"""Placeholder extraction and validation for prompt templates."""

from __future__ import annotations

import re
from typing import Any

from placeholder_registry import load_placeholders_for_context

PLACEHOLDER_PATTERN = re.compile(r"\{\{\s*([a-zA-Z_][a-zA-Z0-9_]*)\s*\}\}")


class PlaceholderValidationError(Exception):
    def __init__(
        self,
        message: str,
        *,
        missing: list[str] | None = None,
        type_errors: list[str] | None = None,
        unknown: list[str] | None = None,
    ):
        super().__init__(message)
        self.missing = missing or []
        self.type_errors = type_errors or []
        self.unknown = unknown or []


def extract_placeholders(template: str) -> set[str]:
    return set(PLACEHOLDER_PATTERN.findall(template))


def _check_value_type(value: Any, value_type: str) -> bool:
    if value_type == "string":
        return isinstance(value, str)
    if value_type == "number":
        return isinstance(value, (int, float)) and not isinstance(value, bool)
    if value_type == "boolean":
        return isinstance(value, bool)
    if value_type == "object":
        return isinstance(value, dict)
    if value_type == "array":
        return isinstance(value, list)
    if value_type == "json":
        return True
    return True


def validate_placeholder_input(
    *,
    template: str,
    context_kind: str,
    values: dict[str, Any],
) -> dict[str, Any]:
    """Validate input values against registry; return metadata including unknown placeholders."""
    registry = {p["placeholder_key"]: p for p in load_placeholders_for_context(context_kind)}
    used = extract_placeholders(template)
    missing: list[str] = []
    type_errors: list[str] = []
    unknown = sorted(key for key in used if key not in registry)

    for key, meta in registry.items():
        if meta["required"] and key not in values:
            missing.append(key)
        if key in values and not _check_value_type(values[key], meta["value_type"]):
            type_errors.append(f"{key}: expected {meta['value_type']}")

    if missing or type_errors:
        raise PlaceholderValidationError(
            "Placeholder validation failed",
            missing=missing,
            type_errors=type_errors,
            unknown=unknown,
        )

    return {
        "used_placeholders": sorted(used),
        "unknown_placeholders": unknown,
        "optional_missing": sorted(
            key for key in registry if not registry[key]["required"] and key not in values
        ),
    }