// Command fluid-control serves the FLUID control-plane APIs.
//
// It publishes revisions and records governance decisions. It is not on the
// request path: ArchitectureBlueprint.md invariant 2 requires the data plane to
// keep serving when this process is down, and that separation is only real if
// nothing here is reachable from the gateway.
//
// This surface must never be exposed to interface consumers. It is the
// mechanism that evolves the interface in response to their behaviour, and a
// consumer able to reach it could drive its own adaptation.
package main

import (
	"context"
	"crypto/ed25519"
	"encoding/base64"
	"errors"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	_ "modernc.org/sqlite"

	"github.com/tegwick/fluid-core/internal/contract"
	"github.com/tegwick/fluid-core/internal/control"
	"github.com/tegwick/fluid-core/internal/evidence"
	"github.com/tegwick/fluid-core/internal/intent"
	"github.com/tegwick/fluid-core/internal/policy"
	"github.com/tegwick/fluid-core/internal/publish"
	"github.com/tegwick/fluid-core/internal/signing"
)

func main() {
	if err := run(); err != nil {
		log.Fatalf("fluid-control: %v", err)
	}
}

func run() error {
	var (
		addr      = flag.String("addr", "127.0.0.1:8081", "listen address")
		store     = flag.String("store", envOr("FLUID_STORE", "fluid.db"), "evidence store path")
		iface     = flag.String("interface", os.Getenv("FLUID_INTERFACE"), "interface identifier")
		keyID     = flag.String("key-id", envOr("FLUID_SIGNING_KEY_ID", "dev"), "signing key identifier")
		keyFile   = flag.String("key-file", os.Getenv("FLUID_SIGNING_KEY"), "base64 ed25519 private key file")
		ephemeral = flag.Bool("ephemeral-key", false, "generate a throwaway signing key (development only)")
	)
	flag.Parse()

	if *iface == "" {
		return errors.New("--interface is required")
	}

	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()

	ev, err := evidence.OpenSQLite(ctx, *store)
	if err != nil {
		return err
	}
	defer ev.Close()

	signer, err := loadSigner(*keyID, *keyFile, *ephemeral)
	if err != nil {
		return err
	}

	intents := intent.New(ev, contract.InterfaceID(*iface))
	gate := policy.NewGate(policy.DefaultLimits())

	pipeline, err := publish.New(publish.Options{
		Gate:    gate,
		Signer:  signer,
		Store:   ev,
		Intents: intents,
	})
	if err != nil {
		return err
	}

	srv := &http.Server{
		Addr:              *addr,
		Handler:           control.NewServer(control.NewRevisionAPI(ev, pipeline), control.NewIntentAPI(intents, gate)).Routes(),
		ReadHeaderTimeout: 10 * time.Second,
	}

	go func() {
		<-ctx.Done()
		shutdown, cancel := context.WithTimeout(context.Background(), 10*time.Second)
		defer cancel()
		_ = srv.Shutdown(shutdown)
	}()

	log.Printf("control plane for %s listening on %s (store %s, signing key %s)",
		*iface, *addr, *store, signer.KeyID())
	log.Printf("public key: %s", base64.StdEncoding.EncodeToString(signer.PublicKey()))

	if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
		return err
	}
	return nil
}

// loadSigner resolves the signing key.
//
// An ephemeral key must be asked for explicitly. Generating one silently when
// none is configured would mean a deployment could sign revisions with a key
// nobody trusts and never notice until the router refused them.
func loadSigner(keyID, keyFile string, ephemeral bool) (*signing.Signer, error) {
	if keyFile != "" {
		raw, err := os.ReadFile(keyFile)
		if err != nil {
			return nil, fmt.Errorf("read signing key: %w", err)
		}
		decoded, err := base64.StdEncoding.DecodeString(trimSpace(string(raw)))
		if err != nil {
			return nil, fmt.Errorf("signing key is not valid base64: %w", err)
		}
		return signing.NewSigner(keyID, ed25519.PrivateKey(decoded))
	}

	if ephemeral {
		signer, _, err := signing.GenerateKey(keyID)
		if err != nil {
			return nil, err
		}
		log.Print("WARNING: using an ephemeral signing key; revisions signed now " +
			"will not verify after a restart")
		return signer, nil
	}

	return nil, errors.New("no signing key: pass --key-file, or --ephemeral-key for development")
}

func trimSpace(s string) string {
	start, end := 0, len(s)
	for start < end && isSpace(s[start]) {
		start++
	}
	for end > start && isSpace(s[end-1]) {
		end--
	}
	return s[start:end]
}

func isSpace(b byte) bool {
	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
}

func envOr(key, fallback string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return fallback
}