"""Convert one EPRO2 SCH_PAGE Document → a KiCad ``.kicad_sch`` S-expr.

Phase-1 scope: paper + wires + junctions + symbol placements (no symbol body
bundled in lib_symbols). KiCad will render the resulting .kicad_sch with
visible wires/junctions but the symbol instances will appear as red question
marks until lib_symbols is populated (next phase).

Coordinate system:
  - EPRO2 schematic uses **mil** as its internal unit.
  - KiCad uses **mm**, with origin top-left, +Y down.
  - Y-axis already aligned (both Y-down), so we just apply ``MIL_TO_MM``.
  - We additionally translate so that the schematic's own bounding box has
    a small margin from page origin — keeps everything visible on A4.
"""

from __future__ import annotations

import math
import uuid as _uuid
from dataclasses import dataclass

from ..project_relations import ProjectRelations
from ..relations import Relations
from ..replay import Document
from .sexpr import Sym, to_sexpr

MIL_TO_MM = 0.0254

# KiCad sch S-expr metadata that doesn't depend on content.
KICAD_SCH_VERSION = 20231120
KICAD_GENERATOR = "facere-epro2"

# Default A4 in mm (KiCad uses these by default for "A4").
PAPER_A4_MM_W = 297.0
PAPER_A4_MM_H = 210.0


@dataclass
class WriteStats:
    wires: int = 0
    junctions: int = 0
    symbol_placements: int = 0
    text: int = 0
    labels: int = 0
    skipped: int = 0
    lib_symbols_embedded: int = 0
    lib_symbols_missing: int = 0


def _new_uuid() -> str:
    return str(_uuid.uuid4())


def _mil(v) -> float:
    """Coerce an EPRO2 mil value to mm. None / non-numeric → 0.0."""
    if v is None:
        return 0.0
    try:
        return float(v) * MIL_TO_MM
    except (TypeError, ValueError):
        return 0.0


def _stroke(width: float = 0.0, kind: str = "default") -> list:
    return [Sym("stroke"), [Sym("width"), width], [Sym("type"), Sym(kind)]]


def write_sch_page(
    doc: Document,
    *,
    title: str | None = None,
    sheet_origin_mm: tuple[float, float] = (25.4, 25.4),
    project_relations: ProjectRelations | None = None,
    sheet_path: str = "/",
    page_num: int = 1,
) -> str:
    """Render a single SCH_PAGE Document as kicad_sch text.

    ``sheet_origin_mm`` is added to every coordinate so the schematic doesn't
    sit at (0,0) (KiCad's title block lives there). Default 1 inch margin.

    When ``project_relations`` is given, the ``lib_symbols`` block is
    populated by resolving each placement's ``partId`` to the SYMBOL doc(s)
    hosting that PART; the body of the first matching SYMBOL is rendered via
    :func:`sym_writer.write_lib_symbol`. If a partId can't be resolved, we
    still emit the placement (KiCad shows a red ``?``).

    ``sheet_path`` and ``page_num`` describe this page's place in a
    hierarchical project. For a standalone page, the defaults emit
    ``(sheet_instances (path "/" (page "1")))`` which KiCad reads as a
    single-sheet project. When this page is included as a child of a root
    schematic, pass ``sheet_path="/<assigned_child_uuid>"`` (the uuid the
    root assigned to its ``(sheet ...)`` block for this child) and the
    page index in the hierarchy (root=1, children=2..N). Without this the
    KiCad hierarchy can't bind the child file to its root entry, and ERC
    treats the child as a disconnected island.
    """
    if doc.doc_type != "SCH_PAGE":
        raise ValueError(f"expected SCH_PAGE doc, got {doc.doc_type!r}")

    rel = Relations.build(doc)
    stats = WriteStats()

    ox, oy = sheet_origin_mm
    elements: list = []

    # 1. Wires from LINE primitives. Each LINE contributes one (wire ...).
    #    EPRO2 binds wires into nets by NAME (WIRE.NET attr), not just geometry,
    #    so we also emit a (label "<NET>") at one endpoint of each named LINE.
    #    Same-named labels on physically distinct LINEs are how KiCad's ERC
    #    recognizes a multi-segment net — without them every LINE looks like a
    #    dangling stub. We label per-LINE (not per-WIRE id) because a single
    #    WIRE op may contain segments that don't share endpoints, and KiCad
    #    flags any unlabeled segment in such a group as wire_dangling.
    wire_net_cache: dict[str, str | None] = {}
    for oid, obj in doc.objects.items():
        if obj.get("_type") != "LINE":
            continue
        x1 = ox + _mil(obj.get("startX"))
        y1 = oy + _mil(obj.get("startY"))
        x2 = ox + _mil(obj.get("endX"))
        y2 = oy + _mil(obj.get("endY"))
        # KiCad rejects degenerate zero-length wires
        if math.isclose(x1, x2) and math.isclose(y1, y2):
            stats.skipped += 1
            continue
        elements.append([
            Sym("wire"),
            [Sym("pts"), [Sym("xy"), x1, y1], [Sym("xy"), x2, y2]],
            _stroke(0.0),
            [Sym("uuid"), _new_uuid()],
        ])
        stats.wires += 1

        wire_id = obj.get("lineGroup")
        if not wire_id:
            continue
        wid = str(wire_id)
        if wid not in wire_net_cache:
            wire_net_cache[wid] = (rel.attrs_dict(wid) or {}).get("NET")
        net = wire_net_cache[wid]
        if not net:
            continue
        # global_label, not local label: EPRO2 nets are project-wide
        # (a "GND" net spans every page in the schematic and physically
        # connects to GND wires on neighbour PCBs). KiCad's local (label)
        # is sheet-scoped and triggers `label_dangling` whenever a name
        # only appears on one sheet — exactly the case we hit on every
        # cross-sheet net before. (global_label) is project-scoped and
        # gets resolved by hierarchical ERC on the root sheet.
        elements.append([
            Sym("global_label"), str(net),
            [Sym("shape"), Sym("passive")],
            [Sym("at"), x1, y1, 0],
            [Sym("effects"), [Sym("font"), [Sym("size"), 1.27, 1.27]],
                              [Sym("justify"), Sym("left")]],
            [Sym("uuid"), _new_uuid()],
        ])
        stats.labels += 1

    # 2. Symbol placements from COMPONENT ops. Body deferred to Phase 2 (lib_symbols).
    #    For now we emit (symbol ...) entries that reference a placeholder lib_id.
    #    KiCad will draw a red ? but the position + properties are correct.
    for cid, comp in rel.components.items():
        x = ox + _mil(comp.get("x"))
        y = oy + _mil(comp.get("y"))
        rot = float(comp.get("rotation") or 0)
        part_id = str(comp.get("partId") or "Unknown")
        attrs = rel.attrs_dict(cid)
        designator = str(attrs.get("Designator") or "")
        value = str(attrs.get("Value") or "")

        sym_block: list = [
            Sym("symbol"),
            [Sym("lib_id"), f"facere:{part_id}"],
            [Sym("at"), x, y, rot],
            [Sym("unit"), 1],
            [Sym("exclude_from_sim"), Sym("no")],
            [Sym("in_bom"), Sym("yes")],
            [Sym("on_board"), Sym("yes")],
            [Sym("dnp"), Sym("no")],
            [Sym("uuid"), _new_uuid()],
            [Sym("property"), "Reference", designator,
                [Sym("at"), x, y - 5, 0],
                [Sym("effects"), [Sym("font"), [Sym("size"), 1.27, 1.27]]]],
            [Sym("property"), "Value", value,
                [Sym("at"), x, y + 5, 0],
                [Sym("effects"), [Sym("font"), [Sym("size"), 1.27, 1.27]]]],
            [Sym("property"), "Footprint", "",
                [Sym("at"), x, y, 0],
                [Sym("effects"), [Sym("font"), [Sym("size"), 1.27, 1.27]],
                                  [Sym("hide"), Sym("yes")]]],
            [Sym("property"), "Datasheet", "",
                [Sym("at"), x, y, 0],
                [Sym("effects"), [Sym("font"), [Sym("size"), 1.27, 1.27]],
                                  [Sym("hide"), Sym("yes")]]],
        ]
        elements.append(sym_block)
        stats.symbol_placements += 1

        # Power-port instances: EPRO2 expresses things like VCC / GND / VBUS
        # as a generic "5-Voltage" symbol whose net name is carried by the
        # placement's `Global Net Name` ATTR (not by the underlying PART).
        # Without a global_label at the pin tip, every such placement
        # shows up as pin_not_connected even though it should anchor the
        # pin to a global rail.
        gnn = attrs.get("Global Net Name")
        if gnn:
            elements.append([
                Sym("global_label"), str(gnn),
                [Sym("shape"), Sym("passive")],
                [Sym("at"), x, y, 0],
                [Sym("effects"), [Sym("font"), [Sym("size"), 1.27, 1.27]],
                                  [Sym("justify"), Sym("left")]],
                [Sym("uuid"), _new_uuid()],
            ])
            stats.labels += 1

    # 3. Text labels from TEXT objects (best-effort — only those with a non-empty value).
    for oid, obj in doc.objects.items():
        if obj.get("_type") != "TEXT":
            continue
        val = str(obj.get("value") or "").strip()
        if not val:
            continue
        x = ox + _mil(obj.get("x"))
        y = oy + _mil(obj.get("y"))
        rot = float(obj.get("rotation") or 0)
        elements.append([
            Sym("text"),
            val,
            [Sym("at"), x, y, rot],
            [Sym("effects"), [Sym("font"), [Sym("size"), 1.27, 1.27]]],
            [Sym("uuid"), _new_uuid()],
        ])
        stats.text += 1

    sch_title = title or (
        (doc.objects.get("META") or {}).get("title")
        or doc.doc_uuid[:12]
    )

    # Populate lib_symbols block from used partIds (Phase 2).
    lib_symbols = _build_lib_symbols(rel, project_relations, stats) \
        if project_relations is not None else [Sym("lib_symbols")]

    sch: list = [
        Sym("kicad_sch"),
        [Sym("version"), KICAD_SCH_VERSION],
        [Sym("generator"), KICAD_GENERATOR],
        [Sym("uuid"), _new_uuid()],
        [Sym("paper"), "A4"],
        [Sym("title_block"),
            [Sym("title"), sch_title],
            [Sym("comment"), 1, f"epro2 doc_uuid: {doc.doc_uuid}"],
            [Sym("comment"), 2, f"editor: {doc.head.get('editVersion','')}"]],
        lib_symbols,
        *elements,
        [Sym("sheet_instances"),
            [Sym("path"), sheet_path, [Sym("page"), str(page_num)]]],
    ]

    # Stash stats on the function for tests / CLI to inspect.
    write_sch_page.last_stats = stats  # type: ignore[attr-defined]
    return to_sexpr(sch, pretty=True)


def _build_lib_symbols(
    sch_rel: Relations,
    pr: ProjectRelations,
    stats: WriteStats,
) -> list:
    """Resolve every COMPONENT.partId on this sheet to a SYMBOL doc and
    embed its body in the ``(lib_symbols ...)`` block.

    Returns the full ``[Sym("lib_symbols"), <symbol entry>, ...]`` list.
    """
    from .sym_writer import write_lib_symbol  # local to avoid cycle

    used_part_ids: set[str] = set()
    for cid, comp in sch_rel.components.items():
        pid = comp.get("partId")
        if pid:
            used_part_ids.add(str(pid))

    block: list = [Sym("lib_symbols")]
    seen_emitted: set[str] = set()
    for pid in sorted(used_part_ids):
        sym_docs = pr.parts_by_id.get(pid, [])
        if not sym_docs:
            stats.lib_symbols_missing += 1
            continue
        # Use first SYMBOL doc. Skip if same partId already emitted (dedupe).
        if pid in seen_emitted:
            continue
        sym_doc = pr.project.documents.get(sym_docs[0])
        if not sym_doc:
            stats.lib_symbols_missing += 1
            continue
        entry = write_lib_symbol(sym_doc)
        if entry is None:
            stats.lib_symbols_missing += 1
            continue
        block.append(entry)
        seen_emitted.add(pid)
        stats.lib_symbols_embedded += 1

    return block