// Copyright 2020 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 proxy

import (
	"bytes"
	"fmt"
	"net/http"
	"sort"
	"strings"
	"sync"
	"time"

	"golang.org/x/mod/semver"
	"golang.org/x/pkgsite/internal/testing/testhelper"
)

// Server represents a proxy server containing the specified modules.
type Server struct {
	mu      sync.Mutex
	modules map[string][]*Module
	mux     *http.ServeMux
}

// Module represents a module version used by the proxy server.
type Module struct {
	ModulePath string
	Version    string
	Files      map[string]string
	zip        []byte
}

// NewServer returns a proxy Server that serves the provided modules.
func NewServer(modules []*Module) *Server {
	s := &Server{
		mux:     http.NewServeMux(),
		modules: map[string][]*Module{},
	}
	for _, m := range modules {
		s.AddModule(m)
	}
	return s
}

// handleInfo creates an info endpoint for the specified module version.
func (s *Server) handleInfo(modulePath, resolvedVersion string) {
	urlPath := fmt.Sprintf("/%s/@v/%s.info", modulePath, resolvedVersion)
	s.mux.HandleFunc(urlPath, func(w http.ResponseWriter, r *http.Request) {
		http.ServeContent(w, r, modulePath, time.Now(), defaultInfo(resolvedVersion))
	})
}

// handleLatest creates an info endpoint for the specified module at the latest
// version.
func (s *Server) handleLatest(modulePath, urlPath string) {
	s.mux.HandleFunc(urlPath, func(w http.ResponseWriter, r *http.Request) {
		modules := s.modules[modulePath]
		resolvedVersion := modules[len(modules)-1].Version
		http.ServeContent(w, r, modulePath, time.Now(), defaultInfo(resolvedVersion))
	})
}

// handleMod creates a mod endpoint for the specified module version.
func (s *Server) handleMod(m *Module) {
	defaultGoMod := func(modulePath string) string {
		// defaultGoMod creates a bare-bones go.mod contents.
		return fmt.Sprintf("module %s\n\ngo 1.12", modulePath)
	}
	goMod := m.Files["go.mod"]
	if goMod == "" {
		goMod = defaultGoMod(m.ModulePath)
	}
	s.mux.HandleFunc(fmt.Sprintf("/%s/@v/%s.mod", m.ModulePath, m.Version),
		func(w http.ResponseWriter, r *http.Request) {
			http.ServeContent(w, r, m.ModulePath, time.Now(), strings.NewReader(goMod))
		})
}

// handleZip creates a zip endpoint for the specified module version.
func (s *Server) handleZip(m *Module) {
	s.mux.HandleFunc(fmt.Sprintf("/%s/@v/%s.zip", m.ModulePath, m.Version),
		func(w http.ResponseWriter, r *http.Request) {
			http.ServeContent(w, r, m.ModulePath, time.Now(), bytes.NewReader(m.zip))
		})
}

// handleList creates a list endpoint for the specified modulePath.
func (s *Server) handleList(modulePath string) {
	s.mux.HandleFunc(fmt.Sprintf("/%s/@v/list", modulePath), func(w http.ResponseWriter, r *http.Request) {
		s.mu.Lock()
		defer s.mu.Unlock()

		var vList []string
		if modules, ok := s.modules[modulePath]; ok {
			for _, v := range modules {
				vList = append(vList, v.Version)
			}
		}
		http.ServeContent(w, r, modulePath, time.Now(), strings.NewReader(strings.Join(vList, "\n")))
	})
}

// AddRoute adds an additional handler to the server.
func (s *Server) AddRoute(route string, fn func(w http.ResponseWriter, r *http.Request)) {
	s.mux.HandleFunc(route, fn)
}

// AddModule adds an additional module to the server.
func (s *Server) AddModule(m *Module) {
	s.mu.Lock()
	defer s.mu.Unlock()

	m = cleanModule(m)

	if _, ok := s.modules[m.ModulePath]; !ok {
		s.handleList(m.ModulePath)
		s.handleLatest(m.ModulePath, fmt.Sprintf("/%s/@latest", m.ModulePath))
		// TODO(https://golang.org/issue/39985): Add endpoint for handling
		// master version.
		s.handleLatest(m.ModulePath, fmt.Sprintf("/%s/@v/master.info", m.ModulePath))
	}
	s.handleInfo(m.ModulePath, m.Version)
	s.handleMod(m)
	s.handleZip(m)

	s.modules[m.ModulePath] = append(s.modules[m.ModulePath], m)
	sort.Slice(s.modules[m.ModulePath], func(i, j int) bool {
		// Return the modules in order of decreasing semver.
		return semver.Compare(s.modules[m.ModulePath][i].Version, s.modules[m.ModulePath][j].Version) < 0
	})
}

const versionTime = "2019-01-30T00:00:00Z"

func cleanModule(m *Module) *Module {
	if m.Version == "" {
		m.Version = "v1.0.0"
	}

	files := map[string]string{}
	for path, contents := range m.Files {
		p := m.ModulePath + "@" + m.Version + "/" + path
		files[p] = contents
	}
	zip, err := testhelper.ZipContents(files)
	if err != nil {
		panic(err)
	}
	m.zip = zip
	return m
}

func defaultInfo(resolvedVersion string) *strings.Reader {
	return strings.NewReader(fmt.Sprintf("{\n\t\"Version\": %q,\n\t\"Time\": %q\n}", resolvedVersion, versionTime))
}