import { useCallback, useEffect, useRef, useState } from 'react';
import type { DragEvent } from 'react';
import { toast } from 'sonner';
import type { WorkspacePane } from '@/api/types';
import { setActivePaneInfo, clearActivePane } from '@/hooks/useActivePane';

export const MAX_PANES = 5;
const STORAGE_KEY = 'boocode.workspace.panes';

function generateId(): string {
  return crypto.randomUUID();
}

function emptyPane(): WorkspacePane {
  return { id: generateId(), kind: 'empty', chatIds: [], activeChatIdx: -1 };
}

function chatPane(chatId: string): WorkspacePane {
  return { id: generateId(), kind: 'chat', chatId, chatIds: [chatId], activeChatIdx: 0 };
}

// v1.9: settings pane factory. No chats, no state beyond identity — the
// SettingsPane component renders Session/Project sections from the
// surrounding session/project.
function settingsPane(): WorkspacePane {
  return { id: generateId(), kind: 'settings', chatIds: [], activeChatIdx: -1 };
}

// v1.9: settings panes are ephemeral. Filter them out before persisting so a
// page reload always returns to a clean workspace; the user re-opens via the
// sidebar Settings button when needed.
function persistablePanes(panes: WorkspacePane[]): WorkspacePane[] {
  return panes.filter((p) => p.kind !== 'settings');
}

// v1.9: per recon decision (c), settings panes don't count toward MAX_PANES.
// Helper used at every pane-insertion site so the rule lives in one place.
function nonSettingsCount(panes: WorkspacePane[]): number {
  return panes.reduce((n, p) => n + (p.kind === 'settings' ? 0 : 1), 0);
}

function loadPanes(sessionId: string): WorkspacePane[] | null {
  try {
    const raw = localStorage.getItem(`${STORAGE_KEY}.${sessionId}`);
    if (!raw) return null;
    const parsed = JSON.parse(raw) as WorkspacePane[];
    if (!Array.isArray(parsed) || parsed.length === 0) return null;
    return parsed;
  } catch {
    return null;
  }
}

function savePanes(sessionId: string, panes: WorkspacePane[]): void {
  try {
    localStorage.setItem(
      `${STORAGE_KEY}.${sessionId}`,
      JSON.stringify(persistablePanes(panes)),
    );
  } catch { /* quota or disabled */ }
}

export interface UseWorkspacePanesResult {
  panes: WorkspacePane[];
  activePaneIdx: number;
  setActivePaneIdx: React.Dispatch<React.SetStateAction<number>>;
  activePaneIdxRef: React.MutableRefObject<number>;
  openChatInPane: (paneIdx: number, chatId: string) => void;
  switchTab: (paneIdx: number, tabIdx: number) => void;
  removeTab: (paneIdx: number, chatId: string) => void;
  closeOtherTabs: (paneIdx: number, keepChatId: string) => void;
  closeTabsToRight: (paneIdx: number, pivotChatId: string) => void;
  closeAllTabs: (paneIdx: number) => void;
  showLandingPage: (paneIdx: number) => void;
  addSplitPane: (kind: 'chat' | 'terminal' | 'agent') => void;
  // v1.9: idempotent open-or-focus for the settings pane singleton. Appends
  // a new settings pane if none exists, otherwise just focuses the existing
  // one. Always succeeds — settings panes don't count toward MAX_PANES.
  openOrFocusSettingsPane: () => void;
  removePane: (idx: number) => void;
  removeChatFromPanes: (chatId: string) => void;
  initializeFirstChatIfEmpty: (chatId: string) => void;
  handlePaneDragStart: (idx: number) => (e: DragEvent<HTMLDivElement>) => void;
  handlePaneDragOver: (idx: number) => (e: DragEvent<HTMLDivElement>) => void;
  handlePaneDragLeave: () => void;
  handlePaneDrop: (targetIdx: number) => (e: DragEvent<HTMLDivElement>) => void;
  handlePaneDragEnd: () => void;
  dragOverIdx: number | null;
  draggingIdxRef: React.MutableRefObject<number | null>;
}

export function useWorkspacePanes(sessionId: string): UseWorkspacePanesResult {
  const [panes, setPanes] = useState<WorkspacePane[]>(() => {
    return loadPanes(sessionId) ?? [emptyPane()];
  });
  const [activePaneIdx, setActivePaneIdx] = useState(0);
  const draggingIdxRef = useRef<number | null>(null);
  const [dragOverIdx, setDragOverIdx] = useState<number | null>(null);

  useEffect(() => {
    savePanes(sessionId, panes);
  }, [sessionId, panes]);

  useEffect(() => {
    const active = panes[activePaneIdx];
    if (!active) {
      clearActivePane();
      return;
    }
    setActivePaneInfo({
      sessionId,
      paneId: active.id,
      kind: active.kind,
      activeFile: null,
    });
  }, [sessionId, panes, activePaneIdx]);

  useEffect(() => {
    return () => {
      clearActivePane();
    };
  }, []);

  const activePaneIdxRef = useRef(activePaneIdx);
  activePaneIdxRef.current = activePaneIdx;

  const openChatInPane = useCallback((paneIdx: number, chatId: string) => {
    setPanes((prev) => {
      const next = [...prev];
      const pane = next[paneIdx]!;
      const existing = pane.chatIds.indexOf(chatId);
      if (existing >= 0) {
        next[paneIdx] = { ...pane, kind: 'chat', chatId, activeChatIdx: existing };
      } else {
        const newIds = [...pane.chatIds, chatId];
        next[paneIdx] = {
          ...pane,
          kind: 'chat',
          chatId,
          chatIds: newIds,
          activeChatIdx: newIds.length - 1,
        };
      }
      return next;
    });
    setActivePaneIdx(paneIdx);
  }, []);

  const switchTab = useCallback((paneIdx: number, tabIdx: number) => {
    setPanes((prev) => {
      const next = [...prev];
      const pane = next[paneIdx]!;
      const chatId = pane.chatIds[tabIdx];
      if (!chatId) return prev;
      next[paneIdx] = { ...pane, chatId, activeChatIdx: tabIdx };
      return next;
    });
  }, []);

  const removeTab = useCallback((paneIdx: number, chatId: string) => {
    setPanes((prev) => {
      const next = [...prev];
      const pane = next[paneIdx]!;
      const nextIds = pane.chatIds.filter((id) => id !== chatId);
      if (nextIds.length === 0) {
        next[paneIdx] = { ...pane, kind: 'empty', chatId: undefined, chatIds: [], activeChatIdx: -1 };
      } else {
        const nextActiveIdx = Math.min(pane.activeChatIdx, nextIds.length - 1);
        next[paneIdx] = {
          ...pane,
          chatIds: nextIds,
          activeChatIdx: nextActiveIdx,
          chatId: nextIds[nextActiveIdx],
        };
      }
      return next;
    });
  }, []);

  // Keep only the right-clicked tab open in this pane.
  const closeOtherTabs = useCallback((paneIdx: number, keepChatId: string) => {
    setPanes((prev) => {
      const next = [...prev];
      const pane = next[paneIdx]!;
      const keepIdx = pane.chatIds.indexOf(keepChatId);
      if (keepIdx < 0) return prev;
      next[paneIdx] = {
        ...pane,
        kind: 'chat',
        chatId: keepChatId,
        chatIds: [keepChatId],
        activeChatIdx: 0,
      };
      return next;
    });
  }, []);

  // Close every tab to the right of the right-clicked one.
  const closeTabsToRight = useCallback((paneIdx: number, pivotChatId: string) => {
    setPanes((prev) => {
      const next = [...prev];
      const pane = next[paneIdx]!;
      const pivotIdx = pane.chatIds.indexOf(pivotChatId);
      if (pivotIdx < 0 || pivotIdx === pane.chatIds.length - 1) return prev;
      const nextIds = pane.chatIds.slice(0, pivotIdx + 1);
      const nextActiveIdx = Math.min(pane.activeChatIdx, nextIds.length - 1);
      next[paneIdx] = {
        ...pane,
        chatIds: nextIds,
        activeChatIdx: nextActiveIdx,
        chatId: nextIds[nextActiveIdx],
      };
      return next;
    });
  }, []);

  // Close every tab in this pane; land on landing page.
  const closeAllTabs = useCallback((paneIdx: number) => {
    setPanes((prev) => {
      const next = [...prev];
      const pane = next[paneIdx]!;
      next[paneIdx] = { ...pane, kind: 'empty', chatId: undefined, chatIds: [], activeChatIdx: -1 };
      return next;
    });
  }, []);

  const showLandingPage = useCallback((paneIdx: number) => {
    setPanes((prev) => {
      const next = [...prev];
      const pane = next[paneIdx]!;
      next[paneIdx] = { ...pane, kind: 'empty', chatId: undefined };
      return next;
    });
  }, []);

  const addSplitPane = useCallback((kind: 'chat' | 'terminal' | 'agent') => {
    if (kind === 'terminal') {
      toast('Terminal panes coming in BooTerm');
      return;
    }
    if (kind === 'agent') {
      toast('Agent panes coming in BooCoder');
      return;
    }
    setPanes((prev) => {
      // v1.9: settings panes are excluded from the MAX cap (decision c).
      if (nonSettingsCount(prev) >= MAX_PANES) {
        toast.error(`Maximum ${MAX_PANES} panes`);
        return prev;
      }
      const next = [...prev, emptyPane()];
      setActivePaneIdx(next.length - 1);
      return next;
    });
  }, []);

  const openOrFocusSettingsPane = useCallback(() => {
    setPanes((prev) => {
      const existingIdx = prev.findIndex((p) => p.kind === 'settings');
      if (existingIdx >= 0) {
        setActivePaneIdx(existingIdx);
        return prev;
      }
      const next = [...prev, settingsPane()];
      setActivePaneIdx(next.length - 1);
      return next;
    });
  }, []);

  const removePane = useCallback((idx: number) => {
    setPanes((prev) => {
      if (prev.length <= 1) return prev;
      const next = prev.filter((_, i) => i !== idx);
      setActivePaneIdx((ai) => Math.min(ai, next.length - 1));
      return next;
    });
  }, []);

  // Replaces a single empty default pane with a chat pane. Used by the initial
  // chat fetch to land on the most-recent open chat if no saved pane state.
  const initializeFirstChatIfEmpty = useCallback((chatId: string) => {
    setPanes((prev) => {
      if (prev.length === 1 && prev[0]!.kind === 'empty') {
        return [chatPane(chatId)];
      }
      return prev;
    });
  }, []);

  const removeChatFromPanes = useCallback((chatId: string) => {
    setPanes((prev) => prev.map((p) => {
      const idx = p.chatIds.indexOf(chatId);
      if (idx < 0) return p;
      const nextIds = p.chatIds.filter((id) => id !== chatId);
      if (nextIds.length === 0) {
        return { ...p, kind: 'empty' as const, chatId: undefined, chatIds: [], activeChatIdx: -1 };
      }
      const nextActiveIdx = Math.min(p.activeChatIdx, nextIds.length - 1);
      return {
        ...p,
        chatIds: nextIds,
        activeChatIdx: nextActiveIdx,
        chatId: nextIds[nextActiveIdx],
      };
    }));
  }, []);

  const handlePaneDragStart = useCallback(
    (idx: number) => (e: DragEvent<HTMLDivElement>) => {
      draggingIdxRef.current = idx;
      e.dataTransfer.effectAllowed = 'move';
      e.dataTransfer.setData('text/plain', String(idx));
    },
    []
  );

  const handlePaneDragOver = useCallback(
    (idx: number) => (e: DragEvent<HTMLDivElement>) => {
      if (draggingIdxRef.current === null) return;
      e.preventDefault();
      e.dataTransfer.dropEffect = 'move';
      if (dragOverIdx !== idx) setDragOverIdx(idx);
    },
    [dragOverIdx]
  );

  const handlePaneDragLeave = useCallback(() => {
    setDragOverIdx(null);
  }, []);

  const handlePaneDrop = useCallback(
    (targetIdx: number) => (e: DragEvent<HTMLDivElement>) => {
      e.preventDefault();
      const fromIdx = draggingIdxRef.current;
      draggingIdxRef.current = null;
      setDragOverIdx(null);
      if (fromIdx === null || fromIdx === targetIdx) return;
      setPanes((prev) => {
        const next = [...prev];
        const [moved] = next.splice(fromIdx, 1);
        if (!moved) return prev;
        next.splice(targetIdx, 0, moved);
        // Keep active selection on the same logical pane (the one being dragged).
        setActivePaneIdx(targetIdx);
        return next;
      });
    },
    []
  );

  const handlePaneDragEnd = useCallback(() => {
    draggingIdxRef.current = null;
    setDragOverIdx(null);
  }, []);

  return {
    panes,
    activePaneIdx,
    setActivePaneIdx,
    activePaneIdxRef,
    openChatInPane,
    openOrFocusSettingsPane,
    switchTab,
    removeTab,
    closeOtherTabs,
    closeTabsToRight,
    closeAllTabs,
    showLandingPage,
    addSplitPane,
    removePane,
    removeChatFromPanes,
    initializeFirstChatIfEmpty,
    handlePaneDragStart,
    handlePaneDragOver,
    handlePaneDragLeave,
    handlePaneDrop,
    handlePaneDragEnd,
    dragOverIdx,
    draggingIdxRef,
  };
}