#!/usr/bin/env python3
"""
merge_prefs.py — Merge Illuscape config patch into Inkscape preferences.xml

Usage:
    python3 merge_prefs.py --prefs ~/.config/inkscape/preferences.xml \
                           --patch config/preferences-patch.xml \
                           --preset cc|cs6
"""
import argparse
import os
import shutil
import tempfile
from pathlib import Path
from xml.etree import ElementTree as ET

PRESET_OVERRIDES = {
    "cc": {
        ("options", "keyboard"): {"file": "illustrator-cc"},
        ("options", "units"): {"doc": "px", "font": "px"},
    },
    "cs6": {
        ("options", "keyboard"): {"file": "illustrator-cs6"},
        ("options", "units"): {"doc": "pt", "font": "pt"},
    },
}


def _atomic_write(tree: ET.ElementTree, path: Path) -> None:
    """Write XML tree atomically — prevents corruption on interrupt."""
    fd, tmp = tempfile.mkstemp(dir=path.parent, suffix=".tmp")
    try:
        with os.fdopen(fd, "w", encoding="utf-8") as fh:
            tree.write(fh, encoding="unicode", xml_declaration=True)
        os.replace(tmp, path)
    except Exception:
        try:
            os.unlink(tmp)
        except OSError:
            pass
        raise


def _merge_nodes(live_parent: ET.Element, patch_parent: ET.Element) -> None:
    """Recursively upsert patch_parent's children into live_parent."""
    for patch_child in patch_parent:
        child_id = patch_child.get("id")
        if child_id is None:
            continue
        live_child = next(
            (c for c in live_parent if c.get("id") == child_id), None
        )
        if live_child is None:
            live_child = ET.SubElement(live_parent, patch_child.tag)
            live_child.set("id", child_id)
        for attr, value in patch_child.attrib.items():
            if attr != "id":
                live_child.set(attr, value)
        _merge_nodes(live_child, patch_child)


def _apply_preset(root: ET.Element, preset: str) -> None:
    """Apply preset-specific overrides (active keys file, document units)."""
    if preset not in PRESET_OVERRIDES:
        raise ValueError(f"Unknown preset {preset!r}. Valid: {list(PRESET_OVERRIDES)}")
    for id_path, attrs in PRESET_OVERRIDES[preset].items():
        node = root
        for id_val in id_path:
            child = next((c for c in node if c.get("id") == id_val), None)
            if child is None:
                child = ET.SubElement(node, "group")
                child.set("id", id_val)
            node = child
        for attr, value in attrs.items():
            node.set(attr, value)


def merge(prefs_path: Path, patch_path: Path, preset: str) -> None:
    """Merge patch into prefs, applying preset overrides. Lenient: creates prefs if missing."""
    patch_tree = ET.parse(patch_path)  # raises FileNotFoundError or ParseError
    patch_root = patch_tree.getroot()

    if not prefs_path.exists():
        # Lenient: seed from patch, let Inkscape fill in the rest on first launch
        prefs_path.parent.mkdir(parents=True, exist_ok=True)
        shutil.copy(patch_path, prefs_path)
        live_tree = ET.parse(prefs_path)
        _apply_preset(live_tree.getroot(), preset)
        _atomic_write(live_tree, prefs_path)
        return

    live_tree = ET.parse(prefs_path)  # raises ParseError on malformed XML
    live_root = live_tree.getroot()

    _merge_nodes(live_root, patch_root)
    _apply_preset(live_root, preset)

    live_tree.write(str(prefs_path), encoding="unicode", xml_declaration=True)


def main() -> None:
    parser = argparse.ArgumentParser(
        description="Merge Illuscape preferences patch into Inkscape preferences.xml"
    )
    parser.add_argument("--prefs", required=True, type=Path)
    parser.add_argument("--patch", required=True, type=Path)
    parser.add_argument("--preset", required=True, choices=["cc", "cs6"])
    args = parser.parse_args()

    merge(args.prefs, args.patch, args.preset)
    print(f"Illuscape preferences merged ({args.preset} preset)")


if __name__ == "__main__":
    main()