/**
 * Input validation utilities for the Ultimate Lists App
 * Provides validation functions and sanitization for user inputs
 */

export interface ValidationResult {
  isValid: boolean
  error?: string
}

/**
 * Sanitize string input by trimming whitespace
 */
export function sanitizeString(input: string | null | undefined): string {
  if (input === null || input === undefined) {
    return ''
  }
  return input.trim()
}

/**
 * Validate list title
 */
export function validateListTitle(title: string): ValidationResult {
  const sanitized = sanitizeString(title)
  
  if (!sanitized) {
    return { isValid: false, error: 'List title is required' }
  }
  
  if (sanitized.length > 200) {
    return { isValid: false, error: 'List title must be less than 200 characters' }
  }
  
  return { isValid: true }
}

/**
 * Validate item/task title
 */
export function validateItemTitle(title: string): ValidationResult {
  const sanitized = sanitizeString(title)
  
  if (!sanitized) {
    return { isValid: false, error: 'Task title is required' }
  }
  
  if (sanitized.length > 200) {
    return { isValid: false, error: 'Task title must be less than 200 characters' }
  }
  
  return { isValid: true }
}

/**
 * Validate hex color format
 */
export function validateColor(color: string): ValidationResult {
  const hexColorRegex = /^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$/
  
  if (!hexColorRegex.test(color)) {
    return { isValid: false, error: 'Invalid color format. Use hex format (e.g., #3B82F6)' }
  }
  
  return { isValid: true }
}

/**
 * Validate priority value
 */
export function validatePriority(priority: string): ValidationResult {
  const validPriorities = ['low', 'medium', 'high']
  
  if (!validPriorities.includes(priority)) {
    return { isValid: false, error: 'Priority must be low, medium, or high' }
  }
  
  return { isValid: true }
}

/**
 * Validate date string format (ISO 8601 or YYYY-MM-DD)
 */
export function validateDateString(dateString: string): ValidationResult {
  if (!dateString) {
    return { isValid: true } // Empty date is valid (optional field)
  }
  
  // Try to parse the date
  const date = new Date(dateString)
  
  // Check if date is valid
  if (isNaN(date.getTime())) {
    return { isValid: false, error: 'Invalid date format. Use YYYY-MM-DD format' }
  }
  
  // Check if date is reasonable (not too far in past or future)
  const minDate = new Date('1900-01-01')
  const maxDate = new Date('2100-12-31')
  
  if (date < minDate || date > maxDate) {
    return { isValid: false, error: 'Date must be between 1900 and 2100' }
  }
  
  return { isValid: true }
}

/**
 * Validate tag string
 */
export function validateTag(tag: string): ValidationResult {
  const sanitized = sanitizeString(tag)
  
  if (!sanitized) {
    return { isValid: false, error: 'Tag cannot be empty' }
  }
  
  if (sanitized.length > 50) {
    return { isValid: false, error: 'Tag must be less than 50 characters' }
  }
  
  // Disallow special characters that might cause issues
  const invalidCharsRegex = /[<>\"']/
  if (invalidCharsRegex.test(sanitized)) {
    return { isValid: false, error: 'Tag contains invalid characters' }
  }
  
  return { isValid: true }
}

/**
 * Validate array of tags
 */
export function validateTags(tags: string[]): ValidationResult {
  if (!Array.isArray(tags)) {
    return { isValid: false, error: 'Tags must be an array' }
  }
  
  if (tags.length > 20) {
    return { isValid: false, error: 'Maximum 20 tags allowed' }
  }
  
  for (const tag of tags) {
    const result = validateTag(tag)
    if (!result.isValid) {
      return result
    }
  }
  
  return { isValid: true }
}

/**
 * Validate description text
 */
export function validateDescription(description: string | null | undefined): ValidationResult {
  if (!description) {
    return { isValid: true } // Description is optional
  }
  
  if (description.length > 2000) {
    return { isValid: false, error: 'Description must be less than 2000 characters' }
  }
  
  return { isValid: true }
}

/**
 * Validate notes text
 */
export function validateNotes(notes: string | null | undefined): ValidationResult {
  if (!notes) {
    return { isValid: true } // Notes are optional
  }
  
  if (notes.length > 5000) {
    return { isValid: false, error: 'Notes must be less than 5000 characters' }
  }
  
  return { isValid: true }
}

/**
 * Sanitize HTML to prevent XSS attacks
 * Basic implementation - strips HTML tags
 */
export function sanitizeHtml(input: string): string {
  return input.replace(/<[^>]*>/g, '')
}

/**
 * Validate and sanitize list creation data
 */
export function validateListData(data: { title: string; color?: string }): {
  isValid: boolean
  errors: Record<string, string>
  sanitized: { title: string; color: string }
} {
  const errors: Record<string, string> = {}
  
  // Validate title
  const titleResult = validateListTitle(data.title)
  if (!titleResult.isValid) {
    errors.title = titleResult.error!
  }
  
  // Validate color if provided
  const color = data.color || '#3B82F6'
  const colorResult = validateColor(color)
  if (!colorResult.isValid) {
    errors.color = colorResult.error!
  }
  
  return {
    isValid: Object.keys(errors).length === 0,
    errors,
    sanitized: {
      title: sanitizeString(data.title),
      color,
    },
  }
}

/**
 * Validate and sanitize item creation data
 */
export function validateItemData(data: {
  title: string
  description?: string | null
  priority?: string
  dueDate?: string | null
  tags?: string[]
  notes?: string | null
}): {
  isValid: boolean
  errors: Record<string, string>
  sanitized: {
    title: string
    description: string | null
    priority: 'low' | 'medium' | 'high'
    dueDate: Date | null
    tags: string[]
    notes: string | null
  }
} {
  const errors: Record<string, string> = {}
  
  // Validate title
  const titleResult = validateItemTitle(data.title)
  if (!titleResult.isValid) {
    errors.title = titleResult.error!
  }
  
  // Validate description
  const descResult = validateDescription(data.description)
  if (!descResult.isValid) {
    errors.description = descResult.error!
  }
  
  // Validate priority
  const priority = data.priority || 'medium'
  const priorityResult = validatePriority(priority)
  if (!priorityResult.isValid) {
    errors.priority = priorityResult.error!
  }
  
  // Validate due date
  let dueDate: Date | null = null
  if (data.dueDate) {
    const dateResult = validateDateString(data.dueDate)
    if (!dateResult.isValid) {
      errors.dueDate = dateResult.error!
    } else {
      dueDate = new Date(data.dueDate)
    }
  }
  
  // Validate tags
  const tags = data.tags || []
  const tagsResult = validateTags(tags)
  if (!tagsResult.isValid) {
    errors.tags = tagsResult.error!
  }
  
  // Validate notes
  const notesResult = validateNotes(data.notes)
  if (!notesResult.isValid) {
    errors.notes = notesResult.error!
  }
  
  return {
    isValid: Object.keys(errors).length === 0,
    errors,
    sanitized: {
      title: sanitizeString(data.title),
      description: data.description ? sanitizeString(data.description) : null,
      priority: priority as 'low' | 'medium' | 'high',
      dueDate,
      tags: tags.map(sanitizeString),
      notes: data.notes ? sanitizeString(data.notes) : null,
    },
  }
}