from __future__ import annotations

PRESSURE_LEVELS = [50, 100, 150, 200, 250, 300, 400, 500, 600, 700, 850, 925, 1000]
PRESSURE_VARIABLES = ["z", "t", "u", "v", "q"]
SURFACE_VARIABLES = [
    "msl", "t2m", "d2m", "sst", "ws10m", "ws100m", "u10m", "v10m",
    "u100m", "v100m", "lcc", "mcc", "hcc", "tcc", "ssr", "ssrd",
    "fdir", "ttr", "tcw", "tp",
]
C85_CHANNEL_NAMES = [f"{name}{level}" for name in PRESSURE_VARIABLES for level in PRESSURE_LEVELS]
C85_CHANNEL_NAMES += SURFACE_VARIABLES
DIAGNOSTIC_CHANNELS = ["ssr", "ssrd", "fdir", "ttr", "tp"]

assert len(C85_CHANNEL_NAMES) == 85


def c85_from_config(config: dict) -> tuple[list[str], list[str]]:
    """Build and validate the fixed C85 channel contract from configuration."""
    variables = config["variables"]
    mapping = variables["mapping"]
    if mapping != {
        "pressure_order": "variable_major",
        "pressure_name": "{variable}{level}",
        "surface_name": "{variable}",
        "source_dataset": "fields",
        "units": "source_native",
        "transform": "identity",
    }:
        raise ValueError("variables.mapping must preserve the C85 source and ordering contract")
    channels = [
        mapping["pressure_name"].format(variable=name, level=level)
        for name in variables["pressure"]
        for level in variables["pressure_levels"]
    ]
    channels.extend(mapping["surface_name"].format(variable=name) for name in variables["surface"])
    diagnostics = list(variables["diagnostic"])
    if channels != C85_CHANNEL_NAMES:
        raise ValueError("Configured variables do not match the required C85 channel order")
    if diagnostics != DIAGNOSTIC_CHANNELS:
        raise ValueError("Configured diagnostic variables do not match the required C85 contract")
    return channels, diagnostics