package main

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

type declaration struct {
	Name     string `json:"name"`
	Kind     string `json:"kind"`
	Receiver string `json:"receiver,omitempty"`
	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{
	"manager.go",
	"pool.go",
	"connection.go",
	"reconnect.go",
	"flow_control.go",
	"submit.go",
	"deliver.go",
	"protocol_log.go",
	"transport.go",
}

var requiredTests = []string{
	"TestConnectionPoolAcquiresAcrossConnections",
	"TestManagerDisconnectChannelRemovesPoolAndStopsReconnects",
	"TestNormalizeUpstreamConfigDefaults",
	"TestFailedSupplierConnectionReconnectsWhenEndpointRecovers",
	"TestHandleConnectionLossNotifiesPendingSubmitters",
	"TestHeartbeatTimeoutClosesConnectionAndSchedulesReconnect",
	"TestReconnectDelayUsesCappedBackoffAndSlowAuthenticationRetry",
	"TestHeartbeatResponseClearsOnlyMatchingRequest",
	"TestSplitSubmitContentUCS2LongMessage",
	"TestAssembleLongUplinkOutOfOrder",
	"TestSubmitRequestPacketUsesCMPP2PacketForCMPP20Channel",
	"TestSubmitRequestPacketUsesCMPP3PacketForCMPP30Channel",
	"TestHandleCMPP2DeliverReceiptPostsReceiptEvent",
	"TestReceiptStatusTreatsNonDeliveredFinalStatesAsUndelivered",
	"TestEmitProtocolLogPostsSafeOutboundPacketEvent",
}

func main() {
	root, err := os.Getwd()
	must(err)
	payload, err := os.ReadFile(filepath.Join(root, "docs", "contracts", "upstream-r7-declarations.json"))
	must(err)
	var contract manifest
	must(json.Unmarshal(payload, &contract))
	if contract.Version != "R7" {
		fail("unexpected contract version %q", contract.Version)
	}

	upstreamDir := filepath.Join(root, "gateway", "internal", "upstream")
	actual := map[string]declaration{}
	for _, name := range requiredFiles {
		path := filepath.Join(upstreamDir, name)
		source, err := os.ReadFile(path)
		must(err)
		if !bytes.HasPrefix(source, []byte("package upstream")) {
			fail("%s must remain in package upstream", name)
		}
		for _, item := range declarationsInFile(path, source) {
			key := declarationKey(item)
			if previous, exists := actual[key]; exists {
				fail("duplicate declaration %s in %s and %s", key, previous.File, item.File)
			}
			actual[key] = item
		}
	}
	for _, expected := range contract.Declarations {
		key := declarationKey(expected)
		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)
		}
	}

	managerSource, err := os.ReadFile(filepath.Join(upstreamDir, "manager.go"))
	must(err)
	if lines := bytes.Count(managerSource, []byte{'\n'}); lines > 250 {
		fail("stable manager.go grew to %d lines", lines)
	}
	for _, entry := range []string{
		"type Manager struct",
		"type ConnectionState struct",
		"func (m *Manager) ConnectChannel(",
		"func (m *Manager) DisconnectChannel(",
	} {
		assertContains(managerSource, entry)
	}
	submitSource, err := os.ReadFile(filepath.Join(upstreamDir, "submit.go"))
	must(err)
	assertContains(submitSource, "func (m *Manager) Submit(")

	controlSource, err := os.ReadFile(filepath.Join(root, "gateway", "internal", "control", "server.go"))
	must(err)
	for _, entry := range []string{
		"*upstream.Manager",
		"s.Upstream.ConnectChannel",
		"s.Upstream.DisconnectChannel",
		"server.Upstream.Submit",
	} {
		assertContains(controlSource, entry)
	}
	mainSource, err := os.ReadFile(filepath.Join(root, "gateway", "cmd", "gateway", "main.go"))
	must(err)
	assertContains(mainSource, "&upstream.Manager{APIBaseURL: apiBaseURL}")

	longMessageSource, err := os.ReadFile(filepath.Join(upstreamDir, "long_message.go"))
	must(err)
	for _, entry := range []string{
		"func splitSubmitContent(",
		"func assembleLongUplink(",
		"func pruneLongUplinkAssemblies(",
	} {
		assertContains(longMessageSource, entry)
	}

	var tests bytes.Buffer
	testFiles, err := filepath.Glob(filepath.Join(upstreamDir, "*_test.go"))
	must(err)
	for _, path := range testFiles {
		source, err := os.ReadFile(path)
		must(err)
		tests.Write(source)
	}
	for _, test := range requiredTests {
		assertContains(tests.Bytes(), "func "+test+"(")
	}

	fmt.Printf(
		"R7 upstream 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, receiver := declarationIdentity(decl)
		start := declarationStart(decl)
		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, Receiver: receiver, File: filepath.Base(path),
			SHA256: hex.EncodeToString(hash[:]),
		})
	}
	return result
}

func declarationIdentity(decl ast.Decl) (name string, kind string, receiver string) {
	switch typed := decl.(type) {
	case *ast.FuncDecl:
		return typed.Name.Name, "func", receiverName(typed)
	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 receiverName(decl *ast.FuncDecl) string {
	if decl.Recv == nil || len(decl.Recv.List) == 0 {
		return ""
	}
	switch typed := decl.Recv.List[0].Type.(type) {
	case *ast.Ident:
		return typed.Name
	case *ast.StarExpr:
		if ident, ok := typed.X.(*ast.Ident); ok {
			return ident.Name
		}
	}
	fail("unsupported receiver for %s", decl.Name.Name)
	return ""
}

func declarationStart(decl ast.Decl) token.Pos {
	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()
		}
	}
	return start
}

func declarationKey(item declaration) string {
	key := item.Kind + ":"
	if item.Receiver != "" {
		key += item.Receiver + "."
	}
	return key + item.Name
}

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, "R7 verification failed: "+format+"\n", args...)
	os.Exit(1)
}