"use client";

import React, {
  type ComponentType,
  type ErrorInfo,
  type ReactNode,
  useCallback,
  useEffect,
  useMemo,
  useRef,
} from "react";
import type {
  UIElement,
  Spec,
  ActionBinding,
  Catalog,
  SchemaDefinition,
  StateStore,
  ComputedFunction,
} from "@json-render/core";
import {
  resolveElementProps,
  resolveBindings,
  resolveActionParam,
  evaluateVisibility,
  getByPath,
  type PropResolutionContext,
  type VisibilityContext as CoreVisibilityContext,
} from "@json-render/core";
import type {
  Components,
  Actions,
  ActionFn,
  SetState,
  StateModel,
  CatalogHasActions,
  EventHandle,
} from "./catalog-types";
import { useIsVisible, useVisibility } from "./contexts/visibility";
import { useActions } from "./contexts/actions";
import { useStateStore } from "./contexts/state";
import { StateProvider } from "./contexts/state";
import { VisibilityProvider } from "./contexts/visibility";
import { ActionProvider } from "./contexts/actions";
import { ValidationProvider } from "./contexts/validation";
import { ConfirmDialog } from "./contexts/actions";
import { RepeatScopeProvider, useRepeatScope } from "./contexts/repeat-scope";

/**
 * Props passed to component renderers
 */
export interface ComponentRenderProps<P = Record<string, unknown>> {
  /** The element being rendered */
  element: UIElement<string, P>;
  /** Rendered children */
  children?: ReactNode;
  /** Emit a named event. The renderer resolves the event to action binding(s) from the element's `on` field. Always provided by the renderer. */
  emit: (event: string) => void;
  /** Get an event handle with metadata (shouldPreventDefault, bound). Use when you need to inspect event bindings. */
  on: (event: string) => EventHandle;
  /**
   * Two-way binding paths resolved from `$bindState` / `$bindItem` expressions.
   * Maps prop name → absolute state path for write-back.
   * Only present when at least one prop uses `{ $bindState: "..." }` or `{ $bindItem: "..." }`.
   */
  bindings?: Record<string, string>;
  /** Whether the parent is loading */
  loading?: boolean;
}

/**
 * Component renderer type
 */
export type ComponentRenderer<P = Record<string, unknown>> = ComponentType<
  ComponentRenderProps<P>
>;

/**
 * Registry of component renderers
 */
export type ComponentRegistry = Record<string, ComponentRenderer<any>>;

/**
 * Props for the Renderer component
 */
export interface RendererProps {
  /** The UI spec to render */
  spec: Spec | null;
  /** Component registry */
  registry: ComponentRegistry;
  /** Whether the spec is currently loading/streaming */
  loading?: boolean;
  /** Fallback component for unknown types */
  fallback?: ComponentRenderer;
}

// ---------------------------------------------------------------------------
// ElementErrorBoundary – catches rendering errors in individual elements so
// a single bad component never crashes the whole page.
// ---------------------------------------------------------------------------

interface ElementErrorBoundaryProps {
  elementType: string;
  children: ReactNode;
}

interface ElementErrorBoundaryState {
  hasError: boolean;
}

class ElementErrorBoundary extends React.Component<
  ElementErrorBoundaryProps,
  ElementErrorBoundaryState
> {
  constructor(props: ElementErrorBoundaryProps) {
    super(props);
    this.state = { hasError: false };
  }

  static getDerivedStateFromError(): ElementErrorBoundaryState {
    return { hasError: true };
  }

  componentDidCatch(error: Error, info: ErrorInfo) {
    console.error(
      `[json-render] Rendering error in <${this.props.elementType}>:`,
      error,
      info.componentStack,
    );
  }

  render() {
    if (this.state.hasError) {
      // Render nothing – the element silently disappears rather than
      // crashing the entire application.
      return null;
    }
    return this.props.children;
  }
}

// ---------------------------------------------------------------------------
// FunctionsContext – provides $computed functions to the element tree
// ---------------------------------------------------------------------------

const EMPTY_FUNCTIONS: Record<string, ComputedFunction> = {};

const FunctionsContext =
  React.createContext<Record<string, ComputedFunction>>(EMPTY_FUNCTIONS);

function useFunctions(): Record<string, ComputedFunction> {
  return React.useContext(FunctionsContext);
}

interface ElementRendererProps {
  element: UIElement;
  spec: Spec;
  registry: ComponentRegistry;
  loading?: boolean;
  fallback?: ComponentRenderer;
}

/**
 * Element renderer component.
 * Memoized to prevent re-rendering all repeat children when state changes.
 */
const ElementRenderer = React.memo(function ElementRenderer({
  element,
  spec,
  registry,
  loading,
  fallback,
}: ElementRendererProps) {
  const repeatScope = useRepeatScope();
  const { ctx } = useVisibility();
  const { execute } = useActions();
  const { getSnapshot, state: watchState } = useStateStore();
  const functions = useFunctions();

  // Build context with repeat scope and $computed functions
  const fullCtx: PropResolutionContext = useMemo(() => {
    const base: PropResolutionContext = repeatScope
      ? {
          ...ctx,
          repeatItem: repeatScope.item,
          repeatIndex: repeatScope.index,
          repeatBasePath: repeatScope.basePath,
        }
      : { ...ctx };
    base.functions = functions;
    return base;
  }, [ctx, repeatScope, functions]);

  // Evaluate visibility (now supports $item/$index inside repeat scopes)
  const isVisible =
    element.visible === undefined
      ? true
      : evaluateVisibility(element.visible, fullCtx);

  // Create emit function that resolves events to action bindings.
  // Must be called before any early return to satisfy Rules of Hooks.
  const onBindings = element.on;
  const emit = useCallback(
    async (eventName: string) => {
      const binding = onBindings?.[eventName];
      if (!binding) return;
      const actionBindings = Array.isArray(binding) ? binding : [binding];
      for (const b of actionBindings) {
        if (!b.params) {
          await execute(b);
          continue;
        }
        // Build a fresh context with live store state so that $state
        // references in later actions see mutations from earlier ones.
        const liveCtx: PropResolutionContext = {
          ...fullCtx,
          stateModel: getSnapshot(),
        };
        const resolved: Record<string, unknown> = {};
        for (const [key, val] of Object.entries(b.params)) {
          resolved[key] = resolveActionParam(val, liveCtx);
        }
        await execute({ ...b, params: resolved });
      }
    },
    [onBindings, execute, fullCtx, getSnapshot],
  );

  // Create on() function that returns an EventHandle with metadata for a specific event.
  const on = useCallback(
    (eventName: string): EventHandle => {
      const binding = onBindings?.[eventName];
      if (!binding) {
        return { emit: () => {}, shouldPreventDefault: false, bound: false };
      }
      const actionBindings = Array.isArray(binding) ? binding : [binding];
      const shouldPreventDefault = actionBindings.some((b) => b.preventDefault);
      return {
        emit: () => emit(eventName),
        shouldPreventDefault,
        bound: true,
      };
    },
    [onBindings, emit],
  );

  // Watch effect: fire actions when watched state paths change.
  // Must be called before any early return to satisfy Rules of Hooks.
  //
  // Two refs serve distinct roles:
  // - `stableWatchRef` (useMemo): holds the last emitted values object so we
  //   can return the same reference when watched values haven't changed,
  //   preventing the downstream useEffect from firing on unrelated state updates.
  // - `prevWatchValues` (useEffect): tracks the previous watched-values snapshot
  //   for change detection. Starts as `null` to skip the initial mount.
  const watchConfig = element.watch;
  const prevWatchValues = useRef<Record<string, unknown> | null>(null);
  const stableWatchRef = useRef<Record<string, unknown> | undefined>(undefined);

  const watchedValues = useMemo(() => {
    if (!watchConfig) return undefined;
    const values: Record<string, unknown> = {};
    for (const path of Object.keys(watchConfig)) {
      values[path] = getByPath(watchState, path);
    }
    const prev = stableWatchRef.current;
    if (prev) {
      const keys = Object.keys(values);
      if (
        keys.length === Object.keys(prev).length &&
        keys.every((k) => values[k] === prev[k])
      ) {
        return prev;
      }
    }
    stableWatchRef.current = values;
    return values;
  }, [watchConfig, watchState]);

  useEffect(() => {
    if (!watchConfig || !watchedValues) return;
    const paths = Object.keys(watchConfig);
    if (paths.length === 0) return;

    const prev = prevWatchValues.current;
    prevWatchValues.current = watchedValues;

    // Skip the initial mount — only fire on changes
    if (prev === null) return;

    let cancelled = false;
    void (async () => {
      for (const path of paths) {
        if (cancelled) break;
        if (watchedValues[path] !== prev[path]) {
          const binding = watchConfig[path];
          if (!binding) continue;
          const bindings = Array.isArray(binding) ? binding : [binding];
          for (const b of bindings) {
            if (cancelled) break;
            if (!b.params) {
              await execute(b);
              if (cancelled) break;
              continue;
            }
            const liveCtx: PropResolutionContext = {
              ...fullCtx,
              stateModel: getSnapshot(),
            };
            const resolved: Record<string, unknown> = {};
            for (const [key, val] of Object.entries(b.params)) {
              resolved[key] = resolveActionParam(val, liveCtx);
            }
            await execute({ ...b, params: resolved });
            if (cancelled) break;
          }
        }
      }
    })().catch(console.error);

    return () => {
      cancelled = true;
    };
  }, [watchConfig, watchedValues, execute, fullCtx, getSnapshot]);

  // Don't render if not visible
  if (!isVisible) {
    return null;
  }

  // Resolve $bindState/$bindItem expressions → bindings map (prop name → state path)
  const rawProps = element.props as Record<string, unknown>;
  const elementBindings = resolveBindings(rawProps, fullCtx);

  // Resolve dynamic prop expressions ($state, $item, $index, $bindState, $bindItem, $cond/$then/$else)
  const resolvedProps = resolveElementProps(rawProps, fullCtx);

  const resolvedElement =
    resolvedProps !== element.props
      ? { ...element, props: resolvedProps }
      : element;

  // Get the component renderer
  const Component = registry[resolvedElement.type] ?? fallback;

  if (!Component) {
    console.warn(`No renderer for component type: ${resolvedElement.type}`);
    return null;
  }

  // ---- Render children (with repeat support) ----
  const children = resolvedElement.repeat ? (
    <RepeatChildren
      element={resolvedElement}
      spec={spec}
      registry={registry}
      loading={loading}
      fallback={fallback}
    />
  ) : (
    resolvedElement.children?.map((childKey) => {
      const childElement = spec.elements[childKey];
      if (!childElement) {
        if (!loading) {
          console.warn(
            `[json-render] Missing element "${childKey}" referenced as child of "${resolvedElement.type}". This element will not render.`,
          );
        }
        return null;
      }
      return (
        <ElementRenderer
          key={childKey}
          element={childElement}
          spec={spec}
          registry={registry}
          loading={loading}
          fallback={fallback}
        />
      );
    })
  );

  return (
    <ElementErrorBoundary elementType={resolvedElement.type}>
      <Component
        element={resolvedElement}
        emit={emit}
        on={on}
        bindings={elementBindings}
        loading={loading}
      >
        {children}
      </Component>
    </ElementErrorBoundary>
  );
});

// ---------------------------------------------------------------------------
// RepeatChildren -- renders child elements once per item in a state array.
// Used when an element has a `repeat` field.
// ---------------------------------------------------------------------------

function RepeatChildren({
  element,
  spec,
  registry,
  loading,
  fallback,
}: {
  element: UIElement;
  spec: Spec;
  registry: ComponentRegistry;
  loading?: boolean;
  fallback?: ComponentRenderer;
}) {
  const { state } = useStateStore();
  const repeat = element.repeat!;
  const statePath = repeat.statePath;

  const items = (getByPath(state, statePath) as unknown[] | undefined) ?? [];

  return (
    <>
      {items.map((itemValue, index) => {
        // Use a stable key: prefer key field, fall back to index
        const key =
          repeat.key && typeof itemValue === "object" && itemValue !== null
            ? String(
                (itemValue as Record<string, unknown>)[repeat.key] ?? index,
              )
            : String(index);

        return (
          <RepeatScopeProvider
            key={key}
            item={itemValue}
            index={index}
            basePath={`${statePath}/${index}`}
          >
            {element.children?.map((childKey) => {
              const childElement = spec.elements[childKey];
              if (!childElement) {
                if (!loading) {
                  console.warn(
                    `[json-render] Missing element "${childKey}" referenced as child of "${element.type}" (repeat). This element will not render.`,
                  );
                }
                return null;
              }
              return (
                <ElementRenderer
                  key={childKey}
                  element={childElement}
                  spec={spec}
                  registry={registry}
                  loading={loading}
                  fallback={fallback}
                />
              );
            })}
          </RepeatScopeProvider>
        );
      })}
    </>
  );
}

/**
 * Main renderer component
 */
export function Renderer({ spec, registry, loading, fallback }: RendererProps) {
  if (!spec || !spec.root) {
    return null;
  }

  const rootElement = spec.elements[spec.root];
  if (!rootElement) {
    return null;
  }

  return (
    <ElementRenderer
      element={rootElement}
      spec={spec}
      registry={registry}
      loading={loading}
      fallback={fallback}
    />
  );
}

/**
 * Props for JSONUIProvider
 */
export interface JSONUIProviderProps {
  /** Component registry */
  registry: ComponentRegistry;
  /**
   * External store (controlled mode). When provided, `initialState` and
   * `onStateChange` are ignored.
   */
  store?: StateStore;
  /** Initial state model (uncontrolled mode) */
  initialState?: Record<string, unknown>;
  /** Action handlers */
  handlers?: Record<
    string,
    (params: Record<string, unknown>) => Promise<unknown> | unknown
  >;
  /** Navigation function */
  navigate?: (path: string) => void;
  /** Custom validation functions */
  validationFunctions?: Record<
    string,
    (value: unknown, args?: Record<string, unknown>) => boolean
  >;
  /** Named functions for `$computed` expressions in props */
  functions?: Record<string, ComputedFunction>;
  /** Callback when state changes (uncontrolled mode) */
  onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
  children: ReactNode;
}

/**
 * Combined provider for all JSONUI contexts
 */
export function JSONUIProvider({
  registry,
  store,
  initialState,
  handlers,
  navigate,
  validationFunctions,
  functions,
  onStateChange,
  children,
}: JSONUIProviderProps) {
  return (
    <StateProvider
      store={store}
      initialState={initialState}
      onStateChange={onStateChange}
    >
      <VisibilityProvider>
        <ValidationProvider customFunctions={validationFunctions}>
          <ActionProvider handlers={handlers} navigate={navigate}>
            <FunctionsContext.Provider value={functions ?? EMPTY_FUNCTIONS}>
              {children}
              <ConfirmationDialogManager />
            </FunctionsContext.Provider>
          </ActionProvider>
        </ValidationProvider>
      </VisibilityProvider>
    </StateProvider>
  );
}

/**
 * Renders the confirmation dialog when needed
 */
function ConfirmationDialogManager() {
  const { pendingConfirmation, confirm, cancel } = useActions();

  if (!pendingConfirmation?.action.confirm) {
    return null;
  }

  return (
    <ConfirmDialog
      confirm={pendingConfirmation.action.confirm}
      onConfirm={confirm}
      onCancel={cancel}
    />
  );
}

// ============================================================================
// defineRegistry
// ============================================================================

/**
 * Result returned by defineRegistry
 */
export interface DefineRegistryResult {
  /** Component registry for `<Renderer registry={...} />` */
  registry: ComponentRegistry;
  /**
   * Create ActionProvider-compatible handlers.
   * Accepts getter functions so handlers always read the latest state/setState
   * (e.g. from React refs).
   */
  handlers: (
    getSetState: () => SetState | undefined,
    getState: () => StateModel,
  ) => Record<string, (params: Record<string, unknown>) => Promise<void>>;
  /**
   * Execute an action by name imperatively
   * (for use outside the React tree, e.g. initial state loading).
   */
  executeAction: (
    actionName: string,
    params: Record<string, unknown> | undefined,
    setState: SetState,
    state?: StateModel,
  ) => Promise<void>;
}

/**
 * Options for defineRegistry.
 *
 * When the catalog declares actions, the `actions` field is required.
 * When the catalog has no actions (or `actions: {}`), the field is optional.
 */
type DefineRegistryOptions<C extends Catalog> = {
  components?: Components<C>;
} & (CatalogHasActions<C> extends true
  ? { actions: Actions<C> }
  : { actions?: Actions<C> });

/**
 * Create a registry from a catalog with components and/or actions.
 *
 * When the catalog declares actions, the `actions` field is required.
 *
 * @example
 * ```tsx
 * // Components only (catalog has no actions)
 * const { registry } = defineRegistry(catalog, {
 *   components: {
 *     Card: ({ props, children }) => (
 *       <div className="card">{props.title}{children}</div>
 *     ),
 *   },
 * });
 *
 * // Both (catalog declares actions)
 * const { registry, handlers, executeAction } = defineRegistry(catalog, {
 *   components: { ... },
 *   actions: { ... },
 * });
 * ```
 */
export function defineRegistry<C extends Catalog>(
  _catalog: C,
  options: DefineRegistryOptions<C>,
): DefineRegistryResult {
  // Build component registry
  const registry: ComponentRegistry = {};
  if (options.components) {
    for (const [name, componentFn] of Object.entries(options.components)) {
      registry[name] = ({
        element,
        children,
        emit,
        on,
        bindings,
        loading,
      }: ComponentRenderProps) => {
        return (componentFn as DefineRegistryComponentFn)({
          props: element.props,
          children,
          emit,
          on,
          bindings,
          loading,
        });
      };
    }
  }

  // Build action helpers
  const actionMap = options.actions
    ? (Object.entries(options.actions) as Array<
        [string, DefineRegistryActionFn]
      >)
    : [];

  const handlers = (
    getSetState: () => SetState | undefined,
    getState: () => StateModel,
  ): Record<string, (params: Record<string, unknown>) => Promise<void>> => {
    const result: Record<
      string,
      (params: Record<string, unknown>) => Promise<void>
    > = {};
    for (const [name, actionFn] of actionMap) {
      result[name] = async (params) => {
        const setState = getSetState();
        const state = getState();
        if (setState) {
          await actionFn(params, setState, state);
        }
      };
    }
    return result;
  };

  const executeAction = async (
    actionName: string,
    params: Record<string, unknown> | undefined,
    setState: SetState,
    state: StateModel = {},
  ): Promise<void> => {
    const entry = actionMap.find(([name]) => name === actionName);
    if (entry) {
      await entry[1](params, setState, state);
    } else {
      console.warn(`Unknown action: ${actionName}`);
    }
  };

  return { registry, handlers, executeAction };
}

/** @internal */
type DefineRegistryComponentFn = (ctx: {
  props: unknown;
  children?: React.ReactNode;
  emit: (event: string) => void;
  on: (event: string) => EventHandle;
  bindings?: Record<string, string>;
  loading?: boolean;
}) => React.ReactNode;

/** @internal */
type DefineRegistryActionFn = (
  params: Record<string, unknown> | undefined,
  setState: SetState,
  state: StateModel,
) => Promise<void>;

// ============================================================================
// NEW API
// ============================================================================

/**
 * Props for renderers created with createRenderer
 */
export interface CreateRendererProps {
  /** The spec to render (AI-generated JSON) */
  spec: Spec | null;
  /**
   * External store (controlled mode). When provided, `state` and
   * `onStateChange` are ignored.
   */
  store?: StateStore;
  /** State context for dynamic values (uncontrolled mode) */
  state?: Record<string, unknown>;
  /** Action handler */
  onAction?: (actionName: string, params?: Record<string, unknown>) => void;
  /** Callback when state changes (uncontrolled mode) */
  onStateChange?: (changes: Array<{ path: string; value: unknown }>) => void;
  /** Named functions for `$computed` expressions in props */
  functions?: Record<string, ComputedFunction>;
  /** Whether the spec is currently loading/streaming */
  loading?: boolean;
  /** Fallback component for unknown types */
  fallback?: ComponentRenderer;
}

/**
 * Component map type - maps component names to React components
 */
export type ComponentMap<
  TComponents extends Record<string, { props: unknown }>,
> = {
  [K in keyof TComponents]: ComponentType<
    ComponentRenderProps<
      TComponents[K]["props"] extends { _output: infer O }
        ? O
        : Record<string, unknown>
    >
  >;
};

/**
 * Create a renderer from a catalog
 *
 * @example
 * ```typescript
 * const DashboardRenderer = createRenderer(dashboardCatalog, {
 *   Card: ({ element, children }) => <div className="card">{children}</div>,
 *   Metric: ({ element }) => <span>{element.props.value}</span>,
 * });
 *
 * // Usage
 * <DashboardRenderer spec={aiGeneratedSpec} state={state} />
 * ```
 */
export function createRenderer<
  TDef extends SchemaDefinition,
  TCatalog extends { components: Record<string, { props: unknown }> },
>(
  catalog: Catalog<TDef, TCatalog>,
  components: ComponentMap<TCatalog["components"]>,
): ComponentType<CreateRendererProps> {
  // Convert component map to registry
  const registry: ComponentRegistry =
    components as unknown as ComponentRegistry;

  // Return the renderer component
  return function CatalogRenderer({
    spec,
    store,
    state,
    onAction,
    onStateChange,
    functions,
    loading,
    fallback,
  }: CreateRendererProps) {
    // Wrap onAction with a Proxy so any action name routes to the callback
    const actionHandlers = onAction
      ? new Proxy(
          {} as Record<
            string,
            (params: Record<string, unknown>) => void | Promise<void>
          >,
          {
            get: (_target, prop: string) => {
              return (params: Record<string, unknown>) =>
                onAction(prop, params);
            },
            has: () => true,
          },
        )
      : undefined;

    return (
      <StateProvider
        store={store}
        initialState={state}
        onStateChange={onStateChange}
      >
        <VisibilityProvider>
          <ValidationProvider>
            <ActionProvider handlers={actionHandlers}>
              <FunctionsContext.Provider value={functions ?? EMPTY_FUNCTIONS}>
                <Renderer
                  spec={spec}
                  registry={registry}
                  loading={loading}
                  fallback={fallback}
                />
                <ConfirmationDialogManager />
              </FunctionsContext.Provider>
            </ActionProvider>
          </ValidationProvider>
        </VisibilityProvider>
      </StateProvider>
    );
  };
}