from __future__ import annotations

from sqlalchemy.ext.asyncio import AsyncSession

from app.enums.llm_billing import LlmBillingConfigKey
from app.services.llm_billing.context import LlmBillingPolicy
from app.services.system_config_cache import get_system_config_values

_DEFAULT_HOLD_CREDITS = 5.0
_FALSE_VALUES = {"0", "false", "no", "off", "disabled"}
_HOLD_CONFIG_KEYS = {
    LlmBillingConfigKey.HOLD_DEFAULT.value,
    LlmBillingConfigKey.HOLD_GENERATION_RECORD_PROMPT.value,
    LlmBillingConfigKey.HOLD_MODULE_IMAGE_PROMPT.value,
    LlmBillingConfigKey.HOLD_MODULE_VIDEO_PROMPT.value,
    LlmBillingConfigKey.HOLD_SHOT_VIDEO_ANALYSIS.value,
    LlmBillingConfigKey.LEGACY_OPTIMIZE_HOLD.value,
}


def _parse_bool(value: str | None, *, default: bool = True) -> bool:
    if value is None or str(value).strip() == "":
        return default
    return str(value).strip().lower() not in _FALSE_VALUES


def _parse_float(value: str | float | int | None) -> float | None:
    try:
        if value is None or str(value).strip() == "":
            return None
        return round(float(value), 2)
    except (TypeError, ValueError):
        return None


def is_llm_hold_config_key(key: str | None) -> bool:
    return bool(key and key in _HOLD_CONFIG_KEYS)


async def get_llm_billing_policy(
    db: AsyncSession,
    *,
    config_key: str | None = None,
    explicit_hold_credits: float | None = None,
    default: float = _DEFAULT_HOLD_CREDITS,
) -> LlmBillingPolicy:
    keys = [LlmBillingConfigKey.ENABLED.value]
    if config_key:
        keys.append(config_key)
    keys.extend(
        [
            LlmBillingConfigKey.HOLD_DEFAULT.value,
            LlmBillingConfigKey.LEGACY_OPTIMIZE_HOLD.value,
        ]
    )
    # 去重并保持优先级；一次读取避免 enabled/scene/default 分散查询。
    ordered_keys = list(dict.fromkeys(keys))
    values = await get_system_config_values(db, ordered_keys)
    enabled = _parse_bool(values.get(LlmBillingConfigKey.ENABLED.value), default=True)
    if not enabled:
        return LlmBillingPolicy(enabled=False, hold_credits=0.0, config_key=config_key)

    if explicit_hold_credits is not None:
        amount = _parse_float(explicit_hold_credits)
        source_key = "explicit"
    else:
        amount = None
        source_key = None
        for key in ordered_keys[1:]:
            parsed = _parse_float(values.get(key))
            if parsed is not None:
                amount = parsed
                source_key = key
                break
        if amount is None:
            amount = round(float(default), 2)
            source_key = "default"

    if amount is None or amount <= 0:
        return LlmBillingPolicy(
            enabled=True,
            hold_credits=float(amount or 0),
            config_key=config_key,
            source_key=source_key,
            valid=False,
            error="启用LLM统一计费时，预扣积分必须大于0",
        )
    return LlmBillingPolicy(
        enabled=True,
        hold_credits=round(float(amount), 2),
        config_key=config_key,
        source_key=source_key,
    )


async def get_llm_hold_credits(
    db: AsyncSession,
    *,
    config_key: str | None = None,
    default: float = _DEFAULT_HOLD_CREDITS,
) -> float:
    policy = await get_llm_billing_policy(db, config_key=config_key, default=default)
    return policy.hold_credits


async def is_llm_billing_enabled(db: AsyncSession) -> bool:
    return (await get_llm_billing_policy(db)).enabled


async def validate_llm_system_config_value(
    db: AsyncSession,
    *,
    key: str,
    value: str,
) -> None:
    """校验后台单项更新，避免启用计费时保存零或负数预扣。"""
    if key == LlmBillingConfigKey.ENABLED.value:
        if not _parse_bool(value, default=True):
            return
        keys = [
            LlmBillingConfigKey.HOLD_DEFAULT.value,
            LlmBillingConfigKey.HOLD_GENERATION_RECORD_PROMPT.value,
            LlmBillingConfigKey.HOLD_MODULE_IMAGE_PROMPT.value,
            LlmBillingConfigKey.HOLD_MODULE_VIDEO_PROMPT.value,
            LlmBillingConfigKey.HOLD_SHOT_VIDEO_ANALYSIS.value,
        ]
        values = await get_system_config_values(db, keys, ttl_seconds=1)
        invalid = [
            config_name
            for config_name in keys
            if (raw_value := values.get(config_name)) is not None
            and str(raw_value).strip() != ""
            and ((parsed := _parse_float(raw_value)) is None or parsed <= 0)
        ]
        if invalid:
            raise ValueError(f"启用LLM统一计费前，请先将以下预扣配置设置为大于0：{', '.join(invalid)}")
        return

    if not is_llm_hold_config_key(key):
        return
    parsed = _parse_float(value)
    enabled_values = await get_system_config_values(db, [LlmBillingConfigKey.ENABLED.value], ttl_seconds=1)
    enabled = _parse_bool(enabled_values.get(LlmBillingConfigKey.ENABLED.value), default=True)
    if enabled and (parsed is None or parsed <= 0):
        raise ValueError("启用LLM统一计费时，预扣积分必须大于0")