#!/usr/bin/env python3

import os
import subprocess
import re
import sys
import argparse
import difflib

# Regex to match brew/cask/tap/mas lines
PKG_RE = re.compile(r'^\s*(brew|cask|tap|mas)\s+["\']([^"\']+)["\'](.*)$')

def get_repo_root():
    try:
        root = subprocess.check_output(['git', 'rev-parse', '--show-toplevel'], 
                                       stderr=subprocess.STDOUT).decode().strip()
        return root
    except subprocess.CalledProcessError:
        return os.getcwd()

def get_ignore_list(repo_root):
    ignore = set()
    paths = [
        os.path.join(repo_root, '.Brewfile.ignore'),
        os.path.expanduser('~/.Brewfile.ignore'),
        os.path.expanduser('~/.config/homebrew/ignore')
    ]
    for path in paths:
        if os.path.exists(path):
            with open(path) as f:
                for line in f:
                    line = line.split('#')[0].strip()
                    if line:
                        ignore.add(line)
    return ignore

def get_current_packages():
    """Runs brew bundle dump and returns lines."""
    try:
        output = subprocess.check_output(['brew', 'bundle', 'dump', '--file=-'], 
                                         stderr=subprocess.DEVNULL).decode()
        return output.splitlines()
    except subprocess.CalledProcessError:
        print("Error: 'brew bundle dump' failed. Is homebrew installed?", file=sys.stderr)
        sys.exit(1)

def parse_brewfile(content):
    """
    Parses Brewfile content.
    Returns:
    - conditional_pkgs: set of (type, name)
    - preserved_footer: string (everything from first conditional onwards)
    """
    lines = content.splitlines()
    conditional_pkgs = set()
    
    # Find the start of the first conditional block
    first_conditional_idx = -1
    in_conditional = 0
    
    for i, line in enumerate(lines):
        stripped = line.strip()
        if stripped.startswith(('if ', 'unless ', 'case ')) and not stripped.endswith('; end'):
            if first_conditional_idx == -1:
                # Look back for comments that might belong to this block
                j = i - 1
                while j >= 0 and (lines[j].strip().startswith('#') or not lines[j].strip()):
                    j -= 1
                first_conditional_idx = j + 1
            in_conditional += 1
        
        if in_conditional > 0:
            match = PKG_RE.match(line)
            if match:
                conditional_pkgs.add((match.group(1), match.group(2)))
            
            if stripped == 'end' or stripped.endswith('; end'):
                in_conditional -= 1

    if first_conditional_idx == -1:
        return set(), ""
    
    footer = "\n".join(lines[first_conditional_idx:])
    return conditional_pkgs, footer

def main(args):
    repo_root = get_repo_root()
    brewfile_path = os.path.join(repo_root, 'Brewfile')
    
    if not os.path.exists(brewfile_path):
        print(f"Error: Brewfile not found at {brewfile_path}", file=sys.stderr)
        sys.exit(1)
        
    with open(brewfile_path) as f:
        old_content = f.read()
        
    conditional_pkgs, footer = parse_brewfile(old_content)
    ignore_list = get_ignore_list(repo_root)
    
    dumped_lines = get_current_packages()
    
    new_unconditional_lines = []
    
    for line in dumped_lines:
        match = PKG_RE.match(line)
        if match:
            pkg_type, pkg_name = match.group(1), match.group(2)
            if pkg_name in ignore_list:
                continue
            if (pkg_type, pkg_name) in conditional_pkgs:
                continue
        
        # If it's not a package line (e.g. comment from dump), we can skip or keep
        if line.strip():
            new_unconditional_lines.append(line)

    # Sort lines by type (tap, brew, cask, mas) then name
    def sort_key(line):
        match = PKG_RE.match(line)
        if not match: return (4, line)
        order = {'tap': 0, 'brew': 1, 'cask': 2, 'mas': 3}
        return (order.get(match.group(1), 4), match.group(2))

    new_unconditional_lines.sort(key=sort_key)
    
    # Build new content
    new_content = "\n".join(new_unconditional_lines)
    if footer:
        if new_unconditional_lines:
            new_content += "\n\n"
        new_content += footer.strip() + "\n"
    else:
        new_content += "\n"

    if new_content == old_content:
        print("Brewfile is already up to date.")
    else:
        if args.dry_run:
            print("Changes detected (dry run):")
            diff = difflib.unified_diff(
                old_content.splitlines(keepends=True),
                new_content.splitlines(keepends=True),
                fromfile='Brewfile (original)',
                tofile='Brewfile (new)'
            )
            sys.stdout.writelines(diff)
        else:
            with open(brewfile_path, 'w') as f:
                f.write(new_content)
            print("Brewfile updated.")

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Update Brewfile while preserving conditionals.")
    parser.add_argument("--dry-run", action="store_true", help="Show changes without applying them.")
    args = parser.parse_args()
    main(args)