package main

import (
	"crypto/ed25519"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"os"
)

type signedFirmware struct {
	PublicKeyBase64 string `json:"public_key_base64"`
	SignatureBase64 string `json:"signature_base64"`
	SHA256          string `json:"sha256"`
	Size            int    `json:"size"`
	Manifest        string `json:"manifest"`
}

func main() {
	if len(os.Args) != 5 {
		fmt.Fprintln(os.Stderr, "usage: firmware-sign <model> <hardware-revision> <version> <file>")
		os.Exit(2)
	}
	content, err := os.ReadFile(os.Args[4])
	if err != nil {
		panic(err)
	}
	result, err := signFirmware(os.Args[1], os.Args[2], os.Args[3], content)
	if err != nil {
		panic(err)
	}
	if err := json.NewEncoder(os.Stdout).Encode(result); err != nil {
		panic(err)
	}
}

func signFirmware(model, hardwareRevision, version string, content []byte) (signedFirmware, error) {
	publicKey, privateKey, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		return signedFirmware{}, err
	}
	digest := sha256.Sum256(content)
	digestText := hex.EncodeToString(digest[:])
	manifest := fmt.Sprintf("firmware-manifest-v1\nmodel=%s\nhardware_revision=%s\nversion=%s\nsha256=%s\nsize=%d\n", model, hardwareRevision, version, digestText, len(content))
	return signedFirmware{
		PublicKeyBase64: base64.StdEncoding.EncodeToString(publicKey),
		SignatureBase64: base64.StdEncoding.EncodeToString(ed25519.Sign(privateKey, []byte(manifest))),
		SHA256:          digestText, Size: len(content), Manifest: manifest,
	}, nil
}