// Mgmt
// Copyright (C) James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.
//
// Additional permission under GNU GPL version 3 section 7
//
// If you modify this program, or any covered work, by linking or combining it
// with embedded mcl code and modules (and that the embedded mcl code and
// modules which link with this program, contain a copy of their source code in
// the authoritative form) containing parts covered by the terms of any other
// license, the licensors of this program grant you additional permission to
// convey the resulting work. Furthermore, the licensors of this program grant
// the original author, James Shubin, additional permission to update this
// additional permission if he deems it necessary to achieve the goals of this
// additional permission.

package resources

import (
	"context"
	"fmt"
	"io"
	"os/exec"
	"os/user"
	"sort"
	"strconv"
	"strings"
	"syscall"

	"github.com/purpleidea/mgmt/engine"
	"github.com/purpleidea/mgmt/engine/traits"
	"github.com/purpleidea/mgmt/util/errwrap"
	"github.com/purpleidea/mgmt/util/recwatch"
)

func init() {
	engine.RegisterResource("user", func() engine.Res { return &UserRes{} })
}

const passwdFile = "/etc/passwd"

// UserRes is a user account resource.
type UserRes struct {
	traits.Base // add the base methods without re-implementation
	traits.Edgeable

	init *engine.Init

	// State is either exists or absent.
	State string `lang:"state" yaml:"state"`

	// UID specifies the usually unique user ID. It must be unique unless
	// AllowDuplicateUID is true.
	UID *uint32 `lang:"uid" yaml:"uid"`

	// GID of the user's primary group.
	GID *uint32 `lang:"gid" yaml:"gid"`

	// Group is the name of the user's primary group.
	Group *string `lang:"group" yaml:"group"`

	// Groups are a list of supplemental groups.
	Groups []string `lang:"groups" yaml:"groups"`

	// HomeDir is the path to the user's home directory.
	HomeDir *string `lang:"homedir" yaml:"homedir"`

	// AllowDuplicateUID is needed for a UID to be non-unique. This is rare
	// but happens if you want more than one username to access the
	// resources of the same UID. See the --non-unique flag in `useradd`.
	AllowDuplicateUID bool `lang:"allowduplicateuid" yaml:"allowduplicateuid"`

	recWatcher *recwatch.RecWatcher
}

// Default returns some sensible defaults for this resource.
func (obj *UserRes) Default() engine.Res {
	return &UserRes{}
}

// Validate if the params passed in are valid data.
func (obj *UserRes) Validate() error {
	const whitelist string = "_abcdefghijklmnopqrstuvwxyz0123456789"

	if obj.State != "exists" && obj.State != "absent" {
		return fmt.Errorf("state must be 'exists' or 'absent'")
	}
	if obj.GID != nil && obj.Group != nil {
		return fmt.Errorf("cannot use both GID and Group")
	}
	if obj.Group != nil {
		if *obj.Group == "" {
			return fmt.Errorf("group cannot be empty string")
		}
		for _, char := range *obj.Group {
			if !strings.Contains(whitelist, string(char)) {
				return fmt.Errorf("group contains invalid character(s)")
			}
		}
	}
	if obj.Groups != nil {
		for _, group := range obj.Groups {
			if group == "" {
				return fmt.Errorf("group cannot be empty string")
			}
			for _, char := range group {
				if !strings.Contains(whitelist, string(char)) {
					return fmt.Errorf("groups list contains invalid character(s)")
				}
			}
		}
	}
	return nil
}

// Init runs some startup code for this resource.
func (obj *UserRes) Init(init *engine.Init) error {
	obj.init = init // save for later

	return nil
}

// Cleanup is run by the engine to clean up after the resource is done.
func (obj *UserRes) Cleanup() error {
	return nil
}

// Watch is the primary listener for this resource and it outputs events.
func (obj *UserRes) Watch(ctx context.Context) error {
	var err error
	obj.recWatcher, err = recwatch.NewRecWatcher(passwdFile, false)
	if err != nil {
		return err
	}
	defer obj.recWatcher.Close()

	obj.init.Running() // when started, notify engine that we're running

	var send = false // send event?
	for {
		if obj.init.Debug {
			obj.init.Logf("watching: %s", passwdFile) // attempting to watch...
		}

		select {
		case event, ok := <-obj.recWatcher.Events():
			if !ok { // channel shutdown
				return nil
			}
			if err := event.Error; err != nil {
				return errwrap.Wrapf(err, "unknown %s watcher error", obj)
			}
			if obj.init.Debug { // don't access event.Body if event.Error isn't nil
				obj.init.Logf("event(%s): %v", event.Body.Name, event.Body.Op)
			}
			send = true

		case <-ctx.Done(): // closed by the engine to signal shutdown
			return nil
		}

		// do all our event sending all together to avoid duplicate msgs
		if send {
			send = false
			obj.init.Event() // notify engine of an event (this can block)
		}
	}
}

// CheckApply method for User resource.
func (obj *UserRes) CheckApply(ctx context.Context, apply bool) (bool, error) {
	exists := true
	usr, err := user.Lookup(obj.Name())
	if err != nil {
		if _, ok := err.(user.UnknownUserError); !ok {
			return false, errwrap.Wrapf(err, "error looking up user")
		}
		exists = false
	}

	if obj.AllowDuplicateUID == false && obj.UID != nil {
		existingUID, err := user.LookupId(strconv.Itoa(int(*obj.UID)))
		if err != nil {
			if _, ok := err.(user.UnknownUserIdError); !ok {
				return false, errwrap.Wrapf(err, "error looking up UID")
			}
		} else if existingUID.Username != obj.Name() {
			return false, fmt.Errorf("the requested UID is already taken")
		}
	}

	if obj.State == "absent" && !exists {
		return true, nil
	}

	if usercheck := true; exists && obj.State == "exists" {
		intUID, err := strconv.Atoi(usr.Uid)
		if err != nil {
			return false, errwrap.Wrapf(err, "error casting UID to int")
		}
		intGID, err := strconv.Atoi(usr.Gid)
		if err != nil {
			return false, errwrap.Wrapf(err, "error casting GID to int")
		}
		if obj.UID != nil && int(*obj.UID) != intUID {
			usercheck = false
		}
		if obj.GID != nil && int(*obj.GID) != intGID {
			usercheck = false
		}
		if obj.HomeDir != nil && *obj.HomeDir != usr.HomeDir {
			usercheck = false
		}
		if usercheck {
			return true, nil
		}
	}

	if !apply {
		return false, nil
	}

	var cmdName string
	var args []string
	if obj.State == "exists" {
		if exists {
			cmdName = "usermod"
			obj.init.Logf("modifying user: %s", obj.Name())
		} else {
			cmdName = "useradd"
			obj.init.Logf("adding user: %s", obj.Name())
		}
		if obj.AllowDuplicateUID {
			args = append(args, "--non-unique")
		}
		if obj.UID != nil {
			args = append(args, "--uid", fmt.Sprintf("%d", *obj.UID))
		}
		if obj.GID != nil {
			args = append(args, "--gid", fmt.Sprintf("%d", *obj.GID))
		}
		if obj.Group != nil {
			args = append(args, "--gid", *obj.Group)
		}
		if obj.Groups != nil {
			args = append(args, "--groups", strings.Join(obj.Groups, ","))
		}
		if obj.HomeDir != nil {
			args = append(args, "--home", *obj.HomeDir)
		}
	}
	if obj.State == "absent" {
		cmdName = "userdel"
		args = []string{}
		obj.init.Logf("deleting user: %s", obj.Name())
	}

	args = append(args, obj.Name())

	cmd := exec.CommandContext(ctx, cmdName, args...)
	cmd.SysProcAttr = &syscall.SysProcAttr{
		Setpgid: true,
		Pgid:    0,
	}

	// open a pipe to get error messages from os/exec
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return false, errwrap.Wrapf(err, "failed to initialize stderr pipe")
	}

	// start the command
	if err := cmd.Start(); err != nil {
		return false, errwrap.Wrapf(err, "cmd failed to start")
	}
	// capture any error messages
	slurp, err := io.ReadAll(stderr)
	if err != nil {
		return false, errwrap.Wrapf(err, "error slurping error message")
	}
	// wait until cmd exits and return error message if any
	if err := cmd.Wait(); err != nil {
		return false, errwrap.Wrapf(err, "%s", slurp)
	}

	return false, nil
}

// Cmp compares two resources and returns an error if they are not equivalent.
func (obj *UserRes) Cmp(r engine.Res) error {
	// we can only compare UserRes to others of the same resource kind
	res, ok := r.(*UserRes)
	if !ok {
		return fmt.Errorf("not a %s", obj.Kind())
	}

	if obj.State != res.State {
		return fmt.Errorf("the State differs")
	}
	if (obj.UID == nil) != (res.UID == nil) {
		return fmt.Errorf("the UID differs")
	}
	if obj.UID != nil && res.UID != nil {
		if *obj.UID != *res.UID {
			return fmt.Errorf("the UID differs")
		}
	}
	if (obj.GID == nil) != (res.GID == nil) {
		return fmt.Errorf("the GID differs")
	}
	if obj.GID != nil && res.GID != nil {
		if *obj.GID != *res.GID {
			return fmt.Errorf("the GID differs")
		}
	}
	if (obj.Groups == nil) != (res.Groups == nil) {
		return fmt.Errorf("the Group differs")
	}
	if obj.Groups != nil && res.Groups != nil {
		if len(obj.Groups) != len(res.Groups) {
			return fmt.Errorf("the Group differs")
		}
		objGroups := obj.Groups
		resGroups := res.Groups
		sort.Strings(objGroups)
		sort.Strings(resGroups)
		for i := range objGroups {
			if objGroups[i] != resGroups[i] {
				return fmt.Errorf("the Group differs at index: %d", i)
			}
		}
	}
	if (obj.HomeDir == nil) != (res.HomeDir == nil) {
		return fmt.Errorf("the HomeDir differs")
	}
	if obj.HomeDir != nil && res.HomeDir != nil {
		if *obj.HomeDir != *res.HomeDir {
			return fmt.Errorf("the HomeDir differs")
		}
	}
	if obj.AllowDuplicateUID != res.AllowDuplicateUID {
		return fmt.Errorf("the AllowDuplicateUID differs")
	}
	return nil
}

// UserUID is the UID struct for UserRes.
type UserUID struct {
	engine.BaseUID
	name string
	uid  *uint32
}

// IFF aka if and only if they are equivalent, return true. If not, false.
func (obj *UserUID) IFF(uid engine.ResUID) bool {
	res, ok := uid.(*UserUID)
	if !ok {
		return false
	}
	if obj.uid != nil && res.uid != nil {
		if *obj.uid != *res.uid {
			return false
		}
	}
	if obj.name != "" && res.name != "" {
		if obj.name != res.name {
			return false
		}
	}
	return true
}

// UserResAutoEdges holds the state of the auto edge generator.
type UserResAutoEdges struct {
	UIDs    []engine.ResUID
	pointer int
}

// AutoEdges returns edges from the user resource to each group found in its
// definition. The groups can be in any of the three applicable fields (GID,
// Group and Groups.) If the user exists, reversed ensures the edge goes from
// group to user, and if the user is absent the edge goes from user to group.
// This ensures that we don't add users to groups that don't exist or delete
// groups before we delete their members.
func (obj *UserRes) AutoEdges() (engine.AutoEdge, error) {
	var result []engine.ResUID
	var reversed bool
	if obj.State == "exists" {
		reversed = true
	}
	if obj.GID != nil {
		result = append(result, &GroupUID{
			BaseUID: engine.BaseUID{
				Reversed: &reversed,
			},
			gid: obj.GID,
		})
	}
	if obj.Group != nil {
		result = append(result, &GroupUID{
			BaseUID: engine.BaseUID{
				Reversed: &reversed,
			},
			name: *obj.Group,
		})
	}
	for _, group := range obj.Groups {
		result = append(result, &GroupUID{
			BaseUID: engine.BaseUID{
				Reversed: &reversed,
			},
			name: group,
		})
	}
	return &UserResAutoEdges{
		UIDs:    result,
		pointer: 0,
	}, nil
}

// Next returns the next automatic edge.
func (obj *UserResAutoEdges) Next() []engine.ResUID {
	if len(obj.UIDs) == 0 {
		return nil
	}
	value := obj.UIDs[obj.pointer]
	obj.pointer++
	return []engine.ResUID{value}
}

// Test gets results of the earlier Next() call, & returns if we should
// continue.
func (obj *UserResAutoEdges) Test(input []bool) bool {
	if len(obj.UIDs) <= obj.pointer {
		return false
	}
	if len(input) != 1 { // in case we get given bad data
		panic(fmt.Sprintf("Expecting a single value!"))
	}
	return true // keep going
}

// UIDs includes all params to make a unique identification of this object. Most
// resources only return one, although some resources can return multiple.
func (obj *UserRes) UIDs() []engine.ResUID {
	x := &UserUID{
		BaseUID: engine.BaseUID{Name: obj.Name(), Kind: obj.Kind()},
		name:    obj.Name(),
		uid:     obj.UID,
	}
	return []engine.ResUID{x}
}

// UnmarshalYAML is the custom unmarshal handler for this struct. It is
// primarily useful for setting the defaults.
func (obj *UserRes) UnmarshalYAML(unmarshal func(interface{}) error) error {
	type rawRes UserRes // indirection to avoid infinite recursion

	def := obj.Default()      // get the default
	res, ok := def.(*UserRes) // put in the right format
	if !ok {
		return fmt.Errorf("could not convert to UserRes")
	}
	raw := rawRes(*res) // convert; the defaults go here

	if err := unmarshal(&raw); err != nil {
		return err
	}

	*obj = UserRes(raw) // restore from indirection with type conversion!
	return nil
}