import { useCallback, useRef } from "react";
import type { AgentGUINodeData } from "../../../types";
import type { AgentGUIConversationSummary } from "../model/agentGuiConversationModel";
import type { AgentGUIConversationRailRevealReason } from "../model/agentGuiConversationRailViewState";
import { rememberAgentGUIActiveConversation } from "../model/agentGuiSessionNavigationMemory";

export type ConversationIntent =
  | { tag: "home" }
  | { tag: "requested"; id: string }
  | {
      tag: "active";
      id: string;
      source?: "activation" | "user-selection";
    };

export interface AgentGUIConversationSelectionOptions {
  reloadConversations?: boolean;
  reveal?: Extract<AgentGUIConversationRailRevealReason, "external-open">;
}

export function resolveConversationSummaryById(
  conversations: readonly AgentGUIConversationSummary[],
  conversationId: string | null | undefined,
  transientConversation: AgentGUIConversationSummary | null = null
): AgentGUIConversationSummary | null {
  const normalized = conversationId?.trim() ?? "";
  if (!normalized) return null;
  return (
    conversations.find((conversation) => conversation.id === normalized) ??
    (transientConversation?.id === normalized ? transientConversation : null)
  );
}

interface AgentConversationSelectionInput {
  activation: {
    canReload(agentSessionId: string): boolean;
    forget(agentSessionId: string): void;
    isPending(agentSessionId: string): boolean;
  };
  conversations: {
    agentTargetIdFor(agentSessionId: string): string | null;
    contains(agentSessionId: string): boolean;
  };
  detail: {
    ensureHydrated(agentSessionId: string): void;
    ensureStateHydrated(agentSessionId: string): void;
    isHydrated(agentSessionId: string): boolean;
    isStateHydrated(agentSessionId: string): boolean;
    markPending(agentSessionId: string): void;
    setLoading(loading: boolean): void;
  };
  hasConversationListQuery(): boolean;
  isMounted(): boolean;
  onMissingConversationListQuery(previousAgentSessionId: string | null): void;
  persistence: {
    update(updater: (current: AgentGUINodeData) => AgentGUINodeData): void;
  };
  rail: {
    clearRevealRequest(): void;
    requestReveal(
      agentSessionId: string,
      reason: AgentGUIConversationRailRevealReason
    ): void;
  };
  selection: {
    clearDetailError(): void;
    getActiveSessionId(): string | null;
    setActiveSessionId(agentSessionId: string | null): void;
    setComposerHome(home: boolean): void;
    setIntent(intent: ConversationIntent): void;
  };
}

export function useAgentConversationSelection(
  input: AgentConversationSelectionInput
) {
  const inputRef = useRef(input);
  inputRef.current = input;

  const persistActiveConversation = useCallback(
    (agentSessionId: string | null, agentTargetId?: string | null) => {
      inputRef.current.persistence.update((current) => {
        const resolvedAgentTargetId = agentSessionId
          ? agentTargetId?.trim() ||
            inputRef.current.conversations.agentTargetIdFor(agentSessionId)
          : null;
        return rememberAgentGUIActiveConversation(
          current,
          agentSessionId,
          resolvedAgentTargetId
        );
      });
    },
    []
  );

  const syncConversationListProjection = useCallback(
    async (_preferredSessionId?: string | null) => {
      const current = inputRef.current;
      if (current.hasConversationListQuery()) return;
      const previous = current.selection.getActiveSessionId();
      current.onMissingConversationListQuery(previous);
      current.selection.setIntent({ tag: "home" });
      current.selection.setComposerHome(true);
      current.selection.setActiveSessionId(null);
      current.detail.setLoading(false);
      current.selection.clearDetailError();
      current.rail.clearRevealRequest();
      persistActiveConversation(null);
    },
    [persistActiveConversation]
  );

  const selectConversation = useCallback(
    (
      agentSessionId: string,
      options?: AgentGUIConversationSelectionOptions
    ) => {
      const normalized = agentSessionId.trim();
      if (!normalized) return;
      const current = inputRef.current;
      const previous = current.selection.getActiveSessionId();
      const detailHydrated = current.detail.isHydrated(normalized);
      const stateHydrated = current.detail.isStateHydrated(normalized);
      const activationPending = current.activation.isPending(normalized);
      current.selection.setComposerHome(false);
      if (previous && previous !== normalized)
        current.activation.forget(previous);
      if (previous !== normalized) {
        if (detailHydrated || activationPending) {
          current.detail.setLoading(false);
        } else {
          current.detail.markPending(normalized);
        }
      }
      const reloadConversations =
        options?.reloadConversations !== false &&
        current.conversations.contains(normalized);
      current.selection.setIntent({
        id: normalized,
        source: "user-selection",
        tag: "active"
      });
      current.selection.setActiveSessionId(normalized);
      current.selection.clearDetailError();
      if (options?.reveal) {
        current.rail.requestReveal(normalized, options.reveal);
      } else {
        current.rail.clearRevealRequest();
      }
      if (!activationPending && current.activation.canReload(normalized)) {
        if (reloadConversations) {
          void syncConversationListProjection(normalized);
        }
        if (!detailHydrated) {
          current.detail.ensureHydrated(normalized);
        } else if (!stateHydrated) {
          current.detail.ensureStateHydrated(normalized);
        }
      }
      persistActiveConversation(normalized);
    },
    [persistActiveConversation, syncConversationListProjection]
  );

  const isCurrentConversation = useCallback(
    (agentSessionId: string) =>
      inputRef.current.isMounted() &&
      inputRef.current.selection.getActiveSessionId() === agentSessionId.trim(),
    []
  );
  const isConversationStale = useCallback(
    (agentSessionId: string) => {
      const normalized = agentSessionId.trim();
      return Boolean(normalized && !isCurrentConversation(normalized));
    },
    [isCurrentConversation]
  );

  return {
    isCurrentConversation,
    isConversationStale,
    persistActiveConversation,
    selectConversation,
    syncConversationListProjection
  };
}