#!/usr/bin/env python3
"""Local backup capacity checks; no deletion, provider contact or app changes.

Candidate limits need operating admission. Estimates reserve complete pipeline
scratch, while RLIMIT_FSIZE bounds individual newly written files. This is not
a filesystem quota or a reservation against unrelated writers.
"""

from __future__ import annotations

import argparse
import json
import os
import resource
import shutil
import stat
from pathlib import Path

FILE_LIMIT = 1024**3
STATE_BUDGET = 8 * 1024**3
MINIMUM_FREE = 8 * 1024**3
CONTROL_MARGIN = 16 * 1024**2
MINIMUM_INODES = 1024


class Refused(ValueError):
    pass


def active_file_limit():
    return resource.getrlimit(resource.RLIMIT_FSIZE)[0]


def enforce_file_limit(maximum=FILE_LIMIT):
    soft, hard = resource.getrlimit(resource.RLIMIT_FSIZE)
    effective = min(
        [maximum] + [value for value in [soft, hard] if value != resource.RLIM_INFINITY]
    )
    if effective <= 0:
        raise Refused("positive_file_limit_required")
    resource.setrlimit(resource.RLIMIT_FSIZE, (effective, effective))
    return effective


def disk_free(path):
    return shutil.disk_usage(path).free


def free_inodes(path):
    return os.statvfs(path).f_favail


def state_usage(root):
    info = root.lstat()
    if (
        not stat.S_ISDIR(info.st_mode)
        or info.st_uid != os.geteuid()
        or info.st_mode & 0o077
        or root.resolve() != root.absolute()
    ):
        raise Refused("private_state_directory_required")

    def onerror(error):
        raise error

    used = max(info.st_size, info.st_blocks * 512)
    for directory, directories, files in os.walk(root, followlinks=False, onerror=onerror):
        for name in directories + files:
            item = (Path(directory) / name).lstat()
            if (
                not (stat.S_ISREG(item.st_mode) or stat.S_ISDIR(item.st_mode))
                or item.st_uid != os.geteuid()
                or item.st_mode & 0o077
                or (stat.S_ISREG(item.st_mode) and item.st_nlink != 1)
            ):
                raise Refused("unsafe_state_entry")
            used += max(item.st_size, item.st_blocks * 512)
    return used


def reserve_plan(
    state,
    *,
    phase="capture",
    require_file_limit=True,
    maximum_file=FILE_LIMIT,
    state_budget=STATE_BUDGET,
    minimum_free=MINIMUM_FREE,
):
    if phase not in {"capture", "resume", "mirror"} or any(
        type(v) is not int or v <= 0 for v in [maximum_file, state_budget, minimum_free]
    ):
        raise Refused("explicit_positive_capacity_profile_required")
    # New capture: dump, content, tar, ciphertext, readback, retained local copy,
    # and temporary rewritten inventory. Sealed retry needs three new large
    # files; mirror needs only its fresh ciphertext readback.
    slots = {"capture": 7, "resume": 3, "mirror": 1}[phase]
    state_reserve = slots * maximum_file + CONTROL_MARGIN
    # The existing command wrapper uses one anonymous output sink outside state.
    disk_reserve = state_reserve + maximum_file
    used, available, inodes = state_usage(state), disk_free(state), free_inodes(state)
    limit = active_file_limit()
    bounded = limit != resource.RLIM_INFINITY and 0 < limit <= maximum_file
    reasons = []
    if used + state_reserve > state_budget:
        reasons.append("local_retention_budget_required")
    if available < minimum_free + disk_reserve:
        reasons.append("disk_headroom_required")
    if inodes < MINIMUM_INODES:
        reasons.append("inode_headroom_required")
    if require_file_limit and not bounded:
        reasons.append("bounded_file_executor_required")
    return {
        "schema": "coulomb.backup-capacity.v1",
        "phase": phase,
        "status": "refused" if reasons else ("ready" if bounded else "reviewed_unbounded_executor"),
        "reasons": reasons,
        "state_bytes": used,
        "state_budget_bytes": state_budget,
        "state_reserve_bytes": state_reserve,
        "disk_reserve_bytes": disk_reserve,
        "free_bytes": available,
        "minimum_free_bytes": minimum_free,
        "free_inodes": inodes,
        "minimum_free_inodes": MINIMUM_INODES,
        "maximum_new_file_bytes": maximum_file,
        "active_file_limit_bytes": limit,
        "bounded_file_executor": bounded,
        "state_modified": False,
        "retained_data_deleted": False,
        "provider_contacted": False,
        "filesystem_blocks_reserved": False,
        "limits_owner_admitted": False,
    }


def require_capacity(state, *, phase="capture"):
    report = reserve_plan(state, phase=phase)
    if report["status"] != "ready":
        raise Refused("backup_capacity_review_required")
    return report


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--state-dir", type=Path, required=True)
    parser.add_argument("--phase", choices=["capture", "resume", "mirror"], default="capture")
    args = parser.parse_args()
    print(
        json.dumps(
            reserve_plan(args.state_dir, phase=args.phase, require_file_limit=False), sort_keys=True
        )
    )


if __name__ == "__main__":
    try:
        main()
    except (ValueError, OSError):
        raise SystemExit("Capacity review refused; inspect private state locally.")