//
// Copyright Amazon.com Inc. or its affiliates.
// All Rights Reserved.
//
// SPDX-License-Identifier: Apache-2.0
//

import Amplify
import Foundation
import SQLite
import AWSPluginsCore

/// Extended types that conform to `Persistable` in order to provide conversion to SQLite's `Binding`
/// types. This is necessary so `Model` properties' map values to a SQLite compatible types.
extension Persistable {

    /// Convert the internal `Persistable` type to a `Binding` compatible value.
    ///
    /// Most often the types will be interchangeable. However, in some cases a custom
    /// conversion might be necessary.
    ///
    /// - Note: a `preconditionFailure` might happen in case the value cannot be converted.
    ///
    /// - Returns: the value as `Binding`
    internal func asBinding() -> Binding {
        let value = self
        let valueType = type(of: value)
        do {
            let binding = try SQLiteModelValueConverter.convertToTarget(from: value,
                                                                        fieldType: .from(type: valueType))
            guard let validBinding = binding else {
                return Fatal.preconditionFailure("""
                Converting \(String(describing: value)) of type \(String(describing: valueType))
                to a SQLite Binding returned a nil value. This is likely a bug in the
                SQLiteModelValueConverter logic.
                """)
            }
            return validBinding
        } catch {
            return Fatal.preconditionFailure("""
            Value \(String(describing: value)) of type \(String(describing: valueType))
            is not a SQLite Binding compatible type. Error: \(error.localizedDescription)

            \(AmplifyErrorMessages.shouldNotHappenReportBugToAWS())
            """)
        }
    }
}

private let logger = Amplify.Logging.logger(forCategory: .dataStore)

extension Model {

    /// Get the values of a `Model` for the fields relevant to a SQL query. The order of the
    /// values follow the same order of the model's columns.
    ///
    /// Use the `fields` parameter to convert just a subset of fields.
    ///
    /// - Parameter fields: an optional subset of fields
    /// - Returns: an array of SQLite's `Binding` compatible type
    internal func sqlValues(for fields: [ModelField]? = nil, modelSchema: ModelSchema) -> [Binding?] {
        let modelFields = fields ?? modelSchema.sortedFields
        let values: [Binding?] = modelFields.map { field in

            var existingFieldOptionalValue: Any??

            // self[field.name] subscript accessor or jsonValue() returns an Any??, we need to do a few things:
            // - `guard` to make sure the field name exists on the model
            // - `guard` to ensure the returned value isn't nil
            // - Attempt to cast to Persistable to ensure the model value isn't incorrectly assigned to a type we
            //   can't handle
            if field.name == ModelIdentifierFormat.Custom.sqlColumnName {
                existingFieldOptionalValue = self.identifier(schema: modelSchema).stringValue
            } else if let jsonModel = self as? JSONValueHolder {
                existingFieldOptionalValue = jsonModel.jsonValue(for: field.name, modelSchema: modelSchema)
            } else {
                existingFieldOptionalValue = self[field.name]
                // Additional attempt to get the internal data, like "_post"
                // TODO: alternatively, check if association or not
                if existingFieldOptionalValue == nil {
                    let internalFieldName = "_\(field.name)"
                    existingFieldOptionalValue = self[internalFieldName]
                }
            }
            
            guard let existingFieldValue = existingFieldOptionalValue else {
                return nil
            }

            guard let anyValue = existingFieldValue else {
                return nil
            }

            // At this point, we have a value: Any. However, remember that Any could itself be an optional, so we're
            // not quite done yet.
            let value: Any
            // swiftlint:disable:next syntactic_sugar
            if case Optional<Any>.some(let unwrappedValue) = anyValue {
                value = unwrappedValue
            } else {
                return nil
            }

            // Now `value` is still an Any, but we've assured ourselves that it's not an Optional, which means we can
            // safely attempt a cast to Persistable below.

            // if value is an associated model, get its id
            if field.isForeignKey,
               case let .model(associatedModelName) = field.type,
               let associatedModelSchema = ModelRegistry.modelSchema(from: associatedModelName) {

                // Check if it is a Model or json object.
                if let associatedModelValue = value as? Model {
                    return associatedModelValue.identifier
                } else if let associatedLazyModel = value as? (any _LazyReferenceValue) {
                    // The identifier (sometimes the FK), comes from the loaded model's identifier or
                    // from the not loaded identifier's stringValue (the value, or the formatted value for CPK)
                    switch associatedLazyModel._state {
                    case .notLoaded(let identifiers):
                        guard let identifiers = identifiers else {
                            return nil
                        }
                        return identifiers.stringValue
                    case .loaded(let model):
                        return model?.identifier
                    }
                } else if let associatedModelJSON = value as? [String: JSONValue] {
                    return associatedPrimaryKeyValue(fromJSON: associatedModelJSON,
                                                     associatedModelSchema: associatedModelSchema)
                }
            }

            // otherwise, delegate to the value converter
            do {
                let binding = try SQLiteModelValueConverter.convertToTarget(from: value, fieldType: field.type)
                return binding
            } catch {
                logger.warn("""
                Error converting \(modelSchema.name).\(field.name) to the proper SQLite Binding.
                Root cause is: \(String(describing: error))
                """)
                return nil
            }

        }

        return values
    }


    /// Given a serialized JSON model, returns the serialized value of its primary key.
    /// The returned value is either the value of the field or the serialization of multiple values in case of a composite PK.
    /// - Parameters:
    ///   - associatedModelJSON: model as JSON value
    ///   - associatedModelSchema: model's schema
    /// - Returns: serialized value of the primary key
    private func associatedPrimaryKeyValue(fromJSON associatedModelJSON: [String: JSONValue],
                                           associatedModelSchema: ModelSchema) -> String {
        let associatedModelPKFields: ModelIdentifierProtocol.Fields

        // get the associated model primary key fields
        associatedModelPKFields = associatedModelSchema.primaryKey.fields.compactMap {
            if case .string(let value) = associatedModelJSON[$0.name] {
                return (name: $0.name, value: value)
            }
            return nil
        }
        // Since Flutter models internally use a general serialized model structure with but
        // different model schemas, we always use an identifier with a ModelIdentifierFormat.Custom format
        return ModelIdentifier<AnyModel, ModelIdentifierFormat.Custom>
            .make(fields: associatedModelPKFields).stringValue
    }

}

extension Array where Element == ModelSchema {

    /// Sort the [ModelSchema] array based on the associations between them.
    ///
    /// The order the tables are created for each model depends on their relationships.
    /// The tables for the models that own the `foreign key` of the relationship can only
    /// be created *after* the other edge of the relationship is created.
    ///
    /// For example:
    ///
    /// ```
    /// Blog (1) - (n) Post (1) - (n) Comment
    /// ```
    /// The `Comment` table can only be created after the `Post`, which can only be
    /// created after `Blog`. Therefore:
    ///
    /// ```
    /// let modelSchemas = [Comment.schema, Post.schema, Blog.schema]
    /// modelSchemas.sortedByDependencyOrder() == [Blog.schema, Post.schema, Comment.schema]
    /// ```
    func sortByDependencyOrder() -> Self {
        var sortedKeys: [String] = []
        var sortMap: [String: ModelSchema] = [:]

        func walkAssociatedModels(of schema: ModelSchema) {
            if !sortedKeys.contains(schema.name) {
                let associatedModelSchemas = schema.sortedFields
                    .filter { $0.isForeignKey }
                    .map { (schema) -> ModelSchema in
                        guard let associatedSchema = ModelRegistry.modelSchema(from: schema.requiredAssociatedModelName)
                        else {
                            return Fatal.preconditionFailure("""
                            Could not retrieve schema for the model \(schema.requiredAssociatedModelName), verify that
                            datastore is initialized.
                            """)
                        }
                        return associatedSchema
                    }
                associatedModelSchemas.forEach(walkAssociatedModels(of:))

                let key = schema.name
                sortedKeys.append(key)
                sortMap[key] = schema
            }
        }

        let sortedStartList = sorted { $0.name < $1.name }
        sortedStartList.forEach(walkAssociatedModels(of:))
        return sortedKeys.map { sortMap[$0]! }
    }

    func hasAssociations() -> Bool {
        contains { modelSchema in
            modelSchema.hasAssociations
        }
    }
}

extension ModelIdentifierFormat.Custom {
    /// Name for composite identifier (multiple fields)
    public static let sqlColumnName = "@@primaryKey"
}