// Copyright 2018 psgo authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package process

import (
	"errors"
	"fmt"
	"os"
	"strconv"
	"time"

	"github.com/containers/psgo/internal/host"
	"github.com/containers/psgo/internal/proc"
	"github.com/moby/sys/user"
	"golang.org/x/sys/unix"
)

// Process includes process-related from the /proc FS.
type Process struct {
	// PID is the process ID.
	Pid string
	// Stat contains data from /proc/$pid/stat.
	Stat proc.Stat
	// Status contains data from /proc/$pid/status.
	Status proc.Status
	// CmdLine contains data from /proc/$pid/cmdline.
	CmdLine []string
	// Label containers data from /proc/$pid/attr/current.
	Label string
	// PidNS contains data from /proc/$pid/ns/pid.
	PidNS string
	// Huser is the effective host user of a container process.
	Huser string
	// Hgroup is the effective host group of a container process.
	Hgroup string
}

// LookupGID returns the textual group ID, if it can be obtained, or the
// decimal representation otherwise.
func LookupGID(gid string) (string, error) {
	gidNum, err := strconv.Atoi(gid)
	if err != nil {
		return "", fmt.Errorf("error parsing group ID: %w", err)
	}
	g, err := user.LookupGid(gidNum)
	if err != nil {
		return gid, nil
	}
	return g.Name, nil
}

// LookupUID return the textual user ID, if it can be obtained, or the decimal
// representation otherwise.
func LookupUID(uid string) (string, error) {
	uidNum, err := strconv.Atoi(uid)
	if err != nil {
		return "", fmt.Errorf("error parsing user ID: %w", err)
	}
	u, err := user.LookupUid(uidNum)
	if err != nil {
		return uid, nil
	}
	return u.Name, nil
}

// New returns a new Process with the specified pid and parses the relevant
// data from /proc and /dev.
func New(pid string, joinUserNS bool) (*Process, error) {
	p := Process{Pid: pid}

	if err := p.parseStat(); err != nil {
		return nil, err
	}
	if err := p.parseStatus(joinUserNS); err != nil {
		return nil, err
	}
	if err := p.parseCmdLine(); err != nil {
		return nil, err
	}
	if err := p.parsePIDNamespace(); err != nil {
		// Ignore permission errors as those occur for some pids when
		// the caller has limited permissions.
		if !os.IsPermission(err) {
			return nil, err
		}
	}
	if err := p.parseLabel(); err != nil {
		return nil, err
	}

	return &p, nil
}

// FromPIDs creates a new Process for each pid.
func FromPIDs(pids []string, joinUserNS bool) ([]*Process, error) {
	processes := []*Process{}
	for _, pid := range pids {
		p, err := New(pid, joinUserNS)
		if err != nil {
			if errors.Is(err, os.ErrNotExist) || errors.Is(err, unix.ESRCH) {
				// proc parsing is racy
				// Let's ignore "does not exist" errors
				continue
			}
			return nil, err
		}
		processes = append(processes, p)
	}
	return processes, nil
}

// parseStat parses /proc/$pid/stat.
func (p *Process) parseStat() error {
	s, err := proc.ParseStat(p.Pid)
	if err != nil {
		return err
	}
	p.Stat = *s
	return nil
}

// parseStatus parses /proc/$pid/status.
func (p *Process) parseStatus(joinUserNS bool) error {
	s, err := proc.ParseStatus(p.Pid, joinUserNS)
	if err != nil {
		return err
	}
	p.Status = *s
	return nil
}

// parseCmdLine parses /proc/$pid/cmdline.
func (p *Process) parseCmdLine() error {
	s, err := proc.ParseCmdLine(p.Pid)
	if err != nil {
		return err
	}
	p.CmdLine = s
	return nil
}

// parsePIDNamespace sets the PID namespace.
func (p *Process) parsePIDNamespace() error {
	pidNS, err := proc.ParsePIDNamespace(p.Pid)
	if err != nil {
		return err
	}
	p.PidNS = pidNS
	return nil
}

// parseLabel parses the security label.
func (p *Process) parseLabel() error {
	label, err := proc.ParseAttrCurrent(p.Pid)
	if err != nil {
		return err
	}
	p.Label = label
	return nil
}

// SetHostData sets all host-related data fields.
func (p *Process) SetHostData() error {
	var err error

	p.Huser, err = LookupUID(p.Status.Uids[1])
	if err != nil {
		return err
	}

	p.Hgroup, err = LookupGID(p.Status.Gids[1])
	if err != nil {
		return err
	}

	return nil
}

// ElapsedTime returns the time.Duration since process p was created.
func (p *Process) ElapsedTime() (time.Duration, error) {
	startTime, err := p.StartTime()
	if err != nil {
		return 0, err
	}
	return time.Since(startTime), nil
}

// StarTime returns the time.Time when process p was started.
func (p *Process) StartTime() (time.Time, error) {
	sinceBoot, err := strconv.ParseInt(p.Stat.Starttime, 10, 64)
	if err != nil {
		return time.Time{}, err
	}
	clockTicks, err := host.ClockTicks()
	if err != nil {
		return time.Time{}, err
	}
	bootTime, err := host.BootTime()
	if err != nil {
		return time.Time{}, err
	}

	sinceBoot = sinceBoot / clockTicks
	return time.Unix(sinceBoot+bootTime, 0), nil
}

// CPUTime returns the cumulative CPU time of process p as a time.Duration.
func (p *Process) CPUTime() (time.Duration, error) {
	user, err := strconv.ParseInt(p.Stat.Utime, 10, 64)
	if err != nil {
		return 0, err
	}
	system, err := strconv.ParseInt(p.Stat.Stime, 10, 64)
	if err != nil {
		return 0, err
	}
	clockTicks, err := host.ClockTicks()
	if err != nil {
		return 0, err
	}
	secs := (user + system) / clockTicks
	cpu := time.Unix(secs, 0)
	return cpu.Sub(time.Unix(0, 0)), nil
}