opencode-cursor-agent/internal/server/anthropic.go

package server

import (
	"encoding/json"
	"fmt"
	"regexp"
	"strings"

	"github.com/daniel/cursor-adapter/internal/sanitize"
	"github.com/daniel/cursor-adapter/internal/types"
)

// systemReminderRe matches <system-reminder>...</system-reminder> blocks
// that Claude Desktop embeds inside user messages.
var systemReminderRe = regexp.MustCompile(`(?s)<system-reminder>.*?</system-reminder>\s*`)

// buildPromptFromAnthropicMessages flattens an Anthropic Messages request
// into a single prompt string suitable for `agent --print`.
//
// "Pure brain + remote executors" design:
//   - DROP all client system messages (mode descriptions / sandbox warnings
//     that make the model refuse).
//   - USE ONLY the adapter's injected system prompt.
//   - RENDER req.Tools as a plain-text inventory of executors that the
//     caller (Claude Desktop / Claude Code / opencode) owns. The brain must
//     know it has remote hands.
//   - RENDER assistant tool_use and user tool_result blocks as readable
//     transcript, so multi-turn ReAct loops keep working.
//   - STRIP <system-reminder> blocks embedded in user messages.
func buildPromptFromAnthropicMessages(req types.AnthropicMessagesRequest, injectedSystemPrompt string) string {
	var prompt strings.Builder

	if injectedSystemPrompt != "" {
		prompt.WriteString("System:\n")
		prompt.WriteString(injectedSystemPrompt)
		prompt.WriteString("\n\n")
	}

	if hints := renderMountHints(extractMountHints(req)); hints != "" {
		prompt.WriteString(hints)
		prompt.WriteString("\n")
	}

	if toolsBlock := renderToolsForBrain(req.Tools); toolsBlock != "" {
		prompt.WriteString(toolsBlock)
		prompt.WriteString("\n")
	}

	for _, msg := range req.Messages {
		text := renderMessageBlocks(msg.Role, msg.Content)
		if text == "" {
			continue
		}
		switch msg.Role {
		case "assistant":
			prompt.WriteString("Assistant: ")
		default:
			prompt.WriteString("User: ")
		}
		prompt.WriteString(text)
		prompt.WriteString("\n\n")
	}

	prompt.WriteString("Assistant:")
	return prompt.String()
}

// renderToolsForBrain converts the Anthropic tools[] array into a readable
// inventory the brain can reason about. The brain is told it MUST emit
// <tool_call>{...}</tool_call> sentinels when it wants to invoke one; the
// proxy translates that into real Anthropic tool_use blocks for the caller.
func renderToolsForBrain(tools []types.AnthropicTool) string {
	if len(tools) == 0 {
		return ""
	}
	var b strings.Builder
	b.WriteString("Available executors (the caller will run these for you):\n")
	for _, t := range tools {
		b.WriteString("- ")
		b.WriteString(t.Name)
		if desc := strings.TrimSpace(t.Description); desc != "" {
			b.WriteString(": ")
			b.WriteString(singleLine(desc))
		}
		if len(t.InputSchema) > 0 {
			b.WriteString("\n  input_schema: ")
			b.WriteString(compactJSON(t.InputSchema))
		}
		b.WriteString("\n")
	}
	b.WriteString("\nTo invoke a tool, output EXACTLY one fenced block (and nothing else for that turn):\n")
	b.WriteString("<tool_call>\n")
	b.WriteString(`{"name":"<tool_name>","input":{...}}` + "\n")
	b.WriteString("</tool_call>\n")
	b.WriteString("If you do NOT need a tool, just answer in plain text.\n")
	return b.String()
}

// renderMessageBlocks renders a single message's content blocks into a
// transcript snippet. Text blocks are sanitised; tool_use blocks render as
// `[tool_call name=... input=...]`; tool_result blocks render as
// `[tool_result for=... ok|error] ...`.
func renderMessageBlocks(role string, content types.AnthropicContent) string {
	var parts []string
	for _, block := range content {
		switch block.Type {
		case "text":
			if block.Text == "" {
				continue
			}
			cleaned := systemReminderRe.ReplaceAllString(block.Text, "")
			cleaned = sanitize.Text(cleaned)
			cleaned = strings.TrimSpace(cleaned)
			if cleaned != "" {
				parts = append(parts, cleaned)
			}
		case "tool_use":
			parts = append(parts, fmt.Sprintf(
				"[tool_call name=%q input=%s]",
				block.Name, compactJSON(block.Input),
			))
		case "tool_result":
			status := "ok"
			if block.IsError {
				status = "error"
			}
			body := renderToolResultContent(block.Content)
			if body == "" {
				body = "(empty)"
			}
			parts = append(parts, fmt.Sprintf(
				"[tool_result for=%s status=%s]\n%s",
				block.ToolUseID, status, body,
			))
		case "image", "document":
			parts = append(parts, fmt.Sprintf("[%s attached]", block.Type))
		}
	}
	return strings.Join(parts, "\n")
}

// renderToolResultContent flattens a tool_result.content payload (which can
// be a string or an array of {type:"text",text:...} blocks) to plain text.
func renderToolResultContent(raw json.RawMessage) string {
	if len(raw) == 0 {
		return ""
	}
	var s string
	if err := json.Unmarshal(raw, &s); err == nil {
		return strings.TrimSpace(s)
	}
	var blocks []struct {
		Type string `json:"type"`
		Text string `json:"text"`
	}
	if err := json.Unmarshal(raw, &blocks); err == nil {
		var out []string
		for _, b := range blocks {
			if b.Type == "text" && b.Text != "" {
				out = append(out, b.Text)
			}
		}
		return strings.TrimSpace(strings.Join(out, "\n"))
	}
	return strings.TrimSpace(string(raw))
}

func compactJSON(raw json.RawMessage) string {
	if len(raw) == 0 {
		return "{}"
	}
	var v interface{}
	if err := json.Unmarshal(raw, &v); err != nil {
		return string(raw)
	}
	out, err := json.Marshal(v)
	if err != nil {
		return string(raw)
	}
	return string(out)
}

func singleLine(s string) string {
	s = strings.ReplaceAll(s, "\r", " ")
	s = strings.ReplaceAll(s, "\n", " ")
	for strings.Contains(s, "  ") {
		s = strings.ReplaceAll(s, "  ", " ")
	}
	return strings.TrimSpace(s)
}