//go:build unix

package host

import (
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"

	"github.com/carlosframework/platform/internal/registry"
)

const registryChildCommand = "__registry-child"

func openRegistryChild(path string, uid, gid int) (*registry.Registry, error) {
	return openRegistryChildMode(path, uid, gid, false)
}

func openRegistryChildReadOnly(path string, uid, gid int) (*registry.Registry, error) {
	return openRegistryChildMode(path, uid, gid, true)
}

func openRegistryChildMode(path string, uid, gid int, readOnly bool) (*registry.Registry, error) {
	if uid <= 0 || gid < 0 {
		return nil, errors.New("registry: invalid service credentials")
	}
	path, err := filepath.Abs(path)
	if err != nil {
		return nil, err
	}
	return registry.OpenRemoteReconnect(path, func() (io.WriteCloser, io.ReadCloser, func() error, error) {
		cmd, err := registryChildExec(path, uid, gid)
		if err != nil {
			return nil, nil, nil, err
		}
		if readOnly {
			cmd.Args = append(cmd.Args, "read-only")
		}
		return registryChildPipes(cmd, uid, gid)
	})
}

func startRegistryChild(cmd *exec.Cmd, path string, uid, gid int) (*registry.Registry, error) {
	input, output, wait, err := registryChildPipes(cmd, uid, gid)
	if err != nil {
		return nil, err
	}
	return registry.OpenRemote(path, input, output, wait)
}

func registryChildPipes(cmd *exec.Cmd, uid, gid int) (io.WriteCloser, io.ReadCloser, func() error, error) {
	if uid <= 0 || gid < 0 {
		return nil, nil, nil, errors.New("registry: invalid service credentials")
	}
	if err := registryChildCloseExec(); err != nil {
		return nil, nil, nil, err
	}
	cmd.Env = []string{}
	if value, ok := os.LookupEnv("CARLOS_HOST_CLAIM"); ok {
		cmd.Env = append(cmd.Env, "CARLOS_HOST_CLAIM="+value)
	}
	cmd.Dir = "/"
	cmd.SysProcAttr = nil
	cmd.Stderr = os.Stderr
	input, err := cmd.StdinPipe()
	if err != nil {
		return nil, nil, nil, err
	}
	output, err := cmd.StdoutPipe()
	if err != nil {
		input.Close()
		return nil, nil, nil, err
	}
	if err = registryChildStart(cmd); err != nil {
		input.Close()
		output.Close()
		return nil, nil, nil, err
	}
	return input, output, cmd.Wait, nil
}

// RunRegistryChild is the private re-exec entry point, before CLI dispatch.
func RunRegistryChild(args []string) error {
	if err := registryChildHarden(); err != nil {
		return err
	}
	closeRegistryExecutable()
	readOnly := len(args) == 4 && args[3] == "read-only"
	if len(args) != 3 && !readOnly {
		return errors.New("registry: invalid child arguments")
	}
	uid, err := strconv.Atoi(args[1])
	if err != nil {
		return err
	}
	gid, err := strconv.Atoi(args[2])
	if err != nil {
		return err
	}
	groups, err := os.Getgroups()
	if err != nil {
		return err
	}
	if uid <= 0 || os.Getuid() != uid || os.Geteuid() != uid || os.Getgid() != gid || os.Getegid() != gid || len(groups) != 0 {
		return fmt.Errorf("registry: child credentials were not dropped")
	}
	if readOnly {
		return registry.ServeRemoteReadOnly(args[0], os.Stdin, os.Stdout)
	}
	return registry.ServeRemote(args[0], os.Stdin, os.Stdout)
}