path: root/internal/lsp/handlers.go

// Summary: LSP JSON-RPC handlers; implements core methods and integrates with the LLM client when enabled.
// Not yet reviewed by a human
package lsp

import (
	"context"
	"encoding/json"
	"fmt"
	"hexai/internal"
	"hexai/internal/llm"
	"hexai/internal/logging"
	"os"
	"strings"
	"time"
)

func (s *Server) handle(req Request) {
    switch req.Method {
	case "initialize":
		s.handleInitialize(req)
	case "initialized":
		s.handleInitialized()
	case "shutdown":
		s.handleShutdown(req)
	case "exit":
		s.handleExit()
	case "textDocument/didOpen":
		s.handleDidOpen(req)
	case "textDocument/didChange":
		s.handleDidChange(req)
	case "textDocument/didClose":
		s.handleDidClose(req)
	case "textDocument/completion":
		s.handleCompletion(req)
    case "textDocument/codeAction":
        s.handleCodeAction(req)
    case "codeAction/resolve":
        s.handleCodeActionResolve(req)
    default:
		if len(req.ID) != 0 {
			s.reply(req.ID, nil, &RespError{Code: -32601, Message: fmt.Sprintf("method not found: %s", req.Method)})
		}
	}
}

func (s *Server) handleInitialize(req Request) {
	version := internal.Version
	if s.llmClient != nil {
		version = version + " [" + s.llmClient.Name() + ":" + s.llmClient.DefaultModel() + "]"
	}
    res := InitializeResult{
        Capabilities: ServerCapabilities{
            TextDocumentSync: 1, // 1 = TextDocumentSyncKindFull
            CompletionProvider: &CompletionOptions{
                ResolveProvider:   false,
                TriggerCharacters: s.triggerChars,
            },
            CodeActionProvider: CodeActionOptions{ResolveProvider: true},
        },
        ServerInfo: &ServerInfo{Name: "hexai", Version: version},
    }
	s.reply(req.ID, res, nil)
}

func (s *Server) handleCodeAction(req Request) {
	var p CodeActionParams
	if err := json.Unmarshal(req.Params, &p); err != nil {
		if len(req.ID) != 0 {
			s.reply(req.ID, []CodeAction{}, nil)
		}
		return
	}
	d := s.getDocument(p.TextDocument.URI)
	if d == nil || len(d.lines) == 0 || s.llmClient == nil {
		if len(req.ID) != 0 {
			s.reply(req.ID, []CodeAction{}, nil)
		}
		return
	}
	sel := extractRangeText(d, p.Range)
	if strings.TrimSpace(sel) == "" {
		if len(req.ID) != 0 {
			s.reply(req.ID, []CodeAction{}, nil)
		}
		return
	}

	actions := make([]CodeAction, 0, 2)
	if a := s.buildRewriteCodeAction(p, sel); a != nil {
		actions = append(actions, *a)
	}
	if a := s.buildDiagnosticsCodeAction(p, sel); a != nil {
		actions = append(actions, *a)
	}
	if len(req.ID) != 0 {
		s.reply(req.ID, actions, nil)
	}
}

func (s *Server) buildRewriteCodeAction(p CodeActionParams, sel string) *CodeAction {
    if instr, cleaned := instructionFromSelection(sel); strings.TrimSpace(instr) != "" {
        payload := struct{
            Type string `json:"type"`
            URI  string `json:"uri"`
            Range Range `json:"range"`
            Instruction string `json:"instruction"`
            Selection string `json:"selection"`
        }{Type: "rewrite", URI: p.TextDocument.URI, Range: p.Range, Instruction: instr, Selection: cleaned}
        raw, _ := json.Marshal(payload)
        ca := CodeAction{Title: "Hexai: rewrite selection", Kind: "refactor.rewrite", Data: raw}
        return &ca
    }
    return nil
}

func (s *Server) buildDiagnosticsCodeAction(p CodeActionParams, sel string) *CodeAction {
    diags := s.diagnosticsInRange(p.Context, p.Range)
    if len(diags) == 0 {
        return nil
    }
    payload := struct{
        Type string `json:"type"`
        URI  string `json:"uri"`
        Range Range `json:"range"`
        Selection string `json:"selection"`
        Diagnostics []Diagnostic `json:"diagnostics"`
    }{Type: "diagnostics", URI: p.TextDocument.URI, Range: p.Range, Selection: sel, Diagnostics: diags}
    raw, _ := json.Marshal(payload)
    ca := CodeAction{Title: "Hexai: resolve diagnostics", Kind: "quickfix", Data: raw}
    return &ca
}

func (s *Server) resolveCodeAction(ca CodeAction) (CodeAction, bool) {
    if s.llmClient == nil || len(ca.Data) == 0 {
        return ca, false
    }
    var payload struct{
        Type string `json:"type"`
        URI  string `json:"uri"`
        Range Range `json:"range"`
        Instruction string `json:"instruction,omitempty"`
        Selection string `json:"selection"`
        Diagnostics []Diagnostic `json:"diagnostics,omitempty"`
    }
    if err := json.Unmarshal(ca.Data, &payload); err != nil {
        return ca, false
    }
    switch payload.Type {
    case "rewrite":
        sys := "You are a precise code refactoring engine. Rewrite the given code strictly according to the instruction. Return only the updated code with no prose or backticks. Preserve formatting where reasonable."
        user := fmt.Sprintf("Instruction: %s\n\nSelected code to transform:\n%s", payload.Instruction, payload.Selection)
        ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
        defer cancel()
        messages := []llm.Message{{Role: "system", Content: sys}, {Role: "user", Content: user}}
        opts := s.llmRequestOpts()
        if text, err := s.llmClient.Chat(ctx, messages, opts...); err == nil {
            if out := stripCodeFences(strings.TrimSpace(text)); out != "" {
                edit := WorkspaceEdit{Changes: map[string][]TextEdit{payload.URI: {{Range: payload.Range, NewText: out}}}}
                ca.Edit = &edit
                return ca, true
            }
        } else {
            logging.Logf("lsp ", "codeAction rewrite llm error: %v", err)
        }
    case "diagnostics":
        sys := "You are a precise code fixer. Resolve the given diagnostics by editing only the selected code. Return only the corrected code with no prose or backticks. Keep behavior and style, and avoid unrelated changes."
        var b strings.Builder
        b.WriteString("Diagnostics to resolve (selection only):\n")
        for i, dgn := range payload.Diagnostics {
            if dgn.Source != "" {
                fmt.Fprintf(&b, "%d. [%s] %s\n", i+1, dgn.Source, dgn.Message)
            } else {
                fmt.Fprintf(&b, "%d. %s\n", i+1, dgn.Message)
            }
        }
        b.WriteString("\nSelected code:\n")
        b.WriteString(payload.Selection)
        ctx, cancel := context.WithTimeout(context.Background(), 12*time.Second)
        defer cancel()
        messages := []llm.Message{{Role: "system", Content: sys}, {Role: "user", Content: b.String()}}
        opts := s.llmRequestOpts()
        if text, err := s.llmClient.Chat(ctx, messages, opts...); err == nil {
            if out := stripCodeFences(strings.TrimSpace(text)); out != "" {
                edit := WorkspaceEdit{Changes: map[string][]TextEdit{payload.URI: {{Range: payload.Range, NewText: out}}}}
                ca.Edit = &edit
                return ca, true
            }
        } else {
            logging.Logf("lsp ", "codeAction diagnostics llm error: %v", err)
        }
    }
    return ca, false
}

func (s *Server) handleCodeActionResolve(req Request) {
    var ca CodeAction
    if err := json.Unmarshal(req.Params, &ca); err != nil {
        if len(req.ID) != 0 {
            s.reply(req.ID, ca, nil)
        }
        return
    }
    if resolved, ok := s.resolveCodeAction(ca); ok {
        s.reply(req.ID, resolved, nil)
        return
    }
    s.reply(req.ID, ca, nil)
}

func (s *Server) llmRequestOpts() []llm.RequestOption {
	opts := []llm.RequestOption{llm.WithMaxTokens(s.maxTokens)}
	if s.codingTemperature != nil {
		opts = append(opts, llm.WithTemperature(*s.codingTemperature))
	}
	return opts
}

// instructionFromSelection extracts the first instruction from selection text.
// Preference order on each line: strict ;text; marker (no inner spaces), then
// a line comment (//, #, --). Returns the instruction string and the selection
// text cleaned of the matched instruction marker or comment.
func instructionFromSelection(sel string) (string, string) {
	lines := splitLines(sel)
	for idx, line := range lines {
		if instr, cleaned, ok := findFirstInstructionInLine(line); ok && strings.TrimSpace(instr) != "" {
			lines[idx] = cleaned
			return instr, strings.Join(lines, "\n")
		}
	}
	return "", sel
}

// findFirstInstructionInLine returns the earliest instruction marker on the
// line and the line with that marker removed. Supported markers, ordered by
// earliest byte offset in the line:
// - ;text; (strict, no space after first ';' or before last ';')
// - /* text */ (single-line only)
// - <!-- text --> (single-line only)
// - // text
// - # text
// - -- text
func findFirstInstructionInLine(line string) (instr string, cleaned string, ok bool) {
	type cand struct {
		start, end int
		text       string
	}
	cands := []cand{}
	if t, l, r, ok := findStrictSemicolonTag(line); ok {
		cands = append(cands, cand{start: l, end: r, text: t})
	}
	if i := strings.Index(line, "/*"); i >= 0 {
		if j := strings.Index(line[i+2:], "*/"); j >= 0 {
			start := i
			end := i + 2 + j + 2
			text := strings.TrimSpace(line[i+2 : i+2+j])
			cands = append(cands, cand{start: start, end: end, text: text})
		}
	}
	if i := strings.Index(line, "<!--"); i >= 0 {
		if j := strings.Index(line[i+4:], "-->"); j >= 0 {
			start := i
			end := i + 4 + j + 3
			text := strings.TrimSpace(line[i+4 : i+4+j])
			cands = append(cands, cand{start: start, end: end, text: text})
		}
	}
	if i := strings.Index(line, "//"); i >= 0 {
		cands = append(cands, cand{start: i, end: len(line), text: strings.TrimSpace(line[i+2:])})
	}
	if i := strings.Index(line, "#"); i >= 0 {
		cands = append(cands, cand{start: i, end: len(line), text: strings.TrimSpace(line[i+1:])})
	}
	if i := strings.Index(line, "--"); i >= 0 {
		cands = append(cands, cand{start: i, end: len(line), text: strings.TrimSpace(line[i+2:])})
	}
	if len(cands) == 0 {
		return "", line, false
	}
	// pick earliest start index
	best := cands[0]
	for _, c := range cands[1:] {
		if c.start >= 0 && (best.start < 0 || c.start < best.start) {
			best = c
		}
	}
	cleaned = strings.TrimRight(line[:best.start]+line[best.end:], " \t")
	return best.text, cleaned, true
}

// findStrictSemicolonTag finds ;text; with no space after first ';' and no space
// before the last ';' on the given line. Returns the text between semicolons,
// the start index of the opening ';', the end index just after the closing ';',
// and whether it was found.
func findStrictSemicolonTag(line string) (string, int, int, bool) {
	pos := 0
	for pos < len(line) {
		j := strings.Index(line[pos:], ";")
		if j < 0 {
			return "", 0, 0, false
		}
		j += pos
		// ensure single ';' (not ';;') and non-space after
		if j+1 >= len(line) || line[j+1] == ';' || line[j+1] == ' ' {
			pos = j + 1
			continue
		}
		k := strings.Index(line[j+1:], ";")
		if k < 0 {
			return "", 0, 0, false
		}
		closeIdx := j + 1 + k
		if closeIdx-1 < 0 || line[closeIdx-1] == ' ' {
			pos = closeIdx + 1
			continue
		}
		inner := strings.TrimSpace(line[j+1 : closeIdx])
		if inner == "" {
			pos = closeIdx + 1
			continue
		}
		end := closeIdx + 1
		return inner, j, end, true
	}
	return "", 0, 0, false
}

// diagnosticsInRange parses the CodeAction context and returns diagnostics
// that overlap the given selection range. If the context is missing or does
// not contain diagnostics, returns an empty slice.
func (s *Server) diagnosticsInRange(ctxRaw json.RawMessage, sel Range) []Diagnostic {
	if len(ctxRaw) == 0 {
		return nil
	}
	var ctx CodeActionContext
	if err := json.Unmarshal(ctxRaw, &ctx); err != nil {
		return nil
	}
	if len(ctx.Diagnostics) == 0 {
		return nil
	}
	out := make([]Diagnostic, 0, len(ctx.Diagnostics))
	for _, d := range ctx.Diagnostics {
		if rangesOverlap(d.Range, sel) {
			out = append(out, d)
		}
	}
	return out
}

// rangesOverlap reports whether two LSP ranges overlap at all.
func rangesOverlap(a, b Range) bool {
	// Normalize ordering
	if greaterPos(a.Start, a.End) {
		a.Start, a.End = a.End, a.Start
	}
	if greaterPos(b.Start, b.End) {
		b.Start, b.End = b.End, b.Start
	}
	// a ends before b starts
	if lessPos(a.End, b.Start) {
		return false
	}
	// b ends before a starts
	if lessPos(b.End, a.Start) {
		return false
	}
	return true
}

func lessPos(p, q Position) bool {
	if p.Line != q.Line {
		return p.Line < q.Line
	}
	return p.Character < q.Character
}

func greaterPos(p, q Position) bool {
	if p.Line != q.Line {
		return p.Line > q.Line
	}
	return p.Character > q.Character
}

// extractRangeText returns the exact text within the given document range.
func extractRangeText(d *document, r Range) string {
	if r.Start.Line == r.End.Line {
		line := d.lines[r.Start.Line]
		if r.Start.Character < 0 {
			r.Start.Character = 0
		}
		if r.End.Character > len(line) {
			r.End.Character = len(line)
		}
		if r.Start.Character > r.End.Character {
			return ""
		}
		return line[r.Start.Character:r.End.Character]
	}
	var b strings.Builder
	// first line
	first := d.lines[r.Start.Line]
	if r.Start.Character < 0 {
		r.Start.Character = 0
	}
	if r.Start.Character > len(first) {
		r.Start.Character = len(first)
	}
	b.WriteString(first[r.Start.Character:])
	b.WriteString("\n")
	// middle lines
	for i := r.Start.Line + 1; i < r.End.Line; i++ {
		b.WriteString(d.lines[i])
		if i+1 <= r.End.Line {
			b.WriteString("\n")
		}
	}
	// last line
	last := d.lines[r.End.Line]
	if r.End.Character < 0 {
		r.End.Character = 0
	}
	if r.End.Character > len(last) {
		r.End.Character = len(last)
	}
	b.WriteString(last[:r.End.Character])
	return b.String()
}

func (s *Server) handleInitialized() {
	logging.Logf("lsp ", "client initialized")
}

func (s *Server) handleShutdown(req Request) {
	s.reply(req.ID, nil, nil)
}

func (s *Server) handleExit() {
	s.exited = true
	os.Exit(0)
}

func (s *Server) handleDidOpen(req Request) {
	var p DidOpenTextDocumentParams
	if err := json.Unmarshal(req.Params, &p); err == nil {
		s.setDocument(p.TextDocument.URI, p.TextDocument.Text)
		s.markActivity()
	}
}

func (s *Server) handleDidChange(req Request) {
    var p DidChangeTextDocumentParams
    if err := json.Unmarshal(req.Params, &p); err == nil {
        if len(p.ContentChanges) > 0 {
            s.setDocument(p.TextDocument.URI, p.ContentChanges[len(p.ContentChanges)-1].Text)
        }
        s.markActivity()
        // Detect in-editor chat trigger lines and respond inline.
        s.detectAndHandleChat(p.TextDocument.URI)
    }
}

func (s *Server) handleDidClose(req Request) {
	var p DidCloseTextDocumentParams
	if err := json.Unmarshal(req.Params, &p); err == nil {
		s.deleteDocument(p.TextDocument.URI)
		s.markActivity()
	}
}

func (s *Server) handleCompletion(req Request) {
	var p CompletionParams
	var docStr string
	if err := json.Unmarshal(req.Params, &p); err == nil {
		above, current, below, funcCtx := s.lineContext(p.TextDocument.URI, p.Position)
		docStr = s.buildDocString(p, above, current, below, funcCtx)
		if s.logContext {
			s.logCompletionContext(p, above, current, below, funcCtx)
		}
		if s.llmClient != nil {
			newFunc := s.isDefiningNewFunction(p.TextDocument.URI, p.Position)
			extra, has := s.buildAdditionalContext(newFunc, p.TextDocument.URI, p.Position)
            items, ok, busy := s.tryLLMCompletion(p, above, current, below, funcCtx, docStr, has, extra)
            if ok {
                s.reply(req.ID, CompletionList{IsIncomplete: false, Items: items}, nil)
                return
            }
            if busy {
                // Inform client that results are incomplete so it may try again shortly.
                logging.Logf("lsp ", "completion busy uri=%s line=%d char=%d returning isIncomplete", p.TextDocument.URI, p.Position.Line, p.Position.Character)
                s.reply(req.ID, CompletionList{IsIncomplete: true, Items: []CompletionItem{}}, nil)
                return
            }
		}
	}
	items := s.fallbackCompletionItems(docStr)
	s.reply(req.ID, CompletionList{IsIncomplete: false, Items: items}, nil)
}

func (s *Server) reply(id json.RawMessage, result any, err *RespError) {
    resp := Response{JSONRPC: "2.0", ID: id, Result: result, Error: err}
    s.writeMessage(resp)
}

// --- in-editor chat (";C ...") ---

// detectAndHandleChat scans the current document for any line that starts with
// ";C" and appears to be awaiting a response (i.e., followed by a blank line
// and no non-empty answer line yet). If found, it asks the LLM and inserts the
// answer below the blank line, leaving exactly one empty line between prompt
// and response.
func (s *Server) detectAndHandleChat(uri string) {
    if s.llmClient == nil {
        return
    }
    d := s.getDocument(uri)
    if d == nil || len(d.lines) == 0 {
        return
    }
    for i, raw := range d.lines {
        // Find last non-space character index
        j := len(raw) - 1
        for j >= 0 {
            if raw[j] == ' ' || raw[j] == '\t' { j--; continue }
            break
        }
        if j < 1 { // need at least two chars for double trigger
            continue
        }
        pair := raw[j-1 : j+1]
        isTrigger := pair == ".." || pair == "??" || pair == "!!" || pair == "::"
        if !isTrigger {
            continue
        }
        // Avoid double-answering: if the next non-empty line starts with '>' we skip.
        k := i + 1
        for k < len(d.lines) && strings.TrimSpace(d.lines[k]) == "" { k++ }
        if k < len(d.lines) && strings.HasPrefix(strings.TrimSpace(d.lines[k]), ">") {
            continue
        }
        // Derive prompt by removing 1 trailing char for punctuation pairs
        removeCount := 1
        base := raw[:j+1-removeCount]
        prompt := strings.TrimSpace(base)
        if prompt == "" {
            continue
        }
        if !s.tryStartLLM() {
            continue
        }
        lineIdx := i
        lastIdx := j
        go func(prompt string, remove int) {
            defer s.endLLM()
            ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
            defer cancel()
            sys := "You are a helpful coding assistant. Answer concisely and clearly."
            // Build short conversation history from the document above this line
            history := s.buildChatHistory(uri, lineIdx, prompt)
            msgs := append([]llm.Message{{Role: "system", Content: sys}}, history...)
            opts := s.llmRequestOpts()
            logging.Logf("lsp ", "chat llm=requesting model=%s", s.llmClient.DefaultModel())
            text, err := s.llmClient.Chat(ctx, msgs, opts...)
            if err != nil {
                logging.Logf("lsp ", "chat llm error: %v", err)
                return
            }
            out := strings.TrimSpace(stripCodeFences(text))
            if out == "" {
                return
            }
            s.applyChatEdits(uri, lineIdx, lastIdx, remove, "> "+out)
        }(prompt, removeCount)
        // Only handle one per change tick to avoid flooding
        break
    }
}

// applyChatEdits removes the triggering punctuation at end of the line and
// inserts two newlines followed by a new line with the response prefixed.
func (s *Server) applyChatEdits(uri string, lineIdx int, lastNonSpace int, removeCount int, response string) {
    d := s.getDocument(uri)
    if d == nil { return }
    // 1) Delete the trailing punctuation (1 or 2 chars)
    delStart := Position{Line: lineIdx, Character: lastNonSpace+1-removeCount}
    delEnd := Position{Line: lineIdx, Character: lastNonSpace+1}
    // 2) Insert two newlines and the response at end-of-line, then one extra
    //    newline so there is exactly one blank line after the reply
    insPos := Position{Line: lineIdx, Character: len(d.lines[lineIdx])}
    resp := strings.TrimRight(response, "\n") + "\n"
    insert := "\n\n" + resp + "\n"
    edits := []TextEdit{
        {Range: Range{Start: delStart, End: delEnd}, NewText: ""},
        {Range: Range{Start: insPos, End: insPos}, NewText: insert},
    }
    we := WorkspaceEdit{Changes: map[string][]TextEdit{uri: edits}}
    s.clientApplyEdit("Hexai: insert chat response", we)
}

// buildChatHistory walks upwards from the current line to collect the most recent
// Q/A pairs in the in-editor transcript. It returns messages in chronological order
// ending with the current user prompt. Limits to a small number of pairs to control tokens.
func (s *Server) buildChatHistory(uri string, lineIdx int, currentPrompt string) []llm.Message {
    d := s.getDocument(uri)
    if d == nil { return []llm.Message{{Role: "user", Content: currentPrompt}} }
    type pair struct{ q string; a string }
    pairs := []pair{}
    i := lineIdx - 1
    // Collect up to 3 recent pairs
    for i >= 0 && len(pairs) < 3 {
        // Skip blank lines
        for i >= 0 && strings.TrimSpace(d.lines[i]) == "" { i-- }
        if i < 0 { break }
        // Expect assistant reply lines starting with ">"
        if !strings.HasPrefix(strings.TrimSpace(d.lines[i]), ">") {
            break
        }
        // Collect contiguous reply block
        var replyLines []string
        for i >= 0 {
            line := strings.TrimSpace(d.lines[i])
            if strings.HasPrefix(line, ">") {
                replyLines = append([]string{strings.TrimSpace(strings.TrimPrefix(line, ">"))}, replyLines...)
                i--
                continue
            }
            break
        }
        // Skip a single blank line that should separate Q from A
        for i >= 0 && strings.TrimSpace(d.lines[i]) == "" { i-- }
        if i < 0 { break }
        // Take the question as the non-empty line above
        q := strings.TrimSpace(d.lines[i])
        // Remove any lingering trigger pair at end if present
        q = stripTrailingTrigger(q)
        pairs = append([]pair{{q: q, a: strings.Join(replyLines, "\n")}}, pairs...)
        i--
        // Continue to find older pairs
    }
    // Build messages
    msgs := make([]llm.Message, 0, len(pairs)*2+1)
    for _, p := range pairs {
        if strings.TrimSpace(p.q) != "" {
            msgs = append(msgs, llm.Message{Role: "user", Content: p.q})
        }
        if strings.TrimSpace(p.a) != "" {
            msgs = append(msgs, llm.Message{Role: "assistant", Content: p.a})
        }
    }
    msgs = append(msgs, llm.Message{Role: "user", Content: currentPrompt})
    return msgs
}

// stripTrailingTrigger removes a single trailing punctuation from the set
// [.,?,!,:] or both semicolons if present at end, mirroring the inline trigger rules.
func stripTrailingTrigger(sx string) string {
    s := strings.TrimRight(sx, " \t")
    if strings.HasSuffix(s, ";;") {
        return strings.TrimRight(strings.TrimSuffix(s, ";;"), " \t")
    }
    if len(s) == 0 { return sx }
    last := s[len(s)-1]
    switch last {
    case '.', '?', '!', ':':
        return strings.TrimRight(s[:len(s)-1], " \t")
    default:
        return sx
    }
}

// clientApplyEdit sends a workspace/applyEdit request to the client.
func (s *Server) clientApplyEdit(label string, edit WorkspaceEdit) {
    params := ApplyWorkspaceEditParams{Label: label, Edit: edit}
    // Build a JSON-RPC request with a fresh id
    id := s.nextReqID()
    req := Request{JSONRPC: "2.0", ID: id, Method: "workspace/applyEdit"}
    // marshal params separately to avoid changing Request type
    b, _ := json.Marshal(params)
    req.Params = b
    s.writeMessage(req)
}

// nextReqID returns a unique json.RawMessage id for server-initiated requests.
func (s *Server) nextReqID() json.RawMessage {
    s.mu.Lock()
    s.nextID++
    idNum := s.nextID
    s.mu.Unlock()
    b, _ := json.Marshal(idNum)
    return b
}

// --- completion helpers ---

func (s *Server) buildDocString(p CompletionParams, above, current, below, funcCtx string) string {
	return fmt.Sprintf("file: %s\nline: %d\nabove: %s\ncurrent: %s\nbelow: %s\nfunction: %s",
		p.TextDocument.URI, p.Position.Line, trimLen(above), trimLen(current), trimLen(below), trimLen(funcCtx))
}

func (s *Server) logCompletionContext(p CompletionParams, above, current, below, funcCtx string) {
	logging.Logf("lsp ", "completion ctx uri=%s line=%d char=%d above=%q current=%q below=%q function=%q",
		p.TextDocument.URI, p.Position.Line, p.Position.Character, trimLen(above), trimLen(current), trimLen(below), trimLen(funcCtx))
}

func (s *Server) tryLLMCompletion(p CompletionParams, above, current, below, funcCtx, docStr string, hasExtra bool, extraText string) ([]CompletionItem, bool, bool) {
    ctx, cancel := context.WithTimeout(context.Background(), 6*time.Second)
    defer cancel()

    // Inline prompt markers (strict ;text; or double-; patterns) explicitly allow triggering.
    inlinePrompt := lineHasInlinePrompt(current)
    // Only invoke LLM when triggered by our characters, manual invoke, or inline prompt markers.
    if !inlinePrompt && !s.isTriggerEvent(p, current) {
        logging.Logf("lsp ", "%scompletion skip=no-trigger line=%d char=%d current=%q%s", logging.AnsiYellow, p.Position.Line, p.Position.Character, trimLen(current), logging.AnsiBase)
        return []CompletionItem{}, true, false
    }

    inParams := inParamList(current, p.Position.Character)

    // Detect manual invoke so we can relax prefix heuristics when user pressed completion key.
    manualInvoke := false
    if p.Context != nil {
        var c struct{
            TriggerKind int `json:"triggerKind"`
        }
        if raw, ok := p.Context.(json.RawMessage); ok {
            _ = json.Unmarshal(raw, &c)
        } else {
            b, _ := json.Marshal(p.Context)
            _ = json.Unmarshal(b, &c)
        }
        if c.TriggerKind == 1 { // Invoked
            manualInvoke = true
        }
    }

    // Build a cache key for this completion context (ignore trailing whitespace
    // before the cursor when forming the key) and try cache before any LLM call.
    key := s.completionCacheKey(p, above, current, below, funcCtx, inParams, hasExtra, extraText)
    if cleaned, ok := s.completionCacheGet(key); ok && strings.TrimSpace(cleaned) != "" {
        logging.Logf("lsp ", "completion cache hit uri=%s line=%d char=%d preview=%s%s%s",
            p.TextDocument.URI, p.Position.Line, p.Position.Character,
            logging.AnsiGreen, logging.PreviewForLog(cleaned), logging.AnsiBase)
        return s.makeCompletionItems(cleaned, inParams, current, p, docStr), true, false
    }
    // If there is a bare ';;' on the current or next line (no valid ';;text;'),
    // do not auto-trigger unless it was a manual invoke.
    if (isBareDoubleSemicolon(current) || isBareDoubleSemicolon(below)) && !manualInvoke {
        logging.Logf("lsp ", "%scompletion skip=empty-double-semicolon line=%d char=%d current=%q%s", logging.AnsiYellow, p.Position.Line, p.Position.Character, trimLen(current), logging.AnsiBase)
        return []CompletionItem{}, true, false
    }

    // Heuristic 1: Require a minimal typed identifier prefix to avoid early triggers,
    // but allow immediate completion after structural trigger chars like '.', ':', '/'.
    if !inParams {
        // Determine the effective cursor index within current line, clamped, and
        // skip over trailing spaces/tabs to support cases like "type Matrix| "
        // where the cursor is after a space following an identifier.
        idx := p.Position.Character
        if idx > len(current) { idx = len(current) }
        // Structural triggers allow no prefix
        allowNoPrefix := false
        if manualInvoke || inlinePrompt {
            allowNoPrefix = true
        }
        if idx > 0 {
            ch := current[idx-1]
            if ch == '.' || ch == ':' || ch == '/' || ch == '_' || ch == ')' {
                allowNoPrefix = true
            }
        }
        if !allowNoPrefix {
            // Walk left over whitespace
            j := idx
            for j > 0 {
                c := current[j-1]
                if c == ' ' || c == '\t' { j--; continue }
                break
            }
            start := computeWordStart(current, j)
            if j-start < 1 { // require at least 1 identifier char
                logging.Logf("lsp ", "%scompletion skip=short-prefix line=%d char=%d current=%q%s", logging.AnsiYellow, p.Position.Line, p.Position.Character, trimLen(current), logging.AnsiBase)
                return []CompletionItem{}, true, false
            }
        }
    }
    // Concurrency guard: if another LLM request is running, skip this one.
    if !s.tryStartLLM() {
        logging.Logf("lsp ", "%scompletion skip=busy another LLM request in flight%s", logging.AnsiYellow, logging.AnsiBase)
        return []CompletionItem{}, false, true
    }
    sysPrompt, userPrompt := buildPrompts(inParams, p, above, current, below, funcCtx)
    messages := []llm.Message{
        {Role: "system", Content: sysPrompt},
        {Role: "user", Content: userPrompt},
    }
	if hasExtra && extraText != "" {
		messages = append(messages, llm.Message{Role: "user", Content: "Additional context:\n" + extraText})
	}

    // If an inline prompt marker is present, make the instruction stricter: code only.
    if inlinePrompt {
        messages[0].Content = "You are a precise code completion/refactoring engine. Output only the code to insert with no prose, no comments, and no backticks. Return raw code only."
    }

    // Compute total sent context size (sum of message contents)
	var sentSize int
	for _, m := range messages {
		sentSize += len(m.Content)
	}
	s.incSentCounters(sentSize)

	opts := []llm.RequestOption{llm.WithMaxTokens(s.maxTokens)}
	if s.codingTemperature != nil {
		opts = append(opts, llm.WithTemperature(*s.codingTemperature))
	}
    logging.Logf("lsp ", "completion llm=requesting model=%s", s.llmClient.DefaultModel())
    text, err := s.llmClient.Chat(ctx, messages, opts...)
    defer s.endLLM()
	if err != nil {
		logging.Logf("lsp ", "llm completion error: %v", err)
		// Log updated averages after this request (even if failed)
		s.logLLMStats()
        return nil, false, false
	}
	// Update response counters (received)
	s.incRecvCounters(len(text))
	s.logLLMStats()
    cleaned := stripCodeFences(strings.TrimSpace(text))
    // For code completion responses, also strip inline single-backtick code spans
    // when the model returns prose like: "Use `expr` here".
    if cleaned != "" {
        if strings.ContainsRune(cleaned, '`') {
            inline := stripInlineCodeSpan(cleaned)
            if strings.TrimSpace(inline) != "" {
                cleaned = inline
            }
        }
    }
    if cleaned != "" { cleaned = stripDuplicateAssignmentPrefix(current[:p.Position.Character], cleaned) }
    if cleaned != "" { cleaned = stripDuplicateGeneralPrefix(current[:p.Position.Character], cleaned) }
    // Preserve the current line's leading indentation only for double-semicolon
    // inline prompts (";;text;"), since strict ";text;" replacements already
    // occur in-place without affecting leading indentation.
    if cleaned != "" && hasDoubleSemicolonTrigger(current) {
        indent := leadingIndent(current)
        if indent != "" {
            cleaned = applyIndent(indent, cleaned)
        }
    }
    if cleaned == "" {
        return nil, false, false
    }

    // Store successful completion in cache
    s.completionCachePut(key, cleaned)

    return s.makeCompletionItems(cleaned, inParams, current, p, docStr), true, false
}

// --- small completion cache (last ~10 entries) ---

func (s *Server) completionCacheKey(p CompletionParams, above, current, below, funcCtx string, inParams bool, hasExtra bool, extraText string) string {
    // Normalize left-of-cursor by trimming trailing spaces/tabs
    idx := p.Position.Character
    if idx > len(current) { idx = len(current) }
    left := strings.TrimRight(current[:idx], " \t")
    right := ""
    if idx < len(current) { right = current[idx:] }
    prov := ""
    model := ""
    if s.llmClient != nil {
        prov = s.llmClient.Name()
        model = s.llmClient.DefaultModel()
    }
    temp := ""
    if s.codingTemperature != nil { temp = fmt.Sprintf("%.3f", *s.codingTemperature) }
    extra := ""
    if hasExtra {
        extra = strings.TrimSpace(extraText)
    }
    // Compose a key from essential context parts
    return strings.Join([]string{
        "v1", // version for future-proofing
        prov,
        model,
        temp,
        p.TextDocument.URI,
        fmt.Sprintf("%d:%d", p.Position.Line, len(left)),
        above,
        left,
        right,
        below,
        funcCtx,
        fmt.Sprintf("params=%t", inParams),
        extra,
    }, "\x1f") // use unit separator to avoid collisions
}

func (s *Server) completionCacheGet(key string) (string, bool) {
    s.mu.Lock()
    defer s.mu.Unlock()
    v, ok := s.compCache[key]
    if !ok {
        return "", false
    }
    // move to most-recent
    s.compCacheTouchLocked(key)
    return v, true
}

func (s *Server) completionCachePut(key, value string) {
    s.mu.Lock()
    defer s.mu.Unlock()
    if s.compCache == nil {
        s.compCache = make(map[string]string)
    }
    if _, exists := s.compCache[key]; !exists {
        s.compCacheOrder = append(s.compCacheOrder, key)
        s.compCache[key] = value
        if len(s.compCacheOrder) > 10 {
            // evict oldest
            old := s.compCacheOrder[0]
            s.compCacheOrder = s.compCacheOrder[1:]
            delete(s.compCache, old)
        }
        return
    }
    // update existing and mark most-recent
    s.compCache[key] = value
    s.compCacheTouchLocked(key)
}

func (s *Server) compCacheTouchLocked(key string) {
    // assumes s.mu is held
    // remove any existing occurrence of key in order slice
    idx := -1
    for i, k := range s.compCacheOrder {
        if k == key { idx = i; break }
    }
    if idx >= 0 {
        s.compCacheOrder = append(append([]string{}, s.compCacheOrder[:idx]...), s.compCacheOrder[idx+1:]...)
    }
    s.compCacheOrder = append(s.compCacheOrder, key)
}

// isTriggerEvent returns true when the completion request appears to be caused
// by typing one of our configured trigger characters. It checks the LSP
// CompletionContext if provided and also falls back to inspecting the character
// immediately to the left of the cursor.
func (s *Server) isTriggerEvent(p CompletionParams, current string) bool {
    // 1) Inspect LSP completion context if present
    if p.Context != nil {
        var ctx struct{
            TriggerKind int    `json:"triggerKind"`
            TriggerCharacter string `json:"triggerCharacter,omitempty"`
        }
        if raw, ok := p.Context.(json.RawMessage); ok {
            _ = json.Unmarshal(raw, &ctx)
        } else {
            b, _ := json.Marshal(p.Context)
            _ = json.Unmarshal(b, &ctx)
        }
        // If the line contains a bare ';;' (no ';;text;'), do not treat as a trigger source.
        if strings.Contains(current, ";;") && !hasDoubleSemicolonTrigger(current) {
            return false
        }
        // TriggerKind 1 = Invoked (manual) — always allow (unless bare ';;' above)
        if ctx.TriggerKind == 1 {
            return true
        }
        // TriggerKind 2 is TriggerCharacter per LSP spec
        if ctx.TriggerKind == 2 {
            if ctx.TriggerCharacter != "" {
                for _, c := range s.triggerChars {
                    if c == ctx.TriggerCharacter {
                        return true
                    }
                }
                return false
            }
            // No character provided but reported as TriggerCharacter; be conservative
            return false
        }
        // For TriggerForIncomplete (3), require manual char check below
    }
    // 2) Fallback: check the character immediately prior to cursor
    idx := p.Position.Character
    if idx <= 0 || idx > len(current) {
        return false
    }
    // Bare ';;' should not trigger via fallback char either
    if strings.Contains(current, ";;") && !hasDoubleSemicolonTrigger(current) {
        return false
    }
    ch := string(current[idx-1])
    for _, c := range s.triggerChars {
        if c == ch {
            return true
        }
    }
    return false
}

func (s *Server) makeCompletionItems(cleaned string, inParams bool, current string, p CompletionParams, docStr string) []CompletionItem {
	te, filter := computeTextEditAndFilter(cleaned, inParams, current, p)
	rm := s.collectPromptRemovalEdits(p.TextDocument.URI)
	label := labelForCompletion(cleaned, filter)
	detail := "Hexai LLM completion"
	if s.llmClient != nil {
		detail = "Hexai " + s.llmClient.Name() + ":" + s.llmClient.DefaultModel()
	}
	return []CompletionItem{{
		Label:               label,
		Kind:                1,
		Detail:              detail,
		InsertTextFormat:    1,
		FilterText:          strings.TrimLeft(filter, " \t"),
		TextEdit:            te,
		AdditionalTextEdits: rm,
		SortText:            "0000",
		Documentation:       docStr,
	}}
}

// small helpers to keep tryLLMCompletion short
func (s *Server) incSentCounters(n int) {
	s.mu.Lock()
	s.llmReqTotal++
	s.llmSentBytesTotal += int64(n)
	s.mu.Unlock()
}

func (s *Server) incRecvCounters(n int) {
	s.mu.Lock()
	s.llmRespTotal++
	s.llmRespBytesTotal += int64(n)
	s.mu.Unlock()
}

func (s *Server) logLLMStats() {
	s.mu.RLock()
	avgSent := int64(0)
	if s.llmReqTotal > 0 {
		avgSent = s.llmSentBytesTotal / s.llmReqTotal
	}
	avgRecv := int64(0)
	if s.llmRespTotal > 0 {
		avgRecv = s.llmRespBytesTotal / s.llmRespTotal
	}
	reqs, sentTot, recvTot := s.llmReqTotal, s.llmSentBytesTotal, s.llmRespBytesTotal
	s.mu.RUnlock()
	mins := time.Since(s.startTime).Minutes()
	if mins <= 0 {
		mins = 0.001
	}
	rpm := float64(reqs) / mins
	sentPerMin := float64(sentTot) / mins
	recvPerMin := float64(recvTot) / mins
	logging.Logf("lsp ", "llm stats reqs=%d avg_sent=%d avg_recv=%d sent_total=%d recv_total=%d rpm=%.2f sent_per_min=%.0f recv_per_min=%.0f", reqs, avgSent, avgRecv, sentTot, recvTot, rpm, sentPerMin, recvPerMin)
}

// collectPromptRemovalEdits returns edits to remove all inline prompt markers.
// Supported form (inclusive):
//   - ";...;" where there is no space immediately after the first ';'
//     and no space immediately before the last ';'. An optional single space
//     after the trailing ';' is also removed for cleanliness.
//
// Multiple markers per line are supported.
func (s *Server) collectPromptRemovalEdits(uri string) []TextEdit {
	d := s.getDocument(uri)
	if d == nil || len(d.lines) == 0 {
		return nil
	}
	var edits []TextEdit
	for i, line := range d.lines {
		edits = append(edits, promptRemovalEditsForLine(line, i)...)
	}
	return edits
}

func promptRemovalEditsForLine(line string, lineNum int) []TextEdit {
	if hasDoubleSemicolonTrigger(line) {
		return []TextEdit{{Range: Range{Start: Position{Line: lineNum, Character: 0}, End: Position{Line: lineNum, Character: len(line)}}, NewText: ""}}
	}
	return collectSemicolonMarkers(line, lineNum)
}

func hasDoubleSemicolonTrigger(line string) bool {
    pos := 0
    for pos < len(line) {
        j := strings.Index(line[pos:], ";;")
        if j < 0 {
            return false
        }
        j += pos
        contentStart := j + 2
        if contentStart >= len(line) {
            return false // nothing after ';;'
        }
        // First content char cannot be space or another ';'
        first := line[contentStart]
        if first == ' ' || first == ';' {
            pos = contentStart + 1
            continue
        }
        // Require at least one content char before a closing ';'
        k := strings.Index(line[contentStart+1:], ";")
        if k < 0 {
            return false
        }
        closeIdx := contentStart + 1 + k
        // Disallow trailing space before closing ';'
        if closeIdx-1 >= 0 && line[closeIdx-1] == ' ' {
            pos = closeIdx + 1
            continue
        }
        return true
    }
    return false
}

func collectSemicolonMarkers(line string, lineNum int) []TextEdit {
	var edits []TextEdit
	startSemi := 0
	for startSemi < len(line) {
		j := strings.Index(line[startSemi:], ";")
		if j < 0 {
			break
		}
		j += startSemi
		k := strings.Index(line[j+1:], ";")
		if k < 0 {
			break
		}
		if j+1 >= len(line) || line[j+1] == ' ' {
			startSemi = j + 1
			continue
		}
		if line[j+1] == ';' {
			startSemi = j + 2
			continue
		}
		closeIdx := j + 1 + k
		if closeIdx-1 < 0 || line[closeIdx-1] == ' ' {
			startSemi = closeIdx + 1
			continue
		}
		if closeIdx-(j+1) < 1 {
			startSemi = closeIdx + 1
			continue
		}
		endChar := closeIdx + 1
		if endChar < len(line) && line[endChar] == ' ' {
			endChar++
		}
		edits = append(edits, TextEdit{Range: Range{Start: Position{Line: lineNum, Character: j}, End: Position{Line: lineNum, Character: endChar}}, NewText: ""})
		startSemi = endChar
	}
	return edits
}

func inParamList(current string, cursor int) bool {
	if !strings.Contains(current, "func ") {
		return false
	}
	open := strings.Index(current, "(")
	close := strings.Index(current, ")")
	return open >= 0 && cursor > open && (close == -1 || cursor <= close)
}

func buildPrompts(inParams bool, p CompletionParams, above, current, below, funcCtx string) (string, string) {
	if inParams {
		sys := "You are a code completion engine for function signatures. Return only the parameter list contents (without parentheses), no braces, no prose. Prefer idiomatic names and types."
		user := fmt.Sprintf("Cursor is inside the function parameter list. Suggest only the parameter list (no parentheses).\nFunction line: %s\nCurrent line (cursor at %d): %s", funcCtx, p.Position.Character, current)
		return sys, user
	}
	sys := "You are a terse code completion engine. Return only the code to insert, no surrounding prose or backticks. Only continue from the cursor; never repeat characters already present to the left of the cursor on the current line (e.g., if 'name :=' is already typed, only return the right-hand side expression)."
	user := fmt.Sprintf("Provide the next likely code to insert at the cursor.\nFile: %s\nFunction/context: %s\nAbove line: %s\nCurrent line (cursor at character %d): %s\nBelow line: %s\nOnly return the completion snippet.", p.TextDocument.URI, funcCtx, above, p.Position.Character, current, below)
	return sys, user
}

func computeTextEditAndFilter(cleaned string, inParams bool, current string, p CompletionParams) (*TextEdit, string) {
	if inParams {
		open := strings.Index(current, "(")
		close := strings.Index(current, ")")
		if open >= 0 {
			left := open + 1
			right := len(current)
			if close >= 0 && close >= left {
				right = close
			}
			if p.Position.Character < right {
				right = p.Position.Character
			}
			te := &TextEdit{Range: Range{Start: Position{Line: p.Position.Line, Character: left}, End: Position{Line: p.Position.Line, Character: right}}, NewText: cleaned}
			var filter string
			if left >= 0 && right >= left && right <= len(current) {
				filter = strings.TrimLeft(current[left:right], " \t")
			}
			return te, filter
		}
	}
	startChar := computeWordStart(current, p.Position.Character)
	te := &TextEdit{Range: Range{Start: Position{Line: p.Position.Line, Character: startChar}, End: Position{Line: p.Position.Line, Character: p.Position.Character}}, NewText: cleaned}
	filter := strings.TrimLeft(current[startChar:p.Position.Character], " \t")
	return te, filter
}

func computeWordStart(current string, at int) int {
	if at > len(current) {
		at = len(current)
	}
	for at > 0 {
		ch := current[at-1]
		if (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9') || ch == '_' {
			at--
			continue
		}
		break
	}
	return at
}

func isIdentChar(ch byte) bool {
    return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9') || ch == '_'
}

// lineHasInlinePrompt returns true if the line contains an inline strict
// semicolon marker ;text; (no spaces at boundaries) or a double-semicolon
// pattern recognized by hasDoubleSemicolonTrigger.
func lineHasInlinePrompt(line string) bool {
    if _, _, _, ok := findStrictSemicolonTag(line); ok {
        return true
    }
    return hasDoubleSemicolonTrigger(line)
}

// leadingIndent returns the run of leading spaces/tabs from the provided line.
func leadingIndent(line string) string {
    i := 0
    for i < len(line) {
        if line[i] == ' ' || line[i] == '\t' {
            i++
            continue
        }
        break
    }
    if i == 0 { return "" }
    return line[:i]
}

// applyIndent prefixes each non-empty line of suggestion with the given indent
// unless it already starts with that indent.
func applyIndent(indent, suggestion string) string {
    if indent == "" || suggestion == "" { return suggestion }
    lines := splitLines(suggestion)
    for i, ln := range lines {
        if strings.TrimSpace(ln) == "" { continue }
        if strings.HasPrefix(ln, indent) { continue }
        lines[i] = indent + ln
    }
    return strings.Join(lines, "\n")
}

// isBareDoubleSemicolon reports whether the line contains a standalone
// double-semicolon marker with no inline content (";;" possibly with only
// whitespace after it). It explicitly excludes the valid form ";;text;".
func isBareDoubleSemicolon(line string) bool {
    t := strings.TrimSpace(line)
    if !strings.Contains(t, ";;") {
        return false
    }
    if hasDoubleSemicolonTrigger(t) {
        return false
    }
    if strings.HasPrefix(t, ";;") {
        rest := strings.TrimSpace(t[2:])
        // Bare if nothing follows or only semicolons/spaces remain without closing pattern
        if rest == "" || rest == ";" {
            return true
        }
    }
    return false
}

// stripDuplicateAssignmentPrefix removes a duplicated assignment prefix (e.g.,
// "name :=") from the beginning of the model suggestion when that same prefix
// already appears immediately to the left of the cursor on the current line.
// Also handles simple '=' assignments.
func stripDuplicateAssignmentPrefix(prefixBeforeCursor, suggestion string) string {
	s2 := strings.TrimLeft(suggestion, " \t")
	// Prefer := if present at end of prefix
	if idx := strings.LastIndex(prefixBeforeCursor, ":="); idx >= 0 && idx+2 <= len(prefixBeforeCursor) {
		// Ensure only spaces follow in prefix (cursor at end of prefix segment)
		tail := prefixBeforeCursor[idx+2:]
		if strings.TrimSpace(tail) == "" {
			// Move left to include identifier and spaces
			start := idx - 1
			for start >= 0 && (isIdentChar(prefixBeforeCursor[start]) || prefixBeforeCursor[start] == ' ' || prefixBeforeCursor[start] == '\t') {
				start--
			}
			start++
			seg := strings.TrimRight(prefixBeforeCursor[start:idx+2], " \t")
			if strings.HasPrefix(s2, seg) {
				return strings.TrimLeft(s2[len(seg):], " \t")
			}
		}
	}
	// Fallback to plain '=' if present
	if idx := strings.LastIndex(prefixBeforeCursor, "="); idx >= 0 {
		if !(idx > 0 && prefixBeforeCursor[idx-1] == ':') { // not := (handled above)
			tail := prefixBeforeCursor[idx+1:]
			if strings.TrimSpace(tail) == "" {
				start := idx - 1
				for start >= 0 && (isIdentChar(prefixBeforeCursor[start]) || prefixBeforeCursor[start] == ' ' || prefixBeforeCursor[start] == '\t') {
					start--
				}
				start++
				seg := strings.TrimRight(prefixBeforeCursor[start:idx+1], " \t")
				if strings.HasPrefix(s2, seg) {
					return strings.TrimLeft(s2[len(seg):], " \t")
				}
			}
		}
	}
	return suggestion
}

// stripDuplicateGeneralPrefix removes any already-typed prefix that the model repeated
// at the beginning of its suggestion. It compares the entire text to the left of the
// cursor (prefixBeforeCursor) against the suggestion, trimming whitespace appropriately,
// and strips the longest sensible overlap. This prevents cases like:
//   prefix:    "func New "
//   suggestion:"func New() *Type"
// resulting in duplicates like "func New func New() *Type".
func stripDuplicateGeneralPrefix(prefixBeforeCursor, suggestion string) string {
    if suggestion == "" { return suggestion }
    s := strings.TrimLeft(suggestion, " \t")
    p := strings.TrimRight(prefixBeforeCursor, " \t")
    // Exact prefix overlap: remove the full typed prefix
    if p != "" && strings.HasPrefix(s, p) {
        return strings.TrimLeft(s[len(p):], " \t")
    }
    // Otherwise, try the longest token-aligned suffix of p that prefixes s
    // Prefer boundaries where the char before the suffix is not an identifier char
    for k := len(p) - 1; k > 0; k-- {
        if !isIdentBoundary(p[k-1]) { continue }
        suf := strings.TrimLeft(p[k:], " \t")
        if suf == "" { continue }
        if strings.HasPrefix(s, suf) {
            return strings.TrimLeft(s[len(suf):], " \t")
        }
    }
    return suggestion
}

func isIdentBoundary(ch byte) bool {
    return !((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9') || ch == '_')
}

// stripCodeFences removes surrounding Markdown code fences from a model
// response when the entire output is wrapped, e.g. starting with "```go" or
// "```" and ending with "```". It returns the inner content unchanged.
func stripCodeFences(s string) string {
	t := strings.TrimSpace(s)
	if t == "" {
		return t
	}
	lines := splitLines(t)
	// find first and last non-empty lines
	start := 0
	for start < len(lines) && strings.TrimSpace(lines[start]) == "" {
		start++
	}
	end := len(lines) - 1
	for end >= 0 && strings.TrimSpace(lines[end]) == "" {
		end--
	}
	if start >= len(lines) || end < 0 || start > end {
		return t
	}
	first := strings.TrimSpace(lines[start])
	last := strings.TrimSpace(lines[end])
	if strings.HasPrefix(first, "```") && last == "```" && end > start {
		inner := strings.Join(lines[start+1:end], "\n")
		return inner
	}
	return t
}

// stripInlineCodeSpan returns only the contents of the first inline backtick
// code span if present, e.g., "some text `x := y()` more" -> "x := y()".
// If no matching pair of backticks exists, it returns the input unchanged.
// This is intended for code completion responses where the model may wrap a
// small snippet in single backticks among prose.
func stripInlineCodeSpan(s string) string {
    t := strings.TrimSpace(s)
    if t == "" {
        return t
    }
    i := strings.IndexByte(t, '`')
    if i < 0 {
        return t
    }
    jrel := strings.IndexByte(t[i+1:], '`')
    if jrel < 0 {
        return t
    }
    j := i + 1 + jrel
    return t[i+1 : j]
}

func labelForCompletion(cleaned, filter string) string {
	label := trimLen(firstLine(cleaned))
	if filter != "" && !strings.HasPrefix(strings.ToLower(label), strings.ToLower(filter)) {
		return filter
	}
	return label
}

func (s *Server) fallbackCompletionItems(docStr string) []CompletionItem {
	return []CompletionItem{{
		Label:         "hexai-complete",
		Kind:          1,
		Detail:        "dummy completion",
		InsertText:    "hexai",
		SortText:      "9999",
		Documentation: docStr,
	}}
}