package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"net/http"
	"strings"
)

type DispatchFunction func(*User, []string, io.ReadCloser) (interface{}, error)

type apiHandler struct {
	PE           *PictureExplorer
	Authenticate func(*http.Request) *User
	routes       map[string](map[string]struct {
		AuthFunction
		DispatchFunction
	})
}

func NewAPIHandler(pe *PictureExplorer, authenticate func(*http.Request) *User) *apiHandler {
	return &apiHandler{
		pe,
		authenticate,
		map[string](map[string]struct {
			AuthFunction
			DispatchFunction
		}){
			"images":  ApiImagesRouting(pe),
			"next":    ApiNextImagesRouting(pe),
			"version": ApiVersionRouting,
		},
	}
}

func (a *apiHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	user := a.Authenticate(r)

	log.Printf("Handling %s API request from %s: %s %s [%s]\n", r.Method, r.RemoteAddr, r.URL.Path, user, r.UserAgent())

	// Extract URL arguments
	var sURL = strings.Split(r.URL.Path[1:], "/")
	if sURL[len(sURL)-1] == "" && len(sURL) > 0 {
		// Remove trailing /
		sURL = sURL[:len(sURL)-1]
	}

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

	var ret interface{}
	var err error = nil

	// Refuse too large requests
	if r.ContentLength < 0 || r.ContentLength > 10485760 || ((r.Method == "DELETE" || r.Method == "GET" || r.Method == "HEAD") && r.ContentLength > 0) {
		http.Error(w, "{errmsg:\"Request too large or request size unknown\"}", http.StatusRequestEntityTooLarge)
		return
	}

	// Route request
	if len(sURL) == 0 {
		err = errors.New(fmt.Sprintf("No action provided"))
	} else if h, ok := a.routes[sURL[0]]; ok {
		if f, ok := h[r.Method]; ok {
			if f.AuthFunction(user, sURL[1:]) {
				ret, err = f.DispatchFunction(user, sURL[1:], r.Body)
			} else {
				w.Header().Set("WWW-Authenticate", "Basic realm=\"YouP0m\"")
				http.Error(w, "{errmsg:\"You are not allowed to do this request.\"}", http.StatusUnauthorized)
				return
			}
		} else {
			err = errors.New(fmt.Sprintf("Invalid action (%s) provided for %s.", r.Method, sURL[0]))
		}
	}

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

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

	if j, err := json.Marshal(ret); err != nil {
		http.Error(w, fmt.Sprintf("{errmsg:%q}", err), http.StatusInternalServerError)
	} else {
		w.WriteHeader(resStatus)
		w.Write(j)
	}
}