package runtime

import (
	"encoding/json"
	"fmt"
	"os/exec"
	"strings"

	"github.com/warkanum/unitdore/sysuser"
)

type Docker struct{}

func (d *Docker) Name() string { return "docker" }

type dockerContainer struct {
	ID      string `json:"ID"`
	Names   string `json:"Names"`
	Image   string `json:"Image"`
	Command string `json:"Command"`
	State   string `json:"State"`
	Labels  string `json:"Labels"`
}

// dockerCmd builds a docker command for the given user scope.
// Returns nil if docker is not installed.
func dockerCmd(user string, args ...string) (*exec.Cmd, error) {
	bin, err := exec.LookPath("docker")
	if err != nil {
		return nil, nil
	}
	return sysuser.Command(user, bin, args...)
}

func (d *Docker) ListRunning(user string) ([]Container, error) {
	cmd, err := dockerCmd(user, "ps", "--format", "json")
	if err != nil {
		return nil, err
	}
	if cmd == nil {
		return nil, nil // docker not installed — not an error
	}

	out, err := cmd.Output()
	if err != nil {
		// Docker installed but daemon not running — treat as no containers
		return nil, nil
	}

	containers := parseDockerPS(out)
	for i := range containers {
		containers[i].User = user
	}
	return containers, nil
}

// parseDockerPS parses `docker ps --format json` output
// (one JSON object per line, not a JSON array).
func parseDockerPS(out []byte) []Container {
	var containers []Container
	for _, line := range strings.Split(strings.TrimSpace(string(out)), "\n") {
		if line == "" {
			continue
		}
		var c dockerContainer
		if err := json.Unmarshal([]byte(line), &c); err != nil {
			continue
		}
		name := strings.TrimPrefix(c.Names, "/")
		// Fall back to short container ID if no name assigned
		if name == "" {
			if len(c.ID) >= 12 {
				name = c.ID[:12]
			} else if c.ID != "" {
				name = c.ID
			} else {
				continue
			}
		}
		containers = append(containers, Container{
			Name:    name,
			Image:   c.Image,
			Command: c.Command,
			Runtime: "docker",
			Labels:  parseDockerLabels(c.Labels),
		})
	}
	return containers
}

// parseDockerLabels parses docker's "k=v,k=v" label string. A segment without
// "=" is a continuation of the previous value (values may contain commas,
// e.g. multiple compose config files).
func parseDockerLabels(s string) map[string]string {
	labels := map[string]string{}
	last := ""
	for _, part := range strings.Split(s, ",") {
		if part == "" {
			continue
		}
		k, v, ok := strings.Cut(part, "=")
		if !ok {
			if last != "" {
				labels[last] += "," + part
			}
			continue
		}
		labels[k] = v
		last = k
	}
	return labels
}

func (d *Docker) Exists(user, name string) (bool, error) {
	cmd, err := dockerCmd(user, "ps", "--format", "{{.Names}}")
	if err != nil {
		return false, err
	}
	if cmd == nil {
		return false, nil
	}

	out, err := cmd.Output()
	if err != nil {
		return false, fmt.Errorf("docker ps: %w", err)
	}

	for _, line := range strings.Split(string(out), "\n") {
		if strings.TrimSpace(line) == name {
			return true, nil
		}
	}
	return false, nil
}