5 files changed, 285 insertions, 0 deletions
diff --git a/src/lib/git/index.test.ts b/src/lib/git/index.test.ts
new file mode 100644
index 0000000..4eedaca
--- /dev/null
+++ b/src/lib/git/index.test.ts
@@ -0,0 +1,40 @@
+import { describe, it } from "@std/testing/bdd";
+import { assertEquals } from "@std/assert";
+import {
+  assertSpyCall,
+  assertSpyCalls,
+  returnsNext,
+  stub,
+} from "@std/testing/mock";
+
+// IMPORTANT: Delay the import of `gitDir` to after the stub
+let gitDir: typeof import("./index.ts").gitDir;
+
+describe("gitDir", () => {
+  it("resolves with trimmed decoded stdout", async () => {
+    const encoded = new TextEncoder().encode(
+      " /home/user/project \n",
+    ) as Uint8Array<ArrayBuffer>;
+    const fakeOutput = Promise.resolve({
+      success: true,
+      code: 0,
+      stdout: encoded,
+      stderr: new Uint8Array(),
+      signal: null,
+    });
+
+    using outputStub = stub(
+      Deno.Command.prototype,
+      "output",
+      returnsNext([fakeOutput]),
+    );
+
+    // Now import gitDir AFTER stubbing
+    ({ gitDir } = await import("./index.ts"));
+
+    const result = await gitDir();
+    assertEquals(result.pathname, "/home/user/project");
+    assertSpyCall(outputStub, 0, { args: [], returned: fakeOutput });
+    assertSpyCalls(outputStub, 1);
+  });
+});
diff --git a/src/lib/git/index.ts b/src/lib/git/index.ts
new file mode 100644
index 0000000..23a13eb
--- /dev/null
+++ b/src/lib/git/index.ts
@@ -0,0 +1,16 @@
+import { get, instanciate } from "../../utils/anonymous.ts";
+
+let cachedGitDir: Promise<URL> | undefined;
+
+export function gitDir(): Promise<URL> {
+  if (!cachedGitDir) {
+    cachedGitDir = new Deno.Command("git", {
+      args: ["rev-parse", "--show-toplevel"],
+    }).output()
+      .then(get("stdout"))
+      .then((x) => `file://${new TextDecoder().decode(x).trim()}/`)
+      .then(instanciate(URL));
+  }
+
+  return cachedGitDir;
+}
diff --git a/src/lib/git/log.test.ts b/src/lib/git/log.test.ts
new file mode 100644
index 0000000..09acb1c
--- /dev/null
+++ b/src/lib/git/log.test.ts
@@ -0,0 +1,71 @@
+import { describe, it } from "@std/testing/bdd";
+import { assertEquals, assertExists } from "@std/assert";
+import {
+  assertSpyCall,
+  assertSpyCalls,
+  returnsNext,
+  stub,
+} from "@std/testing/mock";
+import { getLastCommitForOneOfFiles } from "./log.ts";
+import {
+  emptyCommandOutput,
+  gitDiffTreeCommandOutput,
+  gitDir,
+  gitLogPrettyCommandOutput,
+  gitRevParseCommandOutput,
+} from "../../../tests/fixtures/test_data.ts";
+
+describe("getLastCommitForOneOfFiles", () => {
+  it("returns parsed commit with signature and file info", async () => {
+    const outputs = [
+      gitLogPrettyCommandOutput,
+      gitDiffTreeCommandOutput,
+      gitRevParseCommandOutput,
+    ];
+    using logStub = stub(
+      Deno.Command.prototype,
+      "output",
+      returnsNext(outputs),
+    );
+
+    const file = new URL("file.ts", gitDir);
+    const result = await getLastCommitForOneOfFiles(file);
+
+    assertExists(result);
+    assertEquals(result.hash.short, "abcdef1");
+    assertEquals(result.hash.long, "abcdef1234567890abcdef1234567890abcdef12");
+
+    assertEquals(result.author.name, "Alice");
+    assertEquals(result.committer.email, "bob@example.com");
+
+    assertEquals(result.files.length, 1);
+    assertEquals(result.files[0], {
+      path: file,
+      status: "modified",
+    });
+
+    assertEquals(result.signature?.type, "gpg");
+    assertEquals(result.signature?.signer, "bob@example.com");
+
+    for (let i = 0; i < outputs.length; i++) {
+      assertSpyCall(logStub, i, { args: [], returned: outputs[i] });
+    }
+    assertSpyCalls(logStub, outputs.length);
+  });
+
+  it("returns undefined for empty commit output", async () => {
+    using logStub = stub(
+      Deno.Command.prototype,
+      "output",
+      returnsNext([emptyCommandOutput]),
+    );
+
+    const result = await getLastCommitForOneOfFiles(
+      [new URL("nonexistent.ts", gitDir)],
+    );
+
+    assertEquals(result, undefined);
+    assertSpyCall(logStub, 0, { args: [], returned: emptyCommandOutput });
+    assertSpyCalls(logStub, 1);
+  });
+});
diff --git a/src/lib/git/log.ts b/src/lib/git/log.ts
new file mode 100644
index 0000000..86bbe7b
--- /dev/null
+++ b/src/lib/git/log.ts
@@ -0,0 +1,131 @@
+import { defined } from "../../utils/anonymous.ts";
+import { type MaybeIterable, surelyIterable } from "../../utils/iterator.ts";
+import { gitDir } from "./index.ts";
+import type { Commit, CommitFile } from "./types.ts";
+
+const format = [
+  "H",
+  "h",
+  "aI",
+  "aN",
+  "aE",
+  "cI",
+  "cN",
+  "cE",
+  // "G?",
+  "GS",
+  "GK",
+  "GF",
+  "GG",
+];
+
+export async function getLastCommitForOneOfFiles(
+  sources: MaybeIterable<URL>,
+): Promise<Commit | undefined> {
+  const files = surelyIterable(sources);
+  const gitLog = new Deno.Command("git", {
+    args: [
+      "log",
+      "-1",
+      `--pretty=format:${format.map((x) => `%${x}`).join("%n")}`,
+      "--",
+      ...Iterator.from(files).map((x) => x.pathname),
+    ],
+  });
+
+  const { stdout } = await gitLog.output();
+  const result = new TextDecoder().decode(stdout).trim();
+
+  if (result.length <= 0) {
+    return undefined;
+  }
+
+  const [
+    hash,
+    abbrHash,
+    authorDate,
+    authorName,
+    authorEmail,
+    committerDate,
+    committerName,
+    committerEmail,
+    // signatureValidation,
+    signer,
+    key,
+    keyFingerPrint,
+    ...rawLines
+  ] = result.split("\n");
+
+  const raw = rawLines.join("\n").trim();
+
+  const commit: Commit = {
+    files: await fileStatusFromCommit(hash, Iterator.from(files)),
+    hash: { long: hash, short: abbrHash },
+    author: {
+      date: new Date(authorDate),
+      name: authorName,
+      email: authorEmail,
+    },
+    committer: {
+      date: new Date(committerDate),
+      name: committerName,
+      email: committerEmail,
+    },
+  };
+
+  if (raw.length > 0) {
+    commit.signature = {
+      type: raw.startsWith("gpgsm:")
+        ? "x509"
+        : raw.startsWith("gpg:")
+        ? "gpg"
+        : "ssh",
+      signer,
+      key: { long: keyFingerPrint, short: key },
+      rawMessage: raw,
+    };
+  }
+
+  return commit;
+}
+
+async function fileStatusFromCommit(
+  hash: string,
+  files: Iterable<URL>,
+): Promise<CommitFile[]> {
+  const gitDiffTree = new Deno.Command("git", {
+    args: [
+      "diff-tree",
+      "--no-commit-id",
+      "--name-status",
+      "-r",
+      hash,
+    ],
+  });
+
+  const { stdout } = await gitDiffTree.output();
+  const result = new TextDecoder().decode(stdout).trim().split("\n").filter(
+    defined,
+  );
+
+  const dir = await gitDir();
+  return result.map((line) => {
+    const [status, path] = line.split("\t");
+    if (
+      Iterator.from(files).some((file) =>
+        file.pathname.replace(dir.pathname, "").includes(path)
+      )
+    ) {
+      return {
+        path: new URL(path, dir),
+        status: status === "A"
+          ? "added"
+          : status === "D"
+          ? "deleted"
+          : "modified",
+      } as const;
+    }
+
+    return undefined;
+  }).filter(defined);
+}
diff --git a/src/lib/git/types.ts b/src/lib/git/types.ts
new file mode 100644
index 0000000..672d242
--- /dev/null
+++ b/src/lib/git/types.ts
@@ -0,0 +1,27 @@
+export type CommitFile = {
+  path: URL;
+  status: "added" | "modified" | "deleted";
+};
+
+export type Hash = { long: string; short: string };
+
+export type Contributor = {
+  name: string;
+  email: string;
+  date: Date;
+};
+
+export type SignatureType = "ssh" | "gpg" | "x509";
+
+export type Commit = {
+  files: CommitFile[];
+  hash: Hash;
+  author: Contributor;
+  committer: Contributor;
+  signature?: {
+    type: SignatureType;
+    signer: string;
+    key: Hash;
+    rawMessage: string;
+  };
+};