// Copyright The OpenTelemetry Authors
//
// 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 confmap // import "go.opentelemetry.io/collector/confmap"

import (
	"context"
	"fmt"
)

// Provider is an interface that helps to retrieve a config map and watch for any
// changes to the config map. Implementations may load the config from a file,
// a database or any other source.
//
// The typical usage is the following:
//
//	r, err := provider.Retrieve("file:/path/to/config")
//	// Use r.Map; wait for watcher to be called.
//	r.Close()
//	r, err = provider.Retrieve("file:/path/to/config")
//	// Use r.Map; wait for watcher to be called.
//	r.Close()
//	// repeat retrieve/wait/close cycle until it is time to shut down the Collector process.
//	// ...
//	provider.Shutdown()
type Provider interface {
	// Retrieve goes to the configuration source and retrieves the selected data which
	// contains the value to be injected in the configuration and the corresponding watcher that
	// will be used to monitor for updates of the retrieved value.
	//
	// `uri` must follow the "<scheme>:<opaque_data>" format. This format is compatible
	// with the URI definition (see https://datatracker.ietf.org/doc/html/rfc3986). The "<scheme>"
	// must be always included in the `uri`. The "<scheme>" supported by any provider:
	//   - MUST consist of a sequence of characters beginning with a letter and followed by any
	//     combination of letters, digits, plus ("+"), period ("."), or hyphen ("-").
	//     See https://datatracker.ietf.org/doc/html/rfc3986#section-3.1.
	//   - MUST be at least 2 characters long to avoid conflicting with a driver-letter identifier as specified
	//     in https://tools.ietf.org/id/draft-kerwin-file-scheme-07.html#syntax.
	//   - For testing, all implementation MUST check that confmaptest.ValidateProviderScheme returns no error.
	//
	// `watcher` callback is called when the config changes. watcher may be called from
	// a different go routine. After watcher is called Retrieved.Get should be called
	// to get the new config. See description of Retrieved for more details.
	// watcher may be nil, which indicates that the caller is not interested in
	// knowing about the changes.
	//
	// If ctx is cancelled should return immediately with an error.
	// Should never be called concurrently with itself or with Shutdown.
	Retrieve(ctx context.Context, uri string, watcher WatcherFunc) (*Retrieved, error)

	// Scheme returns the location scheme used by Retrieve.
	Scheme() string

	// Shutdown signals that the configuration for which this Provider was used to
	// retrieve values is no longer in use and the Provider should close and release
	// any resources that it may have created.
	//
	// This method must be called when the Collector service ends, either in case of
	// success or error. Retrieve cannot be called after Shutdown.
	//
	// Should never be called concurrently with itself or with Retrieve.
	// If ctx is cancelled should return immediately with an error.
	Shutdown(ctx context.Context) error
}

type WatcherFunc func(*ChangeEvent)

// ChangeEvent describes the particular change event that happened with the config.
// TODO: see if this can be eliminated.
type ChangeEvent struct {
	// Error is nil if the config is changed and needs to be re-fetched.
	// Any non-nil error indicates that there was a problem with watching the config changes.
	Error error
}

// Retrieved holds the result of a call to the Retrieve method of a Provider object.
type Retrieved struct {
	rawConf   any
	closeFunc CloseFunc
}

type retrievedSettings struct {
	closeFunc CloseFunc
}

// RetrievedOption options to customize Retrieved values.
type RetrievedOption func(*retrievedSettings)

// WithRetrievedClose overrides the default Retrieved.Close function.
// The default Retrieved.Close function does nothing and always returns nil.
func WithRetrievedClose(closeFunc CloseFunc) RetrievedOption {
	return func(settings *retrievedSettings) {
		settings.closeFunc = closeFunc
	}
}

// NewRetrieved returns a new Retrieved instance that contains the data from the raw deserialized config.
// The rawConf can be one of the following types:
//   - Primitives: int, int32, int64, float32, float64, bool, string;
//   - []any;
//   - map[string]any;
func NewRetrieved(rawConf any, opts ...RetrievedOption) (*Retrieved, error) {
	if err := checkRawConfType(rawConf); err != nil {
		return nil, err
	}
	set := retrievedSettings{}
	for _, opt := range opts {
		opt(&set)
	}
	return &Retrieved{rawConf: rawConf, closeFunc: set.closeFunc}, nil
}

// AsConf returns the retrieved configuration parsed as a Conf.
func (r *Retrieved) AsConf() (*Conf, error) {
	if r.rawConf == nil {
		return New(), nil
	}
	val, ok := r.rawConf.(map[string]any)
	if !ok {
		return nil, fmt.Errorf("retrieved value (type=%T) cannot be used as a Conf", r.rawConf)
	}
	return NewFromStringMap(val), nil
}

// AsRaw returns the retrieved configuration parsed as an any which can be one of the following types:
//   - Primitives: int, int32, int64, float32, float64, bool, string;
//   - []any - every member follows the same rules as the given any;
//   - map[string]any - every value follows the same rules as the given any;
func (r *Retrieved) AsRaw() (any, error) {
	return r.rawConf, nil
}

// Close and release any watchers that Provider.Retrieve may have created.
//
// Should block until all resources are closed, and guarantee that `onChange` is not
// going to be called after it returns except when `ctx` is cancelled.
//
// Should never be called concurrently with itself.
func (r *Retrieved) Close(ctx context.Context) error {
	if r.closeFunc == nil {
		return nil
	}
	return r.closeFunc(ctx)
}

// CloseFunc a function equivalent to Retrieved.Close.
type CloseFunc func(context.Context) error

func checkRawConfType(rawConf any) error {
	if rawConf == nil {
		return nil
	}
	switch rawConf.(type) {
	case int, int32, int64, float32, float64, bool, string, []any, map[string]any:
		return nil
	default:
		return fmt.Errorf("unsupported type=%T for retrieved config", rawConf)
	}
}
