feat: integrate tool with gitlab service (#39)

* feat: integrate tool with gitlab service

Fix https://github.com/lampajr/backporting/issues/30

src/service/git/gitlab/gitlab-mapper.ts

@@ -0,0 +1,83 @@
+import { GitPullRequest, GitRepoState, GitRepository } from "@bp/service/git/git.types";
+import GitResponseMapper from "@bp/service/git/git-mapper";
+import { MergeRequestSchema, ProjectSchema } from "@gitbeaker/rest";
+import { Axios } from "axios";
+
+export default class GitLabMapper implements GitResponseMapper<MergeRequestSchema, string> {
+
+  private readonly client;
+  // needs client to perform additional requests
+  constructor(client: Axios) {
+    this.client = client;
+  }
+
+  mapGitState(state: string): GitRepoState {
+    switch (state) {
+      case "opened":
+        return GitRepoState.OPEN;
+      case "closed":
+        return GitRepoState.CLOSED;
+      case "merged":
+        return GitRepoState.MERGED;
+      default:
+        return GitRepoState.LOCKED;
+    }
+  }
+  
+  async mapPullRequest(mr: MergeRequestSchema): Promise<GitPullRequest> {
+    // throw new Error("Method not implemented.");
+    return {
+      number: mr.iid,
+      author: mr.author.username,
+      url: mr.web_url,
+      htmlUrl: mr.web_url,
+      title: mr.title,
+      body: mr.description,
+      state: this.mapGitState(mr.state),
+      merged: this.isMerged(mr),
+      mergedBy: mr.merged_by?.username,
+      reviewers: mr.reviewers?.map((r => r.username)) ?? [],
+      assignees: mr.assignees?.map((r => r.username)) ?? [],
+      sourceRepo: await this.mapSourceRepo(mr),
+      targetRepo: await this.mapTargetRepo(mr),
+      nCommits: 1, // info not present on mr
+      // if mr is merged, use merge_commit_sha otherwise use sha
+      // what is the difference between sha and diff_refs.head_sha?
+      commits: this.isMerged(mr) ? [mr.squash_commit_sha ? mr.squash_commit_sha : mr.merge_commit_sha as string] : [mr.sha]
+    };
+  }
+
+  async mapSourceRepo(mr: MergeRequestSchema): Promise<GitRepository> {
+    const project: ProjectSchema = await this.getProject(mr.source_project_id);
+    
+    return {
+      owner: project.namespace.full_path, // or just proj.path?
+      project: project.path,
+      cloneUrl: project.http_url_to_repo,
+    };
+  }
+
+  async mapTargetRepo(mr: MergeRequestSchema): Promise<GitRepository> {
+    const project: ProjectSchema = await this.getProject(mr.target_project_id);
+    
+    return {
+      owner: project.namespace.full_path, // or just proj.path?
+      project: project.path,
+      cloneUrl: project.http_url_to_repo,
+    };
+  }
+
+  private isMerged(mr: MergeRequestSchema) {
+    return this.mapGitState(mr.state) === GitRepoState.MERGED;
+  }
+
+  private async getProject(projectId: number): Promise<ProjectSchema> {
+    const { data } = await this.client.get(`/projects/${projectId}`);
+    
+    if (!data) {
+      throw new Error(`Project ${projectId} not found`);
+    }
+
+    return data as ProjectSchema;
+  }
+}