package upgrade

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

// RequestLine represents the HTTP Request line
// defined in rfc-2616 : https://tools.ietf.org/html/rfc2616#section-5.1
type RequestLine struct {
	uri     string
	version byte
}

// Read an HTTP request line from a byte array
//
// implements io.Reader
func (rl *RequestLine) Read(b []byte) (int, error) {
	var read = len(b)

	// split by spaces
	parts := bytes.Split(b, []byte(" "))

	if len(parts) != 3 {
		return read, fmt.Errorf("expected 3 space-separated elements, got %d elements", len(parts))
	}

	err := rl.extractHttpMethod(parts[0])
	if err != nil {
		return read, err
	}

	err = rl.extractURI(parts[1])
	if err != nil {
		return read, err
	}

	err = rl.extractHttpVersion(parts[2])
	if err != nil {
		return read, err
	}

	return read, nil

}

// URI of the request line
func (rl RequestLine) URI() string {
	return rl.uri
}

// extractHttpMethod extracts the HTTP method from a []byte
// and checks for errors
// allowed format: OPTIONS|GET|HEAD|POST|PUT|DELETE
func (rl *RequestLine) extractHttpMethod(b []byte) error {
	if string(b) != "GET" {
		return fmt.Errorf("invalid HTTP method '%s', expected 'GET'", b)
	}
	return nil
}

// extractURI extracts the URI from a []byte and checks for errors
// allowed format: /([^/]/)*/?
func (rl *RequestLine) extractURI(b []byte) error {
	checker := regexp.MustCompile("^(?:/[^/]+)*/?$")
	if !checker.Match(b) {
		return fmt.Errorf("invalid URI, expected an absolute path, got '%s'", b)
	}
	rl.uri = string(b)
	return nil

}

// extractHttpVersion extracts the version and checks for errors
// allowed format: [1-9] or [1.9].[0-9]
func (rl *RequestLine) extractHttpVersion(b []byte) error {
	extractor := regexp.MustCompile(`^HTTP/([1-9])(?:\.([0-9]))?$`)

	if !extractor.Match(b) {
		return fmt.Errorf("invalid HTTP version, expected INT or INT.INT, got '%s'", b)
	}
	matches := extractor.FindSubmatch(b)

	var version byte = matches[1][0] - '0'

	var subversion byte = 0
	if len(matches[2]) > 0 {
		subversion = matches[2][0] - '0'
	}

	rl.version = version*10 + subversion
	return nil
}