// Package invite encodes and decodes waste invite strings.
//
// Format: "waste:<url-safe-base64(json)>"
//
// The JSON payload is compatible with yaw2: the `net` field carries the full
// 64-char hex SHA-256("yaw2-net:"+name) hash that yaw2 clients pass directly
// to the signaling server. A yaw2 client that can parse the base64 JSON can join
// the same network without knowing the plaintext name.
//
// Signed invites (waste-go extension): when `inviter` and `sig` are present,
// the invite was issued by a known peer. Receiving peers that enforce
// RequireInvite will reject hellos that carry no valid signed invite.
// YAW/2-only peers ignore both fields.
package invite

import (
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"strings"
)

const prefix = "waste:"

// Invite holds the information needed to join a network.
type Invite struct {
	Anchor  string `json:"anchor"`            // WebSocket anchor URL
	Network string `json:"network"`           // plaintext network name
	Net     string `json:"net,omitempty"`     // 64-char hex SHA-256("yaw2-net:"+name) — yaw2 `net` field
	Inviter string `json:"inviter,omitempty"` // hex Ed25519 pubkey of the signing peer (waste-go extension)
	Sig     string `json:"sig,omitempty"`     // hex Ed25519 sig over canonical payload (waste-go extension)
}

// IsSigned reports whether the invite carries a signature.
func (inv Invite) IsSigned() bool { return inv.Inviter != "" && inv.Sig != "" }

// Signer can sign data and report its own peer ID.
type Signer interface {
	Sign(data []byte) string
	PeerIDHex() string
}

// Verifier verifies an Ed25519 signature given a hex public key.
type Verifier func(publicKeyHex string, data []byte, sigHex string) error

// Encode returns an unsigned waste: invite string (backward compatible).
func Encode(anchor, network string) (string, error) {
	return marshal(Invite{
		Anchor:  anchor,
		Network: network,
		Net:     NetHash(network),
	})
}

// EncodeSigned returns a signed waste: invite string.
// The signature covers: anchor + NUL + network + NUL + net + NUL + inviter.
func EncodeSigned(anchor, network string, signer Signer) (string, error) {
	if anchor == "" {
		return "", fmt.Errorf("anchor URL is required")
	}
	if network == "" {
		return "", fmt.Errorf("network name is required")
	}
	inviter := signer.PeerIDHex()
	net := NetHash(network)
	sig := signer.Sign(sigPayload(anchor, network, net, inviter))
	return marshal(Invite{
		Anchor:  anchor,
		Network: network,
		Net:     net,
		Inviter: inviter,
		Sig:     sig,
	})
}

// Verify checks the invite signature and that the inviter is in the trusted set.
// Unsigned invites return nil — the caller decides whether to accept them.
func Verify(inv Invite, trusted map[string]bool, verify Verifier) error {
	if !inv.IsSigned() {
		return nil
	}
	payload := sigPayload(inv.Anchor, inv.Network, inv.Net, inv.Inviter)
	if err := verify(inv.Inviter, payload, inv.Sig); err != nil {
		return fmt.Errorf("invite signature invalid: %w", err)
	}
	if !trusted[inv.Inviter] {
		return fmt.Errorf("invite signed by unknown peer %s", inv.Inviter[:16])
	}
	return nil
}

// Decode parses a waste: invite string and returns the Invite.
func Decode(s string) (Invite, error) {
	s = strings.TrimSpace(s)
	if !strings.HasPrefix(s, prefix) {
		return Invite{}, fmt.Errorf("not a waste invite (expected 'waste:' prefix)")
	}
	b, err := base64.URLEncoding.DecodeString(strings.TrimPrefix(s, prefix))
	if err != nil {
		return Invite{}, fmt.Errorf("invalid invite: %w", err)
	}
	var inv Invite
	if err := json.Unmarshal(b, &inv); err != nil {
		return Invite{}, fmt.Errorf("invalid invite payload: %w", err)
	}
	if inv.Anchor == "" || inv.Network == "" {
		return Invite{}, fmt.Errorf("invite is missing anchor or network name")
	}
	return inv, nil
}

// NetHash returns the full 64-char hex network hash for the given name.
func NetHash(name string) string {
	h := sha256.Sum256([]byte("yaw2-net:" + name))
	return hex.EncodeToString(h[:])
}

func marshal(inv Invite) (string, error) {
	b, err := json.Marshal(inv)
	if err != nil {
		return "", err
	}
	return prefix + base64.URLEncoding.EncodeToString(b), nil
}

func sigPayload(anchor, network, net, inviter string) []byte {
	return []byte(anchor + "\x00" + network + "\x00" + net + "\x00" + inviter)
}