refactor: streamline Makefile and add diff functionality with tests

[kazeburo]

User description

• modify Makefile and add make lint
• create diff.go and move some fuctions
• fix some lint issues

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PR Type

Enhancement, Tests

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Description

• Extract diff helpers into new diff.go

• Add diff_test.go covering diff and message builders

• Improve main.go error handling and exit codes

• Update Makefile with wildcard targets and lint

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Diagram Walkthrough

flowchart LR
  A["main.go"] -- "extracts diff helpers" --> B["diff.go"]
  B -- "unit tests" --> C["diff_test.go"]
  A -- "better exit codes & error handling" --> A
  D["Makefile"] -- "adds lint target & wildcards" --> D

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File Walkthrough

	Relevant files
Enhancement	diff.go Extract diff helpers into dedicated file                                  diff.go New file containing diff, getLines, buildDiffMsg, and buildNoDifferenceMsg Uses gonp to compute unified diffs between two files Handles io.EOF when reading file preview bytes +81/-0    main.go Improve main error handling and constants                                main.go Remove diff helpers moved to diff.go Add exit-code constants OK, WARNING, CRITICAL, UNKNOWN Improve main error handling for help output and missing command Wrap command error with %w and ignore os.Remove return +19/-82
Tests	diff_test.go Add unit tests for diff helpers                                                    diff_test.go New test file for diff.go functions Covers diff, buildDiffMsg, buildNoDifferenceMsg, and large-result truncation Verifies no-difference case returns empty diff +88/-0    main_test.go Clean up tests after diff extraction                                          main_test.go Remove diff-related tests now in diff_test.go Handle error from file.Seek in TestCmd Ignore os.Remove return value in createTempFile cleanup +5/-84
Configuration changes	Makefile Streamline build targets and add lint                                        Makefile Use *.go wildcard for check-diff and linux targets Add lint target running golangci-lint run ./... +6/-4

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[github-actions]

PR Reviewer Guide 🔍

(Review updated until commit 8a2b0ea)

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Incomplete .PHONY The .PHONY declaration only lists check-diff, but all, linux, check, and lint are also phony targets. If a file named lint, check, linux, or all exists in the project root, make will incorrectly treat the target as up-to-date and skip the recipe. For example, touch lint && make lint would not run golangci-lint. .PHONY: check-diff check-diff: *.go go build $(LDFLAGS) -o check-diff linux: *.go GOOS=linux GOARCH=amd64 go build $(LDFLAGS) -o check-diff check: go test -v ./... lint: golangci-lint run ./...

[github-actions]

Persistent review updated to latest commit 8c4c517

[github-actions]

Persistent review updated to latest commit ac9ed4a

[github-actions]

Persistent review updated to latest commit b51bdf6

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Persistent review updated to latest commit 8a2b0ea

[github-actions]

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