Merge pull request 'add: lib/facts.nix' (#1681) from kenji/clan-core:feature/clanLib into main

Reviewed-on: clan/clan-core#1681

lib/default.nix

@@ -6,8 +6,9 @@
 }:
 {
   evalClanModules = import ./eval-clan-modules { inherit clan-core nixpkgs lib; };
+  buildClan = import ./build-clan { inherit clan-core lib nixpkgs; };
+  facts = import ./facts.nix { inherit lib; };
   inventory = import ./inventory { inherit lib clan-core; };
   jsonschema = import ./jsonschema { inherit lib; };
   modules = import ./description.nix { inherit clan-core lib; };
-  buildClan = import ./build-clan { inherit clan-core lib nixpkgs; };
 }

lib/facts.nix

@@ -0,0 +1,72 @@
+{ lib, ... }:
+machineDir:
+let
+
+  allMachineNames = lib.mapAttrsToList (name: _: name) (builtins.readDir machineDir);
+
+  getFactPath = fact: machine: "${machineDir}/${machine}/facts/${fact}";
+
+  readFact =
+    fact: machine:
+    let
+      path = getFactPath fact machine;
+    in
+    if builtins.pathExists path then builtins.readFile path else null;
+
+  # Example:
+  #
+  # readFactFromAllMachines zerotier-ip
+  # => {
+  #   machineA = "1.2.3.4";
+  #   machineB = "5.6.7.8";
+  # };
+  readFactFromAllMachines =
+    fact:
+    let
+      machines = allMachineNames;
+      facts = lib.genAttrs machines (readFact fact);
+      filteredFacts = lib.filterAttrs (_machine: fact: fact != null) facts;
+    in
+    filteredFacts;
+
+  # all given facts are are set and factvalues are never null.
+  #
+  # Example:
+  #
+  # readFactsFromAllMachines [ "zerotier-ip" "syncthing.pub" ]
+  # => {
+  #   machineA =
+  #     {
+  #       "zerotier-ip" = "1.2.3.4";
+  #       "synching.pub" = "1234";
+  #     };
+  #   machineB =
+  #     {
+  #       "zerotier-ip" = "5.6.7.8";
+  #       "synching.pub" = "23456719";
+  #     };
+  # };
+  readFactsFromAllMachines =
+    facts:
+    let
+      # machine -> fact -> factvalue
+      machinesFactsAttrs = lib.genAttrs allMachineNames (
+        machine: lib.genAttrs facts (fact: readFact fact machine)
+      );
+      # remove all machines which don't have all facts set
+      filteredMachineFactAttrs = lib.filterAttrs (
+        _machine: values: builtins.all (fact: values.${fact} != null) facts
+      ) machinesFactsAttrs;
+    in
+    filteredMachineFactAttrs;
+
+in
+{
+  inherit
+    allMachineNames
+    getFactPath
+    readFact
+    readFactFromAllMachines
+    readFactsFromAllMachines
+    ;
+}