  let dont = null,
    changes = state.changeByRange((range) => {
      let pos = range.from,
        { doc } = state;
      if (range.empty && markdownLanguage.isActiveAt(state, range.from)) {
        let line = doc.lineAt(pos);
        let context = getContext(
          contextNodeForDelete(tree, pos),
          line.text,
          doc
        );
        if (context.length) {
          let inner = context[context.length - 1];
          let spaceEnd =
            inner.to - inner.spaceAfter.length + (inner.spaceAfter ? 1 : 0);
          // Delete extra trailing space after markup
          if (
            pos - line.from > spaceEnd &&
            !/\S/.test(line.text.slice(spaceEnd, pos - line.from))
          )
            return {
              range: EditorSelection.cursor(line.from + spaceEnd),
              changes: { from: line.from + spaceEnd, to: pos },
            };
          if (pos - line.from == spaceEnd) {
            let start = line.from + inner.from;
            // Replace a list item marker with blank space
            if (
              inner.item &&
              inner.node.from < inner.item.from &&
              /\S/.test(line.text.slice(inner.from, inner.to))
            )
              return {
                range,
                changes: {
                  from: start,
                  to: line.from + inner.to,
                  insert: inner.blank(),
                },
              };
            // Delete one level of indentation
            if (start < pos)
              return {
                range: EditorSelection.cursor(start),
                changes: { from: start, to: pos },
              };
          }
        }
      }
      return (dont = { range });
    });
  if (dont) return false;
  dispatch(
    state.update(changes, { scrollIntoView: true, userEvent: "delete" })
  );
  return true;
};