# this code is slightly modified from https://github.com/edolstra/flake-compat
##
## Copyright (c) 2020-2021 Eelco Dolstra and the flake-compat contributors
##
## Permission is hereby granted, free of charge, to any person obtaining
## a copy of this software and associated documentation files (the
## "Software"), to deal in the Software without restriction, including
## without limitation the rights to use, copy, modify, merge, publish,
## distribute, sublicense, and/or sell copies of the Software, and to
## permit persons to whom the Software is furnished to do so, subject to
## the following conditions:
##
## The above copyright notice and this permission notice shall be
## included in all copies or substantial portions of the Software.
##
## THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
## EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
## MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
## NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
## LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
## OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
## WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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 =
    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 { })
        );
        inherit (info) rev lastModified narHash;
        shortRev = builtins.substring 0 7 info.rev;
        lastModifiedDate = formatSecondsSinceEpoch info.lastModified;
      }
    else if info.type == "git" then
      {
        outPath = builtins.fetchGit (
          {
            inherit (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 { })
        );
        inherit (info) lastModified narHash;
        lastModifiedDate = formatSecondsSinceEpoch info.lastModified;
      }
      // (
        if info ? rev then
          {
            inherit (info) rev;
            shortRev = builtins.substring 0 7 info.rev;
          }
        else
          { }
      )
    else if info.type == "path" then
      {
        outPath = builtins.path { inherit (info) path; };
        inherit (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 if info.type == "sourcehut" then
      {
        inherit (info) rev narHash lastModified;
        outPath = fetchTarball (
          {
            url = "https://${info.host or "git.sr.ht"}/${info.owner}/${info.repo}/archive/${info.rev}.tar.gz";
          }
          // (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
fetchTree