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/*
 * Copyright 2019 and onwards Makoto Yui
 *
 * 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.
 */
package matrix4j.matrix.sparse.floats;

import matrix4j.matrix.ColumnMajorFloatMatrix;
import matrix4j.matrix.builders.CSCMatrixBuilder;
import matrix4j.utils.lang.ArrayUtils;
import matrix4j.utils.lang.Preconditions;
import matrix4j.vector.Vector;
import matrix4j.vector.VectorProcedure;

import java.util.Arrays;

import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;

/**
 * Compressed Sparse Column matrix optimized for column major access.
 *
 * @link http://netlib.org/linalg/html_templates/node92.html#SECTION00931200000000000000
 */
public final class CSCFloatMatrix extends ColumnMajorFloatMatrix {

    @Nonnull
    private final int[] columnPointers;
    @Nonnull
    private final int[] rowIndices;
    @Nonnull
    private final float[] values;

    private final int numRows;
    private final int numColumns;
    private final int nnz;

    public CSCFloatMatrix(@Nonnull int[] columnPointers, @Nonnull int[] rowIndices,
            @Nonnull float[] values, int numRows, int numColumns) {
        super();
        Preconditions.checkArgument(columnPointers.length >= 1,
            "rowPointers must be greater than 0: " + columnPointers.length);
        Preconditions.checkArgument(rowIndices.length == values.length, "#rowIndices ("
                + rowIndices.length + ") must be equals to #values (" + values.length + ")");
        this.columnPointers = columnPointers;
        this.rowIndices = rowIndices;
        this.values = values;
        this.numRows = numRows;
        this.numColumns = numColumns;
        this.nnz = values.length;
    }

    @Nonnull
    public int[] getColumnPointers() {
        return columnPointers;
    }

    @Nonnull
    public int[] getRowIndices() {
        return rowIndices;
    }

    @Nonnull
    public float[] getValues() {
        return values;
    }

    @Override
    public boolean isSparse() {
        return true;
    }

    @Override
    public boolean readOnly() {
        return true;
    }

    @Override
    public boolean swappable() {
        return false;
    }

    @Override
    public int nnz() {
        return nnz;
    }

    @Override
    public int numRows() {
        return numRows;
    }

    @Override
    public int numColumns() {
        return numColumns;
    }

    @Override
    public int numColumns(final int row) {
        checkRowIndex(row, numRows);

        return ArrayUtils.count(rowIndices, row);
    }

    @Override
    public double[] getRow(final int index) {
        checkRowIndex(index, numRows);

        final double[] row = new double[numColumns];

        final int numCols = columnPointers.length - 1;
        for (int j = 0; j < numCols; j++) {
            final int k = Arrays.binarySearch(rowIndices, columnPointers[j], columnPointers[j + 1],
                index);
            if (k >= 0) {
                row[j] = values[k];
            }
        }

        return row;
    }

    @Override
    public double[] getRow(final int index, @Nonnull final double[] dst) {
        checkRowIndex(index, numRows);

        final int last = Math.min(dst.length, columnPointers.length - 1);
        for (int j = 0; j < last; j++) {
            final int k = Arrays.binarySearch(rowIndices, columnPointers[j], columnPointers[j + 1],
                index);
            if (k >= 0) {
                dst[j] = values[k];
            } else {
                dst[j] = 0.d;
            }
        }
        for (int j = last; j < dst.length; j++) {
            dst[j] = 0.d;
        }

        return dst;
    }

    @Override
    public float[] getRow(final int index, @Nonnull final float[] dst) {
        checkRowIndex(index, numRows);

        final int last = Math.min(dst.length, columnPointers.length - 1);
        for (int j = 0; j < last; j++) {
            final int k = Arrays.binarySearch(rowIndices, columnPointers[j], columnPointers[j + 1],
                index);
            if (k >= 0) {
                dst[j] = values[k];
            } else {
                dst[j] = 0.f;
            }
        }
        for (int j = last; j < dst.length; j++) {
            dst[j] = 0.f;
        }

        return dst;
    }

    @Override
    public void getRow(final int index, @Nonnull final Vector row) {
        checkRowIndex(index, numRows);
        row.clear();

        for (int j = 0, last = columnPointers.length - 1; j < last; j++) {
            final int k = Arrays.binarySearch(rowIndices, columnPointers[j], columnPointers[j + 1],
                index);
            if (k >= 0) {
                float v = values[k];
                row.set(j, v);
            }
        }
    }

    @Override
    public float get(final int row, final int col, final float defaultValue) {
        checkIndex(row, col, numRows, numColumns);

        int index = getIndex(row, col);
        if (index < 0) {
            return defaultValue;
        }
        return values[index];
    }

    @Override
    public float getAndSet(final int row, final int col, final float value) {
        checkIndex(row, col, numRows, numColumns);

        final int index = getIndex(row, col);
        if (index < 0) {
            throw new UnsupportedOperationException(
                "Cannot update value in row " + row + ", col " + col);
        }

        float old = values[index];
        values[index] = value;
        return old;
    }

    @Override
    public void set(final int row, final int col, final float value) {
        checkIndex(row, col, numRows, numColumns);

        final int index = getIndex(row, col);
        if (index < 0) {
            throw new UnsupportedOperationException(
                "Cannot update value in row " + row + ", col " + col);
        }
        values[index] = value;
    }

    private int getIndex(@Nonnegative final int row, @Nonnegative final int col) {
        int leftIn = columnPointers[col];
        int rightEx = columnPointers[col + 1];
        final int index = Arrays.binarySearch(rowIndices, leftIn, rightEx, row);
        if (index >= 0 && index >= values.length) {
            throw new IndexOutOfBoundsException(
                "Value index " + index + " out of range " + values.length);
        }
        return index;
    }

    @Override
    public void swap(final int row1, final int row2) {
        throw new UnsupportedOperationException();
    }

    @Override
    public void eachInColumn(final int col, @Nonnull final VectorProcedure procedure,
            final boolean nullOutput) {
        checkColIndex(col, numColumns);

        final int startIn = columnPointers[col];
        final int endEx = columnPointers[col + 1];

        if (nullOutput) {
            for (int row = 0, i = startIn; row < numRows; row++) {
                if (i < endEx && row == rowIndices[i]) {
                    float v = values[i++];
                    procedure.apply(row, v);
                } else {
                    procedure.apply(row, 0.f);
                }
            }
        } else {
            for (int j = startIn; j < endEx; j++) {
                int row = rowIndices[j];
                float v = values[j];
                procedure.apply(row, v);
            }
        }
    }

    @Override
    public void eachNonZeroInColumn(final int col, @Nonnull final VectorProcedure procedure) {
        checkColIndex(col, numColumns);

        final int startIn = columnPointers[col];
        final int endEx = columnPointers[col + 1];
        for (int j = startIn; j < endEx; j++) {
            int row = rowIndices[j];
            final float v = values[j];
            if (v != 0.f) {
                procedure.apply(row, v);
            }
        }
    }

    @Override
    public CSRFloatMatrix toRowMajorMatrix() {
        final int[] rowPointers = new int[numRows + 1];
        final int[] colIndices = new int[nnz];
        final float[] csrValues = new float[nnz];

        // compute nnz per for each row
        for (int i = 0; i < rowIndices.length; i++) {
            rowPointers[rowIndices[i]]++;
        }
        for (int i = 0, sum = 0; i < numRows; i++) {
            int curr = rowPointers[i];
            rowPointers[i] = sum;
            sum += curr;
        }
        rowPointers[numRows] = nnz;

        for (int j = 0; j < numColumns; j++) {
            for (int i = columnPointers[j], last = columnPointers[j + 1]; i < last; i++) {
                int col = rowIndices[i];
                int dst = rowPointers[col];

                colIndices[dst] = j;
                csrValues[dst] = values[i];

                rowPointers[col]++;
            }
        }

        // shift column pointers
        for (int i = 0, last = 0; i <= numRows; i++) {
            int tmp = rowPointers[i];
            rowPointers[i] = last;
            last = tmp;
        }

        return new CSRFloatMatrix(rowPointers, colIndices, csrValues, numColumns);
    }

    @Override
    public CSCMatrixBuilder builder() {
        return new CSCMatrixBuilder(nnz);
    }

}