using System.IO.Abstractions;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Graphics;
using ErsatzTV.Infrastructure.Data;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

namespace ErsatzTV.Infrastructure.Streaming.Graphics;

public static class GraphicsElementSeeder
{
    // The pre-#732 default, kept verbatim so an installation still carrying it byte-for-byte can
    // be recognised as unmodified and upgraded. Never edit an entry here -- it is a fingerprint of
    // what we shipped, not a template. Add a new entry when the current default changes again.
    private const string OnNowNextYamlV1 =
        """
        name: On Now / Next
        epg_entries: 2
        location: BottomLeft
        horizontal_margin_percent: 4
        vertical_margin_percent: 8
        width_percent: 42
        text_fit: Wrap
        text_align: Left
        z_index: 100
        # transparent until 4s in, fade in 1s, hold 6s, fade out 1s
        opacity_expression: "LinearFadeDuration(content_seconds, 4, 1, 6)"
        base_style: now
        styles:
          - name: now
            font_family: "Noto Sans"
            font_size: 30
            font_weight: 700
            text_color: "#FFFFFF"
            halo_color: "#000000"
            halo_width: 2
          - name: sub
            font_family: "Noto Sans"
            font_size: 22
            font_weight: 400
            text_color: "#DDDDDD"
            halo_color: "#000000"
            halo_width: 2
          - name: next
            font_family: "Noto Sans"
            font_size: 22
            font_weight: 400
            text_color: "#DDDDDD"
            halo_color: "#000000"
            halo_width: 2
        text: |
          [now]NOW  {{ Epg[0].Title }}[/now]
          {{ if Epg[0].SubTitle }}[sub]{{ Epg[0].SubTitle }}[/sub]{{ end }}
          {{ if (array.size Epg) > 1 }}[next]NEXT  {{ Epg[1].Title }}[/next]{{ end }}
        """;

    private const string OnNowNextYaml =
        """
        name: On Now / Next
        epg_entries: 2
        location: BottomLeft
        horizontal_margin_percent: 4
        vertical_margin_percent: 8
        width_percent: 42
        text_fit: Wrap
        text_align: Left
        z_index: 100
        # transparent until 4s in, fade in 1s, hold 6s, fade out 1s
        opacity_expression: "LinearFadeDuration(content_seconds, 4, 1, 6)"
        # #732: a translucent box carries legibility over both bright and dark content. The halo is
        # cut from 2 to 1 rather than dropped -- the box is translucent, so bright content still
        # shows through behind the glyphs, but 2px of halo ON TOP of a box over-darkens the text.
        background_color: "#000000"
        background_opacity_percent: 65
        background_padding: 14
        background_corner_radius: 8
        # A translucent black box vanishes into dark content, so the box needs an edge of its own.
        # Low-alpha white reads as a hairline on dark frames without becoming a hard line on bright ones.
        border_color: "#59FFFFFF"
        border_width: 1
        base_style: now
        styles:
          - name: now
            font_family: "Noto Sans"
            font_size: 30
            font_weight: 700
            text_color: "#FFFFFF"
            halo_color: "#000000"
            halo_width: 1
          - name: sub
            font_family: "Noto Sans"
            font_size: 22
            font_weight: 400
            text_color: "#DDDDDD"
            halo_color: "#000000"
            halo_width: 1
          - name: next
            font_family: "Noto Sans"
            font_size: 22
            font_weight: 400
            text_color: "#DDDDDD"
            halo_color: "#000000"
            halo_width: 1
        text: |
          [now]NOW  {{ Epg[0].Title }}[/now]
          {{ if Epg[0].SubTitle }}[sub]{{ Epg[0].SubTitle }}[/sub]{{ end }}
          {{ if (array.size Epg) > 1 }}[next]NEXT  {{ Epg[1].Title }}[/next]{{ end }}
        """;

    // Every default we have ever shipped, most recent first. A file matching one of these was
    // written by us and never touched, so replacing it is an upgrade rather than a clobber.
    private static readonly string[] SupersededDefaults = [OnNowNextYamlV1];

    public static async Task SeedOnNowNext(
        TvContext context,
        IFileSystem fileSystem,
        ILogger logger,
        CancellationToken cancellationToken)
    {
        string folder = FileSystemLayout.GraphicsElementsTextTemplatesFolder;
        string target = fileSystem.Path.Combine(folder, GraphicsElementDefaults.OnNowNextFileName);

        string seededKey = ConfigElementKey.GraphicsOnNowNextSeeded.Key;
        bool alreadySeeded = await context.ConfigElements.AnyAsync(c => c.Key == seededKey, cancellationToken);

        if (alreadySeeded)
        {
            // Already-seeded installations never revisit the file, so a change to the default would
            // otherwise reach new databases only. Upgrade the ones still carrying an untouched
            // earlier default; anything an operator edited no longer matches and is left alone.
            //
            // Deliberately no CreateDirectory on this branch: before #732 it touched the filesystem
            // not at all, so an already-seeded install stays bootable on a read-only /config.
            await UpgradeUnmodifiedTemplate(fileSystem, target, logger, cancellationToken);
            await EnsureBuiltInElementRow(context, fileSystem, target, cancellationToken);
            return;
        }

        if (!fileSystem.Directory.Exists(folder))
        {
            fileSystem.Directory.CreateDirectory(folder);
        }

        // Adopt an operator's existing file untouched; only write when absent.
        if (!fileSystem.File.Exists(target))
        {
            await fileSystem.File.WriteAllTextAsync(target, OnNowNextYaml, cancellationToken);
        }

        await context.ConfigElements.AddAsync(
            new ConfigElement { Key = seededKey, Value = "true" },
            cancellationToken);
        await context.SaveChangesAsync(cancellationToken);

        await EnsureBuiltInElementRow(context, fileSystem, target, cancellationToken);
    }

    /// <summary>
    /// `RefreshGraphicsElements` is what normally turns a template file into a `GraphicsElement` row,
    /// but it runs on the scheduler/stream-start path -- long after startup. Creating the row here
    /// removes that ordering dependency, so `AttachOnNowNextByDefault` below can never mark itself
    /// done against an element that simply had not been discovered yet.
    /// </summary>
    private static async Task EnsureBuiltInElementRow(
        TvContext context,
        IFileSystem fileSystem,
        string target,
        CancellationToken cancellationToken)
    {
        if (!fileSystem.File.Exists(target))
        {
            return;
        }

        bool exists = await context.GraphicsElements.AnyAsync(e => e.Path == target, cancellationToken);
        if (exists)
        {
            return;
        }

        // Name is display-only (identity is the filename), but leaving it null sorts the built-in
        // element into the unnamed bucket at the bottom of the SPA list until the first refresh.
        await context.GraphicsElements.AddAsync(
            new Core.Domain.GraphicsElement
            {
                Path = target,
                Kind = GraphicsElementKind.Text,
                Name = GraphicsElementDefaults.OnNowNextName
            },
            cancellationToken);
        await context.SaveChangesAsync(cancellationToken);
    }

    /// <summary>
    /// #732: the On Now / Next overlay is a default, not an opt-in. Existing channels predate that
    /// decision, so attach the built-in element to them once.
    /// </summary>
    /// <remarks>
    /// The marker is written only once the built-in element RESOLVES, so an install whose row does
    /// not exist yet is retried on the next startup rather than stranded permanently. Once written,
    /// no channel is ever re-attached. While still armed the backfill cannot tell a deliberately
    /// cleared channel from an untouched one -- a single global flag cannot express both
    /// properties; see <c>graphics.on-now-next-on-by-default</c> for why that trade is made this
    /// way. Every channel created after the marker gets the element from
    /// <c>ChannelGraphicsDefaults.Attach</c> instead, which BOTH create paths call.
    /// </remarks>
    public static async Task AttachOnNowNextByDefault(TvContext context, CancellationToken cancellationToken)
    {
        string key = ConfigElementKey.GraphicsOnNowNextDefaultAttached.Key;
        if (await context.ConfigElements.AnyAsync(c => c.Key == key, cancellationToken))
        {
            return;
        }

        Option<int> maybeElementId = await GetBuiltInElementId(context, cancellationToken);
        if (maybeElementId.IsNone)
        {
            // Nothing to attach TO. Writing the marker here would strand every channel permanently
            // on the one population this exists for, so stay armed and try again next startup.
            return;
        }

        foreach (int elementId in maybeElementId)
        {
            // HLS Direct has no frame pipeline to draw into, so an attachment there would be inert
            // while still reading as "on" in the editor.
            List<int> channelIds = await context.Channels
                .Where(c => c.StreamingMode != StreamingMode.HttpLiveStreamingDirect)
                .Where(c => c.ChannelGraphicsElements.All(cge => cge.GraphicsElementId != elementId))
                .Select(c => c.Id)
                .ToListAsync(cancellationToken);

            foreach (int channelId in channelIds)
            {
                await context.AddAsync(
                    new ChannelGraphicsElement { ChannelId = channelId, GraphicsElementId = elementId },
                    cancellationToken);
            }
        }

        await context.ConfigElements.AddAsync(
            new ConfigElement { Key = key, Value = "true" },
            cancellationToken);
        await context.SaveChangesAsync(cancellationToken);
    }

    /// <summary>
    /// Identity is the filename, never the user-editable Name (the #67 lesson carried into #74).
    /// The Kind is part of it: the five template folders are separate namespaces, so an unrelated
    /// image/motion/subtitle/script element may legitimately be named `on-now-next.yml` too, and
    /// filename alone would hand back whichever row the unordered query happened to return first.
    /// </summary>
    public static async Task<Option<int>> GetBuiltInElementId(
        TvContext context,
        CancellationToken cancellationToken)
    {
        List<(int Id, string Path)> candidates = await context.GraphicsElements
            .Where(e => e.Kind == GraphicsElementKind.Text)
            .Select(e => new { e.Id, e.Path })
            .ToListAsync(cancellationToken)
            .Map(rows => rows.Select(r => (r.Id, r.Path)).ToList());

        var matches = candidates
            .Where(c => System.IO.Path.GetFileName(c.Path) == GraphicsElementDefaults.OnNowNextFileName)
            .OrderBy(c => c.Id)
            .ToList();

        // Lowest id wins if two text templates somehow share the filename, so the choice is stable
        // across restarts rather than dependent on query order.
        return matches.Count == 0 ? Option<int>.None : matches[0].Id;
    }

    private static async Task UpgradeUnmodifiedTemplate(
        IFileSystem fileSystem,
        string target,
        ILogger logger,
        CancellationToken cancellationToken)
    {
        // This runs inside the blocking database-startup path, ahead of DatabaseIsReady(). Before
        // #732 the already-seeded branch never touched the filesystem at all, so an unreadable or
        // read-only template is a state that used to boot fine -- it must not become a failure to
        // start. Cosmetic upgrade, best effort.
        try
        {
            if (!fileSystem.File.Exists(target))
            {
                return;
            }

            string existing = await fileSystem.File.ReadAllTextAsync(target, cancellationToken);
            if (!SupersededDefaults.Any(d => IsSameTemplate(existing, d)))
            {
                return;
            }

            // Write-then-move, never write in place. WriteAllTextAsync truncates first, so an
            // interrupted write (disk full, IO fault, cancellation) would leave a partial file that
            // matches no fingerprint and is therefore never repaired on a later boot -- the overlay
            // would just be gone, permanently, on every channel carrying it.
            //
            // The temp name is random per call. A fixed one is shared by two containers on the same
            // config volume, where one can truncate it while the other is mid-write and then rename
            // the partial file over the live template. The process id is NOT good enough here: the
            // image uses an exec-form ENTRYPOINT, so every container's PID namespace makes this
            // process 1 and every container computes the same name. A random name also means a temp
            // left by a crashed earlier boot is never reused. Only ever delete the path this call
            // created.
            string temp = $"{target}.{fileSystem.Path.GetRandomFileName()}.upgrade.tmp";
            try
            {
                await fileSystem.File.WriteAllTextAsync(temp, OnNowNextYaml, cancellationToken);

                // Deliberately NO in-place fallback when this throws. rename(2) onto a mountpoint
                // is EBUSY, so a single-file bind mount of this template will not be upgraded --
                // accepted, because reaching that case needs a pinned file that is ALSO byte-identical
                // to a shipped default, and the alternative is reintroducing the truncation this
                // whole dance exists to prevent, on every IO fault rather than just that one.
                fileSystem.File.Move(temp, target, true);
            }
            finally
            {
                // Cleanup must never REPLACE the exception that brought us here. Without this inner
                // catch, a delete that throws while unwinding a cancellation swaps the
                // OperationCanceledException for an IOException, which the outer filter then
                // swallows -- so a real shutdown would be silently downgraded to a warning.
                try
                {
                    if (fileSystem.File.Exists(temp))
                    {
                        fileSystem.File.Delete(temp);
                    }
                }
                catch (Exception cleanupEx)
                {
                    logger.LogDebug(cleanupEx, "Could not remove the temporary upgrade file {Path}", temp);
                }
            }
        }
        // Recoverable filesystem faults only. Catching everything would swallow genuinely fatal
        // runtime failures (OutOfMemory and friends) and continue booting a compromised process;
        // letting IO escape would turn a file permission into a restart loop. Cancellation
        // propagates so shutdown is not swallowed.
        // OperationCanceledException is deliberately absent from this list so a real shutdown
        // propagates -- but only a real one: an OCE raised while the token is NOT cancelled is just
        // another faulty read, and letting it escape is the restart loop this catch exists to stop.
        catch (Exception ex) when ((ex is IOException
                                       or UnauthorizedAccessException
                                       or NotSupportedException
                                       or System.Security.SecurityException)
                                   || (ex is OperationCanceledException
                                       && !cancellationToken.IsCancellationRequested))
        {
            logger.LogWarning(
                ex,
                "Could not upgrade the built-in graphics template at {Path}; leaving it as-is",
                target);
        }
    }

    // Compare on content, ignoring the line endings and trailing whitespace an editor or a volume
    // mount may rewrite. This is a fingerprint check, not a parse: anything that is not one of our
    // own shipped defaults must fall through untouched.
    private static bool IsSameTemplate(string left, string right) =>
        string.Equals(Normalize(left), Normalize(right), StringComparison.Ordinal);

    private static string Normalize(string value) =>
        value.Replace("\r\n", "\n", StringComparison.Ordinal).TrimEnd();
}