using General_Ledger_Service.Exceptions;
using General_Ledger_Service.Interfaces.Repositories;
using General_Ledger_Service.Models;

namespace General_Ledger_Service.Services
{
    // Extracted from AccountService (2026-07-31) so BankService's auto-created "Bank"/"Cash" GL
    // hierarchy (see BankService.CreateBankAccountAsync/CreateCashAccountAsync) can reuse the same
    // Rule 8.1 code-generation scheme instead of duplicating it - same shared-static-helper shape
    // as RecursiveTreeQueries/DepthGuard (CLAUDE.md Rule 11), not a base class.
    public static class AccountCodeGenerator
    {
        private static readonly Dictionary<short, int> AccountTypeBlockStart = new()
        {
            [1] = 1000, // Asset
            [2] = 2000, // Liability
            [3] = 3000, // Equity
            [4] = 4000, // Income
            [5] = 5000  // Expense
        };

        public static async Task<string> GenerateAsync(IAccountRepository accountRepository, short accountTypeId, Account? parent)
        {
            if (parent != null)
            {
                for (var suffix = 1; suffix <= 99; suffix++)
                {
                    var code = $"{parent.AccountCode}-{suffix:D2}";

                    if (code.Length > 20)
                    {
                        throw new BadRequestException("Cannot generate an account code: nesting is too deep for the 20-character account code column.");
                    }

                    if (await accountRepository.GetByCodeAsync(code) is null)
                    {
                        return code;
                    }
                }

                throw new BadRequestException("Maximum number of child accounts under this parent has been reached.");
            }

            if (!AccountTypeBlockStart.TryGetValue(accountTypeId, out var blockStart))
            {
                throw new BadRequestException(
                    $"Invalid accountTypeId '{accountTypeId}'. Must be one of: 1 (Asset), 2 (Liability), 3 (Equity), 4 (Income), 5 (Expense).");
            }

            // Probes each of the 10 designed slots directly rather than trusting a root count,
            // since pre-existing accounts created before this generation scheme existed (manually
            // coded, e.g. "5100") don't necessarily occupy slots in count order - a count-based
            // guess can collide with one of those and crash on the DB's unique constraint instead
            // of failing cleanly.
            for (var slot = 0; slot < 10; slot++)
            {
                var code = (blockStart + slot * 100).ToString();
                if (await accountRepository.GetByCodeAsync(code) is null)
                {
                    return code;
                }
            }

            throw new BadRequestException("Maximum number of root-level accounts for this account type has been reached.");
        }
    }
}