package web

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"os/signal"
	"strings"
	"sync"
	"syscall"

	"git.akyoto.dev/go/router"
)

// Server is the interface for an HTTP server.
type Server interface {
	Get(path string, handler Handler)
	Request(method string, path string, body io.Reader) Response
	Router() *router.Router[Handler]
	Run(address string) error
	Use(handlers ...Handler)
}

// server is an HTTP server.
type server struct {
	pool         sync.Pool
	handlers     []Handler
	router       *router.Router[Handler]
	errorHandler func(Context, error)
}

// NewServer creates a new HTTP server.
func NewServer() Server {
	r := &router.Router[Handler]{}
	s := &server{
		router: r,
		handlers: []Handler{
			func(c Context) error {
				ctx := c.(*context)
				handler := r.LookupNoAlloc(ctx.request.method, ctx.request.path, ctx.request.addParameter)

				if handler == nil {
					ctx.SetStatus(404)
					return nil
				}

				return handler(c)
			},
		},
		errorHandler: func(ctx Context, err error) {
			log.Println(ctx.Request().Path(), err)
		},
	}

	s.pool.New = func() any {
		return s.newContext()
	}

	return s
}

// Get registers your function to be called when the given GET path has been requested.
func (s *server) Get(path string, handler Handler) {
	s.Router().Add("GET", path, handler)
}

// Request performs a synthetic request and returns the response.
// This function keeps the response in memory so it's slightly slower than a real request.
// However it is very useful inside tests where you don't want to spin up a real web server.
func (s *server) Request(method string, url string, body io.Reader) Response {
	ctx := s.newContext()
	s.handleRequest(ctx, method, url, io.Discard)
	return ctx.Response()
}

// Run starts the server on the given address.
func (s *server) Run(address string) error {
	listener, err := net.Listen("tcp", address)

	if err != nil {
		return err
	}

	defer listener.Close()

	go func() {
		for {
			conn, err := listener.Accept()

			if err != nil {
				continue
			}

			go s.handleConnection(conn)
		}
	}()

	stop := make(chan os.Signal, 1)
	signal.Notify(stop, os.Interrupt, syscall.SIGTERM)
	<-stop
	return nil
}

// Router returns the router used by the server.
func (s *server) Router() *router.Router[Handler] {
	return s.router
}

// Use adds handlers to your handlers chain.
func (s *server) Use(handlers ...Handler) {
	last := s.handlers[len(s.handlers)-1]
	s.handlers = append(s.handlers[:len(s.handlers)-1], handlers...)
	s.handlers = append(s.handlers, last)
}

// handleConnection handles an accepted connection.
func (s *server) handleConnection(conn net.Conn) {
	defer conn.Close()
	reader := bufio.NewReader(conn)

	for {
		message, err := reader.ReadString('\n')

		if err != nil {
			return
		}

		space := strings.IndexByte(message, ' ')

		if space <= 0 {
			continue
		}

		method := message[:space]

		if method != "GET" {
			continue
		}

		lastSpace := strings.LastIndexByte(message, ' ')

		if lastSpace == -1 {
			lastSpace = len(message)
		}

		url := message[space+1 : lastSpace]

		ctx := s.pool.Get().(*context)
		s.handleRequest(ctx, method, url, conn)
		ctx.body = ctx.body[:0]
		ctx.params = ctx.params[:0]
		ctx.handlerCount = 0
		ctx.status = 200
		s.pool.Put(ctx)
	}
}

// handleRequest handles the given request.
func (s *server) handleRequest(ctx *context, method string, url string, writer io.Writer) {
	ctx.method = method
	ctx.scheme, ctx.host, ctx.path, ctx.query = parseURL(url)

	err := s.handlers[0](ctx)

	if err != nil {
		s.errorHandler(ctx, err)
	}

	fmt.Fprintf(writer, "HTTP/1.1 %d %s\r\nContent-Length: %d\r\n%s\r\n%s", ctx.status, "OK", len(ctx.body), ctx.response.headerText(), ctx.body)
}

// newContext allocates a new context with the default state.
func (s *server) newContext() *context {
	return &context{
		server: s,
		request: request{
			params: make([]router.Parameter, 0, 8),
		},
		response: response{
			body:   make([]byte, 0, 1024),
			status: 200,
		},
	}
}

// parseURL parses a URL and returns the scheme, host, path and query.
func parseURL(url string) (scheme string, host string, path string, query string) {
	schemePos := strings.Index(url, "://")

	if schemePos != -1 {
		scheme = url[:schemePos]
		url = url[schemePos+len("://"):]
	}

	pathPos := strings.IndexByte(url, '/')

	if pathPos != -1 {
		host = url[:pathPos]
		url = url[pathPos:]
	}

	queryPos := strings.IndexByte(url, '?')

	if queryPos != -1 {
		path = url[:queryPos]
		query = url[queryPos+1:]
		return
	}

	path = url
	return
}