import os, time
from PyQt4.QtCore import *
from PyQt4.QtXml import *
from PyQt4.QtGui import *
from qgis import *

image_path = PATH_TO_IMAGE
export_path = EXPORT_PATH
template = PATH_TO_TEMPLATE


def exportMap(tempFile, canvas, bbox, outName):
    template_file = file(tempFile)
    template_content = template_file.read()
    template_file.close()
    document = QDomDocument()
    document.setContent(template_content)
    composer = QgsComposition(canvas.mapSettings())
    composer.loadFromTemplate(document)
    map_item = composer.getComposerItemById('main_map')
    map_item.setMapCanvas(canvas)
    bbox.scale(1.2)
    map_item.zoomToExtent(bbox)
    canvas.refresh()
    map_item.updateCachedImage()
    legend_item = composer.getComposerItemById('legend')
    legend_item.updateLegend()
    composer.refreshItems()
    composer.update()
    composer.exportAsPDF(outName)

# get map canvas
canvas = iface.mapCanvas()
li = iface.legendInterface()

# list all layers
layers = li.layers()
# get specific layer by displayed name
lakes = [l for l in layers if l.name() == 'lakes'][0]
iface.legendInterface().setLayerVisible(lakes, True)
# load raster
image = image_path
raster = QgsRasterLayer(image, QFileInfo(image).baseName())
iface.addRasterLayer(image)
canvas.refresh()
# make sure vector layer is on top
root = QgsProject.instance().layerTreeRoot()
for ch in root.children():
    if ch.layerName() == lakes.name():
        clone = ch.clone()
        root.insertChildNode(0, clone)
        root.removeChildNode(ch)

for feat in lakes.getFeatures():
    outname = abbrev[feat.attribute('name')] + '_' + QFileInfo(image).baseName() + '.pdf'
    outfile = os.path.join(export_path, outname)
    # select single feature based on attribute "name"
    expr = QgsExpression(""" "name" = '{0}' """.format(feat.attribute('name')))
    selection = [l.id() for l in lakes.getFeatures(QgsFeatureRequest(expr))]
    lakes.setSelectedFeatures(selection)
    # zoom to selected feature
    canvas.zoomToSelected(lakes)
    # bounding box of selected feature
    bbox = lakes.boundingBoxOfSelected()
    # deselect
    lakes.setSelectedFeatures([])
    # apply local stretch to active raster layer
    iface.setActiveLayer(raster)
    iface.mainWindow().findChild(QAction, 'mActionLocalCumulativeCutStretch').trigger()
    exportMap(template, canvas, bbox, outfile)

# remove raster
for ch in root.children():
    if ch.layerName() == raster.name():
        root.removeChildNode(ch)