#!/usr/bin/env python3
"""Extract a Python project's module-import graph as autolayout graph JSON.

Walks a package/project directory, parses each module with `ast`, builds the
intra-project import edges, and (by default) applies transitive reduction so
the diagram stays readable instead of becoming a hairball. The output feeds
autolayout.py:

  python3 pyimports.py myproject -o graph.json
  python3 autolayout.py graph.json -o diagram.drawio

Transitive reduction uses Graphviz `tred` (drops edges implied by a longer
path); pass --no-reduce to keep every import edge. Only intra-project imports
are kept — third-party and stdlib imports are ignored.

Usage: python3 pyimports.py <project_dir> [-o graph.json] [--direction TB|LR] [--no-reduce]
"""
import argparse
import ast
import json
import os
import re
import subprocess
import sys


def discover(root):
    """Map dotted module name -> file path for every .py under root, plus the
    package prefix. If root is itself a package (has __init__.py), module names
    are qualified with its name so the project's own absolute imports resolve."""
    root = os.path.abspath(root)
    base = os.path.basename(root) if os.path.exists(os.path.join(root, "__init__.py")) else ""
    modules = {}
    for dirpath, _, files in os.walk(root):
        for fn in files:
            if not fn.endswith(".py"):
                continue
            rel = os.path.relpath(os.path.join(dirpath, fn), root)[:-3]  # strip .py
            parts = rel.split(os.sep)
            if parts[-1] == "__init__":
                parts = parts[:-1]                                       # package = its dir
            parts = ([base] + parts) if base else parts
            if parts:
                modules[".".join(parts)] = os.path.join(dirpath, fn)
    return modules, base


def resolve(name, current, modules):
    """Resolve a dotted name to the longest known module prefix (or None)."""
    parts = name.split(".") if name else []
    while parts:
        cand = ".".join(parts)
        if cand in modules and cand != current:
            return cand
        parts = parts[:-1]
    return None


def edges_of(name, path, modules):
    """Intra-project modules imported by `name`."""
    pkg = name if path.endswith("__init__.py") else name.rsplit(".", 1)[0] if "." in name else ""
    found = set()
    try:
        with open(path, encoding="utf-8") as f:
            tree = ast.parse(f.read(), filename=path)
    except SyntaxError:
        return found
    for node in ast.walk(tree):
        if isinstance(node, ast.Import):                     # import a.b.c
            for alias in node.names:
                target = resolve(alias.name, name, modules)
                if target:
                    found.add(target)
        elif isinstance(node, ast.ImportFrom):               # from a.b import c
            if node.level:                                   # relative: climb level-1 packages
                base = pkg.split(".") if pkg else []
                base = base[: len(base) - (node.level - 1)]
                prefix = ".".join(base)
                mod = f"{prefix}.{node.module}" if prefix and node.module else (node.module or prefix)
            else:
                mod = node.module or ""
            target = resolve(mod, name, modules)
            if target:
                found.add(target)
            for alias in node.names:                         # `from pkg import submodule`
                sub = f"{mod}.{alias.name}" if mod else alias.name
                target = resolve(sub, name, modules)
                if target:
                    found.add(target)
    return found


def transitive_reduce(nodes, edges):
    """Drop edges implied by a longer path, via Graphviz `tred`."""
    idx = {n: i for i, n in enumerate(nodes)}
    dot = "digraph{" + "".join(f"{idx[s]}->{idx[t]};" for s, t in edges) + "}"
    try:
        out = subprocess.run(["tred"], input=dot, capture_output=True,
                             text=True, check=True).stdout
    except (FileNotFoundError, subprocess.CalledProcessError) as exc:
        sys.stderr.write(f"warning: tred unavailable, keeping all edges ({exc})\n")
        return edges
    rev = {i: n for n, i in idx.items()}
    return [(rev[int(a)], rev[int(b)]) for a, b in re.findall(r"(\d+)\s*->\s*(\d+)", out)]


def main():
    ap = argparse.ArgumentParser(description="Python import graph -> autolayout graph JSON.")
    ap.add_argument("project", help="package or project directory")
    ap.add_argument("-o", "--output", help="output JSON path (default: stdout)")
    ap.add_argument("--direction", default="TB", choices=["TB", "LR"])
    ap.add_argument("--group", action="store_true",
                    help="group nodes into containers by sub-package")
    ap.add_argument("--no-reduce", action="store_true",
                    help="keep every edge (skip transitive reduction)")
    args = ap.parse_args()

    modules, base = discover(args.project)
    if not modules:
        sys.exit(f"error: no .py modules found under {args.project}")
    edges = sorted({(name, t) for name, path in modules.items()
                    for t in edges_of(name, path, modules)})
    raw = len(edges)
    if not args.no_reduce:
        edges = transitive_reduce(list(modules), edges)
    # Drop the shared package prefix from labels for readability; ids stay full.
    strip = base + "." if base else ""
    label = lambda m: m[len(strip):] if strip and m.startswith(strip) else m

    def node(m):
        d = {"id": m, "label": label(m)}
        if args.group:
            rest = label(m).split(".")
            if len(rest) > 1:                            # nested under a sub-package
                d["group"] = "/".join(rest[:-1])         # full sub-package path -> nested boxes
        return d

    graph = {
        "direction": args.direction,
        "nodes": [node(m) for m in modules],
        "edges": [{"source": s, "target": t} for s, t in edges],
    }
    text = json.dumps(graph, indent=2)
    if args.output:
        with open(args.output, "w", encoding="utf-8") as f:
            f.write(text)
        sys.stderr.write(f"wrote {args.output}\n")
    else:
        sys.stdout.write(text)
    note = "" if args.no_reduce else f" (reduced from {raw})"
    sys.stderr.write(f"{len(modules)} modules, {len(edges)} edges{note}\n")


if __name__ == "__main__":
    main()