package services

import (
	"bytes"
	"strings"
	"testing"
	"time"
)

func sampleLessons() []LessonExport {
	return []LessonExport{
		{DayOfWeek: 1, PeriodIndex: 1, StartTime: "08:00", EndTime: "08:45",
			ClassName: "5a", SubjectName: "Mathe", SubjectCode: "M",
			TeacherName: "Schmidt, Anna", RoomName: "A101", Pinned: false},
		{DayOfWeek: 2, PeriodIndex: 1, StartTime: "08:00", EndTime: "08:45",
			ClassName: "5a", SubjectName: "Deutsch, Klasse 5", SubjectCode: "D",
			TeacherName: "Mueller, Bob", RoomName: "", Pinned: true},
	}
}

func TestWriteCSV_HeaderAndRows(t *testing.T) {
	var buf bytes.Buffer
	if err := WriteCSV(&buf, sampleLessons()); err != nil {
		t.Fatalf("WriteCSV failed: %v", err)
	}
	out := buf.String()

	wantHeader := "day_of_week,period_index,start_time,end_time,class,subject,subject_code,teacher,room,pinned"
	if !strings.Contains(out, wantHeader) {
		t.Errorf("CSV missing header line; got:\n%s", out)
	}
	if !strings.Contains(out, "1,1,08:00,08:45,5a,Mathe,M,\"Schmidt, Anna\",A101,false") {
		t.Errorf("CSV missing first row; got:\n%s", out)
	}
	// Commas inside subject name must be quoted.
	if !strings.Contains(out, "\"Deutsch, Klasse 5\"") {
		t.Errorf("CSV should quote comma in subject name; got:\n%s", out)
	}
	if !strings.Contains(out, ",true") {
		t.Errorf("Pinned flag should serialise as 'true'; got:\n%s", out)
	}
}

func TestWriteICS_StructureAndDates(t *testing.T) {
	weekStart := time.Date(2026, 8, 24, 0, 0, 0, 0, time.UTC) // a Monday
	var buf bytes.Buffer
	if err := WriteICS(&buf, sampleLessons(), weekStart, "Schuljahr 26/27"); err != nil {
		t.Fatalf("WriteICS failed: %v", err)
	}
	out := buf.String()

	for _, want := range []string{
		"BEGIN:VCALENDAR\r\n",
		"VERSION:2.0\r\n",
		"PRODID:-//BreakPilot//Timetable//DE\r\n",
		"BEGIN:VEVENT\r\n",
		"END:VEVENT\r\n",
		"END:VCALENDAR\r\n",
		"DTSTART:20260824T080000",
		"DTSTART:20260825T080000",
		"SUMMARY:Mathe (5a)",
		"LOCATION:A101",
		"Schuljahr 26/27",
	} {
		if !strings.Contains(out, want) {
			t.Errorf("ICS missing %q in output", want)
		}
	}
}

func TestICSEscape_SpecialChars(t *testing.T) {
	tests := []struct {
		in, want string
	}{
		{"plain", "plain"},
		{"a,b", "a\\,b"},
		{"x;y", "x\\;y"},
		{"line1\nline2", "line1\\nline2"},
	}
	for _, tt := range tests {
		got := icsEscape(tt.in)
		if got != tt.want {
			t.Errorf("icsEscape(%q) = %q, want %q", tt.in, got, tt.want)
		}
	}
}

func TestNextMonday(t *testing.T) {
	// Verify the offset arithmetic for every weekday — 2026-08-22 is a Saturday.
	cases := []struct {
		ref    time.Time
		wantMo string
	}{
		{time.Date(2026, 8, 24, 0, 0, 0, 0, time.UTC), "2026-08-24"}, // Mon → same day
		{time.Date(2026, 8, 25, 0, 0, 0, 0, time.UTC), "2026-08-31"}, // Tue → next Mon
		{time.Date(2026, 8, 23, 0, 0, 0, 0, time.UTC), "2026-08-24"}, // Sun → next Mon
		{time.Date(2026, 8, 22, 0, 0, 0, 0, time.UTC), "2026-08-24"}, // Sat → next Mon
	}
	for _, tt := range cases {
		got := NextMonday(tt.ref).Format("2006-01-02")
		if got != tt.wantMo {
			t.Errorf("NextMonday(%s) = %s, want %s", tt.ref.Format("2006-01-02"), got, tt.wantMo)
		}
	}
}