/*
   Copyright The containerd 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.
*/

/*
   Portions from:
   - https://github.com/moby/moby/blob/v20.10.6/api/types/container/container_top.go
   - https://github.com/moby/moby/blob/v20.10.6/daemon/top_unix.go
   Copyright (C) The Moby authors.
   Licensed under the Apache License, Version 2.0
   NOTICE: https://github.com/moby/moby/blob/v20.10.6/NOTICE
*/

package container

import (
	"context"
	"fmt"
	"regexp"
	"strconv"
	"strings"

	"github.com/containerd/containerd"
	"github.com/containerd/nerdctl/pkg/api/types"
	"github.com/containerd/nerdctl/pkg/idutil/containerwalker"
)

// ContainerTopOKBody is from https://github.com/moby/moby/blob/v20.10.6/api/types/container/container_top.go
//
// ContainerTopOKBody OK response to ContainerTop operation
type ContainerTopOKBody struct { //nolint:revive

	// Each process running in the container, where each is process
	// is an array of values corresponding to the titles.
	//
	// Required: true
	Processes [][]string `json:"Processes"`

	// The ps column titles
	// Required: true
	Titles []string `json:"Titles"`
}

// Top performs the equivalent of running `top` inside of container(s)
func Top(ctx context.Context, client *containerd.Client, containers []string, opt types.ContainerTopOptions) error {
	walker := &containerwalker.ContainerWalker{
		Client: client,
		OnFound: func(ctx context.Context, found containerwalker.Found) error {
			if found.MatchCount > 1 {
				return fmt.Errorf("multiple IDs found with provided prefix: %s", found.Req)
			}
			return containerTop(ctx, opt.Stdout, client, found.Container.ID(), strings.Join(containers[1:], " "))
		},
	}

	n, err := walker.Walk(ctx, containers[0])
	if err != nil {
		return err
	} else if n == 0 {
		return fmt.Errorf("no such container %s", containers[0])
	}
	return nil
}

// appendProcess2ProcList is from https://github.com/moby/moby/blob/v20.10.6/daemon/top_unix.go#L49-L55
func appendProcess2ProcList(procList *ContainerTopOKBody, fields []string) {
	// Make sure number of fields equals number of header titles
	// merging "overhanging" fields
	process := fields[:len(procList.Titles)-1]
	process = append(process, strings.Join(fields[len(procList.Titles)-1:], " "))
	procList.Processes = append(procList.Processes, process)
}

// psPidsArg is from https://github.com/moby/moby/blob/v20.10.6/daemon/top_unix.go#L119-L131
//
// psPidsArg converts a slice of PIDs to a string consisting
// of comma-separated list of PIDs prepended by "-q".
// For example, psPidsArg([]uint32{1,2,3}) returns "-q1,2,3".
func psPidsArg(pids []uint32) string {
	b := []byte{'-', 'q'}
	for i, p := range pids {
		b = strconv.AppendUint(b, uint64(p), 10)
		if i < len(pids)-1 {
			b = append(b, ',')
		}
	}
	return string(b)
}

// validatePSArgs is from https://github.com/moby/moby/blob/v20.10.6/daemon/top_unix.go#L19-L35
func validatePSArgs(psArgs string) error {
	// NOTE: \\s does not detect unicode whitespaces.
	// So we use fieldsASCII instead of strings.Fields in parsePSOutput.
	// See https://github.com/docker/docker/pull/24358
	// nolint: gosimple
	re := regexp.MustCompile(`\s+(\S*)=\s*(PID\S*)`)
	for _, group := range re.FindAllStringSubmatch(psArgs, -1) {
		if len(group) >= 3 {
			k := group[1]
			v := group[2]
			if k != "pid" {
				return fmt.Errorf("specifying \"%s=%s\" is not allowed", k, v)
			}
		}
	}
	return nil
}

// fieldsASCII is from https://github.com/moby/moby/blob/v20.10.6/daemon/top_unix.go#L37-L47
//
// fieldsASCII is similar to strings.Fields but only allows ASCII whitespaces
func fieldsASCII(s string) []string {
	fn := func(r rune) bool {
		switch r {
		case '\t', '\n', '\f', '\r', ' ':
			return true
		}
		return false
	}
	return strings.FieldsFunc(s, fn)
}

// hasPid is from https://github.com/moby/moby/blob/v20.10.6/daemon/top_unix.go#L57-L64
func hasPid(procs []uint32, pid int) bool {
	for _, p := range procs {
		if int(p) == pid {
			return true
		}
	}
	return false
}

// parsePSOutput is from https://github.com/moby/moby/blob/v20.10.6/daemon/top_unix.go#L66-L117
func parsePSOutput(output []byte, procs []uint32) (*ContainerTopOKBody, error) {
	procList := &ContainerTopOKBody{}

	lines := strings.Split(string(output), "\n")
	procList.Titles = fieldsASCII(lines[0])

	pidIndex := -1
	for i, name := range procList.Titles {
		if name == "PID" {
			pidIndex = i
			break
		}
	}
	if pidIndex == -1 {
		return nil, fmt.Errorf("couldn't find PID field in ps output")
	}

	// loop through the output and extract the PID from each line
	// fixing #30580, be able to display thread line also when "m" option used
	// in "docker top" client command
	preContainedPidFlag := false
	for _, line := range lines[1:] {
		if len(line) == 0 {
			continue
		}
		fields := fieldsASCII(line)

		var (
			p   int
			err error
		)

		if fields[pidIndex] == "-" {
			if preContainedPidFlag {
				appendProcess2ProcList(procList, fields)
			}
			continue
		}
		p, err = strconv.Atoi(fields[pidIndex])
		if err != nil {
			return nil, fmt.Errorf("unexpected pid '%s': %s", fields[pidIndex], err)
		}

		if hasPid(procs, p) {
			preContainedPidFlag = true
			appendProcess2ProcList(procList, fields)
			continue
		}
		preContainedPidFlag = false
	}
	return procList, nil
}
