"""Standardized error codes, categories, and unified error-response format.

Every API error response follows the schema:

    {
        "code": "not_found",
        "detail": "Resource not found",
        "field": null,
        "trace_id": "a1b2c3d4",
        "retryable": false,
        "category": "permanent"
    }

``ErrorCategory`` classifies errors so callers can decide retry strategy.
"""

from __future__ import annotations

from enum import StrEnum
from typing import Any


class ErrorCategory(StrEnum):
    """Error classification for retry decisions."""

    TRANSIENT = "transient"   # retryable: timeout, rate-limit, connection
    PERMANENT = "permanent"    # non-retryable: validation, permission, not_found
    PARTIAL = "partial"        # partly successful: batch, bulk operations


ERROR_CODES: dict[str, dict[str, Any]] = {
    # ── Original 6 codes ──
    "not_found":          {"status": 404, "message": "Resource not found",          "category": ErrorCategory.PERMANENT,  "retryable": False},
    "permission_denied":  {"status": 403, "message": "Permission denied",           "category": ErrorCategory.PERMANENT,  "retryable": False},
    "validation_error":   {"status": 422, "message": "Validation failed",            "category": ErrorCategory.PERMANENT,  "retryable": False},
    "rate_limited":       {"status": 429, "message": "Too many requests",            "category": ErrorCategory.TRANSIENT,  "retryable": True},
    "internal_error":     {"status": 500, "message": "Internal server error",        "category": ErrorCategory.TRANSIENT,  "retryable": True},
    "service_unavailable": {"status": 503, "message": "Service temporarily unavailable", "category": ErrorCategory.TRANSIENT, "retryable": True},
    # ── New codes (B-ERR-FMT) ──
    "forbidden":          {"status": 403, "message": "Forbidden",                    "category": ErrorCategory.PERMANENT,  "retryable": False},
    "conflict":           {"status": 409, "message": "Conflict with current state",  "category": ErrorCategory.PERMANENT,  "retryable": False},
    "unprocessable":      {"status": 422, "message": "Unprocessable entity",         "category": ErrorCategory.PERMANENT,  "retryable": False},
    "not_implemented":    {"status": 501, "message": "Not implemented",               "category": ErrorCategory.PERMANENT,  "retryable": False},
    "service_timeout":    {"status": 504, "message": "Service timed out",             "category": ErrorCategory.TRANSIENT,  "retryable": True},
    "bad_gateway":        {"status": 502, "message": "Bad gateway",                   "category": ErrorCategory.TRANSIENT,  "retryable": True},
    # ── Partial success ──
    "partial_success":    {"status": 207, "message": "Partial success",               "category": ErrorCategory.PARTIAL,    "retryable": False},
}


class ApiError(Exception):
    """Application-level error with code, category, and retryable flag.

    Attributes:
        code: Error code key from ``ERROR_CODES``.
        detail: Human-readable detail message.
        field: Optional field name that caused the error.
        status: HTTP status code.
        category: ``ErrorCategory`` for retry decisions.
        retryable: Whether the caller may retry the request.
    """

    def __init__(
        self,
        code: str,
        detail: str | None = None,
        field: str | None = None,
        status: int | None = None,
        category: ErrorCategory | None = None,
        retryable: bool | None = None,
    ):
        meta = ERROR_CODES.get(code, {})
        self.code = code
        self.detail = detail or meta.get("message", "Unknown error")
        self.field = field
        self.status = status or meta.get("status", 500)
        self.category = category or meta.get("category", ErrorCategory.TRANSIENT)
        self.retryable = retryable if retryable is not None else meta.get("retryable", True)
        super().__init__(self.detail)

    def to_response(self, trace_id: str | None = None) -> dict[str, Any]:
        """Build the unified error-response dict."""
        resp: dict[str, Any] = {
            "code": self.code,
            "detail": self.detail,
            "field": self.field,
            "trace_id": trace_id,
            "retryable": self.retryable,
            "category": self.category.value if isinstance(self.category, ErrorCategory) else str(self.category),
        }
        return resp


# ── Exception classification helper ──────────────────────────────────────────

# Transient error indicators
_TRANSIENT_KEYWORDS = frozenset({
    "timeout", "timed out", "rate limit", "rate_limit", "429", "503", "502", "504",
    "service unavailable", "overloaded", "connection reset", "connection aborted",
    "temporary", "transient", "retry",
})

# Permanent error indicators
_PERMANENT_KEYWORDS = frozenset({
    "authentication", "auth", "401", "403", "unauthorized", "forbidden",
    "invalid api key", "invalid_api_key", "validation", "invalid_request",
    "400", "bad request", "model_not_found", "not found", "404", "409",
    "conflict", "not implemented", "501", "permission",
})

# Partial error indicators
_PARTIAL_KEYWORDS = frozenset({
    "partial", "batch", "bulk", "some failed", "multi-status", "207",
})


def classify_exception(exc: Exception) -> ErrorCategory:
    """Classify an exception into an ``ErrorCategory``.

    Uses string matching on the exception message and type name.
    Falls back to ``ErrorCategory.TRANSIENT`` for unknown errors (safer to retry).

    Args:
        exc: The exception to classify.

    Returns:
        ``ErrorCategory.TRANSIENT``, ``ErrorCategory.PERMANENT``, or
        ``ErrorCategory.PARTIAL``.
    """
    # If it's already an ApiError, use its category
    if isinstance(exc, ApiError):
        return exc.category if isinstance(exc.category, ErrorCategory) else ErrorCategory(exc.category)

    import asyncio as _asyncio

    msg = str(exc).lower()
    exc_type_name = type(exc).__name__.lower()

    # Check partial first — batch/bulk errors
    if any(kw in msg or kw in exc_type_name for kw in _PARTIAL_KEYWORDS):
        return ErrorCategory.PARTIAL

    # Check permanent — auth/validation/permission errors should never be retried
    if any(kw in msg or kw in exc_type_name for kw in _PERMANENT_KEYWORDS):
        return ErrorCategory.PERMANENT

    # Check transient
    if any(kw in msg or kw in exc_type_name for kw in _TRANSIENT_KEYWORDS):
        return ErrorCategory.TRANSIENT

    # asyncio.TimeoutError is always transient
    if isinstance(exc, (_asyncio.TimeoutError, TimeoutError, ConnectionError)):
        return ErrorCategory.TRANSIENT

    # Default: treat as transient (safe to retry)
    return ErrorCategory.TRANSIENT


def build_error_response(
    code: str,
    detail: str | None = None,
    field: str | None = None,
    status: int | None = None,
    trace_id: str | None = None,
) -> dict[str, Any]:
    """Build a unified error-response dict without raising an exception."""
    meta = ERROR_CODES.get(code, {})
    return {
        "code": code,
        "detail": detail or meta.get("message", "Unknown error"),
        "field": field,
        "trace_id": trace_id,
        "retryable": meta.get("retryable", True),
        "category": meta.get("category", ErrorCategory.TRANSIENT).value
        if isinstance(meta.get("category"), ErrorCategory)
        else str(meta.get("category", ErrorCategory.TRANSIENT)),
    }