// 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 http

import (
	"fmt"
	"io"
	"net/textproto"
	"sort"
	"strings"
)

// A Header represents the key-value pairs in an HTTP header.
type Header map[string][]string

// Add adds the key, value pair to the header.
// It appends to any existing values associated with key.
func (h Header) Add(key, value string) {
	textproto.MIMEHeader(h).Add(key, value)
}

// Set sets the header entries associated with key to
// the single element value.  It replaces any existing
// values associated with key.
func (h Header) Set(key, value string) {
	textproto.MIMEHeader(h).Set(key, value)
}

// Get gets the first value associated with the given key.
// If there are no values associated with the key, Get returns "".
// To access multiple values of a key, access the map directly
// with CanonicalHeaderKey.
func (h Header) Get(key string) string {
	return textproto.MIMEHeader(h).Get(key)
}

// Del deletes the values associated with key.
func (h Header) Del(key string) {
	textproto.MIMEHeader(h).Del(key)
}

// Write writes a header in wire format.
func (h Header) Write(w io.Writer) error {
	return h.WriteSubset(w, nil)
}

var headerNewlineToSpace = strings.NewReplacer("\n", " ", "\r", " ")

// WriteSubset writes a header in wire format.
// If exclude is not nil, keys where exclude[key] == true are not written.
func (h Header) WriteSubset(w io.Writer, exclude map[string]bool) error {
	keys := make([]string, 0, len(h))
	for k := range h {
		if exclude == nil || !exclude[k] {
			keys = append(keys, k)
		}
	}
	sort.Strings(keys)
	for _, k := range keys {
		for _, v := range h[k] {
			v = headerNewlineToSpace.Replace(v)
			v = strings.TrimSpace(v)
			if _, err := fmt.Fprintf(w, "%s: %s\r\n", k, v); err != nil {
				return err
			}
		}
	}
	return nil
}

// CanonicalHeaderKey returns the canonical format of the
// header key s.  The canonicalization converts the first
// letter and any letter following a hyphen to upper case;
// the rest are converted to lowercase.  For example, the
// canonical key for "accept-encoding" is "Accept-Encoding".
func CanonicalHeaderKey(s string) string { return textproto.CanonicalMIMEHeaderKey(s) }