dotfiles/c_.nix

# a small helper that only builds on top of builtins functions
{src}@inputs:
builtins // (let 
formatSecondsSinceEpoch = t:
let
rem = x: y: x - x / y * y;
days = t / 86400;
secondsInDay = rem t 86400;
hours = secondsInDay / 3600;
minutes = (rem secondsInDay 3600) / 60;
seconds = rem t 60;

# Courtesy of https://stackoverflow.com/a/32158604.
z = days + 719468;
era = (if z >= 0 then z else z - 146096) / 146097;
doe = z - era * 146097;
yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365;
y = yoe + era * 400;
doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
mp = (5 * doy + 2) / 153;
d = doy - (153 * mp + 2) / 5 + 1;
m = mp + (if mp < 10 then 3 else -9);
y' = y + (if m <= 2 then 1 else 0);

pad = s: if builtins.stringLength s < 2 then "0" + s else s;
in "${toString y'}${pad (toString m)}${pad (toString d)}${pad (toString hours)}"
+ "${pad (toString minutes)}${pad (toString seconds)}";

fetchTree =
# this is the value of flake.lock#lock.nodes.${input_name}.locked
{type
, host? ""
, owner? ""
, repo? ""
, rev? ""
, submodules? ""
, path? ""
, narHash? null
, lastModified? 0
}@info:
if info.type == "github" then
{ outPath =
  fetchTarball
    ({ url = "https://api.${info.host or "github.com"}/repos/"
     + "${info.owner}/${info.repo}/tarball/${info.rev}"; }
     // (if info ? narHash then { sha256 = info.narHash; } else {})
    );
  rev = info.rev;
  shortRev = builtins.substring 0 7 info.rev;
  lastModified = info.lastModified;
  lastModifiedDate = formatSecondsSinceEpoch info.lastModified;
  narHash = info.narHash;
}
else if info.type == "git" then
{ outPath =
  builtins.fetchGit
    ({ url = info.url; }
     // (if info ? rev then { inherit (info) rev; } else {})
     // (if info ? ref then { inherit (info) ref; } else {})
     // (if info ? submodules then { inherit (info) submodules; } else {})
    );
  lastModified = info.lastModified;
  lastModifiedDate = formatSecondsSinceEpoch info.lastModified;
  narHash = info.narHash;
} // (if info ? rev then {
rev = info.rev;
shortRev = builtins.substring 0 7 info.rev;
} else {
})
else if info.type == "path" then
{ outPath = builtins.path { 
  path = if builtins.substring 0 1 info.path != "/"
    then src + ("/" + info.path)  # make this absolute path by prepending ./
    else info.path; # it's already an absolute path
                          };
narHash = info.narHash;
}
else if info.type == "tarball" then
{ outPath =
  fetchTarball
    ({ inherit (info) url; }
     // (if info ? narHash then { sha256 = info.narHash; } else {})
    );
}
else if info.type == "gitlab" then
{ inherit (info) rev narHash lastModified;
  outPath =
    fetchTarball
    ({ url = "https://${info.host or "gitlab.com"}/api/v4/projects/${info.owner}%2F${info.repo}/repository/archive.tar.gz?sha=${info.rev}"; }
     // (if info ? narHash then { sha256 = info.narHash; } else {})
    );
  shortRev = builtins.substring 0 7 info.rev;
}
else
# FIXME: add Mercurial, tarball inputs.
throw "flake input has unsupported input type '${info.type}'";
in {
  inherit fetchTree;
})