package main

import (
	"bufio"
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"go/ast"
	"go/format"
	"go/parser"
	"go/token"
	"io"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"runtime"
	"sort"
	"strconv"
	"strings"
	"unicode"

	"gotlin/internal/lang"
)

const (
	textDocumentSyncFull      = 1
	diagnosticSeverityError   = 1
	diagnosticSeverityWarning = 2
	symbolKindPackage         = 4
	symbolKindClass           = 5
	symbolKindMethod          = 6
	symbolKindField           = 8
	symbolKindVariable        = 13
	symbolKindFunction        = 12
	symbolKindInterface       = 11
	symbolKindEnum            = 10
	symbolKindModule          = 2
)

var offsetPattern = regexp.MustCompile(` at (\d+)`)

func main() {
	server := server{
		in:        bufio.NewReader(os.Stdin),
		out:       os.Stdout,
		docs:      map[string]documentState{},
		goplsPath: resolveGoplsPath(),
	}
	if err := server.run(); err != nil && !errors.Is(err, io.EOF) {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

type server struct {
	in        *bufio.Reader
	out       io.Writer
	docs      map[string]documentState
	shutdown  bool
	goplsPath string
}

type documentState struct {
	text           string
	program        *lang.Program
	diagnostics    []diagnostic
	symbols        []symbol
	packageSymbols []symbol
}

type symbol struct {
	Name    string
	Kind    int
	Detail  string
	Range   rng
	Targets []string
	URI     string
}

type variableDeclInfo struct {
	Name    string
	Mutable bool
	Type    string
}

type request struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      json.RawMessage `json:"id,omitempty"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params,omitempty"`
}

type response struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      json.RawMessage `json:"id,omitempty"`
	Result  any             `json:"result"`
	Error   *respError      `json:"error,omitempty"`
}

type respError struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

type notification struct {
	JSONRPC string `json:"jsonrpc"`
	Method  string `json:"method"`
	Params  any    `json:"params,omitempty"`
}

type didOpenParams struct {
	TextDocument textDocumentItem `json:"textDocument"`
}

type didChangeParams struct {
	TextDocument   versionedTextDocumentIdentifier `json:"textDocument"`
	ContentChanges []contentChange                 `json:"contentChanges"`
}

type didCloseParams struct {
	TextDocument textDocumentIdentifier `json:"textDocument"`
}

type hoverParams struct {
	TextDocument textDocumentIdentifier `json:"textDocument"`
	Position     position               `json:"position"`
}

type definitionParams struct {
	TextDocument textDocumentIdentifier `json:"textDocument"`
	Position     position               `json:"position"`
}

type textDocumentItem struct {
	URI  string `json:"uri"`
	Text string `json:"text"`
}

type versionedTextDocumentIdentifier struct {
	URI string `json:"uri"`
}

type textDocumentIdentifier struct {
	URI string `json:"uri"`
}

type contentChange struct {
	Text string `json:"text"`
}

type publishDiagnosticsParams struct {
	URI         string       `json:"uri"`
	Diagnostics []diagnostic `json:"diagnostics"`
}

type diagnostic struct {
	Range    rng    `json:"range"`
	Severity int    `json:"severity,omitempty"`
	Source   string `json:"source,omitempty"`
	Code     string `json:"code,omitempty"`
	Message  string `json:"message"`
}

type rng struct {
	Start position `json:"start"`
	End   position `json:"end"`
}

type position struct {
	Line      int `json:"line"`
	Character int `json:"character"`
}

type location struct {
	URI   string `json:"uri"`
	Range rng    `json:"range"`
}

type stdlibTarget struct {
	PackagePath string
	SymbolName  string
}

type stdlibSymbol struct {
	FileName string
	Start    position
	End      position
	Decl     string
	Doc      string
}

func (s *server) run() error {
	for {
		msg, err := readMessage(s.in)
		if err != nil {
			return err
		}

		var req request
		if err := json.Unmarshal(msg, &req); err != nil {
			return err
		}

		if err := s.handle(req); err != nil {
			return err
		}
		if s.shutdown && req.Method == "exit" {
			return nil
		}
	}
}

func (s *server) handle(req request) error {
	switch req.Method {
	case "initialize":
		return s.writeResponse(response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Result: map[string]any{
				"capabilities": map[string]any{
					"textDocumentSync":   textDocumentSyncFull,
					"hoverProvider":      true,
					"definitionProvider": true,
				},
				"serverInfo": map[string]any{
					"name":    "gotlin-lsp",
					"version": "0.2.0",
				},
			},
		})
	case "initialized":
		return nil
	case "shutdown":
		s.shutdown = true
		return s.writeResponse(response{JSONRPC: "2.0", ID: req.ID, Result: nil})
	case "exit":
		return nil
	case "textDocument/didOpen":
		var params didOpenParams
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return err
		}
		s.docs[params.TextDocument.URI] = s.buildDocumentState(params.TextDocument.URI, params.TextDocument.Text)
		return s.publishDiagnostics(params.TextDocument.URI)
	case "textDocument/didChange":
		var params didChangeParams
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return err
		}
		text := ""
		if len(params.ContentChanges) > 0 {
			text = params.ContentChanges[len(params.ContentChanges)-1].Text
		}
		s.docs[params.TextDocument.URI] = s.buildDocumentState(params.TextDocument.URI, text)
		return s.publishDiagnostics(params.TextDocument.URI)
	case "textDocument/didClose":
		var params didCloseParams
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return err
		}
		delete(s.docs, params.TextDocument.URI)
		return s.writeNotification(notification{
			JSONRPC: "2.0",
			Method:  "textDocument/publishDiagnostics",
			Params:  publishDiagnosticsParams{URI: params.TextDocument.URI, Diagnostics: []diagnostic{}},
		})
	case "textDocument/hover":
		var params hoverParams
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return err
		}
		return s.writeResponse(response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Result:  s.hover(params.TextDocument.URI, params.Position),
		})
	case "textDocument/definition":
		var params definitionParams
		if err := json.Unmarshal(req.Params, &params); err != nil {
			return err
		}
		return s.writeResponse(response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Result:  s.definition(params.TextDocument.URI, params.Position),
		})
	default:
		if len(req.ID) == 0 {
			return nil
		}
		return s.writeResponse(response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Error:   &respError{Code: -32601, Message: "method not found"},
		})
	}
}

func buildDocumentState(text string) documentState {
	state := documentState{text: text, diagnostics: []diagnostic{}}
	program, err := lang.Parse(text)
	if err != nil {
		state.diagnostics = []diagnostic{diagnosticFromError(text, err)}
		return state
	}
	state.program = program
	_, semanticDiagnostics := lang.AnalyzeWithContext(program, nil)
	state.symbols = indexSymbols(text, program)
	state.diagnostics = diagnosticsFromSemantic(text, semanticDiagnostics)
	if len(semanticDiagnostics) == 0 {
		if _, err := lang.GenerateGo(program); err != nil {
			state.diagnostics = append(state.diagnostics, diagnosticFromError(text, err))
		}
	}
	return state
}

func (s *server) buildDocumentState(uri, text string) documentState {
	state := documentState{text: text, diagnostics: []diagnostic{}}
	program, err := lang.Parse(text)
	if err != nil {
		state.diagnostics = []diagnostic{diagnosticFromError(text, err)}
		return state
	}
	state.program = program
	programs, symbols := s.packageContext(uri, program.PackagePath, text)
	_, semanticDiagnostics := lang.AnalyzeWithContext(program, programs)
	state.symbols = indexSymbols(text, program)
	state.packageSymbols = symbols
	state.diagnostics = diagnosticsFromSemantic(text, semanticDiagnostics)
	return state
}

func (s *server) packageContext(currentURI, packagePath, currentText string) ([]*lang.Program, []symbol) {
	path, ok := filePathFromURI(currentURI)
	if !ok {
		return nil, nil
	}
	root := nearestModuleRoot(filepath.Dir(path))
	if root == "" {
		root = filepath.Dir(path)
	}
	var programs []*lang.Program
	var symbols []symbol
	_ = filepath.WalkDir(root, func(candidate string, entry os.DirEntry, err error) error {
		if err != nil || entry.IsDir() || filepath.Ext(candidate) != ".gt" {
			return nil
		}
		candidateURI := fileURI(candidate)
		text := ""
		if candidateURI == currentURI {
			text = currentText
		} else if open, found := s.docs[candidateURI]; found {
			text = open.text
		} else if data, readErr := os.ReadFile(candidate); readErr == nil {
			text = string(data)
		}
		if text == "" {
			return nil
		}
		program, parseErr := lang.Parse(text)
		if parseErr != nil || program.PackagePath != packagePath {
			return nil
		}
		if candidateURI != currentURI {
			programs = append(programs, program)
		}
		for _, sym := range indexSymbols(text, program) {
			sym.URI = candidateURI
			symbols = append(symbols, sym)
		}
		return nil
	})
	return programs, symbols
}

func nearestModuleRoot(directory string) string {
	for {
		if _, err := os.Stat(filepath.Join(directory, "go.mod")); err == nil {
			return directory
		}
		parent := filepath.Dir(directory)
		if parent == directory {
			return ""
		}
		directory = parent
	}
}

func filePathFromURI(uri string) (string, bool) {
	parsed, err := url.Parse(uri)
	if err != nil || parsed.Scheme != "file" {
		return "", false
	}
	path, err := url.PathUnescape(parsed.Path)
	if err != nil {
		return "", false
	}
	return filepath.Clean(filepath.FromSlash(path)), true
}

func fileURI(path string) string { return "file://" + filepath.ToSlash(filepath.Clean(path)) }

func (s *server) publishDiagnostics(uri string) error {
	state, ok := s.docs[uri]
	if !ok {
		return nil
	}
	diagnostics := state.diagnostics
	if diagnostics == nil {
		diagnostics = []diagnostic{}
	}
	return s.writeNotification(notification{
		JSONRPC: "2.0",
		Method:  "textDocument/publishDiagnostics",
		Params: publishDiagnosticsParams{
			URI:         uri,
			Diagnostics: diagnostics,
		},
	})
}

func (s *server) hover(uri string, pos position) any {
	state, ok := s.docs[uri]
	if !ok {
		return nil
	}
	word, _ := wordAtPosition(state.text, pos)
	if word == "" {
		return nil
	}
	if result := stdlibHover(state, pos); result != nil {
		return result
	}
	for _, sym := range state.symbols {
		if sym.Name != word {
			continue
		}
		if !rangeContains(sym.Range, pos) && !contains(sym.Targets, word) {
			// allow hover on usages by name match
		}
		return map[string]any{
			"contents": map[string]any{
				"kind":  "markdown",
				"value": "```gotlin\n" + sym.Detail + "\n```",
			},
		}
	}
	for _, sym := range state.packageSymbols {
		if sym.Name == word {
			return map[string]any{"contents": map[string]any{"kind": "markdown", "value": "```gotlin\n" + sym.Detail + "\n```"}}
		}
	}
	if value, ok := builtinHoverDetail(word); ok {
		return map[string]any{
			"contents": map[string]any{
				"kind":  "markdown",
				"value": "```gotlin\n" + value + "\n```",
			},
		}
	}
	if result := s.goplsHover(state, pos); result != nil {
		return result
	}
	return nil
}

func (s *server) definition(uri string, pos position) any {
	state, ok := s.docs[uri]
	if !ok {
		return nil
	}
	word, _ := wordAtPosition(state.text, pos)
	if word == "" {
		return nil
	}
	if result := stdlibDefinition(state, pos); result != nil {
		return result
	}
	for _, sym := range state.symbols {
		if sym.Name == word {
			return []location{{URI: uri, Range: sym.Range}}
		}
	}
	for _, sym := range state.packageSymbols {
		if sym.Name == word && sym.URI != "" {
			return []location{{URI: sym.URI, Range: sym.Range}}
		}
	}
	if result := s.goplsDefinition(state, pos); result != nil {
		return result
	}
	return nil
}

func (s *server) goplsHover(state documentState, pos position) any {
	if s.goplsPath == "" || state.program == nil {
		return nil
	}
	query, tokenStart, ok := goplsQueryAtPosition(state.text, pos)
	if !ok {
		return nil
	}
	source, targetOffset, cleanup, err := prepareGoplsSource(state.program, state.text, query, tokenStart)
	if err != nil {
		return nil
	}
	defer cleanup()

	output, err := exec.Command(s.goplsPath, "hover", fmt.Sprintf("%s:#%d", source, targetOffset)).CombinedOutput()
	if err != nil || len(bytes.TrimSpace(output)) == 0 {
		return nil
	}
	return map[string]any{
		"contents": map[string]any{
			"kind":  "markdown",
			"value": "```go\n" + strings.TrimSpace(string(output)) + "\n```",
		},
	}
}

func stdlibHover(state documentState, pos position) any {
	target, ok := resolveStdlibTarget(state, pos)
	if !ok {
		return nil
	}
	sym, ok := findStdlibSymbol(target)
	if !ok {
		return nil
	}
	var value strings.Builder
	value.WriteString("```go\n")
	value.WriteString(sym.Decl)
	value.WriteString("\n```")
	if sym.Doc != "" {
		value.WriteString("\n")
		value.WriteString(sym.Doc)
	}
	return map[string]any{
		"contents": map[string]any{
			"kind":  "markdown",
			"value": value.String(),
		},
	}
}

func stdlibDefinition(state documentState, pos position) any {
	target, ok := resolveStdlibTarget(state, pos)
	if !ok {
		return nil
	}
	sym, ok := findStdlibSymbol(target)
	if !ok {
		return nil
	}
	return []location{{
		URI: "file://" + filepath.Clean(sym.FileName),
		Range: rng{
			Start: sym.Start,
			End:   sym.End,
		},
	}}
}

func (s *server) goplsDefinition(state documentState, pos position) any {
	if s.goplsPath == "" || state.program == nil {
		return nil
	}
	query, tokenStart, ok := goplsQueryAtPosition(state.text, pos)
	if !ok {
		return nil
	}
	source, targetOffset, cleanup, err := prepareGoplsSource(state.program, state.text, query, tokenStart)
	if err != nil {
		return nil
	}
	tempDir := filepath.Dir(source)
	defer cleanup()

	output, err := exec.Command(s.goplsPath, "definition", fmt.Sprintf("%s:#%d", source, targetOffset)).CombinedOutput()
	if err != nil || len(bytes.TrimSpace(output)) == 0 {
		return nil
	}
	loc, ok := parseGoplsDefinition(string(output))
	if !ok {
		return nil
	}
	if isTempGoplsLocation(loc, tempDir) {
		return nil
	}
	return []location{loc}
}

func indexSymbols(text string, program *lang.Program) []symbol {
	var symbols []symbol
	lines := strings.Split(text, "\n")

	if program.PackagePath != "" {
		if r, ok := findLineMatch(lines, regexp.MustCompile(`^\s*package\s+([A-Za-z_][\w.-]*(?:\.[A-Za-z_][\w.-]*)*)`), 1); ok {
			symbols = append(symbols, symbol{
				Name:   lastPackageSegment(program.PackagePath),
				Kind:   symbolKindPackage,
				Detail: "package " + program.PackagePath,
				Range:  r,
			})
		}
	}

	importRanges := findAllLineMatches(lines, regexp.MustCompile(`^\s*import\s+((?:[A-Za-z_][\w-]*\.)*[A-Za-z_][\w-]*)(?:\s+((?:[A-Za-z_][\w-]*\.)*[A-Za-z_][\w-]*))?`))
	for i, imp := range program.Imports {
		name := importAlias(imp)
		if i < len(importRanges) {
			symbols = append(symbols, symbol{
				Name:   name,
				Kind:   symbolKindModule,
				Detail: renderImportDetail(imp),
				Range:  importRanges[i],
			})
		}
	}

	interfaceRanges := findAllLineMatches(lines, regexp.MustCompile(`^\s*interface\s+([A-Za-z_][A-Za-z0-9_]*)`))
	for i, decl := range program.Interfaces {
		r := rng{}
		if i < len(interfaceRanges) {
			r = interfaceRanges[i]
		}
		symbols = append(symbols, symbol{
			Name:   decl.Name,
			Kind:   symbolKindInterface,
			Detail: renderInterfaceSignature(decl),
			Range:  r,
		})
		for _, method := range decl.Methods {
			symbols = append(symbols, symbol{
				Name:    method.Name,
				Kind:    symbolKindMethod,
				Detail:  renderFunctionSignatureFromParts(method.Name, method.Params, method.ReturnType),
				Range:   r,
				Targets: []string{decl.Name},
			})
		}
	}

	enumRanges := findAllLineMatches(lines, regexp.MustCompile(`^\s*enum\s+([A-Za-z_][A-Za-z0-9_]*)`))
	for i, decl := range program.Enums {
		r := rng{}
		if i < len(enumRanges) {
			r = enumRanges[i]
		}
		symbols = append(symbols, symbol{Name: decl.Name, Kind: symbolKindEnum, Detail: "enum " + decl.Name, Range: r})
		for _, variant := range decl.Variants {
			symbols = append(symbols, symbol{Name: variant.Name, Kind: symbolKindVariable, Detail: decl.Name + "." + variant.Name, Range: r, Targets: []string{decl.Name}})
		}
	}

	classRanges := findAllLineMatches(lines, regexp.MustCompile(`^\s*(?:data\s+)?class\s+([A-Za-z_][A-Za-z0-9_]*)`))
	for i, decl := range program.Classes {
		r := rng{}
		if i < len(classRanges) {
			r = classRanges[i]
		}
		symbols = append(symbols, symbol{
			Name:   decl.Name,
			Kind:   symbolKindClass,
			Detail: renderClassSignature(decl),
			Range:  r,
		})
		for _, field := range decl.Fields {
			symbols = append(symbols, symbol{
				Name:    field.Name,
				Kind:    symbolKindField,
				Detail:  renderFieldSignature(decl.Name, field),
				Range:   r,
				Targets: []string{decl.Name},
			})
		}
		for _, method := range decl.Methods {
			symbols = append(symbols, symbol{
				Name:    method.Name,
				Kind:    symbolKindMethod,
				Detail:  renderMethodSignature(decl.Name, method),
				Range:   r,
				Targets: []string{decl.Name},
			})
		}
	}
	funcRanges := findAllLineMatches(lines, regexp.MustCompile(`^\s*fun\s+([A-Za-z_][A-Za-z0-9_]*)`))
	for i, fn := range program.Functions {
		detail := renderFunctionSignature(fn)
		r := rng{}
		if i < len(funcRanges) {
			r = funcRanges[i]
		}
		symbols = append(symbols, symbol{
			Name:   fn.Name,
			Kind:   symbolKindFunction,
			Detail: detail,
			Range:  r,
		})
	}

	varRanges := findAllLineNamedMatches(lines, regexp.MustCompile(`^\s*(?:val|var)\s+([A-Za-z_][A-Za-z0-9_]*)`), 1)
	varInfos := collectVariableDeclInfos(program)
	varInfoByName := map[string][]variableDeclInfo{}
	for _, info := range varInfos {
		varInfoByName[info.Name] = append(varInfoByName[info.Name], info)
	}
	for i, decl := range varRanges {
		mutable := false
		typ := ""
		if queue := varInfoByName[decl.Name]; len(queue) > 0 {
			match := queue[0]
			varInfoByName[decl.Name] = queue[1:]
			mutable = match.Mutable
			typ = match.Type
		} else if i < len(varInfos) {
			// Fallback for parser/regex mismatches.
			mutable = varInfos[i].Mutable
			typ = varInfos[i].Type
		}
		symbols = append(symbols, symbol{
			Name:   decl.Name,
			Kind:   symbolKindVariable,
			Detail: renderVariableSignature(decl.Name, mutable, typ),
			Range:  decl.Range,
		})
	}

	return symbols
}

func diagnosticsFromSemantic(text string, semantic []lang.SemanticDiagnostic) []diagnostic {
	diagnostics := make([]diagnostic, 0, len(semantic))
	for _, item := range semantic {
		start := offsetToPosition(text, item.Span.Start)
		endOffset := item.Span.End
		if endOffset <= item.Span.Start {
			endOffset = item.Span.Start + 1
		}
		diagnostics = append(diagnostics, diagnostic{
			Range:    rng{Start: start, End: offsetToPosition(text, endOffset)},
			Severity: int(item.Severity),
			Source:   "gotlin",
			Code:     item.Code,
			Message:  item.Message,
		})
	}
	return diagnostics
}

func diagnosticFromError(text string, err error) diagnostic {
	start := position{}
	end := position{}

	if match := offsetPattern.FindStringSubmatch(err.Error()); len(match) == 2 {
		if offset, convErr := strconv.Atoi(match[1]); convErr == nil {
			start = offsetToPosition(text, offset)
			end = start
			end.Character++
		}
	}

	return diagnostic{
		Range:    rng{Start: start, End: end},
		Severity: diagnosticSeverityError,
		Source:   "gotlin",
		Message:  err.Error(),
	}
}

func offsetToPosition(text string, offset int) position {
	runes := []rune(text)
	if offset < 0 {
		offset = 0
	}
	if offset > len(runes) {
		offset = len(runes)
	}
	line := 0
	char := 0
	for i := 0; i < offset; i++ {
		if runes[i] == '\n' {
			line++
			char = 0
			continue
		}
		char++
	}
	return position{Line: line, Character: char}
}

func positionToOffset(text string, pos position) int {
	runes := []rune(text)
	line := 0
	char := 0
	for i, r := range runes {
		if line == pos.Line && char == pos.Character {
			return i
		}
		if r == '\n' {
			line++
			char = 0
			if line > pos.Line {
				return i
			}
			continue
		}
		char++
	}
	return len(runes)
}

func wordAtPosition(text string, pos position) (string, rng) {
	runes := []rune(text)
	offset := positionToOffset(text, pos)
	if len(runes) == 0 {
		return "", rng{}
	}
	if offset >= len(runes) {
		offset = len(runes) - 1
	}
	if !isWordRune(runes[offset]) && offset > 0 && isWordRune(runes[offset-1]) {
		offset--
	}
	if !isWordRune(runes[offset]) {
		return "", rng{}
	}
	start := offset
	for start > 0 && isWordRune(runes[start-1]) {
		start--
	}
	end := offset
	for end+1 < len(runes) && isWordRune(runes[end+1]) {
		end++
	}
	return string(runes[start : end+1]), rng{
		Start: offsetToPosition(text, start),
		End:   offsetToPosition(text, end+1),
	}
}

func findWordRange(text string, word string) rng {
	runes := []rune(text)
	target := []rune(word)
	for i := 0; i+len(target) <= len(runes); i++ {
		if string(runes[i:i+len(target)]) != word {
			continue
		}
		beforeOk := i == 0 || !isWordRune(runes[i-1])
		afterOk := i+len(target) == len(runes) || !isWordRune(runes[i+len(target)])
		if beforeOk && afterOk {
			return rng{
				Start: offsetToPosition(text, i),
				End:   offsetToPosition(text, i+len(target)),
			}
		}
	}
	return rng{}
}

func isWordRune(r rune) bool {
	return unicode.IsLetter(r) || unicode.IsDigit(r) || r == '_'
}

func readMessage(r *bufio.Reader) ([]byte, error) {
	contentLength := -1
	for {
		line, err := r.ReadString('\n')
		if err != nil {
			return nil, err
		}
		line = strings.TrimRight(line, "\r\n")
		if line == "" {
			break
		}
		if strings.HasPrefix(strings.ToLower(line), "content-length:") {
			value := strings.TrimSpace(line[len("content-length:"):])
			n, err := strconv.Atoi(value)
			if err != nil {
				return nil, err
			}
			contentLength = n
		}
	}
	if contentLength < 0 {
		return nil, fmt.Errorf("missing Content-Length header")
	}
	body := make([]byte, contentLength)
	if _, err := io.ReadFull(r, body); err != nil {
		return nil, err
	}
	return body, nil
}

func (s *server) writeResponse(resp response) error {
	data, err := json.Marshal(resp)
	if err != nil {
		return err
	}
	return writeMessage(s.out, data)
}

func (s *server) writeNotification(note notification) error {
	data, err := json.Marshal(note)
	if err != nil {
		return err
	}
	return writeMessage(s.out, data)
}

func writeMessage(w io.Writer, payload []byte) error {
	var buf bytes.Buffer
	fmt.Fprintf(&buf, "Content-Length: %d\r\n\r\n", len(payload))
	buf.Write(payload)
	_, err := w.Write(buf.Bytes())
	return err
}

func findLineMatch(lines []string, pattern *regexp.Regexp, capture int) (rng, bool) {
	matches := findAllLineMatches(lines, pattern)
	if capture == 1 && len(matches) > 0 {
		return matches[0], true
	}
	return rng{}, false
}

func findAllLineMatches(lines []string, pattern *regexp.Regexp) []rng {
	var out []rng
	for i, line := range lines {
		idx := pattern.FindStringSubmatchIndex(line)
		if idx == nil || len(idx) < 4 {
			continue
		}
		start := idx[2]
		end := idx[3]
		out = append(out, rng{
			Start: position{Line: i, Character: utf16Len(line[:start])},
			End:   position{Line: i, Character: utf16Len(line[:end])},
		})
	}
	return out
}

type namedRange struct {
	Name  string
	Range rng
}

func findAllLineNamedMatches(lines []string, pattern *regexp.Regexp, capture int) []namedRange {
	var out []namedRange
	for i, line := range lines {
		matches := pattern.FindAllStringSubmatchIndex(line, -1)
		for _, idx := range matches {
			cStart := capture * 2
			cEnd := cStart + 1
			if cEnd >= len(idx) || idx[cStart] < 0 || idx[cEnd] < 0 {
				continue
			}
			start := idx[cStart]
			end := idx[cEnd]
			name := line[start:end]
			out = append(out, namedRange{
				Name: name,
				Range: rng{
					Start: position{Line: i, Character: utf16Len(line[:start])},
					End:   position{Line: i, Character: utf16Len(line[:end])},
				},
			})
		}
	}
	return out
}

func utf16Len(s string) int {
	return len([]rune(s))
}

func lastPackageSegment(path string) string {
	parts := strings.Split(path, ".")
	return parts[len(parts)-1]
}

func importAlias(imp lang.ImportDecl) string {
	if imp.Alias != "" {
		return imp.Alias
	}
	path := strings.TrimPrefix(imp.Path, "go.")
	parts := strings.Split(path, ".")
	return parts[len(parts)-1]
}

func renderImportDetail(imp lang.ImportDecl) string {
	if imp.Alias != "" {
		return "import " + imp.Alias + " " + imp.Path
	}
	return "import " + imp.Path
}

func renderFunctionSignature(fn lang.FunctionDecl) string {
	name := fn.Name
	if len(fn.TypeParams) > 0 {
		name += "<" + strings.Join(fn.TypeParams, ", ") + ">"
	}
	return renderFunctionSignatureFromParts(name, fn.Params, fn.ReturnType)
}

func renderFunctionSignatureFromParts(name string, fnParams []lang.Param, returnType string) string {
	var params []string
	for _, param := range fnParams {
		params = append(params, param.Name+": "+param.Type)
	}
	signature := "fun " + name + "(" + strings.Join(params, ", ") + ")"
	if returnType != "" && returnType != "Unit" {
		signature += ": " + returnType
	}
	return signature
}

func renderInterfaceSignature(decl lang.InterfaceDecl) string {
	return "interface " + decl.Name
}

func renderClassSignature(decl lang.ClassDecl) string {
	var b strings.Builder
	b.WriteString("class ")
	b.WriteString(decl.Name)
	if len(decl.TypeParams) > 0 {
		b.WriteString("<")
		b.WriteString(strings.Join(decl.TypeParams, ", "))
		b.WriteString(">")
	}

	var fields []string
	for _, field := range decl.Fields {
		keyword := "val"
		if field.Mutable {
			keyword = "var"
		}
		fields = append(fields, keyword+" "+field.Name+": "+field.Type)
	}
	if len(decl.Fields) > 0 {
		b.WriteString("(")
		b.WriteString(strings.Join(fields, ", "))
		b.WriteString(")")
	}
	if len(decl.Parents) > 0 {
		b.WriteString(": ")
		b.WriteString(strings.Join(decl.Parents, ", "))
	}
	return b.String()
}

func renderMethodSignature(className string, fn lang.FunctionDecl) string {
	return className + "." + renderFunctionSignature(fn)
}

func renderFieldSignature(className string, field lang.FieldDecl) string {
	keyword := "val"
	if field.Mutable {
		keyword = "var"
	}
	return className + "." + keyword + " " + field.Name + ": " + field.Type
}

func renderVariableSignature(name string, mutable bool, typ string) string {
	keyword := "val"
	if mutable {
		keyword = "var"
	}
	if typ != "" {
		return keyword + " " + name + ": " + typ
	}
	return keyword + " " + name
}

func collectVariableDeclInfos(program *lang.Program) []variableDeclInfo {
	var result []variableDeclInfo
	var walk func([]lang.Stmt)
	walk = func(statements []lang.Stmt) {
		for _, statement := range statements {
			switch value := statement.(type) {
			case lang.VarDecl:
				typ := value.Type
				if typ == "" {
					resolved := lang.ResolvedType(value.Value)
					if resolved.String() != "<unknown>" {
						typ = resolved.String()
					}
				}
				result = append(result, variableDeclInfo{Name: value.Name, Mutable: value.Mutable, Type: typ})
			case lang.MultiVarDecl:
				types := make([]string, len(value.Names))
				if fallible, ok := lang.ResolvedType(value.Value).(lang.GenericType); ok && fallible.Base.String() == "Result" && len(fallible.Args) == 2 && len(types) == 2 {
					types[0] = fallible.Args[0].String()
					types[1] = fallible.Args[1].String() + "?"
				} else if tuple, ok := lang.ResolvedType(value.Value).(lang.TupleType); ok && len(tuple.Elements) == len(types) {
					for index, element := range tuple.Elements {
						types[index] = element.String()
					}
				}
				for index, name := range value.Names {
					result = append(result, variableDeclInfo{Name: name, Mutable: value.Mutable, Type: types[index]})
				}
			case lang.IfStmt:
				walk(value.Then)
				walk(value.Else)
			case lang.WhileStmt:
				walk(value.Body)
			case lang.ForEachStmt:
				walk(value.Body)
			case lang.MatchStmt:
				for _, matchCase := range value.Cases {
					walk(matchCase.Body)
				}
			case lang.TryCatchStmt:
				walk(value.TryBody)
				walk(value.CatchBody)
			}
		}
	}
	for _, function := range program.Functions {
		walk(function.Body)
	}
	for _, class := range program.Classes {
		for _, method := range class.Methods {
			walk(method.Body)
		}
	}
	return result
}

func resolveStdlibTarget(state documentState, pos position) (stdlibTarget, bool) {
	if state.program == nil {
		return stdlibTarget{}, false
	}
	imports := map[string]string{}
	for _, imp := range state.program.Imports {
		if strings.HasPrefix(imp.Path, `"`) {
			continue
		}
		imports[importAlias(imp)] = importPathToGoPath(imp.Path)
	}
	if len(imports) == 0 {
		return stdlibTarget{}, false
	}

	query, _, ok := goplsQueryAtPosition(state.text, pos)
	if ok {
		if alias, symbol, found := splitSelectorQuery(query); found {
			if pkgPath, ok := imports[alias]; ok {
				return stdlibTarget{
					PackagePath: pkgPath,
					SymbolName:  symbol,
				}, true
			}
			if inferredAlias, ok := receiverImportAlias(state.program, alias); ok {
				if pkgPath, ok := imports[inferredAlias]; ok {
					return stdlibTarget{
						PackagePath: pkgPath,
						SymbolName:  symbol,
					}, true
				}
			}
		}
		if pkgPath, ok := imports[query]; ok {
			return stdlibTarget{
				PackagePath: pkgPath,
			}, true
		}
	}

	word, _ := wordAtPosition(state.text, pos)
	if word == "" {
		return stdlibTarget{}, false
	}
	if pkgPath, ok := imports[word]; ok {
		return stdlibTarget{
			PackagePath: pkgPath,
		}, true
	}
	if _, r := wordAtPosition(state.text, pos); r != (rng{}) {
		if rootAlias, ok := inferSelectorRootAlias(state.text, r); ok {
			if pkgPath, ok := imports[rootAlias]; ok {
				return stdlibTarget{
					PackagePath: pkgPath,
					SymbolName:  word,
				}, true
			}
			if inferredAlias, ok := receiverImportAlias(state.program, rootAlias); ok {
				if pkgPath, ok := imports[inferredAlias]; ok {
					return stdlibTarget{
						PackagePath: pkgPath,
						SymbolName:  word,
					}, true
				}
			}
		}
	}
	return stdlibTarget{}, false
}

func inferSelectorRootAlias(text string, tokenRange rng) (string, bool) {
	runes := []rune(text)
	start := positionToOffset(text, tokenRange.Start)
	if start <= 0 || start > len(runes) {
		return "", false
	}
	if runes[start-1] != '.' {
		return "", false
	}

	i := start - 2
	parensDepth := 0
	for i >= 0 {
		ch := runes[i]
		switch ch {
		case ')':
			parensDepth++
			i--
			continue
		case '(':
			if parensDepth > 0 {
				parensDepth--
				i--
				continue
			}
		}
		if parensDepth > 0 {
			i--
			continue
		}
		if unicode.IsSpace(ch) {
			i--
			continue
		}
		if isWordRune(ch) {
			end := i + 1
			for i >= 0 && isWordRune(runes[i]) {
				i--
			}
			startWord := i + 1
			ident := string(runes[startWord:end])

			j := i
			for j >= 0 && unicode.IsSpace(runes[j]) {
				j--
			}
			if j >= 0 && runes[j] == '.' {
				i = j - 1
				continue
			}
			return ident, true
		}
		return "", false
	}
	return "", false
}

func receiverImportAlias(program *lang.Program, receiver string) (string, bool) {
	for _, class := range program.Classes {
		for _, field := range class.Fields {
			if field.Name != receiver {
				continue
			}
			if alias, ok := firstTypeImportAlias(field.Type); ok {
				return alias, true
			}
		}
	}
	return "", false
}

func firstTypeImportAlias(typ string) (string, bool) {
	typ = strings.TrimSpace(typ)
	for strings.HasPrefix(typ, "*") {
		typ = strings.TrimPrefix(typ, "*")
	}
	dot := strings.Index(typ, ".")
	if dot <= 0 {
		return "", false
	}
	return typ[:dot], true
}

func splitSelectorQuery(query string) (string, string, bool) {
	index := strings.Index(query, ".")
	if index <= 0 || index+1 >= len(query) {
		return "", "", false
	}
	return query[:index], query[index+1:], true
}

func findStdlibSymbol(target stdlibTarget) (stdlibSymbol, bool) {
	dir, ok := resolvePackageDir(target.PackagePath)
	if !ok {
		return stdlibSymbol{}, false
	}
	fset := token.NewFileSet()
	pkgs, err := parser.ParseDir(fset, dir, func(info os.FileInfo) bool {
		return !strings.HasSuffix(info.Name(), "_test.go")
	}, parser.ParseComments)
	if err != nil || len(pkgs) == 0 {
		return stdlibSymbol{}, false
	}

	pkg := firstASTPackage(pkgs)
	if pkg == nil {
		return stdlibSymbol{}, false
	}
	files := packageFiles(pkg)
	if len(files) == 0 {
		return stdlibSymbol{}, false
	}

	if target.SymbolName == "" {
		file := files[0]
		start := fset.Position(file.Name.Pos())
		end := fset.Position(file.Name.End())
		decl := "package " + pkg.Name
		doc := strings.TrimSpace(commentText(file.Doc))
		return stdlibSymbol{
			FileName: start.Filename,
			Start:    tokenPosition(start),
			End:      tokenPosition(end),
			Decl:     decl,
			Doc:      doc,
		}, true
	}

	for _, file := range files {
		for _, decl := range file.Decls {
			if sym, ok := matchStdlibDecl(fset, decl, target.SymbolName); ok {
				return sym, true
			}
		}
	}
	return stdlibSymbol{}, false
}

func resolvePackageDir(packagePath string) (string, bool) {
	stdlibDir := filepath.Join(resolveGoRoot(), "src", filepath.FromSlash(packagePath))
	if info, err := os.Stat(stdlibDir); err == nil && info.IsDir() {
		return stdlibDir, true
	}

	if listed := goListPackageDir(packagePath); listed != "" {
		return listed, true
	}

	if cached := findInModuleCache(packagePath); cached != "" {
		return cached, true
	}

	return "", false
}

func goListPackageDir(packagePath string) string {
	output, err := exec.Command("go", "list", "-f", "{{.Dir}}", packagePath).Output()
	if err != nil {
		return ""
	}
	dir := strings.TrimSpace(string(output))
	if dir == "" {
		return ""
	}
	if info, err := os.Stat(dir); err == nil && info.IsDir() {
		return dir
	}
	return ""
}

func findInModuleCache(packagePath string) string {
	modCache := strings.TrimSpace(goEnv("GOMODCACHE"))
	if modCache == "" {
		goPath := strings.TrimSpace(goEnv("GOPATH"))
		if goPath != "" {
			parts := filepath.SplitList(goPath)
			if len(parts) > 0 {
				modCache = filepath.Join(parts[0], "pkg", "mod")
			}
		}
	}
	if modCache == "" {
		return ""
	}

	parts := strings.Split(packagePath, "/")
	for i := len(parts); i >= 1; i-- {
		modulePath := strings.Join(parts[:i], "/")
		subPath := strings.Join(parts[i:], "/")
		pattern := filepath.Join(modCache, escapeModulePath(modulePath)+"@*")
		matches, _ := filepath.Glob(pattern)
		if len(matches) == 0 {
			continue
		}
		sort.Strings(matches)
		for j := len(matches) - 1; j >= 0; j-- {
			candidate := matches[j]
			if subPath != "" {
				candidate = filepath.Join(candidate, filepath.FromSlash(subPath))
			}
			if info, err := os.Stat(candidate); err == nil && info.IsDir() {
				return candidate
			}
		}
	}
	return ""
}

func escapeModulePath(path string) string {
	var b strings.Builder
	for _, r := range path {
		if r >= 'A' && r <= 'Z' {
			b.WriteRune('!')
			b.WriteRune(r + ('a' - 'A'))
			continue
		}
		b.WriteRune(r)
	}
	return b.String()
}

func importPathToGoPath(path string) string {
	trimmed := strings.TrimPrefix(path, "go.")
	parts := strings.Split(trimmed, ".")
	if len(parts) >= 3 && isDomainTLD(parts[1]) {
		return parts[0] + "." + parts[1] + "/" + strings.Join(parts[2:], "/")
	}
	return strings.ReplaceAll(trimmed, ".", "/")
}

func isDomainTLD(segment string) bool {
	switch segment {
	case "com", "org", "net", "io", "dev", "app", "ai":
		return true
	default:
		return false
	}
}

func firstASTPackage(pkgs map[string]*ast.Package) *ast.Package {
	names := make([]string, 0, len(pkgs))
	for name := range pkgs {
		names = append(names, name)
	}
	sort.Strings(names)
	for _, name := range names {
		return pkgs[name]
	}
	return nil
}

func packageFiles(pkg *ast.Package) []*ast.File {
	names := make([]string, 0, len(pkg.Files))
	for name := range pkg.Files {
		names = append(names, name)
	}
	sort.Strings(names)
	files := make([]*ast.File, 0, len(names))
	for _, name := range names {
		files = append(files, pkg.Files[name])
	}
	return files
}

func matchStdlibDecl(fset *token.FileSet, decl ast.Decl, symbolName string) (stdlibSymbol, bool) {
	switch d := decl.(type) {
	case *ast.FuncDecl:
		if d.Name == nil || d.Name.Name != symbolName {
			return stdlibSymbol{}, false
		}
		return newStdlibSymbol(fset, d.Name.Pos(), d.Name.End(), formatFuncDecl(fset, d), commentText(d.Doc)), true
	case *ast.GenDecl:
		for _, spec := range d.Specs {
			switch s := spec.(type) {
			case *ast.TypeSpec:
				if s.Name.Name != symbolName {
					continue
				}
				return newStdlibSymbol(fset, s.Name.Pos(), s.Name.End(), formatGenDecl(fset, d, s), specCommentText(d.Doc, s.Doc, s.Comment)), true
			case *ast.ValueSpec:
				for _, name := range s.Names {
					if name.Name != symbolName {
						continue
					}
					return newStdlibSymbol(fset, name.Pos(), name.End(), formatGenDecl(fset, d, s), specCommentText(d.Doc, s.Doc, s.Comment)), true
				}
			}
		}
	}
	return stdlibSymbol{}, false
}

func newStdlibSymbol(fset *token.FileSet, start token.Pos, end token.Pos, decl string, doc string) stdlibSymbol {
	startPos := fset.Position(start)
	endPos := fset.Position(end)
	return stdlibSymbol{
		FileName: startPos.Filename,
		Start:    tokenPosition(startPos),
		End:      tokenPosition(endPos),
		Decl:     strings.TrimSpace(decl),
		Doc:      strings.TrimSpace(doc),
	}
}

func formatFuncDecl(fset *token.FileSet, decl *ast.FuncDecl) string {
	copyDecl := *decl
	copyDecl.Body = nil
	return formatNode(fset, &copyDecl)
}

func formatGenDecl(fset *token.FileSet, decl *ast.GenDecl, spec ast.Spec) string {
	copyDecl := &ast.GenDecl{
		Tok: decl.Tok,
		Specs: []ast.Spec{
			spec,
		},
	}
	return formatNode(fset, copyDecl)
}

func formatNode(fset *token.FileSet, node any) string {
	var buf bytes.Buffer
	if err := format.Node(&buf, fset, node); err != nil {
		return ""
	}
	return buf.String()
}

func commentText(group *ast.CommentGroup) string {
	if group == nil {
		return ""
	}
	return strings.TrimSpace(group.Text())
}

func specCommentText(groups ...*ast.CommentGroup) string {
	for _, group := range groups {
		if text := commentText(group); text != "" {
			return text
		}
	}
	return ""
}

func tokenPosition(pos token.Position) position {
	return position{
		Line:      pos.Line - 1,
		Character: pos.Column - 1,
	}
}

func resolveGoRoot() string {
	if value := strings.TrimSpace(os.Getenv("GOROOT")); value != "" {
		return value
	}
	if value := strings.TrimSpace(goEnv("GOROOT")); value != "" {
		return value
	}
	return runtime.GOROOT()
}

func copyScope(scope map[string]bool) map[string]bool {
	dup := make(map[string]bool, len(scope))
	for k, v := range scope {
		dup[k] = v
	}
	return dup
}

func isBuiltin(name string) bool {
	_, ok := builtinDetails[name]
	return ok
}

func builtinHoverDetail(name string) (string, bool) {
	value, ok := builtinDetails[name]
	return value, ok
}

var builtinDetails = map[string]string{
	"println":        "fun println(value: Any): Unit",
	"runCatching":    "fun runCatching(block: () -> Unit): Result",
	"Channel":        "fun Channel<T>(capacity: Int = 0): Channel<T>",
	"listOf":         "fun listOf<T>(values: T...): List<T>",
	"mutableListOf":  "fun mutableListOf<T>(values: T...): MutableList<T>",
	"mapOf":          "fun mapOf<K, V>(pairs: Any...): Map<K, V>",
	"mutableMapOf":   "fun mutableMapOf<K, V>(pairs: Any...): MutableMap<K, V>",
	"ByteSlice":      "fun ByteSlice(value: String | Int): ByteSlice",
	"append":         "fun append<T>(values: List<T>, value: T): List<T>",
	"keys":           "fun keys<K, V>(values: Map<K, V>): List<K>",
	"goAssert":       "fun goAssert<T>(value: Any): T",
	"len":            "fun len(value: Any): Int",
	"cap":            "fun cap(value: Any): Int",
	"make":           "fun make<T>(size: Int): T",
	"new":            "fun new<T>(): *T",
	"copy":           "fun copy(target: Any, source: Any): Int",
	"delete":         "fun delete(map: Any, key: Any): Unit",
	"close":          "fun close(channel: Any): Unit",
	"panic":          "fun panic(value: Any): Unit",
	"recover":        "fun recover(): Any",
	"string":         "fun string(value: Any): String",
	"int":            "fun int(value: Any): Int",
	"float64":        "fun float64(value: Any): Double",
	"bool":           "fun bool(value: Any): Boolean",
	"sql":            "typed PostgreSQL query DSL",
	"set":            "fun set(target: Any, value: Any): Unit",
	"now":            "fun now(): time.Time",
	"runBlocking":    "fun runBlocking(block: suspend () -> Unit): Unit",
	"coroutineScope": "suspend fun coroutineScope(block: suspend () -> Unit): Unit",
	"launch":         "suspend fun launch(block: suspend () -> Unit): Unit",
	"async":          "suspend fun async<T>(block: suspend () -> T): Deferred<T>",
	"delay":          "suspend fun delay(ms: Int): Unit",
	"withTimeout":    "suspend fun withTimeout(ms: Int, block: suspend () -> Unit): Unit",
	"isActive":       "suspend fun isActive(): Boolean",
}

func contains(values []string, needle string) bool {
	for _, value := range values {
		if value == needle {
			return true
		}
	}
	return false
}

func rangeContains(r rng, p position) bool {
	if p.Line < r.Start.Line || p.Line > r.End.Line {
		return false
	}
	if p.Line == r.Start.Line && p.Character < r.Start.Character {
		return false
	}
	if p.Line == r.End.Line && p.Character > r.End.Character {
		return false
	}
	return true
}

func uniqueDiagnostics(input []diagnostic) []diagnostic {
	seen := map[string]bool{}
	var out []diagnostic
	for _, d := range input {
		key := fmt.Sprintf("%d:%d:%d:%d:%s", d.Range.Start.Line, d.Range.Start.Character, d.Range.End.Line, d.Range.End.Character, d.Message)
		if seen[key] {
			continue
		}
		seen[key] = true
		out = append(out, d)
	}
	return out
}

func resolveGoplsPath() string {
	if configured := strings.TrimSpace(os.Getenv("GOTLIN_GOPLS_PATH")); configured != "" {
		return configured
	}
	if path, err := exec.LookPath("gopls"); err == nil {
		return path
	}
	for _, dir := range goBinCandidates() {
		path := filepath.Join(dir, "gopls")
		if info, err := os.Stat(path); err == nil && !info.IsDir() {
			return path
		}
	}
	return ""
}

func goBinCandidates() []string {
	var dirs []string
	seen := map[string]bool{}
	add := func(dir string) {
		dir = strings.TrimSpace(dir)
		if dir == "" || seen[dir] {
			return
		}
		seen[dir] = true
		dirs = append(dirs, dir)
	}

	add(os.Getenv("GOBIN"))
	for _, part := range filepath.SplitList(os.Getenv("GOPATH")) {
		add(filepath.Join(part, "bin"))
	}
	if home, err := os.UserHomeDir(); err == nil {
		add(filepath.Join(home, "go", "bin"))
	}
	for _, value := range []string{goEnv("GOBIN"), goEnv("GOPATH")} {
		for _, part := range filepath.SplitList(value) {
			if filepath.Base(part) == "bin" {
				add(part)
				continue
			}
			add(filepath.Join(part, "bin"))
		}
	}
	return dirs
}

func goEnv(name string) string {
	output, err := exec.Command("go", "env", name).Output()
	if err != nil {
		return ""
	}
	return strings.TrimSpace(string(output))
}

func goplsQueryAtPosition(text string, pos position) (string, int, bool) {
	word, r := wordAtPosition(text, pos)
	if word == "" {
		return "", 0, false
	}
	startOffset := positionToOffset(text, r.Start)
	runes := []rune(text)

	if startOffset > 0 && runes[startOffset-1] == '.' {
		leftEnd := startOffset - 1
		leftStart := leftEnd - 1
		for leftStart >= 0 && isWordRune(runes[leftStart]) {
			leftStart--
		}
		leftStart++
		if leftStart < leftEnd {
			receiver := string(runes[leftStart:leftEnd])
			return receiver + "." + word, startOffset, true
		}
	}

	return word, startOffset, true
}

func prepareGoplsSource(program *lang.Program, gotlinSource string, query string, tokenStart int) (string, int, func(), error) {
	goSrc, err := lang.GenerateGo(program)
	if err != nil {
		return "", 0, func() {}, err
	}

	preferredLine := offsetToPosition(gotlinSource, tokenStart).Line
	targetOffset := findQueryOffset(string(goSrc), query, preferredLine)
	if targetOffset < 0 {
		targetOffset = findQueryOffset(string(goSrc), lastQuerySegment(query), preferredLine)
	}
	if targetOffset < 0 {
		return "", 0, func() {}, fmt.Errorf("query %q not found in generated Go", query)
	}

	dir, err := os.MkdirTemp("", "gotlin-gopls-*")
	if err != nil {
		return "", 0, func() {}, err
	}
	cleanup := func() { _ = os.RemoveAll(dir) }

	source := filepath.Join(dir, "main.go")
	if err := os.WriteFile(source, goSrc, 0o644); err != nil {
		cleanup()
		return "", 0, func() {}, err
	}
	if err := os.WriteFile(filepath.Join(dir, "go.mod"), []byte("module gotlin-gopls-temp\n\ngo 1.25\n"), 0o644); err != nil {
		cleanup()
		return "", 0, func() {}, err
	}

	return source, targetOffset, cleanup, nil
}

func findQueryOffset(source string, query string, preferredLine int) int {
	if query == "" {
		return -1
	}
	indices := allQueryOffsets(source, query)
	if len(indices) == 0 {
		return -1
	}
	bestIndex := indices[0]
	bestDistance := absInt(byteLineNumber(source, bestIndex) - preferredLine)
	for _, index := range indices[1:] {
		distance := absInt(byteLineNumber(source, index) - preferredLine)
		if distance < bestDistance {
			bestIndex = index
			bestDistance = distance
		}
	}
	return bestIndex
}

func lastQuerySegment(query string) string {
	if idx := strings.LastIndex(query, "."); idx >= 0 && idx+1 < len(query) {
		return query[idx+1:]
	}
	return query
}

func parseGoplsDefinition(output string) (location, bool) {
	line := strings.TrimSpace(output)
	if line == "" {
		return location{}, false
	}
	first := strings.Split(line, "\n")[0]
	re := regexp.MustCompile(`^(.*):(\d+):(\d+)-(\d+):`)
	match := re.FindStringSubmatch(first)
	if len(match) != 5 {
		return location{}, false
	}
	lineNo, err1 := strconv.Atoi(match[2])
	startCol, err2 := strconv.Atoi(match[3])
	endCol, err3 := strconv.Atoi(match[4])
	if err1 != nil || err2 != nil || err3 != nil {
		return location{}, false
	}
	path := filepath.Clean(match[1])
	return location{
		URI: "file://" + path,
		Range: rng{
			Start: position{Line: lineNo - 1, Character: startCol - 1},
			End:   position{Line: lineNo - 1, Character: endCol - 1},
		},
	}, true
}

func isTempGoplsLocation(loc location, tempDir string) bool {
	path := strings.TrimPrefix(loc.URI, "file://")
	cleanPath := filepath.Clean(path)
	cleanTempDir := filepath.Clean(tempDir)
	return cleanPath == cleanTempDir || strings.HasPrefix(cleanPath, cleanTempDir+string(os.PathSeparator))
}

func allQueryOffsets(source string, query string) []int {
	var offsets []int
	for start := 0; start < len(source); {
		index := strings.Index(source[start:], query)
		if index < 0 {
			break
		}
		offset := start + index
		offsets = append(offsets, offset)
		start = offset + len(query)
	}
	return offsets
}

func byteLineNumber(source string, offset int) int {
	if offset < 0 {
		offset = 0
	}
	if offset > len(source) {
		offset = len(source)
	}
	line := 0
	for i := 0; i < offset; i++ {
		if source[i] == '\n' {
			line++
		}
	}
	return line
}

func absInt(n int) int {
	if n < 0 {
		return -n
	}
	return n
}