using System;
using System.Collections.Generic;

/*
 * Copyright 2007 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace com.google.zxing.qrcode.detector
{

	using NotFoundException = com.google.zxing.NotFoundException;
	using ResultPointCallback = com.google.zxing.ResultPointCallback;
	using BitMatrix = com.google.zxing.common.BitMatrix;


	/// <summary>
	/// <p>This class attempts to find alignment patterns in a QR Code. Alignment patterns look like finder
	/// patterns but are smaller and appear at regular intervals throughout the image.</p>
	/// 
	/// <p>At the moment this only looks for the bottom-right alignment pattern.</p>
	/// 
	/// <p>This is mostly a simplified copy of <seealso cref="FinderPatternFinder"/>. It is copied,
	/// pasted and stripped down here for maximum performance but does unfortunately duplicate
	/// some code.</p>
	/// 
	/// <p>This class is thread-safe but not reentrant. Each thread must allocate its own object.</p>
	/// 
	/// @author Sean Owen
	/// </summary>
	internal sealed class AlignmentPatternFinder
	{

	  private readonly BitMatrix image;
	  private readonly IList<AlignmentPattern> possibleCenters;
	  private readonly int startX;
	  private readonly int startY;
	  private readonly int width;
	  private readonly int height;
	  private readonly float moduleSize;
	  private readonly int[] crossCheckStateCount;
	  private readonly ResultPointCallback resultPointCallback;

	  /// <summary>
	  /// <p>Creates a finder that will look in a portion of the whole image.</p>
	  /// </summary>
	  /// <param name="image"> image to search </param>
	  /// <param name="startX"> left column from which to start searching </param>
	  /// <param name="startY"> top row from which to start searching </param>
	  /// <param name="width"> width of region to search </param>
	  /// <param name="height"> height of region to search </param>
	  /// <param name="moduleSize"> estimated module size so far </param>
	  internal AlignmentPatternFinder(BitMatrix image, int startX, int startY, int width, int height, float moduleSize, ResultPointCallback resultPointCallback)
	  {
		this.image = image;
		this.possibleCenters = new List<AlignmentPattern>(5);
		this.startX = startX;
		this.startY = startY;
		this.width = width;
		this.height = height;
		this.moduleSize = moduleSize;
		this.crossCheckStateCount = new int[3];
		this.resultPointCallback = resultPointCallback;
	  }

	  /// <summary>
	  /// <p>This method attempts to find the bottom-right alignment pattern in the image. It is a bit messy since
	  /// it's pretty performance-critical and so is written to be fast foremost.</p>
	  /// </summary>
	  /// <returns> <seealso cref="AlignmentPattern"/> if found </returns>
	  /// <exception cref="NotFoundException"> if not found </exception>
//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in .NET:
//ORIGINAL LINE: AlignmentPattern find() throws com.google.zxing.NotFoundException
	  internal AlignmentPattern find()
	  {
		int startX = this.startX;
		int height = this.height;
		int maxJ = startX + width;
		int middleI = startY + (height >> 1);
		// We are looking for black/white/black modules in 1:1:1 ratio;
		// this tracks the number of black/white/black modules seen so far
		int[] stateCount = new int[3];
		for (int iGen = 0; iGen < height; iGen++)
		{
		  // Search from middle outwards
		  int i = middleI + ((iGen & 0x01) == 0 ? (iGen + 1) >> 1 : -((iGen + 1) >> 1));
		  stateCount[0] = 0;
		  stateCount[1] = 0;
		  stateCount[2] = 0;
		  int j = startX;
		  // Burn off leading white pixels before anything else; if we start in the middle of
		  // a white run, it doesn't make sense to count its length, since we don't know if the
		  // white run continued to the left of the start point
		  while (j < maxJ && !image.get(j, i))
		  {
			j++;
		  }
		  int currentState = 0;
		  while (j < maxJ)
		  {
			if (image.get(j, i))
			{
			  // Black pixel
			  if (currentState == 1) // Counting black pixels
			  {
				stateCount[currentState]++;
			  } // Counting white pixels
			  else
			  {
				if (currentState == 2) // A winner?
				{
				  if (foundPatternCross(stateCount)) // Yes
				  {
					AlignmentPattern confirmed = handlePossibleCenter(stateCount, i, j);
					if (confirmed != null)
					{
					  return confirmed;
					}
				  }
				  stateCount[0] = stateCount[2];
				  stateCount[1] = 1;
				  stateCount[2] = 0;
				  currentState = 1;
				}
				else
				{
				  stateCount[++currentState]++;
				}
			  }
			} // White pixel
			else
			{
			  if (currentState == 1) // Counting black pixels
			  {
				currentState++;
			  }
			  stateCount[currentState]++;
			}
			j++;
		  }
		  if (foundPatternCross(stateCount))
		  {
			AlignmentPattern confirmed = handlePossibleCenter(stateCount, i, maxJ);
			if (confirmed != null)
			{
			  return confirmed;
			}
		  }

		}

		// Hmm, nothing we saw was observed and confirmed twice. If we had
		// any guess at all, return it.
		if (possibleCenters.Count > 0)
		{
		  return possibleCenters[0];
		}

		throw NotFoundException.NotFoundInstance;
	  }

	  /// <summary>
	  /// Given a count of black/white/black pixels just seen and an end position,
	  /// figures the location of the center of this black/white/black run.
	  /// </summary>
	  private static float centerFromEnd(int[] stateCount, int end)
	  {
		return (float)(end - stateCount[2]) - stateCount[1] / 2.0f;
	  }

	  /// <param name="stateCount"> count of black/white/black pixels just read </param>
	  /// <returns> true iff the proportions of the counts is close enough to the 1/1/1 ratios
	  ///         used by alignment patterns to be considered a match </returns>
	  private bool foundPatternCross(int[] stateCount)
	  {
		float moduleSize = this.moduleSize;
		float maxVariance = moduleSize / 2.0f;
		for (int i = 0; i < 3; i++)
		{
		  if (Math.Abs(moduleSize - stateCount[i]) >= maxVariance)
		  {
			return false;
		  }
		}
		return true;
	  }

	  /// <summary>
	  /// <p>After a horizontal scan finds a potential alignment pattern, this method
	  /// "cross-checks" by scanning down vertically through the center of the possible
	  /// alignment pattern to see if the same proportion is detected.</p>
	  /// </summary>
	  /// <param name="startI"> row where an alignment pattern was detected </param>
	  /// <param name="centerJ"> center of the section that appears to cross an alignment pattern </param>
	  /// <param name="maxCount"> maximum reasonable number of modules that should be
	  /// observed in any reading state, based on the results of the horizontal scan </param>
	  /// <returns> vertical center of alignment pattern, or <seealso cref="Float#NaN"/> if not found </returns>
	  private float crossCheckVertical(int startI, int centerJ, int maxCount, int originalStateCountTotal)
	  {
		BitMatrix image = this.image;

		int maxI = image.Height;
		int[] stateCount = crossCheckStateCount;
		stateCount[0] = 0;
		stateCount[1] = 0;
		stateCount[2] = 0;

		// Start counting up from center
		int i = startI;
		while (i >= 0 && image.get(centerJ, i) && stateCount[1] <= maxCount)
		{
		  stateCount[1]++;
		  i--;
		}
		// If already too many modules in this state or ran off the edge:
		if (i < 0 || stateCount[1] > maxCount)
		{
		  return float.NaN;
		}
		while (i >= 0 && !image.get(centerJ, i) && stateCount[0] <= maxCount)
		{
		  stateCount[0]++;
		  i--;
		}
		if (stateCount[0] > maxCount)
		{
		  return float.NaN;
		}

		// Now also count down from center
		i = startI + 1;
		while (i < maxI && image.get(centerJ, i) && stateCount[1] <= maxCount)
		{
		  stateCount[1]++;
		  i++;
		}
		if (i == maxI || stateCount[1] > maxCount)
		{
		  return float.NaN;
		}
		while (i < maxI && !image.get(centerJ, i) && stateCount[2] <= maxCount)
		{
		  stateCount[2]++;
		  i++;
		}
		if (stateCount[2] > maxCount)
		{
		  return float.NaN;
		}

		int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
		if (5 * Math.Abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal)
		{
		  return float.NaN;
		}

		return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i) : float.NaN;
	  }

	  /// <summary>
	  /// <p>This is called when a horizontal scan finds a possible alignment pattern. It will
	  /// cross check with a vertical scan, and if successful, will see if this pattern had been
	  /// found on a previous horizontal scan. If so, we consider it confirmed and conclude we have
	  /// found the alignment pattern.</p>
	  /// </summary>
	  /// <param name="stateCount"> reading state module counts from horizontal scan </param>
	  /// <param name="i"> row where alignment pattern may be found </param>
	  /// <param name="j"> end of possible alignment pattern in row </param>
	  /// <returns> <seealso cref="AlignmentPattern"/> if we have found the same pattern twice, or null if not </returns>
	  private AlignmentPattern handlePossibleCenter(int[] stateCount, int i, int j)
	  {
		int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
		float centerJ = centerFromEnd(stateCount, j);
		float centerI = crossCheckVertical(i, (int) centerJ, 2 * stateCount[1], stateCountTotal);
		if (!float.IsNaN(centerI))
		{
		  float estimatedModuleSize = (float)(stateCount[0] + stateCount[1] + stateCount[2]) / 3.0f;
		  foreach (AlignmentPattern center in possibleCenters)
		  {
			// Look for about the same center and module size:
			if (center.aboutEquals(estimatedModuleSize, centerI, centerJ))
			{
			  return center.combineEstimate(centerI, centerJ, estimatedModuleSize);
			}
		  }
		  // Hadn't found this before; save it
		  AlignmentPattern point = new AlignmentPattern(centerJ, centerI, estimatedModuleSize);
		  possibleCenters.Add(point);
		  if (resultPointCallback != null)
		  {
			resultPointCallback.foundPossibleResultPoint(point);
		  }
		}
		return null;
	  }

	}

}