from __future__ import annotations

from dataclasses import dataclass
from pathlib import Path
from typing import Any

import yaml


class WorkflowSpecError(ValueError):
    """Raised when a workflow spec cannot be parsed or is incomplete."""


@dataclass(slots=True)
class WorkflowSpec:
    name: str
    provider: str
    frontmatter: dict[str, Any]
    body: str
    source_path: Path


def _split_frontmatter(raw_text: str) -> tuple[str, str]:
    if not raw_text.startswith("---"):
        raise WorkflowSpecError("workflow spec must start with frontmatter")

    parts = raw_text.split("\n---", 1)
    if len(parts) != 2:
        raise WorkflowSpecError("workflow spec frontmatter is not terminated")

    frontmatter_text = parts[0][4:]
    body = parts[1].lstrip("\r\n")
    return frontmatter_text, body


def load_workflow_spec(path: str | Path) -> WorkflowSpec:
    source_path = Path(path)
    raw_text = source_path.read_text(encoding="utf-8")
    frontmatter_text, body = _split_frontmatter(raw_text)

    payload = yaml.safe_load(frontmatter_text) or {}
    if not isinstance(payload, dict):
        raise WorkflowSpecError("workflow spec frontmatter must be a mapping")
    if True in payload and "on" not in payload:
        payload["on"] = payload.pop(True)

    name = str(payload.get("name") or "").strip()
    provider = str(payload.get("provider") or "").strip()
    if not name:
        raise WorkflowSpecError("workflow spec is missing required field: name")
    if not provider:
        raise WorkflowSpecError("workflow spec is missing required field: provider")

    return WorkflowSpec(
        name=name,
        provider=provider,
        frontmatter=payload,
        body=body,
        source_path=source_path,
    )