package builder

import (
	"strings"
	"testing"
)

func TestTruncateOutput(t *testing.T) {
	tests := []struct {
		name      string
		input     string
		keepLines int
		wantLines int
		wantOmit  bool
	}{
		{
			name:      "short output unchanged",
			input:     "line1\nline2\nline3",
			keepLines: 50,
			wantLines: 3,
			wantOmit:  false,
		},
		{
			name:      "exactly at threshold unchanged",
			input:     strings.Join(makeLines(100), "\n"),
			keepLines: 50,
			wantLines: 100,
			wantOmit:  false,
		},
		{
			name:      "over threshold truncated",
			input:     strings.Join(makeLines(150), "\n"),
			keepLines: 50,
			wantLines: 103, // 50 + 1 (empty) + 1 (omitted msg) + 1 (empty) + 50
			wantOmit:  true,
		},
		{
			name:      "large output truncated",
			input:     strings.Join(makeLines(1000), "\n"),
			keepLines: 50,
			wantLines: 103,
			wantOmit:  true,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got := truncateOutput(tt.input, tt.keepLines)
			gotLines := strings.Split(got, "\n")

			if len(gotLines) != tt.wantLines {
				t.Errorf("got %d lines, want %d", len(gotLines), tt.wantLines)
			}

			hasOmit := strings.Contains(got, "lines omitted")
			if hasOmit != tt.wantOmit {
				t.Errorf("got omit marker = %v, want %v", hasOmit, tt.wantOmit)
			}

			if tt.wantOmit {
				// Verify first and last lines are preserved
				inputLines := strings.Split(tt.input, "\n")
				firstLine := inputLines[0]
				lastLine := inputLines[len(inputLines)-1]
				if !strings.HasPrefix(got, firstLine+"\n") {
					t.Errorf("first line not preserved, got prefix %q, want %q",
						gotLines[0], firstLine)
				}
				if !strings.HasSuffix(got, lastLine) {
					t.Errorf("last line not preserved, got suffix %q, want %q",
						gotLines[len(gotLines)-1], lastLine)
				}
			}
		})
	}
}

func makeLines(n int) []string {
	lines := make([]string, n)
	for i := range lines {
		lines[i] = "line " + strings.Repeat("x", i%80)
	}
	return lines
}

func TestTruncateOutputPreservesContent(t *testing.T) {
	// Create input with distinct first and last lines
	lines := make([]string, 200)
	for i := range lines {
		lines[i] = "middle"
	}
	lines[0] = "FIRST"
	lines[49] = "LAST_OF_HEAD"
	lines[150] = "FIRST_OF_TAIL"
	lines[199] = "LAST"

	input := strings.Join(lines, "\n")
	got := truncateOutput(input, 50)

	if !strings.Contains(got, "FIRST") {
		t.Error("missing FIRST")
	}
	if !strings.Contains(got, "LAST_OF_HEAD") {
		t.Error("missing LAST_OF_HEAD")
	}
	if !strings.Contains(got, "FIRST_OF_TAIL") {
		t.Error("missing FIRST_OF_TAIL")
	}
	if !strings.Contains(got, "LAST") {
		t.Error("missing LAST")
	}
	if !strings.Contains(got, "(100 lines omitted)") {
		t.Errorf("wrong omitted count, got: %s", got)
	}
}