package link

import (
	"bytes"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"regexp"
	"strings"
	"sync"
	"testing"
	"time"

	"github.com/novox/mesh-controller/internal/beside"
)

// The Go implementation, held to the shared fixtures (novox/hq ADR 0074, design 19).
//
// **Read from the SDK's own conformance directory, never copied by hand**: a fixture written into each
// implementation is two fixtures, and two fixtures drift, which is the failure the suite exists to prevent.
// Which SDK is read is the one this tree's go.mod pins, never the one a desktop happens to hold beside this
// checkout (novox/hq issue 449):
//
//   - in a merge check, the fixture as it stands at that pin in the mesh-sdk clone the build seat places
//     beside the check — read with `git show`, because the clone is checked out at the *running*
//     controller's pin, and a pull request moving the SDK must be judged against the SDK it moves to, or it
//     passes the check and fails everywhere after it rolls out. A pin the clone lacks fails the test; a
//     missing clone reads the captured copy and says so loudly, until mesh-controller #220 has rolled out
//     and the build seat clones mesh-sdk (then its follow-up makes a missing clone fail again);
//   - elsewhere, the copy captured in testdata/beside at the commit testdata/beside/CAPTURED names, held to
//     go.mod by TestTheCapturedSDKIsTheOneGoModPins.
//
// In a merge check the captured copy is also compared with the clone at the captured commit, byte for byte,
// so a hand-edited copy cannot pass for the SDK's.
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"`
}

// sdkModule is the Go module of the SDK the controller is built against.
const sdkModule = "git.novox.be/novox/mesh-sdk/go"

// The tree's go.mod, and the captured copy, as this package finds them.
var (
	goModFile   = filepath.Join("..", "..", "go.mod")
	capturedSDK = filepath.Join(beside.Captured(), "mesh-sdk")
	capturedLog = filepath.Join(beside.Captured(), "CAPTURED")
)

func loadFixture(t *testing.T, name string) fixture {
	t.Helper()
	raw, from, err := sdkFixture(os.Getenv(beside.Env), goModFile, capturedSDK, capturedLog, name)
	if err != nil {
		// Failed, never skipped: a skip here passed the suite with nothing judged.
		t.Fatal(err)
	}
	t.Logf("%s: %s", name, from)
	if strings.HasPrefix(from, notJudged) {
		// Said on the check's own output too, where `go test` without -v prints no log of a passing test.
		saidNotJudged.Do(func() { fmt.Fprintln(os.Stderr, "internal/link conformance: "+from) })
	}
	var f fixture
	if err := json.Unmarshal(raw, &f); err != nil {
		t.Fatalf("%s: %v", name, err)
	}
	return f
}

// notJudged opens what a merge check without the SDK's clone says; saidNotJudged says it once on stderr.
const notJudged = "NOT JUDGED AGAINST THE CLONE"

var saidNotJudged sync.Once

// sdkFixture is one conformance fixture and where it was read: from the mesh-sdk clone in root (a merge
// check's MESH_CHECK_BESIDE) at the pin of goMod, or, with no root, from the captured copy.
func sdkFixture(root, goMod, captured, capturedLog, name string) ([]byte, string, error) {
	file := path.Join("conformance", name)
	readCaptured := func() ([]byte, error) {
		raw, err := os.ReadFile(filepath.Join(captured, filepath.FromSlash(file)))
		if err != nil {
			return nil, fmt.Errorf("the captured SDK's %s: %w", file, err)
		}
		return raw, nil
	}
	if root == "" {
		raw, err := readCaptured()
		return raw, "the copy captured in testdata/beside (see CAPTURED); a merge check reads the SDK's clone " +
			"at this tree's pin", err
	}
	clone := filepath.Join(root, "mesh-sdk")
	if _, err := os.Stat(clone); err != nil {
		// A build seat asked by a controller from before mesh-controller #220 places no mesh-sdk beside the
		// check, so #220 could never pass its own check if this failed. Until #220 has rolled out, the
		// captured copy is read and the log says so loudly; the follow-up of novox/hq issue 449 makes this
		// a failure again.
		at, cerr := capturedCommit(capturedLog)
		if cerr != nil {
			return nil, "", cerr
		}
		raw, rerr := readCaptured()
		return raw, fmt.Sprintf(notJudged+": the seat placed no mesh-sdk beside this check in "+
			"%s=%s (it does once mesh-controller #220 has rolled out); read the captured copy at %s", beside.Env,
			root, at), rerr
	}
	ref, err := sdkRef(goMod)
	if err != nil {
		return nil, "", err
	}
	raw, err := gitShow(clone, ref, file)
	if err != nil {
		return nil, "", fmt.Errorf("the mesh-sdk clone beside this check has no %s at %s, the SDK this tree's "+
			"go.mod pins: %w", file, ref, err)
	}
	// The captured copy is the SDK's own, never edited by hand: the clone at the captured commit says so.
	at, err := capturedCommit(capturedLog)
	if err != nil {
		return nil, "", err
	}
	theirs, err := gitShow(clone, at, file)
	if err != nil {
		return nil, "", fmt.Errorf("the mesh-sdk clone has no %s at %s, the commit CAPTURED names: %w", file, at, err)
	}
	ours, err := os.ReadFile(filepath.Join(captured, filepath.FromSlash(file)))
	if err != nil {
		return nil, "", fmt.Errorf("the captured SDK's %s: %w", file, err)
	}
	if !bytes.Equal(ours, theirs) {
		return nil, "", fmt.Errorf("the captured %s is not mesh-sdk's at %s, the commit CAPTURED names: it was "+
			"edited or captured wrong; capture it again as CAPTURED says", file, at)
	}
	return raw, "mesh-sdk cloned beside this check, at " + ref + " (this tree's go.mod)", nil
}

// gitShow is one file of a repository at a ref. safe.directory, because the clone is the build seat's and
// the test may run as another user.
func gitShow(repository, ref, file string) ([]byte, error) {
	cmd := exec.Command("git", "-c", "safe.directory=*", "-C", repository, "show", ref+":"+file)
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	out, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("git show %s:%s: %v: %s", ref, file, err, strings.TrimSpace(stderr.String()))
	}
	return out, nil
}

// pseudoCommit is the commit a Go pseudo-version names: v0.1.11-0.20261009143344-f047d0a4a970 → f047d0a4a970.
var pseudoCommit = regexp.MustCompile(`-([0-9a-f]{12})$`)

// sdkRef is the SDK repository's ref a go.mod pins: a pseudo-version's commit, or a release's tag (the SDK
// tags its Go module under go/).
func sdkRef(goMod string) (string, error) {
	raw, err := os.ReadFile(goMod)
	if err != nil {
		return "", err
	}
	version := ""
	for _, line := range strings.Split(string(raw), "\n") {
		fields := strings.Fields(strings.TrimPrefix(strings.TrimSpace(line), "require "))
		if len(fields) >= 2 && fields[0] == sdkModule {
			version = fields[1]
		}
	}
	if m := pseudoCommit.FindStringSubmatch(version); m != nil {
		return m[1], nil
	}
	if strings.HasPrefix(version, "v") {
		return "go/" + version, nil
	}
	return "", fmt.Errorf("%s pins no version of %s that names a commit or a tag", goMod, sdkModule)
}

// capturedCommit is the commit testdata/beside/CAPTURED names for mesh-sdk.
func capturedCommit(capturedLog string) (string, error) {
	raw, err := os.ReadFile(capturedLog)
	if err != nil {
		return "", err
	}
	at := regexp.MustCompile(`(?m)^mesh-sdk\s+([0-9a-f]{40})\s`).FindSubmatch(raw)
	if at == nil {
		return "", fmt.Errorf("%s names no commit for mesh-sdk", capturedLog)
	}
	return string(at[1]), nil
}

// The captured SDK is the one this controller is built against: when go.mod moves the SDK, the copy moves
// with it, or the tests away from a merge check judge an SDK the controller no longer uses (novox/hq issue
// 449).
func TestTheCapturedSDKIsTheOneGoModPins(t *testing.T) {
	pinned, err := sdkRef(goModFile)
	if err != nil {
		t.Fatal(err)
	}
	at, err := capturedCommit(capturedLog)
	if err != nil {
		t.Fatal(err)
	}
	if strings.HasPrefix(pinned, "go/") || !strings.HasPrefix(at, pinned) {
		t.Errorf("the SDK is captured at %s but go.mod pins %s: capture it again at the pinned commit, as "+
			"testdata/beside/CAPTURED says", at, pinned)
	}
}

// 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",
	}
}