/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */
package main

import (
	"net/http"
	"path"
	"regexp"
	"strings"
)

type GoProxyRequestOp int

const (
	GoProxyRequestNone GoProxyRequestOp = iota
	GoProxyRequestList
	GoProxyRequestInfo
	GoProxyRequestMod
	GoProxyRequestZip
	GoProxyRequestLatest
)

type GoProxyRequest struct {
	URI,
	Module, // The Go module name
	ImportPath, // Module without major version
	Host, // The part of the module name resolved in DNS
	RepoPath, // The URI path of the git repo
	Repo, // Git repository name; last component of RepoPath
	Version, // "Canonical" version (e.g. v2.1, v1.0.3, etc.)
	VersionMajor, // v1, v2, etc.
	Extension string // .info, .mod, .zip
	Op GoProxyRequestOp
}

var Major = regexp.MustCompile(`^v[0-9]+$`)
var Version = regexp.MustCompile(`^v[0-9]+((\.[0-9]+)(\.[0-9]+)?)?$`)

func parseGoProxyPath(
	req *http.Request,
	gpr *GoProxyRequest,
) {
	// This should be
	// /go/<module>[/{ @v/{ list | $version.{info|mod|zip} } | @latest }]
	clean := path.Clean(req.URL.Path)
	gpr.URI = path.Join(req.Host, clean)
	gpr.Host = req.Host
	gpr.Module = req.Host
	gpr.ImportPath = req.Host
	gpr.RepoPath = req.Host

	vector := strings.Split(clean, "/")
	i := 0
	i++ // empty subpath
	if i < len(vector) && vector[i] == "go" {
		gpr.Module = path.Join(gpr.Module, vector[i])
		i++
	}
	if i < len(vector) {
		gpr.Repo = vector[i]
		gpr.Module = path.Join(gpr.Module, gpr.Repo)
		gpr.ImportPath = gpr.Module
		gpr.RepoPath = path.Join(gpr.RepoPath, gpr.Repo)
		i++
	}
	if i < len(vector) && Major.MatchString(vector[i]) {
		gpr.VersionMajor = vector[i]
		gpr.Module = path.Join(gpr.Module, gpr.VersionMajor)
		i++
	}
	if i < len(vector) && vector[i] == "@latest" {
		gpr.Op = GoProxyRequestLatest
		return
	}
	if i+1 >= len(vector) || vector[i] != "@v" {
		return
	}
	// @v
	i++
	if vector[i] == "list" {
		gpr.Op = GoProxyRequestList
		return
	}
	ext := path.Ext(vector[i])
	tmp := strings.TrimSuffix(vector[i], ext)
	if !Version.MatchString(tmp) {
		return
	}
	// @version
	gpr.Version = tmp
	switch ext {
	case ".info":
		gpr.Op = GoProxyRequestInfo
		gpr.Extension = ext
	case ".mod":
		gpr.Op = GoProxyRequestMod
		gpr.Extension = ext
	case ".zip":
		gpr.Op = GoProxyRequestZip
		gpr.Extension = ext
	}
}