"""Canonical MAS v0.1 local-part generator.

Generators are stricter than parsers: they never emit both a facet and an
interaction, and they enforce the 64-octet SMTP limit after encoding.
"""

from __future__ import annotations

from typing import Optional

from .parser import MasSyntaxError, parse_local_part


def generate_local_part(target: str, *, facet: Optional[str] = None,
                        interaction: Optional[str] = None) -> str:
    if facet is not None and interaction is not None:
        raise MasSyntaxError("generator-facet-and-interaction",
                             "v0.1 generators MUST NOT emit both '+' and '!'")
    s = target
    if facet is not None:
        s += "+" + facet
    if interaction is not None:
        s += "!" + interaction
    parsed = parse_local_part(s)  # enforces grammar, emptiness, reserved ops, length
    if str(parsed.target) != target or (parsed.facet and parsed.facet.value) != facet \
            or (parsed.interaction and parsed.interaction.mode) != interaction:
        raise MasSyntaxError("generator-component", "a component contains a MAS operator")
    return s


def resource_local_part(resource_type: str, resource_id: str, *, facet: Optional[str] = None,
                        interaction: Optional[str] = None) -> str:
    if not resource_type or not resource_id:
        raise MasSyntaxError("generator-empty", "resource type and id must be non-empty")
    if "=" in resource_type:
        raise MasSyntaxError("invalid-resource-type", "resource type must not contain '='")
    return generate_local_part(f"{resource_type}={resource_id}", facet=facet,
                               interaction=interaction)