refactor: extract coverage parser and percent helpers

dprint.json

@@ -1,6 +1,6 @@
 {
 	"$schema": "https://dprint.dev/schemas/v0.json",
-	"lineWidth": 100,
+	"lineWidth": 1000,
 	"useTabs": true,
 	"indentWidth": 4,
 	"yaml": {

package.json

@@ -23,9 +23,9 @@
 		"fmt": "dprint fmt",
 		"fmt:check": "dprint check",
 		"typecheck": "tsc --noEmit",
-		"test": "bun test",
-		"test:watch": "bun test --watch",
-		"test:coverage": "bun test --coverage",
+		"test": "bun test --concurrent",
+		"test:watch": "bun test --watch --concurrent",
+		"test:coverage": "bun test --coverage --concurrent",
 		"lint": "bun run typecheck && bun run fmt:check"
 	},
 	"dependencies": {

src/context.ts

@@ -2,6 +2,14 @@ import * as github from "@actions/github";
 
 type Context = typeof github.context;
 
+function isPrEvent(context: Context): boolean {
+	return context.eventName === "pull_request" || context.eventName === "pull_request_target";
+}
+
+function stripRefsPrefix(ref: string): string {
+	return ref.replace("refs/heads/", "");
+}
+
 /**
  * Resolve the PR number from the event context using a priority chain:
  *
@@ -24,7 +32,7 @@ export async function resolvePrNumber(
 	}
 
 	// 2. Direct PR trigger
-	if (context.eventName === "pull_request" || context.eventName === "pull_request_target") {
+	if (isPrEvent(context)) {
 		const num = context.payload.pull_request?.number;
 		if (typeof num === "number") return num;
 	}
@@ -83,24 +91,30 @@ export function resolveHeadSha(context: Context = github.context): string {
  * Resolve the base branch for cache key scoping.
  *
  * Under `workflow_run`, `context.ref` points to the *default* branch, not the
- * PR base. Use `head_branch` from the triggering run instead. Falls back to the
- * explicit `base-branch` input or `main`.
+ * PR base. Prefer the base ref of the triggering PR when it is available.
+ * Falls back to the explicit `base-branch` input or the current ref.
  */
 export function resolveBaseBranch(
 	inputBaseBranch: string,
 	context: Context = github.context,
 ): string {
 	if (inputBaseBranch) return inputBaseBranch;
 
-	if (context.eventName === "pull_request" || context.eventName === "pull_request_target") {
+	if (isPrEvent(context)) {
 		return context.payload.pull_request?.base?.ref ?? "main";
 	}
 
 	if (context.eventName === "workflow_run") {
-		return context.payload.workflow_run?.head_branch ?? "main";
+		const prs: unknown[] | undefined = context.payload.workflow_run?.pull_requests;
+		if (Array.isArray(prs) && prs.length > 0) {
+			const first = prs[0] as { base?: { ref?: string; }; };
+			if (first.base?.ref) return first.base.ref;
+		}
+
+		return stripRefsPrefix(context.ref) || "main";
 	}
 
-	return context.ref.replace("refs/heads/", "") || "main";
+	return stripRefsPrefix(context.ref) || "main";
 }
 
 /**
@@ -109,15 +123,15 @@ export function resolveBaseBranch(
  * Under `workflow_run`, the head branch comes from the triggering workflow.
  */
 export function resolveCurrentBranch(context: Context = github.context): string {
-	if (context.eventName === "pull_request" || context.eventName === "pull_request_target") {
+	if (isPrEvent(context)) {
 		return context.payload.pull_request?.head?.ref
-			?? context.ref.replace("refs/heads/", "");
+			?? stripRefsPrefix(context.ref);
 	}
 
 	if (context.eventName === "workflow_run") {
 		return context.payload.workflow_run?.head_branch
-			?? context.ref.replace("refs/heads/", "");
+			?? stripRefsPrefix(context.ref);
 	}
 
-	return context.ref.replace("refs/heads/", "");
+	return stripRefsPrefix(context.ref);
 }

src/context_test.ts

@@ -116,7 +116,6 @@ describe("resolveHeadSha", () => {
 	test("returns workflow_run.head_sha for workflow_run event", () => {
 		const ctx = makeContext({
 			eventName: "workflow_run",
-			sha: "default-sha",
 			payload: { workflow_run: { head_sha: "wr-sha-456" } },
 		});
 		expect(resolveHeadSha(ctx)).toBe("wr-sha-456");
@@ -171,10 +170,15 @@ describe("resolveBaseBranch", () => {
 		expect(resolveBaseBranch("", ctx)).toBe("develop");
 	});
 
-	test("returns workflow_run.head_branch for workflow_run event", () => {
+	test("returns workflow_run pull request base ref for workflow_run event", () => {
 		const ctx = makeContext({
 			eventName: "workflow_run",
-			payload: { workflow_run: { head_branch: "wr-base" } },
+			payload: {
+				workflow_run: {
+					head_branch: "feature-branch",
+					pull_requests: [{ base: { ref: "wr-base" } }],
+				},
+			},
 		});
 		expect(resolveBaseBranch("", ctx)).toBe("wr-base");
 	});
@@ -184,12 +188,13 @@ describe("resolveBaseBranch", () => {
 		expect(resolveBaseBranch("", ctx)).toBe("main");
 	});
 
-	test("returns main when workflow_run has no head_branch", () => {
+	test("falls back to current ref when workflow_run has no PR base ref", () => {
 		const ctx = makeContext({
 			eventName: "workflow_run",
+			ref: "refs/heads/default-branch",
 			payload: { workflow_run: {} },
 		});
-		expect(resolveBaseBranch("", ctx)).toBe("main");
+		expect(resolveBaseBranch("", ctx)).toBe("default-branch");
 	});
 
 	test("input override takes precedence over PR payload", () => {

src/diff.ts

@@ -1,3 +1,7 @@
+import {
+	calculatePercent,
+	roundDelta,
+} from "./percent.js";
 import type {
 	CoverageArtifact,
 	CoverageReport,
@@ -29,7 +33,7 @@ export function computeFileDiffs(
 			baseCoveredLines: base?.coveredLines ?? null,
 			baseTotalLines: base?.totalLines ?? null,
 			basePercent: base?.percent ?? null,
-			delta: base ? Math.round((head.percent - base.percent) * 100) / 100 : null,
+			delta: base ? roundDelta(head.percent, base.percent) : null,
 		});
 	}
 
@@ -70,7 +74,7 @@ export function buildToolReport(
 
 	const coveredLines = headFiles.reduce((s, f) => s + f.coveredLines, 0);
 	const totalLines = headFiles.reduce((s, f) => s + f.totalLines, 0);
-	const percent = totalLines > 0 ? Math.round((coveredLines / totalLines) * 10000) / 100 : 100;
+	const percent = calculatePercent(coveredLines, totalLines);
 
 	let baseCoveredLines: number | null = null;
 	let baseTotalLines: number | null = null;
@@ -80,10 +84,8 @@ export function buildToolReport(
 	if (baseFiles && baseFiles.length > 0) {
 		baseCoveredLines = baseFiles.reduce((s, f) => s + f.coveredLines, 0);
 		baseTotalLines = baseFiles.reduce((s, f) => s + f.totalLines, 0);
-		basePercent = baseTotalLines > 0
-			? Math.round((baseCoveredLines / baseTotalLines) * 10000) / 100
-			: 100;
-		delta = Math.round((percent - basePercent) * 100) / 100;
+		basePercent = calculatePercent(baseCoveredLines, baseTotalLines);
+		delta = roundDelta(percent, basePercent);
 	}
 
 	return {
@@ -108,15 +110,16 @@ export function buildToolReport(
 export function buildFullReport(toolReports: ToolCoverageReport[]): CoverageReport {
 	const coveredLines = toolReports.reduce((s, t) => s + t.summary.coveredLines, 0);
 	const totalLines = toolReports.reduce((s, t) => s + t.summary.totalLines, 0);
-	const percent = totalLines > 0 ? Math.round((coveredLines / totalLines) * 10000) / 100 : 100;
+	const percent = calculatePercent(coveredLines, totalLines);
 
 	let basePercent: number | null = null;
 	let delta: number | null = null;
+	const allToolsComparable = toolReports.every((t) => t.summary.baseTotalLines !== null);
 	const baseCovered = toolReports.reduce((s, t) => s + (t.summary.baseCoveredLines ?? 0), 0);
 	const baseTotal = toolReports.reduce((s, t) => s + (t.summary.baseTotalLines ?? 0), 0);
-	if (baseTotal > 0) {
-		basePercent = Math.round((baseCovered / baseTotal) * 10000) / 100;
-		delta = Math.round((percent - basePercent) * 100) / 100;
+	if (allToolsComparable && baseTotal > 0) {
+		basePercent = calculatePercent(baseCovered, baseTotal);
+		delta = roundDelta(percent, basePercent);
 	}
 
 	return {

src/diff_test.ts

@@ -124,4 +124,30 @@ describe("buildFullReport", () => {
 		expect(report.overall.percent).toBe(65);
 		expect(report.tools).toHaveLength(2);
 	});
+
+	test("omits overall delta when any tool lacks base data", () => {
+		const withBase = buildToolReport(
+			"bun",
+			[{ file: "a.ts", coveredLines: 8, totalLines: 10, percent: 80 }],
+			{
+				tool: "bun",
+				files: [{ file: "a.ts", coveredLines: 7, totalLines: 10, percent: 70 }],
+				commitSha: "abc123",
+				branch: "main",
+				timestamp: "2025-01-01T00:00:00Z",
+			},
+			[],
+		);
+		const withoutBase = buildToolReport(
+			"go",
+			[{ file: "b.go", coveredLines: 8, totalLines: 10, percent: 80 }],
+			null,
+			[],
+		);
+
+		const report = buildFullReport([withBase, withoutBase]);
+
+		expect(report.overall.basePercent).toBeNull();
+		expect(report.overall.delta).toBeNull();
+	});
 });

src/go.ts

@@ -1,3 +1,4 @@
+import { calculatePercent } from "./percent.js";
 import type { FileCoverage } from "./types.js";
 
 /**
@@ -59,7 +60,7 @@ export function parseGoCover(content: string): FileCoverage[] {
 
 	const results: FileCoverage[] = [];
 	for (const [file, { covered, total }] of fileMap) {
-		const percent = total > 0 ? Math.round((covered / total) * 10000) / 100 : 100;
+		const percent = calculatePercent(covered, total);
 		results.push({ file, coveredLines: covered, totalLines: total, percent });
 	}
 

src/index.ts

@@ -20,8 +20,14 @@ import {
 	buildFullReport,
 	buildToolReport,
 } from "./diff.js";
-import { parseGoCover } from "./go.js";
-import { parseLcov } from "./lcov.js";
+import {
+	getCoverageParser,
+	getSupportedCoverageTools,
+} from "./parser.js";
+import {
+	formatPercent,
+	formatPercentValue,
+} from "./percent.js";
 import { renderReport } from "./render.js";
 import type {
 	ArtifactInput,
@@ -69,18 +75,19 @@ function parseFile(tool: string, filePath: string): { files: FileCoverage[]; war
 	}
 
 	try {
-		switch (tool) {
-			case "lcov":
-			case "bun":
-			case "node":
-				return { files: parseLcov(content), warnings };
-			case "go":
-			case "gocover":
-				return { files: parseGoCover(content), warnings };
-			default:
-				warnings.push(`Unknown tool "${tool}". Supported: bun, lcov, node, go, gocover.`);
-				return { files: [], warnings };
+		const parser = getCoverageParser(tool);
+		if (!parser) {
+			warnings.push(`Unknown tool "${tool}". Supported: ${getSupportedCoverageTools().join(", ")}.`);
+			return {
+				files: [],
+				warnings,
+			};
 		}
+
+		return {
+			files: parser(content),
+			warnings,
+		};
 	} catch (err: unknown) {
 		warnings.push(
 			`Failed to parse \`${filePath}\` as ${tool} coverage: ${(err as Error).message}`,
@@ -142,8 +149,8 @@ async function run(): Promise<void> {
 			const report = buildToolReport(input.tool, headFiles, baseArtifact, warnings);
 			toolReports.push(report);
 
-			// Check for decreases
-			if (report.summary.delta !== null && report.summary.delta < 0) {
+			// Match the public contract: any file-level decrease trips the flag.
+			if (report.files.some((file) => file.delta !== null && file.delta < 0)) {
 				anyDecrease = true;
 			}
 
@@ -172,7 +179,7 @@ async function run(): Promise<void> {
 		const markdown = renderReport(fullReport, marker, colorize, commitInfo);
 
 		// Set outputs
-		core.setOutput("overall-coverage", fullReport.overall.percent.toFixed(2));
+		core.setOutput("overall-coverage", formatPercentValue(fullReport.overall.percent));
 		core.setOutput("coverage-decreased", anyDecrease ? "true" : "false");
 
 		// Post / update PR comment
@@ -209,9 +216,7 @@ async function run(): Promise<void> {
 		// Threshold check
 		if (threshold > 0 && fullReport.overall.percent < threshold) {
 			core.setFailed(
-				`Overall coverage ${
-					fullReport.overall.percent.toFixed(2)
-				}% is below threshold ${threshold}%`,
+				`Overall coverage ${formatPercent(fullReport.overall.percent)} is below threshold ${threshold}%`,
 			);
 			return;
 		}

src/lcov.ts

@@ -1,3 +1,4 @@
+import { calculatePercent } from "./percent.js";
 import type { FileCoverage } from "./types.js";
 
 /**
@@ -62,9 +63,7 @@ export function parseLcov(content: string): FileCoverage[] {
 			coveredLines = lhProvided ?? 0;
 		}
 
-		const percent = totalLines > 0
-			? Math.round((coveredLines / totalLines) * 10000) / 100
-			: 100;
+		const percent = calculatePercent(coveredLines, totalLines);
 
 		results.push({ file, coveredLines, totalLines, percent });
 	}

src/parser.ts

@@ -0,0 +1,23 @@
+import { parseGoCover } from "./go.js";
+import { parseLcov } from "./lcov.js";
+import type { FileCoverage } from "./types.js";
+
+export type CoverageParser = (content: string) => FileCoverage[];
+
+const COVERAGE_PARSER_ENTRIES: [string, CoverageParser][] = [
+	["lcov", parseLcov],
+	["bun", parseLcov],
+	["node", parseLcov],
+	["go", parseGoCover],
+	["gocover", parseGoCover],
+];
+
+const COVERAGE_PARSERS = new Map<string, CoverageParser>(COVERAGE_PARSER_ENTRIES);
+
+export function getCoverageParser(tool: string): CoverageParser | undefined {
+	return COVERAGE_PARSERS.get(tool);
+}
+
+export function getSupportedCoverageTools(): string[] {
+	return COVERAGE_PARSER_ENTRIES.map(([tool]) => tool);
+}