package agentcontainers

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"net"
	"os/user"
	"slices"
	"sort"
	"strconv"
	"strings"
	"time"

	"golang.org/x/exp/maps"
	"golang.org/x/xerrors"

	"github.com/coder/coder/v2/agent/agentcontainers/dcspec"
	"github.com/coder/coder/v2/agent/agentexec"
	"github.com/coder/coder/v2/agent/usershell"
	"github.com/coder/coder/v2/coderd/util/ptr"
	"github.com/coder/coder/v2/codersdk"
)

// DockerEnvInfoer is an implementation of agentssh.EnvInfoer that returns
// information about a container.
type DockerEnvInfoer struct {
	usershell.SystemEnvInfo
	container string
	user      *user.User
	userShell string
	env       []string
}

// EnvInfo returns information about the environment of a container.
func EnvInfo(ctx context.Context, execer agentexec.Execer, container, containerUser string) (*DockerEnvInfoer, error) {
	var dei DockerEnvInfoer
	dei.container = container

	if containerUser == "" {
		// Get the "default" user of the container if no user is specified.
		// TODO: handle different container runtimes.
		cmd, args := wrapDockerExec(container, "", "whoami")
		stdout, stderr, err := run(ctx, execer, cmd, args...)
		if err != nil {
			return nil, xerrors.Errorf("get container user: run whoami: %w: %s", err, stderr)
		}
		if len(stdout) == 0 {
			return nil, xerrors.Errorf("get container user: run whoami: empty output")
		}
		containerUser = stdout
	}
	// Now that we know the username, get the required info from the container.
	// We can't assume the presence of `getent` so we'll just have to sniff /etc/passwd.
	cmd, args := wrapDockerExec(container, containerUser, "cat", "/etc/passwd")
	stdout, stderr, err := run(ctx, execer, cmd, args...)
	if err != nil {
		return nil, xerrors.Errorf("get container user: read /etc/passwd: %w: %q", err, stderr)
	}

	scanner := bufio.NewScanner(strings.NewReader(stdout))
	var foundLine string
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if !strings.HasPrefix(line, containerUser+":") {
			continue
		}
		foundLine = line
		break
	}
	if err := scanner.Err(); err != nil {
		return nil, xerrors.Errorf("get container user: scan /etc/passwd: %w", err)
	}
	if foundLine == "" {
		return nil, xerrors.Errorf("get container user: no matching entry for %q found in /etc/passwd", containerUser)
	}

	// Parse the output of /etc/passwd. It looks like this:
	// postgres:x:999:999::/var/lib/postgresql:/bin/bash
	passwdFields := strings.Split(foundLine, ":")
	if len(passwdFields) != 7 {
		return nil, xerrors.Errorf("get container user: invalid line in /etc/passwd: %q", foundLine)
	}

	// The fifth entry in /etc/passwd contains GECOS information, which is a
	// comma-separated list of fields. The first field is the user's full name.
	gecos := strings.Split(passwdFields[4], ",")
	fullName := ""
	if len(gecos) > 1 {
		fullName = gecos[0]
	}

	dei.user = &user.User{
		Gid:      passwdFields[3],
		HomeDir:  passwdFields[5],
		Name:     fullName,
		Uid:      passwdFields[2],
		Username: containerUser,
	}
	dei.userShell = passwdFields[6]

	// We need to inspect the container labels for remoteEnv and append these to
	// the resulting docker exec command.
	// ref: https://code.visualstudio.com/docs/devcontainers/attach-container
	env, err := devcontainerEnv(ctx, execer, container)
	if err != nil { // best effort.
		return nil, xerrors.Errorf("read devcontainer remoteEnv: %w", err)
	}
	dei.env = env

	return &dei, nil
}

func (dei *DockerEnvInfoer) User() (*user.User, error) {
	// Clone the user so that the caller can't modify it
	u := *dei.user
	return &u, nil
}

func (dei *DockerEnvInfoer) Shell(string) (string, error) {
	return dei.userShell, nil
}

func (dei *DockerEnvInfoer) ModifyCommand(cmd string, args ...string) (string, []string) {
	// Wrap the command with `docker exec` and run it as the container user.
	// There is some additional munging here regarding the container user and environment.
	dockerArgs := []string{
		"exec",
		// The assumption is that this command will be a shell command, so allocate a PTY.
		"--interactive",
		"--tty",
		// Run the command as the user in the container.
		"--user",
		dei.user.Username,
		// Set the working directory to the user's home directory as a sane default.
		"--workdir",
		dei.user.HomeDir,
	}

	// Append the environment variables from the container.
	for _, e := range dei.env {
		dockerArgs = append(dockerArgs, "--env", e)
	}

	// Append the container name and the command.
	dockerArgs = append(dockerArgs, dei.container, cmd)
	return "docker", append(dockerArgs, args...)
}

// devcontainerEnv is a helper function that inspects the container labels to
// find the required environment variables for running a command in the container.
func devcontainerEnv(ctx context.Context, execer agentexec.Execer, container string) ([]string, error) {
	stdout, stderr, err := runDockerInspect(ctx, execer, container)
	if err != nil {
		return nil, xerrors.Errorf("inspect container: %w: %q", err, stderr)
	}

	ins, _, err := convertDockerInspect(stdout)
	if err != nil {
		return nil, xerrors.Errorf("inspect container: %w", err)
	}

	if len(ins) != 1 {
		return nil, xerrors.Errorf("inspect container: expected 1 container, got %d", len(ins))
	}

	in := ins[0]
	if in.Labels == nil {
		return nil, nil
	}

	// We want to look for the devcontainer metadata, which is in the
	// value of the label `devcontainer.metadata`.
	rawMeta, ok := in.Labels["devcontainer.metadata"]
	if !ok {
		return nil, nil
	}

	meta := make([]dcspec.DevContainer, 0)
	if err := json.Unmarshal([]byte(rawMeta), &meta); err != nil {
		return nil, xerrors.Errorf("unmarshal devcontainer.metadata: %w", err)
	}

	// The environment variables are stored in the `remoteEnv` key.
	env := make([]string, 0)
	for _, m := range meta {
		for k, v := range m.RemoteEnv {
			if v == nil { // *string per spec
				// devcontainer-cli will set this to the string "null" if the value is
				// not set. Explicitly setting to an empty string here as this would be
				// more expected here.
				v = ptr.Ref("")
			}
			env = append(env, fmt.Sprintf("%s=%s", k, *v))
		}
	}
	slices.Sort(env)
	return env, nil
}

// wrapDockerExec is a helper function that wraps the given command and arguments
// with a docker exec command that runs as the given user in the given
// container. This is used to fetch information about a container prior to
// running the actual command.
func wrapDockerExec(containerName, userName, cmd string, args ...string) (string, []string) {
	dockerArgs := []string{"exec", "--interactive"}
	if userName != "" {
		dockerArgs = append(dockerArgs, "--user", userName)
	}
	dockerArgs = append(dockerArgs, containerName, cmd)
	return "docker", append(dockerArgs, args...)
}

// Helper function to run a command and return its stdout and stderr.
// We want to differentiate stdout and stderr instead of using CombinedOutput.
// We also want to differentiate between a command running successfully with
// output to stderr and a non-zero exit code.
func run(ctx context.Context, execer agentexec.Execer, cmd string, args ...string) (stdout, stderr string, err error) {
	var stdoutBuf, stderrBuf strings.Builder
	execCmd := execer.CommandContext(ctx, cmd, args...)
	execCmd.Stdout = &stdoutBuf
	execCmd.Stderr = &stderrBuf
	err = execCmd.Run()
	stdout = strings.TrimSpace(stdoutBuf.String())
	stderr = strings.TrimSpace(stderrBuf.String())
	return stdout, stderr, err
}

// dockerCLI is an implementation for Docker CLI that lists containers.
type dockerCLI struct {
	execer agentexec.Execer
}

var _ ContainerCLI = (*dockerCLI)(nil)

func NewDockerCLI(execer agentexec.Execer) ContainerCLI {
	return &dockerCLI{
		execer: execer,
	}
}

func (dcli *dockerCLI) List(ctx context.Context) (codersdk.WorkspaceAgentListContainersResponse, error) {
	var stdoutBuf, stderrBuf bytes.Buffer
	// List all container IDs, one per line, with no truncation
	cmd := dcli.execer.CommandContext(ctx, "docker", "ps", "--all", "--quiet", "--no-trunc")
	cmd.Stdout = &stdoutBuf
	cmd.Stderr = &stderrBuf
	if err := cmd.Run(); err != nil {
		// TODO(Cian): detect specific errors:
		// - docker not installed
		// - docker not running
		// - no permissions to talk to docker
		return codersdk.WorkspaceAgentListContainersResponse{}, xerrors.Errorf("run docker ps: %w: %q", err, strings.TrimSpace(stderrBuf.String()))
	}

	ids := make([]string, 0)
	scanner := bufio.NewScanner(&stdoutBuf)
	for scanner.Scan() {
		tmp := strings.TrimSpace(scanner.Text())
		if tmp == "" {
			continue
		}
		ids = append(ids, tmp)
	}
	if err := scanner.Err(); err != nil {
		return codersdk.WorkspaceAgentListContainersResponse{}, xerrors.Errorf("scan docker ps output: %w", err)
	}

	res := codersdk.WorkspaceAgentListContainersResponse{
		Containers: make([]codersdk.WorkspaceAgentContainer, 0, len(ids)),
		Warnings:   make([]string, 0),
	}
	dockerPsStderr := strings.TrimSpace(stderrBuf.String())
	if dockerPsStderr != "" {
		res.Warnings = append(res.Warnings, dockerPsStderr)
	}
	if len(ids) == 0 {
		return res, nil
	}

	// now we can get the detailed information for each container
	// Run `docker inspect` on each container ID.
	// NOTE: There is an unavoidable potential race condition where a
	// container is removed between `docker ps` and `docker inspect`.
	// In this case, stderr will contain an error message but stdout
	// will still contain valid JSON. We will just end up missing
	// information about the removed container. We could potentially
	// log this error, but I'm not sure it's worth it.
	dockerInspectStdout, dockerInspectStderr, err := runDockerInspect(ctx, dcli.execer, ids...)
	if err != nil {
		return codersdk.WorkspaceAgentListContainersResponse{}, xerrors.Errorf("run docker inspect: %w: %s", err, dockerInspectStderr)
	}

	if len(dockerInspectStderr) > 0 {
		res.Warnings = append(res.Warnings, string(dockerInspectStderr))
	}

	outs, warns, err := convertDockerInspect(dockerInspectStdout)
	if err != nil {
		return codersdk.WorkspaceAgentListContainersResponse{}, xerrors.Errorf("convert docker inspect output: %w", err)
	}
	res.Warnings = append(res.Warnings, warns...)
	res.Containers = append(res.Containers, outs...)

	return res, nil
}

// runDockerInspect is a helper function that runs `docker inspect` on the given
// container IDs and returns the parsed output.
// The stderr output is also returned for logging purposes.
func runDockerInspect(ctx context.Context, execer agentexec.Execer, ids ...string) (stdout, stderr []byte, err error) {
	if ctx.Err() != nil {
		// If the context is done, we don't want to run the command.
		return []byte{}, []byte{}, ctx.Err()
	}
	var stdoutBuf, stderrBuf bytes.Buffer
	cmd := execer.CommandContext(ctx, "docker", append([]string{"inspect"}, ids...)...)
	cmd.Stdout = &stdoutBuf
	cmd.Stderr = &stderrBuf
	err = cmd.Run()
	stdout = bytes.TrimSpace(stdoutBuf.Bytes())
	stderr = bytes.TrimSpace(stderrBuf.Bytes())
	if err != nil {
		if ctx.Err() != nil {
			// If the context was canceled while running the command,
			// return the context error instead of the command error,
			// which is likely to be "signal: killed".
			return stdout, stderr, ctx.Err()
		}
		if bytes.Contains(stderr, []byte("No such object:")) {
			// This can happen if a container is deleted between the time we check for its existence and the time we inspect it.
			return stdout, stderr, nil
		}
		return stdout, stderr, err
	}
	return stdout, stderr, nil
}

// To avoid a direct dependency on the Docker API, we use the docker CLI
// to fetch information about containers.
type dockerInspect struct {
	ID              string                       `json:"Id"`
	Created         time.Time                    `json:"Created"`
	Config          dockerInspectConfig          `json:"Config"`
	Name            string                       `json:"Name"`
	Mounts          []dockerInspectMount         `json:"Mounts"`
	State           dockerInspectState           `json:"State"`
	NetworkSettings dockerInspectNetworkSettings `json:"NetworkSettings"`
}

type dockerInspectConfig struct {
	Image  string            `json:"Image"`
	Labels map[string]string `json:"Labels"`
}

type dockerInspectPort struct {
	HostIP   string `json:"HostIp"`
	HostPort string `json:"HostPort"`
}

type dockerInspectMount struct {
	Source      string `json:"Source"`
	Destination string `json:"Destination"`
	Type        string `json:"Type"`
}

type dockerInspectState struct {
	Running  bool   `json:"Running"`
	ExitCode int    `json:"ExitCode"`
	Error    string `json:"Error"`
}

type dockerInspectNetworkSettings struct {
	Ports map[string][]dockerInspectPort `json:"Ports"`
}

func (dis dockerInspectState) String() string {
	if dis.Running {
		return "running"
	}
	var sb strings.Builder
	_, _ = sb.WriteString("exited")
	if dis.ExitCode != 0 {
		_, _ = sb.WriteString(fmt.Sprintf(" with code %d", dis.ExitCode))
	} else {
		_, _ = sb.WriteString(" successfully")
	}
	if dis.Error != "" {
		_, _ = sb.WriteString(fmt.Sprintf(": %s", dis.Error))
	}
	return sb.String()
}

func convertDockerInspect(raw []byte) ([]codersdk.WorkspaceAgentContainer, []string, error) {
	var warns []string
	var ins []dockerInspect
	if err := json.NewDecoder(bytes.NewReader(raw)).Decode(&ins); err != nil {
		return nil, nil, xerrors.Errorf("decode docker inspect output: %w", err)
	}
	outs := make([]codersdk.WorkspaceAgentContainer, 0, len(ins))

	// Say you have two containers:
	//  - Container A with Host IP 127.0.0.1:8000 mapped to container port 8001
	//  - Container B with Host IP [::1]:8000 mapped to container port 8001
	// A request to localhost:8000 may be routed to either container.
	// We don't know which one for sure, so we need to surface this to the user.
	// Keep track of all host ports we see. If we see the same host port
	// mapped to multiple containers on different host IPs, we need to
	// warn the user about this.
	// Note that we only do this for loopback or unspecified IPs.
	// We'll assume that the user knows what they're doing if they bind to
	// a specific IP address.
	hostPortContainers := make(map[int][]string)

	for _, in := range ins {
		out := codersdk.WorkspaceAgentContainer{
			CreatedAt: in.Created,
			// Remove the leading slash from the container name
			FriendlyName: strings.TrimPrefix(in.Name, "/"),
			ID:           in.ID,
			Image:        in.Config.Image,
			Labels:       in.Config.Labels,
			Ports:        make([]codersdk.WorkspaceAgentContainerPort, 0),
			Running:      in.State.Running,
			Status:       in.State.String(),
			Volumes:      make(map[string]string, len(in.Mounts)),
		}

		if in.NetworkSettings.Ports == nil {
			in.NetworkSettings.Ports = make(map[string][]dockerInspectPort)
		}
		portKeys := maps.Keys(in.NetworkSettings.Ports)
		// Sort the ports for deterministic output.
		sort.Strings(portKeys)
		// If we see the same port bound to both ipv4 and ipv6 loopback or unspecified
		// interfaces to the same container port, there is no point in adding it multiple times.
		loopbackHostPortContainerPorts := make(map[int]uint16, 0)
		for _, pk := range portKeys {
			for _, p := range in.NetworkSettings.Ports[pk] {
				cp, network, err := convertDockerPort(pk)
				if err != nil {
					warns = append(warns, fmt.Sprintf("convert docker port: %s", err.Error()))
					// Default network to "tcp" if we can't parse it.
					network = "tcp"
				}
				hp, err := strconv.Atoi(p.HostPort)
				if err != nil {
					warns = append(warns, fmt.Sprintf("convert docker host port: %s", err.Error()))
					continue
				}
				if hp > 65535 || hp < 1 { // invalid port
					warns = append(warns, fmt.Sprintf("convert docker host port: invalid host port %d", hp))
					continue
				}

				// Deduplicate host ports for loopback and unspecified IPs.
				if isLoopbackOrUnspecified(p.HostIP) {
					if found, ok := loopbackHostPortContainerPorts[hp]; ok && found == cp {
						// We've already seen this port, so skip it.
						continue
					}
					loopbackHostPortContainerPorts[hp] = cp
					// Also keep track of the host port and the container ID.
					hostPortContainers[hp] = append(hostPortContainers[hp], in.ID)
				}
				out.Ports = append(out.Ports, codersdk.WorkspaceAgentContainerPort{
					Network: network,
					Port:    cp,
					// #nosec G115 - Safe conversion since Docker ports are limited to uint16 range
					HostPort: uint16(hp),
					HostIP:   p.HostIP,
				})
			}
		}

		if in.Mounts == nil {
			in.Mounts = []dockerInspectMount{}
		}
		// Sort the mounts for deterministic output.
		sort.Slice(in.Mounts, func(i, j int) bool {
			return in.Mounts[i].Source < in.Mounts[j].Source
		})
		for _, k := range in.Mounts {
			out.Volumes[k.Source] = k.Destination
		}
		outs = append(outs, out)
	}

	// Check if any host ports are mapped to multiple containers.
	for hp, ids := range hostPortContainers {
		if len(ids) > 1 {
			warns = append(warns, fmt.Sprintf("host port %d is mapped to multiple containers on different interfaces: %s", hp, strings.Join(ids, ", ")))
		}
	}

	return outs, warns, nil
}

// convertDockerPort converts a Docker port string to a port number and network
// example: "8080/tcp" -> 8080, "tcp"
//
//	"8080" -> 8080, "tcp"
func convertDockerPort(in string) (uint16, string, error) {
	parts := strings.Split(in, "/")
	p, err := strconv.ParseUint(parts[0], 10, 16)
	if err != nil {
		return 0, "", xerrors.Errorf("invalid port format: %s", in)
	}
	switch len(parts) {
	case 1:
		// assume it's a TCP port
		return uint16(p), "tcp", nil
	case 2:
		return uint16(p), parts[1], nil
	default:
		return 0, "", xerrors.Errorf("invalid port format: %s", in)
	}
}

// convenience function to check if an IP address is loopback or unspecified
func isLoopbackOrUnspecified(ips string) bool {
	nip := net.ParseIP(ips)
	if nip == nil {
		return false // technically correct, I suppose
	}
	return nip.IsLoopback() || nip.IsUnspecified()
}

// DetectArchitecture detects the architecture of a container by inspecting its
// image.
func (dcli *dockerCLI) DetectArchitecture(ctx context.Context, containerName string) (string, error) {
	// Inspect the container to get the image name, which contains the architecture.
	stdout, stderr, err := runCmd(ctx, dcli.execer, "docker", "inspect", "--format", "{{.Config.Image}}", containerName)
	if err != nil {
		return "", xerrors.Errorf("inspect container %s: %w: %s", containerName, err, stderr)
	}
	imageName := string(stdout)
	if imageName == "" {
		return "", xerrors.Errorf("no image found for container %s", containerName)
	}

	stdout, stderr, err = runCmd(ctx, dcli.execer, "docker", "inspect", "--format", "{{.Architecture}}", imageName)
	if err != nil {
		return "", xerrors.Errorf("inspect image %s: %w: %s", imageName, err, stderr)
	}
	arch := string(stdout)
	if arch == "" {
		return "", xerrors.Errorf("no architecture found for image %s", imageName)
	}
	return arch, nil
}

// Copy copies a file from the host to a container.
func (dcli *dockerCLI) Copy(ctx context.Context, containerName, src, dst string) error {
	_, stderr, err := runCmd(ctx, dcli.execer, "docker", "cp", src, containerName+":"+dst)
	if err != nil {
		return xerrors.Errorf("copy %s to %s:%s: %w: %s", src, containerName, dst, err, stderr)
	}
	return nil
}

// ExecAs executes a command in a container as a specific user.
func (dcli *dockerCLI) ExecAs(ctx context.Context, containerName, uid string, args ...string) ([]byte, error) {
	execArgs := []string{"exec"}
	if uid != "" {
		altUID := uid
		if uid == "root" {
			// UID 0 is more portable than the name root, so we use that
			// because  some containers may not have a user named "root".
			altUID = "0"
		}
		execArgs = append(execArgs, "--user", altUID)
	}
	execArgs = append(execArgs, containerName)
	execArgs = append(execArgs, args...)

	stdout, stderr, err := runCmd(ctx, dcli.execer, "docker", execArgs...)
	if err != nil {
		return nil, xerrors.Errorf("exec in container %s as user %s: %w: %s", containerName, uid, err, stderr)
	}
	return stdout, nil
}

// runCmd is a helper function that runs a command with the given
// arguments and returns the stdout and stderr output.
func runCmd(ctx context.Context, execer agentexec.Execer, cmd string, args ...string) (stdout, stderr []byte, err error) {
	var stdoutBuf, stderrBuf bytes.Buffer
	c := execer.CommandContext(ctx, cmd, args...)
	c.Stdout = &stdoutBuf
	c.Stderr = &stderrBuf
	err = c.Run()
	stdout = bytes.TrimSpace(stdoutBuf.Bytes())
	stderr = bytes.TrimSpace(stderrBuf.Bytes())
	return stdout, stderr, err
}