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package com.apollographql.cache.normalized.api

import com.apollographql.apollo.api.CompiledListType
import com.apollographql.apollo.api.CompiledNamedType
import com.apollographql.apollo.api.CompiledNotNullType
import com.apollographql.apollo.api.isComposite

/**
 * A [CacheResolver] that resolves objects and list of objects and falls back to the default resolver for scalar fields.
 * It is intended to simplify the usage of [CacheResolver] when no special handling is needed for scalar fields.
 *
 * Override [cacheKeyForField] to compute a cache key for a field of composite type.
 * Override [listOfCacheKeysForField] to compute a list of cache keys for a field of 'list-of-composite' type.
 *
 * For simplicity, this only handles one level of lists. Implement [CacheResolver] if you need arbitrary nested lists of objects.
 */
abstract class CacheKeyResolver : CacheResolver {
  /**
   * Returns the computed cache key for a composite field.
   *
   * If the field is of object type, you can get the object typename with `field.type.rawType().name`.
   * If the field is of interface or union type, the concrete object typename is not predictable and the returned [CacheKey] must be unique
   * in the whole schema as it cannot be namespaced by the typename anymore.
   *
   * If the returned [CacheKey] is null, the resolver will use the default handling and use any previously cached value.
   */
  abstract fun cacheKeyForField(context: ResolverContext): CacheKey?

  /**
   * For a field that contains a list of objects, [listOfCacheKeysForField] returns a list of [CacheKey]s where each [CacheKey] identifies an object.
   *
   * If the field is of object type, you can get the object typename with `field.type.rawType().name`.
   * If the field is of interface or union type, the concrete object typename is not predictable and the returned [CacheKey] must be unique
   * in the whole schema as it cannot be namespaced by the typename anymore.
   *
   * If an individual [CacheKey] is null, the resulting object will be null in the response.
   * If the returned list of [CacheKey]s is null, the resolver will use the default handling and use any previously cached value.
   */
  open fun listOfCacheKeysForField(context: ResolverContext): List? = null

  final override fun resolveField(context: ResolverContext): Any? {
    var type = context.field.type
    if (type is CompiledNotNullType) {
      type = type.ofType
    }
    if (type is CompiledNamedType && type.isComposite()) {
      val result = cacheKeyForField(context)
      if (result != null) {
        return result
      }
    }

    if (type is CompiledListType) {
      type = type.ofType
      if (type is CompiledNotNullType) {
        type = type.ofType
      }
      if (type is CompiledNamedType && type.isComposite()) {
        val result = listOfCacheKeysForField(context)
        if (result != null) {
          return result
        }
      }
    }

    return DefaultCacheResolver.resolveField(context)
  }
}