package api

import (
	"bytes"
	"crypto/sha256"
	"encoding/binary"
	"encoding/json"
	"errors"
	"io"
	"log"
	"math/rand"
	"net/http"
)

// options are the things that we may need to know about a request to fulfill it properly
type options struct {
	KeyType   string    `json:"kty"`
	Seed      int64     `json:"-"`
	SeedStr   string    `json:"seed"`
	rndReader io.Reader `json:"-"`
}

func getOpts(r *http.Request) (*options, error) {
	rndReader := RandomReader
	tok := make(map[string]interface{})
	decoder := json.NewDecoder(r.Body)
	err := decoder.Decode(&tok)
	if nil != err && io.EOF != err {
		log.Printf("json decode error: %s", err)
		return nil, errors.New("Bad Request: invalid json body")
	}
	defer r.Body.Close()

	var seed int64
	seedStr, _ := tok["seed"].(string)
	if "" != seedStr {
		if len(seedStr) > 256 {
			return nil, errors.New("Bad Request: base64 seed should be <256 characters (and is truncated to 64-bits anyway)")
		}
		b := sha256.Sum256([]byte(seedStr))
		seed, _ = binary.ReadVarint(bytes.NewReader(b[0:8]))
	}

	var n int
	if 0 != seed {
		rnd := rand.New(rand.NewSource(seed))
		rndReader = rnd
		n = rnd.Intn(2)
	} else {
		n = rand.Intn(2)
	}

	kty, _ := tok["kty"].(string)
	if "" == kty {
		if 0 == n {
			kty = "RSA"
		} else {
			kty = "EC"
		}
	}

	return &options{
		KeyType:   kty,
		Seed:      seed,
		rndReader: rndReader,
	}, nil
}