import { Connection } from "@solana/web3.js";
import { Buffer } from "buffer";
import { RegistryState, MAX_ACTIVE_MARKETS } from "../types.js";
import { getRegistryAddress } from "./pda.js";

// Registry account size (excluding 8-byte discriminator):
// - bump: u8 (1 byte)
// - active_count: u16 (2 bytes)
// - active_weeks: [u32; 1] (4 bytes)
// - last_week_number: u32 (4 bytes)
// - total_markets_count: u32 (4 bytes)
// Total: 15 bytes
const REGISTRY_STATE_SIZE = 1 + 2 + 4 * MAX_ACTIVE_MARKETS + 4 + 4;

/**
 * Parse a RegistryState account from raw buffer data
 *
 * @param data - Raw account data buffer (excluding 8-byte discriminator)
 * @returns Parsed RegistryState object
 * @throws Error if buffer is too small
 *
 * @example
 * ```typescript
 * const registryPda = getRegistryAddress();
 * const accountInfo = await connection.getAccountInfo(registryPda);
 * if (accountInfo) {
 *   // Skip 8-byte discriminator
 *   const registry = parseRegistryAccount(accountInfo.data.slice(8));
 *   console.log('Active weeks:', registry.activeWeeks);
 * }
 * ```
 */
export function parseRegistryAccount(data: Uint8Array | Buffer): RegistryState {
  // Convert to Buffer for consistent API (Buffer extends Uint8Array)
  const buffer = Buffer.from(data);

  if (buffer.length < REGISTRY_STATE_SIZE) {
    throw new Error(
      `Buffer too small for RegistryState: expected at least ${REGISTRY_STATE_SIZE} bytes, got ${buffer.length}`
    );
  }

  let offset = 0;

  // bump: u8
  const bump = buffer.readUInt8(offset);
  offset += 1;

  // active_count: u16
  const activeCount = buffer.readUInt16LE(offset);
  offset += 2;

  // active_weeks: [u32; MAX_ACTIVE_MARKETS] - only read up to activeCount
  const activeWeeks: number[] = [];
  for (let i = 0; i < activeCount && i < MAX_ACTIVE_MARKETS; i++) {
    activeWeeks.push(buffer.readUInt32LE(offset + i * 4));
  }
  offset += 4 * MAX_ACTIVE_MARKETS;

  // last_week_number: u32
  const lastWeekNumber = buffer.readUInt32LE(offset);
  offset += 4;

  // total_markets_count: u32
  const totalMarketsCount = buffer.readUInt32LE(offset);

  return {
    bump,
    activeCount,
    activeWeeks,
    lastWeekNumber,
    totalMarketsCount,
  };
}

/**
 * Fetch and parse the registry account
 *
 * @param connection - Solana connection
 * @returns RegistryState or null if account doesn't exist
 *
 * @example
 * ```typescript
 * const registry = await fetchRegistry(connection);
 * if (registry) {
 *   console.log(`${registry.activeCount} active markets`);
 *   for (const weekNumber of registry.activeWeeks) {
 *     console.log(`  Week ${weekNumber}`);
 *   }
 * }
 * ```
 */
export async function fetchRegistry(connection: Connection): Promise<RegistryState | null> {
  const registryPda = getRegistryAddress();
  const accountInfo = await connection.getAccountInfo(registryPda);

  if (!accountInfo) {
    return null;
  }

  // Skip 8-byte Anchor discriminator
  return parseRegistryAccount(accountInfo.data.slice(8));
}

/**
 * Get all active market week numbers
 *
 * @param connection - Solana connection
 * @returns Array of active week numbers, or empty array if registry doesn't exist
 *
 * @example
 * ```typescript
 * const activeWeeks = await getActiveMarketWeeks(connection);
 * for (const weekNumber of activeWeeks) {
 *   const marketPda = getMarketAddress(weekNumber);
 *   // Fetch market data...
 * }
 * ```
 */
export async function getActiveMarketWeeks(connection: Connection): Promise<number[]> {
  const registry = await fetchRegistry(connection);
  return registry?.activeWeeks ?? [];
}