"""
Kazah Tender materials (module of the import runner, see import_assets.py).

Needs SourceArt/Kazah/kazah_manifest.json (Tools/export_kazah.ps1 makes it). Always rebuilds the cheap things
(material graphs and instances) so they cannot drift from the manifest; that is safe to repeat.

What it makes (all under /Game/Vehicles/Kazah/Materials):
  MI_<material>      one instance per Blender material (14), parameters from the manifest

M1 (DESIGN_UE.md section 7.9): the instances are parented to the game's masters /Game/Materials/M_DescentSurface (AmbientMix 0)
and /Game/Materials/M_DescentGlass, built by the look track's helpers (Tools/ue/_helpers_look.py), so the Tender gets the water
ambient term and the same glass as the rest of the game. The two M0 masters, M_Kazah_Opaque and M_Kazah_Glass, are deleted.
Instance names and paths are unchanged.

Leaves `ctx.shared["kazah_instances"]` = {blender material name: MaterialInstanceConstant} for the mesh module.
"""
import importlib.util
import json
import os

import unreal

GAME_DIR = "/Game/Vehicles/Kazah"
MAT_DIR = GAME_DIR + "/Materials"

# Blender's emission strength is in "watts per square metre"-ish units; in Unreal the emissive value is a
# luminance multiplier. These factors make the exported glow read the same in a dark scene.
EMISSIVE_SCALE = {"lens": 9.0, "emissive": 6.0}


def build_material_instances(ctx, manifest, opaque, glass):
    """One MaterialInstanceConstant per Blender material, parameters straight from the manifest."""
    MEL, EAL = ctx.mel, ctx.eal
    instances = {}
    for name, m in manifest["materials"].items():
        mi_name = "MI_" + name[3:] if name.startswith("KZ_") else "MI_" + name
        kind = m["kind"]
        parent = glass if kind == "glass" else opaque
        mi = ctx.get_or_create(MAT_DIR, mi_name, unreal.MaterialInstanceConstant, unreal.MaterialInstanceConstantFactoryNew())
        mi.set_editor_property("parent", parent)
        bc = m["base_color"]
        MEL.set_material_instance_vector_parameter_value(mi, "BaseColor", unreal.LinearColor(bc[0], bc[1], bc[2], 1.0))
        MEL.set_material_instance_scalar_parameter_value(mi, "Roughness", float(m["roughness"]))
        if kind == "glass":
            pass  # opacity / fresnel / IOR come from the master's defaults
        else:
            MEL.set_material_instance_scalar_parameter_value(mi, "Metallic", float(m["metallic"]))
            strength = float(m["emissive_strength"]) * EMISSIVE_SCALE.get(kind, 0.0)
            ec = m["emissive_color"] if strength > 0.0 else [0.0, 0.0, 0.0]
            MEL.set_material_instance_vector_parameter_value(mi, "EmissiveColor", unreal.LinearColor(ec[0], ec[1], ec[2], 1.0))
            MEL.set_material_instance_scalar_parameter_value(mi, "EmissiveStrength", strength if strength > 0.0 else 0.0)
        MEL.update_material_instance(mi)
        EAL.save_loaded_asset(mi)
        instances[name] = mi
        ctx.log("material %-28s -> %s (%s)" % (name, mi_name, kind))
    return instances


def _look_helpers(ctx):
    spec = importlib.util.spec_from_file_location("descent_helpers_look", os.path.join(ctx.project_dir, "Tools", "ue", "_helpers_look.py"))
    module = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(module)
    return module


def run(ctx):
    manifest_path = os.path.join(ctx.project_dir, "SourceArt", "Kazah", "kazah_manifest.json")
    if not os.path.isfile(manifest_path):
        raise RuntimeError("no manifest at %s - run Tools/export_kazah.ps1 first" % manifest_path)
    with open(manifest_path, "r", encoding="utf-8") as f:
        manifest = json.load(f)

    for d in (GAME_DIR, MAT_DIR):
        ctx.eal.make_directory(d)
    h = _look_helpers(ctx)
    mpc = h.ensure_mpc(ctx)
    opaque = h.ensure_surface_master(ctx, mpc)
    glass = h.ensure_glass_master(ctx)
    ctx.shared["kazah_instances"] = build_material_instances(ctx, manifest, opaque, glass)
    # The M0 masters are no longer used by anything: delete them (instances were re-parented above).
    for old in ("M_Kazah_Opaque", "M_Kazah_Glass"):
        path = MAT_DIR + "/" + old
        if ctx.eal.does_asset_exist(path):
            ctx.eal.delete_asset(path)
            ctx.log("deleted the M0 master " + path)