/*
 * Copyright 2023-2024 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.android.fhir.impl

import android.content.Context
import com.google.android.fhir.FhirEngine
import com.google.android.fhir.FhirEngineProvider
import com.google.android.fhir.LocalChange
import com.google.android.fhir.SearchResult
import com.google.android.fhir.db.Database
import com.google.android.fhir.logicalId
import com.google.android.fhir.search.Search
import com.google.android.fhir.search.count
import com.google.android.fhir.search.getIncludeQuery
import com.google.android.fhir.search.getQuery
import com.google.android.fhir.search.getRevIncludeQuery
import com.google.android.fhir.sync.ConflictResolver
import com.google.android.fhir.sync.Resolved
import com.google.android.fhir.sync.upload.DefaultResourceConsolidator
import com.google.android.fhir.sync.upload.LocalChangeFetcherFactory
import com.google.android.fhir.sync.upload.LocalChangesFetchMode
import com.google.android.fhir.sync.upload.SyncUploadProgress
import com.google.android.fhir.sync.upload.UploadRequestResult
import java.time.OffsetDateTime
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.firstOrNull
import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.flow.onEach
import org.hl7.fhir.r4.model.Resource
import org.hl7.fhir.r4.model.ResourceType

/** Implementation of [FhirEngine]. */
internal class FhirEngineImpl(private val database: Database, private val context: Context) :
  FhirEngine {
  override suspend fun create(vararg resource: Resource): List<String> {
    return database.insert(*resource)
  }

  override suspend fun get(type: ResourceType, id: String): Resource {
    return database.select(type, id)
  }

  override suspend fun update(vararg resource: Resource) {
    database.update(*resource)
  }

  override suspend fun delete(type: ResourceType, id: String) {
    database.delete(type, id)
  }

  override suspend fun <R : Resource> search(search: Search): List<SearchResult<R>> {
    val baseResources = database.search<R>(search.getQuery())
    val includedResources =
      if (search.forwardIncludes.isEmpty() || baseResources.isEmpty()) {
        null
      } else {
        database.searchForwardReferencedResources(
          search.getIncludeQuery(includeIds = baseResources.map { it.uuid }),
        )
      }
    val revIncludedResources =
      if (search.revIncludes.isEmpty() || baseResources.isEmpty()) {
        null
      } else {
        database.searchReverseReferencedResources(
          search.getRevIncludeQuery(
            includeIds =
              baseResources.map { "${it.resource.resourceType}/${it.resource.logicalId}" },
          ),
        )
      }

    return baseResources.map { (uuid, baseResource) ->
      SearchResult(
        baseResource,
        included =
          includedResources
            ?.asSequence()
            ?.filter { it.baseResourceUUID == uuid }
            ?.groupBy({ it.searchIndex }, { it.resource }),
        revIncluded =
          revIncludedResources
            ?.asSequence()
            ?.filter {
              it.baseResourceTypeWithId == "${baseResource.fhirType()}/${baseResource.logicalId}"
            }
            ?.groupBy({ it.resource.resourceType to it.searchIndex }, { it.resource }),
      )
    }
  }

  override suspend fun count(search: Search): Long {
    return search.count(database)
  }

  override suspend fun getLastSyncTimeStamp(): OffsetDateTime? {
    return FhirEngineProvider.getFhirDataStore(context).readLastSyncTimestamp()
  }

  override suspend fun clearDatabase() {
    database.clearDatabase()
  }

  override suspend fun getLocalChanges(type: ResourceType, id: String): List<LocalChange> {
    return database.getLocalChanges(type, id)
  }

  override suspend fun purge(type: ResourceType, id: String, forcePurge: Boolean) {
    database.purge(type, setOf(id), forcePurge)
  }

  override suspend fun purge(type: ResourceType, ids: Set<String>, forcePurge: Boolean) {
    database.purge(type, ids, forcePurge)
  }

  override suspend fun syncDownload(
    conflictResolver: ConflictResolver,
    download: suspend () -> Flow<List<Resource>>,
  ) {
    download().collect { resources ->
      database.withTransaction {
        val resolved =
          resolveConflictingResources(
            resources,
            getConflictingResourceIds(resources),
            conflictResolver,
          )
        database.insertSyncedResources(resources)
        saveResolvedResourcesToDatabase(resolved)
      }
    }
  }

  private suspend fun saveResolvedResourcesToDatabase(resolved: List<Resource>?) {
    resolved?.let {
      database.deleteUpdates(it)
      database.update(*it.toTypedArray())
    }
  }

  private suspend fun resolveConflictingResources(
    resources: List<Resource>,
    conflictingResourceIds: Set<String>,
    conflictResolver: ConflictResolver,
  ) =
    resources
      .filter { conflictingResourceIds.contains(it.logicalId) }
      .map { conflictResolver.resolve(database.select(it.resourceType, it.logicalId), it) }
      .filterIsInstance<Resolved>()
      .map { it.resolved }
      .takeIf { it.isNotEmpty() }

  private suspend fun getConflictingResourceIds(resources: List<Resource>) =
    resources
      .map { it.logicalId }
      .toSet()
      .intersect(database.getAllLocalChanges().map { it.resourceId }.toSet())

  override suspend fun syncUpload(
    localChangesFetchMode: LocalChangesFetchMode,
    upload: (suspend (List<LocalChange>) -> Flow<UploadRequestResult>),
  ): Flow<SyncUploadProgress> = flow {
    val resourceConsolidator = DefaultResourceConsolidator(database)
    val localChangeFetcher = LocalChangeFetcherFactory.byMode(localChangesFetchMode, database)

    emit(
      SyncUploadProgress(
        remaining = localChangeFetcher.total,
        initialTotal = localChangeFetcher.total,
      ),
    )

    while (localChangeFetcher.hasNext()) {
      val localChanges = localChangeFetcher.next()
      val uploadRequestResult =
        upload(localChanges)
          .onEach { result ->
            resourceConsolidator.consolidate(result)
            val newProgress =
              when (result) {
                is UploadRequestResult.Success -> localChangeFetcher.getProgress()
                is UploadRequestResult.Failure ->
                  localChangeFetcher.getProgress().copy(uploadError = result.uploadError)
              }
            emit(newProgress)
          }
          .firstOrNull { it is UploadRequestResult.Failure }

      if (uploadRequestResult is UploadRequestResult.Failure) {
        break
      }
    }
  }
}