import re

import yaml

from pre_commit.util import yaml_load


def _indent(s: str) -> str:
    lines = s.splitlines(True)
    return ''.join(' ' * 4 + line if line.strip() else line for line in lines)


def _is_header_line(line: str) -> bool:
    return line.startswith(('#', '---')) or not line.strip()


def _migrate_map(contents: str) -> str:
    # Find the first non-header line
    lines = contents.splitlines(True)
    i = 0
    # Only loop on non empty configuration file
    while i < len(lines) and _is_header_line(lines[i]):
        i += 1

    header = ''.join(lines[:i])
    rest = ''.join(lines[i:])

    if isinstance(yaml_load(contents), list):
        # If they are using the "default" flow style of yaml, this operation
        # will yield a valid configuration
        try:
            trial_contents = f'{header}repos:\n{rest}'
            yaml_load(trial_contents)
            contents = trial_contents
        except yaml.YAMLError:
            contents = f'{header}repos:\n{_indent(rest)}'

    return contents


def _migrate_sha_to_rev(contents: str) -> str:
    return re.sub(r'(\n\s+)sha:', r'\1rev:', contents)


def migrate_config(config_file: str, quiet: bool = False) -> int:
    with open(config_file) as f:
        orig_contents = contents = f.read()

    contents = _migrate_map(contents)
    contents = _migrate_sha_to_rev(contents)

    if contents != orig_contents:
        with open(config_file, 'w') as f:
            f.write(contents)

        print('Configuration has been migrated.')
    elif not quiet:
        print('Configuration is already migrated.')
    return 0