// This file is part of the happyDomain (R) project.
// Copyright (c) 2020-2026 happyDomain
// Authors: Pierre-Olivier Mercier, et al.
//
// This program is offered under a commercial and under the AGPL license.
// For commercial licensing, contact us at <contact@happydomain.org>.
//
// For AGPL licensing:
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

// Package checker implements an SSH server security checker for
// happyDomain. It probes each SSH endpoint associated with an
// abstract.Server service and produces a structured report covering
// reachability, banner/version posture, algorithm negotiation
// (KEX/HostKey/Cipher/MAC/Compression), authentication method exposure
// and SSHFP host-key fingerprint validation.
package checker

import "time"

// ObservationKeySSH is the observation key this checker writes.
const ObservationKeySSH = "ssh"

// Option ids on CheckerOptions.
const (
	OptionService          = "service"
	OptionDomainName       = "domain_name"
	OptionPorts            = "ports"
	OptionProbeTimeoutMs   = "probeTimeoutMs"
	OptionIncludeAuthProbe = "includeAuthProbe"
)

// Defaults.
const (
	DefaultSSHPort        = 22
	DefaultProbeTimeoutMs = 10000
	MaxConcurrentProbes   = 16
)

// Severity levels used in Issue.Severity.
const (
	SeverityCrit = "crit"
	SeverityWarn = "warn"
	SeverityInfo = "info"
	SeverityOK   = "ok"
)

// SSHData is the full collected payload written under ObservationKeySSH.
type SSHData struct {
	Domain      string       `json:"domain,omitempty"`
	Endpoints   []SSHProbe   `json:"endpoints"`
	SSHFP       SSHFPSummary `json:"sshfp"`
	CollectedAt time.Time    `json:"collected_at"`
}

// SSHFPSummary captures the SSHFP records declared for the service and
// whether a usable chain (DNSSEC) is available.
type SSHFPSummary struct {
	Records []SSHFPRecord `json:"records,omitempty"`
	// Present indicates whether the service carries at least one SSHFP RR.
	Present bool `json:"present"`
}

// SSHFPRecord is a single SSHFP record as declared in the zone.
type SSHFPRecord struct {
	Algorithm   uint8  `json:"algorithm"`   // 1=RSA, 2=DSA, 3=ECDSA, 4=Ed25519
	Type        uint8  `json:"type"`        // 1=SHA-1, 2=SHA-256
	Fingerprint string `json:"fingerprint"` // hex, lowercase
}

// SSHProbe is the outcome of probing a single SSH endpoint.
type SSHProbe struct {
	Host         string `json:"host"`
	Port         uint16 `json:"port"`
	Address      string `json:"address"`
	IP           string `json:"ip,omitempty"`
	IsIPv6       bool   `json:"ipv6,omitempty"`
	TCPConnected bool   `json:"tcp_connected"`

	// Banner is the SSH protocol banner (e.g. "SSH-2.0-OpenSSH_9.3p1").
	Banner    string `json:"banner,omitempty"`
	SoftVer   string `json:"software_version,omitempty"`
	ProtoVer  string `json:"protocol_version,omitempty"`
	Vendor    string `json:"vendor,omitempty"`
	ElapsedMS int64  `json:"elapsed_ms,omitempty"`
	Error     string `json:"error,omitempty"`

	// Algorithms negotiated by the server.
	KEX        []string `json:"kex_algorithms,omitempty"`
	HostKey    []string `json:"host_key_algorithms,omitempty"`
	CiphersC2S []string `json:"ciphers_c2s,omitempty"`
	CiphersS2C []string `json:"ciphers_s2c,omitempty"`
	MACsC2S    []string `json:"macs_c2s,omitempty"`
	MACsS2C    []string `json:"macs_s2c,omitempty"`
	CompC2S    []string `json:"compression_c2s,omitempty"`
	CompS2C    []string `json:"compression_s2c,omitempty"`

	// Host keys observed during KEX. Multiple entries can appear if the
	// server advertises several host-key types and we probe each in a
	// second pass.
	HostKeys []HostKeyInfo `json:"host_keys,omitempty"`

	// Authentication methods advertised for a dummy "none" auth attempt.
	AuthMethods         []string `json:"auth_methods,omitempty"`
	PasswordAuth        bool     `json:"password_auth,omitempty"`
	KeyboardInteractive bool     `json:"keyboard_interactive,omitempty"`
	PublicKeyAuth       bool     `json:"public_key_auth,omitempty"`
	AuthProbeAttempted  bool     `json:"auth_probe_attempted,omitempty"`

	// Stage is the furthest probe stage the connection reached. One of
	// "dial", "banner", "banner_write", "kexinit_read", "kexinit_parse",
	// "kexinit_ok", "handshake_ok". Empty means the dial failed before
	// even being attempted.
	Stage string `json:"stage,omitempty"`
}

// HostKeyInfo captures an observed host key and its computed fingerprints.
type HostKeyInfo struct {
	Type             string `json:"type"`            // e.g. "ssh-ed25519"
	Bits             int    `json:"bits,omitempty"`  // key size (bits)
	SHA256           string `json:"sha256"`          // hex fingerprint (lowercase, no colons)
	SHA1             string `json:"sha1"`            // hex fingerprint (lowercase, no colons)
	SSHFPAlgo        uint8  `json:"sshfp_algorithm"` // the SSHFP algorithm number matching this key type
	SSHFPMatchSHA256 bool   `json:"sshfp_match_sha256"`
	SSHFPMatchSHA1   bool   `json:"sshfp_match_sha1"`
}

// Issue is a single SSH finding surfaced to consumers.
type Issue struct {
	Code     string `json:"code"`
	Severity string `json:"severity"`
	Message  string `json:"message,omitempty"`
	Fix      string `json:"fix,omitempty"`
	// Endpoint is the "host:port" this issue applies to (empty for
	// service-level issues such as missing SSHFP).
	Endpoint string `json:"endpoint,omitempty"`
}