/**
 * Offline SOAP Cache Utility
 *
 * Uses IndexedDB to cache consultation data (consultation info + SOAP + patient)
 * locally for offline access. Supports up to 50 entries with automatic eviction
 * of the oldest entries when the limit is exceeded.
 */

import type { SoapData } from '../api'

// ================================================================
// Types
// ================================================================

/** Consultation summary stored alongside SOAP and patient data */
export interface CachedConsultationInfo {
  id: string
  animal_name: string
  species: string
  breed: string
  age: string
  sex: string
  weight: string
  doctor_name: string
  status: string
  created_at: string
}

/** Patient data stored in the cache */
export interface CachedPatientInfo {
  animal_name: string
  species: string
  breed: string
  age: string
  weight: string
  allergy_history: string
}

/** Full cache entry matching the shared record pattern */
export interface CachedConsultation {
  /** Consultation ID (also the cache key) */
  id: string
  /** Consultation summary metadata */
  consultation: CachedConsultationInfo
  /** SOAP data (may be null if not yet generated) */
  soap: SoapData | null
  /** Patient information */
  patient: CachedPatientInfo | null
  /** Unix timestamp (ms) when this entry was cached */
  cached_at: number
}

// ================================================================
// Constants
// ================================================================

const DB_NAME = 'vetcopilot_offline_cache'
const DB_VERSION = 1
const STORE_NAME = 'consultations'
const MAX_ENTRIES = 50

// ================================================================
// IndexedDB helpers
// ================================================================

/** Open (or create) the IndexedDB database */
function openDB(): Promise<IDBDatabase> {
  return new Promise((resolve, reject) => {
    const request = indexedDB.open(DB_NAME, DB_VERSION)

    request.onupgradeneeded = (event) => {
      const db = (event.target as IDBOpenDBRequest).result
      if (!db.objectStoreNames.contains(STORE_NAME)) {
        const store = db.createObjectStore(STORE_NAME, { keyPath: 'id' })
        // Create an index on cached_at for efficient eviction queries
        store.createIndex('cached_at', 'cached_at', { unique: false })
      }
    }

    request.onsuccess = (event) => {
      resolve((event.target as IDBOpenDBRequest).result)
    }

    request.onerror = (event) => {
      reject(
        new Error(
          `Failed to open IndexedDB: ${(event.target as IDBOpenDBRequest).error?.message ?? 'unknown error'}`,
        ),
      )
    }

    request.onblocked = () => {
      reject(new Error('IndexedDB blocked: close other tabs using this database'))
    }
  })
}

/** Perform a read-write transaction on the store and return its result */
async function withStore<T>(
  mode: IDBTransactionMode,
  callback: (store: IDBObjectStore) => IDBRequest<T>,
): Promise<T> {
  const db = await openDB()
  return new Promise<T>((resolve, reject) => {
    const transaction = db.transaction(STORE_NAME, mode)
    const store = transaction.objectStore(STORE_NAME)
    const request = callback(store)

    request.onsuccess = () => {
      resolve(request.result)
    }

    request.onerror = () => {
      reject(
        new Error(
          `IndexedDB request failed: ${request.error?.message ?? 'unknown error'}`,
        ),
      )
    }

    // Close DB when transaction completes (or fails)
    transaction.oncomplete = () => {
      db.close()
    }
    transaction.onerror = () => {
      db.close()
      reject(
        new Error(
          `IndexedDB transaction failed: ${transaction.error?.message ?? 'unknown error'}`,
        ),
      )
    }
    transaction.onabort = () => {
      db.close()
      reject(new Error('IndexedDB transaction aborted'))
    }
  })
}

// ================================================================
// Eviction
// ================================================================

/**
 * Remove the oldest entries if the store exceeds MAX_ENTRIES.
 * Uses the cached_at index to find and delete the oldest.
 */
async function evictOldestIfNeeded(): Promise<void> {
  const db = await openDB()

  return new Promise((resolve, reject) => {
    const transaction = db.transaction(STORE_NAME, 'readwrite')
    const store = transaction.objectStore(STORE_NAME)

    const countRequest = store.count()

    countRequest.onsuccess = () => {
      const count = countRequest.result
      if (count <= MAX_ENTRIES) {
        db.close()
        resolve()
        return
      }

      const excess = count - MAX_ENTRIES
      const index = store.index('cached_at')
      const cursorRequest = index.openCursor()

      let deleted = 0

      cursorRequest.onsuccess = (event) => {
        const cursor = (event.target as IDBRequest<IDBCursorWithValue>).result
        if (cursor && deleted < excess) {
          cursor.delete()
          deleted++
          cursor.continue()
        }
        // Cursor exhausted or enough deleted
      }
    }

    countRequest.onerror = () => {
      db.close()
      reject(new Error('Failed to count cached entries'))
    }

    transaction.oncomplete = () => {
      db.close()
      resolve()
    }
    transaction.onerror = () => {
      db.close()
      reject(new Error('Eviction transaction failed'))
    }
    transaction.onabort = () => {
      db.close()
      reject(new Error('Eviction transaction aborted'))
    }
  })
}

// ================================================================
// Public API
// ================================================================

/**
 * Cache a full consultation record (consultation info + SOAP + patient).
 *
 * If an entry with the same ID already exists, it will be replaced.
 * After insertion, if total entries exceed MAX_ENTRIES (50), the oldest
 * entries are automatically evicted.
 */
export async function cacheConsultation(
  data: CachedConsultation,
): Promise<void> {
  await withStore('readwrite', (store) => store.put(data))
  await evictOldestIfNeeded()
}

/**
 * Retrieve a single cached consultation by its ID.
 * Returns null if the consultation is not cached.
 */
export async function getCachedConsultation(
  id: string,
): Promise<CachedConsultation | null> {
  try {
    const result = await withStore<CachedConsultation | undefined>(
      'readonly',
      (store) => store.get(id),
    )
    return result ?? null
  } catch {
    return null
  }
}

/**
 * Retrieve all cached consultations ordered by cached_at descending (newest first).
 */
export async function getAllCachedConsultations(): Promise<CachedConsultation[]> {
  try {
    const db = await openDB()

    return new Promise((resolve, reject) => {
      const transaction = db.transaction(STORE_NAME, 'readonly')
      const store = transaction.objectStore(STORE_NAME)
      const results: CachedConsultation[] = []

      const request = store.openCursor()

      request.onsuccess = (event) => {
        const cursor = (event.target as IDBRequest<IDBCursorWithValue>).result
        if (cursor) {
          results.push(cursor.value as CachedConsultation)
          cursor.continue()
        } else {
          // Sort newest first
          results.sort((a, b) => b.cached_at - a.cached_at)
          resolve(results)
        }
      }

      request.onerror = () => {
        reject(new Error('Failed to read all cached items'))
      }

      transaction.oncomplete = () => {
        db.close()
      }
      transaction.onerror = () => {
        db.close()
        reject(new Error('Transaction failed'))
      }
      transaction.onabort = () => {
        db.close()
        reject(new Error('Transaction aborted'))
      }
    })
  } catch {
    return []
  }
}

/**
 * Remove a single cached consultation by its ID.
 */
export async function removeConsultation(id: string): Promise<void> {
  await withStore('readwrite', (store) => store.delete(id))
}

/**
 * Remove all cached consultations from the store.
 */
export async function clearAll(): Promise<void> {
  await withStore('readwrite', (store) => store.clear())
}