"""Generate firmware C++ header and Python module from modbus_registers.yaml.

The YAML at ``firmware/ar_autopilot_v1/modbus_registers.yaml`` is the single
source of truth for the Modbus RTU register map shared between the ESP32
firmware and the Python tooling / Studio simulator. This script regenerates:

- ``firmware/ar_autopilot_v1/src/protocols/modbus_registers.h``
- ``arautopilot/shared/modbus_register_map.py``

Run from the repository root:

    python tools/gen_modbus_registers.py
"""

from __future__ import annotations

import argparse
import sys
from dataclasses import dataclass
from pathlib import Path
from typing import Any

import yaml

REPO_ROOT = Path(__file__).resolve().parent.parent
YAML_PATH = REPO_ROOT / "firmware/ar_autopilot_v1/modbus_registers.yaml"
HEADER_PATH = (
    REPO_ROOT / "firmware/ar_autopilot_v1/src/protocols/modbus_registers.h"
)
PY_PATH = REPO_ROOT / "arautopilot/shared/modbus_register_map.py"


@dataclass(frozen=True)
class Entry:
    addr: int
    name: str
    desc: str
    unit: str = ""
    scale: float = 1.0
    offset: float = 0.0


@dataclass(frozen=True)
class RegisterMap:
    schema_version: str
    slave_id: int
    baudrate: int
    parity: str
    data_bits: int
    stop_bits: int
    discretes: list[Entry]
    coils: list[Entry]
    inputs: list[Entry]
    holdings: list[Entry]


def load_yaml(path: Path) -> RegisterMap:
    raw: dict[str, Any] = yaml.safe_load(path.read_text(encoding="utf-8"))

    def to_entries(items: list[dict[str, Any]]) -> list[Entry]:
        out: list[Entry] = []
        seen: set[int] = set()
        for item in items:
            addr = int(item["addr"])
            if addr in seen:
                raise ValueError(f"duplicate address {addr} in {path.name}")
            seen.add(addr)
            out.append(
                Entry(
                    addr=addr,
                    name=str(item["name"]),
                    desc=str(item.get("desc", "")),
                    unit=str(item.get("unit", "")),
                    scale=float(item.get("scale", 1.0)),
                    offset=float(item.get("offset", 0.0)),
                )
            )
        out.sort(key=lambda e: e.addr)
        return out

    return RegisterMap(
        schema_version=str(raw["schema_version"]),
        slave_id=int(raw["slave_id"]),
        baudrate=int(raw["baudrate"]),
        parity=str(raw["parity"]),
        data_bits=int(raw["data_bits"]),
        stop_bits=int(raw["stop_bits"]),
        discretes=to_entries(raw.get("discretes", [])),
        coils=to_entries(raw.get("coils", [])),
        inputs=to_entries(raw.get("inputs", [])),
        holdings=to_entries(raw.get("holdings", [])),
    )


def _max_addr(entries: list[Entry]) -> int:
    return max((e.addr for e in entries), default=-1)


def render_header(rm: RegisterMap) -> str:
    lines: list[str] = []
    a = lines.append
    a("// =============================================================================")
    a("//  modbus_registers.h -- AR-Autopilot Modbus RTU register map")
    a("// =============================================================================")
    a("//")
    a("//  AUTO-GENERATED. Do not edit by hand.")
    a("//  Source: firmware/ar_autopilot_v1/modbus_registers.yaml")
    a("//  Regenerate with: python tools/gen_modbus_registers.py")
    a("// =============================================================================")
    a("")
    a("#pragma once")
    a("")
    a("#include <cstdint>")
    a("")
    a("namespace arautopilot::protocols::modbus {")
    a("")
    a(f'constexpr const char* MAP_SCHEMA_VERSION = "{rm.schema_version}";')
    a(f"constexpr uint8_t  SLAVE_ID  = {rm.slave_id};")
    a(f"constexpr uint32_t BAUDRATE  = {rm.baudrate};")
    a(f'constexpr char     PARITY    = \'{rm.parity}\';')
    a(f"constexpr uint8_t  DATA_BITS = {rm.data_bits};")
    a(f"constexpr uint8_t  STOP_BITS = {rm.stop_bits};")
    a("")

    def block(kind: str, prefix: str, entries: list[Entry]) -> None:
        a(f"// ----- {kind} -----")
        a(f"constexpr uint16_t {prefix}_COUNT = {len(entries)};")
        max_a = _max_addr(entries)
        a(f"constexpr uint16_t {prefix}_MAX_ADDR = {max_a};")
        a("")
        for e in entries:
            a(f"// {e.desc}")
            extras = []
            if e.unit:
                extras.append(f"unit={e.unit}")
            if e.scale != 1.0:
                extras.append(f"scale={e.scale}")
            if e.offset != 0.0:
                extras.append(f"offset={e.offset}")
            if extras:
                a("// " + ", ".join(extras))
            a(f"constexpr uint16_t {prefix}_{e.name} = {e.addr};")
        a("")

    block("Discrete inputs (read-only bits)", "DISCRETE", rm.discretes)
    block("Coils (read-write bits)", "COIL", rm.coils)
    block("Input registers (read-only words)", "INPUT", rm.inputs)
    block("Holding registers (read-write words)", "HOLDING", rm.holdings)

    a("}  // namespace arautopilot::protocols::modbus")
    a("")
    return "\n".join(lines)


def render_python(rm: RegisterMap) -> str:
    lines: list[str] = []
    a = lines.append
    a('"""AR-Autopilot Modbus RTU register map -- generated mirror of the firmware.')
    a("")
    a("AUTO-GENERATED. Do not edit by hand.")
    a("Source: firmware/ar_autopilot_v1/modbus_registers.yaml")
    a("Regenerate with: python tools/gen_modbus_registers.py")
    a('"""')
    a("")
    a("from __future__ import annotations")
    a("")
    a("from dataclasses import dataclass")
    a("")
    a("")
    a("@dataclass(frozen=True)")
    a("class Reg:")
    a('    """One Modbus register entry as seen from Python tooling."""')
    a("    addr: int")
    a("    name: str")
    a("    desc: str = \"\"")
    a("    unit: str = \"\"")
    a("    scale: float = 1.0")
    a("    offset: float = 0.0")
    a("")
    a("")
    a(f'MAP_SCHEMA_VERSION = "{rm.schema_version}"')
    a(f"SLAVE_ID = {rm.slave_id}")
    a(f"BAUDRATE = {rm.baudrate}")
    a(f'PARITY = "{rm.parity}"')
    a(f"DATA_BITS = {rm.data_bits}")
    a(f"STOP_BITS = {rm.stop_bits}")
    a("")

    def block(group_name: str, entries: list[Entry]) -> None:
        a(f"# {group_name.upper()}")
        a(f"{group_name.upper()}: dict[str, Reg] = {{")
        for e in entries:
            a(
                f'    "{e.name}": Reg('
                f"addr={e.addr}, "
                f'name="{e.name}", '
                f'desc={e.desc!r}, '
                f'unit="{e.unit}", '
                f"scale={e.scale}, "
                f"offset={e.offset}),"
            )
        a("}")
        a("")

    block("discretes", rm.discretes)
    block("coils", rm.coils)
    block("inputs", rm.inputs)
    block("holdings", rm.holdings)

    a("ALL_GROUPS: dict[str, dict[str, Reg]] = {")
    a('    "discretes": DISCRETES,')
    a('    "coils": COILS,')
    a('    "inputs": INPUTS,')
    a('    "holdings": HOLDINGS,')
    a("}")
    a("")
    return "\n".join(lines)


def main(argv: list[str] | None = None) -> int:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument(
        "--check",
        action="store_true",
        help="Exit non-zero if the generated files are out of date; do not write.",
    )
    args = parser.parse_args(argv)

    rm = load_yaml(YAML_PATH)
    header = render_header(rm)
    pymod = render_python(rm)

    if args.check:
        ok = True
        for path, expected in ((HEADER_PATH, header), (PY_PATH, pymod)):
            actual = path.read_text(encoding="utf-8") if path.exists() else ""
            if actual != expected:
                print(f"OUT-OF-DATE: {path.relative_to(REPO_ROOT)}", file=sys.stderr)
                ok = False
        return 0 if ok else 1

    HEADER_PATH.parent.mkdir(parents=True, exist_ok=True)
    PY_PATH.parent.mkdir(parents=True, exist_ok=True)
    HEADER_PATH.write_text(header, encoding="utf-8")
    PY_PATH.write_text(pymod, encoding="utf-8")
    print(f"wrote {HEADER_PATH.relative_to(REPO_ROOT)}")
    print(f"wrote {PY_PATH.relative_to(REPO_ROOT)}")
    print(
        f"  discretes={len(rm.discretes)}  coils={len(rm.coils)}  "
        f"inputs={len(rm.inputs)}  holdings={len(rm.holdings)}"
    )
    return 0


if __name__ == "__main__":
    raise SystemExit(main())