package upgrade

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

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

// Parse parses the first HTTP request line
func (r *Line) Parse(b []byte) error {

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

	// 2. Fail when missing parts
	if len(parts) != 3 {
		return fmt.Errorf("expected 3 space-separated elements, got %d elements", len(parts))
	}

	// 3. Extract HTTP method
	err := r.extractHttpMethod(parts[0])
	if err != nil {
		return err
	}

	// 4. Extract URI
	err = r.extractURI(parts[1])
	if err != nil {
		return err
	}

	// 5. Extract version
	err = r.extractHttpVersion(parts[2])
	if err != nil {
		return err
	}

	return nil

}

// GetURI returns the actual URI
func (r Line) GetURI() string {
	return r.uri
}

// extractHttpMethod extracts the HTTP method from a []byte
// and checks for errors
// allowed format: OPTIONS|GET|HEAD|POST|PUT|DELETE
func (r *Line) extractHttpMethod(b []byte) error {

	switch string(b) {
	// case "OPTIONS": r.method = OPTIONS
	case "GET":
		r.method = Get
	// case "HEAD":    r.method = HEAD
	// case "POST":    r.method = POST
	// case "PUT":     r.method = PUT
	// case "DELETE":  r.method = DELETE

	default:
		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 (r *Line) extractURI(b []byte) error {

	// 1. Check format
	checker := regexp.MustCompile("^(?:/[^/]+)*/?$")
	if !checker.Match(b) {
		return fmt.Errorf("invalid URI, expected an absolute path, got '%s'", b)
	}

	// 2. Store
	r.uri = string(b)

	return nil

}

// extractHttpVersion extracts the version and checks for errors
// allowed format: [1-9] or [1.9].[0-9]
func (r *Line) extractHttpVersion(b []byte) error {

	// 1. Extract version parts
	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)
	}

	// 2. Extract version number
	matches := extractor.FindSubmatch(b)
	var version byte = matches[1][0] - '0'

	// 3. Extract subversion (if exists)
	var subVersion byte = 0
	if len(matches[2]) > 0 {
		subVersion = matches[2][0] - '0'
	}

	// 4. Store version (x 10 to fit uint8)
	r.version = version*10 + subVersion

	return nil
}