// Copyright 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 config provides internal implementation of Configs.
package config

import (
	"fmt"
	"maps"
	"reflect"

	"github.com/tink-crypto/tink-go/v2/core/registry"
	"github.com/tink-crypto/tink-go/v2/internal/internalapi"
	"github.com/tink-crypto/tink-go/v2/key"
)

// Config keeps a collection of functions that create a primitive from
// [key.Key].
type Config struct {
	primitiveConstructors map[reflect.Type]func(key key.Key) (any, error)
	keysetManagers        map[string]registry.KeyManager
}

// PrimitiveFromKey creates a primitive from the given [key.Key]. Returns an
// error if there is no primitiveConstructor registered for the given key.
//
// This implements [keyset.Config].
func (c *Config) PrimitiveFromKey(k key.Key, _ internalapi.Token) (any, error) {
	keyType := reflect.TypeOf(k)
	creator, ok := c.primitiveConstructors[keyType]
	if !ok {
		return nil, fmt.Errorf("PrimitiveFromKey: no primitive creator from key %v registered", keyType)
	}
	return creator(k)
}

// Builder keeps a collection of functions that create a primitive from
// [key.Key].
type Builder struct {
	config Config
}

// RegisterPrimitiveConstructor registers a primitiveConstructor for the keyType.
// Not thread-safe.
//
// Returns an error if a primitiveConstructor for the keyType already
// registered (no matter whether it's the same object or different, since
// constructors are of type [Func] and they are never considered equal in Go
// unless they are nil).
func (b *Builder) RegisterPrimitiveConstructor(keyType reflect.Type, constructor func(key key.Key) (any, error), _ internalapi.Token) error {
	if _, ok := b.config.primitiveConstructors[keyType]; ok {
		return fmt.Errorf("RegisterPrimitiveConstructor: attempt to register a different primitive constructor for the same key type %v", keyType)
	}
	b.config.primitiveConstructors[keyType] = constructor
	return nil
}

// Build creates a [Config] from the [Builder].
func (b *Builder) Build() Config {
	c := Config{
		primitiveConstructors: maps.Clone(b.config.primitiveConstructors),
		keysetManagers:        maps.Clone(b.config.keysetManagers),
	}
	return c
}

// NewBuilder creates an empty [Builder].
func NewBuilder() *Builder {
	return &Builder{
		config: Config{
			primitiveConstructors: map[reflect.Type]func(key key.Key) (any, error){},
			keysetManagers:        map[string]registry.KeyManager{},
		},
	}
}