{ pkgs, lib }:

let
  # Static per-Minecraft-version pins. Real "latest-recommended" resolution
  # would need network access at eval time, so for now every supported
  # targetVersion needs an entry here.
  versionTable = {
    "1.21.1" = {
      neoVersion = "21.1.244";
      minecraftVersionRange = "[1.21.1]";
      loaderVersionRange = "[1,)";
      parchmentMinecraftVersion = "1.21.1";
      parchmentMappingsVersion = "2024.11.17";
      templateDir = "1.21.x";
    };
  };
  trace = value: builtins.trace value value;
in

{ modPath }:

let
  evaluated = lib.evalModules {
    modules = [ ../modules/mod-meta.nix ../modules/mod-blocks.nix modPath  ];
  };
  cfg = evaluated.config;

  versionInfo =
    versionTable.${cfg.targetVersion} or (throw
      "snowy: unsupported targetVersion '${cfg.targetVersion}'. Supported versions: ${lib.concatStringsSep ", " (lib.attrNames versionTable)}");

  resolvedNeoVersion =
    if cfg.frameworkVersion == "latest-recommended"
    then versionInfo.neoVersion
    else cfg.frameworkVersion;

  # Hand-written files (customClass, blocks.*.customClass, ...) are given as plain
  # strings, e.g. "./src/CreateSilicon.java" -- snowy never reads their content or
  # location, it only needs the class name (the file's basename) to generate the
  # matching Base class and wire up imports/registration on the generated side. The
  # actual file is expected to already live at the real Gradle-conventional path
  # (src/main/java/{package}/...) in the project directory the shellHook runs from.
  classNameFromPath = p: if p == null then null else lib.removeSuffix ".java" (baseNameOf p);

  splitBlockId = id:
    let parts = lib.splitString ":" id;
    in
    assert lib.assertMsg (builtins.length parts == 2)
      "snowy: block id '${id}' must be of the form '<namespace>:<path>'";
    { namespace = builtins.elemAt parts 0; path = builtins.elemAt parts 1; };

  blocksList = lib.mapAttrsToList
    (id: blockCfg:
      let
        split = splitBlockId id;
        hasEnoughTextures = blockCfg.textures != null && (
          blockCfg.textures.all != null
          || (blockCfg.textures.top != null && blockCfg.textures.bottom != null
              && (blockCfg.textures.side != null
                  || (blockCfg.textures.north != null && blockCfg.textures.south != null
                      && blockCfg.textures.east != null && blockCfg.textures.west != null)))
        );
      in
      assert lib.assertMsg (split.namespace == cfg.modid)
        "snowy: block '${id}' namespace must match modid '${cfg.modid}'";
      assert lib.assertMsg (!(blockCfg.textures != null && blockCfg.customModel))
        "snowy: block '${id}': textures and customModel are mutually exclusive";
      assert lib.assertMsg (blockCfg.customModel || hasEnoughTextures)
        "snowy: block '${id}': textures must set 'all', or 'top'+'bottom'+('side' or all four side faces), unless customModel is set";
      assert lib.assertMsg (!(blockCfg.item.texture != null && blockCfg.item.customModel))
        "snowy: block '${id}': item.texture and item.customModel are mutually exclusive";
      {
        inherit id;
        inherit (split) path;
        displayName = blockCfg.displayName;
        properties = blockCfg.properties;
        customClassName = classNameFromPath blockCfg.customClass;
        textures = blockCfg.textures;
        customModel = blockCfg.customModel;
        item = blockCfg.item;
        blockEntity =
          if blockCfg.blockEntity == null then null
          else {
            customClassName = classNameFromPath blockCfg.blockEntity.class;
            tickerClient = blockCfg.blockEntity.ticker.client;
            tickerServer = blockCfg.blockEntity.ticker.server;
          };
      })
    cfg.blocks;

  capitalizedModid = lib.toUpper (lib.substring 0 1 cfg.modid) + lib.substring 1 (-1) cfg.modid;

  templateContext = cfg // {
    neoVersion = resolvedNeoVersion;
    inherit (versionInfo) minecraftVersionRange loaderVersionRange parchmentMinecraftVersion parchmentMappingsVersion;
    customClassName = classNameFromPath cfg.customClass;
    customClientClassName = classNameFromPath cfg.customClientClass;
    blocks = blocksList;
    blocksClassName = "${capitalizedModid}Blocks";
    blockEntitiesClassName = "${capitalizedModid}BlockEntities";
  };

  configJson = pkgs.writeText "snowy-mod-config-${cfg.modid}.json" (builtins.toJSON templateContext);

  packagePath = builtins.replaceStrings [ "." ] [ "/" ] cfg.javaPackage;

  pythonEnv = pkgs.python3.withPackages (ps: [ ps.jinja2 ]);

  generated = pkgs.runCommand "snowy-generated-${cfg.modid}" {
    nativeBuildInputs = [ pythonEnv ];
  } ''
    mkdir -p $out
    python3 ${../codegen/main.py} \
      --config ${configJson} \
      --templates ${../templates}/${versionInfo.templateDir} \
      --out $out
  '';

  # The `gradle wrapper` task validates its distribution URL over the network,
  # which the (non-fixed-output) Nix build sandbox blocks. Instead, fetch the
  # three wrapper artifacts verbatim (fixed-output derivations may use the
  # network) from the upstream NeoForge MDK, which already pins Gradle 9.2.1,
  # and write gradle-wrapper.properties ourselves.
  gradleWrapperVersion = "9.2.1";
  mdkWrapperBase = "https://raw.githubusercontent.com/NeoForgeMDKs/MDK-1.21.1-ModDevGradle/main";

  gradlew = pkgs.fetchurl {
    url = "${mdkWrapperBase}/gradlew";
    sha256 = "0284687nawivy3gz16r4zcssv61a3g1ssvyxmxh5g7vl5v2v91xi";
  };
  gradlewBat = pkgs.fetchurl {
    url = "${mdkWrapperBase}/gradlew.bat";
    sha256 = "1kg2qjh904cz6da71l30pa1sfbdb707lr4lp4c1jvclgxc9jf44l";
  };
  gradleWrapperJar = pkgs.fetchurl {
    url = "${mdkWrapperBase}/gradle/wrapper/gradle-wrapper.jar";
    sha256 = "0wk157gn9nh2d7v9j7mfy46csb31iv5qxsx4qsdvachwvv24lfkx";
  };
  gradleWrapperProperties = pkgs.writeText "gradle-wrapper.properties" ''
    distributionBase=GRADLE_USER_HOME
    distributionPath=wrapper/dists
    distributionUrl=https\://services.gradle.org/distributions/gradle-${gradleWrapperVersion}-bin.zip
    networkTimeout=10000
    validateDistributionUrl=true
    zipStoreBase=GRADLE_USER_HOME
    zipStorePath=wrapper/dists
  '';

  gradleWrapper = pkgs.runCommand "snowy-gradle-wrapper" { } ''
    mkdir -p $out/gradle/wrapper
    install -m755 ${gradlew} $out/gradlew
    install -m755 ${gradlewBat} $out/gradlew.bat
    install -m644 ${gradleWrapperJar} $out/gradle/wrapper/gradle-wrapper.jar
    install -m644 ${gradleWrapperProperties} $out/gradle/wrapper/gradle-wrapper.properties
  '';
in
assert lib.assertMsg (cfg.targetFramework == [ "neoforge" ])
  "snowy: only targetFramework = [ \"neoforge\" ] is currently supported, got: [ ${lib.concatStringsSep " " cfg.targetFramework} ]";
pkgs.mkShell {
  packages = [ pkgs.jdk21 pkgs.gradle ];

  shellHook = ''
    echo "snowy: refreshing generated NeoForge project files in $(pwd)"

    # Only ever touch this explicit, framework-owned set of paths -- this is the
    # real project root now (not an isolated throwaway directory), so it may also
    # contain the mod author's own unrelated files (.git, flake.nix, an IDE config,
    # hand-written sources outside src/main/java/**/generated, ...) that must never
    # be swept up by this cleanup.
    rm -rf build.gradle settings.gradle gradle.properties .gitignore \
      gradlew gradlew.bat gradle \
      src/main/resources/META-INF \
      "src/main/resources/assets/${cfg.modid}/blockstates" \
      "src/main/java/${packagePath}/generated"

    cp -r --no-preserve=mode,ownership ${generated}/. ./
    cp -r --no-preserve=mode,ownership ${gradleWrapper}/. ./
    chmod +x gradlew

    echo "snowy: done. ./gradlew build"
  '';
}