package header

import (
	"regexp"
	"fmt"
	"strings"
	"bytes"
)

// parse tries to return a 'T' (httpHeader) from a byte array
func Parse(b []byte) (*T, error) {

	/* (1) Split by ':' */
	parts := bytes.Split(b, []byte(": "))

	if len(parts) != 2 {
		return nil, fmt.Errorf("Invalid HTTP header format '%s'", b)
	}

	/* (2) Create instance */
	inst := new(T)

	/* (3) Check for header name */
	switch strings.ToLower(string(parts[0])) {
		case "host":                     inst.Name = HOST
		case "upgrade":                  inst.Name = UPGRADE
		case "connection":               inst.Name = CONNECTION
		case "origin":                   inst.Name = ORIGIN
		case "sec-websocket-key":        inst.Name = WSKEY
		case "sec-websocket-protocol":   inst.Name = WSPROTOCOL
		case "sec-websocket-extensions": inst.Name = WSEXTENSIONS
		case "sec-websocket-version":    inst.Name = WSVERSION
		default:                         inst.Name = UNKNOWN
	}

	/* (4) Check format */
	checker := regexp.MustCompile(`^(?:[^,]+,\s*)*[^,]+$`)
	if !checker.Match(parts[1]) {
		return nil, fmt.Errorf("Invalid HTTP header value format '%s'", parts[1]);
	}

	/* (5) Normalise format */
	normaliser := regexp.MustCompile(`,\s+`)
	values := normaliser.ReplaceAll(parts[1], []byte(","))

	/* (5) Split values */
	inst.Values = bytes.Split(values, []byte(","))

	return inst, nil

}