Parse version manifest and download forge libraries.

TODO:
Integrate base url propagation.
Integrate PackXZExtract to calculate hashes  of jar.pack.xz files.
OR ammend the distribution spec to accept different hash algos (requires helioslauncher update).

src/resolver/forge/adapter/forge18.resolver.ts

@@ -1,5 +1,12 @@
+import AdmZip from 'adm-zip'
+import { createHash } from 'crypto'
+import { lstat, readFile, Stats } from 'fs-extra'
+import { VersionManifest } from '../../../model/forge/versionmanifest'
+import { Artifact } from '../../../model/spec/artifact'
 import { Module } from '../../../model/spec/module'
+import { Type } from '../../../model/spec/type'
 import { ForgeRepoStructure } from '../../../model/struct/repo/forgerepo.struct'
+import { MavenUtil } from '../../../util/maven'
 import { ForgeResolver } from '../forge.resolver'
 
 export class Forge18Adapter extends ForgeResolver {
@@ -18,8 +25,7 @@ export class Forge18Adapter extends ForgeResolver {
     }
 
     public async getModule(): Promise<Module> {
-        await this.getForgeByVersion()
-        return null as unknown as Module
+        return this.getForgeByVersion()
     }
 
     public isForVersion(version: string) {
@@ -33,7 +39,7 @@ export class Forge18Adapter extends ForgeResolver {
         console.debug(`Checking for forge version at ${targetLocalPath}..`)
         if (!await forgeRepo.artifactExists(targetLocalPath)) {
             console.debug(`Forge not found locally, initializing download..`)
-            await forgeRepo.downloadArtifact(
+            await forgeRepo.downloadArtifactByComponents(
                 this.REMOTE_REPOSITORY,
                 ForgeRepoStructure.FORGE_GROUP,
                 ForgeRepoStructure.FORGE_ARTIFACT,
@@ -42,11 +48,81 @@ export class Forge18Adapter extends ForgeResolver {
             console.debug('Using locally discovered forge.')
         }
         console.debug(`Beginning processing of Forge v${this.forgeVersion} (Minecraft ${this.minecraftVersion})`)
+
+        const forgeUniversalBuffer = await readFile(targetLocalPath)
+        const zip = new AdmZip(forgeUniversalBuffer)
+        const zipEntries = zip.getEntries()
+
+        let versionManifest
+
+        for (const entry of zipEntries) {
+            if (entry.entryName === 'version.json') {
+                versionManifest = zip.readAsText(entry)
+                break
+            }
+        }
+
+        if (!versionManifest) {
+            throw new Error('Failed to find version.json in forge universal jar.')
+        }
+
+        versionManifest = JSON.parse(versionManifest) as VersionManifest
+
+        const forgeModule: Module = {
+            id: MavenUtil.mavenComponentsToIdentifier(
+                ForgeRepoStructure.FORGE_GROUP,
+                ForgeRepoStructure.FORGE_ARTIFACT,
+                artifactVersion, 'universal'
+            ),
+            name: 'Minecraft Forge',
+            type: Type.ForgeHosted,
+            artifact: this.generateArtifact(forgeUniversalBuffer, await lstat(targetLocalPath)),
+            subModules: []
+        }
+
+        for (const lib of versionManifest.libraries) {
+            if (lib.name.startsWith('net.minecraftforge:forge:')) {
+                // We've already processed forge.
+                continue
+            }
+            console.debug(`Processing ${lib.name}..`)
+
+            const libRepo = this.repoStructure.getLibRepoStruct()
+            const extension = this.determineExtension(lib.checksums)
+            const localPath = libRepo.getArtifactById(lib.name, extension) as string
+
+            if (!await libRepo.artifactExists(localPath)) {
+                console.debug(`Not found locally, downloading..`)
+                await libRepo.downloadArtifactById(lib.url || 'https://libraries.minecraft.net/', lib.name, extension)
+            } else {
+                console.debug('Using local copy.')
+            }
+
+            const libBuf = await readFile(localPath)
+            const stats = await lstat(localPath)
+
+            forgeModule.subModules?.push({
+                id: lib.name,
+                name: `Minecraft Forge (${MavenUtil.getMavenComponents(lib.name)?.artifact})`,
+                type: Type.Library,
+                artifact: this.generateArtifact(libBuf, stats)
+            })
+
+        }
+
+        return forgeModule
     }
 
-    // TODO
-    // extract manifest
-    // parse manifest
-    // return module
+    private generateArtifact(buf: Buffer, stats: Stats): Artifact {
+        return {
+            size: stats.size,
+            MD5: createHash('md5').update(buf).digest('hex'),
+            url: 'TODO'
+        }
+    }
+
+    private determineExtension(checksums: string[] | undefined) {
+        return checksums != null && checksums.length > 1 ? 'jar.pack.xz' : 'jar'
+    }
 
 }