using Godot;
using System;

using Rokojori.Extensions;
namespace Rokojori
{
  /** How one control-map texel's 32 bits are divided up.

      Terrain3D fixes this in shader macros. Here it is a Resource, for one
      reason: it is the <marked>only</marked> description of the layout, and both
      sides read it. The pack pass and the decoders in
      Shading/Library/ControlMap.gdshaderinc ( through PushToMaterial ) cannot
      drift apart, because neither of them knows an offset - they are both told.

      Hard-coding the offsets would be an optimization, and the cost it buys is
      a handful of shifts per fragment against the certainty that a layout change
      means editing two files that have to agree.

      <marked>Only bit sizes are authored.</marked> Offsets are derived by packing
      the fields from bit 0 upwards in a fixed order, so a layout is always
      internally valid and a widened field pushes the rest along rather than
      silently overlapping one.

      THE WIDTHS, AND WHY THEY ARE BETTER THAN TERRAIN3D'S
      ------------------------------------------------------------------------
      The default adds up to 27 of 32 bits - the same budget Terrain3D spends -
      but buys 32 rotation steps instead of 16 and 16 scale steps instead of 8,
      because the base/overlay blend drops from 8 bits to 6.

      That is affordable here and not there: with the weight-stack edit format the
      blend is <marked>derived</marked> at pack time from the two largest texture
      weights rather than authored by hand, and 64 steps of crossfade is already
      past what a ground transition can show. Terrain3D has to leave room for
      someone painting a blend value directly.

      The 5 spare bits are deliberately left spare. A custom channel should be
      easy to add; none is built.

      OVERFLOW IS THE USER'S PROBLEM
      ------------------------------------------------------------------------
      A layout past 32 bits warns and lets the high fields truncate. It does not
      clamp and it does not rearrange, because either one would silently give the
      user a layout they did not ask for. Safe to be this blunt because nothing
      is ever persisted as control-map pixel data - the map is generated from the
      layer stack every session, so re-rendering is the entire migration.
  */
  [Tool]
  [GlobalClass]
  public partial class ControlMapFormat:Resource
  {
    public const int TotalBits = 32;

    /* THE AUTHORED WIDTHS
       ------------------------------------------------------------------------
       FIELD ORDER is low bits first: base, overlay, blend, rotation, scale,
       hole, navigable. The order itself is arbitrary - nothing reads a field
       without being told where it is - but it is fixed rather than exported,
       because a reorderable order is a second thing that could disagree with
       itself and buys nothing.
    */

    BitSizeEnum _numTexturesBits = BitSizeEnum.Bits5_32Values;

    /** How many ground textures an index can reach, for <marked>both</marked>
        the base and the overlay index.

        One width rather than two, even though Terrain3D-style layouts sometimes
        narrow the overlay to buy bits back. Two widths that can disagree is a
        state where a texture is paintable as a base and not as an overlay, which
        is a bug report waiting to happen for a few bits that the blend field
        already gave back.
    */
    [Export]
    public BitSizeEnum numTexturesBits
    {
      get => _numTexturesBits;
      set { _numTexturesBits = value; EmitChanged(); }
    }

    BitSizeEnum _textureBlendBits = BitSizeEnum.Bits6_64Values;

    /** Resolution of the base-to-overlay crossfade. Derived at pack time from
        the weight stack, not authored, which is why 6 bits is enough.
    */
    [Export]
    public BitSizeEnum textureBlendBits
    {
      get => _textureBlendBits;
      set { _textureBlendBits = value; EmitChanged(); }
    }

    BitSizeEnum _rotationBits = BitSizeEnum.Bits5_32Values;

    /** How many uv rotation steps over a full turn. 5 bits is 32 steps of
        11.25 degrees.
    */
    [Export]
    public BitSizeEnum rotationBits
    {
      get => _rotationBits;
      set { _rotationBits = value; EmitChanged(); }
    }

    BitSizeEnum _scaleBits = BitSizeEnum.Bits4_16Values;

    /** How many uv scale steps. The value is scaleMin + raw * scaleStep. */
    [Export]
    public BitSizeEnum scaleBits
    {
      get => _scaleBits;
      set { _scaleBits = value; EmitChanged(); }
    }

    bool _holeFlag = true;

    /** Whether the terrain is absent here. The consumer discards or writes a
        NaN vertex; see the preview shader.

        A bool rather than a width, because a 3-bit hole flag was never a
        meaningful thing to be able to ask for.
    */
    [Export]
    public bool holeFlag
    {
      get => _holeFlag;
      set { _holeFlag = value; EmitChanged(); }
    }

    bool _navigationFlag = true;

    /** Whether the terrain is walkable here. Never reaches the shader's output -
        it is read by the navmesh bake and by the flag read in ControlMap_shade.
    */
    [Export]
    public bool navigationFlag
    {
      get => _navigationFlag;
      set { _navigationFlag = value; EmitChanged(); }
    }

    [ExportGroup( "Scale Mapping" )]

    float _scaleMin = 1;

    /** The uv multiplier a raw scale of 0 means. Deliberately 1 by default, so
        an all-zero control map - which is what a freshly allocated one is -
        renders every texture at its authored size rather than at some arbitrary
        step. Every other field is neutral at 0 for the same reason.
    */
    [Export]
    public float scaleMin
    {
      get => _scaleMin;
      set { _scaleMin = value; EmitChanged(); }
    }

    float _scaleStep = 0.25f;

    /** How much one scale step adds to the multiplier. With the default 4 bits
        and 0.25, the range is 1.0 to 4.75 - finer tiling only. Set a negative
        step with a higher scaleMin to tile coarser instead.
    */
    [Export]
    public float scaleStep
    {
      get => _scaleStep;
      set { _scaleStep = value; EmitChanged(); }
    }


    /* DERIVED WIDTHS
       ------------------------------------------------------------------------
       The authored values as plain bit counts. Named ...BitCount throughout so
       there is never a question of which of the two a name means.
    */

    public int baseBitCount => (int) numTexturesBits;
    public int overlayBitCount => (int) numTexturesBits;
    public int blendBitCount => (int) textureBlendBits;
    public int rotationBitCount => (int) rotationBits;
    public int scaleBitCount => (int) scaleBits;
    public int holeBitCount => holeFlag ? 1 : 0;
    public int navigableBitCount => navigationFlag ? 1 : 0;


    /* DERIVED OFFSETS
       ------------------------------------------------------------------------
       Each field is ( offset, bits ), which is exactly the ivec2 the shader
       takes. A bit count of 0 gives a field the shader reads as absent.
    */

    public int baseOffset => 0;
    public int overlayOffset => baseOffset + baseBitCount;
    public int blendOffset => overlayOffset + overlayBitCount;
    public int rotationOffset => blendOffset + blendBitCount;
    public int scaleOffset => rotationOffset + rotationBitCount;
    public int holeOffset => scaleOffset + scaleBitCount;
    public int navigableOffset => holeOffset + holeBitCount;

    public int usedBits => navigableOffset + navigableBitCount;

    /** True when the layout does not fit. Nothing enforces it - the widths are
        individually legal but their sum is not checked - so the generator checks
        this and warns rather than silently writing a flag into nowhere.
    */
    public bool isOverflowing => usedBits > TotalBits;

    public Vector2I baseField => new Vector2I( baseOffset, baseBitCount );
    public Vector2I overlayField => new Vector2I( overlayOffset, overlayBitCount );
    public Vector2I blendField => new Vector2I( blendOffset, blendBitCount );
    public Vector2I rotationField => new Vector2I( rotationOffset, rotationBitCount );
    public Vector2I scaleField => new Vector2I( scaleOffset, scaleBitCount );
    public Vector2I holeField => new Vector2I( holeOffset, holeBitCount );
    public Vector2I navigableField => new Vector2I( navigableOffset, navigableBitCount );

    /** How many textures an index can address. */
    public int maxTextures => baseBitCount <= 0 ? 1 : 1 << baseBitCount;


    /* PACKING
       ------------------------------------------------------------------------
       The CPU half. Mirrors ControlMap_extract and the decoders on top of it -
       and mirrors them by construction, since both are driven by the same
       offsets above.

       The pack pass itself is a compute shader and does none of this; these stay
       because a seeded test, a navmesh query and a debug pattern all need to
       speak the format without a GPU dispatch.
    */

    static uint Mask( int bits )
    {
      if ( bits <= 0 )
      {
        return 0;
      }

      return bits >= 32 ? uint.MaxValue : ( 1u << bits ) - 1u;
    }

    static uint Write( uint control, int offset, int bits, int value )
    {
      if ( bits <= 0 )
      {
        return control;
      }

      var mask = Mask( bits );
      var raw = (uint) Mathf.Clamp( value, 0, (int) mask ) & mask;

      return control | ( raw << offset );
    }

    public int Read( uint control, Vector2I field )
    {
      if ( field.Y <= 0 )
      {
        return 0;
      }

      return (int) ( ( control >> field.X ) & Mask( field.Y ) );
    }

    /** A blend of 0..1 as its raw field value. The maximum maps to the field's
        maximum, so both endpoints are reachable.
    */
    public int BlendToRaw( float blend )
    {
      if ( blendBitCount <= 0 )
      {
        return 0;
      }

      return Mathf.RoundToInt( Mathf.Clamp( blend, 0, 1 ) * Mask( blendBitCount ) );
    }

    public float RawToBlend( int raw )
    {
      return blendBitCount <= 0 ? 0 : raw / (float) Mask( blendBitCount );
    }

    /** A rotation in radians as its raw field value. Divided by the step
        <marked>count</marked> rather than by the maximum, because the quantity
        wraps - mapping the last step onto a full turn would make it a duplicate
        of 0 and waste it.
    */
    public int RotationToRaw( float radians )
    {
      if ( rotationBitCount <= 0 )
      {
        return 0;
      }

      var steps = 1 << rotationBitCount;
      var turns = radians / Mathf.Tau;

      // Mathf.PosMod so a negative angle wraps rather than clamping to 0.
      return Mathf.PosMod( Mathf.RoundToInt( turns * steps ), steps );
    }

    public float RawToRotation( int raw )
    {
      return rotationBitCount <= 0 ? 0 : raw / (float) ( 1 << rotationBitCount ) * Mathf.Tau;
    }

    /** A uv multiplier as its raw field value, inverting the shader's
        scaleMin + raw * scaleStep.
    */
    public int ScaleToRaw( float scale )
    {
      if ( scaleBitCount <= 0 || Mathf.Abs( scaleStep ) < 0.000001f )
      {
        return 0;
      }

      return Mathf.RoundToInt( ( scale - scaleMin ) / scaleStep );
    }

    public float RawToScale( int raw )
    {
      return scaleBitCount <= 0 ? 1 : scaleMin + raw * scaleStep;
    }

    /** One texel's control value.

        blend is 0..1, rotation is radians, scale is the uv multiplier - the same
        units the decoders hand back, so a caller never sees a raw field value
        unless it wants to.
    */
    public uint Pack(
      int baseIndex, int overlayIndex, float blend, float rotation, float scale,
      bool hole = false, bool navigable = true
    )
    {
      return PackRaw(
        baseIndex, overlayIndex,
        BlendToRaw( blend ), RotationToRaw( rotation ), ScaleToRaw( scale ),
        hole, navigable
      );
    }

    /** Pack from raw field values, for a caller that is stepping a field rather
        than expressing a quantity - a debug pattern walking every rotation, for
        instance.
    */
    public uint PackRaw(
      int baseIndex, int overlayIndex, int blendRaw, int rotationRaw, int scaleRaw,
      bool hole = false, bool navigable = true
    )
    {
      uint control = 0;

      control = Write( control, baseOffset, baseBitCount, baseIndex );
      control = Write( control, overlayOffset, overlayBitCount, overlayIndex );
      control = Write( control, blendOffset, blendBitCount, blendRaw );
      control = Write( control, rotationOffset, rotationBitCount, rotationRaw );
      control = Write( control, scaleOffset, scaleBitCount, scaleRaw );
      control = Write( control, holeOffset, holeBitCount, hole ? 1 : 0 );
      control = Write( control, navigableOffset, navigableBitCount, navigable ? 1 : 0 );

      return control;
    }

    /** The neutral texel: texture 0, no overlay, no rotation, scale 1, not a
        hole, navigable. Identical to PackRaw with every raw value 0 except the
        navigable bit, which is what makes a zero-filled map sane.
    */
    public uint packedDefault => PackRaw( 0, 0, 0, 0, 0, false, true );


    /* STORAGE
       ------------------------------------------------------------------------
       The map is a single-channel float texture, so a control value travels as
       the float with those exact bits. Not a conversion - a reinterpretation,
       undone on the GPU by floatBitsToUint.

       R32F and not R32UI, and this is not a preference: Godot's Image has no
       integer formats, and texture_rd_create maps an RD format to an
       Image::Format before wrapping it - so no integer-format texture can ever
       become a Texture2D. Measured in the phase 0 probe. imageStore to an r32f
       target through uintBitsToFloat was measured bit-exact for both NaN
       patterns, so the reinterpretation is safe through a compute write.

       Which is also why the map must never be filtered, mipmapped or stored in
       any format that renormalizes: a control value is frequently a NaN or a
       denormal bit pattern as a float, and anything that does arithmetic on it
       is free to flush it to zero.
    */

    public static float ToStorage( uint control )
    {
      return BitConverter.Int32BitsToSingle( unchecked( (int) control ) );
    }

    public static uint FromStorage( float stored )
    {
      return unchecked( (uint) BitConverter.SingleToInt32Bits( stored ) );
    }


    /** Pushes the layout and its value mapping onto a material declaring
        ControlMapShader's block.
    */
    public void PushToMaterial( Material material )
    {
      if ( material == null )
      {
        return;
      }

      ControlMapShader.baseField.Set( material, baseField );
      ControlMapShader.overlayField.Set( material, overlayField );
      ControlMapShader.blendField.Set( material, blendField );

      // The one place the two vocabularies meet. The shader side calls this the
      // angle field, because what it decodes is radians; the authoring side
      // calls it rotation, because what the user picks is how finely a texel can
      // be turned. Mapped here rather than renamed on either side - the include
      // is a render-side contract that predates this resource, and its symbols
      // are deliberately left untouched so that the first time Godot compiles it
      // is a test of the include alone.
      ControlMapShader.angleField.Set( material, rotationField );

      ControlMapShader.scaleField.Set( material, scaleField );
      ControlMapShader.holeField.Set( material, holeField );
      ControlMapShader.navigableField.Set( material, navigableField );

      ControlMapShader.scaleMin.Set( material, scaleMin );
      ControlMapShader.scaleStep.Set( material, scaleStep );
    }
  }
}