from typing import Any, Dict

from .todo_item_types import Todo, TodoValidation
from .todo_item_validate_draft import draft_errors, is_iso_date, trim_space

_FIELD_ORDER = ("id", "title", "notes", "priority", "due", "tags", "recurrence", "createdAt", "completedAt", "order")


def is_utc_timestamp(text: Any) -> bool:
    """YYYY-MM-DDTHH:MM:SS, an optional 1-9 digit fraction, then Z."""
    if not isinstance(text, str) or len(text) < 20:
        return False
    if not is_iso_date(text[0:10]) or text[10] != "T" or text[13] != ":" or text[16] != ":":
        return False

    def two(at: int, most: int) -> bool:
        a, b = text[at], text[at + 1]
        return "0" <= a <= "9" and "0" <= b <= "9" and int(a + b) <= most

    if not (two(11, 23) and two(14, 59) and two(17, 59)):
        return False
    rest = text[19:]
    if rest.startswith("."):
        n = 1
        while n < len(rest) and "0" <= rest[n] <= "9":
            n += 1
        if n == 1 or n > 10:
            return False
        rest = rest[n:]
    return rest == "Z"


def validate_todo(todo: Todo) -> TodoValidation:
    """Check a stored todo: the draft rules plus id, trimmed title, timestamps, completion and order."""
    found: Dict[str, str] = dict(draft_errors(todo))
    if trim_space(todo.id) == "":
        found["id"] = "Every todo needs an id."
    if "title" not in found and trim_space(todo.title) != todo.title:
        found["title"] = "Remove the spaces around the title."
    if not is_utc_timestamp(todo.created_at):
        found["createdAt"] = "Record when it was created as a UTC timestamp, e.g. 2026-09-28T09:30:00Z."
    if todo.done and todo.completed_at is None:
        found["completedAt"] = "A done todo needs the time it was completed."
    elif not todo.done and todo.completed_at is not None:
        found["completedAt"] = "An open todo cannot have a completion time."
    elif todo.completed_at is not None and not is_utc_timestamp(todo.completed_at):
        found["completedAt"] = "Record when it was completed as a UTC timestamp, e.g. 2026-09-28T09:30:00Z."
    order = todo.order
    if isinstance(order, bool) or not isinstance(order, int) or order < 0:
        found["order"] = "Order must be a whole number, 0 or more."
    errors = {field: found[field] for field in _FIELD_ORDER if field in found}
    return TodoValidation(valid=len(errors) == 0, errors=errors)