ForgejoKit/Tests/ForgejoKitTests/DiffParserTests.swift

@testable import ForgejoKit
import Foundation
import Testing

struct DiffParserTests {
    // MARK: - Empty and minimal input

    @Test func parseEmptyString() {
        let result = DiffParser.parse("")
        #expect(result.files.isEmpty)
    }

    @Test func parseGarbageInput() {
        let result = DiffParser.parse("this is not a diff")
        #expect(result.files.isEmpty)
    }

    // MARK: - Single file diff

    @Test func parseSingleFileAddition() {
        let diff = [
            "diff --git a/hello.txt b/hello.txt",
            "new file mode 100644",
            "--- /dev/null",
            "+++ b/hello.txt",
            "@@ -0,0 +1,3 @@",
            "+line one",
            "+line two",
            "+line three",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files.count == 1)

        let file = result.files[0]
        #expect(file.oldName == "/dev/null")
        #expect(file.newName == "hello.txt")
        #expect(file.hunks.count == 1)

        let hunk = file.hunks[0]
        #expect(hunk.lines.count == 4)
        #expect(hunk.lines[0].type == .header)
        #expect(hunk.lines[1].type == .addition)
        #expect(hunk.lines[2].type == .addition)
        #expect(hunk.lines[3].type == .addition)
    }

    @Test func parseSingleFileDeletion() {
        let diff = [
            "diff --git a/old.txt b/old.txt",
            "deleted file mode 100644",
            "--- a/old.txt",
            "+++ /dev/null",
            "@@ -1,2 +0,0 @@",
            "-removed line one",
            "-removed line two",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files.count == 1)

        let file = result.files[0]
        #expect(file.oldName == "old.txt")
        #expect(file.newName == "/dev/null")
    }

    @Test func parseSingleFileModification() {
        let diff = [
            "diff --git a/file.txt b/file.txt",
            "--- a/file.txt",
            "+++ b/file.txt",
            "@@ -1,3 +1,3 @@",
            " context line",
            "-old line",
            "+new line",
            " another context",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files.count == 1)

        let hunk = result.files[0].hunks[0]
        #expect(hunk.lines.count == 5)

        let contextLine = hunk.lines[1]
        #expect(contextLine.type == .context)
        #expect(contextLine.oldLineNumber == 1)
        #expect(contextLine.newLineNumber == 1)

        let deletionLine = hunk.lines[2]
        #expect(deletionLine.type == .deletion)
        #expect(deletionLine.content == "old line")
        #expect(deletionLine.oldLineNumber == 2)
        #expect(deletionLine.newLineNumber == nil)

        let additionLine = hunk.lines[3]
        #expect(additionLine.type == .addition)
        #expect(additionLine.content == "new line")
        #expect(additionLine.oldLineNumber == nil)
        #expect(additionLine.newLineNumber == 2)

        let trailingContext = hunk.lines[4]
        #expect(trailingContext.type == .context)
        #expect(trailingContext.oldLineNumber == 3)
        #expect(trailingContext.newLineNumber == 3)
    }

    // MARK: - Multiple files

    @Test func parseMultipleFiles() {
        let diff = [
            "diff --git a/a.txt b/a.txt",
            "--- a/a.txt",
            "+++ b/a.txt",
            "@@ -1 +1 @@",
            "-old a",
            "+new a",
            "diff --git a/b.txt b/b.txt",
            "--- a/b.txt",
            "+++ b/b.txt",
            "@@ -1 +1 @@",
            "-old b",
            "+new b",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files.count == 2)
        #expect(result.files[0].newName == "a.txt")
        #expect(result.files[1].newName == "b.txt")
    }

    // MARK: - Multiple hunks

    @Test func parseMultipleHunks() {
        let diff = [
            "diff --git a/file.txt b/file.txt",
            "--- a/file.txt",
            "+++ b/file.txt",
            "@@ -1,3 +1,3 @@",
            " context",
            "-old first",
            "+new first",
            " context",
            "@@ -10,3 +10,3 @@",
            " context",
            "-old second",
            "+new second",
            " context",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files[0].hunks.count == 2)

        let hunk2 = result.files[0].hunks[1]
        let contextLine = hunk2.lines[1]
        #expect(contextLine.oldLineNumber == 10)
        #expect(contextLine.newLineNumber == 10)
    }

    // MARK: - Line number tracking

    @Test func lineNumbersTrackCorrectlyWithMultipleAdditions() {
        let diff = [
            "diff --git a/file.txt b/file.txt",
            "--- a/file.txt",
            "+++ b/file.txt",
            "@@ -5,4 +5,6 @@",
            " context",
            "+added one",
            "+added two",
            " old context",
            "-removed",
            "+replaced",
            " trailing",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        let lines = result.files[0].hunks[0].lines

        let ctx1 = lines[1]
        #expect(ctx1.oldLineNumber == 5)
        #expect(ctx1.newLineNumber == 5)

        let add1 = lines[2]
        #expect(add1.newLineNumber == 6)
        #expect(add1.oldLineNumber == nil)

        let add2 = lines[3]
        #expect(add2.newLineNumber == 7)

        let ctx2 = lines[4]
        #expect(ctx2.oldLineNumber == 6)
        #expect(ctx2.newLineNumber == 8)

        let del = lines[5]
        #expect(del.oldLineNumber == 7)
        #expect(del.newLineNumber == nil)

        let repl = lines[6]
        #expect(repl.newLineNumber == 9)
        #expect(repl.oldLineNumber == nil)

        let trailing = lines[7]
        #expect(trailing.oldLineNumber == 8)
        #expect(trailing.newLineNumber == 10)
    }

    // MARK: - Hunk header parsing

    @Test func hunkHeaderWithFunctionContext() {
        let diff = [
            "diff --git a/main.swift b/main.swift",
            "--- a/main.swift",
            "+++ b/main.swift",
            "@@ -42,6 +42,7 @@ func doSomething() {",
            " context",
            "+new line",
            " context",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        let firstLine = result.files[0].hunks[0].lines[1]
        #expect(firstLine.oldLineNumber == 42)
        #expect(firstLine.newLineNumber == 42)
    }

    // MARK: - File name extraction

    @Test func fileNameExtractedFromMinusPlus() {
        let diff = [
            "diff --git a/src/app.swift b/src/app.swift",
            "--- a/src/app.swift",
            "+++ b/src/app.swift",
            "@@ -1 +1 @@",
            "-old",
            "+new",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files[0].oldName == "src/app.swift")
        #expect(result.files[0].newName == "src/app.swift")
    }

    @Test func fileNameFallsBackToGitHeader() {
        let diff = [
            "diff --git a/image.png b/image.png",
            "Binary files differ",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files.count == 1)
        #expect(result.files[0].oldName == "image.png")
        #expect(result.files[0].newName == "image.png")
    }

    // MARK: - Commit diff (new file from Forgejo API)

    @Test func parseCommitDiffNewFile() {
        let diff = [
            "diff --git a/src/main.py b/src/main.py",
            "new file mode 100644",
            "index 0000000..67e9324",
            "--- /dev/null",
            "+++ b/src/main.py",
            "@@ -0,0 +1 @@",
            "+def main():\\n    print(\"Main module\")",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files.count == 1)

        let file = result.files[0]
        #expect(file.oldName == "/dev/null")
        #expect(file.newName == "src/main.py")
        #expect(file.hunks.count == 1)

        let hunk = file.hunks[0]
        #expect(hunk.lines[0].type == .header)
        #expect(hunk.lines[1].type == .addition)
        #expect(hunk.lines[1].newLineNumber == 1)
        #expect(hunk.lines[1].oldLineNumber == nil)
    }

    @Test func parseCommitDiffMultipleFiles() {
        let diff = [
            "diff --git a/hello.py b/hello.py",
            "new file mode 100644",
            "--- /dev/null",
            "+++ b/hello.py",
            "@@ -0,0 +1,2 @@",
            "+print(\"hello\")",
            "+print(\"world\")",
            "diff --git a/README.md b/README.md",
            "--- a/README.md",
            "+++ b/README.md",
            "@@ -1,2 +1,3 @@",
            " # Project",
            "+",
            "+New section",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        #expect(result.files.count == 2)

        #expect(result.files[0].newName == "hello.py")
        #expect(result.files[0].oldName == "/dev/null")
        #expect(result.files[0].hunks[0].lines.count(where: { $0.type == .addition }) == 2)

        #expect(result.files[1].newName == "README.md")
        #expect(result.files[1].oldName == "README.md")
        let readmeHunk = result.files[1].hunks[0]
        #expect(readmeHunk.lines.count(where: { $0.type == .context }) == 1)
        #expect(readmeHunk.lines.count(where: { $0.type == .addition }) == 2)
    }

    // MARK: - No newline at end of file sentinel

    @Test func noNewlineAtEndOfFileSentinelIsSkipped() {
        let diff = [
            "diff --git a/file.txt b/file.txt",
            "--- a/file.txt",
            "+++ b/file.txt",
            "@@ -1,2 +1,2 @@",
            " context",
            "-old line",
            "\\ No newline at end of file",
            "+new line",
            "\\ No newline at end of file",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        let hunk = result.files[0].hunks[0]
        // Header + context + deletion + addition = 4 lines (sentinels skipped)
        #expect(hunk.lines.count == 4)
        #expect(hunk.lines[0].type == .header)
        #expect(hunk.lines[1].type == .context)
        #expect(hunk.lines[2].type == .deletion)
        #expect(hunk.lines[3].type == .addition)
        // diffPosition should be consecutive without gaps from the sentinel
        #expect(hunk.lines[1].diffPosition == 1)
        #expect(hunk.lines[2].diffPosition == 2)
        #expect(hunk.lines[3].diffPosition == 3)
    }

    // MARK: - DiffLine identity

    @Test func eachLineHasUniqueId() {
        let diff = [
            "diff --git a/f.txt b/f.txt",
            "--- a/f.txt",
            "+++ b/f.txt",
            "@@ -1,2 +1,2 @@",
            "-a",
            "+b",
        ].joined(separator: "\n")

        let result = DiffParser.parse(diff)
        let ids = result.files[0].hunks[0].lines.map(\.id)
        let uniqueIds = Set(ids)
        #expect(ids.count == uniqueIds.count)
    }
}