// Command datekeys encrypts, inspects and opens DateKeyCap (.dkc) files.
//
//	datekeys encrypt -at 2030-01-01T00:00:00Z -in secret.txt -out secret.dkc
//	datekeys encrypt -at 2030-01-01T00:00:00Z -policy time_and_key -dkk key.dkk -in secret.txt -out secret.dkc
//	datekeys inspect -in secret.dkc
//	datekeys decrypt -in secret.dkc -out secret.txt [-dkk key.dkk] [-identity key.txt]
//	datekeys datekey resolve -at 2030-01-01T00:00:00Z
//	datekeys profile hash
//
// Encryption never touches the network. Decryption fetches the release from
// public drand relays and verifies it locally. Outputs are written to a
// temporary file in the destination directory and published only when
// complete; existing files are never overwritten.
package main

import (
	"context"
	"encoding/hex"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"io"
	"os"
	"strings"
	"time"

	"filippo.io/age"

	datekeys "github.com/datekeys/datekeys-go"
	"github.com/datekeys/datekeys-go/accesskey"
	"github.com/datekeys/datekeys-go/capsule"
	"github.com/datekeys/datekeys-go/datekey"
	"github.com/datekeys/datekeys-go/profile"
	"github.com/datekeys/datekeys-go/provider/drand"
)

const usage = `usage:
  datekeys encrypt -at TIME -in FILE -out FILE.dkc [-policy time_only|time_and_key] [-recipient age1...]... [-dkk FILE.dkk]
  datekeys decrypt -in FILE.dkc -out FILE [-dkk FILE.dkk] [-identity FILE]... [-relay URL]...
  datekeys inspect -in FILE.dkc [-json]
  datekeys datekey resolve -at TIME
  datekeys profile hash [-in PROFILE.cbor]

TIME is RFC 3339 with a time zone, for example 2030-01-01T00:00:00Z.`

// errUsage reports a malformed command line; main prints the usage text.
var errUsage = errors.New("invalid command line; run 'datekeys help'")

// longHorizon is the product policy threshold for the harvest-now,
// decrypt-later warning (spec §53).
const longHorizon = 365 * 24 * time.Hour

func main() {
	if err := run(os.Args[1:], os.Stdout, os.Stderr, time.Now); err != nil {
		if errors.Is(err, errUsage) {
			fmt.Fprintln(os.Stderr, usage)
			os.Exit(2)
		}
		fmt.Fprintln(os.Stderr, "datekeys:", err)
		if code := datekeys.Code(err); code != "" {
			fmt.Fprintln(os.Stderr, "datekeys: error code", code)
		}
		os.Exit(1)
	}
}

type multi []string

func (m *multi) String() string     { return strings.Join(*m, ",") }
func (m *multi) Set(v string) error { *m = append(*m, v); return nil }

// run is the CLI; the clock is injected for tests (only the CLI reads the
// wall clock).
func run(args []string, stdout, stderr io.Writer, now func() time.Time) error {
	if len(args) == 0 {
		return errUsage
	}
	switch args[0] {
	case "encrypt":
		return encrypt(args[1:], stderr, now)
	case "decrypt":
		return decrypt(args[1:], stderr, now)
	case "inspect":
		return inspect(args[1:], stdout)
	case "datekey":
		if len(args) < 2 || args[1] != "resolve" {
			return errUsage
		}
		return resolve(args[2:], stdout)
	case "profile":
		if len(args) < 2 || args[1] != "hash" {
			return errUsage
		}
		return profileHash(args[2:], stdout)
	case "-h", "-help", "--help", "help":
		fmt.Fprintln(stdout, usage)
		return nil
	}
	return errUsage
}

func newFlags(name string) *flag.FlagSet {
	fs := flag.NewFlagSet(name, flag.ContinueOnError)
	fs.SetOutput(io.Discard)
	return fs
}

func parse(fs *flag.FlagSet, args []string) error {
	if err := fs.Parse(args); err != nil {
		return fmt.Errorf("%s: %w", fs.Name(), err)
	}
	if fs.NArg() != 0 {
		return fmt.Errorf("%s: unexpected arguments %q", fs.Name(), fs.Args())
	}
	return nil
}

func parseTime(s string) (time.Time, error) {
	t, err := time.Parse(time.RFC3339Nano, s)
	if err != nil {
		return time.Time{}, fmt.Errorf("invalid -at %q: RFC 3339 with a time zone is required", s)
	}
	return t, nil
}

func encrypt(args []string, stderr io.Writer, now func() time.Time) error {
	fs := newFlags("encrypt")
	at := fs.String("at", "", "unlock time, RFC 3339")
	in := fs.String("in", "", "plaintext file")
	out := fs.String("out", "", "new .dkc file; never overwritten")
	policy := fs.String("policy", "time_only", "time_only or time_and_key")
	dkk := fs.String("dkk", "", "time_and_key: new .dkk file for a portable access key")
	var recipients multi
	fs.Var(&recipients, "recipient", "time_and_key: X25519 recipient age1... (repeatable)")
	if err := parse(fs, args); err != nil {
		return err
	}
	unlock, err := parseTime(*at)
	if err != nil {
		return err
	}
	pol, err := capsule.ParsePolicy(*policy)
	if err != nil {
		return err
	}
	if *in == "" || *out == "" {
		return errors.New("encrypt: -in and -out are required")
	}
	opts := capsule.EncryptOptions{Profile: profile.Quicknet(), UnlockAt: unlock, Policy: pol, NewPortableKey: *dkk != "", Now: now}
	for _, r := range recipients {
		x, err := age.ParseX25519Recipient(r)
		if err != nil {
			return fmt.Errorf("encrypt: %w", err)
		}
		opts.Recipients = append(opts.Recipients, x)
	}
	if *dkk != "" {
		if err := checkNew(*dkk); err != nil {
			return err
		}
	}
	src, err := os.Open(*in)
	if err != nil {
		return err
	}
	defer src.Close()
	var res *capsule.Result
	err = writeAtomic(*out, func(w io.Writer) error {
		res, err = capsule.Encrypt(w, src, opts)
		return err
	})
	if err != nil {
		return err
	}
	if res.PortableKey != nil {
		defer res.PortableKey.Wipe()
		if err := writeAtomic(*dkk, func(w io.Writer) error { return accesskey.Encode(w, res.PortableKey) }); err != nil {
			return fmt.Errorf("the capsule was written to %s but its .dkk could not be: %w", *out, err)
		}
	}
	fmt.Fprintf(stderr, "Encrypted locally for %s (round %d)\n  datekey    %s\n  capsule_id %x\n",
		res.UnlockAt.Format(time.RFC3339), res.DateKey.Round, res.DateKey.Compact(), res.CapsuleID)
	if res.PortableKey != nil {
		fmt.Fprintf(stderr, "  access key %s: keep it secret; it is valid for this capsule only\n", *dkk)
	}
	if res.UnlockAt.Sub(now()) > longHorizon {
		fmt.Fprintln(stderr, "warning: Quicknet V1 timelock is not post-quantum. The ciphertext may stay available for years,\n"+
			"         and its future confidentiality depends on the provider and on the underlying cryptography (spec §53).")
	}
	return nil
}

func decrypt(args []string, stderr io.Writer, now func() time.Time) error {
	fs := newFlags("decrypt")
	in := fs.String("in", "", ".dkc file")
	out := fs.String("out", "", "new plaintext file; never overwritten")
	dkk := fs.String("dkk", "", "portable access key (.dkk)")
	timeout := fs.Duration("timeout", 30*time.Second, "release request timeout")
	var identities, relays multi
	fs.Var(&identities, "identity", "age identity file with X25519 keys (repeatable)")
	fs.Var(&relays, "relay", "drand relay base URL (repeatable); default: public relays")
	if err := parse(fs, args); err != nil {
		return err
	}
	if *in == "" || *out == "" {
		return errors.New("decrypt: -in and -out are required")
	}
	reg, err := profile.Default()
	if err != nil {
		return err
	}
	opts := capsule.OpenOptions{Registry: reg, Source: drand.New(relays...), Now: now}
	for _, path := range identities {
		ids, err := readIdentities(path)
		if err != nil {
			return err
		}
		opts.Identities = append(opts.Identities, ids...)
	}
	if *dkk != "" {
		f, err := os.Open(*dkk)
		if err != nil {
			return err
		}
		k, err := accesskey.Decode(f)
		f.Close()
		if err != nil {
			return err
		}
		defer k.Wipe()
		opts.AccessKey = k
	}
	src, err := os.Open(*in)
	if err != nil {
		return err
	}
	defer src.Close()
	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
	defer cancel()
	var opened *capsule.Opened
	err = writeAtomic(*out, func(w io.Writer) error {
		opened, err = capsule.Open(ctx, w, src, opts)
		return err
	})
	if err != nil {
		return err
	}
	fmt.Fprintf(stderr, "Decrypted capsule %s (round %d, unlocked at %s); release verified locally\n",
		opened.Inspection.Header.CapsuleIDHex(), opened.Release.Round, opened.Inspection.UnlockAt.Format(time.RFC3339))
	return nil
}

func readIdentities(path string) ([]age.Identity, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	ids, err := age.ParseIdentities(f)
	if err != nil {
		return nil, fmt.Errorf("%s: %w", path, err)
	}
	return ids, nil
}

type inspectView struct {
	File         string                `json:"file"`
	CapsuleID    string                `json:"capsule_id,omitempty"`
	DateKey      string                `json:"datekey,omitempty"`
	Profile      string                `json:"profile,omitempty"`
	Round        uint64                `json:"round,omitempty"`
	UnlockAt     string                `json:"unlock_at,omitempty"`
	AccessPolicy string                `json:"access_policy,omitempty"`
	Valid        bool                  `json:"valid"`
	Error        string                `json:"error,omitempty"`
	Checks       []capsule.CheckResult `json:"checks"`
}

// inspect runs steps 1 to 8 only: it never requests a release and never uses
// a secret.
func inspect(args []string, stdout io.Writer) error {
	fs := newFlags("inspect")
	in := fs.String("in", "", ".dkc file")
	asJSON := fs.Bool("json", false, "JSON output")
	if err := parse(fs, args); err != nil {
		return err
	}
	if *in == "" {
		return errors.New("inspect: -in is required")
	}
	reg, err := profile.Default()
	if err != nil {
		return err
	}
	f, err := os.Open(*in)
	if err != nil {
		return err
	}
	defer f.Close()
	result, inspectErr := capsule.Inspect(f, capsule.InspectOptions{Registry: reg})
	v := inspectView{File: *in, Valid: inspectErr == nil, Error: datekeys.Code(inspectErr), Checks: result.Checks}
	if h := result.Header; h != nil {
		v.CapsuleID, v.DateKey, v.Profile, v.Round, v.AccessPolicy = h.CapsuleIDHex(), h.DateKey.Compact(), h.DateKey.ProfileID, h.DateKey.Round, h.Policy.String()
	}
	if !result.UnlockAt.IsZero() {
		v.UnlockAt = result.UnlockAt.Format(time.RFC3339)
	}
	if *asJSON {
		enc := json.NewEncoder(stdout)
		enc.SetIndent("", "  ")
		if err := enc.Encode(v); err != nil {
			return err
		}
	} else {
		fmt.Fprintf(stdout, "%s\n", v.File)
		for _, c := range v.Checks {
			mark := "ok  "
			if !c.OK {
				mark = "FAIL"
			}
			fmt.Fprintf(stdout, "  [%s] step %2d %-26s %s\n", mark, c.Step, c.Name, c.Detail)
		}
		if v.Valid {
			fmt.Fprintf(stdout, "  valid before unlock; opens at %s (round %d, %s)\n", v.UnlockAt, v.Round, v.AccessPolicy)
		}
	}
	return inspectErr
}

type resolveView struct {
	DateKey   string `json:"datekey"`
	Profile   string `json:"profile"`
	Round     uint64 `json:"round"`
	Requested string `json:"requested"`
	UnlockAt  string `json:"unlock_at"`
}

func resolve(args []string, stdout io.Writer) error {
	fs := newFlags("datekey resolve")
	at := fs.String("at", "", "instant, RFC 3339")
	if err := parse(fs, args); err != nil {
		return err
	}
	t, err := parseTime(*at)
	if err != nil {
		return err
	}
	p := profile.Quicknet()
	d, err := datekey.Resolve(p, t)
	if err != nil {
		return err
	}
	return json.NewEncoder(stdout).Encode(resolveView{
		DateKey: d.Compact(), Profile: d.ProfileID, Round: d.Round,
		Requested: t.Format(time.RFC3339Nano), UnlockAt: d.UnlockAt(p).Format(time.RFC3339),
	})
}

func profileHash(args []string, stdout io.Writer) error {
	fs := newFlags("profile hash")
	in := fs.String("in", "", "Deterministic CBOR profile file; default: the pinned Quicknet profile")
	if err := parse(fs, args); err != nil {
		return err
	}
	p := profile.Quicknet()
	if *in != "" {
		b, err := os.ReadFile(*in)
		if err != nil {
			return err
		}
		if p, err = profile.Decode(b); err != nil {
			return err
		}
	}
	b, err := p.CanonicalCBOR()
	if err != nil {
		return err
	}
	h, err := p.Hash()
	if err != nil {
		return err
	}
	pinned := *in == "" || hex.EncodeToString(h[:]) == profile.QuicknetProfileHash
	return json.NewEncoder(stdout).Encode(map[string]any{
		"profile_id":     p.ID,
		"profile_hash":   hex.EncodeToString(h[:]),
		"canonical_cbor": hex.EncodeToString(b),
		"pinned":         pinned,
	})
}