using DatReaderWriter.DBObjs;
using WorldBuilder.Shared.Models;

namespace AcDream.Core.World;

/// <summary>
/// Bridges acdream's dat types into WorldBuilder's data shapes for the
/// Phase N rendering migration. See
/// <c>docs/architecture/worldbuilder-inventory.md</c> for the full strategy.
/// </summary>
internal static class WbSceneryAdapter
{
    private const int VerticesPerSide = 9;
    private const int TerrainSize     = VerticesPerSide * VerticesPerSide; // 81

    /// <summary>
    /// Builds a 9×9 = 81-entry <see cref="TerrainEntry"/> array from a
    /// <see cref="LandBlock"/>'s packed terrain bits + height bytes. WB's
    /// <c>TerrainUtils.OnRoad</c> / <c>GetNormal</c> / <c>GetHeight</c>
    /// consume this shape.
    ///
    /// Field mapping (<c>TerrainInfo</c> → <see cref="TerrainEntry"/>):
    ///   <c>TerrainInfo.Road</c>    (bits 0-1)   → <see cref="TerrainEntry.Road"/>
    ///   <c>TerrainInfo.Type</c>    (bits 2-6)   → <see cref="TerrainEntry.Type"/>
    ///   <c>TerrainInfo.Scenery</c> (bits 11-15) → <see cref="TerrainEntry.Scenery"/>
    ///   <c>LandBlock.Height[i]</c>              → <see cref="TerrainEntry.Height"/>
    /// </summary>
    /// <remarks>
    /// No runtime length guards are needed here because
    /// <c>DatReaderWriter.DBObjs.LandBlock</c>'s default constructor
    /// self-initializes both <c>Terrain</c> and <c>Height</c> to fixed-length
    /// arrays of exactly 81 elements (9×9 vertices per landblock). Any caller
    /// that constructs a synthetic <see cref="LandBlock"/> with partial arrays
    /// will receive an <see cref="IndexOutOfRangeException"/> at the first
    /// mis-sized index, which is the correct fast-fail behaviour for a
    /// contract violation of this kind.
    /// </remarks>
    public static TerrainEntry[] BuildTerrainEntries(LandBlock block)
    {
        ArgumentNullException.ThrowIfNull(block);

        var entries = new TerrainEntry[TerrainSize];
        for (int i = 0; i < TerrainSize; i++)
        {
            var ti = block.Terrain[i];
            entries[i] = new TerrainEntry(
                height:     block.Height[i],
                texture:    (byte)ti.Type,
                scenery:    ti.Scenery,
                road:       ti.Road,
                encounters: null);
        }
        return entries;
    }
}