package main

import (
	"crypto/hmac"
	"crypto/sha512"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"net/http"
	"strconv"
	"time"

	"github.com/julienschmidt/httprouter"

	"git.nemunai.re/srs/adlin/libadlin"
)

var router = httprouter.New()

func Router() *httprouter.Router {
	return router
}

type DispatchFunction func(httprouter.Params, []byte) (interface{}, error)

func remoteValidatorHandler(f func(http.ResponseWriter, *http.Request, httprouter.Params)) func(http.ResponseWriter, *http.Request, httprouter.Params) {
	return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
		expectedMAC := hmac.New(sha512.New, []byte(adlin.SharedSecret)).Sum([]byte(fmt.Sprintf("%d", time.Now().Unix()/10)))
		previousMAC := hmac.New(sha512.New, []byte(adlin.SharedSecret)).Sum([]byte(fmt.Sprintf("%d", time.Now().Unix()/10-1)))

		if aauth, err := base64.StdEncoding.DecodeString(r.Header.Get("X-ADLIN-Authentication")); err != nil {
			http.Error(w, fmt.Sprintf("{\"errmsg\":%q}\n", err), http.StatusUnauthorized)
		} else if !hmac.Equal(expectedMAC, aauth) && !hmac.Equal(previousMAC, aauth) {
			http.Error(w, fmt.Sprintf("{\"errmsg\":%q}\n", "Bad authentication header"), http.StatusUnauthorized)
		} else {
			f(w, r, ps)
		}
	}
}

func rawHandler(f func(http.ResponseWriter, *http.Request, httprouter.Params, []byte), access ...func(*adlin.Student, *http.Request) error) func(http.ResponseWriter, *http.Request, httprouter.Params) {
	return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
		if addr := r.Header.Get("X-Forwarded-For"); addr != "" {
			r.RemoteAddr = addr
		}
		log.Printf("%s \"%s %s\" [%s]\n", r.RemoteAddr, r.Method, r.URL.Path, r.UserAgent())

		w.Header().Set("Content-Type", "application/json")

		// Read Authorization header
		var student *adlin.Student = nil
		if cookie, err := r.Cookie("auth"); err == nil {
			if sessionid, err := base64.StdEncoding.DecodeString(cookie.Value); err != nil {
				http.Error(w, fmt.Sprintf(`{"errmsg": %q}`, err), http.StatusNotAcceptable)
				return
			} else if session, err := adlin.GetSession(sessionid); err != nil {
				http.Error(w, fmt.Sprintf(`{"errmsg": %q}`, err), http.StatusUnauthorized)
				return
			} else if session.IdStudent == nil {
				student = nil
			} else if std, err := adlin.GetStudent(int(*session.IdStudent)); err != nil {
				http.Error(w, fmt.Sprintf(`{"errmsg": %q}`, err), http.StatusUnauthorized)
				return
			} else {
				student = std
			}
		}

		// Check access limitation
		for _, a := range access {
			if err := a(student, r); err != nil {
				http.Error(w, fmt.Sprintf(`{"errmsg":%q}`, err), http.StatusForbidden)
				return
			}
		}

		// Read the body
		if r.ContentLength < 0 || r.ContentLength > 6553600 {
			http.Error(w, "{errmsg:\"Request too large or request size unknown\"}", http.StatusRequestEntityTooLarge)
			return
		}
		var body []byte
		if r.ContentLength > 0 {
			tmp := make([]byte, 1024)
			for {
				n, err := r.Body.Read(tmp)
				for j := 0; j < n; j++ {
					body = append(body, tmp[j])
				}
				if err != nil || n <= 0 {
					break
				}
			}
		}

		f(w, r, ps, body)
	}
}

func responseHandler(f func(*http.Request, httprouter.Params, []byte) (interface{}, error)) func(http.ResponseWriter, *http.Request, httprouter.Params, []byte) {
	return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params, body []byte) {
		ret, err := f(r, ps, body)

		// Format response
		resStatus := http.StatusOK
		if err != nil {
			ret = map[string]string{"errmsg": err.Error()}
			resStatus = http.StatusBadRequest
			log.Println(r.RemoteAddr, resStatus, err.Error())
		}

		if ret == nil {
			ret = map[string]string{"errmsg": "Page not found"}
			resStatus = http.StatusNotFound
		}

		if str, found := ret.(string); found {
			w.WriteHeader(resStatus)
			io.WriteString(w, str)
			w.Write([]byte("\n"))
		} else if bts, found := ret.([]byte); found {
			w.WriteHeader(resStatus)
			w.Write(bts)
		} else if j, err := json.Marshal(ret); err != nil {
			http.Error(w, fmt.Sprintf("{\"errmsg\":%q}\n", err), http.StatusInternalServerError)
		} else {
			w.WriteHeader(resStatus)
			w.Write(j)
			w.Write([]byte("\n"))
		}
	}
}

func challengeHandler(f func(*http.Request, []byte, int) (interface{}, error)) func(*http.Request, httprouter.Params, []byte) (interface{}, error) {
	return func(r *http.Request, ps httprouter.Params, body []byte) (interface{}, error) {
		return f(r, body, 0)
	}
}

func definedChallengeHandler(f func(*http.Request, []byte, int) (interface{}, error), chid int) func(*http.Request, httprouter.Params, []byte) (interface{}, error) {
	return func(r *http.Request, ps httprouter.Params, body []byte) (interface{}, error) {
		return f(r, body, chid)
	}
}

func apiRawHandler(f func(http.ResponseWriter, httprouter.Params, []byte) (interface{}, error), access ...func(*adlin.Student, *http.Request) error) func(http.ResponseWriter, *http.Request, httprouter.Params) {
	return rawHandler(func(w http.ResponseWriter, r *http.Request, ps httprouter.Params, b []byte) {
		responseHandler(func(_ *http.Request, ps httprouter.Params, b []byte) (interface{}, error) {
			return f(w, ps, b)
		})(w, r, ps, b)
	}, access...)
}

func apiHandler(f DispatchFunction, access ...func(*adlin.Student, *http.Request) error) func(http.ResponseWriter, *http.Request, httprouter.Params) {
	return rawHandler(responseHandler(func(_ *http.Request, ps httprouter.Params, b []byte) (interface{}, error) { return f(ps, b) }), access...)
}

func apiAuthHandler(f func(*adlin.Student, httprouter.Params, []byte) (interface{}, error), access ...func(*adlin.Student, *http.Request) error) func(http.ResponseWriter, *http.Request, httprouter.Params) {
	return rawHandler(responseHandler(func(r *http.Request, ps httprouter.Params, b []byte) (interface{}, error) {
		if cookie, err := r.Cookie("auth"); err != nil {
			return nil, errors.New("Authorization required")
		} else if sessionid, err := base64.StdEncoding.DecodeString(cookie.Value); err != nil {
			return nil, err
		} else if session, err := adlin.GetSession(sessionid); err != nil {
			return nil, err
		} else if session.IdStudent == nil {
			return nil, errors.New("Authorization required")
		} else if std, err := adlin.GetStudent(int(*session.IdStudent)); err != nil {
			return nil, err
		} else {
			return f(std, ps, b)
		}
	}), access...)
}

func studentHandler(f func(*adlin.Student, []byte) (interface{}, error)) func(httprouter.Params, []byte) (interface{}, error) {
	return func(ps httprouter.Params, body []byte) (interface{}, error) {
		if sid, err := strconv.Atoi(string(ps.ByName("sid"))); err != nil {
			if student, err := adlin.GetStudentByLogin(ps.ByName("sid")); err != nil {
				return nil, err
			} else {
				return f(student, body)
			}
		} else if student, err := adlin.GetStudent(sid); err != nil {
			return nil, err
		} else {
			return f(student, body)
		}
	}
}