/*
 * Minio Go Library for Amazon S3 Compatible Cloud Storage
 * Copyright 2017 Minio, Inc.
 *
 * 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 credentials

import "fmt"

// A Chain will search for a provider which returns credentials
// and cache that provider until Retrieve is called again.
//
// The Chain provides a way of chaining multiple providers together
// which will pick the first available using priority order of the
// Providers in the list.
//
// If none of the Providers retrieve valid credentials Value, ChainProvider's
// Retrieve() will return the error, collecting all errors from all providers.
//
// If a Provider is found which returns valid credentials Value ChainProvider
// will cache that Provider for all calls to IsExpired(), until Retrieve is
// called again.
//
//     creds := credentials.NewChainCredentials(
//         []credentials.Provider{
//             &credentials.EnvAWSS3{},
//             &credentials.EnvMinio{},
//         })
//
//     // Usage of ChainCredentials.
//     mc, err := minio.NewWithCredentials(endpoint, creds, secure, "us-east-1")
//     if err != nil {
//          log.Fatalln(err)
//     }
//
type Chain struct {
	Providers []Provider
	curr      Provider
}

// NewChainCredentials returns a pointer to a new Credentials object
// wrapping a chain of providers.
func NewChainCredentials(providers []Provider) *Credentials {
	return New(&Chain{
		Providers: append([]Provider{}, providers...),
	})
}

// Retrieve returns the credentials value or error if no provider returned
// without error.
//
// If a provider is found it will be cached and any calls to IsExpired()
// will return the expired state of the cached provider.
func (c *Chain) Retrieve() (Value, error) {
	var errs []error
	for _, p := range c.Providers {
		creds, err := p.Retrieve()
		if err != nil {
			errs = append(errs, err)
			continue
		} // Success.
		c.curr = p
		return creds, nil
	}
	c.curr = nil
	return Value{}, fmt.Errorf("No valid providers found %v", errs)
}

// IsExpired will returned the expired state of the currently cached provider
// if there is one.  If there is no current provider, true will be returned.
func (c *Chain) IsExpired() bool {
	if c.curr != nil {
		return c.curr.IsExpired()
	}

	return true
}