using System;

using UnityEngine;

using Framework.Services;

namespace Framework.Support {

  /// <summary>Stores a material to be assigned to a renderer's material slot</summary>
  [Serializable]
  public class MaterialAssignment {

    /// <summary>Renderer on which the material assignment will take place</summary>
    /// <remarks>
    ///   This can be null, in which case the material will be assigned to the renderer
    ///   to which the MaterialRandomizer has been added.
    /// </remarks>
    public Renderer Renderer;

    /// <summary>Index of the slot to which hte material will be assigned</summary>
    public int SlotIndex;

    /// <summary>Material that will be assigned to the slot</summary>
    public Material Material;

  }

  /// <summary>Set of material assignments that can be picked by the randomizer</summary>
  [Serializable]
  public class MaterialAssignmentSet {

    /// <summary>Likelihood that this material set will be chosen</summary>
    /// <remarks>
    ///   <para>
    ///     The fraction of these points against the sum of all points becomes the likelihood
    ///     with which this material will be chosen.
    ///   </para>
    ///   <para>
    ///     Example 1: Two assignments, both with Likelihood 1: each assignment has
    ///     a 50% chance of being selected.
    ///   </para>
    ///   <para>
    ///     Example 2: Two assignments, with with Likelihood 10, the other 20. The one with
    ///     likelihood 20 will have a 67% chance (20 out of 30) of being selected.
    ///   </para>
    /// </remarks>
    public int Likelihood;

    /// <summary>Material assignments this set consists of</summary>
    public MaterialAssignment[] Assignments;

  }

  /// <summary>Assigns a random set of materials to a mesh upon load</summary>
  public class MaterialRandomizer : ScriptComponent {

    /// <summary>Material variants that can be assigned to the randomizer's renderer</summary>
    public MaterialAssignmentSet[] Variants;

    /// <summary>Called once before the game object is updated for the first time</summary>
    protected void Start() {
      if((this.Variants == null) || (this.Variants.Length == 0)) {
        Debug.LogWarning(
          "Material randomizer component on '" + name + "' has no material sets " +
          "sets defined. Randomizer will do nothing"
        );
        return;
      }

      int variantIndex = pickVariant();
      applyMaterialSet(this.Variants[variantIndex]);
    }

    /// <summary>Picks a random material variant using the defined likelihoods</summary>
    /// <returns>The picked material variant</returns>
    private int pickVariant() {

      // Sum up the likelihoods of all defined variants
      int sum = this.Variants[0].Likelihood;
      for(int index = 1; index < this.Variants.Length; ++index) {
        sum += this.Variants[index].Likelihood;
      }

      // Pick a random number within that sum
      int choice = UnityEngine.Random.Range(0, sum);

      // Now figure out which variant this number falls into
      sum = 0;
      for(int index = 0; index < this.Variants.Length; ++index) {
        sum += this.Variants[0].Likelihood;
        if(choice < sum) {
          return index;
        }
      }

      // Never reached, but static analysis can't see this
      return 0;

    }

    /// <summary>Apply the specified material set to the game object's renderer</summary>
    /// <param name="set">Material set that will be applied</param>
    private void applyMaterialSet(MaterialAssignmentSet set) {
      if(set.Assignments == null) {
        return;
      }

      bool warningDisplayed = false;
      Renderer ownRenderer = null;
      for(int index = 0; index < set.Assignments.Length; ++index) {
        Renderer renderer;

        // If there's no renderer defined, the assignment goes to our own renderer
        if(set.Assignments[index].Renderer == null) {

          // If we alaready displayed a warning, we know our own renderer is missing
          // and can stop trying right away
          if(warningDisplayed) {
            continue;
          }

          // If we haven't looked up our renderer yet, see if the game object to which
          // we're attached has a renderer component.
          if(ownRenderer == null) {
            ownRenderer = GetComponent<Renderer>();
            if(ownRenderer == null) {
              Debug.LogWarning(
                "MaterialRandomizer on '" + name + "' does not have a renderer to " +
                "assign one or more materials to."
              );
              warningDisplayed = true;
              continue;
            }
          }

          renderer = ownRenderer;

        } else { // Renderer has been specified explicitly, use it

          renderer = set.Assignments[index].Renderer;

        }

        // We've got our renderer, do the material assignment (which requires us to replace
        // the whole array because the Unity developers decided to return a copy of
        // the material array instead of exposing a proxy IList)
        Material[] materials = renderer.materials;
        int slotIndex = set.Assignments[index].SlotIndex;
        materials[slotIndex] = set.Assignments[index].Material;
        renderer.materials = materials;

      }
    }

  }

} // namespace Framework.Support