package mcp

import "encoding/json"

// ProtocolVersion is the MCP protocol revision Nexus advertises. Nexus is
// lenient on the client's requested version and echoes a supported one.
const ProtocolVersion = "2025-06-18"

// Method names used by MCP.
const (
	MethodInitialize    = "initialize"
	MethodInitialized   = "notifications/initialized"
	MethodPing          = "ping"
	MethodToolsList     = "tools/list"
	MethodToolsCall     = "tools/call"
	MethodToolListChged = "notifications/tools/list_changed"
)

// Implementation identifies a client or server implementation.
type Implementation struct {
	Name    string `json:"name"`
	Version string `json:"version"`
}

// ToolsCapability describes tool-related server capabilities.
type ToolsCapability struct {
	ListChanged bool `json:"listChanged,omitempty"`
}

// Capabilities is the (subset of) MCP capabilities Nexus cares about.
type Capabilities struct {
	Tools     *ToolsCapability `json:"tools,omitempty"`
	Resources *struct {
		ListChanged bool `json:"listChanged,omitempty"`
		Subscribe   bool `json:"subscribe,omitempty"`
	} `json:"resources,omitempty"`
	Prompts *struct {
		ListChanged bool `json:"listChanged,omitempty"`
	} `json:"prompts,omitempty"`
}

// InitializeParams are the params for the initialize request.
type InitializeParams struct {
	ProtocolVersion string         `json:"protocolVersion"`
	Capabilities    Capabilities   `json:"capabilities"`
	ClientInfo      Implementation `json:"clientInfo"`
}

// InitializeResult is the result of an initialize request.
type InitializeResult struct {
	ProtocolVersion string         `json:"protocolVersion"`
	Capabilities    Capabilities   `json:"capabilities"`
	ServerInfo      Implementation `json:"serverInfo"`
	Instructions    string         `json:"instructions,omitempty"`
}

// ToolDefinition is a tool as described by tools/list.
type ToolDefinition struct {
	Name        string         `json:"name"`
	Title       string         `json:"title,omitempty"`
	Description string         `json:"description,omitempty"`
	InputSchema map[string]any `json:"inputSchema,omitempty"`
}

// ListToolsParams are the params for tools/list.
type ListToolsParams struct {
	Cursor string `json:"cursor,omitempty"`
}

// ListToolsResult is the result of tools/list.
type ListToolsResult struct {
	Tools      []ToolDefinition `json:"tools"`
	NextCursor string           `json:"nextCursor,omitempty"`
}

// CallToolParams are the params for tools/call.
type CallToolParams struct {
	Name      string          `json:"name"`
	Arguments json.RawMessage `json:"arguments,omitempty"`
}

// ContentBlock is one item of tool result content. Only the common fields are
// modeled; unknown fields survive round-trips because callers pass the raw
// result through where possible.
type ContentBlock struct {
	Type string `json:"type"`
	Text string `json:"text,omitempty"`
	// For image/audio/resource blocks these carry through opaquely.
	Data     string          `json:"data,omitempty"`
	MimeType string          `json:"mimeType,omitempty"`
	Resource json.RawMessage `json:"resource,omitempty"`
}

// CallToolResult is the result of tools/call.
type CallToolResult struct {
	Content []ContentBlock `json:"content"`
	IsError bool           `json:"isError,omitempty"`
}

// TextResult is a convenience constructor for a single text-content result.
func TextResult(text string, isError bool) CallToolResult {
	return CallToolResult{
		Content: []ContentBlock{{Type: "text", Text: text}},
		IsError: isError,
	}
}