"""Pad net on the PCB vs pin net on the schematic graph.

Silent when either side has no name. Power-flag footprints (#PWR) skipped.

KiCad PCB net names often keep a root-sheet ``/`` (and nested sheet path)
that a flattened schematic netlist omits. Those are the same net: do not
emit per-pad reconnect findings.
"""

from __future__ import annotations

from backend.periscopex.models import DesignGraph, Finding, LayoutGraph


def normalize_kicad_hierarchy_net(name: str) -> str:
    """Drop leading slashes; keep inner sheet path (``sheet/NET``)."""
    n = (name or "").strip().replace("\\", "/")
    while n.startswith("/"):
        n = n[1:]
    while n.endswith("/") and n:
        n = n[:-1]
    return n


def kicad_nets_match(a: str, b: str) -> bool:
    """True if schematic and PCB names are the same KiCad net.

    Equal strings match. After stripping leading ``/``, equal names match
    (``/ESP32_EN`` vs ``ESP32_EN``). A flattened leaf also matches a nested
    path that ends with ``/{leaf}`` (``REGN`` vs ``/power/REGN``). Different
    sheets that only share a last segment (``sheet1/CLK`` vs ``sheet2/CLK``)
    do not match each other.
    """
    if not a or not b:
        return False
    if a == b:
        return True
    na = normalize_kicad_hierarchy_net(a)
    nb = normalize_kicad_hierarchy_net(b)
    if not na or not nb:
        return False
    if na == nb:
        return True
    return na.endswith("/" + nb) or nb.endswith("/" + na)


def _ensure_recommendation(f: Finding) -> Finding:
    if not (f.recommendation or "").strip():
        f.recommendation = (
            "Align the PCB pad net with the schematic pin, then re-run PCB review."
        )
    return f


def _hierarchy_only_mismatch(pcb_net: str, sch_net: str) -> bool:
    """PCB vs schematic differ only by KiCad sheet-path prefix."""
    if pcb_net == sch_net:
        return False
    return kicad_nets_match(pcb_net, sch_net)


def check_pcb_net_match(
    graph: DesignGraph,
    layout: LayoutGraph | None,
) -> list[Finding]:
    if layout is None or not layout.footprints:
        return []
    findings: list[Finding] = []
    sch_refs = {
        ref for ref in graph.components
        if not ref.startswith("#")
    }
    pcb_refs = {
        ref for ref in layout.footprints
        if not ref.startswith("#")
    }

    for ref in sorted(sch_refs - pcb_refs):
        comp = graph.components[ref]
        findings.append(_ensure_recommendation(Finding(
            designator=ref,
            mpn=comp.mpn or "",
            aspect="pcb_match",
            finding=f"{ref} is in the schematic but has no footprint on the PCB.",
            why="Layout review cannot check a part that is not placed.",
            status="WARNING",
            recommendation=f"Place {ref} on the board or remove it from the schematic/BOM.",
            source="pcb_net_match",
            rule_id="PE-LAY-002",
            pins=[],
        )))

    real: list[tuple[str, str, str, str]] = []  # ref, pad, pcb_net, sch_net
    hierarchy: list[tuple[str, str, str, str]] = []

    for ref, fp in sorted(layout.footprints.items()):
        if ref.startswith("#"):
            continue
        comp = graph.components.get(ref)
        if comp is None:
            continue
        for pad in fp.pads:
            if not pad.net or not pad.number:
                continue
            sch_net = graph.pin_net(ref, pad.number)
            if not sch_net:
                continue
            if pad.net == sch_net:
                continue
            if _hierarchy_only_mismatch(pad.net, sch_net):
                hierarchy.append((ref, pad.number, pad.net, sch_net))
                continue
            real.append((ref, pad.number, pad.net, sch_net))

    if hierarchy and not real:
        examples: list[str] = []
        seen_pairs: set[tuple[str, str]] = set()
        for _ref, _pad, pcb_net, sch_net in hierarchy:
            pair = (pcb_net, sch_net)
            if pair in seen_pairs:
                continue
            seen_pairs.add(pair)
            examples.append(f"PCB '{pcb_net}' ↔ schematic '{sch_net}'")
            if len(examples) >= 8:
                break
        extra = len(seen_pairs) - len(examples)
        example_txt = "; ".join(examples)
        if extra > 0:
            example_txt += f" (+{extra} more)"
        first_ref = hierarchy[0][0]
        first_comp = graph.components.get(first_ref)
        findings.append(_ensure_recommendation(Finding(
            designator=first_ref,
            mpn=(first_comp.mpn if first_comp else "") or "",
            aspect="pcb_match",
            finding=(
                "Schematic and PCB net names differ only by KiCad hierarchy "
                f"prefix ({len(hierarchy)} pads). Examples: {example_txt}."
            ),
            why=(
                "KiCad stores board nets with a leading '/' and optional sheet "
                "path; a flattened schematic netlist usually omits that prefix. "
                "These pads are the same electrical nets."
            ),
            status="INFO",
            recommendation=(
                "Update the PCB from the schematic (or re-export a netlist with "
                "the same hierarchy flattening) so names match. Do not retouch "
                "individual pads."
            ),
            source="pcb_net_match",
            rule_id="PE-LAY-003",
            pins=[],
        )))

    for ref, pad_no, pcb_net, sch_net in real:
        comp = graph.components[ref]
        findings.append(_ensure_recommendation(Finding(
            designator=ref,
            mpn=comp.mpn or "",
            aspect="pcb_match",
            finding=(
                f"{ref}.{pad_no} PCB net '{pcb_net}' does not match "
                f"schematic net '{sch_net}'."
            ),
            why=(
                "Datasheet and SI checks follow schematic net names. "
                "A pad on the wrong net is a layout error, not a BOM typo."
            ),
            status="ERROR",
            recommendation=(
                f"Reconnect pad {ref}.{pad_no} to '{sch_net}' "
                f"(or fix the schematic if the PCB is authoritative)."
            ),
            source="pcb_net_match",
            rule_id="PE-LAY-001",
            net=pcb_net,
            pins=[pad_no],
        )))
    return findings