// Package process is the low-level abstraction for a Tor instance.
//
// The standard use is to create a Creator with NewCreator and the path to the
// Tor executable. The child package 'embedded' can be used if Tor is statically
// linked in the binary. Most developers will prefer the tor package adjacent to
// this one for a higher level abstraction over the process and control port
// connection.
package process

import (
	"context"
	"fmt"
	"net"
	"os"
	"os/exec"
	"strconv"
	"strings"

	"git.openprivacy.ca/openprivacy/bine/torutil"
)

// Process is the interface implemented by Tor processes.
type Process interface {
	// Start starts the Tor process in the background and returns. It is
	// analagous to os/exec.Cmd.Start.
	Start() error
	// Wait waits for the Tor process to exit and returns error if it was not a
	// successful exit. It is analagous to os/exec.Cmd.Wait.
	Wait() error
	// ControlConn is used for statically linked, embedded processes to create
	// a controller connection. For non-embedded processes or Tor versions that
	// don't support embedded control connections, ErrControlConnUnsupported is
	// returned. Note, this should only be called once per process before
	// Start, and the connection does not need to be closed.
	EmbeddedControlConn() (net.Conn, error)
}

// Creator is the interface for process creation.
type Creator interface {
	New(ctx context.Context, args ...string) (Process, error)
}

type CmdCreatorFunc func(ctx context.Context, args ...string) (*exec.Cmd, error)

// NewCreator creates a Creator for external Tor process execution based on the
// given exe path.
func NewCreator(exePath string) Creator {
	return CmdCreatorFunc(func(ctx context.Context, args ...string) (*exec.Cmd, error) {
		cmd := exec.CommandContext(ctx, exePath, args...)
		cmd.Stdout = os.Stdout
		cmd.Stderr = os.Stderr
		return cmd, nil
	})
}

type exeProcess struct {
	*exec.Cmd
}

func (c CmdCreatorFunc) New(ctx context.Context, args ...string) (Process, error) {
	cmd, err := c(ctx, args...)
	return &exeProcess{cmd}, err
}

// ErrControlConnUnsupported is returned by Process.EmbeddedControlConn when
// it is unsupported.
var ErrControlConnUnsupported = fmt.Errorf("Control conn not supported")

func (e *exeProcess) EmbeddedControlConn() (net.Conn, error) {
	return nil, ErrControlConnUnsupported
}

// ControlPortFromFileContents reads a control port file that is written by Tor
// when ControlPortWriteToFile is set.
func ControlPortFromFileContents(contents string) (int, error) {
	contents = strings.TrimSpace(contents)
	_, port, ok := torutil.PartitionString(contents, ':')
	if !ok || !strings.HasPrefix(contents, "PORT=") {
		return 0, fmt.Errorf("Invalid port format: %v", contents)
	}
	return strconv.Atoi(port)
}
