"""Build provenance and exact-file SHA-256, shared by CCS, Keil and CLI builds.

prepare runs BEFORE compiling; seal runs AFTER binary conversion and size checks.
The digest is external to the image, avoiding the self-hashing paradox. No MCU
protocol encoding lives here: the generated header contains scalar constants.
"""
from __future__ import annotations

import argparse
from datetime import datetime, timezone
import hashlib
import json
import os
from pathlib import Path
import subprocess


def git_state(repository: Path) -> dict:
    """Record full commits, and flag untracked sources as well as tracked edits.

    Generated outputs must be ignored in the repository. Unlike Climate's older
    helper, a new, untracked source file must not look like a clean release.
    """
    def git(*args):
        return subprocess.check_output(
            ["git", "-C", str(repository), *args], stderr=subprocess.DEVNULL,
            text=True, encoding="utf-8").strip()
    try:
        commit = git("rev-parse", "HEAD")
        dirty = bool(git("status", "--porcelain", "--untracked-files=normal"))
        return {"commit": commit, "dirty": dirty}
    except (OSError, subprocess.CalledProcessError):
        return {"commit": None, "dirty": None}


def write_atomic(path: Path, text: str):
    path.parent.mkdir(parents=True, exist_ok=True)
    temporary = path.with_name(path.name + ".tmp")
    temporary.write_text(text, encoding="utf-8", newline="\n")
    temporary.replace(path)


def prepare(repository: Path, templates: Path, config: Path, output: Path) -> dict:
    settings = json.loads(config.read_text(encoding="utf-8"))
    version = settings["version"]
    if (len(version) != 3 or any(type(v) is not int for v in version)
            or not all(0 <= v <= limit for v, limit in zip(version, (255, 255, 999)))):
        raise ValueError("version must be [major 0..255, minor 0..255, patch 0..999]")
    for field in ("product", "target"):
        if not isinstance(settings.get(field), str) or not settings[field].strip():
            raise ValueError(f"missing {field}")
    source, dependency = git_state(repository), git_state(templates)
    # A clean application built with a modified templates checkout is dirty too.
    known = source["commit"] is not None and dependency["commit"] is not None
    dirty = bool(source["dirty"] or dependency["dirty"])
    build_id = (source["commit"][:7] + "+" if dirty else source["commit"][:8]) if known else "NOGIT000"
    # UTC has an explicit interpretation across build PCs; SOURCE_DATE_EPOCH is
    # supported for reproducible release builds, not silently inferred from Git.
    epoch = os.environ.get("SOURCE_DATE_EPOCH")
    stamp = datetime.fromtimestamp(int(epoch), timezone.utc) if epoch else datetime.now(timezone.utc)
    stamp = stamp.replace(microsecond=0)
    if not 2000 <= stamp.year <= 2199:
        raise ValueError("build year outside firmware-info v1 range")
    metadata = {"schema": 1, "product": settings["product"], "target": settings["target"],
                "version": version, "build_id": build_id, "built_at_utc": stamp.isoformat(),
                "source": source, "templates": dependency,
                "identity_contract": 1, "identity_register_count": 12}
    constants = dict(zip(("FIRMWARE_VERSION_MAJOR", "FIRMWARE_VERSION_MINOR", "FIRMWARE_VERSION_PATCH"), version))
    constants.update(dict(zip(("FI_YEAR", "FI_MONTH", "FI_DAY", "FI_HOUR", "FI_MINUTE", "FI_SECOND"),
                              (stamp.year, stamp.month, stamp.day, stamp.hour, stamp.minute, stamp.second))))
    constants.update({f"FI_ID_{i}": ord(c) for i, c in enumerate(build_id)})
    header = "/* Generated before compilation. Do not edit or commit. UTC stamp. */\n#ifndef FIRMWARE_IDENTITY_H\n#define FIRMWARE_IDENTITY_H\n"
    header += f'#define FIRMWARE_BUILD_ID "{build_id}"\n'
    header += "".join(f"#define {key} {value}U\n" for key, value in constants.items())
    header += "#endif\n"
    # Rewriting the header forces the identity compilation unit to be rebuilt.
    # Sharing this directory between concurrent configurations is unsupported.
    write_atomic(output / "firmware_identity.h", header)
    write_atomic(output / "firmware_identity.json", json.dumps(metadata, indent=2) + "\n")
    return metadata


def seal(image: Path, metadata_path: Path) -> dict:
    metadata = json.loads(metadata_path.read_text(encoding="utf-8"))
    data = image.read_bytes()
    if not data:
        raise ValueError("empty firmware image")
    # Seal records the exact file sent to the programmer, including SCI8 headers.
    # It does not claim that the device has measured RAM/Flash or authenticated it.
    metadata.update({"file": image.name, "size_bytes": len(data),
                     "sha256": hashlib.sha256(data).hexdigest()})
    write_atomic(image.with_suffix(image.suffix + ".manifest.json"), json.dumps(metadata, indent=2) + "\n")
    write_atomic(image.with_suffix(image.suffix + ".sha256"), f'{metadata["sha256"]}  {image.name}\n')
    return metadata


def verify(image: Path, manifest: Path) -> dict:
    metadata = json.loads(manifest.read_text(encoding="utf-8"))
    data = image.read_bytes()
    if len(data) != metadata["size_bytes"] or hashlib.sha256(data).hexdigest() != metadata["sha256"]:
        raise ValueError("firmware size/SHA-256 does not match manifest")
    return metadata


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    sub = parser.add_subparsers(dest="command", required=True)
    p = sub.add_parser("prepare")
    for name in ("repository", "templates", "config", "output"):
        p.add_argument("--" + name, type=Path, required=True)
    p = sub.add_parser("seal")
    p.add_argument("--image", type=Path, required=True)
    p.add_argument("--metadata", dest="metadata_path", type=Path, required=True)
    p = sub.add_parser("verify")
    p.add_argument("--image", type=Path, required=True)
    p.add_argument("--manifest", type=Path, required=True)
    args = vars(parser.parse_args())
    command = args.pop("command")
    result = {"prepare": prepare, "seal": seal, "verify": verify}[command](**args)
    print(json.dumps(result, ensure_ascii=False))


if __name__ == "__main__":
    main()