/*
 * Teleport
 * Copyright (C) 2023  Gravitational, Inc.
 *
 * 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 <http://www.gnu.org/licenses/>.
 */

package sshutils

import (
	"encoding/binary"

	"github.com/gravitational/trace"
	"golang.org/x/crypto/ssh"

	"github.com/gravitational/teleport"
)

// EnvReqParams are parameters for env request
type EnvReqParams struct {
	Name  string
	Value string
}

// WinChangeReqParams specifies parameters for window changes
type WinChangeReqParams struct {
	W   uint32
	H   uint32
	Wpx uint32
	Hpx uint32
}

// PTYReqParams specifies parameters for pty change window
type PTYReqParams struct {
	Env   string
	W     uint32
	H     uint32
	Wpx   uint32
	Hpx   uint32
	Modes string
}

// ForwardedTCPIPRequest specifies parameters for opening a port forwarding
// channel from the server.
type ForwardedTCPIPRequest struct {
	Addr     string
	Port     uint32
	OrigAddr string
	OrigPort uint32
}

// CheckAndSetDefaults checks and sets default values.
func (req *ForwardedTCPIPRequest) CheckAndSetDefaults() error {
	if req.Addr == "" {
		return trace.BadParameter("missing field Addr")
	}
	if req.Port == 0 {
		return trace.BadParameter("missing field Port")
	}
	if req.OrigAddr == "" {
		return trace.BadParameter("missing field OrigAddr")
	}
	if req.OrigPort == 0 {
		return trace.BadParameter("missing field OrigPort")
	}
	return nil
}

// TerminalModes converts encoded terminal modes into a ssh.TerminalModes map.
// The encoding is described in: https://tools.ietf.org/html/rfc4254#section-8
//
//	All 'encoded terminal modes' (as passed in a pty request) are encoded
//	into a byte stream.  It is intended that the coding be portable
//	across different environments.  The stream consists of opcode-
//	argument pairs wherein the opcode is a byte value.  Opcodes 1 to 159
//	have a single uint32 argument.  Opcodes 160 to 255 are not yet
//	defined, and cause parsing to stop (they should only be used after
//	any other data).  The stream is terminated by opcode TTY_OP_END
//	(0x00).
//
// In practice, this means encoded terminal modes get translated like below:
//
//	0x80 0x00 0x00 0x38 0x40  0x81 0x00 0x00 0x38 0x40  0x35 0x00 0x00 0x00 0x00  0x00
//	|___|__________________|  |___|__________________|  |___|__________________|  |__|
//	       0x80: 0x3840              0x81: 0x3840              0x35: 0x00         0x00
//	ssh.TTY_OP_ISPEED: 14400  ssh.TTY_OP_OSPEED: 14400         ssh.ECHO:0
func (p *PTYReqParams) TerminalModes() (ssh.TerminalModes, error) {
	terminalModes := ssh.TerminalModes{}

	if len(p.Modes) == 1 && p.Modes[0] == 0 {
		return terminalModes, nil
	}

	chunkSize := 5
	for i := 0; i < len(p.Modes); i = i + chunkSize {
		// the first byte of the chunk is the key
		key := p.Modes[i]

		// a key with value 0 means is the termination of the stream
		if key == 0 {
			break
		}

		// the remaining 4 bytes of the chunk are the value
		if i+chunkSize > len(p.Modes) {
			return nil, trace.BadParameter("invalid terminal modes encoding")
		}
		value := binary.BigEndian.Uint32([]byte(p.Modes[i+1 : i+chunkSize]))

		terminalModes[key] = value
	}

	return terminalModes, nil
}

// Check validates PTY parameters.
func (p *PTYReqParams) Check() error {
	if p.W > maxSize || p.W < minSize {
		return trace.BadParameter("bad width: %v", p.W)
	}
	if p.H > maxSize || p.H < minSize {
		return trace.BadParameter("bad height: %v", p.H)
	}

	return nil
}

// CheckAndSetDefaults validates PTY parameters and ensures parameters
// are within default values.
func (p *PTYReqParams) CheckAndSetDefaults() error {
	if p.W > maxSize || p.W < minSize {
		p.W = teleport.DefaultTerminalWidth
	}
	if p.H > maxSize || p.H < minSize {
		p.H = teleport.DefaultTerminalHeight
	}

	return nil
}

// ExecReq specifies parameters for a "exec" request.
type ExecReq struct {
	Command string
}

// SubsystemReq specifies the parameters for a "subsystem" request.
type SubsystemReq struct {
	Name string
}

// SessionEnvVar is environment variable for SSH session
const SessionEnvVar = "TELEPORT_SESSION"

const (
	// ExecRequest is a request to run a command.
	ExecRequest = "exec"

	// ShellRequest is a request for a shell.
	ShellRequest = "shell"

	// EnvRequest is a request to set an environment variable.
	EnvRequest = "env"

	// SubsystemRequest is a request to run a subsystem.
	SubsystemRequest = "subsystem"

	// WindowChangeRequest is a request to change window.
	WindowChangeRequest = "window-change"

	// PTYRequest is a request for PTY.
	PTYRequest = "pty-req"

	// AgentForwardRequest is SSH agent request.
	AgentForwardRequest = "auth-agent-req@openssh.com"

	// AuthAgentRequest is a request to a SSH client to open an agent channel.
	AuthAgentRequest = "auth-agent@openssh.com"

	// X11ForwardRequest is a request to initiate X11 forwarding.
	X11ForwardRequest = "x11-req"

	// X11ChannelRequest is the type of an X11 forwarding channel.
	X11ChannelRequest = "x11"

	// PuTTYSimpleRequest is a PuTTY-specific channel name which it automatically requests when it proxies
	// connections. Teleport does not support this channel type, so deliberately ignores requests for it.
	PuTTYSimpleRequest = "simple@putty.projects.tartarus.org"

	// PuTTYWinadjRequest is a PuTTY-specific channel name which it automatically requests to measure window
	// size on active connections, expecting a failure response from the server.
	PuTTYWinadjRequest = "winadj@putty.projects.tartarus.org"
)

const (
	minSize = 1
	maxSize = 4096
)