import { useCallback, useEffect, useRef, useState, type DragEvent, type KeyboardEvent } from 'react';
import { Send } from 'lucide-react';
import { toast } from 'sonner';
import { Textarea } from '@/components/ui/textarea';
import { Button } from '@/components/ui/button';
import {
  flattenToMessage,
  inferLanguage,
  looksBinary,
  MAX_FILE_SIZE_BYTES,
  PASTE_INLINE_MAX_LINES,
  type Attachment,
} from '@/lib/attachments';
import { AttachmentChip } from '@/components/AttachmentChip';
import { AttachmentPreviewModal } from '@/components/AttachmentPreviewModal';
import { FileMentionPopover } from '@/components/FileMentionPopover';
import { DropOverlay } from '@/components/DropOverlay';
import { AgentPicker } from '@/components/AgentPicker';
import { api } from '@/api/client';
import { sessionEvents } from '@/hooks/sessionEvents';
import { useViewport } from '@/hooks/useViewport';

const MAX_ATTACHMENTS = 10;

interface Props {
  disabled?: boolean;
  projectId: string;
  // Batch 9: optional so callers that pre-date the agent picker still compile.
  // When omitted, the toolbar row is hidden entirely.
  agentId?: string | null;
  onAgentChange?: (agentId: string | null) => void | Promise<void>;
  onSend: (content: string) => void | Promise<void>;
  onForceSend?: (content: string) => void | Promise<void>;
}

export function ChatInput({ disabled, projectId, agentId, onAgentChange, onSend, onForceSend }: Props) {
  const { isMobile } = useViewport();
  const [value, setValue] = useState('');
  const [busy, setBusy] = useState(false);
  const [attachments, setAttachments] = useState<Attachment[]>([]);
  const [previewAttachment, setPreviewAttachment] = useState<Attachment | null>(null);
  const [isDraggingOver, setIsDraggingOver] = useState(false);
  const dropRootRef = useRef<HTMLDivElement | null>(null);
  const pasteCounterRef = useRef(0);
  const [mentionState, setMentionState] = useState<{
    open: boolean;
    query: string;
    atIdx: number;
    anchorRect: { top: number; left: number };
  } | null>(null);
  const [fileIndex, setFileIndex] = useState<string[] | null>(null);
  const textareaRef = useRef<HTMLTextAreaElement | null>(null);

  function addAttachment(a: Attachment) {
    setAttachments(prev => {
      if (prev.length >= MAX_ATTACHMENTS) {
        toast.error(`Max ${MAX_ATTACHMENTS} attachments per message`);
        return prev;
      }
      return [...prev, a];
    });
  }

  const addAttachmentRef = useRef(addAttachment);
  addAttachmentRef.current = addAttachment;

  useEffect(() => {
    return sessionEvents.subscribe((event) => {
      if (event.type !== 'attach_chat_file') return;
      addAttachmentRef.current({
        id: crypto.randomUUID(),
        ...event.attachment,
      });
    });
  }, []);

  function removeAttachment(id: string) {
    setAttachments(prev => prev.filter(a => a.id !== id));
  }

  async function submit() {
    const text = value.trim();
    if (!text && attachments.length === 0) return;
    if (disabled || busy) return;
    setBusy(true);
    try {
      const body = flattenToMessage(attachments, text);
      await onSend(body);
      setValue('');
      setAttachments([]);
    } catch (err) {
      toast.error(err instanceof Error ? err.message : 'failed to send');
    } finally {
      setBusy(false);
    }
  }

  function getCaretCoords(textarea: HTMLTextAreaElement): { top: number; left: number } {
    const mirror = document.createElement('div');
    const style = window.getComputedStyle(textarea);

    const properties = [
      'fontFamily', 'fontSize', 'fontWeight', 'fontStyle',
      'letterSpacing', 'lineHeight', 'textTransform', 'wordSpacing',
      'textIndent', 'paddingTop', 'paddingRight', 'paddingBottom', 'paddingLeft',
      'borderTopWidth', 'borderRightWidth', 'borderBottomWidth', 'borderLeftWidth',
      'boxSizing', 'whiteSpace', 'overflowWrap',
    ] as const;

    mirror.style.position = 'absolute';
    mirror.style.visibility = 'hidden';
    mirror.style.overflow = 'hidden';
    mirror.style.width = style.width;
    for (const prop of properties) {
      mirror.style[prop] = style[prop];
    }
    mirror.style.whiteSpace = 'pre-wrap';
    mirror.style.overflowWrap = 'break-word';

    const textBefore = textarea.value.slice(0, textarea.selectionStart);
    mirror.textContent = textBefore;

    const span = document.createElement('span');
    span.textContent = '​'; // zero-width space
    mirror.appendChild(span);

    document.body.appendChild(mirror);

    const taRect = textarea.getBoundingClientRect();
    const spanRect = span.getBoundingClientRect();
    const mirrorRect = mirror.getBoundingClientRect();

    const top = taRect.top + (spanRect.top - mirrorRect.top) - textarea.scrollTop + span.offsetHeight;
    const left = taRect.left + (spanRect.left - mirrorRect.left);

    document.body.removeChild(mirror);

    return { top, left };
  }

  function handleChange(e: React.ChangeEvent<HTMLTextAreaElement>) {
    const newValue = e.target.value;
    setValue(newValue);

    const ta = e.target;
    const pos = ta.selectionStart;

    // Check for @ trigger
    if (pos > 0 && newValue[pos - 1] === '@') {
      const charBefore = pos >= 2 ? newValue[pos - 2] : null;
      if (charBefore === null || charBefore === ' ' || charBefore === '\n') {
        const coords = getCaretCoords(ta);
        setMentionState({ open: true, query: '', atIdx: pos - 1, anchorRect: coords });
        if (!fileIndex) {
          api.projects.files(projectId).then(r => setFileIndex(r.files)).catch(() => {});
        }
        return;
      }
    }

    // Update query if popover is open — use stored atIdx
    if (mentionState?.open) {
      const { atIdx } = mentionState;
      if (atIdx < pos && newValue[atIdx] === '@') {
        const query = newValue.slice(atIdx + 1, pos);
        setMentionState(prev => prev ? { ...prev, query } : null);
      } else {
        setMentionState(null);
      }
    }
  }

  async function handleMentionSelect(path: string) {
    const atIdx = mentionState?.atIdx ?? -1;
    const ta = textareaRef.current;
    const caretPos = ta?.selectionStart ?? value.length;
    setMentionState(null);

    try {
      const result = await api.projects.viewFile(projectId, path);
      if (atIdx >= 0) {
        const cleaned = value.slice(0, atIdx) + value.slice(caretPos);
        setValue(cleaned);
        if (ta) {
          requestAnimationFrame(() => {
            ta.selectionStart = ta.selectionEnd = atIdx;
            ta.focus();
          });
        }
      }
      addAttachment({
        id: crypto.randomUUID(),
        kind: 'file',
        filename: path,
        language: inferLanguage(path),
        content: result.content,
        source: '@',
      });
    } catch {
      toast.error('Failed to load file');
    }
  }

  const closeMention = useCallback(() => setMentionState(null), []);

  // ---- Drag & drop (F1 + F3 + F4) ----------------------------------------
  // The drop zone is the outer ChatInput container (ref'd as dropRootRef).
  // onDragLeave only clears the highlight when the cursor leaves the
  // container, not when it crosses into a child element.

  async function processDroppedFile(file: File) {
    // Size gate
    if (file.size > MAX_FILE_SIZE_BYTES) {
      const mb = (file.size / (1024 * 1024)).toFixed(1);
      toast.error(`File ${file.name} is too large (${mb} MB). Limit is 5 MB.`);
      return;
    }
    // Read once as ArrayBuffer so we can do byte-level binary detection
    // before deciding whether to decode as text.
    let buf: ArrayBuffer;
    try {
      buf = await file.arrayBuffer();
    } catch (err) {
      toast.error(`Failed to read ${file.name}: ${err instanceof Error ? err.message : String(err)}`);
      return;
    }
    if (looksBinary(buf)) {
      toast.error(`${file.name} appears to be binary.`);
      return;
    }
    const text = new TextDecoder('utf-8', { fatal: false }).decode(buf);
    addAttachment({
      id: crypto.randomUUID(),
      kind: 'file',
      filename: file.name,
      language: inferLanguage(file.name),
      content: text,
      source: 'drop',
    });
  }

  function isFolderItem(item: DataTransferItem | undefined): boolean {
    if (!item) return false;
    // webkitGetAsEntry is non-standard but supported in Chromium + Safari.
    // If unavailable, we conservatively treat the entry as a file.
    const entry =
      typeof item.webkitGetAsEntry === 'function' ? item.webkitGetAsEntry() : null;
    if (entry && entry.isDirectory) return true;
    // Heuristic fallback: folders dragged from Finder have type === '' and
    // a 0-byte File. The empty-type alone isn't reliable for files (some
    // plaintext drops also lack a type), so we only flag when the entry
    // explicitly says directory.
    return false;
  }

  async function handleDroppedItems(dt: DataTransfer) {
    // Snapshot items first because reading files inside the loop can
    // detach the DataTransfer between awaits.
    const itemsArray: { file: File | null; isFolder: boolean }[] = [];
    if (dt.items && dt.items.length > 0) {
      for (let i = 0; i < dt.items.length; i++) {
        const it = dt.items[i];
        if (!it || it.kind !== 'file') continue;
        const folder = isFolderItem(it);
        const file = folder ? null : it.getAsFile();
        itemsArray.push({ file, isFolder: folder });
      }
    } else {
      for (let i = 0; i < dt.files.length; i++) {
        const f = dt.files[i];
        if (f) itemsArray.push({ file: f, isFolder: false });
      }
    }

    let remainingSlots = MAX_ATTACHMENTS - attachments.length;
    let folderRejected = false;
    for (const { file, isFolder } of itemsArray) {
      if (isFolder) {
        if (!folderRejected) {
          toast.error('Folders are not supported');
          folderRejected = true;
        }
        continue;
      }
      if (!file) continue;
      if (remainingSlots <= 0) {
        toast.error(`Attachment limit reached (${MAX_ATTACHMENTS}).`);
        return;
      }
      await processDroppedFile(file);
      remainingSlots -= 1;
    }
  }

  function onDragEnter(e: DragEvent<HTMLDivElement>) {
    if (disabled || busy) return;
    e.preventDefault();
    setIsDraggingOver(true);
  }

  function onDragOver(e: DragEvent<HTMLDivElement>) {
    if (disabled || busy) return;
    e.preventDefault();
    e.dataTransfer.dropEffect = 'copy';
  }

  function onDragLeave(e: DragEvent<HTMLDivElement>) {
    // Only clear when the cursor actually leaves the root container.
    // relatedTarget is the element being entered; if it's inside the root,
    // ignore — we're just crossing into a child.
    const root = dropRootRef.current;
    if (!root) return;
    const related = e.relatedTarget as Node | null;
    if (related && root.contains(related)) return;
    setIsDraggingOver(false);
  }

  function onDrop(e: DragEvent<HTMLDivElement>) {
    e.preventDefault();
    setIsDraggingOver(false);
    if (disabled || busy) return;
    void handleDroppedItems(e.dataTransfer);
  }
  // ---- end Drag & drop -----------------------------------------------------

  // ---- Paste-as-attachment (F2) -------------------------------------------
  // Pasting >PASTE_INLINE_MAX_LINES lines of text becomes a chip rather than
  // inline content. Image pastes are rejected with a toast. If both text and
  // image are present (e.g. screenshot tool that sets both), prefer text.

  function onPaste(e: React.ClipboardEvent<HTMLTextAreaElement>) {
    const cd = e.clipboardData;
    if (!cd) return;
    const text = cd.getData('text/plain');
    const hasImage = Array.from(cd.items ?? []).some((it) =>
      it.type.startsWith('image/'),
    );
    if (text) {
      const lineCount = text.split('\n').length;
      if (lineCount > PASTE_INLINE_MAX_LINES) {
        e.preventDefault();
        pasteCounterRef.current += 1;
        addAttachment({
          id: crypto.randomUUID(),
          kind: 'paste',
          filename: `pasted-${pasteCounterRef.current}.txt`,
          language: 'plaintext',
          content: text,
          source: 'paste',
        });
      }
      // <= threshold: let default paste insert inline.
      return;
    }
    if (hasImage) {
      e.preventDefault();
      toast.error('Image paste is not supported. Drop a file or paste text.');
    }
  }
  // ---- end Paste-as-attachment --------------------------------------------

  function onKeyDown(e: KeyboardEvent<HTMLTextAreaElement>) {
    if (mentionState?.open) return;
    // IME safety: never act on Enter while an IME composition is in flight
    // (CJK input methods commit composition via Enter). Without this, the
    // first Enter of a Japanese/Chinese/Korean composition would submit
    // instead of finalizing the candidate.
    if (e.nativeEvent.isComposing) return;
    if (e.key === 'Enter' && e.shiftKey && (e.metaKey || e.ctrlKey) && onForceSend) {
      e.preventDefault();
      void forceSubmit();
      return;
    }
    if (e.key === 'Enter' && (e.metaKey || e.ctrlKey)) {
      e.preventDefault();
      void submit();
      return;
    }
    // Bare Enter: sends on desktop, inserts a newline on mobile (per spec —
    // send is via the dedicated button on touch devices).
    if (e.key === 'Enter' && !e.shiftKey && !isMobile) {
      e.preventDefault();
      void submit();
    }
  }

  async function forceSubmit() {
    const text = value.trim();
    if (!text || !onForceSend) return;
    if (busy) return;
    setBusy(true);
    try {
      const body = flattenToMessage(attachments, text);
      await onForceSend(body);
      setValue('');
      setAttachments([]);
    } catch (err) {
      toast.error(err instanceof Error ? err.message : 'force send failed');
    } finally {
      setBusy(false);
    }
  }

  return (
    <div
      ref={dropRootRef}
      className="border-t relative"
      style={{ paddingBottom: 'env(safe-area-inset-bottom)' }}
      onDragEnter={onDragEnter}
      onDragOver={onDragOver}
      onDragLeave={onDragLeave}
      onDrop={onDrop}
    >
      <DropOverlay visible={isDraggingOver} />
      <div className="max-w-[1000px] mx-auto w-full">
      {attachments.length > 0 && (
        <div className="flex flex-wrap gap-1.5 px-4 pt-3">
          {attachments.map(a => (
            <AttachmentChip
              key={a.id}
              attachment={a}
              onRemove={removeAttachment}
              onPreview={setPreviewAttachment}
            />
          ))}
        </div>
      )}
      {/* Batch 9 toolbar — agent picker. Sits above the input row so it
          doesn't compete with the send button for vertical alignment.
          When Batch 7 lands, ModelPicker and the + button join this row. */}
      {onAgentChange && (
        <div className="px-4 pt-2 flex items-center gap-1.5">
          <AgentPicker
            projectId={projectId}
            value={agentId ?? null}
            onChange={onAgentChange}
          />
        </div>
      )}
      <div className="px-4 py-3 flex items-end gap-2">
        <Textarea
          ref={textareaRef}
          value={value}
          onChange={handleChange}
          onKeyDown={onKeyDown}
          onPaste={onPaste}
          placeholder={
            isMobile
              ? 'Ask about this project. Tap send to submit.'
              : 'Ask about this project. Enter to send · Shift+Enter for newline.'
          }
          disabled={disabled || busy}
          rows={3}
          className="resize-none min-h-[68px] max-h-[240px]"
        />
        <Button
          onClick={() => void submit()}
          disabled={disabled || busy || (!value.trim() && attachments.length === 0)}
          size="icon-lg"
          aria-label="Send"
        >
          <Send />
        </Button>
      </div>
      </div>
      <AttachmentPreviewModal
        attachment={previewAttachment}
        onClose={() => setPreviewAttachment(null)}
      />
      {mentionState?.open && (
        <FileMentionPopover
          query={mentionState.query}
          files={fileIndex ?? []}
          anchorRect={mentionState.anchorRect}
          onSelect={handleMentionSelect}
          onClose={closeMention}
        />
      )}
    </div>
  );
}