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Common module of Exasol Virtual Schema Adapters for Document Data Sources.
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package com.exasol.adapter.document.mapping.reader;

import static java.util.stream.Collectors.*;

import java.util.*;
import java.util.Map.Entry;

import com.exasol.adapter.document.edml.EdmlDefinition;
import com.exasol.adapter.document.edml.ExasolDocumentMappingLanguageException;
import com.exasol.adapter.document.edml.deserializer.EdmlDeserializer;
import com.exasol.adapter.document.edml.validator.EdmlSchemaValidator;
import com.exasol.adapter.document.mapping.*;
import com.exasol.adapter.document.mapping.auto.SchemaInferencer;
import com.exasol.adapter.document.mapping.converter.MappingConversionPipeline;
import com.exasol.adapter.document.properties.EdmlInput;
import com.exasol.errorreporting.ExaError;

/**
 * EDML: This class reads a {@link SchemaMapping} from JSON files.
 * 
 * The JSON files must follow the schema defined in {@code resources/schemas/edml-1.5.0.json}. Documentation of schema
 * mapping definitions can be found at {@code doc/user_guide/edml_user_guide.md}.
 * 
 */
public class JsonSchemaMappingReader {
    private final TableKeyFetcher tableKeyFetcher;
    private final SchemaInferencer schemaInferencer;

    /**
     * Create an instance of {@link JsonSchemaMappingReader}.
     *
     * @param tableKeyFetcher  remote database specific {@link TableKeyFetcher}
     * @param schemaInferencer mapping auto inferencer
     * @throws ExasolDocumentMappingLanguageException if schema mapping invalid
     */
    public JsonSchemaMappingReader(final TableKeyFetcher tableKeyFetcher, final SchemaInferencer schemaInferencer) {
        this.tableKeyFetcher = tableKeyFetcher;
        this.schemaInferencer = schemaInferencer;
    }

    /**
     * Read the schema mapping.
     *
     * @param edmlInputs EDML inputs
     * @return read schema mappings
     */
    public SchemaMapping readSchemaMapping(final List edmlInputs) {
        final EdmlSchemaValidator jsonSchemaMappingValidator = new EdmlSchemaValidator();
        final List tables = new ArrayList<>();
        // validate the schema for all the edml inputs
        for (final EdmlInput edmlInput : edmlInputs) {
            jsonSchemaMappingValidator.validate(edmlInput.getEdmlString());
            try {
                tables.addAll(parseDefinition(edmlInput.getEdmlString()));
            } catch (final ExasolDocumentMappingLanguageException exception) {
                throw getParseFailedException(edmlInput.getSource(), exception);
            }
        }
        validate(tables);
        return new SchemaMapping(tables);
    }

    private ExasolDocumentMappingLanguageException getParseFailedException(final String source,
            final ExasolDocumentMappingLanguageException exception) {
        return new ExasolDocumentMappingLanguageException(ExaError.messageBuilder("F-VSD-81")
                .message("Semantic-validation error in schema mapping {{mapping definition}}.", source).toString(),
                exception);
    }

    /** Make a list of table mappings from the EDML string */
    private List parseDefinition(final String edmlString) {
        final EdmlDefinition edmlDefinition = new EdmlDeserializer().deserialize(edmlString);
        return new MappingConversionPipeline(this.tableKeyFetcher, this.schemaInferencer).convert(edmlDefinition);
    }

    private void validate(final List tables) {
        final Set duplicateDestinationTableNames = tables.stream()
                .collect(groupingBy(TableMapping::getExasolName, counting())) //
                .entrySet().stream() //
                .filter(entry -> entry.getValue() > 1) //
                .map(Entry::getKey) //
                .collect(toSet());
        if (!duplicateDestinationTableNames.isEmpty()) {
            throw new ExasolDocumentMappingLanguageException(ExaError.messageBuilder("E-VSD-104")
                    .message("Found duplicate destination table names {{table names}}.", duplicateDestinationTableNames)
                    .mitigation("Ensure that each mapping uses a unique value for 'destinationTable'.").toString());
        }
    }
}