"""Exact, verified INI value inspection and replacement."""

from __future__ import annotations

import os
from pathlib import Path
import shutil
from typing import Any

from .filesystem import sha256_file


class IniError(ValueError):
	"""Raised when an INI override cannot be applied exactly."""


def inspect_ini_value(path: Path, section: str, key: str) -> dict[str, Any]:
	if path.is_symlink() or not path.is_file():
		raise IniError(f"INI path is missing or unsafe: {path}")
	text = _read_ini_text(path)
	_, value = _find_ini_value(text, section, key)
	state = path.stat()
	return {
		"path": str(path),
		"section": section,
		"key": key,
		"value": value,
		"sha256": sha256_file(path),
		"size": state.st_size,
		"mtime_ns": state.st_mtime_ns,
	}


def override_ini_value(
	path: Path,
	section: str,
	key: str,
	expected: str,
	value: str,
) -> dict[str, Any]:
	before = inspect_ini_value(path, section, key)
	if before["value"] != expected:
		raise IniError(
			f"INI value mismatch for [{section}] {key}: "
			f"expected {expected!r}, found {before['value']!r}"
		)
	text = _read_ini_text(path)
	line_index, _ = _find_ini_value(text, section, key)
	lines = text.splitlines(keepends=True)
	body = lines[line_index].rstrip("\r\n")
	newline = lines[line_index][len(body) :]
	left, separator, right = body.partition("=")
	if not separator:
		raise IniError(f"INI key has no equals separator: [{section}] {key}")
	leading = right[: len(right) - len(right.lstrip())]
	trailing = right[len(right.rstrip()) :]
	lines[line_index] = f"{left}={leading}{value}{trailing}{newline}"
	updated = "".join(lines)
	if updated == text:
		raise IniError(f"INI override made no change: [{section}] {key}")
	temporary = path.with_name(f".{path.name}.{os.getpid()}.tmp")
	if temporary.exists() or temporary.is_symlink():
		raise IniError(f"INI temporary path already exists: {temporary}")
	try:
		with temporary.open("w", encoding="utf-8", newline="") as stream:
			stream.write(updated)
			stream.flush()
			os.fsync(stream.fileno())
		shutil.copystat(path, temporary, follow_symlinks=False)
		temporary.replace(path)
	finally:
		if temporary.exists() or temporary.is_symlink():
			temporary.unlink()
	after = inspect_ini_value(path, section, key)
	if after["value"] != value:
		raise IniError(f"INI override verification failed: [{section}] {key}")
	if after["sha256"] == before["sha256"]:
		raise IniError(f"INI hash did not change: [{section}] {key}")
	return {
		"ok": True,
		"before": before,
		"after": after,
		"expected": expected,
		"value": value,
	}


def _read_ini_text(path: Path) -> str:
	with path.open("r", encoding="utf-8", newline="") as stream:
		return stream.read()


def _find_ini_value(text: str, section: str, key: str) -> tuple[int, str]:
	current_section: str | None = None
	matches: list[tuple[int, str]] = []
	for index, line in enumerate(text.splitlines(keepends=True)):
		stripped = line.strip()
		if stripped.startswith("[") and stripped.endswith("]"):
			current_section = stripped[1:-1].strip()
			continue
		if current_section is None or current_section.casefold() != section.casefold():
			continue
		if not stripped or stripped.startswith((";", "#")):
			continue
		left, separator, right = line.rstrip("\r\n").partition("=")
		if separator and left.strip().casefold() == key.casefold():
			matches.append((index, right.strip()))
	if not matches:
		raise IniError(f"INI key not found: [{section}] {key}")
	if len(matches) != 1:
		raise IniError(f"INI key is duplicated: [{section}] {key}")
	return matches[0]