#  Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
#  See https://llvm.org/LICENSE.txt for license information.
#  SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
"""
Frontend to the compiler, allowing various ways to import code.
"""

import ast
import inspect
import sys

from _npcomp.mlir import ir
from _npcomp.mlir.dialect import ScfDialectHelper
from npcomp.dialect import Numpy

from . import logging

__all__ = [
    "ImportFrontend",
]


# TODO: Remove this hack in favor of a helper function that combines
# multiple dialect helpers so that we don't need to deal with the sharp
# edge of initializing multiple native base classes.
class AllDialectHelper(Numpy.DialectHelper, ScfDialectHelper):

  def __init__(self, *args, **kwargs):
    Numpy.DialectHelper.__init__(self, *args, **kwargs)
    ScfDialectHelper.__init__(self, *args, **kwargs)


class ImportFrontend:
  """Frontend for importing various entities into a Module."""

  def __init__(self, ir_context: ir.MLIRContext = None):
    self._ir_context = ir.MLIRContext() if not ir_context else ir_context
    self._ir_module = self._ir_context.new_module()
    self._helper = AllDialectHelper(self._ir_context,
                                    ir.OpBuilder(self._ir_context))

  @property
  def ir_context(self):
    return self._ir_context

  @property
  def ir_module(self):
    return self._ir_module

  @property
  def ir_h(self):
    return self._helper

  def import_global_function(self, f):
    """Imports a global function.

    This facility is not general and does not allow customization of the
    containing environment, method import, etc.

    Most errors are emitted via the MLIR context's diagnostic infrastructure,
    but errors related to extracting source, etc are raised directly.

    Args:
      f: The python callable.
    """
    h = self.ir_h
    ir_c = self.ir_context
    ir_m = self.ir_module
    filename = inspect.getsourcefile(f)
    source_lines, start_lineno = inspect.getsourcelines(f)
    source = "".join(source_lines)
    ast_root = ast.parse(source, filename=filename)
    ast.increment_lineno(ast_root, start_lineno - 1)
    ast_fd = ast_root.body[0]
    filename_ident = ir_c.identifier(filename)

    # Define the function.
    # TODO: Much more needs to be done here (arg/result mapping, etc)
    logging.debug(":::::::")
    logging.debug("::: Importing global function {}:\n{}", ast_fd.name,
                  ast.dump(ast_fd, include_attributes=True))
    h.builder.set_file_line_col(filename_ident, ast_fd.lineno,
                                ast_fd.col_offset)
    h.builder.insert_before_terminator(ir_m.first_block)
    ir_f_type = h.function_type([], [h.basicpy_UnknownType])
    ir_f = h.func_op(ast_fd.name, ir_f_type, create_entry_block=True)

    fctx = FunctionContext(ir_c=ir_c,
                           ir_f=ir_f,
                           ir_h=h,
                           filename_ident=filename_ident)
    fdimport = FunctionDefImporter(fctx, ast_fd)
    fdimport.import_body()
    return ir_f


class FunctionContext:
  """Accounting information for importing a function."""
  __slots__ = [
      "ir_c",
      "ir_f",
      "ir_h",
      "filename_ident",
      "local_name_value_map",
  ]

  def __init__(self, ir_c, ir_f, ir_h, filename_ident):
    self.ir_c = ir_c
    self.ir_f = ir_f
    self.ir_h = ir_h
    self.filename_ident = filename_ident
    self.local_name_value_map = dict()

  def abort(self, message):
    """Emits an error diagnostic and raises an exception to abort."""
    loc = self.current_loc
    ir.emit_error(loc, message)
    raise EmittedError(loc, message)

  @property
  def current_loc(self):
    return self.ir_h.builder.current_loc

  def update_loc(self, ast_node):
    self.ir_h.builder.set_file_line_col(self.filename_ident, ast_node.lineno,
                                        ast_node.col_offset)

  def map_local_name(self, name, value):
    self.local_name_value_map[name] = value
    logging.debug("Map name({}) -> value({})", name, value)


class BaseNodeVisitor(ast.NodeVisitor):
  """Base class of a node visitor that aborts on unhandled nodes."""
  IMPORTER_TYPE = "<unknown>"

  def __init__(self, fctx):
    super().__init__()
    self.fctx = fctx

  def visit(self, node):
    self.fctx.update_loc(node)
    return super().visit(node)

  def generic_visit(self, ast_node):
    logging.debug("UNHANDLED NODE: {}", ast.dump(ast_node))
    self.fctx.abort("unhandled python %s AST node '%s'" %
                    (self.IMPORTER_TYPE, ast_node.__class__.__name__))


class FunctionDefImporter(BaseNodeVisitor):
  """AST visitor for importing a function's statements.

  Handles nodes that are direct children of a FunctionDef.
  """
  IMPORTER_TYPE = "statement"

  def __init__(self, fctx, ast_fd):
    super().__init__(fctx)
    self.ast_fd = ast_fd

  def import_body(self):
    for ast_stmt in self.ast_fd.body:
      logging.debug("STMT: {}", ast.dump(ast_stmt, include_attributes=True))
      self.visit(ast_stmt)

  def visit_Assign(self, ast_node):
    expr = ExpressionImporter(self.fctx)
    expr.visit(ast_node.value)
    for target in ast_node.targets:
      self.fctx.update_loc(target)
      if not isinstance(target.ctx, ast.Store):
        # TODO: Del, AugStore, etc
        self.fctx.abort("Unsupported assignment context type %s" %
                        target.ctx.__class__.__name__)
      self.fctx.map_local_name(target.id, expr.value)

  def visit_Return(self, ast_node):
    ir_h = self.fctx.ir_h
    expr = ExpressionImporter(self.fctx)
    expr.visit(ast_node.value)
    casted = ir_h.basicpy_unknown_cast_op(ir_h.basicpy_UnknownType,
                                          expr.value).result
    ir_h.return_op([casted])


class ExpressionImporter(BaseNodeVisitor):
  IMPORTER_TYPE = "expression"

  def __init__(self, fctx):
    super().__init__(fctx)
    self.value = None

  def visit(self, node):
    super().visit(node)
    assert self.value, ("ExpressionImporter did not assign a value (%r)" %
                        (ast.dump(node),))

  def sub_evaluate(self, sub_node):
    sub_importer = ExpressionImporter(self.fctx)
    sub_importer.visit(sub_node)
    return sub_importer.value

  def emit_constant(self, value):
    ir_c = self.fctx.ir_c
    ir_h = self.fctx.ir_h
    if value is True:
      self.value = ir_h.basicpy_bool_constant_op(True).result
    elif value is False:
      self.value = ir_h.basicpy_bool_constant_op(False).result
    elif value is None:
      self.value = ir_h.basicpy_singleton_op(ir_h.basicpy_NoneType).result
    elif isinstance(value, int):
      # TODO: Configurable type mapping
      ir_type = ir_h.i64_type
      ir_attr = ir_c.integer_attr(ir_type, value)
      self.value = ir_h.constant_op(ir_type, ir_attr).result
    elif isinstance(value, float):
      # TODO: Configurable type mapping
      ir_type = ir_h.f64_type
      ir_attr = ir_c.float_attr(ir_type, value)
      self.value = ir_h.constant_op(ir_type, ir_attr).result
    elif isinstance(value, str):
      self.value = ir_h.basicpy_str_constant_op(value).result
    elif isinstance(value, bytes):
      self.value = ir_h.basicpy_bytes_constant_op(value).result
    elif isinstance(value, type(...)):
      self.value = ir_h.basicpy_singleton_op(ir_h.basicpy_EllipsisType).result
    else:
      self.fctx.abort("unknown constant type '%r'" % (value,))

  def visit_BinOp(self, ast_node):
    ir_h = self.fctx.ir_h
    left = self.sub_evaluate(ast_node.left)
    right = self.sub_evaluate(ast_node.right)
    self.value = ir_h.basicpy_binary_expr_op(
        ir_h.basicpy_UnknownType, left, right,
        ast_node.op.__class__.__name__).result

  def visit_Compare(self, ast_node):
    # Short-circuit comparison (degenerates to binary comparison when just
    # two operands).
    ir_h = self.fctx.ir_h
    false_value = ir_h.basicpy_bool_constant_op(False).result

    def emit_next(left_value, comparisons):
      operation, right_node = comparisons[0]
      comparisons = comparisons[1:]
      right_value = self.sub_evaluate(right_node)
      compare_result = ir_h.basicpy_binary_compare_op(
          left_value, right_value, operation.__class__.__name__).result
      # Terminate by yielding the final compare result.
      if not comparisons:
        return compare_result

      # Emit 'if' op and recurse. The if op takes an i1 (core dialect
      # requirement) and returns a basicpy.BoolType. Since this is an 'and',
      # all else clauses yield a false value.
      compare_result_i1 = ir_h.basicpy_bool_cast_op(ir_h.i1_type,
                                                    compare_result).result
      if_op, then_ip, else_ip = ir_h.scf_if_op([ir_h.basicpy_BoolType],
                                               compare_result_i1, True)
      orig_ip = ir_h.builder.insertion_point
      # Build the else clause.
      ir_h.builder.insertion_point = else_ip
      ir_h.scf_yield_op([false_value])
      # Build the then clause.
      ir_h.builder.insertion_point = then_ip
      nested_result = emit_next(right_value, comparisons)
      ir_h.scf_yield_op([nested_result])
      ir_h.builder.insertion_point = orig_ip
      return if_op.result

    self.value = emit_next(self.sub_evaluate(ast_node.left),
                           list(zip(ast_node.ops, ast_node.comparators)))

  def visit_Name(self, ast_node):
    if not isinstance(ast_node.ctx, ast.Load):
      self.fctx.abort("Unsupported expression name context type %s" %
                      ast_node.ctx.__class__.__name__)
    # TODO: Need to apply scope rules: local, global, ...
    value = self.fctx.local_name_value_map.get(ast_node.id)
    if value is None:
      self.fctx.abort("Local variable '%s' has not been assigned" % ast_node.id)
    self.value = value

  if sys.version_info < (3, 8, 0):
    # <3.8 breaks these out into separate AST classes.
    def visit_Num(self, ast_node):
      self.emit_constant(ast_node.n)

    def visit_Str(self, ast_node):
      self.emit_constant(ast_node.s)

    def visit_Bytes(self, ast_node):
      self.emit_constant(ast_node.s)

    def visit_NameConstant(self, ast_node):
      self.emit_constant(ast_node.value)

    def visit_Ellipsis(self, ast_node):
      self.emit_constant(...)
  else:

    def visit_Constant(self, ast_node):
      self.emit_constant(ast_node.value)


class EmittedError(Exception):
  """Exception subclass that indicates an error diagnostic has been emitted.

  By throwing, this lets us abort and handle at a higher level so as not
  to duplicate diagnostics.
  """

  def __init__(self, loc, message):
    super().__init__("%s (at %r)" % (message, loc))
    self.loc = loc