import { useCallback, useEffect, useMemo, useRef, useState } from "react";
import {
  Box,
  ClickAwayListener,
  List,
  ListItemButton,
  Paper,
  Popper,
  TextField,
} from "@mui/material";
import {
  filterMentionCandidates,
  findActiveMentionQuery,
  insertMentionToken,
  type MentionLookup,
} from "@/domain/work-orders/utils/comment-mentions";

type CommentMentionComposerProps = {
  value: string;
  onChange: (value: string) => void;
  candidates: MentionLookup[];
  placeholder?: string;
  disabled?: boolean;
  rows?: number;
  onSubmit?: () => void;
};

type MentionCandidateMenuProps = {
  open: boolean;
  anchorEl: HTMLElement | null;
  candidates: MentionLookup[];
  highlightIndex: number;
  onSelect: (user: MentionLookup) => void;
};

function MentionCandidateMenu({
  open,
  anchorEl,
  candidates,
  highlightIndex,
  onSelect,
}: MentionCandidateMenuProps) {
  return (
    <Popper open={open} anchorEl={anchorEl} placement="bottom-start" className="z-50">
      <Paper elevation={4} className="mt-1 max-h-48 overflow-y-auto">
        <List dense disablePadding>
          {candidates.map((candidate, index) => (
            <ListItemButton
              key={String(candidate.id)}
              selected={index === highlightIndex}
              onMouseDown={(event) => event.preventDefault()}
              onClick={() => onSelect(candidate)}
            >
              @{candidate.name}
            </ListItemButton>
          ))}
        </List>
      </Paper>
    </Popper>
  );
}

export function CommentMentionComposer({
  value,
  onChange,
  candidates,
  placeholder = "Type a comment...",
  disabled = false,
  rows = 2,
  onSubmit,
}: CommentMentionComposerProps) {
  const inputRef = useRef<HTMLTextAreaElement | HTMLInputElement>(null);
  const [anchorEl, setAnchorEl] = useState<HTMLElement | null>(null);
  const [cursor, setCursor] = useState(0);
  const [menuOpen, setMenuOpen] = useState(false);
  const [highlightIndex, setHighlightIndex] = useState(0);

  const activeQuery = useMemo(() => findActiveMentionQuery(value, cursor), [value, cursor]);

  const filteredCandidates = useMemo(
    () => filterMentionCandidates(candidates, activeQuery?.query ?? ""),
    [activeQuery?.query, candidates],
  );

  const showMenu = Boolean(menuOpen && activeQuery && filteredCandidates.length > 0);

  useEffect(() => {
    setHighlightIndex(0);
  }, [activeQuery?.query, activeQuery?.start]);

  const syncCursor = useCallback((textOverride?: string) => {
    const element = inputRef.current;
    if (!element) {
      return;
    }

    const text = textOverride ?? element.value;
    const nextCursor = element.selectionStart ?? text.length;
    setCursor(nextCursor);
    setMenuOpen(Boolean(findActiveMentionQuery(text, nextCursor)));
  }, []);

  const handleChange = (nextValue: string) => {
    onChange(nextValue);
    requestAnimationFrame(() => {
      syncCursor(nextValue);
    });
  };

  const applyMention = useCallback(
    (user: MentionLookup) => {
      if (!activeQuery) {
        return;
      }

      const { nextText, nextCursor } = insertMentionToken(value, activeQuery.start, cursor, user);
      onChange(nextText);
      setMenuOpen(false);
      setHighlightIndex(0);

      requestAnimationFrame(() => {
        const element = inputRef.current;
        if (!element) {
          return;
        }
        element.focus();
        element.setSelectionRange(nextCursor, nextCursor);
        setCursor(nextCursor);
      });
    },
    [activeQuery, cursor, onChange, value],
  );

  const handleKeyDown = (event: React.KeyboardEvent<HTMLDivElement>) => {
    if (showMenu) {
      if (event.key === "ArrowDown") {
        event.preventDefault();
        setHighlightIndex((current) => (current + 1) % filteredCandidates.length);
        return;
      }

      if (event.key === "ArrowUp") {
        event.preventDefault();
        setHighlightIndex(
          (current) => (current - 1 + filteredCandidates.length) % filteredCandidates.length,
        );
        return;
      }

      if (event.key === "Enter" && !event.shiftKey) {
        event.preventDefault();
        const selected = filteredCandidates[highlightIndex];
        if (selected) {
          applyMention(selected);
        }
        return;
      }

      if (event.key === "Escape") {
        event.preventDefault();
        setMenuOpen(false);
        return;
      }
    }

    if (event.key === "Enter" && (event.metaKey || event.ctrlKey) && onSubmit) {
      event.preventDefault();
      onSubmit();
    }
  };

  return (
    <ClickAwayListener onClickAway={() => setMenuOpen(false)}>
      <Box
        className="relative"
        ref={(node: HTMLDivElement | null) => {
          setAnchorEl(node);
        }}
      >
        <TextField
          inputRef={inputRef}
          multiline
          rows={rows}
          fullWidth
          value={value}
          onChange={(event) => handleChange(event.target.value)}
          onClick={() => syncCursor()}
          onKeyUp={() => syncCursor()}
          onSelect={() => syncCursor()}
          onKeyDown={handleKeyDown}
          placeholder={placeholder}
          disabled={disabled}
        />

        <MentionCandidateMenu
          open={showMenu}
          anchorEl={anchorEl}
          candidates={filteredCandidates}
          highlightIndex={highlightIndex}
          onSelect={applyMention}
        />
      </Box>
    </ClickAwayListener>
  );
}