import sympy

from mako.template import Template
from pathlib import Path

import boltzgen.kernel.target

class Generator:
    def __init__(self, descriptor, moments, collision):
        self.descriptor = descriptor
        self.moments    = moments
        self.collision  = collision

    def instantiate(self, target, template, float_type, layout_impl, geometry, extras = []):
        template_path = Path(__file__).parent/("template/%s.%s.mako" % (template, target))
        if not template_path.exists():
            raise Exception("Target '%s' doesn't provide '%s'" % (target, template))

        return Template(filename = str(template_path)).render(
            descriptor = self.descriptor,
            geometry   = geometry,
            layout     = layout_impl,

            moments_subexpr    = self.moments[0],
            moments_assignment = self.moments[1],
            collision_subexpr    = self.collision[0],
            collision_assignment = self.collision[1],
            ccode = sympy.ccode,

            float_type = float_type,

            extras = extras
        )

    def kernel(self, target, precision, layout, cell_index, geometry, functions, extras = []):
        cell_index_impl = eval("boltzgen.kernel.target.cell_index.%s" % cell_index)
        if cell_index_impl is None:
            raise Exception("There is no cell indexing scheme '%s'" % (target, layout))
        else:
            cell_index_impl = cell_index_impl(geometry)

        layout_impl = eval("boltzgen.kernel.target.layout.%s" % layout)
        if layout_impl is None:
            raise Exception("There is no layout '%s'" % (target, layout))
        else:
            layout_impl = layout_impl(self.descriptor, cell_index_impl, geometry)

        if geometry.dimension() != self.descriptor.d:
            raise Exception('Geometry dimension must match descriptor dimension')

        float_type = eval("boltzgen.kernel.target.precision.%s" % target).get_float_type(precision)

        return "\n".join(map(
            lambda f: self.instantiate(target, f, float_type, layout_impl, geometry, extras),
            functions))