from sextante.core.GeoAlgorithm import GeoAlgorithm
from sextante.outputs.OutputVector import OutputVector
from sextante.parameters.ParameterVector import ParameterVector
from qgis.core import *
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from sextante.parameters.ParameterString import ParameterString
from sextante.core.QGisLayers import QGisLayers
import os
from PyQt4 import QtGui
from sextante.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException


class FieldsCalculator(GeoAlgorithm):

    INPUT_LAYER = "INPUT_LAYER"
    FIELD_NAME = "FIELD_NAME"
    FORMULA = "FORMULA"
    OUTPUT_LAYER ="OUTPUT_LAYER"

    def getIcon(self):
        return QtGui.QIcon(os.path.dirname(__file__) + "/../images/toolbox.png")

    def defineCharacteristics(self):
        self.name = "Field calculator"
        self.group = "Algorithms for vector layers"
        self.addParameter(ParameterVector(self.INPUT_LAYER, "Input layer", ParameterVector.VECTOR_TYPE_ANY, False))
        self.addParameter(ParameterString(self.FIELD_NAME, "Result field name"))
        self.addParameter(ParameterString(self.FORMULA, "Formula"))
        self.addOutput(OutputVector(self.OUTPUT_LAYER, "Output layer"))

    def processAlgorithm(self, progress):
        fieldname = self.getParameterValue(self.FIELD_NAME)
        formula = self.getParameterValue(self.FORMULA)
        output = self.getOutputFromName(self.OUTPUT_LAYER)
        vlayer = QGisLayers.getObjectFromUri(self.getParameterValue(self.INPUT_LAYER))
        vprovider = vlayer.dataProvider()
        allAttrs = vprovider.attributeIndexes()
        vprovider.select( allAttrs )
        fields = vprovider.fields()
        fields[len(fields)] = QgsField(fieldname, QVariant.Double)
        writer = output.getVectorWriter(fields, vprovider.geometryType(), vprovider.crs() )
        inFeat = QgsFeature()
        outFeat = QgsFeature()
        inGeom = QgsGeometry()
        nFeat = vprovider.featureCount()
        nElement = 0
        while vprovider.nextFeature(inFeat):
            progress.setPercentage(int((100 * nElement)/nFeat))
            attrs = inFeat.attributeMap()
            expression = formula
            for (k,attr) in attrs.iteritems():
                expression = expression.replace(str(fields[k].name()), str(attr.toString()))
            try:
                result = eval(expression)
            except Exception:
                raise GeoAlgorithmExecutionException("Problem evaluation formula: Wrong field values or formula")
            nElement += 1
            inGeom = inFeat.geometry()
            outFeat.setGeometry( inGeom )
            atMap = inFeat.attributeMap()
            outFeat.setAttributeMap( atMap )
            outFeat.addAttribute( len(vprovider.fields()), QVariant(result) )
            writer.addFeature( outFeat )
        del writer


    def checkParameterValuesBeforeExecuting(self):
        ##TODO check that formula is correct and fields exist
        pass