// @ledgerflow/shared/index.js
// Shared utilities for all Lambda functions

const { DynamoDBClient } = require("@aws-sdk/client-dynamodb");
const { DynamoDBDocumentClient } = require("@aws-sdk/lib-dynamodb");

// ─── HTTP Response Helpers ───────────────────────────────────────────────────

const ALLOWED_ORIGINS = [
  process.env.ALLOWED_ORIGIN || "*",
  "http://localhost:3000",
];

function getCorsHeaders(event) {
  const origin = event?.headers?.origin || event?.headers?.Origin || "";
  const matched = ALLOWED_ORIGINS.includes(origin) ? origin : ALLOWED_ORIGINS[0];
  return {
    "Access-Control-Allow-Origin": matched,
    "Access-Control-Allow-Headers": "Content-Type,Authorization",
    "Access-Control-Allow-Methods": "GET,POST,PUT,PATCH,DELETE,OPTIONS",
    "Content-Type": "application/json",
  };
}

// Static fallback for responses that don't have event context
const CORS_HEADERS = {
  "Access-Control-Allow-Origin": process.env.ALLOWED_ORIGIN || "*",
  "Access-Control-Allow-Headers": "Content-Type,Authorization",
  "Access-Control-Allow-Methods": "GET,POST,PUT,PATCH,DELETE,OPTIONS",
  "Content-Type": "application/json",
};

function ok(body, statusCode = 200) {
  return {
    statusCode,
    headers: CORS_HEADERS,
    body: JSON.stringify(body),
  };
}

function created(body) {
  return ok(body, 201);
}

function noContent() {
  return { statusCode: 204, headers: CORS_HEADERS, body: "" };
}

function badRequest(message, details = null) {
  return {
    statusCode: 400,
    headers: CORS_HEADERS,
    body: JSON.stringify({ error: "Bad Request", message, details }),
  };
}

function unauthorized(message = "Unauthorized") {
  return {
    statusCode: 401,
    headers: CORS_HEADERS,
    body: JSON.stringify({ error: "Unauthorized", message }),
  };
}

function forbidden(message = "Forbidden") {
  return {
    statusCode: 403,
    headers: CORS_HEADERS,
    body: JSON.stringify({ error: "Forbidden", message }),
  };
}

function notFound(resource = "Resource") {
  return {
    statusCode: 404,
    headers: CORS_HEADERS,
    body: JSON.stringify({ error: "Not Found", message: `${resource} not found` }),
  };
}

function conflict(message) {
  return {
    statusCode: 409,
    headers: CORS_HEADERS,
    body: JSON.stringify({ error: "Conflict", message }),
  };
}

function serverError(message = "Internal server error", err = null) {
  if (err) console.error("[ERROR]", err);
  return {
    statusCode: 500,
    headers: CORS_HEADERS,
    body: JSON.stringify({ error: "Internal Server Error", message }),
  };
}

// ─── DynamoDB Client ─────────────────────────────────────────────────────────

let _docClient = null;

function getDocClient() {
  if (!_docClient) {
    const base = new DynamoDBClient({ region: process.env.AWS_REGION || "us-east-1" });
    _docClient = DynamoDBDocumentClient.from(base, {
      marshallOptions: { removeUndefinedValues: true },
    });
  }
  return _docClient;
}

// ─── Table Names ─────────────────────────────────────────────────────────────

const TABLES = {
  POS:          process.env.POS_TABLE          || "ledgerflow-pos",
  INVOICES:     process.env.INVOICES_TABLE     || "ledgerflow-invoices",
  EDI_TX:       process.env.EDI_TX_TABLE       || "ledgerflow-edi-transactions",
  SESSIONS:     process.env.SESSIONS_TABLE     || "ledgerflow-sessions",
  SETTINGS:     process.env.SETTINGS_TABLE     || "ledgerflow-settings",
};

// ─── Pagination Helper ───────────────────────────────────────────────────────

function parsePagination(queryParams = {}) {
  const limit = Math.min(parseInt(queryParams.limit || "50", 10), 200);
  const cursor = queryParams.cursor || null;
  return { limit, cursor };
}

function paginatedResponse(items, lastKey, total = null) {
  return {
    items,
    cursor: lastKey ? Buffer.from(JSON.stringify(lastKey)).toString("base64") : null,
    ...(total !== null && { total }),
  };
}

function decodeCursor(cursor) {
  if (!cursor) return undefined;
  try {
    return JSON.parse(Buffer.from(cursor, "base64").toString("utf-8"));
  } catch {
    return undefined;
  }
}

// ─── ID Generation ───────────────────────────────────────────────────────────

function genId(prefix = "") {
  const ts = Date.now().toString(36);
  const rand = Math.random().toString(36).slice(2, 8);
  return `${prefix}${ts}${rand}`.toUpperCase();
}

// ─── Input Validation ────────────────────────────────────────────────────────

function parseBody(event) {
  if (!event.body) return {};
  try {
    return JSON.parse(event.body);
  } catch {
    throw new ValidationError("Invalid JSON body");
  }
}

class ValidationError extends Error {
  constructor(message, details = null) {
    super(message);
    this.name = "ValidationError";
    this.details = details;
  }
}

function require_fields(obj, fields) {
  const missing = fields.filter((f) => !obj[f] && obj[f] !== 0);
  if (missing.length) {
    throw new ValidationError(`Missing required fields: ${missing.join(", ")}`);
  }
}

// ─── Lambda Handler Wrapper ──────────────────────────────────────────────────
// Catches errors, handles OPTIONS preflight, extracts auth context

function handler(fn) {
  return async (event, context) => {
    const corsHeaders = getCorsHeaders(event);

    // CORS preflight
    if (event.requestContext?.http?.method === "OPTIONS" || event.httpMethod === "OPTIONS") {
      return { statusCode: 200, headers: corsHeaders, body: "" };
    }

    // Attach authenticated user from authorizer context
    const user = event.requestContext?.authorizer?.lambda || null;

    try {
      const response = await fn(event, context, user);
      // Override CORS origin with the matched request origin
      if (response?.headers) response.headers["Access-Control-Allow-Origin"] = corsHeaders["Access-Control-Allow-Origin"];
      return response;
    } catch (err) {
      if (err instanceof ValidationError) {
        return badRequest(err.message, err.details);
      }
      console.error("[UNHANDLED]", err);
      return serverError("An unexpected error occurred", err);
    }
  };
}

module.exports = {
  // Response
  ok, created, noContent, badRequest, unauthorized, forbidden,
  notFound, conflict, serverError,
  CORS_HEADERS,
  // DynamoDB
  getDocClient, TABLES,
  // Pagination
  parsePagination, paginatedResponse, decodeCursor,
  // Util
  genId, parseBody, require_fields, handler,
  ValidationError,
};