#!/usr/bin/env python3
"""
Import Graph Visualizer — Issue #133

Parses Python files in a codebase and generates a module-level import
dependency graph in DOT format. Detects circular imports.

Usage:
  python3 scripts/import_graph.py /path/to/hermes-agent
  python3 scripts/import_graph.py /path/to/hermes-agent --output deps.dot
  python3 scripts/import_graph.py /path/to/hermes-agent --render-png
"""

import argparse
import ast
import sys
from pathlib import Path
from collections import defaultdict
from typing import Dict, Set, List, Optional


def python_files(root: Path) -> List[Path]:
    """Yield all .py files under root, excluding common noise dirs."""
    exlude_dirs = {'.git', '__pycache__', '.venv', 'venv', 'node_modules', 'dist', 'build', '.tox'}
    for path in root.rglob('*.py'):
        if any(part in exlude_dirs for part in path.parts):
            continue
        yield path


def module_name(filepath: Path, root: Path) -> str:
    """Convert a .py file path to its dotted module name relative to root."""
    rel = filepath.relative_to(root)
    parts = list(rel.parts)
    if parts[-1] == '__init__.py':
        parts = parts[:-1]  # package __init__ → the package itself
    elif parts[-1].endswith('.py'):
        parts[-1] = parts[-1][:-3]  # strip .py
    # Remove any __pycache__ segments
    parts = [p for p in parts if p != '__pycache__']
    return '.'.join(parts)


def compute_package_base(filepath: Path) -> Path:
    """Return the directory containing the top-level __init__.py for this file's package.
    For a file at a/b/c/d.py, return a/b/c if c is a package, else a/b, else a."""
    parent = filepath.parent
    while parent != parent.parent:  # while we can go up
        if (parent / '__init__.py').exists():
            parent = parent.parent
        else:
            break
    return parent


def resolve_import(from_node: ast.ImportFrom, current_file: Path, root: Path) -> Optional[str]:
    """Resolve a single ImportFrom target to an absolute dotted module name.
    Returns None if the import is external (stdlib/third-party) or unresolvable."""
    level = from_node.level  # 0 = absolute, >0 = relative
    imported = from_node.module  # may be None for `from . import X`

    # External (stdlib/third-party) if level==0 and not a local package
    # We detect local packages by checking if the module path could exist under root

    if level == 0 and imported:
        # Absolute import — check if it points to something inside the scanned root
        candidate = root / imported.replace('.', '/')
        if candidate.exists() or (candidate / '__init__.py').exists():
            return imported
        # Could be a submodule of something we're scanning
        # e.g. from hermes.tools import foo and we're scanning hermes/
        return imported

    # Relative import
    # Compute the package base of the current file
    package_base = compute_package_base(current_file)
    rel_to_base = current_file.parent.relative_to(package_base) if package_base != current_file.parent else Path()

    if level == 1:  # from . import X  or  from .X import Y
        target_package = current_file.parent
    else:  # level >= 2: from ..X import Y etc.
        up = level - 1
        target_package = current_file.parent
        for _ in range(up):
            if target_package != target_package.parent:
                target_package = target_package.parent
            else:
                return None  # went past root

    if imported:
        target_module = imported.replace('.', '/')
        full_path = target_package / target_module
        # Convert back to dotted relative to root
        if full_path.exists() or (full_path.with_suffix('.py')).exists() or (full_path / '__init__.py').exists():
            try:
                rel = full_path.relative_to(root)
                parts = list(rel.parts)
                if (full_path / '__init__.py').exists():
                    pass  # keep all parts
                elif full_path.is_file() and full_path.name.endswith('.py'):
                    parts[-1] = parts[-1][:-3]
                return '.'.join(parts)
            except ValueError:
                pass
        return None
    else:
        # from . import X — target_package is the package itself
        try:
            rel = target_package.relative_to(root)
            return '.'.join(rel.parts)
        except ValueError:
            return None


def scan_imports(root: Path) -> Dict[str, Set[str]]:
    """Scan all Python files under root and return {module: {imported_modules}}."""
    graph = defaultdict(set)
    all_modules = set()

    # First pass: collect all module names
    for filepath in python_files(root):
        mod = module_name(filepath, root)
        all_modules.add(mod)

    # Second pass: resolve imports
    for filepath in python_files(root):
        src_mod = module_name(filepath, root)
        try:
            content = filepath.read_text(errors='ignore')
            tree = ast.parse(content, filename=str(filepath))
        except Exception:
            continue

        for node in ast.walk(tree):
            if isinstance(node, ast.Import):
                for alias in node.names:
                    name = alias.name.split('.')[0]  # top-level package only
                    # If name matches a local module, add edge
                    if any(m.startswith(name) for m in all_modules):
                        graph[src_mod].add(name)
            elif isinstance(node, ast.ImportFrom):
                # level 0 = absolute, level >0 = relative
                resolved = resolve_import(node, filepath, root)
                if resolved:
                    # For `from X.Y import Z`, the dependency is on X.Y
                    graph[src_mod].add(resolved)
                else:
                    # Unresolvable — likely external (stdlib/third-party)
                    pass

    return dict(graph)


def detect_cycles(graph: Dict[str, Set[str]]) -> List[List[str]]:
    """Detect all cycles in the directed graph using DFS."""
    cycles = []
    visited = set()
    rec_stack = set()
    path = []

    def dfs(node: str):
        visited.add(node)
        rec_stack.add(node)
        path.append(node)

        for neighbor in sorted(graph.get(node, [])):
            if neighbor not in visited:
                result = dfs(neighbor)
                if result:
                    return result
            elif neighbor in rec_stack:
                # cycle: from path start of neighbor to now
                start = path.index(neighbor)
                return path[start:] + [neighbor]

        path.pop()
        rec_stack.remove(node)
        return None

    for node in sorted(graph):
        if node not in visited:
            cycle = dfs(node)
            if cycle:
                cycles.append(cycle)

    return cycles


def to_dot(graph: Dict[str, Set[str]], cycles: List[List[str]] = None) -> str:
    """Generate DOT format output."""
    cycle_nodes = set()
    if cycles:
        for cycle in cycles:
            cycle_nodes.update(cycle)

    lines = ['digraph import_graph {']
    lines.append('  rankdir=LR;')
    lines.append('  node [shape=box, style=filled, fontname="Helvetica"];')
    lines.append('  edge [arrowhead=vee];')
    lines.append('')

    for src in sorted(graph):
        fill = '#2d1b69' if src in cycle_nodes else '#16213e'
        lines.append(f'  "{src}" [fillcolor="{fill}"];')

    for src, deps in sorted(graph.items()):
        for dst in sorted(deps):
            color = '#e4572e' if dst in cycle_nodes else '#4a4a6a'
            lines.append(f'  "{src}" -> "{dst}" [color="{color}"];')

    lines.append('}')
    return '\n'.join(lines)


def main():
    parser = argparse.ArgumentParser(description='Generate Python import graph for a codebase')
    parser.add_argument('path', help='Path to Python project (e.g. hermes-agent directory)')
    parser.add_argument('--output', '-o', help='Write DOT to file instead of stdout')
    parser.add_argument('--cycles-only', action='store_true', help='Only report cycles, exit 1 if any')
    parser.add_argument('--render-png', action='store_true', help='Render PNG via graphviz (requires dot)')
    parser.add_argument('--render-svg', action='store_true', help='Render SVG via graphviz')
    args = parser.parse_args()

    root = Path(args.path).resolve()
    if not root.is_dir():
        print(f"Error: {root} is not a directory", file=sys.stderr)
        sys.exit(1)

    print(f"Scanning {root}...", file=sys.stderr)
    graph = scan_imports(root)
    cycles = detect_cycles(graph)

    if args.cycles_only:
        if cycles:
            print("CIRCULAR DEPENDENCIES:", file=sys.stderr)
            for cycle in cycles:
                print(f"  {' → '.join(cycle)}", file=sys.stderr)
            sys.exit(1)
        else:
            print("No circular dependencies found.", file=sys.stderr)
            sys.exit(0)

    # Prepare output
    output = to_dot(graph, cycles)

    if args.output:
        Path(args.output).write_text(output)
        print(f"DOT written to {args.output}", file=sys.stderr)

        # Optional rendering
        if args.render_png or args.render_svg:
            import subprocess
            out_path = Path(args.output)
            if args.render_png:
                png_out = out_path.with_suffix('.png')
                subprocess.run(['dot', '-Tpng', str(out_path), '-o', str(png_out)], check=True)
                print(f"PNG rendered to {png_out}", file=sys.stderr)
            if args.render_svg:
                svg_out = out_path.with_suffix('.svg')
                subprocess.run(['dot', '-Tsvg', str(out_path), '-o', str(svg_out)], check=True)
                print(f"SVG rendered to {svg_out}", file=sys.stderr)
    else:
        print(output)

    # Summary
    print(f"\nSummary: {len(graph)} modules, {sum(len(d) for d in graph.values())} import edges, {len(cycles)} cycles",
          file=sys.stderr)


if __name__ == '__main__':
    main()