// mcp-json.ts - Helpers for extracting structured data from MCP tool content

import type { McpContent } from "./types.js";

function tryParseJson(text: string): unknown | null {
  const trimmed = text.trim();
  if (!trimmed) {
    return null;
  }

  // Direct JSON
  if (trimmed.startsWith("{") || trimmed.startsWith("[")) {
    try {
      return JSON.parse(trimmed) as unknown;
    } catch {
      return null;
    }
  }

  // JSON fenced block inside markdown
  // Only accept ```json or a plain ``` fence (no language)
  const fencedMatch = trimmed.match(/```(\S*)\s*([\s\S]*?)```/i);
  if (fencedMatch) {
    const lang = fencedMatch[1].trim().toLowerCase();
    if (lang && lang !== "json") {
      return null;
    }

    const fencedBody = fencedMatch[2].trim();
    if (fencedBody.startsWith("{") || fencedBody.startsWith("[")) {
      try {
        return JSON.parse(fencedBody) as unknown;
      } catch {
        return null;
      }
    }
  }

  return null;
}

export function extractTextContent(content: McpContent[]): string {
  return content
    .filter((c): c is { type: "text"; text: string } => c.type === "text")
    .map((c) => c.text)
    .join("\n");
}

export function extractJsonContent(content: McpContent[]): unknown | null {
  // Prefer explicit resource payloads
  for (const item of content) {
    if (item.type !== "resource") {
      continue;
    }

    if (typeof item.resource?.text === "string") {
      const parsed = tryParseJson(item.resource.text);
      if (parsed !== null) {
        return parsed;
      }
    }
  }

  // Fall back to text payloads
  const text = extractTextContent(content);
  const parsed = tryParseJson(text);
  if (parsed !== null) {
    return parsed;
  }

  return null;
}