// NGnius 2020-01-30

package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"strconv"
)

func boardHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != "GET" {
		w.WriteHeader(405)
		return
	}
	w.Header().Add("content-type", "application/json")
	w.Header().Add("Access-Control-Allow-Origin", "*")
	args := r.URL.Query()
	// check args pre-conditions
	if !checkArgExists(args, "board", w) {
		return
	}
	board := args.Get("board")
	if !checkArgExists(args, "count", w) || !checkArgInt(args, "count", w, 0) {
		return
	}
	count, _ := strconv.Atoi(args.Get("count"))
	if !checkArgExists(args, "start", w) || !checkArgInt(args, "start", w, 0) {
		return
	}
	start, _ := strconv.Atoi(args.Get("start"))
	// execute query
	result := NewResult("", r.URL.String())
	b, ok := boards[board]
	if !ok {
		w.WriteHeader(404)
		return
	}
	if len(b.Entries) < start+count {
		count = len(b.Entries) - start
	}
	// result.Items = b.Entries[start : start+count]
	for _, entry := range b.Entries[start : start+count] {
		item := entry
		result.Items = append(result.Items, &item)
	}
	result.Query = fmt.Sprintf("load board[%s] from %d to %d", board, start, count+start)
	result.Complete()
	data, err := json.Marshal(result)
	if err != nil {
		w.WriteHeader(500)
		return
	}
	w.Write(data)
}

func checkArgExists(values url.Values, key string, w http.ResponseWriter) (ok bool) {
	ok = values.Get(key) != ""
	if !ok {
		w.WriteHeader(400)
	}
	return
}

func checkArgInt(values url.Values, key string, w http.ResponseWriter, min int) (ok bool) {
	intVal, err := strconv.Atoi(values.Get(key))
	ok = err == nil && intVal >= min
	if !ok {
		w.WriteHeader(400)
	}
	return
}