// Package profile implements Provider Profiles (spec §10-§13): their
// Deterministic CBOR encoding, profile_hash, validation and the locally
// pinned registry that forms the client's root of trust.
package profile

import (
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"math"
	"time"

	"github.com/drand/drand/v2/common/chain"
	"github.com/drand/drand/v2/crypto"

	datekeys "g.activething.com/go/DateKeys"
	"g.activething.com/go/DateKeys/codec"
)

// Schema constants of the Provider Profile CBOR map (spec §11).
const (
	TypeTag       = "datekeys-provider-profile"
	SchemaVersion = 1
)

// ProviderDrand is the only provider implemented by this module (spec §12).
const ProviderDrand = "drand"

// MaxUnixTime is 9999-12-31T23:59:59Z. Round times beyond it are rejected so
// that every effective time stays representable in RFC 3339 and every round
// computation stays within int64.
const MaxUnixTime int64 = 253402300799

// Field limits enforced by Validate. They are implementation limits; spec §74
// leaves the definitive field limits open.
const (
	maxIDLen        = 128
	maxNameLen      = 64
	maxPublicKeyLen = 1024
	maxPeriod       = 24 * time.Hour
)

// Profile is an immutable Provider Profile (spec §10). Treat values as
// read-only; registries hand out copies.
type Profile struct {
	ID          string        // key 2, profile_id, for example "datekeys:quicknet:v1"
	Provider    string        // key 3, for example "drand"
	Network     string        // key 4, provider network identifier, for example "quicknet"
	ChainHash   [32]byte      // key 5
	PublicKey   []byte        // key 6, provider group public key
	Period      time.Duration // key 7, encoded as whole seconds
	GenesisTime int64         // key 8, Unix seconds
	Scheme      string        // key 9, for example "bls-unchained-g1-rfc9380"
	GenesisSeed [32]byte      // key 10
}

// wire is the CBOR map of spec §11, keys 2 to 10; keys 0 and 1 are the
// constants TypeTag and SchemaVersion. Every key is required.
type wire struct {
	ID          string // key 2
	Provider    string // key 3
	Network     string // key 4
	ChainHash   []byte // key 5
	PublicKey   []byte // key 6
	Period      uint64 // key 7, 1..2^53-1
	GenesisTime uint64 // key 8, 0..2^53-1
	Scheme      string // key 9
	GenesisSeed []byte // key 10
}

// wireKeys is the number of keys of the map, all required.
const wireKeys = 11

// unbounded bounds a field only by the input: its rule carries its own error
// code (spec §57) and Validate checks it after decoding.
const unbounded = math.MaxInt

func (w *wire) encode(e *codec.Encoder) {
	e.Map(wireKeys)
	e.Uint(0)
	e.Text(TypeTag)
	e.Uint(1)
	e.Uint(SchemaVersion)
	e.Uint(2)
	e.Text(w.ID)
	e.Uint(3)
	e.Text(w.Provider)
	e.Uint(4)
	e.Text(w.Network)
	e.Uint(5)
	e.Bstr(w.ChainHash)
	e.Uint(6)
	e.Bstr(w.PublicKey)
	e.Uint(7)
	e.Uint(w.Period)
	e.Uint(8)
	e.Uint(w.GenesisTime)
	e.Uint(9)
	e.Text(w.Scheme)
	e.Uint(10)
	e.Bstr(w.GenesisSeed)
}

// decode reads the map with every CDDL rule whose violation is
// ErrNonCanonicalCBOR; the names and the public key are left to Validate.
func (w *wire) decode(d *codec.Decoder) error {
	pairs, err := d.Map(wireKeys)
	if err != nil {
		return err
	}
	if pairs != wireKeys {
		return fmt.Errorf("%d keys, want all %d: %w", pairs, wireKeys, datekeys.ErrNonCanonicalCBOR)
	}
	for want := range uint64(wireKeys) {
		k, err := d.Key()
		if err != nil {
			return err
		}
		if k != want {
			return fmt.Errorf("key %d where key %d was expected: %w", k, want, datekeys.ErrNonCanonicalCBOR)
		}
		switch k {
		case 0:
			_, err = d.Text(len(TypeTag))
		case 1:
			_, err = d.Uint(SchemaVersion)
		case 2:
			w.ID, err = d.Text(unbounded)
		case 3:
			w.Provider, err = d.Text(unbounded)
		case 4:
			w.Network, err = d.Text(unbounded)
		case 5:
			w.ChainHash, err = d.Bstr(32, 32)
		case 6:
			w.PublicKey, err = d.Bstr(0, unbounded)
		case 7:
			// Spec §11: period in 1..2^53-1.
			if w.Period, err = d.Uint(codec.MaxSafeUint); err == nil && w.Period == 0 {
				err = fmt.Errorf("period 0: %w", datekeys.ErrNonCanonicalCBOR)
			}
		case 8:
			// Spec §11: genesis_time in 0..2^53-1, unsigned.
			w.GenesisTime, err = d.Uint(codec.MaxSafeUint)
		case 9:
			w.Scheme, err = d.Text(unbounded)
		case 10:
			w.GenesisSeed, err = d.Bstr(32, 32)
		}
		if err != nil {
			return fmt.Errorf("key %d: %w", k, err)
		}
	}
	return d.EndMap()
}

// Clone returns a deep copy of p.
func (p *Profile) Clone() *Profile {
	c := *p
	c.PublicKey = bytes.Clone(p.PublicKey)
	return &c
}

// CanonicalCBOR returns the exact Deterministic CBOR bytes of spec §11.
func (p *Profile) CanonicalCBOR() ([]byte, error) {
	if p.Period <= 0 || p.Period%time.Second != 0 {
		return nil, fmt.Errorf("profile: period %s is not a positive whole number of seconds: %w", p.Period, datekeys.ErrNonCanonicalCBOR)
	}
	// Spec §11: genesis_time in 0..2^53-1. The period needs no such check:
	// a time.Duration holds at most about 9.2e9 seconds.
	if p.GenesisTime < 0 || p.GenesisTime > codec.MaxSafeUint {
		return nil, fmt.Errorf("profile: genesis time %d outside 0..%d: %w", p.GenesisTime, int64(codec.MaxSafeUint), datekeys.ErrNonCanonicalCBOR)
	}
	w := wire{
		ID:          p.ID,
		Provider:    p.Provider,
		Network:     p.Network,
		ChainHash:   p.ChainHash[:],
		PublicKey:   p.PublicKey,
		Period:      uint64(p.Period / time.Second),
		GenesisTime: uint64(p.GenesisTime),
		Scheme:      p.Scheme,
		GenesisSeed: p.GenesisSeed[:],
	}
	var e codec.Encoder
	w.encode(&e)
	return e.Out()
}

// Hash returns profile_hash = SHA-256(exact_deterministic_cbor_bytes) (spec §11).
//
// A profile_hash declared by a remote party has no security value; security
// comes from the profile pinned locally (spec §11, §13).
func (p *Profile) Hash() ([32]byte, error) {
	b, err := p.CanonicalCBOR()
	if err != nil {
		return [32]byte{}, err
	}
	return sha256.Sum256(b), nil
}

// Decode parses the Deterministic CBOR encoding of a Provider Profile and
// validates it. It does not make the profile trusted: only a Registry built by
// the caller does (spec §13).
func Decode(b []byte) (*Profile, error) {
	if err := codec.CheckSchema(b, TypeTag, SchemaVersion); err != nil {
		return nil, fmt.Errorf("profile: %w", err)
	}
	var w wire
	if err := codec.Unmarshal(b, w.decode, w.encode); err != nil {
		return nil, fmt.Errorf("profile: %w", err)
	}
	if w.Period > uint64(maxPeriod/time.Second) {
		return nil, fmt.Errorf("profile: period %d s out of range: %w", w.Period, datekeys.ErrNonCanonicalCBOR)
	}
	p := &Profile{
		ID:          w.ID,
		Provider:    w.Provider,
		Network:     w.Network,
		PublicKey:   w.PublicKey,
		Period:      time.Duration(w.Period) * time.Second,
		GenesisTime: int64(w.GenesisTime),
		Scheme:      w.Scheme,
	}
	copy(p.ChainHash[:], w.ChainHash)
	copy(p.GenesisSeed[:], w.GenesisSeed)
	if err := p.Validate(); err != nil {
		return nil, err
	}
	return p, nil
}

// Validate checks the syntax of every field and, for drand profiles, that the
// scheme is supported, that the public key is a valid group element and that
// the chain hash is the drand chain-info hash of the other parameters. The
// last check is the self-verification kept from the prototype: a profile whose
// parameters do not produce its own chain hash is rejected.
func (p *Profile) Validate() error {
	if !ValidID(p.ID) {
		return fmt.Errorf("profile: invalid profile_id %q: %w", p.ID, datekeys.ErrUnknownProfile)
	}
	if !validName(p.Provider) || !validName(p.Network) || !validName(p.Scheme) {
		return fmt.Errorf("profile %s: invalid provider, network or scheme name: %w", p.ID, datekeys.ErrUnknownProfile)
	}
	if len(p.PublicKey) == 0 || len(p.PublicKey) > maxPublicKeyLen {
		return fmt.Errorf("profile %s: invalid public key length %d: %w", p.ID, len(p.PublicKey), datekeys.ErrUnknownProfile)
	}
	if p.Period <= 0 || p.Period > maxPeriod || p.Period%time.Second != 0 {
		return fmt.Errorf("profile %s: invalid period %s: %w", p.ID, p.Period, datekeys.ErrUnknownProfile)
	}
	if p.GenesisTime <= 0 || p.GenesisTime >= MaxUnixTime {
		return fmt.Errorf("profile %s: invalid genesis time %d: %w", p.ID, p.GenesisTime, datekeys.ErrUnknownProfile)
	}
	if p.Provider != ProviderDrand {
		return fmt.Errorf("profile %s: unsupported provider %q: %w", p.ID, p.Provider, datekeys.ErrUnknownProfile)
	}
	return p.validateDrand()
}

func (p *Profile) validateDrand() error {
	scheme, err := p.DrandScheme()
	if err != nil {
		return err
	}
	switch scheme.Name {
	case crypto.SigsOnG1ID, crypto.UnchainedSchemeID, crypto.ShortSigSchemeID:
	default:
		return fmt.Errorf("profile %s: scheme %q is not supported by tlock: %w", p.ID, scheme.Name, datekeys.ErrUnknownProfile)
	}
	key := scheme.KeyGroup.Point()
	if err := key.UnmarshalBinary(p.PublicKey); err != nil {
		return fmt.Errorf("profile %s: public key is not a %s group element: %w", p.ID, scheme.Name, datekeys.ErrUnknownProfile)
	}
	if key.Equal(key.Null()) {
		return fmt.Errorf("profile %s: public key is the identity element: %w", p.ID, datekeys.ErrUnknownProfile)
	}
	info := chain.Info{
		PublicKey:   key,
		ID:          p.Network,
		Period:      p.Period,
		Scheme:      p.Scheme,
		GenesisTime: p.GenesisTime,
		GenesisSeed: p.GenesisSeed[:],
	}
	if !bytes.Equal(info.Hash(), p.ChainHash[:]) {
		return fmt.Errorf("profile %s: parameters hash to chain %s, not the pinned %s: %w",
			p.ID, info.HashString(), hex.EncodeToString(p.ChainHash[:]), datekeys.ErrProfileMismatch)
	}
	return nil
}

// DrandScheme returns a fresh drand scheme object for p. Fresh objects avoid
// sharing mutable kyber state between callers.
func (p *Profile) DrandScheme() (*crypto.Scheme, error) {
	if p.Provider != ProviderDrand {
		return nil, fmt.Errorf("profile %s: provider %q is not drand: %w", p.ID, p.Provider, datekeys.ErrUnknownProfile)
	}
	scheme, err := crypto.SchemeFromName(p.Scheme)
	if err != nil {
		return nil, fmt.Errorf("profile %s: %v: %w", p.ID, err, datekeys.ErrUnknownProfile)
	}
	return scheme, nil
}

// ChainHashHex returns the lowercase hexadecimal chain hash, the form used in
// tlock stanzas and drand relay URLs.
func (p *Profile) ChainHashHex() string { return hex.EncodeToString(p.ChainHash[:]) }

// MaxRound is the last round whose round time is not after MaxUnixTime.
func (p *Profile) MaxRound() uint64 {
	period := int64(p.Period / time.Second)
	if period <= 0 || p.GenesisTime >= MaxUnixTime {
		return 0
	}
	return uint64((MaxUnixTime-p.GenesisTime)/period) + 1
}

// ValidID reports whether s is a syntactically valid profile_id: 1 to 128
// characters from [a-z0-9:._-], starting with a letter or digit. The restricted
// alphabet keeps the dk1_ JSON form free of escapes (spec §18, §19).
func ValidID(s string) bool {
	if len(s) == 0 || len(s) > maxIDLen || !alnum(s[0]) {
		return false
	}
	for i := 0; i < len(s); i++ {
		c := s[i]
		if !alnum(c) && c != ':' && c != '.' && c != '_' && c != '-' {
			return false
		}
	}
	return true
}

func validName(s string) bool {
	if len(s) == 0 || len(s) > maxNameLen || !alnum(s[0]) {
		return false
	}
	for i := 0; i < len(s); i++ {
		c := s[i]
		if !alnum(c) && c != '.' && c != '_' && c != '-' {
			return false
		}
	}
	return true
}

func alnum(c byte) bool { return (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') }