using Microsoft.Extensions.Logging;
using ScadaLink.CentralUI.Components.Shared;
using ScadaLink.Commons.Entities.Sites;
using ScadaLink.Commons.Messages.Audit;

namespace ScadaLink.CentralUI.Components.Pages.SiteCalls;

/// <summary>
/// Code-behind for the central Site Calls report page (Site Call Audit #22). A
/// near-mirror of <see cref="ScadaLink.CentralUI.Components.Pages.Notifications.NotificationReport"/>:
/// it queries the central <c>SiteCalls</c> table via
/// <see cref="ScadaLink.Communication.CommunicationService.QuerySiteCallsAsync"/>,
/// shows a filterable/keyset-paged grid and a detail modal, and relays Retry/Discard
/// of <c>Parked</c> cached calls to their owning site.
///
/// <para>
/// Unlike the Notification report, the query response uses a <c>(CreatedAtUtc DESC,
/// TrackedOperationId DESC)</c> keyset cursor rather than page numbers, so paging
/// keeps a stack of the cursors that opened each page (to step backwards) plus the
/// response's <c>NextAfter*</c> cursor (to step forwards).
/// </para>
///
/// <para>
/// Retry/Discard relay to the owning site has a distinct <see cref="SiteCallRelayOutcome.SiteUnreachable"/>
/// outcome — central is an eventually-consistent mirror, not the source of truth, so
/// a relay that never reaches the site is a transient transport condition, surfaced
/// to the operator differently from a generic failure.
/// </para>
/// </summary>
public partial class SiteCallsReport
{
    private const int PageSize = 50;

    private ToastNotification _toast = default!;
    private List<Site> _sites = new();

    // List
    private List<SiteCallSummary>? _siteCalls;
    private bool _loading;
    private string? _listError;
    private bool _actionInProgress;

    // Keyset paging. The first page is opened with the empty (null, null) cursor.
    // _cursorStack holds the cursors of the PREVIOUSLY visited pages — it is empty
    // on page 1, has one entry on page 2, and so on; Previous pops it. _nextCursor
    // is the cursor for the following page, echoed back by the last query.
    private readonly Stack<(DateTime? AfterCreatedAtUtc, Guid? AfterId)> _cursorStack = new();
    private (DateTime? AfterCreatedAtUtc, Guid? AfterId) _currentCursor = (null, null);
    private (DateTime? AfterCreatedAtUtc, Guid? AfterId)? _nextCursor;

    // Row detail modal
    private SiteCallSummary? _detailSiteCall;
    private SiteCallDetail? _detail;
    private bool _detailLoading;
    private string? _detailError;

    // Filters
    private string _statusFilter = string.Empty;
    private string _channelFilter = string.Empty;
    private string _siteFilter = string.Empty;
    private string _targetFilter = string.Empty;
    private bool _stuckOnly;
    private DateTime? _fromFilter;
    private DateTime? _toFilter;

    private bool HasNextPage => _nextCursor is not null;

    protected override async Task OnInitializedAsync()
    {
        try
        {
            _sites = (await SiteRepository.GetAllSitesAsync()).ToList();
        }
        catch (Exception ex)
        {
            // Non-fatal — the source-site filter just falls back to raw site IDs.
            Logger.LogWarning(ex, "Failed to load sites for the Site Calls source-site filter.");
        }

        await RefreshAll();
    }

    /// <summary>Re-fetch the current page (Refresh button, and after a relay action).</summary>
    private async Task RefreshAll()
    {
        await FetchPage(_currentCursor);
    }

    /// <summary>Apply the filters and start again from the first page.</summary>
    private async Task Search()
    {
        _cursorStack.Clear();
        await FetchPage((null, null));
    }

    private async Task PrevPage()
    {
        if (_cursorStack.Count == 0)
        {
            return;
        }

        // The top of the stack is the cursor of the page BEFORE the current one.
        var previousCursor = _cursorStack.Pop();
        await FetchPage(previousCursor);
    }

    private async Task NextPage()
    {
        if (_nextCursor is not { } next)
        {
            return;
        }

        // Stepping forward: remember the current page's cursor so Previous can
        // return to it.
        _cursorStack.Push(_currentCursor);
        await FetchPage(next);
    }

    /// <summary>
    /// Fetch one keyset page starting after <paramref name="cursor"/>.
    /// </summary>
    private async Task FetchPage(
        (DateTime? AfterCreatedAtUtc, Guid? AfterId) cursor)
    {
        _loading = true;
        _listError = null;
        try
        {
            var request = new SiteCallQueryRequest(
                CorrelationId: Guid.NewGuid().ToString("N"),
                StatusFilter: NullIfEmpty(_statusFilter),
                SourceSiteFilter: NullIfEmpty(_siteFilter),
                ChannelFilter: NullIfEmpty(_channelFilter),
                TargetKeyword: NullIfEmpty(_targetFilter),
                StuckOnly: _stuckOnly,
                FromUtc: ToUtc(_fromFilter),
                ToUtc: ToUtc(_toFilter),
                AfterCreatedAtUtc: cursor.AfterCreatedAtUtc,
                AfterId: cursor.AfterId,
                PageSize: PageSize);

            var response = await CommunicationService.QuerySiteCallsAsync(request);
            if (response.Success)
            {
                _siteCalls = response.SiteCalls.ToList();
                _currentCursor = cursor;

                // The response echoes the last row's cursor. A short page (fewer
                // rows than requested) has no further page even if a cursor came
                // back, so gate Next on a full page too.
                _nextCursor = response.NextAfterCreatedAtUtc is { } nextCreated
                              && response.NextAfterId is { } nextId
                              && _siteCalls.Count == PageSize
                    ? (nextCreated, nextId)
                    : null;
            }
            else
            {
                _listError = response.ErrorMessage ?? "Query failed.";
            }
        }
        catch (Exception ex)
        {
            _listError = $"Query failed: {ex.Message}";
        }
        _loading = false;
    }

    private async Task RetrySiteCall(SiteCallSummary c)
    {
        var confirmed = await Dialog.ConfirmAsync(
            "Retry cached call",
            $"Relay a retry of cached call {ShortId(c.TrackedOperationId)} (\"{c.Target}\") " +
            $"to site {SiteName(c.SourceSite)}?");
        if (!confirmed) return;

        _actionInProgress = true;
        try
        {
            var response = await CommunicationService.RetrySiteCallAsync(
                new RetrySiteCallRequest(Guid.NewGuid().ToString("N"), c.TrackedOperationId, c.SourceSite));
            ShowRelayOutcome(response.Outcome, response.SiteReachable, response.ErrorMessage,
                appliedMessage: $"Retry of {ShortId(c.TrackedOperationId)} relayed to {SiteName(c.SourceSite)}.");
            if (response.Success)
            {
                await RefreshAll();
            }
        }
        catch (Exception ex)
        {
            _toast.ShowError($"Retry failed: {ex.Message}");
        }
        _actionInProgress = false;
    }

    private async Task DiscardSiteCall(SiteCallSummary c)
    {
        var confirmed = await Dialog.ConfirmAsync(
            "Discard cached call",
            $"Relay a discard of cached call {ShortId(c.TrackedOperationId)} (\"{c.Target}\") " +
            $"to site {SiteName(c.SourceSite)}? This cannot be undone.",
            danger: true);
        if (!confirmed) return;

        _actionInProgress = true;
        try
        {
            var response = await CommunicationService.DiscardSiteCallAsync(
                new DiscardSiteCallRequest(Guid.NewGuid().ToString("N"), c.TrackedOperationId, c.SourceSite));
            ShowRelayOutcome(response.Outcome, response.SiteReachable, response.ErrorMessage,
                appliedMessage: $"Discard of {ShortId(c.TrackedOperationId)} relayed to {SiteName(c.SourceSite)}.");
            if (response.Success)
            {
                await RefreshAll();
            }
        }
        catch (Exception ex)
        {
            _toast.ShowError($"Discard failed: {ex.Message}");
        }
        _actionInProgress = false;
    }

    /// <summary>
    /// Surface a relay outcome on the toast — exactly one toast per relay
    /// response. The <see cref="SiteCallRelayOutcome.SiteUnreachable"/> case is
    /// deliberately distinct from a generic failure: the action was not applied
    /// but the operator can retry once the site is back online.
    /// </summary>
    /// <remarks>
    /// The <see cref="SiteCallRelayOutcome"/> switch is exhaustive, so it owns
    /// the single toast. <paramref name="siteReachable"/> is a redundant
    /// cross-check on the same signal (the contract sets it <c>false</c> only
    /// for <see cref="SiteCallRelayOutcome.SiteUnreachable"/>); it is folded
    /// INTO the <see cref="SiteCallRelayOutcome.OperationFailed"/> case rather
    /// than firing a second toast — an <c>OperationFailed</c> response that also
    /// reports an unreachable site shows the unreachable wording, once.
    /// </remarks>
    private void ShowRelayOutcome(
        SiteCallRelayOutcome outcome, bool siteReachable, string? errorMessage, string appliedMessage)
    {
        switch (outcome)
        {
            case SiteCallRelayOutcome.Applied:
                _toast.ShowSuccess(appliedMessage);
                break;
            case SiteCallRelayOutcome.NotParked:
                _toast.ShowInfo(errorMessage
                    ?? "The site reported nothing to do — the cached call is no longer parked.");
                break;
            case SiteCallRelayOutcome.SiteUnreachable:
                _toast.ShowError(errorMessage
                    ?? "Site unreachable — the relay did not reach the owning site. "
                       + "Try again once the site is back online.");
                break;
            case SiteCallRelayOutcome.OperationFailed when !siteReachable:
                // An OperationFailed response that nonetheless reports the site
                // unreachable: trust the reachability signal and show the
                // unreachable wording instead of the generic failure message.
                _toast.ShowError(errorMessage
                    ?? "Site unreachable — the relay did not reach the owning site. "
                       + "Try again once the site is back online.");
                break;
            case SiteCallRelayOutcome.OperationFailed:
            default:
                _toast.ShowError(errorMessage ?? "The site could not apply the action.");
                break;
        }
    }

    private async Task ShowDetail(SiteCallSummary c)
    {
        // The summary fields render immediately from the grid row; the full detail
        // (HttpStatus, all timestamps, LastError) fills in once the fetch completes.
        _detailSiteCall = c;
        _detail = null;
        _detailError = null;
        _detailLoading = true;
        StateHasChanged();

        try
        {
            var response = await CommunicationService.GetSiteCallDetailAsync(
                new SiteCallDetailRequest(Guid.NewGuid().ToString("N"), c.TrackedOperationId));
            if (response.Success && response.Detail != null)
            {
                _detail = response.Detail;
            }
            else
            {
                _detailError = response.ErrorMessage ?? "Failed to load site call detail.";
            }
        }
        catch (Exception ex)
        {
            _detailError = $"Failed to load site call detail: {ex.Message}";
        }
        _detailLoading = false;
    }

    private void CloseDetail()
    {
        _detailSiteCall = null;
        _detail = null;
        _detailError = null;
        _detailLoading = false;
    }

    private async Task RetryFromDetail(SiteCallSummary c)
    {
        await RetrySiteCall(c);
        // RefreshAll replaces the row list; close the modal so the user sees the
        // refreshed grid rather than a now-stale detail snapshot.
        CloseDetail();
    }

    private async Task DiscardFromDetail(SiteCallSummary c)
    {
        await DiscardSiteCall(c);
        CloseDetail();
    }

    private void ClearFilters()
    {
        _statusFilter = string.Empty;
        _channelFilter = string.Empty;
        _siteFilter = string.Empty;
        _targetFilter = string.Empty;
        _stuckOnly = false;
        _fromFilter = null;
        _toFilter = null;
    }

    private bool HasActiveFilters =>
        !string.IsNullOrEmpty(_statusFilter) ||
        !string.IsNullOrEmpty(_channelFilter) ||
        !string.IsNullOrEmpty(_siteFilter) ||
        !string.IsNullOrEmpty(_targetFilter) ||
        _stuckOnly ||
        _fromFilter != null ||
        _toFilter != null;

    private string SiteName(string siteId) =>
        _sites.FirstOrDefault(s => s.SiteIdentifier == siteId)?.Name ?? siteId;

    private static string? NullIfEmpty(string s) => string.IsNullOrWhiteSpace(s) ? null : s.Trim();

    /// <summary>
    /// The filter inputs are UTC wall-clock — stamp <see cref="DateTimeKind.Utc"/>
    /// on the local-typed value so the query is unambiguous.
    /// </summary>
    private static DateTime? ToUtc(DateTime? value) =>
        value == null ? null : DateTime.SpecifyKind(value.Value, DateTimeKind.Utc);

    /// <summary>
    /// The <c>SiteCalls</c> timestamps are UTC <see cref="DateTime"/>; wrap them as
    /// a <see cref="DateTimeOffset"/> for <c>TimestampDisplay</c>.
    /// </summary>
    private static DateTimeOffset? AsOffset(DateTime? value) =>
        value == null
            ? null
            : new DateTimeOffset(DateTime.SpecifyKind(value.Value, DateTimeKind.Utc));

    // A Guid's "N" format is always exactly 32 hex chars, so the [..12] slice is
    // always in range — no length guard needed.
    private static string ShortId(Guid id) => id.ToString("N")[..12];

    private static string StatusBadgeClass(string status) => status switch
    {
        "Delivered" => "bg-success",
        "Parked" => "bg-danger",
        "Failed" => "bg-danger",
        "Attempted" => "bg-warning text-dark",
        "Forwarded" => "bg-info text-dark",
        "Submitted" => "bg-info text-dark",
        "Discarded" => "bg-secondary",
        _ => "bg-light text-dark"
    };
}