"""Compose a Low-throttle fuel correction on top of an already-composed map.

Second layer in a two-step derivation:
    20262Map.hex
      -> compose_arrow_delete.py -> 20262-arrow-delete-composed.hex   (layer 1)
      -> compose_lowthrottle.py  -> 20262-arrow-delete-lowthrottle-composed.hex  (layer 2)

Layer 2 is additive on top of layer 1's own values, not a fresh edit of stock
20262 -- it composes with whatever layer 1 already did (SAI/O2 off, idle-CO
trim), the same "respect what's already there" principle used throughout
this project.

Motivation (2026-09-10 session): real-world reports of stalling/choking
under ~10% throttle and while blipping the throttle at low speed, after
snorkel removal with no main-table correction for the extra airflow.
Confirmed via a real percentage-delta pulled from a genuine reference file
that also had its snorkel removed: `20184dynoTuneSteveO2-Disable.hex` vs
its own stock baseline `20186Map.hex`, in the "Low-throttle fuel" tables
(cyl 1 @ fe=15, cyl 2 @ fe=16 -- see TABLES.md), restricted to the
throttle columns actually implicated by the reported symptom (raw
throttle-axis value <= 100, i.e. <= 10.0%).

Method: percentage delta, not flat additive -- VE/fuel-mass values scale
with magnitude, and Arrow's own low-throttle table already differs from
stock (it has its own exhaust-specific correction baked in), so the right
operation is "apply the same proportional richening the reference delete
map needed" on top of whatever value is already there, not overwrite it.

    pct(row, col)  = (delete_ref[row][col] - stock_ref[row][col]) / stock_ref[row][col]
    new(row, col)  = round(base[row][col] * (1 + pct(row, col)))

Usage:
    python3 compose_lowthrottle.py \\
        derived/20262-arrow-delete-composed.hex \\
        20186Map.hex 20184dynoTuneSteveO2-Disable.hex \\
        derived/20262-arrow-delete-lowthrottle-composed.hex
"""

from __future__ import annotations

import struct
import sys

import checksum
from decode_map import decode, encode
from table_map import resolve
from toggle_devices import repack, unpack

LOW_THROTTLE_TABLES = ("Low-throttle fuel — cyl 1", "Low-throttle fuel — cyl 2")
MAX_SANE_VALUE = 20000  # real VE values in every reference file top out ~11000


def _table_by_name(resolved: dict, name: str) -> dict:
    for t in resolved["tables"]:
        if t["name"] == name:
            return t
    raise KeyError(name)


def compose(base_raw: bytes, stock_raw: bytes, delete_raw: bytes, base_path: str, stock_path: str, delete_path: str) -> tuple[bytes, list[str]]:
    base_dec = decode(base_raw)
    base_rom, positions = unpack(base_dec)
    base_rom = bytearray(base_rom)

    base_resolved = resolve(base_path)
    stock_resolved = resolve(stock_path)
    delete_resolved = resolve(delete_path)

    throttle_axis = base_resolved["throttle_axis"]
    low_cols = [i for i, v in enumerate(throttle_axis) if v <= 100]

    notes = [f"low-throttle columns touched (raw<=100): {[throttle_axis[c] for c in low_cols]}"]

    for name in LOW_THROTTLE_TABLES:
        base_t = _table_by_name(base_resolved, name)
        stock_t = _table_by_name(stock_resolved, name)
        delete_t = _table_by_name(delete_resolved, name)

        off = base_t["offset"]  # this file's OWN resolved offset, not another file's
        rows, cols = base_t["rows"], base_t["cols"]

        changed = 0
        pct_min, pct_max = None, None
        for row in range(rows):
            for col in low_cols:
                stock_v = stock_t["data"][row][col]
                delete_v = delete_t["data"][row][col]
                base_v = base_t["data"][row][col]

                pct = (delete_v - stock_v) / stock_v if stock_v else 0.0
                new_v = round(base_v * (1 + pct))
                new_v = max(0, min(65535, new_v))

                if new_v > MAX_SANE_VALUE:
                    notes.append(
                        f"  WARNING {name} row={row} col={col}: "
                        f"computed {new_v} exceeds sanity bound {MAX_SANE_VALUE}"
                    )

                if new_v != base_v:
                    changed += 1
                    pct_min = pct if pct_min is None else min(pct_min, pct)
                    pct_max = pct if pct_max is None else max(pct_max, pct)

                byte_off = off + (row * cols + col) * 2
                struct.pack_into(">H", base_rom, byte_off, new_v)

        pct_range = f"{pct_min:+.1%} to {pct_max:+.1%}" if changed else "no change"
        notes.append(f"{name} (0x{off:05X}): {changed} cells touched, delta range {pct_range}")

    before_sum = checksum.stored(bytes(base_rom))
    checksum.patch(base_rom)
    after_sum = checksum.compute(bytes(base_rom))
    notes.append(f"checksum: stored {before_sum:04x} (stale) -> patched {after_sum:04x}")

    repacked = repack(base_dec, bytes(base_rom), positions)
    out = encode(repacked)
    assert decode(out) == repacked, "round-trip failed"
    return out, notes


def main() -> int:
    if len(sys.argv) != 5:
        print(
            "usage: compose_lowthrottle.py <base_composed.hex> <stock.hex> "
            "<delete_reference.hex> <outfile.hex>",
            file=sys.stderr,
        )
        return 2
    base_path, stock_path, delete_path, out_path = sys.argv[1:5]
    out, notes = compose(
        open(base_path, "rb").read(),
        open(stock_path, "rb").read(),
        open(delete_path, "rb").read(),
        base_path, stock_path, delete_path,
    )
    open(out_path, "wb").write(out)
    for n in notes:
        print(" ", n)
    print(f"wrote {out_path} ({len(out)} bytes)")
    print("NOTE: only the under-~10%-throttle columns of the two Low-throttle")
    print("      fuel tables were touched. Main fuel tables (>10% throttle)")
    print("      remain untouched stock-Arrow calibration.")
    return 0


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