package ssh

import (
	"fmt"
	"strings"
)

// Client describes one OpenSSH program netssh can run. The programs share
// ssh's connection options but differ in flags and destination syntax.
type Client struct {
	Name    string        // binary name: ssh, sftp, or scp
	withArg map[byte]bool // short flags that consume a value
	port    byte          // flag for the port: -p (ssh) or -P (sftp, scp)
	user    byte          // flag for the login user; 0 when only user@ or -o User work
	paths   bool          // destinations are host[:path]
}

var (
	// SSH is the default client; its flag table is flagsWithArg.
	SSH = Client{Name: "ssh", withArg: flagsWithArg, port: 'p', user: 'l'}
	// SFTP follows sftp(1): -l is a bandwidth limit, -P the port.
	SFTP = Client{Name: "sftp", withArg: flagSet("BbcDFiJloPRSsX"), port: 'P', paths: true}
	// SCP follows scp(1); unlike sftp, -B and -R take no value.
	SCP = Client{Name: "scp", withArg: flagSet("cDFiJloPSX"), port: 'P', paths: true}
)

func flagSet(flags string) map[byte]bool {
	set := make(map[byte]bool, len(flags))
	for i := 0; i < len(flags); i++ {
		set[flags[i]] = true
	}
	return set
}

// PortArgs returns the arguments that set port for this client.
func (c Client) PortArgs(port string) []string { return []string{"-" + string(c.port), port} }

// UserArgs returns the arguments that set the login user for this client.
func (c Client) UserArgs(user string) []string {
	if c.user == 0 {
		return []string{"-o", "User=" + user}
	}
	return []string{"-" + string(c.user), user}
}

// Operand is a remote scp argument such as user@host:/path.
type Operand struct {
	Idx  int
	User string
	Host string
	Path string
}

// Operands returns the remote operands of scp arguments. All remote operands
// must name the same host, because one set of options applies per call.
func (c Client) Operands(args []string) ([]Operand, error) {
	start := c.optionsEnd(args)
	var out []Operand
	for i := start; i < len(args); i++ {
		arg := args[i]
		if strings.HasPrefix(arg, "scp://") || strings.HasPrefix(arg, "sftp://") {
			return nil, fmt.Errorf("%q: use host:path instead of a URI", arg)
		}
		dest, path, remote := splitRemote(arg)
		if !remote {
			continue
		}
		host, user := splitUserHost(dest)
		if host == "" {
			continue
		}
		if len(out) > 0 && !strings.EqualFold(out[0].Host, host) {
			return nil, fmt.Errorf("scp between two remote hosts (%s, %s) is not supported; copy in two steps", out[0].Host, host)
		}
		out = append(out, Operand{Idx: i, User: user, Host: host, Path: path})
	}
	return out, nil
}

// optionsEnd returns the index of the first operand; scp, like ssh, stops
// option parsing at the first non-option or after "--".
func (c Client) optionsEnd(args []string) int {
	end := c.insertionPoint(args)
	if end < len(args) && args[end] == "--" {
		end++
	}
	return end
}

// insertionPoint is where added options still count as options: before the
// first operand or before "--".
func (c Client) insertionPoint(args []string) int {
	for i := 0; i < len(args); i++ {
		arg := args[i]
		if arg == "--" {
			return i
		}
		if !strings.HasPrefix(arg, "-") || len(arg) < 2 {
			return i
		}
		if c.takesSeparateValue(arg) {
			i++
		}
	}
	return len(args)
}

// splitRemote mirrors scp's colon(): an argument is remote when a ':' comes
// before any '/'. A leading "[" starts a bracketed IPv6 address.
func splitRemote(arg string) (dest, path string, remote bool) {
	if strings.HasPrefix(arg, "/") || strings.HasPrefix(arg, ".") {
		return "", "", false
	}
	inBracket := false
	for i := 0; i < len(arg); i++ {
		switch arg[i] {
		case '[':
			inBracket = true
		case ']':
			inBracket = false
		case '/':
			if !inBracket {
				return "", "", false
			}
		case ':':
			if !inBracket {
				return arg[:i], arg[i+1:], true
			}
		}
	}
	return "", "", false
}

// HasForwardFlag reports whether -L, -R, or -D (or the -o equivalents) was given.
func (c Client) HasForwardFlag(args []string) bool {
	return c.hasOption(args, 'L', "LocalForward") || c.hasOption(args, 'R', "RemoteForward") || c.hasOption(args, 'D', "DynamicForward")
}