"""Rule action expansion into concrete task specs.

Boundary: no imports from temporalio, sqlalchemy, fastapi, or any
activity_core.* module outside rules/.
"""

from __future__ import annotations

import re
from dataclasses import asdict
from typing import Any

from activity_core.rules.evaluator import UnsafeExpression, evaluate_condition
from activity_core.rules.models import TaskSpec

_PLACEHOLDER_RE = re.compile(r"\{([a-zA-Z_][a-zA-Z0-9_.]*)\}")
_PATH_RE = re.compile(r"^(event|context)(?:\.[a-zA-Z_][a-zA-Z0-9_]*)+$")


def expand_rule_actions(rules: list[dict], event: Any, context: dict) -> list[dict]:
    """Evaluate rule conditions and render matching actions as TaskSpec dicts.

    A rule can opt into per-item expansion with ``for_each``:

        for_each: context.repos.repos
        bind_as: repo

    Each list item is then available as ``context.repo`` while rendering the
    condition and action fields. Without ``for_each``, a rule is evaluated once
    against the original context.
    """
    task_specs: list[dict] = []
    for rule in rules:
        for bound_context in _iteration_contexts(rule, event, context):
            if not _condition_matches(rule, event, bound_context):
                continue
            task_specs.append(_task_spec_for_rule(rule, event, bound_context))
    return task_specs


def _iteration_contexts(rule: dict, event: Any, context: dict) -> list[dict]:
    for_each = rule.get("for_each")
    if not for_each:
        return [context]
    if not isinstance(for_each, str) or not _PATH_RE.fullmatch(for_each):
        raise UnsafeExpression(f"invalid for_each path: {for_each!r}")

    values = _resolve_field(for_each, event, context)
    if values is None:
        return []
    if not isinstance(values, list):
        raise UnsafeExpression(f"for_each path does not resolve to a list: {for_each!r}")

    bind_as = rule.get("bind_as", "item")
    if not isinstance(bind_as, str) or not re.fullmatch(r"[a-zA-Z_][a-zA-Z0-9_]*", bind_as):
        raise UnsafeExpression(f"invalid bind_as name: {bind_as!r}")

    contexts: list[dict] = []
    for value in values:
        bound = dict(context)
        bound[bind_as] = value
        contexts.append(bound)
    return contexts


def _condition_matches(rule: dict, event: Any, context: dict) -> bool:
    return evaluate_condition(rule.get("condition", ""), event, context)


def _task_spec_for_rule(rule: dict, event: Any, context: dict) -> dict:
    action = rule.get("action", {})
    spec = TaskSpec(
        title=str(_render_value(action.get("task_template", rule.get("id", "")), event, context) or ""),
        description=str(_render_value(action.get("description", ""), event, context) or ""),
        target_repo=_string_or_none(_render_value(action.get("target_repo"), event, context)),
        priority=str(_render_value(action.get("priority", "medium"), event, context) or "medium"),
        labels=_render_labels(action.get("labels", []), event, context),
        due_in_days=_int_or_none(_render_value(action.get("due_in_days"), event, context)),
        source_type="rule",
        source_id=rule.get("id", ""),
    )
    result = asdict(spec)
    result["condition"] = rule.get("condition", "")
    return result


def _render_labels(value: Any, event: Any, context: dict) -> list[str]:
    if not isinstance(value, list):
        return []
    rendered = []
    for item in value:
        rendered_item = _render_value(item, event, context)
        if rendered_item is not None:
            rendered.append(str(rendered_item))
    return rendered


def _render_value(value: Any, event: Any, context: dict) -> Any:
    if isinstance(value, str):
        if _PATH_RE.fullmatch(value):
            return _resolve_field(value, event, context)
        if "{" in value and "}" in value:
            return _PLACEHOLDER_RE.sub(
                lambda match: _string_or_empty(
                    _resolve_field(match.group(1), event, context)
                ),
                value,
            )
    return value


def _resolve_field(field_path: str, event: Any, context: dict) -> Any:
    if not _PATH_RE.fullmatch(field_path):
        raise UnsafeExpression(f"invalid field path: {field_path!r}")
    root, tail = field_path.split(".", 1)
    if root == "event":
        return _resolve_path(event, tail)
    return _resolve_path(context, tail)


def _resolve_path(obj: Any, path: str) -> Any:
    current = obj
    for part in path.split("."):
        if current is None:
            return None
        if isinstance(current, dict):
            current = current.get(part)
        else:
            current = getattr(current, part, None)
    return current


def _string_or_none(value: Any) -> str | None:
    if value is None:
        return None
    return str(value)


def _string_or_empty(value: Any) -> str:
    if value is None:
        return ""
    if isinstance(value, (dict, list)):
        raise UnsafeExpression("template placeholder resolved to a non-scalar value")
    return str(value)


def _int_or_none(value: Any) -> int | None:
    if value is None:
        return None
    try:
        return int(value)
    except (TypeError, ValueError) as exc:
        raise UnsafeExpression(f"field cannot be converted to int: {value!r}") from exc