'use client';

import * as React from 'react';
import * as Slot from 'radix-ui/slot';
import {
  Controller,
  FormProvider,
  useFormContext,
  useFormState,
  type ControllerProps,
  type FieldPath,
  type FieldValues,
} from 'react-hook-form';

import { cn } from '@/lib/utils';
import { Label } from '@/components/label/label';

/**
 * react-hook-form bindings.
 *
 * `react-hook-form` is an **optional peer dependency** — install it in your app
 * if you import from this subpath. Everything else in the kit works without it.
 *
 * The value here is the wiring, not the styling: `FormControl` links the input
 * to its label, description and error message via `aria-describedby` and sets
 * `aria-invalid`, so validation state is announced instead of only being shown.
 *
 * ```tsx
 * const form = useForm<Values>({ resolver: zodResolver(schema) });
 *
 * <Form {...form}>
 *   <form onSubmit={form.handleSubmit(onSubmit)}>
 *     <FormField
 *       control={form.control}
 *       name="email"
 *       render={({ field }) => (
 *         <FormItem>
 *           <FormLabel>Email</FormLabel>
 *           <FormControl><Input {...field} /></FormControl>
 *           <FormDescription>We never share it.</FormDescription>
 *           <FormMessage />
 *         </FormItem>
 *       )}
 *     />
 *   </form>
 * </Form>
 * ```
 */
const Form = FormProvider;

type FormFieldContextValue<
  TFieldValues extends FieldValues = FieldValues,
  TName extends FieldPath<TFieldValues> = FieldPath<TFieldValues>,
> = {
  name: TName;
};

const FormFieldContext = React.createContext<FormFieldContextValue | null>(null);

type FormItemContextValue = {
  id: string;
};

const FormItemContext = React.createContext<FormItemContextValue | null>(null);

const FormField = <
  TFieldValues extends FieldValues = FieldValues,
  TName extends FieldPath<TFieldValues> = FieldPath<TFieldValues>,
>(
  props: ControllerProps<TFieldValues, TName>
) => {
  return (
    <FormFieldContext.Provider value={{ name: props.name }}>
      <Controller {...props} />
    </FormFieldContext.Provider>
  );
};

/**
 * Reads the ids and validation state of the enclosing field. Throws with a
 * useful message rather than failing silently when used out of context.
 */
const useFormField = () => {
  const fieldContext = React.useContext(FormFieldContext);
  const itemContext = React.useContext(FormItemContext);
  const { getFieldState } = useFormContext();

  if (!fieldContext) {
    throw new Error('useFormField must be used within a <FormField>');
  }
  if (!itemContext) {
    throw new Error('useFormField must be used within a <FormItem>');
  }

  const formState = useFormState({ name: fieldContext.name });
  const fieldState = getFieldState(fieldContext.name, formState);
  const { id } = itemContext;

  return {
    id,
    name: fieldContext.name,
    formItemId: `${id}-form-item`,
    formDescriptionId: `${id}-form-item-description`,
    formMessageId: `${id}-form-item-message`,
    ...fieldState,
  };
};

function FormItem({ className, ...props }: React.ComponentProps<'div'>) {
  const id = React.useId();

  return (
    <FormItemContext.Provider value={{ id }}>
      <div data-slot="form-item" className={cn('grid gap-2', className)} {...props} />
    </FormItemContext.Provider>
  );
}

function FormLabel({ className, ...props }: React.ComponentProps<typeof Label>) {
  const { error, formItemId } = useFormField();

  return (
    <Label
      data-slot="form-label"
      data-error={!!error}
      className={cn('data-[error=true]:text-destructive', className)}
      htmlFor={formItemId}
      {...props}
    />
  );
}

/** Wraps the actual input and connects it to the label, hint and error. */
function FormControl(props: React.ComponentProps<typeof Slot.Root>) {
  const { error, formItemId, formDescriptionId, formMessageId } = useFormField();

  return (
    <Slot.Root
      data-slot="form-control"
      id={formItemId}
      aria-describedby={error ? `${formDescriptionId} ${formMessageId}` : formDescriptionId}
      aria-invalid={!!error}
      {...props}
    />
  );
}

function FormDescription({ className, ...props }: React.ComponentProps<'p'>) {
  const { formDescriptionId } = useFormField();

  return (
    <p
      data-slot="form-description"
      id={formDescriptionId}
      className={cn('text-sm text-muted-foreground', className)}
      {...props}
    />
  );
}

/** Renders the field's validation error, or its children when there is none. */
function FormMessage({ className, children, ...props }: React.ComponentProps<'p'>) {
  const { error, formMessageId } = useFormField();
  const body = error ? String(error?.message ?? '') : children;

  if (!body) return null;

  return (
    <p
      data-slot="form-message"
      id={formMessageId}
      className={cn('text-sm text-destructive', className)}
      {...props}
    >
      {body}
    </p>
  );
}

export {
  useFormField,
  Form,
  FormItem,
  FormLabel,
  FormControl,
  FormDescription,
  FormMessage,
  FormField,
};