import { toValue } from 'vue'
import { opnFetch } from '~/composables/useOpnApi.js'

/**
 * @fileoverview Composable for initializing form data, with complete handling of 
 * form state persistence, URL parameters, and default values.
 */
export function useFormInitialization(formConfig, form, pendingSubmission) {
  /**
   * Applies URL parameters to the form data.
   * @param {URLSearchParams} params - The URL search parameters.
   */
  const applyUrlParameters = (params) => {
    if (!params) return
    
    // First, handle regular parameters
    params.forEach((value, key) => {
      // Skip array parameters for now
      if (key.endsWith('[]')) return
      
      try {
        // Try to parse JSON if the value starts with '{'
        const parsedValue = (typeof value === 'string' && value.startsWith('{')) 
          ? JSON.parse(value) 
          : value
          
        form[key] = parsedValue
      } catch {
        // If parsing fails, use the original value
        form[key] = value
      }
    })
    
    // Handle array parameters (key[])
    const paramKeys = [...new Set([...params.keys()])]
    paramKeys.forEach(key => {
      if (key.endsWith('[]')) {
        const arrayValues = params.getAll(key)
        if (arrayValues.length > 0) {
          const baseKey = key.slice(0, -2)
          form[baseKey] = arrayValues
        }
      }
    })
  }

  /**
   * Applies default data to form fields that don't already have values.
   * @param {Object} defaultData - Default data object.
   */
  const applyDefaultValues = (defaultData) => {
    if (!defaultData || Object.keys(defaultData).length === 0) return
    
    for (const key in defaultData) {
      if (Object.hasOwnProperty.call(defaultData, key) && form[key] === undefined) {
        form[key] = defaultData[key]
      }
    }
  }

  /**
   * Updates special fields like dates with today's date if configured.
   * @param {Array} fields - Form fields
   */
  const updateSpecialFields = () => {
    formConfig.value.properties.forEach(field => {
      // Handle date fields with prefill_today
      if (field.type === 'date' && field.prefill_today) {
        form[field.id] = new Date().toISOString()
      }
      // Handle matrix fields with prefill data
      else if (field.type === 'matrix' && !form[field.id] && field.prefill) {
        form[field.id] = {...field.prefill}
      } else if (field.id && !form[field.id]) {
        form[field.id] = field.prefill
      }
    })
  }

  /**
   * Attempts to load form data from an existing submission.
   * @param {String} submissionId - ID of the submission to load
   * @returns {Promise<Boolean>} - Whether loading was successful
   */
  const tryLoadFromSubmissionId = async (submissionId) => {
    const submissionIdValue = toValue(submissionId)
    if (!submissionIdValue) return false
    const config = toValue(formConfig) // Get the form config value
    const slug = config?.slug // Extract the slug

    if (!slug) {
      console.error('Cannot load submission: Form slug is missing from config.')
      form.reset() // Reset if config is invalid
      return false
    }

    // Use the correct route format: /forms/{slug}/submissions/{submission_id}
    return opnFetch(`/forms/${slug}/submissions/${submissionIdValue}`)
      .then(submissionData => {
        if (submissionData.data) {
          form.resetAndFill(submissionData.data)
          return true
        } else {
          console.warn(`Submission ${submissionIdValue} for form ${slug} loaded but returned no data.`)
          form.reset()
          return false
        }
      })
      .catch(error => {
        console.error(`Error loading submission ${submissionIdValue} for form ${slug}:`, error)
        form.reset()
        return false
      })
  }

  /**
   * Attempts to load form data from pendingSubmission in localStorage.
   * @returns {Boolean} - Whether loading was successful
   */
  const tryLoadFromPendingSubmission = () => {
    // Skip on server or if pendingSubmission is not available
    if (import.meta.server || !pendingSubmission) {
      return false
    }
    
    // Check if auto-save is enabled for this form
    if (!pendingSubmission.enabled?.value) {
      return false
    }
    
    // Get the saved data
    const pendingData = pendingSubmission.get()
    
    if (!pendingData || Object.keys(pendingData).length === 0) {
      return false
    }
    
    form.resetAndFill(pendingData)
    return true
  }

  /**
   * Main method to initialize the form data.
   * Follows a clear priority order:
   * 1. Load from submission ID (if provided)
   * 2. Load from pendingSubmission (localStorage) - client-side only
   * 3. Apply URL parameters
   * 4. Apply default values for fields
   * 
   * @param {Object} options - Initialization options
   * @param {String} [options.submissionId] - ID of submission to load
   * @param {URLSearchParams} [options.urlParams] - URL parameters
   * @param {Object} [options.defaultData] - Default data to apply
   * @param {Array} [options.fields] - Form fields for special handling
   */
  const initialize = async (options = {}) => {
    const config = toValue(formConfig)
    
    // 1. Reset form state
    form.reset()
    form.errors.clear()
    
    // 2. Try loading from submission ID
    if (options.submissionId) {
      const loaded = await tryLoadFromSubmissionId(options.submissionId)
      if (loaded) return // Exit if loaded successfully
    }
    
    // 3. Try loading from pendingSubmission
    if (tryLoadFromPendingSubmission()) {
      updateSpecialFields()
      return // Exit if loaded successfully
    }
    
    // 4. Start with empty form data
    const formData = {}
    
    // 5. Apply URL parameters
    if (options.urlParams) {
      applyUrlParameters(options.urlParams)
    }
    
    // 6. Apply special field handling
    updateSpecialFields()
    
    // 7. Apply default data from config or options
    const defaultData = options.defaultData || config?.default_data
    if (defaultData) {
      for (const key in defaultData) {
        if (!formData[key]) { // Only if not already set
          formData[key] = defaultData[key]
        }
      }
    }
    
    // 8. Fill the form with the collected data
    if (Object.keys(formData).length > 0) {
      form.resetAndFill(formData)
    }
  }

  return {
    initialize,
    applyUrlParameters,
    applyDefaultValues
  }
}