# Copyright lowRISC contributors.
# Licensed under the Apache License, Version 2.0, see LICENSE for details.
# SPDX-License-Identifier: Apache-2.0

import os


def find_tool(tool_name: str) -> str:
    '''Return a string describing how to invoke the given RISC-V tool

    Try to resolve the tool in the following way, stopping after the first
    match:

    1. Use the path set in the RV32_TOOL_<tool_name> environment variable.
    2. Use the path set in $TOOLCHAIN_PATH/bin/riscv32-unknown-elf-<tool_name>.
    3. Look for riscv32-unknown-elf-<tool_name> in the system PATH.
    4. Look in the default toolchain install location, /tools/riscv/bin.

    For methods (1) and (2), if the expected environment variable is set but
    the tool isn't found, an error is printed. An error is also printed if
    neither environment variables is set and methods (3) and (4) fail.
    '''
    tool_env_var = 'RV32_TOOL_' + tool_name.upper()
    configured_tool_path = os.environ.get(tool_env_var)
    if configured_tool_path is not None:
        if not os.path.exists(configured_tool_path):
            raise RuntimeError('No such file: {!r} (derived from the '
                               '{!r} environment variable when trying '
                               'to find the {!r} tool).'.format(
                                   configured_tool_path, tool_env_var,
                                   tool_name))
        return configured_tool_path

    expanded = 'riscv32-unknown-elf-' + tool_name
    toolchain_path = os.environ.get('TOOLCHAIN_PATH')
    if toolchain_path is not None:
        tool_path = os.path.join(toolchain_path, 'bin', expanded)
        if not os.path.exists(tool_path):
            raise RuntimeError('No such file: {!r} (derived from the '
                               'TOOLCHAIN_PATH environment variable when '
                               'trying to find the {!r} tool).'
                               .format(tool_path, tool_name))
        return tool_path

    default_location = '/tools/riscv/bin'
    paths = os.get_exec_path() + [default_location]
    for exec_path in paths:
        tool_path = os.path.join(exec_path, expanded)
        if os.path.exists(tool_path):
            return tool_path

    raise RuntimeError('Unable to find {!r} in PATH or in {!r}. Set the {!r} '
                       'or TOOLCHAIN_PATH environment variable if you '
                       'installed your RISC-V toolchain in an alternate '
                       'location.'
                       .format(expanded, default_location, tool_env_var))