import { useState, useEffect, useCallback } from 'react';

/**
 * Form Validation Hooks
 * Provides validation logic and utilities for form components
 */

export interface ValidationRule {
  value: any;
  message: string;
}

export interface ValidationRules {
  required?: boolean | string;
  minLength?: ValidationRule;
  maxLength?: ValidationRule;
  pattern?: ValidationRule;
  min?: ValidationRule;
  max?: ValidationRule;
  email?: boolean | string;
  url?: boolean | string;
  number?: boolean | string;
  custom?: (value: any) => string | null;
}

export interface ValidationError {
  field: string;
  message: string;
}

export interface FormErrors {
  [key: string]: string[];
}

/**
 * Validates a single field value against validation rules
 */
export function validateField(
  value: any,
  rules: ValidationRules,
  fieldName: string
): string[] {
  const errors: string[] = [];

  // Required validation
  if (rules.required) {
    const requiredMessage = typeof rules.required === 'string'
      ? rules.required
      : `${fieldName} is required`;
    
    if (value === null || value === undefined || value === '') {
      errors.push(requiredMessage);
    }
  }

  // Only validate other rules if there's a value (unless required)
  if (value === null || value === undefined || value === '') {
    return errors;
  }

  // Min length validation
  if (rules.minLength) {
    const min = rules.minLength.value;
    const message = rules.minLength.message || `${fieldName} must be at least ${min} characters`;
    
    if (typeof value === 'string' && value.length < min) {
      errors.push(message);
    }
  }

  // Max length validation
  if (rules.maxLength) {
    const max = rules.maxLength.value;
    const message = rules.maxLength.message || `${fieldName} must be at most ${max} characters`;
    
    if (typeof value === 'string' && value.length > max) {
      errors.push(message);
    }
  }

  // Pattern validation
  if (rules.pattern) {
    const pattern = rules.pattern.value;
    const message = rules.pattern.message || `${fieldName} format is invalid`;
    
    if (typeof value === 'string' && !pattern.test(value)) {
      errors.push(message);
    }
  }

  // Min value validation
  if (rules.min) {
    const min = rules.min.value;
    const message = rules.min.message || `${fieldName} must be at least ${min}`;
    
    if (typeof value === 'number' && value < min) {
      errors.push(message);
    }
  }

  // Max value validation
  if (rules.max) {
    const max = rules.max.value;
    const message = rules.max.message || `${fieldName} must be at most ${max}`;
    
    if (typeof value === 'number' && value > max) {
      errors.push(message);
    }
  }

  // Email validation
  if (rules.email) {
    const message = typeof rules.email === 'string'
      ? rules.email
      : 'Please enter a valid email address';
    
    const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
    if (typeof value === 'string' && !emailRegex.test(value)) {
      errors.push(message);
    }
  }

  // URL validation
  if (rules.url) {
    const message = typeof rules.url === 'string'
      ? rules.url
      : 'Please enter a valid URL';
    
    try {
      new URL(value);
    } catch {
      errors.push(message);
    }
  }

  // Number validation
  if (rules.number) {
    const message = typeof rules.number === 'string'
      ? rules.number
      : 'Please enter a valid number';
    
    if (isNaN(Number(value))) {
      errors.push(message);
    }
  }

  // Custom validation
  if (rules.custom) {
    const customError = rules.custom(value);
    if (customError) {
      errors.push(customError);
    }
  }

  return errors;
}

/**
 * Validates an entire form against validation rules
 */
export function validateForm<T extends Record<string, any>>(
  values: T,
  validationRules: Record<keyof T, ValidationRules>
): { isValid: boolean; errors: FormErrors } {
  const errors: FormErrors = {};
  let isValid = true;

  Object.keys(validationRules).forEach((fieldName) => {
    const fieldRules = validationRules[fieldName as keyof T];
    const fieldValue = values[fieldName];
    const fieldErrors = validateField(fieldValue, fieldRules, fieldName);

    if (fieldErrors.length > 0) {
      errors[fieldName] = fieldErrors;
      isValid = false;
    }
  });

  return { isValid, errors };
}

/**
 * Hook for form validation
 */
export function useFormValidation<T extends Record<string, any>>(
  initialValues: T,
  validationRules: Record<keyof T, ValidationRules>
) {
  const [values, setValues] = useState<T>(initialValues);
  const [errors, setErrors] = useState<FormErrors>({});
  const [touched, setTouched] = useState<Record<keyof T, boolean>>(
    Object.keys(initialValues).reduce((acc, key) => {
      acc[key as keyof T] = false;
      return acc;
    }, {} as Record<keyof T, boolean>)
  );
  const [isValid, setIsValid] = useState(false);

  const validate = useCallback(() => {
    const validation = validateForm(values, validationRules);
    setErrors(validation.errors);
    setIsValid(validation.isValid);
    return validation;
  }, [values, validationRules]);

  useEffect(() => {
    validate();
  }, [validate]);

  const setFieldValue = (field: keyof T, value: any) => {
    setValues((prev) => ({ ...prev, [field]: value }));
    setTouched((prev) => ({ ...prev, [field]: true }));
  };

  const setFieldError = (field: keyof T, error: string) => {
    setErrors((prev) => ({
      ...prev,
      [field]: [...(prev[field as string] || []), error],
    }));
  };

  const clearFieldError = (field: keyof T) => {
    setErrors((prev) => {
      const newErrors = { ...prev };
      delete newErrors[field as string];
      return newErrors;
    });
  };

  const reset = () => {
    setValues(initialValues);
    setErrors({});
    setTouched(
      Object.keys(initialValues).reduce((acc, key) => {
        acc[key as keyof T] = false;
        return acc;
      }, {} as Record<keyof T, boolean>)
    );
    setIsValid(false);
  };

  const setAllTouched = () => {
    setTouched(
      Object.keys(values).reduce((acc, key) => {
        acc[key as keyof T] = true;
        return acc;
      }, {} as Record<keyof T, boolean>)
    );
  };

  return {
    values,
    errors,
    touched,
    isValid,
    setFieldValue,
    setFieldError,
    clearFieldError,
    validate,
    reset,
    setAllTouched,
    setValues,
  };
}