package main

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net"
	"net/http"
	"sort"
	"strconv"
	"strings"
	"time"
)

type unixRoundTripper struct{ sock string }

func (u unixRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
	transport := &http.Transport{
		DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
			var d net.Dialer
			return d.DialContext(ctx, "unix", u.sock)
		},
		DisableKeepAlives: false,
	}
	clone := req.Clone(req.Context())
	clone.URL.Scheme = "http"
	clone.URL.Host = "docker"
	return transport.RoundTrip(clone)
}

func dockerContainers(ctx context.Context, sock string) ([]dockerContainer, error) {
	client := &http.Client{Transport: unixRoundTripper{sock: sock}, Timeout: 4 * time.Second}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "http://docker/containers/json?all=0", nil)
	if err != nil {
		return nil, err
	}
	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("docker API: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
		return nil, fmt.Errorf("docker API returned %s: %s", resp.Status, strings.TrimSpace(string(body)))
	}
	var items []dockerContainer
	dec := json.NewDecoder(io.LimitReader(resp.Body, 4<<20))
	if err := dec.Decode(&items); err != nil {
		return nil, fmt.Errorf("decode Docker response: %w", err)
	}
	return items, nil
}

func cleanName(names []string) string {
	if len(names) == 0 {
		return "container"
	}
	name := strings.TrimPrefix(names[0], "/")
	if name == "" {
		return "container"
	}
	return name
}

func dnsLabel(value string) string {
	value = strings.ToLower(value)
	var b strings.Builder
	dash := false
	for _, r := range value {
		ok := (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9')
		if ok {
			b.WriteRune(r)
			dash = false
		} else if b.Len() > 0 && !dash {
			b.WriteByte('-')
			dash = true
		}
	}
	out := strings.Trim(b.String(), "-")
	if out == "" {
		out = "app"
	}
	if len(out) > 48 {
		out = strings.Trim(out[:48], "-")
	}
	return out
}

func serviceIdentity(c dockerContainer, p dockerPort) (key, technical string) {
	name := cleanName(c.Names)
	project := c.Labels["com.docker.compose.project"]
	composeService := c.Labels["com.docker.compose.service"]
	replica := c.Labels["com.docker.compose.container-number"]
	suffix := strconv.Itoa(int(p.PrivatePort))
	if project != "" && composeService != "" {
		if replica == "" {
			replica = name
		}
		key = fmt.Sprintf("compose:%s/%s/%s:%d/%s", project, composeService, replica, p.PrivatePort, p.Type)
		technicalBase := project + "-" + composeService
		if replica != "1" {
			technicalBase += "-" + replica
		}
		technical = dnsLabel(technicalBase + "-" + suffix)
	} else {
		key = fmt.Sprintf("container:%s:%d/%s", name, p.PrivatePort, p.Type)
		technical = dnsLabel(name + "-" + suffix)
	}
	return key, technical
}

func servicesFrom(containers []dockerContainer) []service {
	byKey := make(map[string]*service)
	bindingSeen := make(map[string]map[string]struct{})
	for _, c := range containers {
		name := cleanName(c.Names)
		for _, p := range c.Ports {
			if p.PublicPort == 0 || p.Type != "tcp" {
				continue
			}
			if bind := net.ParseIP(strings.TrimSpace(p.IP)); bind != nil && bind.IsLoopback() {
				continue
			}
			key, technical := serviceIdentity(c, p)
			item := byKey[key]
			if item == nil {
				id := c.ID
				if len(id) > 12 {
					id = id[:12]
				}
				item = &service{
					Key: key, TechnicalName: technical, ContainerID: id, ContainerName: name,
					Image: c.Image, PrivatePort: p.PrivatePort, Protocol: p.Type,
				}
				byKey[key] = item
				bindingSeen[key] = make(map[string]struct{})
			}
			bindIP := strings.TrimSpace(p.IP)
			dedupe := bindIP + "|" + strconv.Itoa(int(p.PublicPort))
			if _, ok := bindingSeen[key][dedupe]; ok {
				continue
			}
			bindingSeen[key][dedupe] = struct{}{}
			item.Bindings = append(item.Bindings, binding{BindIP: bindIP, PublicPort: p.PublicPort})
		}
	}
	out := make([]service, 0, len(byKey))
	for _, item := range byKey {
		sort.Slice(item.Bindings, func(i, j int) bool {
			left := net.ParseIP(strings.TrimSpace(item.Bindings[i].BindIP))
			right := net.ParseIP(strings.TrimSpace(item.Bindings[j].BindIP))
			leftWildcard := left == nil || left.IsUnspecified()
			rightWildcard := right == nil || right.IsUnspecified()
			if leftWildcard != rightWildcard {
				return !leftWildcard
			}
			if item.Bindings[i].BindIP != item.Bindings[j].BindIP {
				return item.Bindings[i].BindIP < item.Bindings[j].BindIP
			}
			return item.Bindings[i].PublicPort < item.Bindings[j].PublicPort
		})
		out = append(out, *item)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Key < out[j].Key })
	return out
}