// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package image

import (
	
	
	
	
	
)

// ErrFormat indicates that decoding encountered an unknown format.
var ErrFormat = errors.New("image: unknown format")

// A format holds an image format's name, magic header and how to decode it.
type format struct {
	name, magic  string
	decode       func(io.Reader) (Image, error)
	decodeConfig func(io.Reader) (Config, error)
}

// Formats is the list of registered formats.
var (
	formatsMu     sync.Mutex
	atomicFormats atomic.Value
)

// RegisterFormat registers an image format for use by Decode.
// Name is the name of the format, like "jpeg" or "png".
// Magic is the magic prefix that identifies the format's encoding. The magic
// string can contain "?" wildcards that each match any one byte.
// Decode is the function that decodes the encoded image.
// DecodeConfig is the function that decodes just its configuration.
func (,  string,  func(io.Reader) (Image, error),  func(io.Reader) (Config, error)) {
	formatsMu.Lock()
	,  := atomicFormats.Load().([]format)
	atomicFormats.Store(append(, format{, , , }))
	formatsMu.Unlock()
}

// A reader is an io.Reader that can also peek ahead.
type reader interface {
	io.Reader
	Peek(int) ([]byte, error)
}

// asReader converts an io.Reader to a reader.
func asReader( io.Reader) reader {
	if ,  := .(reader);  {
		return 
	}
	return bufio.NewReader()
}

// Match reports whether magic matches b. Magic may contain "?" wildcards.
func match( string,  []byte) bool {
	if len() != len() {
		return false
	}
	for ,  := range  {
		if [] !=  && [] != '?' {
			return false
		}
	}
	return true
}

// Sniff determines the format of r's data.
func sniff( reader) format {
	,  := atomicFormats.Load().([]format)
	for ,  := range  {
		,  := .Peek(len(.magic))
		if  == nil && match(.magic, ) {
			return 
		}
	}
	return format{}
}

// Decode decodes an image that has been encoded in a registered format.
// The string returned is the format name used during format registration.
// Format registration is typically done by an init function in the codec-
// specific package.
func ( io.Reader) (Image, string, error) {
	 := asReader()
	 := sniff()
	if .decode == nil {
		return nil, "", ErrFormat
	}
	,  := .decode()
	return , .name, 
}

// DecodeConfig decodes the color model and dimensions of an image that has
// been encoded in a registered format. The string returned is the format name
// used during format registration. Format registration is typically done by
// an init function in the codec-specific package.
func ( io.Reader) (Config, string, error) {
	 := asReader()
	 := sniff()
	if .decodeConfig == nil {
		return Config{}, "", ErrFormat
	}
	,  := .decodeConfig()
	return , .name, 
}