package edgeconfig

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"
)

// reloadPath is the endpoint the nginx-side handler serves. The handler
// (baked into the nginx image) does: content check → nginx -t → nginx -s
// reload, and is idempotent — reloading an unchanged config is a no-op.
const reloadPath = "/reload"

// HTTPReloader fans reloads out to a fixed list of nginx instances by
// host:port. This is the dev/compose provider (Docker embedded DNS names)
// and the transport KubeReloader uses per discovered pod.
type HTTPReloader struct {
	client  *http.Client
	targets []string // host:port list, e.g. ["nginx:8081"]
}

// NewHTTPReloader targets is a comma-separated host:port list
// (EDGE_RELOAD_TARGETS=nginx:8081 or "10.0.0.4:8081,10.0.0.5:8081").
func NewHTTPReloader(targets string) (*HTTPReloader, error) {
	var out []string
	for _, t := range strings.Split(targets, ",") {
		t = strings.TrimSpace(t)
		if t == "" {
			continue
		}
		if _, _, err := net.SplitHostPort(t); err != nil {
			return nil, fmt.Errorf("edgeconfig: bad target %q: %w", t, err)
		}
		out = append(out, t)
	}
	if len(out) == 0 {
		return nil, fmt.Errorf("edgeconfig: no reload targets configured")
	}
	return &HTTPReloader{
		client:  &http.Client{Timeout: 10 * time.Second},
		targets: out,
	}, nil
}

// Reload posts to every target concurrently and aggregates results.
// A target that fails validation (nginx -t) returns its error in the
// result; the caller decides on retry/alert. Never panics on partial
// failure — partial success is reported, not swallowed.
func (h *HTTPReloader) Reload(ctx context.Context) Result {
	res := Result{Targets: make([]TargetResult, len(h.targets))}
	var wg sync.WaitGroup
	for i, t := range h.targets {
		wg.Add(1)
		go func(i int, target string) {
			defer wg.Done()
			res.Targets[i] = TargetResult{Target: target, Err: h.post(ctx, target)}
		}(i, t)
	}
	wg.Wait()
	return res
}

func (h *HTTPReloader) post(ctx context.Context, target string) error {
	url := "http://" + target + reloadPath
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, nil)
	if err != nil {
		return err
	}
	resp, err := h.client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	body, _ := io.ReadAll(io.LimitReader(resp.Body, 4<<10))
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("reload failed: %s: %s", resp.Status, strings.TrimSpace(string(body)))
	}
	return nil
}

// NullReloader succeeds without doing anything — tests and deployments
// where the static floor config is sufficient.
type NullReloader struct{}

func (NullReloader) Reload(context.Context) Result { return Result{} }

// HandlerResult is the JSON body the nginx-side handler replies with;
// shared here so producers can decode it in tests/integrations.
type HandlerResult struct {
	Reloaded bool   `json:"reloaded"`          // false = content unchanged, no-op
	Checksum uint32 `json:"checksum"`          // adler32 of current fragment set
	Message  string `json:"message,omitempty"` // validation error detail on failure
}

// PostReload is a helper for tests and the kube provider's per-pod call:
// one POST to target, decoding the handler's JSON reply.
func PostReload(ctx context.Context, client *http.Client, target string) (HandlerResult, error) {
	if client == nil {
		client = &http.Client{Timeout: 10 * time.Second}
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
		"http://"+target+reloadPath, bytes.NewReader(nil))
	if err != nil {
		return HandlerResult{}, err
	}
	resp, err := client.Do(req)
	if err != nil {
		return HandlerResult{}, err
	}
	defer resp.Body.Close()
	var hr HandlerResult
	if err := json.NewDecoder(io.LimitReader(resp.Body, 4<<10)).Decode(&hr); err != nil {
		return HandlerResult{}, fmt.Errorf("decode reload reply (%s): %w", resp.Status, err)
	}
	if resp.StatusCode != http.StatusOK {
		return hr, fmt.Errorf("reload failed: %s: %s", resp.Status, hr.Message)
	}
	return hr, nil
}