package link

import (
	"encoding/json"
	"os"
	"path/filepath"
	"regexp"
	"testing"
	"time"
)

// The Go implementation, held to the shared fixtures (novox/hq ADR 0074, design 19).
//
// **Read from the sdk's conformance directory by sibling path**, the way the lab finds its
// siblings — deliberately not copied here. A fixture copied into each implementation is two
// fixtures, and two fixtures drift, which is the exact failure the suite exists to prevent.
type fixture struct {
	Name  string `json:"name"`
	Given struct {
		Module  string            `json:"module"`
		Node    string            `json:"node"`
		Key     string            `json:"key"`
		Body    map[string]any    `json:"body"`
		Headers map[string]string `json:"headers"`
	} `json:"given"`
	Wire struct {
		Subject         string            `json:"subject"`
		RequiredHeaders []string          `json:"requiredHeaders"`
		HeaderFormats   map[string]string `json:"headerFormats"`
	} `json:"wire"`
}

func loadFixture(t *testing.T, name string) fixture {
	t.Helper()
	path := filepath.Join("..", "..", "..", "mesh-sdk", "conformance", name)
	raw, err := os.ReadFile(path)
	if err != nil {
		t.Skipf("the sdk's conformance fixtures are not beside this checkout: %v", err)
	}
	var f fixture
	if err := json.Unmarshal(raw, &f); err != nil {
		t.Fatalf("%s: %v", name, err)
	}
	return f
}

// Every header the fixture requires is one this implementation actually sets.
func TestTheGoEmitterSetsEveryRequiredHeader(t *testing.T) {
	f := loadFixture(t, "events/module-event.json")
	sent := goEventHeaders(f.Given.Key, f.Given.Module, f.Given.Node)
	for _, want := range f.Wire.RequiredHeaders {
		if _, ok := sent[want]; !ok {
			t.Errorf("the Go emitter does not set %q, which the fixture requires — an event it "+
				"emits is one a conforming consumer refuses", want)
		}
	}
}

// And each value is in the shape the fixture pins, because a header present but differently
// formatted is the disagreement that does not announce itself.
func TestTheGoEmittersHeaderFormatsMatch(t *testing.T) {
	f := loadFixture(t, "events/module-event.json")
	sent := goEventHeaders(f.Given.Key, f.Given.Module, f.Given.Node)

	if got := sent["content-type"]; got != f.Wire.HeaderFormats["content-type"] {
		t.Errorf("content-type is %q, the fixture says %q", got, f.Wire.HeaderFormats["content-type"])
	}
	if _, err := time.Parse(time.RFC3339, sent["x-time"]); err != nil {
		t.Errorf("x-time %q is not RFC3339, which the fixture requires: %v", sent["x-time"], err)
	}
	if pattern := f.Wire.HeaderFormats["x-event-id"]; pattern != "" {
		if !regexp.MustCompile(pattern).MatchString(sent["x-event-id"]) {
			t.Errorf("x-event-id %q does not match %q", sent["x-event-id"], pattern)
		}
	}
	// The origin the envelope claims is the one the bus enforces by namespace. A disagreement
	// here means the envelope is lying about where it came from.
	if sent["x-source"] != f.Given.Module {
		t.Errorf("x-source is %q for module %q", sent["x-source"], f.Given.Module)
	}
}

// The subject a module's event lands on is derived, not carried — so this implementation must
// derive the same one the fixture names.
func TestTheGoSubjectMatchesTheFixture(t *testing.T) {
	f := loadFixture(t, "events/module-event.json")
	got := "mesh.mod." + f.Given.Module + ".event." + f.Given.Key
	if got != f.Wire.Subject {
		t.Errorf("this implementation would publish on %q; the fixture says %q", got, f.Wire.Subject)
	}
}

// goEventHeaders is the header set EmitEvent produces, factored so conformance can see it
// without a broker. Kept beside the emitter so the two cannot drift apart silently.
func goEventHeaders(eventType, source, node string) map[string]string {
	id, err := eventID()
	if err != nil {
		panic(err)
	}
	return map[string]string{
		"x-event-id":   id,
		"x-source":     source,
		"x-node":       node,
		"x-time":       time.Now().UTC().Format(time.RFC3339),
		"content-type": "application/json",
	}
}