// Package docker lists running containers through the Docker Engine API so agents
// can offer them as targets. It speaks plain HTTP over the engine's socket, with
// no dependency on the Docker SDK.
package docker

import (
	"context"
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"net/url"
	"os"
	"runtime"
	"sort"
	"strings"
	"time"

	"git.veillax.com/Veillax/reef/model"
)

func host() string {
	if h := os.Getenv("DOCKER_HOST"); h != "" {
		return h
	}
	if runtime.GOOS == "windows" {
		return "npipe:////./pipe/docker_engine"
	}
	return "unix:///var/run/docker.sock"
}

func dialer(h string) (func(ctx context.Context, network, addr string) (net.Conn, error), error) {
	u, err := url.Parse(h)
	if err != nil {
		return nil, err
	}
	switch u.Scheme {
	case "unix":
		path := u.Path
		return func(ctx context.Context, _, _ string) (net.Conn, error) {
			var d net.Dialer
			return d.DialContext(ctx, "unix", path)
		}, nil
	case "tcp", "http":
		addr := u.Host
		return func(ctx context.Context, _, _ string) (net.Conn, error) {
			var d net.Dialer
			return d.DialContext(ctx, "tcp", addr)
		}, nil
	case "npipe":
		return dialPipe(strings.ReplaceAll(u.Path, "/", `\`)), nil
	}
	return nil, fmt.Errorf("unsupported DOCKER_HOST %q", h)
}

// List returns the running containers, or an error if Docker isn't reachable.
func List(ctx context.Context) ([]model.Container, error) {
	dial, err := dialer(host())
	if err != nil {
		return nil, err
	}
	c := &http.Client{Timeout: 5 * time.Second, Transport: &http.Transport{DialContext: dial, DisableKeepAlives: true}}
	req, _ := http.NewRequestWithContext(ctx, "GET", "http://docker/containers/json", nil)
	resp, err := c.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != 200 {
		return nil, fmt.Errorf("docker returned %d", resp.StatusCode)
	}
	var raw []struct {
		ID    string   `json:"Id"`
		Names []string `json:"Names"`
		Image string
		State string
		Ports []struct {
			PrivatePort int
			PublicPort  int
			Type        string
		}
		NetworkSettings struct {
			Networks map[string]struct{ IPAddress string }
		}
	}
	if err := json.NewDecoder(resp.Body).Decode(&raw); err != nil {
		return nil, err
	}
	out := []model.Container{}
	for _, r := range raw {
		c := model.Container{ID: r.ID, Image: r.Image, State: r.State, Ports: []model.ContainerPort{}, Networks: map[string]string{}}
		if len(c.ID) > 12 {
			c.ID = c.ID[:12]
		}
		if len(r.Names) > 0 {
			c.Name = strings.TrimPrefix(r.Names[0], "/")
		}
		seen := map[string]bool{}
		for _, p := range r.Ports {
			key := fmt.Sprintf("%d/%d/%s", p.PrivatePort, p.PublicPort, p.Type)
			if seen[key] {
				continue // docker lists IPv4 and IPv6 bindings separately
			}
			seen[key] = true
			c.Ports = append(c.Ports, model.ContainerPort{Private: p.PrivatePort, Public: p.PublicPort, Type: p.Type})
		}
		for n, v := range r.NetworkSettings.Networks {
			if v.IPAddress != "" {
				c.Networks[n] = v.IPAddress
			}
		}
		out = append(out, c)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	return out, nil
}