# Copyright (c) Streamlit Inc. (2018-2022) Snowflake Inc. (2022)
#
# 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.

import ast
import contextlib
import re
import textwrap
import traceback
from typing import Any, Dict, Iterable, Optional

from streamlit.runtime.metrics_util import gather_metrics

_SPACES_RE = re.compile("\\s*")
_EMPTY_LINE_RE = re.compile("\\s*\n")


@gather_metrics("echo")
@contextlib.contextmanager
def echo(code_location="above"):
    """Use in a `with` block to draw some code on the app, then execute it.

    Parameters
    ----------
    code_location : "above" or "below"
        Whether to show the echoed code before or after the results of the
        executed code block.

    Example
    -------
    >>> import streamlit as st
    >>>
    >>> with st.echo():
    >>>     st.write('This code will be printed')

    """
    from streamlit import code, empty, source_util, warning

    if code_location == "below":
        show_code = code
        show_warning = warning
    else:
        placeholder = empty()
        show_code = placeholder.code
        show_warning = placeholder.warning

    try:
        # Get stack frame *before* running the echoed code. The frame's
        # line number will point to the `st.echo` statement we're running.
        frame = traceback.extract_stack()[-3]
        filename, start_line = frame.filename, frame.lineno or 0

        # Read the file containing the source code of the echoed statement.
        with source_util.open_python_file(filename) as source_file:
            source_lines = source_file.readlines()

        # Use ast to parse the Python file and find the code block to display
        root_node = ast.parse("".join(source_lines))
        line_to_node_map: Dict[int, Any] = {}

        def collect_body_statements(node: ast.AST) -> None:
            if not hasattr(node, "body"):
                return
            for child in ast.iter_child_nodes(node):
                # If child doesn't have "lineno", it is not something we could display
                if hasattr(child, "lineno"):
                    line_to_node_map[child.lineno] = child
                    collect_body_statements(child)

        collect_body_statements(root_node)

        # In AST module the lineno (line numbers) are 1-indexed,
        # so we decrease it by 1 to lookup in source lines list
        echo_block_start_line = line_to_node_map[start_line].body[0].lineno - 1
        echo_block_end_line = line_to_node_map[start_line].end_lineno
        lines_to_display = source_lines[echo_block_start_line:echo_block_end_line]

        code_string = textwrap.dedent("".join(lines_to_display))

        # Run the echoed code...
        yield

        # And draw the code string to the app!
        show_code(code_string, "python")

    except FileNotFoundError as err:
        show_warning("Unable to display code. %s" % err)


def _get_initial_indent(lines: Iterable[str]) -> int:
    """Return the indent of the first non-empty line in the list.
    If all lines are empty, return 0.
    """
    for line in lines:
        indent = _get_indent(line)
        if indent is not None:
            return indent

    return 0


def _get_indent(line: str) -> Optional[int]:
    """Get the number of whitespaces at the beginning of the given line.
    If the line is empty, or if it contains just whitespace and a newline,
    return None.
    """
    if _EMPTY_LINE_RE.match(line) is not None:
        return None

    match = _SPACES_RE.match(line)
    return match.end() if match is not None else 0
