import subprocess
from typing import Callable, Dict, List, NamedTuple, Optional, Sequence

import bashlex

# a function that takes a command and the environment, and returns the result
EnvironmentExecutor = Callable[[List[str], Dict[str, str]], str]


def local_environment_executor(command: List[str], env: Dict[str, str]) -> str:
    return subprocess.check_output(command, env=env, universal_newlines=True)


class NodeExecutionContext(NamedTuple):
    environment: Dict[str, str]
    input: str
    executor: EnvironmentExecutor


def evaluate(value: str, environment: Dict[str, str], executor: Optional[EnvironmentExecutor] = None) -> str:
    if not value:
        # empty string evaluates to empty string
        # (but trips up bashlex)
        return ''

    command_node = bashlex.parsesingle(value)

    if len(command_node.parts) != 1:
        raise ValueError(f'"{value}" has too many parts')

    value_word_node = command_node.parts[0]

    return evaluate_node(
        value_word_node,
        context=NodeExecutionContext(environment=environment, input=value, executor=executor or local_environment_executor)
    )


def evaluate_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
    if node.kind == 'word':
        return evaluate_word_node(node, context=context)
    elif node.kind == 'commandsubstitution':
        node_result = evaluate_command_node(node.command, context=context)
        # bash removes training newlines in command substitution
        return node_result.rstrip()
    elif node.kind == 'parameter':
        return evaluate_parameter_node(node, context=context)
    else:
        raise ValueError(f'Unsupported bash construct: "{node.kind}"')


def evaluate_word_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
    value: str = node.word

    for part in node.parts:
        part_string = context.input[part.pos[0]:part.pos[1]]
        part_value = evaluate_node(part, context=context)

        if part_string not in value:
            raise RuntimeError(
                'bash parse failed. part "{}" not found in "{}". Word was "{}". Full input was "{}"'.format(
                    part_string, value, node.word, context.input,
                )
            )

        value = value.replace(part_string, part_value, 1)

    return value


def evaluate_command_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
    if any(n.kind == 'operator' for n in node.parts):
        return evaluate_nodes_as_compound_command(node.parts, context=context)
    else:
        return evaluate_nodes_as_simple_command(node.parts, context=context)


def evaluate_nodes_as_compound_command(nodes: Sequence[bashlex.ast.node], context: NodeExecutionContext) -> str:
    # bashlex doesn't support any operators besides ';' inside command
    # substitutions, so we only need to handle that case. We do so assuming
    # that `set -o errexit` is on, because it's easier to code!

    result = ''
    for node in nodes:
        if node.kind == 'command':
            result += evaluate_command_node(node, context=context)
        elif node.kind == 'operator':
            if node.op == ';':
                pass
            else:
                raise ValueError(f'Unsupported bash operator: "{node.op}"')
        else:
            raise ValueError(f'Unsupported bash node in compound command: "{node.kind}"')

    return result


def evaluate_nodes_as_simple_command(nodes: List[bashlex.ast.node], context: NodeExecutionContext) -> str:
    command = [evaluate_node(part, context=context) for part in nodes]
    return context.executor(command, context.environment)


def evaluate_parameter_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
    return context.environment.get(node.value, '')