{ lib
, pep440
, pep508
, pep518
, ...
}:

lib.fix (self:
let
  inherit (builtins) match elemAt foldl' typeOf attrNames head tail mapAttrs length filter split;
  inherit (lib) optionalAttrs flatten;
  inherit (import ./util.nix { inherit lib; }) splitComma;

  # Translate author from a string like "Name <email>" to a structured set as defined by PEP-621.
  translateAuthor = a:
    let
      mAt = elemAt (match "^(.+) <(.+)>$" a);
    in
    { name = mAt 0; email = mAt 1; };

  # Normalize dependecy from poetry dependencies table from (string || set) -> set
  normalizeDep = name: dep: (
    let
      type = typeOf dep;
    in
    if type == "string" then {
      inherit name;
      version = dep;
    }
    else if type == "set" then dep // { inherit name; }
    else throw "Unexpected type: ${type}"
  );

  # Rewrite the right hand side version for caret comparisons according to the rules laid out in
  # https://python-poetry.org/docs/dependency-specification/#caret-requirements
  rewriteCaretRhs = release:
    let
      state = foldl'
        (state: v:
          let
            nonzero = state.nonzero || v != 0;
          in
          state // {
            release = state.release ++ [
              (
                if nonzero && !state.nonzero then (v + 1)
                else if nonzero then 0
                else v
              )
            ];
            inherit nonzero;
          })
        {
          release = [ ];
          nonzero = false;
        }
        release;
    in
    if !state.nonzero
    then ([ (head state.release + 1) ] ++ tail state.release)
    else state.release;

  # Poetry dependency tables are of mixed types:
  # [tool.poetry.dependencies]
  # python = "^3.8"
  # cachecontrol = { version = "^0.13.0", extras = ["filecache"] }
  # foo = [
  #     {version = "<=1.9", python = ">=3.6,<3.8"},
  #     {version = "^2.0", python = ">=3.8"}
  # ]
  #
  # These are all valid. Normalize the input to a list of:
  # [
  #   { name = "python"; version = "^3.8"; }
  #   { name = "cachecontrol"; version = "^0.13.0"; extras = ["filecache"]; }
  #   { name = "foo"; version = "<=1.9";  python = ">=3.6,<3.8"; }
  #   { name = "foo"; version = "^2.0"; python = ">=3.8"; }
  # ]
  normalizeDependendenciesToList = deps: foldl'
    (acc: name: acc ++ (
      let
        dep = deps.${name};
      in
      if typeOf dep == "list" then map (normalizeDep name) dep
      else [ (normalizeDep name dep) ]
    )) [ ]
    (attrNames deps);

  # Normalized version of parseVersionCond'
  parseVersionConds = s: flatten (map self.parseVersionCond (splitComma s));

  dummyMarker = {
    type = "bool";
    value = true;
  };

  # Analogous to pep508.parseString
  parseDependency = dep:
    let
      # Poetry has Python as a separate field in the structured dependency object.
      # This is non-standard. Rewrite these expressions as a nested set of logical ANDs that
      # looks like regular parsed markers as if they were standard PEP-508, just written in a bit of a funky
      # nested way that no human would do.
      markers = foldl'
        (rhs: pyCond: {
          type = "boolOp";
          op = "and";
          lhs = {
            type = "compare";
            inherit (pyCond) op;
            lhs = {
              type = "variable";
              value = "python_version";
            };
            rhs = {
              type = "version";
              value = pyCond.version;
            };
          };
          inherit rhs;
        })
        (
          # Encode no markers as a marker that always evaluates to true to simplify fold logi above.
          if dep ? markers then pep508.parseMarkers dep.markers else dummyMarker
        )
        (if dep ? python then parseVersionConds dep.python else [ ]);

    in
    {
      inherit (dep) name;
      conditions = parseVersionConds dep.version;
      extras = dep.extras or [ ];
      url = dep.url or null;
      markers = if markers == dummyMarker then null else markers;
    };

in
{
  /*
    Translate a Pyproject.toml from Poetry to PEP-621 project metadata.
    This function transposes a PEP-621 project table on top of an existing Pyproject.toml populated with data from `tool.poetry`.
    Notably does not translate dependencies/optional-dependencies.

    For parsing dependencies from Poetry see `lib.poetry.parseDependencies`.

    Type: translatePoetryProject :: AttrSet -> lambda

    Example:
      # translatePoetryProject (lib.importTOML ./pyproject.toml)
      { }  # TOML contents, structure omitted. See PEP-621 for more information on data members.
    */
  translatePoetryProject = pyproject: assert !(pyproject ? project); let
    inherit (pyproject.tool) poetry;
  in
  pyproject // {
    project = {
      inherit (poetry) name version description;
      authors = map translateAuthor poetry.authors;
      urls = optionalAttrs (poetry ? homepage)
        {
          Homepage = poetry.homepage;
        } // optionalAttrs (poetry ? repository) {
        Repository = poetry.repository;
      } // optionalAttrs (poetry ? documentation) {
        Documentation = poetry.documentation;
      };
    } // optionalAttrs (poetry ? license) {
      license.text = poetry.license;
    } // optionalAttrs (poetry ? maintainers) {
      maintainers = map translateAuthor poetry.maintainers;
    } // optionalAttrs (poetry ? readme) {
      inherit (poetry) readme;
    } // optionalAttrs (poetry ? keywords) {
      inherit (poetry) keywords;
    } // optionalAttrs (poetry ? classifiers) {
      inherit (poetry) classifiers;
    };
  };

  /* Parse dependencies from pyproject.toml (Poetry edition).
     This function is analogous to `lib.pep621.parseDependencies`.

     Type: parseDependencies :: AttrSet -> AttrSet

     Example:
       # parseDependencies {
       #
       #   pyproject = (lib.importTOML ./pyproject.toml);
       # }
       {
         dependencies = [ ];  # List of parsed PEP-508 strings (lib.pep508.parseString)
         extras = {
           dev = [ ];  # List of parsed PEP-508 strings (lib.pep508.parseString)
         };
         build-systems = [ ];  # PEP-518 build-systems (List of parsed PEP-508 strings)
       }
  */
  parseDependencies = pyproject: {
    dependencies = map parseDependency (normalizeDependendenciesToList (pyproject.tool.poetry.dependencies or { }));
    extras = mapAttrs (_: g: map parseDependency (normalizeDependendenciesToList g.dependencies)) pyproject.tool.poetry.group or { };
    build-systems = pep518.parseBuildSystems pyproject;
  };

  /* Parse a version conditional.
     Supports additional non-standard operators `^` and `~` used by Poetry.

     Because some expressions desugar to multiple expressions parseVersionCond returns a list.

     Type: parseVersionCond :: string -> [ AttrSet ]
  */
  parseVersionCond = cond: (
    let
      m = match "^([~[:digit:]^])(.+)$" cond;
      mAt = elemAt m;
      c = mAt 0;
      rest = mAt 1;
      # Pad version before parsing as it's _much_ easier to reason about
      # once they're the same length
      version = pep440.parseVersion (lib.versions.pad 3 rest);

      # Count the number of segments in the input to use an an index in ~ rewriting
      segments = length (filter (tok: typeOf tok == "string") (split "\\." rest));
    in
    if m == null then [ (pep440.parseVersionCond cond) ]
    # Desugar ~ into >= && <
    else if c == "~" then [
      {
        op = ">=";
        inherit version;
      }
      {
        op = "<";
        version = version // {
          release = lib.imap0 (i: tok: if i >= segments - 1 then 0 else if i == segments - 2 then (tok + 1) else tok) version.release;
        };
      }
    ]
    # Desugar ^ into >= && <
    else if c == "^" then [
      {
        op = ">=";
        inherit version;
      }
      {
        op = "<";
        version = version // {
          release = rewriteCaretRhs version.release;
        };
      }
    ]
    # Versions without operators are exact matches, add operator according to PEP-440
    else [{
      op = "==";
      inherit version;
    }]
  );

})