Resclone/src/main/java/io/gitlab/jfronny/resclone/fetchers/GitHubFetcher.java

package io.gitlab.jfronny.resclone.fetchers;

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import io.gitlab.jfronny.resclone.Resclone;
import io.gitlab.jfronny.resclone.util.UrlUtils;
import org.jetbrains.annotations.Nullable;

import java.io.IOException;

public class GitHubFetcher extends PackFetcher {

    @Override
    public String getSourceTypeName() {
        return "github";
    }

    @Override
    String getDownloadUrl(String baseUrl) throws Exception {
        String[] parts = baseUrl.split("/");

        if (parts.length < 2) {
            throw new Exception("Minimum source must contain \"user/repo\".");
        }

        /* "user/repo" - Gets from latest commit of main/master branch. */
        else if (parts.length == 2) {
            return getFromBranch(parts[0] + "/" + parts[1], null);
        }

        /* "user/repo/branch/branchName" - Gets from latest commit of specified branch. */
        else if (parts[2].equalsIgnoreCase("branch")) {
            if (parts.length < 4) throw new Exception("Missing branch name in source definition.");
            else {
                Resclone.LOGGER.info("Getting from " + parts[3] + " branch.");
                return getFromBranch(parts[0] + "/" + parts[1], parts[3]);
            }
        }

        /* "user/repo/release" - Gets from the latest release. */
        else if (parts[2].equalsIgnoreCase("release")) {
            try {
                JsonObject latestRelease = UrlUtils.readJsonFromURL("https://api.github.com/repos/" + parts[0] + "/" + parts[1] + "/releases/latest", JsonObject.class);
                String res = null;

                for (JsonElement element : latestRelease.get("assets").getAsJsonArray()) {
                    JsonObject o = element.getAsJsonObject();
                    if ("application/x-zip-compressed".equals(o.get("content_type").getAsString()) || o.get("name").getAsString().endsWith(".zip")) {
                        res = o.get("browser_download_url").getAsString();
                        break;
                    }
                }

                Resclone.LOGGER.info("Getting from latest release.");

                if (res == null) return latestRelease.get("zipball_url").getAsString();
                else return res;

            } catch (Throwable e) {
                throw new Exception("Failed to get github release asset", e);
            }
        }

        /* "user/repo/tag/tagNum" - Gets from a specified tag. */
        else if (parts[2].equalsIgnoreCase("tag")) {
            if (parts.length < 4) throw new Exception("Missing tag number in source definition.");
            else {
                return getFromTag(parts[0], parts[1], parts[3]);
            }
        }

        return null;
    }

    private String getFromBranch(String repo, @Nullable String branch) {
        if (branch == null) {
            try {
                branch = UrlUtils.readJsonFromURL("https://api.github.com/repos/" + repo, JsonObject.class).get("default_branch").getAsString();
            } catch (IOException e) {
                Resclone.LOGGER.error("Failed to fetch branch for " + repo + ". Choosing \"main\"", e);
                branch = "main";
            }
        }
        Resclone.LOGGER.info("Getting " + repo + " from " + branch + " branch.");
        return "https://codeload.github.com/" + repo + "/legacy.zip/refs/heads/" + branch;
    }

    private String getFromTag(String user, String repo, String tag) {
        Resclone.LOGGER.info("Getting from tag " + tag + ".");
        return "https://codeload.github.com/" + user + "/" + repo + "/legacy.zip/refs/tags/" + tag;
    }

}