import { useCallback, useEffect, useRef, useState } from "react";
import type { ProjectMember } from "@/lib/api";
import { getProjectMembers } from "@/lib/api";

interface Props {
  projectSlug: string;
  value: string;
  onChange: (value: string) => void;
  onSubmit: () => void;
  placeholder?: string;
  disabled?: boolean;
}

export default function MentionInput({ projectSlug, value, onChange, onSubmit, placeholder, disabled }: Props) {
  const [members, setMembers] = useState<ProjectMember[]>([]);
  const [showDropdown, setShowDropdown] = useState(false);
  const [filter, setFilter] = useState("");
  const [selectedIdx, setSelectedIdx] = useState(0);
  const [mentionStart, setMentionStart] = useState(-1);
  const inputRef = useRef<HTMLTextAreaElement>(null);
  const dropdownRef = useRef<HTMLDivElement>(null);

  // Load members once
  useEffect(() => {
    if (!projectSlug) return;
    getProjectMembers(projectSlug).then(setMembers).catch(() => {});
  }, [projectSlug]);

  const filtered = members.filter((m) =>
    m.name.toLowerCase().includes(filter.toLowerCase()) ||
    m.slug.toLowerCase().includes(filter.toLowerCase())
  );

  const insertMention = useCallback((member: ProjectMember) => {
    if (mentionStart < 0) return;
    const before = value.slice(0, mentionStart);
    const after = value.slice(inputRef.current?.selectionStart ?? value.length);
    const newValue = `${before}@${member.slug} ${after}`;
    onChange(newValue);
    setShowDropdown(false);
    setMentionStart(-1);
    // Focus and set cursor after mention
    requestAnimationFrame(() => {
      const el = inputRef.current;
      if (el) {
        const pos = before.length + member.slug.length + 2; // @slug + space
        el.focus();
        el.setSelectionRange(pos, pos);
      }
    });
  }, [value, mentionStart, onChange]);

  const handleChange = (e: React.ChangeEvent<HTMLTextAreaElement>) => {
    const newVal = e.target.value;
    onChange(newVal);

    const cursorPos = e.target.selectionStart;
    // Find @ before cursor
    const textBeforeCursor = newVal.slice(0, cursorPos);
    const lastAt = textBeforeCursor.lastIndexOf("@");

    if (lastAt >= 0) {
      // Check: @ must be at start or after whitespace
      const charBefore = lastAt > 0 ? textBeforeCursor[lastAt - 1] : " ";
      if (/\s/.test(charBefore) || lastAt === 0) {
        const query = textBeforeCursor.slice(lastAt + 1);
        // No spaces in mention query
        if (!/\s/.test(query)) {
          setMentionStart(lastAt);
          setFilter(query);
          setShowDropdown(true);
          setSelectedIdx(0);
          return;
        }
      }
    }
    setShowDropdown(false);
  };

  const handleKeyDown = (e: React.KeyboardEvent<HTMLTextAreaElement>) => {
    if (showDropdown && filtered.length > 0) {
      if (e.key === "ArrowDown") {
        e.preventDefault();
        setSelectedIdx((i) => (i + 1) % filtered.length);
        return;
      }
      if (e.key === "ArrowUp") {
        e.preventDefault();
        setSelectedIdx((i) => (i - 1 + filtered.length) % filtered.length);
        return;
      }
      if (e.key === "Enter" || e.key === "Tab") {
        e.preventDefault();
        insertMention(filtered[selectedIdx]);
        return;
      }
      if (e.key === "Escape") {
        e.preventDefault();
        setShowDropdown(false);
        return;
      }
    }

    if (e.key === "Enter" && !e.shiftKey && !showDropdown) {
      e.preventDefault();
      onSubmit();
    }
  };

  const ICON: Record<string, string> = { human: "👤", agent: "🤖" };

  return (
    <div className="relative flex-1">
      <textarea
        ref={inputRef}
        value={value}
        onChange={handleChange}
        onKeyDown={handleKeyDown}
        placeholder={placeholder}
        disabled={disabled}
        rows={1}
        className="w-full bg-[var(--bg)] border border-[var(--border)] rounded-lg px-4 py-2 text-sm outline-none focus:border-[var(--accent)] resize-none"
        style={{ minHeight: "38px", maxHeight: "120px" }}
        onInput={(e) => {
          const el = e.currentTarget;
          el.style.height = "auto";
          el.style.height = Math.min(el.scrollHeight, 120) + "px";
        }}
      />
      {showDropdown && filtered.length > 0 && (
        <div
          ref={dropdownRef}
          className="absolute bottom-full left-0 mb-1 w-64 bg-[var(--surface)] border border-[var(--border)] rounded-lg shadow-lg overflow-hidden z-50"
        >
          {filtered.map((m, i) => (
            <button
              key={m.id}
              className={`w-full text-left px-3 py-2 text-sm flex items-center gap-2 hover:bg-white/10 ${
                i === selectedIdx ? "bg-white/10" : ""
              }`}
              onMouseDown={(e) => {
                e.preventDefault(); // prevent blur
                insertMention(m);
              }}
            >
              <span>{ICON[m.type] || "👤"}</span>
              <span className="font-medium">{m.name}</span>
              <span className="text-[var(--muted)]">@{m.slug}</span>
            </button>
          ))}
        </div>
      )}
    </div>
  );
}