import { registerTemplateHelpers } from '@src/core/instructions/templateHelpers.js';
import type { MCPServerParams } from '@src/core/types/transport.js';
import type { ContextData } from '@src/types/context.js';
import Handlebars from 'handlebars';
/**
* Simple Handlebars template renderer
*
* Replaces the complex TemplateVariableExtractor with direct template rendering.
* Renders template configurations with context data and returns the result.
*
* This approach:
* - Eliminates variable extraction complexity
* - Uses rendered config hash for instance identification
* - Leverages existing Handlebars helpers and battle-tested rendering
* - Uses {{var}} syntax (standard Handlebars)
*/
export class HandlebarsTemplateRenderer {
constructor() {
// Register existing helpers from the codebase
registerTemplateHelpers();
}
/**
* Render a template configuration with the provided context
*
* @param templateConfig - Configuration with {{variable}} placeholders
* @param context - Context data to substitute into templates
* @returns Rendered configuration with all variables replaced
*/
renderTemplate(templateConfig: MCPServerParams, context: ContextData): MCPServerParams {
// Deep clone to avoid mutating the original configuration
const config = JSON.parse(JSON.stringify(templateConfig)) as MCPServerParams;
// Render command string
if (config.command && typeof config.command === 'string') {
config.command = this.renderString(config.command, context);
}
// Render args array elements
if (config.args) {
config.args = config.args.map((arg: string | number | boolean) =>
typeof arg === 'string' ? this.renderString(arg, context) : String(arg),
);
}
// Render environment variables
if (config.env) {
if (Array.isArray(config.env)) {
// Handle array format: just convert non-string elements to strings
config.env = config.env.map((item) => String(item));
} else {
// Handle record format: render string values
const renderedEnv: Record<string, string> = {};
for (const [key, value] of Object.entries(config.env)) {
if (typeof value === 'string') {
renderedEnv[key] = this.renderString(value, context);
} else {
renderedEnv[key] = String(value);
}
}
config.env = renderedEnv;
}
}
// Render other string fields that might contain templates
const stringFields: Array<keyof MCPServerParams> = ['cwd', 'url'];
stringFields.forEach((field) => {
const fieldValue = config[field];
if (fieldValue && typeof fieldValue === 'string') {
// Use type assertion to safely assign the rendered string
(config as Record<string, unknown>)[field] = this.renderString(fieldValue, context);
}
});
return config;
}
/**
* Render a single string template with context
*
* @param template - String with {{variable}} placeholders
* @param context - Context data for substitution
* @returns Rendered string with variables replaced
*/
private renderString(template: string, context: ContextData): string {
// Quick check to skip compilation if no template variables
if (!template.includes('{{')) {
return template;
}
try {
const compiled = Handlebars.compile(template);
return compiled(context);
} catch {
// Return original template if rendering fails
// This maintains graceful degradation
return template;
}
}
}
