using ErsatzTV.Application.Configuration;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Domain.Filler;

namespace ErsatzTV.Application.Channels;

/// <summary>
///     A single guide programme resolved from one or more <see cref="PlayoutItem" />s: the
///     <see cref="DisplayItem" /> whose metadata is shown, plus the coalesced <see cref="Start" />/
///     <see cref="Stop" /> window and whether the originating item carried a custom title.
/// </summary>
public readonly record struct ChannelGuideEntry(
    PlayoutItem DisplayItem,
    DateTimeOffset Start,
    DateTimeOffset Stop,
    bool HasCustomTitle);

/// <summary>
///     Shared guide-group / filler-merge projection. This is the single source of truth for turning a
///     channel's sorted <see cref="PlayoutItem" />s into guide programmes; both the XMLTV cache builder
///     (<see cref="RefreshChannelDataHandler" />) and the JSON guide query
///     (<see cref="GetChannelGuideDataHandler" />) consume it so the two representations cannot drift.
///     The XMLTV path formats <see cref="ChannelGuideEntry.Start" />/<see cref="ChannelGuideEntry.Stop" />
///     into the XMLTV timestamp strings; the JSON path returns them (and the display item's
///     <see cref="FillerKind" />) directly and lets the UI decide how to render filler.
/// </summary>
public static class ChannelGuideProjector
{
    public static IEnumerable<ChannelGuideEntry> Project(
        PlayoutScheduleKind scheduleKind,
        IReadOnlyList<PlayoutItem> sorted,
        XmltvTimeZone timeZone,
        XmltvBlockBehavior blockBehavior) =>
        scheduleKind switch
        {
            PlayoutScheduleKind.Block => ProjectBlock(sorted, timeZone, blockBehavior),
            _ => ProjectFlood(sorted, timeZone)
        };

    // Classic / Sequential / Scripted / ExternalJson: skip leading non-preroll filler, then coalesce
    // each guide group (following filler) into a single programme using the display item's GuideFinish
    // override when present.
    private static IEnumerable<ChannelGuideEntry> ProjectFlood(
        IReadOnlyList<PlayoutItem> sorted,
        XmltvTimeZone timeZone)
    {
        // skip all filler that isn't pre-roll
        var i = 0;
        while (i < sorted.Count && sorted[i].FillerKind != FillerKind.None &&
               sorted[i].FillerKind != FillerKind.PreRoll)
        {
            i++;
        }

        while (i < sorted.Count)
        {
            PlayoutItem startItem = sorted[i];
            int j = i;
            while (sorted[j].FillerKind != FillerKind.None && j + 1 < sorted.Count)
            {
                j++;
            }

            PlayoutItem displayItem = sorted[j];
            bool hasCustomTitle = !string.IsNullOrWhiteSpace(startItem.CustomTitle);

            int finishIndex = j;
            while (finishIndex + 1 < sorted.Count && (sorted[finishIndex + 1].GuideGroup == startItem.GuideGroup
                                                      || sorted[finishIndex + 1].FillerKind is FillerKind.GuideMode
                                                          or FillerKind.PostRoll or FillerKind.Tail
                                                          or FillerKind.Fallback or FillerKind.DecoDefault))
            {
                finishIndex++;
            }

            PlayoutItem finishItem = sorted[finishIndex];
            i = finishIndex;

            DateTimeOffset startTime = timeZone switch
            {
                XmltvTimeZone.Utc => new DateTimeOffset(startItem.Start, TimeSpan.Zero),
                _ => startItem.StartOffset
            };

            DateTimeOffset stopTime = (timeZone, displayItem.GuideFinishOffset.HasValue) switch
            {
                (XmltvTimeZone.Utc, true) => new DateTimeOffset(displayItem.GuideFinish!.Value, TimeSpan.Zero),
                (XmltvTimeZone.Utc, false) => new DateTimeOffset(finishItem.Finish, TimeSpan.Zero),
                (_, true) => displayItem.GuideFinishOffset!.Value,
                (_, false) => finishItem.FinishOffset
            };

            yield return new ChannelGuideEntry(displayItem, startTime, stopTime, hasCustomTitle);

            i++;
        }
    }

    // Block: group by guide window, drop filler entirely, then either use the items' actual times or
    // split the group window evenly across the non-filler items.
    private static IEnumerable<ChannelGuideEntry> ProjectBlock(
        IReadOnlyList<PlayoutItem> sorted,
        XmltvTimeZone timeZone,
        XmltvBlockBehavior blockBehavior)
    {
        var groups = sorted.GroupBy(s => new { s.GuideStart, s.GuideFinish, s.GuideGroup });
        foreach (var group in groups)
        {
            var itemsToInclude = group.Filter(g => g.FillerKind is FillerKind.None).ToList();
            if (itemsToInclude.Count == 0)
            {
                continue;
            }

            switch (blockBehavior)
            {
                case XmltvBlockBehavior.UseActualTimes:
                    foreach (PlayoutItem item in itemsToInclude)
                    {
                        DateTimeOffset actualStart = timeZone switch
                        {
                            XmltvTimeZone.Utc => new DateTimeOffset(item.Start, TimeSpan.Zero),
                            _ => new DateTimeOffset(item.Start, TimeSpan.Zero).ToLocalTime()
                        };

                        DateTimeOffset actualFinish = timeZone switch
                        {
                            XmltvTimeZone.Utc => new DateTimeOffset(item.Finish, TimeSpan.Zero),
                            _ => new DateTimeOffset(item.Finish, TimeSpan.Zero).ToLocalTime()
                        };

                        yield return new ChannelGuideEntry(item, actualStart, actualFinish, false);
                    }

                    break;
                case XmltvBlockBehavior.SplitTimeEvenly:
                default:
                    DateTime groupStart = group.Key.GuideStart!.Value;
                    DateTime groupFinish = group.Key.GuideFinish!.Value;
                    TimeSpan groupDuration = groupFinish - groupStart;

                    TimeSpan perItem = groupDuration / itemsToInclude.Count;

                    DateTimeOffset currentStart = timeZone switch
                    {
                        XmltvTimeZone.Utc => new DateTimeOffset(groupStart, TimeSpan.Zero),
                        _ => new DateTimeOffset(groupStart, TimeSpan.Zero).ToLocalTime()
                    };

                    DateTimeOffset currentFinish = currentStart + perItem;

                    foreach (PlayoutItem item in itemsToInclude)
                    {
                        yield return new ChannelGuideEntry(item, currentStart, currentFinish, false);

                        currentStart = currentFinish;
                        currentFinish += perItem;
                    }

                    break;
            }
        }
    }
}