// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.tensor.serialization;

import com.yahoo.lang.MutableInteger;
import com.yahoo.slime.ArrayTraverser;
import com.yahoo.slime.Cursor;
import com.yahoo.slime.Inspector;
import com.yahoo.slime.JsonDecoder;
import com.yahoo.slime.ObjectTraverser;
import com.yahoo.slime.Slime;
import com.yahoo.slime.Type;
import com.yahoo.tensor.IndexedTensor;
import com.yahoo.tensor.MixedTensor;
import com.yahoo.tensor.Tensor;
import com.yahoo.tensor.TensorAddress;
import com.yahoo.tensor.TensorType;

import java.util.Iterator;

/**
 * Writes tensors on the JSON format used in Vespa tensor document fields:
 * A JSON map containing a 'cells' or 'values' array.
 * See <a href="https://docs.vespa.ai/en/reference/document-json-format.html">
 * https://docs.vespa.ai/en/reference/document-json-format.html</a>
 *
 * @author bratseth
 */
public class JsonFormat {

    /** Serializes the given tensor value into JSON format */
    public static byte[] encode(Tensor tensor) {
        Slime slime = new Slime();
        Cursor root = slime.setObject();
        encodeCells(tensor, root);
        return com.yahoo.slime.JsonFormat.toJsonBytes(slime);
    }

    /** Serializes the given tensor type and value into JSON format */
    public static byte[] encodeWithType(Tensor tensor) {
        Slime slime = new Slime();
        Cursor root = slime.setObject();
        root.setString("type", tensor.type().toString());
        encodeCells(tensor, root);
        return com.yahoo.slime.JsonFormat.toJsonBytes(slime);
    }

    private static void encodeCells(Tensor tensor, Cursor rootObject) {
        Cursor cellsArray = rootObject.setArray("cells");
        for (Iterator<Tensor.Cell> i = tensor.cellIterator(); i.hasNext(); ) {
            Tensor.Cell cell = i.next();
            Cursor cellObject = cellsArray.addObject();
            encodeAddress(tensor.type(), cell.getKey(), cellObject.setObject("address"));
            cellObject.setDouble("value", cell.getValue());
        }
    }

    private static void encodeAddress(TensorType type, TensorAddress address, Cursor addressObject) {
        for (int i = 0; i < address.size(); i++)
            addressObject.setString(type.dimensions().get(i).name(), address.label(i));
    }

    /** Deserializes the given tensor from JSON format */
    // NOTE: This must be kept in sync with com.yahoo.document.json.readers.TensorReader in the document module
    public static Tensor decode(TensorType type, byte[] jsonTensorValue) {
        Tensor.Builder builder = Tensor.Builder.of(type);
        Inspector root = new JsonDecoder().decode(new Slime(), jsonTensorValue).get();

        if (root.field("cells").valid())
            decodeCells(root.field("cells"), builder);
        else if (root.field("values").valid())
            decodeValues(root.field("values"), builder);
        else if (root.field("blocks").valid())
            decodeBlocks(root.field("blocks"), builder);
        else if (builder.type().dimensions().stream().anyMatch(d -> d.isIndexed())) // sparse can be empty
            throw new IllegalArgumentException("Expected a tensor value to contain either 'cells' or 'values'");
        return builder.build();
    }

    private static void decodeCells(Inspector cells, Tensor.Builder builder) {
        if ( cells.type() == Type.ARRAY)
            cells.traverse((ArrayTraverser) (__, cell) -> decodeCell(cell, builder));
        else if (cells.type() == Type.OBJECT)
            cells.traverse((ObjectTraverser) (key, value) -> decodeSingleDimensionCell(key, value, builder));
        else
            throw new IllegalArgumentException("Excepted 'cells' to contain an array or obejct, not " + cells.type());
    }

    private static void decodeCell(Inspector cell, Tensor.Builder builder) {
        TensorAddress address = decodeAddress(cell.field("address"), builder.type());

        Inspector value = cell.field("value");
        if (value.type() != Type.LONG && value.type() != Type.DOUBLE)
            throw new IllegalArgumentException("Excepted a cell to contain a numeric value called 'value'");

        builder.cell(address, value.asDouble());
    }

    private static void decodeSingleDimensionCell(String key, Inspector value, Tensor.Builder builder) {
        builder.cell(asAddress(key, builder.type()), decodeNumeric(value));
    }

    private static void decodeValues(Inspector values, Tensor.Builder builder) {
        if ( ! (builder instanceof IndexedTensor.BoundBuilder))
            throw new IllegalArgumentException("The 'values' field can only be used with dense tensors. " +
                                               "Use 'cells' or 'blocks' instead");
        IndexedTensor.BoundBuilder indexedBuilder = (IndexedTensor.BoundBuilder)builder;
        if (values.type() == Type.STRING) {
            double[] decoded = decodeHexString(values.asString(), builder.type().valueType());
            for (int i = 0; i < decoded.length; i++) {
                indexedBuilder.cellByDirectIndex(i, decoded[i]);
            }
            return;
        }
        if ( values.type() != Type.ARRAY)
            throw new IllegalArgumentException("Excepted 'values' to contain an array, not " + values.type());

        MutableInteger index = new MutableInteger(0);
        values.traverse((ArrayTraverser) (__, value) -> {
            if (value.type() != Type.LONG && value.type() != Type.DOUBLE)
                throw new IllegalArgumentException("Excepted the values array to contain numbers, not " + value.type());
            indexedBuilder.cellByDirectIndex(index.next(), value.asDouble());
        });
    }

    private static void decodeBlocks(Inspector values, Tensor.Builder builder) {
        if ( ! (builder instanceof MixedTensor.BoundBuilder))
            throw new IllegalArgumentException("The 'blocks' field can only be used with mixed tensors with bound dimensions. " +
                                               "Use 'cells' or 'values' instead");
        MixedTensor.BoundBuilder mixedBuilder = (MixedTensor.BoundBuilder) builder;

        if (values.type() == Type.ARRAY)
            values.traverse((ArrayTraverser) (__, value) -> decodeBlock(value, mixedBuilder));
        else if (values.type() == Type.OBJECT)
            values.traverse((ObjectTraverser) (key, value) -> decodeSingleDimensionBlock(key, value, mixedBuilder));
        else
            throw new IllegalArgumentException("Excepted 'blocks' to contain an array or object, not " + values.type());
    }

    private static void decodeBlock(Inspector block, MixedTensor.BoundBuilder mixedBuilder) {
        if (block.type() != Type.OBJECT)
            throw new IllegalArgumentException("Expected an item in a 'blocks' array to be an object, not " + block.type());
        mixedBuilder.block(decodeAddress(block.field("address"), mixedBuilder.type().mappedSubtype()),
                           decodeValues(block.field("values"), mixedBuilder));
    }

    private static void decodeSingleDimensionBlock(String key, Inspector value, MixedTensor.BoundBuilder mixedBuilder) {
        if (value.type() != Type.ARRAY)
            throw new IllegalArgumentException("Expected an item in a 'blocks' array to be an object, not " + value.type());
        mixedBuilder.block(asAddress(key, mixedBuilder.type().mappedSubtype()),
                           decodeValues(value, mixedBuilder));
    }

    private static byte decodeHex(String input, int index) {
        int d = Character.digit(input.charAt(index), 16);
        if (d < 0) {
            throw new IllegalArgumentException("Invalid digit '"+input.charAt(index)+"' at index "+index+" in input "+input);
        }
        return (byte)d;
    }

    private static double[] decodeHexStringAsBytes(String input) {
        int l = input.length() / 2;
        double[] result = new double[l];
        int idx = 0;
        for (int i = 0; i < l; i++) {
            byte v = decodeHex(input, idx++);
            v <<= 4;
            v += decodeHex(input, idx++);
            result[i] = v;
        }
        return result;
    }

    private static double[] decodeHexStringAsBFloat16s(String input) {
        int l = input.length() / 4;
        double[] result = new double[l];
        int idx = 0;
        for (int i = 0; i < l; i++) {
            int v = decodeHex(input, idx++);
            v <<= 4; v += decodeHex(input, idx++);
            v <<= 4; v += decodeHex(input, idx++);
            v <<= 4; v += decodeHex(input, idx++);
            v <<= 16;
            result[i] = Float.intBitsToFloat(v);
        }
        return result;
    }

    private static double[] decodeHexStringAsFloats(String input) {
        int l = input.length() / 8;
        double[] result = new double[l];
        int idx = 0;
        for (int i = 0; i < l; i++) {
            int v = 0;
            for (int j = 0; j < 8; j++) {
                v <<= 4;
                v += decodeHex(input, idx++);
            }
            result[i] = Float.intBitsToFloat(v);
        }
        return result;
    }

    private static double[] decodeHexStringAsDoubles(String input) {
        int l = input.length() / 16;
        double[] result = new double[l];
        int idx = 0;
        for (int i = 0; i < l; i++) {
            long v = 0;
            for (int j = 0; j < 16; j++) {
                v <<= 4;
                v += decodeHex(input, idx++);
            }
            result[i] = Double.longBitsToDouble(v);
        }
        return result;
    }

    private static double[] decodeHexString(String input, TensorType.Value valueType) {
        switch(valueType) {
            case INT8:
                return decodeHexStringAsBytes(input);
            case BFLOAT16:
                return decodeHexStringAsBFloat16s(input);
            case FLOAT:
                return decodeHexStringAsFloats(input);
            case DOUBLE:
                return decodeHexStringAsDoubles(input);
            default:
                throw new IllegalArgumentException("Cannot handle value type: "+valueType);
        }
    }

    private static double[] decodeValues(Inspector valuesField, MixedTensor.BoundBuilder mixedBuilder) {
        double[] values = new double[(int)mixedBuilder.denseSubspaceSize()];
        if (valuesField.type() == Type.ARRAY) {
            valuesField.traverse((ArrayTraverser) (index, value) -> values[index] = decodeNumeric(value));
        } else if (valuesField.type() == Type.STRING) {
            double[] decoded = decodeHexString(valuesField.asString(), mixedBuilder.type().valueType());
            for (int i = 0; i < decoded.length; i++) {
                values[i] = decoded[i];
            }
        } else {
            throw new IllegalArgumentException("Expected a block to contain a 'values' array");
        }
        return values;
    }

    private static TensorAddress decodeAddress(Inspector addressField, TensorType type) {
        if (addressField.type() != Type.OBJECT)
            throw new IllegalArgumentException("Expected an 'address' object, not " + addressField.type());
        TensorAddress.Builder builder = new TensorAddress.Builder(type);
        addressField.traverse((ObjectTraverser) (dimension, label) -> builder.add(dimension, label.asString()));
        return builder.build();
    }

    private static TensorAddress asAddress(String label, TensorType type) {
        if (type.dimensions().size() != 1)
            throw new IllegalArgumentException("Expected a tensor with a single dimension but got " + type);
        return new TensorAddress.Builder(type).add(type.dimensions().get(0).name(), label).build();
    }

    private static double decodeNumeric(Inspector numericField) {
        if (numericField.type() != Type.LONG && numericField.type() != Type.DOUBLE)
            throw new IllegalArgumentException("Excepted a number, not " + numericField.type());
        return numericField.asDouble();
    }

}