// Command datekeys encrypts, inspects and opens DateKeyCap (.dkc) files.
//
//	datekeys encrypt -at 2030-01-01T00:00:00Z -in fotos -in carta.txt -comment "Para Ana" -out regalo.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 regalo.dkc
//	datekeys decrypt -in regalo.dkc -out regalo [-dkk key.dkk] [-identity key.txt]
//	datekeys datekey resolve -at 2030-01-01T00:00:00Z
//	datekeys profile hash
//	datekeys version
//
// 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. The files of a format 3
// capsule go to a new folder, staged inside it and moved into place only
// when every check has passed.
package main

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

	"filippo.io/age"

	datekeys "g.activething.com/go/DateKeys"
	"g.activething.com/go/DateKeys/accesskey"
	"g.activething.com/go/DateKeys/capsule"
	"g.activething.com/go/DateKeys/datekey"
	"g.activething.com/go/DateKeys/internal/inspectview"
	"g.activething.com/go/DateKeys/profile"
	"g.activething.com/go/DateKeys/provider/drand"
)

const usage = `usage:
  datekeys encrypt -at TIME -in FILE|FOLDER... -out FILE.dkc [-comment TEXT] [-author TEXT] [-no-mtime] [-policy time_only|time_and_key] [-recipient age1...]... [-dkk FILE.dkk] [-padding reforzado|bloque256]
  datekeys decrypt -in FILE.dkc -out PATH [-dkk FILE.dkk] [-identity FILE]... [-relay URL]...
  datekeys inspect -in FILE.dkc [-json]
  datekeys datekey resolve -at TIME
  datekeys profile hash [-in PROFILE.cbor]
  datekeys version

TIME is RFC 3339 with a time zone, for example 2030-01-01T00:00:00Z.
encrypt writes capsule format 3: the files of each -in, a folder by its name
and the files below it, with an optional comment and declared author. The
content is padded, by default with the rule reforzado, and a time_and_key
capsule holds 16 slots, from 1 to 16 credentials and a dummy in each slot
left (spec §29, §39). decrypt writes the files of a format 3 capsule to the
new folder PATH, and the content of formats 1 and 2 to the new file PATH.`

// 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:], stdout, 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 "version", "-version", "--version":
		if len(args) != 1 {
			return errUsage
		}
		// The module version (a tag, or the pseudo-version of the commit a
		// checkout was built from), the specification it implements and the
		// toolchain.
		fmt.Fprintf(stdout, "datekeys %s\nspecification %s\n%s %s/%s\n", datekeys.Version(), datekeys.SpecVersion, runtime.Version(), runtime.GOOS, runtime.GOARCH)
		return nil
	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")
	var ins multi
	fs.Var(&ins, "in", "file or folder to encrypt (repeatable)")
	out := fs.String("out", "", "new .dkc file; never overwritten")
	comment := fs.String("comment", "", "comment for whoever opens the capsule, shown as text of the creator")
	author := fs.String("author", "", "declared author, shown as text of the creator that proves nothing")
	noMTime := fs.Bool("no-mtime", false, "leave out the modification times of the files")
	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")
	padding := fs.String("padding", "reforzado", "padding rule of the content: reforzado or bloque256")
	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
	}
	var code capsule.Padding
	switch *padding {
	case capsule.Reforzado.String():
		code = capsule.Reforzado
	case capsule.Bloque256.String():
		code = capsule.Bloque256
	default:
		return fmt.Errorf("encrypt: unknown padding rule %q: reforzado or bloque256", *padding)
	}
	if *out == "" || len(ins) == 0 && *comment == "" {
		return errors.New("encrypt: -out, and -in or -comment, are required")
	}
	opts := capsule.EncryptOptions{Profile: profile.Quicknet(), UnlockAt: unlock, Policy: pol, NewPortableKey: *dkk != "", Padding: code,
		Comment: *comment, Author: *author, 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
		}
	}
	sources, skipped, err := collect(ins, !*noMTime)
	if err != nil {
		return fmt.Errorf("encrypt: %w", err)
	}
	var res *capsule.Result
	err = writeAtomic(*out, func(w io.Writer) error {
		res, err = capsule.EncryptFiles(w, sources, 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  format     %d: %d files, %d bytes of content, padded to %d (%s)\n",
		res.UnlockAt.Format(time.RFC3339), res.DateKey.Round, res.DateKey.Compact(), res.CapsuleID, res.Format, len(res.Head.Files), res.Length, res.PaddedLength, res.Padding)
	for _, p := range skipped {
		fmt.Fprintf(stderr, "  left out   %s, which the system creates on its own\n", p)
	}
	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, stdout, stderr io.Writer, now func() time.Time) error {
	fs := newFlags("decrypt")
	in := fs.String("in", "", ".dkc file")
	out := fs.String("out", "", "new folder (format 3) or file (formats 1 and 2); 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 != "" {
		// Open decodes the .dkk at step 9.a, and only for a time_and_key
		// capsule, so that its errors come in the order of spec §63.
		f, err := os.Open(*dkk)
		if err != nil {
			return err
		}
		defer f.Close()
		opts.AccessKeyFile = f
	}
	src, err := os.Open(*in)
	if err != nil {
		return err
	}
	defer src.Close()
	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
	defer cancel()
	// The format decides the output: a new folder for the files of format 3,
	// a new file for the content of formats 1 and 2. A prelude that does not
	// parse goes the second way, and Open reports it at step 1 or 2.
	var pre [capsule.PreludeSize]byte
	n, _ := src.ReadAt(pre[:], 0)
	var opened *capsule.Opened
	if p, perr := capsule.ParsePrelude(pre[:n]); perr == nil && p.Format == capsule.Format3 {
		if err := checkNew(*out); err != nil {
			return err
		}
		// The folder is created at step 17, after the release is requested:
		// its parent must be a folder before then.
		if info, err := os.Stat(filepath.Dir(*out)); err != nil || !info.IsDir() {
			return fmt.Errorf("decrypt: %s cannot be created: %s is not a folder", *out, filepath.Dir(*out))
		}
		opts.Sink = &dirSink{dir: *out}
		if opened, err = capsule.Open(ctx, nil, src, opts); err != nil {
			return err
		}
	} else {
		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))
	if opened.Format == capsule.Format3 {
		fmt.Fprintf(stderr, "  format 3, %d files\n", len(opened.Head.Files))
		if len(opened.Head.Files) == 0 {
			fmt.Fprintf(stderr, "  no files: %s was not created\n", *out)
		}
		present(stdout, opened, *out, outputWidth(stdout))
		return nil
	}
	fmt.Fprintf(stderr, "  format %d, %d bytes of content\n", opened.Format, opened.PayloadLength)
	if opened.Format == capsule.Format1 {
		// Spec §55.2, §70: format 1 hides neither the number of credentials
		// nor the exact length of the content.
		fmt.Fprintln(stderr, "  format 1 does not hide the number of credentials or the exact length of the content")
	}
	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
}

// 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.New(*in, result, inspectErr)
	if *asJSON {
		if err := v.WriteJSON(stdout); err != nil {
			return err
		}
	} else {
		v.WriteText(stdout)
	}
	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,
	})
}