internal/parsers/diff/parser.go

@@ -3,6 +3,7 @@ package diff
 import (
 	"fmt"
 	"os"
+	"strings"
 
 	"focs.ji.sjtu.edu.cn/git/FOCS-dev/JOJ3/internal/stage"
 )
@@ -26,25 +27,83 @@ func (*Diff) Run(results []stage.ExecutorResult, confAny any) (
 	if len(conf.Cases) != len(results) {
 		return nil, true, fmt.Errorf("cases number not match")
 	}
+
 	var res []stage.ParserResult
 	for i, caseConf := range conf.Cases {
 		result := results[i]
 		score := 0
+		var comment string
+
 		stdout, err := os.ReadFile(caseConf.StdoutPath)
 		if err != nil {
 			return nil, true, err
 		}
-		// TODO: more compare strategies
+
+		// If no difference, assign score
 		if string(stdout) == result.Files["stdout"] {
 			score = caseConf.Score
-		}
-		res = append(res, stage.ParserResult{
-			Score: score,
-			Comment: fmt.Sprintf(
+			comment = fmt.Sprintf(
 				"executor status: run time: %d ns, memory: %d bytes",
 				result.RunTime, result.Memory,
-			),
+			)
+		} else {
+			// Convert stdout to string and split by lines
+			stdoutLines := strings.Split(string(stdout), "\n")
+			resultLines := strings.Split(result.Files["stdout"], "\n")
+
+			// Find the first difference
+			diffIndex := findFirstDifferenceIndex(stdoutLines, resultLines)
+			if diffIndex != -1 {
+				// Get the surrounding lines from both stdout and result
+				stdoutContext := getContextLines(stdoutLines, diffIndex, 10)
+				resultContext := getContextLines(resultLines, diffIndex, 10)
+				comment = comment + fmt.Sprintf(
+					"difference found at line %d:\nExpected output:\n%s\nActual output:\n%s",
+					diffIndex+1,
+					resultContext,
+					stdoutContext,
+				)
+			}
+		}
+
+		res = append(res, stage.ParserResult{
+			Score:   score,
+			Comment: comment,
 		})
 	}
+
 	return res, false, nil
 }
+
+// findFirstDifferenceIndex finds the index of the first line where stdout and result differ.
+func findFirstDifferenceIndex(stdoutLines, resultLines []string) int {
+	maxLines := len(stdoutLines)
+	if len(resultLines) > maxLines {
+		maxLines = len(resultLines)
+	}
+
+	for i := 0; i < maxLines; i++ {
+		if i >= len(stdoutLines) || i >= len(resultLines) || stdoutLines[i] != resultLines[i] {
+			return i
+		}
+	}
+	return -1
+}
+
+// getContextLines returns the surrounding lines of the specified index.
+func getContextLines(lines []string, index, contextSize int) string {
+	start := index - contextSize
+	if start < 0 {
+		start = 0
+	}
+	end := index + contextSize + 1
+	if end > len(lines) {
+		end = len(lines)
+	}
+
+	var context strings.Builder
+	for i := start; i < end; i++ {
+		context.WriteString(fmt.Sprintf("%d: %s\n", i+1, lines[i]))
+	}
+	return context.String()
+}