using System;
using System.Threading;
using System.Threading.Tasks;
using GB5Shared.DTO.Framework.Login;
using GB5Shared.QueryExecutor;

namespace GB5Shared.GenerateAutoNumber
{
    /// <summary>
    /// Single shared service for all document number generation in GB5.
    /// Covers standard documents (MMHead, Indent, etc.) and task-style entities.
    ///
    /// Wraps VoucherNumberService (atomic MBIZTRANSACTIONKEYS counter) and adds
    /// the document-type-specific rules on top.
    ///
    /// NOGenerationType (MBIZTRANSACTIONTYPE.NOGENERATIONTYPE):
    ///   0 = Auto     — atomically increments MBIZTRANSACTIONKEYS counter
    ///   1 = Manual   — validates user-supplied number length ≤ NumberSize
    ///   2 = Contract — formats as ContractDocumentNumber/RevisionNumber
    ///
    /// Registration: services.AddScoped&lt;DocumentNumberService&gt;()
    /// </summary>
    public class DocumentNumberService
    {
        private readonly VoucherNumberService _voucherNumberService;
        private readonly IQueryExecutor _queryExecutor;

        public DocumentNumberService(VoucherNumberService voucherNumberService, IQueryExecutor queryExecutor)
        {
            _voucherNumberService = voucherNumberService;
            _queryExecutor        = queryExecutor;
        }

        // ── Standard document number (MMHead, Indent, etc.) ───────────────────────────

        /// <summary>
        /// Returns the document number to stamp on a new head document.
        /// Only call for new documents (MMHeadId == 0); updates keep their existing number.
        /// </summary>
        /// <param name="bizTransactionTypeId">BizTransactionType PK — for counter lookup.</param>
        /// <param name="documentDate">Document date — for period bucketing and date-format tokens.</param>
        /// <param name="currentNumber">User-supplied number (kept for Manual; ignored for Auto/Contract).</param>
        /// <param name="contractDocumentNumber">Contract reference number (NOGenerationType==2 only).</param>
        /// <param name="revisionNumber">Revision identifier (NOGenerationType==2 only).</param>
        /// <param name="noGenerationType">0=Auto, 1=Manual, 2=Contract — MBIZTRANSACTIONTYPE.NOGENERATIONTYPE.</param>
        /// <param name="numberSize">Max allowed length for manual validation — MBIZTRANSACTIONTYPE.NUMBERSIZE.</param>
        /// <param name="login">Current user session.</param>
        /// <param name="ct">Cancellation token.</param>
        public async Task<string> GenerateDocumentNumberAsync(
            int bizTransactionTypeId,
            DateOnly documentDate,
            string? currentNumber,
            string? contractDocumentNumber,
            string? revisionNumber,
            byte noGenerationType,
            short numberSize,
            LoginDTO login,
            CancellationToken ct = default)
        {
            switch (noGenerationType)
            {
                case 0: // Auto — VoucherNumberService manages the MBIZTRANSACTIONKEYS counter
                    var generated = await _voucherNumberService
                        .GetNextVoucherNumberAsync(bizTransactionTypeId, documentDate, login, null, ct)
                        .ConfigureAwait(false);
                    // VoucherNumberService returns null only for NOGenerationType==1; cannot happen here.
                    return generated ?? throw new InvalidOperationException(
                        $"Auto-generation returned null for BizTransactionTypeId={bizTransactionTypeId}. Contact Administrator.");

                case 1: // Manual — user-supplied number; validate presence and length
                    if (string.IsNullOrWhiteSpace(currentNumber))
                        throw new InvalidOperationException(
                            $"Document number is required for BizTransactionTypeId={bizTransactionTypeId} " +
                            "(manual number generation is configured).");
                    if (numberSize > 0 && currentNumber.Length > numberSize)
                        throw new InvalidOperationException(
                            $"Document number '{currentNumber}' (length {currentNumber.Length}) exceeds " +
                            $"the allowed size ({numberSize}) defined in BizTransactionType settings.");
                    return currentNumber;

                case 2: // Contract — derive number from the linked contract reference
                    if (string.IsNullOrEmpty(contractDocumentNumber))
                        return currentNumber ?? string.Empty;
                    return string.IsNullOrEmpty(revisionNumber)
                        ? contractDocumentNumber
                        : $"{contractDocumentNumber}/{revisionNumber}";

                default:
                    return currentNumber ?? string.Empty;
            }
        }

        // ── Task-style number (uniqueness loop + type-letter prefix) ─────────────────

        /// <summary>
        /// Generates the next unique task number, or returns <c>null</c> when
        /// NOGenerationType == 1 (Manual) — the caller keeps the user-supplied number.
        ///
        /// Runs outside any transaction — LASTNO in MBIZTRANSACTIONKEYS always advances
        /// in auto-commit regardless of the caller's outer transaction outcome.
        ///
        /// The retry loop skips numbers already present in the target table — a self-heal
        /// for orphaned rows from an earlier bug. In normal operation one iteration executes.
        /// Mirrors GB4: Task.Number = DetailTypeLetter + GetNextVnoWithSameSession(...)
        /// </summary>
        /// <param name="bizTransactionTypeId">BizTransactionType PK.</param>
        /// <param name="taskDate">Task date for period bucketing and date-format tokens.</param>
        /// <param name="detailType">
        ///   Controls the number prefix letter:
        ///   0=MileStone→M, 1=RollUp→R, 2=Heading→H, 3=Work→W, default→T
        /// </param>
        /// <param name="checkExistsSql">
        ///   SQL returning COUNT(1) when @TaskNumber already exists in the caller's table.
        ///   Passed by the caller so this service has no dependency on table-specific queries.
        ///   Example: "SELECT COUNT(1) FROM TTASK WHERE TASKNUMBER = @TaskNumber"
        /// </param>
        /// <param name="login">Current user session.</param>
        /// <param name="ct">Cancellation token.</param>
        public async Task<string?> GenerateUniqueTaskNumberAsync(
            int bizTransactionTypeId,
            DateOnly taskDate,
            byte detailType,
            string checkExistsSql,
            LoginDTO login,
            CancellationToken ct = default)
        {
            for (int attempt = 0; attempt < 20; attempt++)
            {
                string? vno = await _voucherNumberService.GetNextVoucherNumberAsync(
                    bizTransactionTypeId,
                    taskDate,
                    login,
                    transaction: null,        // auto-commit — LASTNO never rolled back
                    ct: ct,
                    prefixOverride: string.Empty);

                if (vno == null)
                    return null;              // Manual mode — caller keeps user-supplied number

                string candidate = BuildTaskNumber(detailType, vno);

                int existing = await _queryExecutor.ExecuteScalarAsync<int>(
                    login,
                    checkExistsSql,
                    new { TaskNumber = candidate });

                if (existing == 0)
                    return candidate;         // Number is free — use it

                // Number already taken by an orphaned row — advance LASTNO and retry
            }

            throw new InvalidOperationException(
                $"Could not generate a unique task number for BizTransactionTypeId=" +
                $"{bizTransactionTypeId} after 20 attempts. Contact Administrator.");
        }

        // ── Private helpers ───────────────────────────────────────────────────────────

        /// <summary>
        /// Prepends the DetailType prefix letter to the VNO string.
        /// DetailType: 0=MileStone→M, 1=RollUp→R, 2=Heading→H, 3=Work→W, default→T
        /// </summary>
        private static string BuildTaskNumber(byte detailType, string vno)
        {
            string prefix = detailType switch
            {
                0 => "M",
                1 => "R",
                2 => "H",
                3 => "W",
                _ => "T"
            };
            return prefix + vno;
        }
    }
}