package main

import (
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

type declaration struct {
	Name   string `json:"name"`
	Kind   string `json:"kind"`
	File   string `json:"file"`
	SHA256 string `json:"sha256"`
}

type manifest struct {
	Version      string        `json:"version"`
	Source       string        `json:"source"`
	Declarations []declaration `json:"declarations"`
}

var requiredFiles = []string{
	"server.go",
	"authentication.go",
	"submit.go",
	"sessions.go",
	"delivery.go",
	"acknowledgement.go",
	"pending_recovery.go",
	"protocol_log.go",
	"transport.go",
}

var requiredTests = []string{
	"TestInboundServerAuthenticatesAndSubmits",
	"TestInboundServerProcessesSubmitWithinAuthenticatedConnectionWindow",
	"TestBoundedSubmitWindowAndAggregateSlotSnapshot",
	"TestInboundServerForwardsLongMessageFragmentsWithoutUDHAndAcknowledgesEachSubmit",
	"TestSubmitResponsePrecedesQueuedFailureReceipt",
	"TestDailyLimitRejectsSubmitSynchronouslyWithoutPendingReceipt",
	"TestInboundServerNegotiatesCMPP2AndUsesAuthenticatedAccountForSubmit",
	"TestNormalizeInboundSubmitSupportsCMPP2AndCMPP3",
	"TestDownstreamDeliveryRequiresAcknowledgement",
	"TestReceiptLookupDoesNotFallbackToAccountBeforeSubmitMappingExists",
	"TestDownstreamDeliveryReportsAckTimeout",
	"TestRecoverPendingCandidatesWritesWaitingConnectionStatus",
	"TestSubmitResponseProtocolLoggerEmitsActualPacketDirection",
	"TestDownstreamDeliverProtocolLoggerEmitsReceiptPacket",
}

func main() {
	root, err := os.Getwd()
	must(err)
	manifestPath := filepath.Join(root, "docs", "contracts", "inbound-r6-declarations.json")
	payload, err := os.ReadFile(manifestPath)
	must(err)
	var contract manifest
	must(json.Unmarshal(payload, &contract))
	if contract.Version != "R6" {
		fail("unexpected contract version %q", contract.Version)
	}

	inboundDir := filepath.Join(root, "gateway", "internal", "inbound")
	actual := map[string]declaration{}
	for _, name := range requiredFiles {
		path := filepath.Join(inboundDir, name)
		source, err := os.ReadFile(path)
		must(err)
		if !bytes.HasPrefix(source, []byte("package inbound")) {
			fail("%s must remain in package inbound", name)
		}
		for _, item := range declarationsInFile(path, source) {
			key := item.Kind + ":" + item.Name
			if previous, exists := actual[key]; exists {
				fail("duplicate declaration %s in %s and %s", key, previous.File, item.File)
			}
			actual[key] = item
		}
	}
	if os.Getenv("UPDATE_INBOUND_R6_CONTRACT") == "1" {
		contract.Declarations = contract.Declarations[:0]
		for _, item := range actual {
			contract.Declarations = append(contract.Declarations, item)
		}
		sort.Slice(contract.Declarations, func(i, j int) bool {
			if contract.Declarations[i].File != contract.Declarations[j].File {
				return contract.Declarations[i].File < contract.Declarations[j].File
			}
			if contract.Declarations[i].Name == contract.Declarations[j].Name {
				return contract.Declarations[i].Kind < contract.Declarations[j].Kind
			}
			return contract.Declarations[i].Name < contract.Declarations[j].Name
		})
		updated, err := json.MarshalIndent(contract, "", "  ")
		must(err)
		must(os.WriteFile(manifestPath, append(updated, '\n'), 0o644))
		fmt.Printf("R6 inbound contract updated with %d declarations.\n", len(contract.Declarations))
	}

	for _, expected := range contract.Declarations {
		key := expected.Kind + ":" + expected.Name
		item, ok := actual[key]
		if !ok {
			fail("missing declaration %s expected in %s", key, expected.File)
		}
		if item.File != expected.File {
			fail("%s moved to %s, expected %s", key, item.File, expected.File)
		}
		if item.SHA256 != expected.SHA256 {
			fail("%s implementation changed: %s != %s", key, item.SHA256, expected.SHA256)
		}
	}

	serverSource, err := os.ReadFile(filepath.Join(inboundDir, "server.go"))
	must(err)
	if lines := bytes.Count(serverSource, []byte{'\n'}); lines > 100 {
		fail("stable server.go grew to %d lines", lines)
	}
	assertContains(serverSource, "func (s Server) ListenAndServe() error")
	assertContains(serverSource, "s.handleLogin")
	assertContains(serverSource, "s.handleSubmit")
	assertContains(serverSource, "s.handleActivity")
	assertContains(serverSource, "s.handleConnectionClosed")

	controlSource, err := os.ReadFile(filepath.Join(root, "gateway", "internal", "control", "server.go"))
	must(err)
	for _, entry := range []string{
		"inbound.DisconnectAccount(",
		"inbound.PushReceiptWithResult(",
		"inbound.PushUplinkWithResult(",
	} {
		assertContains(controlSource, entry)
	}

	var tests bytes.Buffer
	for _, name := range []string{"server_test.go", "protocol_log_test.go", "presence_test.go", "recovery_test.go"} {
		source, err := os.ReadFile(filepath.Join(inboundDir, name))
		must(err)
		tests.Write(source)
	}
	for _, test := range requiredTests {
		assertContains(tests.Bytes(), "func "+test+"(")
	}

	fmt.Printf(
		"R6 inbound facade verified: %d declarations across %d focused files; stable entries and %d critical tests preserved.\n",
		len(contract.Declarations), len(requiredFiles), len(requiredTests),
	)
}

func declarationsInFile(path string, source []byte) []declaration {
	fset := token.NewFileSet()
	file, err := parser.ParseFile(fset, path, source, parser.ParseComments)
	must(err)
	var result []declaration
	for _, decl := range file.Decls {
		if gen, ok := decl.(*ast.GenDecl); ok && gen.Tok == token.IMPORT {
			continue
		}
		name, kind := declarationName(decl)
		start := decl.Pos()
		switch typed := decl.(type) {
		case *ast.FuncDecl:
			if typed.Doc != nil {
				start = typed.Doc.Pos()
			}
		case *ast.GenDecl:
			if typed.Doc != nil {
				start = typed.Doc.Pos()
			}
		}
		code := strings.TrimSpace(string(source[fset.Position(start).Offset:fset.Position(decl.End()).Offset]))
		hash := sha256.Sum256([]byte(strings.ReplaceAll(code, "\r\n", "\n")))
		result = append(result, declaration{
			Name: name, Kind: kind, File: filepath.Base(path), SHA256: hex.EncodeToString(hash[:]),
		})
	}
	return result
}

func declarationName(decl ast.Decl) (string, string) {
	switch typed := decl.(type) {
	case *ast.FuncDecl:
		return typed.Name.Name, "func"
	case *ast.GenDecl:
		if len(typed.Specs) == 0 {
			fail("empty declaration")
		}
		switch spec := typed.Specs[0].(type) {
		case *ast.TypeSpec:
			return spec.Name.Name, "type"
		case *ast.ValueSpec:
			return spec.Names[0].Name, strings.ToLower(typed.Tok.String())
		}
	}
	fail("unsupported declaration %T", decl)
	return "", ""
}

func assertContains(source []byte, fragment string) {
	if !bytes.Contains(source, []byte(fragment)) {
		fail("required invariant not found: %s", fragment)
	}
}

func must(err error) {
	if err != nil {
		panic(err)
	}
}

func fail(format string, args ...any) {
	fmt.Fprintf(os.Stderr, "R6 verification failed: "+format+"\n", args...)
	os.Exit(1)
}