/*
 * Copyright Red Hat, Inc. and/or its affiliates
 * and other contributors as indicated by the @author tags and
 * the COPYRIGHT.txt file distributed with this work.
 *
 * 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 org.teiid.query.function;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;

import org.teiid.api.exception.query.InvalidFunctionException;
import org.teiid.api.exception.query.QueryResolverException;
import org.teiid.core.CoreConstants;
import org.teiid.core.types.DataTypeManager;
import org.teiid.core.types.Transform;
import org.teiid.metadata.AggregateAttributes;
import org.teiid.metadata.FunctionMethod;
import org.teiid.metadata.FunctionParameter;
import org.teiid.query.QueryPlugin;
import org.teiid.query.function.metadata.FunctionCategoryConstants;
import org.teiid.query.resolver.util.ResolverUtil;
import org.teiid.query.sql.symbol.AggregateSymbol;
import org.teiid.query.sql.symbol.AggregateSymbol.Type;
import org.teiid.query.sql.symbol.Constant;
import org.teiid.query.sql.symbol.Expression;
import org.teiid.query.sql.symbol.Function;
import org.teiid.translator.SourceSystemFunctions;



/**
 * The function library is the primary way for the system to find out what
 * functions are available, resolve function signatures, and invoke system
 * and user-defined functions.
 */
public class FunctionLibrary {

	// Special type conversion functions
	public static final String CONVERT = "convert"; //$NON-NLS-1$
	public static final String CAST = "cast"; //$NON-NLS-1$

    // Special lookup function
    public static final String LOOKUP = "lookup"; //$NON-NLS-1$

    // Special user function
    public static final String USER = "user"; //$NON-NLS-1$
    // Special environment variable lookup function
    public static final String ENV = "env"; //$NON-NLS-1$
    public static final String SYS_PROP = "sys_prop"; //$NON-NLS-1$
    public static final String ENV_VAR = "env_var"; //$NON-NLS-1$
    public static final String SESSION_ID = "session_id"; //$NON-NLS-1$
    
    // Misc.
    public static final String DECODESTRING = "decodestring"; //$NON-NLS-1$
    public static final String DECODEINTEGER = "decodeinteger"; //$NON-NLS-1$
    public static final String COMMAND_PAYLOAD = "commandpayload"; //$NON-NLS-1$
    
    public static final String CONCAT = "CONCAT"; //$NON-NLS-1$
    public static final String CONCAT2 = "CONCAT2"; //$NON-NLS-1$
    public static final String CONCAT_OPERATOR = "||"; //$NON-NLS-1$
    public static final String SUBSTRING = "substring"; //$NON-NLS-1$
    public static final String NVL = "NVL"; //$NON-NLS-1$
    public static final String IFNULL = "IFNULL"; //$NON-NLS-1$
    
    public static final String FROM_UNIXTIME = "from_unixtime"; //$NON-NLS-1$
    public static final String TIMESTAMPADD = "timestampadd"; //$NON-NLS-1$
    
    public static final String PARSETIME = "parsetime"; //$NON-NLS-1$
    public static final String PARSEDATE = "parsedate"; //$NON-NLS-1$
    public static final String FORMATTIME = "formattime"; //$NON-NLS-1$
    public static final String FORMATDATE = "formatdate"; //$NON-NLS-1$
    
    public static final String NULLIF = "nullif"; //$NON-NLS-1$
    public static final String COALESCE = "coalesce"; //$NON-NLS-1$

    public static final String SPACE = "space"; //$NON-NLS-1$
	public static final String ARRAY_GET = "array_get"; //$NON-NLS-1$
	public static final String JSONARRAY = "jsonarray"; //$NON-NLS-1$
	
	public static final String MVSTATUS = "mvstatus"; //$NON-NLS-1$
	
	public static final Set<String> INTERNAL_SCHEMAS = new TreeSet<String>(String.CASE_INSENSITIVE_ORDER);
	
	static {
		INTERNAL_SCHEMAS.add(CoreConstants.SYSTEM_MODEL);
		INTERNAL_SCHEMAS.add(CoreConstants.SYSTEM_ADMIN_MODEL);
		INTERNAL_SCHEMAS.add(CoreConstants.ODBC_MODEL);
	}
	
    // Function tree for system functions (never reloaded)
    private FunctionTree systemFunctions;

    // Function tree for user-defined functions
    private FunctionTree[] userFunctions;

	/**
	 * Construct the function library.  This should be called only once by the
	 * FunctionLibraryManager.
	 */
	public FunctionLibrary(FunctionTree systemFuncs, FunctionTree... userFuncs) {
        systemFunctions = systemFuncs;
       	userFunctions = userFuncs;
	}
	
	public FunctionTree[] getUserFunctions() {
		return userFunctions;
	}
	
	public FunctionTree getSystemFunctions() {
		return systemFunctions;
	}

    /**
     * Get all function categories, sorted in alphabetical order
     * @return List of function category names, sorted in alphabetical order
     */
    public List<String> getFunctionCategories() {
        // Remove category duplicates
        TreeSet<String> categories = new TreeSet<String>();
        categories.addAll( systemFunctions.getCategories() );
        if (this.userFunctions != null) {
	        for (FunctionTree tree: this.userFunctions) {
	        	categories.addAll(tree.getCategories());
	        }
        }

        ArrayList<String> categoryList = new ArrayList<String>(categories);
        return categoryList;
    }

    /**
     * Get all function in a category.
     * @param category Category name
     * @return List of {@link FunctionMethod}s in a category
     */
    public List<FunctionMethod> getFunctionsInCategory(String category) {
        List<FunctionMethod> forms = new ArrayList<FunctionMethod>();
        forms.addAll(systemFunctions.getFunctionsInCategory(category));
        if (this.userFunctions != null) {
	        for (FunctionTree tree: this.userFunctions) {
	        	forms.addAll(tree.getFunctionsInCategory(category));
	        }
        }
        return forms;
    }

    /**
     * Find function form based on function name and # of arguments.
     * @param name Function name
     * @param numArgs Number of arguments
     * @return Corresponding form or null if not found
     */
    public boolean hasFunctionMethod(String name, int numArgs) {
        List<FunctionMethod> methods = systemFunctions.findFunctionMethods(name, numArgs);
        if (!methods.isEmpty()) {
        	return true;
        }
        if(this.userFunctions != null) {
        	for (FunctionTree tree: this.userFunctions) {
        		methods = tree.findFunctionMethods(name, numArgs);
        		if (!methods.isEmpty()) {
        			return true;
        		}
        	}
        }
        return false;
    }

	/**
	 * Find a function descriptor given a name and the types of the arguments.
	 * This method matches based on case-insensitive function name and
     * an exact match of the number and types of parameter arguments.
     * @param name Name of the function to resolve
     * @param types Array of classes representing the types
     * @return Descriptor if found, null if not found
	 */
	public FunctionDescriptor findFunction(String name, Class<?>[] types) {
        // First look in system functions
        FunctionDescriptor descriptor = systemFunctions.getFunction(name, types);

        // If that fails, check the user defined functions
        if(descriptor == null && this.userFunctions != null) {
        	for (FunctionTree tree: this.userFunctions) {
        		descriptor = tree.getFunction(name, types);
        		if (descriptor != null) {
        			break;
        		}
        	}
        }

        return descriptor;
	}
	
	/**
	 * Find a function descriptor given a name and the types of the arguments.
	 * This method matches based on case-insensitive function name and
     * an exact match of the number and types of parameter arguments.
     * @param name Name of the function to resolve
     * @param types Array of classes representing the types
     * @return Descriptor if found, null if not found
	 */
	public List<FunctionDescriptor> findAllFunctions(String name, Class<?>[] types) {
        // First look in system functions
        FunctionDescriptor descriptor = systemFunctions.getFunction(name, types);

        // If that fails, check the user defined functions
        if(descriptor == null && this.userFunctions != null) {
        	List<FunctionDescriptor> result = new LinkedList<FunctionDescriptor>();
        	for (FunctionTree tree: this.userFunctions) {
        		descriptor = tree.getFunction(name, types);
        		if (descriptor != null) {
        			//pushdown function takes presedence 
        			//TODO: there may be multiple translators contributing functions with the same name / types
        			//need "conformed" logic so that the right pushdown can occur
        			if (CoreConstants.SYSTEM_MODEL.equals(descriptor.getSchema())) {
        				return Arrays.asList(descriptor);
        			}
        			result.add(descriptor);
        		}
        	}
        	return result;
        }
        if (descriptor != null) {
        	return Arrays.asList(descriptor);
        }
        return Collections.emptyList();
	}
	
	public static class ConversionResult {
		public ConversionResult(FunctionMethod method) {
			this.method = method;
		}
		public FunctionMethod method;
		public boolean needsConverion;
	}

	/**
	 * Get the conversions that are needed to call the named function with arguments
	 * of the given type.  In the case of an exact match, the list will contain all nulls.
	 * In other cases the list will contain one or more non-null values where the value
	 * is a conversion function that can be used to convert to the proper types for
	 * executing the function.
     * @param name Name of function
	 * @param returnType
	 * @param args 
	 * @param types Existing types passed to the function
	 * @throws InvalidFunctionException 
	 * @throws QueryResolverException 
	 */
	public ConversionResult determineNecessaryConversions(String name, Class<?> returnType, Expression[] args, Class<?>[] types, boolean hasUnknownType) throws InvalidFunctionException {
        //First find existing functions with same name and same number of parameters
        final Collection<FunctionMethod> functionMethods = new LinkedList<FunctionMethod>();
        functionMethods.addAll( this.systemFunctions.findFunctionMethods(name, types.length) );
        if (this.userFunctions != null) {
	        for (FunctionTree tree: this.userFunctions) {
	        	functionMethods.addAll( tree.findFunctionMethods(name, types.length) );
	        }
        }
        
        //Score each match, reject any where types can not be converted implicitly       
        //Score of current method (lower score means better match with less converts
        //Current best score (lower score is best.  Higher score results in more implicit conversions
        int bestScore = Integer.MAX_VALUE;
        boolean ambiguous = false;
        FunctionMethod result = null;
        boolean isSystem = false;
        boolean narrowing = false;
                
        outer: for (FunctionMethod nextMethod : functionMethods) {
            int currentScore = 0; 
            boolean nextNarrowing = false;
            final List<FunctionParameter> methodTypes = nextMethod.getInputParameters();
            //Holder for current signature with converts where required
            
            //Iterate over the parameters adding conversions where required or failing when
            //no implicit conversion is possible
            for(int i = 0; i < types.length; i++) {
                final String tmpTypeName = methodTypes.get(Math.min(i, methodTypes.size() - 1)).getRuntimeType();
                Class<?> targetType = DataTypeManager.getDataTypeClass(tmpTypeName);

                Class<?> sourceType = types[i];
                if (sourceType == null) {
                    currentScore++;
                    continue;
                }
                if (sourceType.isArray()&& targetType.isArray()
                        && sourceType.getComponentType().equals(targetType.getComponentType())) {
                    currentScore++;
                    continue;                    
                }
                if (sourceType.isArray()) {
                    if (isVarArgArrayParam(nextMethod, types, i, targetType)) {
                		//vararg array parameter
                		continue;
                	}
                    //treat the array as object type until proper type handling is added
                	sourceType = DataTypeManager.DefaultDataClasses.OBJECT;
                }
				try {
					Transform t = getConvertFunctionDescriptor(sourceType, targetType);
					if (t != null) {
		                if (t.isExplicit()) {
		                	if (!(args[i] instanceof Constant) || ResolverUtil.convertConstant(DataTypeManager.getDataTypeName(sourceType), tmpTypeName, (Constant)args[i]) == null) {
		                		continue outer;
		                	}
		                	nextNarrowing = true;
		                	currentScore++;
		                } else {
		                	currentScore++;
		                }
					}
				} catch (InvalidFunctionException e) {
					continue outer;
				}
            }
            
            //If the method is valid match and it is the current best score, capture those values as current best match
            if (currentScore > bestScore) {
                continue;
            }
            
            if (hasUnknownType) {
            	if (returnType != null) {
            		try {
						Transform t = getConvertFunctionDescriptor(DataTypeManager.getDataTypeClass(nextMethod.getOutputParameter().getRuntimeType()), returnType);
						if (t != null) {
							if (t.isExplicit()) {
								//there still may be a common type, but use any other valid conversion over this one
								currentScore += types.length + 1;
								nextNarrowing = true;
							} else {
								currentScore++;
							}
						}
					} catch (InvalidFunctionException e) {
						//there still may be a common type, but use any other valid conversion over this one
						currentScore += (types.length * types.length);
					}
            	}
            }
            
            if (nextNarrowing && result != null && !narrowing) {
            	continue;
            }

            boolean useNext = false;
            
            if (!nextNarrowing && narrowing) {
            	useNext = true;
            }
            
        	boolean isSystemNext = nextMethod.getParent() == null || INTERNAL_SCHEMAS.contains(nextMethod.getParent().getName());
        	if ((isSystem && isSystemNext) || (!isSystem && !isSystemNext && result != null)) {
    			int partCount = partCount(result.getName());
    			int nextPartCount = partCount(nextMethod.getName());
    			if (partCount < nextPartCount) {
    				//the current is more specific
    				//this makes us more consistent with the table resolving logic
    				continue outer; 
    			}
    			if (nextPartCount < partCount) {
    				useNext = true;
    			}
        	} else if (isSystemNext) {
        		useNext = true;
        	}
        	
            if (currentScore == bestScore && !useNext) {
            	ambiguous = true;
            	boolean useCurrent = false;
            	List<FunctionParameter> bestParams = result.getInputParameters();
				for (int j = 0; j < types.length; j++) {
            		String t1 = bestParams.get(Math.min(j, bestParams.size() - 1)).getRuntimeType();
            		String t2 = methodTypes.get((Math.min(j, methodTypes.size() - 1))).getRuntimeType();
            		
            		if (types[j] == null || t1.equals(t2)) {
            			continue;
            		}
            		
            		String commonType = ResolverUtil.getCommonRuntimeType(new String[] {t1, t2});
            		
            		if (commonType == null) {
            			continue outer; //still ambiguous
            		}
            		
            		if (commonType.equals(t1)) {
            			if (!useCurrent) {
            				useNext = true;
            			}
            		} else if (commonType.equals(t2)) {
            			if (!useNext) {
            				useCurrent = true;
            			}
            		} else {
            			continue outer;
            		}
            	}
				if (useCurrent) {
					ambiguous = false; //prefer narrower
				} else {
					String sysName = result.getProperty(FunctionMethod.SYSTEM_NAME, false);
					String sysNameOther = nextMethod.getProperty(FunctionMethod.SYSTEM_NAME, false);
					if (sysName != null && sysName.equalsIgnoreCase(sysNameOther)) {
						ambiguous = false;
					}
				}
            }
            
            if (currentScore < bestScore || useNext) {
            	ambiguous = false;
                if (currentScore == 0 && isSystemNext) {
                    return new ConversionResult(nextMethod);
                }    
                
                bestScore = currentScore;
                result = nextMethod;
                isSystem = isSystemNext;
                narrowing = nextNarrowing;
            }            
        }
        
        if (ambiguous) {
        	throw GENERIC_EXCEPTION;
        }
        
        ConversionResult cr = new ConversionResult(result);
        if (result != null) {
        	cr.needsConverion = (bestScore != 0);
        }
        return cr;
	}
	
	private int partCount(String name) {
		int result = 0;
		int index = 0;
		while (true) {
			index = name.indexOf('.', index+1);
			if (index > 0) {
				result++;
			} else {
				break;
			}
		}
		return result;
	}

	public FunctionDescriptor[] getConverts(FunctionMethod method, Class<?>[] types) {
        final List<FunctionParameter> methodTypes = method.getInputParameters();
        FunctionDescriptor[] result = new FunctionDescriptor[types.length];
        for(int i = 0; i < types.length; i++) {
        	//treat all varags as the same type
            final String tmpTypeName = methodTypes.get(Math.min(i, methodTypes.size() - 1)).getRuntimeType();
            Class<?> targetType = DataTypeManager.getDataTypeClass(tmpTypeName);

            Class<?> sourceType = types[i];
            if (sourceType == null) {
                result[i] = findTypedConversionFunction(DataTypeManager.DefaultDataClasses.NULL, targetType);
            } else if (sourceType != targetType){
            	if (isVarArgArrayParam(method, types, i, targetType)) {
            		//vararg array parameter
            		continue;
            	}
            	result[i] = findTypedConversionFunction(sourceType, targetType);
            }
        }
        return result;
	}

	public boolean isVarArgArrayParam(FunctionMethod method, Class<?>[] types,
			int i, Class<?> targetType) {
		return i == types.length - 1 && method.isVarArgs() && i == method.getInputParameterCount() - 1 
				&& types[i].isArray() && targetType.isAssignableFrom(types[i].getComponentType());
	}
	
	private static final InvalidFunctionException GENERIC_EXCEPTION = new InvalidFunctionException(QueryPlugin.Event.TEIID30419); 
	
	private Transform getConvertFunctionDescriptor(Class<?> sourceType, Class<?> targetType) throws InvalidFunctionException {
        //If exact match no conversion necessary
        if(sourceType.equals(targetType)) {
            return null;
        }
        Transform result = DataTypeManager.getTransform(sourceType, targetType);
        //Else see if an implicit conversion is possible.
        if(result == null){
             throw GENERIC_EXCEPTION;
        }
        return result;
	}

    /**
     * Find conversion function and set return type to proper type.   
     * @param sourceType The source type class
     * @param targetType The target type class
     * @return A CONVERT function descriptor or null if not possible
     */
    public FunctionDescriptor findTypedConversionFunction(Class<?> sourceType, Class<?> targetType) {
    	//TODO: should array to string be prohibited?    	
        FunctionDescriptor fd = findFunction(CONVERT, new Class[] {sourceType, DataTypeManager.DefaultDataClasses.STRING});
        if (fd != null) {
            return copyFunctionChangeReturnType(fd, targetType);
        }
        return null;
    }

	/**
	 * Return a copy of the given FunctionDescriptor with the sepcified return type.
	 * @param fd FunctionDescriptor to be copied.
	 * @param returnType The return type to apply to the copied FunctionDescriptor.
	 * @return The copy of FunctionDescriptor.
	 */
    public FunctionDescriptor copyFunctionChangeReturnType(FunctionDescriptor fd, Class<?> returnType) {
        if(fd != null) {
        	FunctionDescriptor fdImpl = fd;
            FunctionDescriptor copy = fdImpl.clone();
            copy.setReturnType(returnType);
            return copy;
        }
        return fd;
    }
    
    public static boolean isConvert(Function function) {
        Expression[] args = function.getArgs();
        String funcName = function.getName();
        
        return args.length == 2 && (funcName.equalsIgnoreCase(FunctionLibrary.CONVERT) || funcName.equalsIgnoreCase(FunctionLibrary.CAST));
    }
    
    /**
     * Return a list of the most general forms of built-in aggregate functions.
     * <br/>count(*) - is not included
     * <br/>textagg - is not included due to its non standard syntax
     * 
     * @param includeAnalytic - true to include analytic functions that must be windowed
     * @return
     */
    public List<FunctionMethod> getBuiltInAggregateFunctions(boolean includeAnalytic) {
    	ArrayList<FunctionMethod> result = new ArrayList<FunctionMethod>();
    	if (this.systemFunctions != null) {
	    	FunctionDescriptor stExtent = this.systemFunctions.getFunction(SourceSystemFunctions.ST_EXTENT, new Class[] {DataTypeManager.DefaultDataClasses.GEOMETRY});
	    	result.add(stExtent.getMethod());
    	}
    	for (Type type : AggregateSymbol.Type.values()) {
			AggregateAttributes aa = new AggregateAttributes();
			if (type.isAnalytical()) {
	            if (!includeAnalytic) {
	                continue;
	            }
	            aa.setAnalytic(true);
	            aa.setAllowsDistinct(false);
	            aa.setAllowsOrderBy(false);
			}
    		String returnType = null;
    		String[] argTypes = null;
    		aa.setAllowsDistinct(true);
    		switch (type) {
    		case TEXTAGG:
    		case USER_DEFINED:
    			continue;
			case DENSE_RANK:
			case RANK:
			case ROW_NUMBER:
				aa.setAllowsDistinct(false);
				returnType = DataTypeManager.DefaultDataTypes.INTEGER;
				argTypes = new String[] {};
				break;
			case ANY:
			case SOME:
			case EVERY:
				returnType = DataTypeManager.DefaultDataTypes.BOOLEAN;
				argTypes = new String[] {DataTypeManager.DefaultDataTypes.BOOLEAN};
				break;
			case COUNT:
				returnType = DataTypeManager.DefaultDataTypes.INTEGER;
				argTypes = new String[] {DataTypeManager.DefaultDataTypes.OBJECT};
				break;
			case MAX:
			case MIN:
			case AVG:
			case SUM:
				returnType = DataTypeManager.DefaultDataTypes.OBJECT;
				argTypes = new String[] {DataTypeManager.DefaultDataTypes.OBJECT};
				break;
			case STDDEV_POP:
			case STDDEV_SAMP:
			case VAR_POP:
			case VAR_SAMP:
				returnType = DataTypeManager.DefaultDataTypes.DOUBLE;
				argTypes = new String[] {DataTypeManager.DefaultDataTypes.DOUBLE};
				break;
			case STRING_AGG:
				returnType = DataTypeManager.DefaultDataTypes.OBJECT;
				argTypes = new String[] {DataTypeManager.DefaultDataTypes.OBJECT};
				aa.setAllowsOrderBy(true);
				break;
			case ARRAY_AGG:
				returnType = DataTypeManager.DefaultDataTypes.OBJECT;
				argTypes = new String[] {DataTypeManager.getDataTypeName(DataTypeManager.getArrayType(DataTypeManager.DefaultDataClasses.OBJECT))};
				aa.setAllowsOrderBy(true);
				aa.setAllowsDistinct(false);
				break;
			case JSONARRAY_AGG:
				returnType = DataTypeManager.DefaultDataTypes.CLOB;
				argTypes = new String[] {DataTypeManager.DefaultDataTypes.OBJECT};
				aa.setAllowsOrderBy(true);
				aa.setAllowsDistinct(false);
				break;
			case XMLAGG:
				returnType = DataTypeManager.DefaultDataTypes.XML;
				argTypes = new String[] {DataTypeManager.DefaultDataTypes.XML};
				aa.setAllowsOrderBy(true);
				aa.setAllowsDistinct(false);
				break;
			case FIRST_VALUE:
			case LAST_VALUE:
                returnType = DataTypeManager.DefaultDataTypes.OBJECT;
                argTypes = new String[] {DataTypeManager.DefaultDataTypes.OBJECT};
                break;
			case LEAD:
            case LAG:
                returnType = DataTypeManager.DefaultDataTypes.OBJECT;
                argTypes = new String[] {DataTypeManager.DefaultDataTypes.OBJECT, DataTypeManager.DefaultDataTypes.INTEGER, DataTypeManager.DefaultDataTypes.OBJECT};
                break;
            case NTILE:
                returnType = DataTypeManager.DefaultDataTypes.INTEGER;
                argTypes = new String[] {DataTypeManager.DefaultDataTypes.INTEGER};
                break;
            case PERCENT_RANK:
                returnType = DataTypeManager.DefaultDataTypes.DOUBLE;
                argTypes = new String[] {};
                break;
            case CUME_DIST:
                returnType = DataTypeManager.DefaultDataTypes.DOUBLE;
                argTypes = new String[] {};
                break;
            case NTH_VALUE:
                returnType = DataTypeManager.DefaultDataTypes.OBJECT;
                argTypes = new String[] {DataTypeManager.DefaultDataTypes.OBJECT, DataTypeManager.DefaultDataTypes.INTEGER};
                break;
    		}
			FunctionMethod fm = FunctionMethod.createFunctionMethod(type.name(), type.name(), FunctionCategoryConstants.AGGREGATE, returnType, argTypes);
			fm.setAggregateAttributes(aa);
    		result.add(fm);
    	}
    	return result;
    }
}
