"""Cost computation and attribution (架构文档 §13, FR-BILL-08)."""

from __future__ import annotations

from decimal import Decimal

from packages.llm.cost import (
    AICallRecord,
    CompositeAICallRecorder,
    InMemoryAICallRecorder,
    ModelRate,
    NullAICallRecorder,
    RateTable,
    compute_cost_cents,
)
from packages.llm.recording import PrometheusAICallRecorder
from packages.llm.types import Usage

RATE = ModelRate(
    input_cents_per_mtok=Decimal("100"),
    cached_input_cents_per_mtok=Decimal("10"),
    output_cents_per_mtok=Decimal("200"),
)


def test_cached_tokens_are_billed_at_the_cheaper_rate() -> None:
    usage = Usage(tokens_in=1_000_000, tokens_out=0, tokens_cached=1_000_000)
    assert compute_cost_cents(usage, RATE) == Decimal("10.000000")


def test_uncached_input_is_billed_at_the_full_rate() -> None:
    usage = Usage(tokens_in=1_000_000, tokens_out=0, tokens_cached=0)
    assert compute_cost_cents(usage, RATE) == Decimal("100.000000")


def test_mixed_usage_splits_cached_and_uncached_input() -> None:
    # 3.7k input of which 3k cached, 800 output — the §7.2 Agent token budget.
    usage = Usage(tokens_in=3700, tokens_out=800, tokens_cached=3000)
    expected = (
        Decimal(700) * RATE.input_cents_per_mtok
        + Decimal(3000) * RATE.cached_input_cents_per_mtok
        + Decimal(800) * RATE.output_cents_per_mtok
    ) / Decimal(1_000_000)
    assert compute_cost_cents(usage, RATE) == expected.quantize(Decimal("0.000001"))


def test_zero_usage_costs_nothing() -> None:
    assert compute_cost_cents(Usage(), RATE) == Decimal("0.000000")


def test_billable_input_never_goes_negative() -> None:
    usage = Usage(tokens_in=100, tokens_cached=500)
    assert usage.billable_input == 0


def test_rate_table_falls_back_so_unknown_models_are_never_free() -> None:
    default = ModelRate(Decimal("1"), Decimal("1"), Decimal("1"))
    table = RateTable({"deepseek-v4-flash": RATE}, default=default)
    assert table.for_model("deepseek-v4-flash") is RATE
    assert table.for_model("some-new-model") is default
    assert table.known_models() == ("deepseek-v4-flash",)


def _record(success: bool = True) -> AICallRecord:
    return AICallRecord(
        call_id=1,
        scene="agent_chat",
        provider="deepseek",
        model="deepseek-v4-flash",
        success=success,
        usage=Usage(tokens_in=10, tokens_out=5, tokens_cached=2),
        latency_ms=120,
        cost_cents=Decimal("0.5"),
    )


async def test_with_defaults_stamps_created_at() -> None:
    stamped = _record().with_defaults()
    assert stamped.created_at is not None
    assert stamped.with_defaults() is stamped


async def test_in_memory_recorder_collects_records() -> None:
    recorder = InMemoryAICallRecorder()
    await recorder.record(_record())
    assert len(recorder.records) == 1


async def test_null_recorder_is_a_no_op() -> None:
    assert await NullAICallRecorder().record(_record()) is None


async def test_composite_recorder_fans_out() -> None:
    first, second = InMemoryAICallRecorder(), InMemoryAICallRecorder()
    await CompositeAICallRecorder(first, second, PrometheusAICallRecorder()).record(_record())
    assert len(first.records) == len(second.records) == 1