package schedule

import (
	"testing"
	"time"
)

func TestComputeNextRandomRunStaysInsideWindowAndIsStable(t *testing.T) {
	loc := time.Local
	now := time.Date(2026, 5, 18, 0, 30, 0, 0, loc) // Monday
	policy := RandomPolicy{
		Days:        []time.Weekday{time.Monday},
		TimeMode:    TimeModeRandomWindow,
		WindowStart: time.Hour,
		WindowEnd:   5 * time.Hour,
		Seed:        42,
	}

	first, err := ComputeNextRandomRun(policy, nil, nil, now)
	if err != nil {
		t.Fatalf("ComputeNextRandomRun returned error: %v", err)
	}
	second, err := ComputeNextRandomRun(policy, nil, nil, now)
	if err != nil {
		t.Fatalf("ComputeNextRandomRun returned error on second call: %v", err)
	}
	if first == nil || second == nil {
		t.Fatal("expected next run")
	}
	if !first.Equal(*second) {
		t.Fatalf("expected stable run for same seed/day, got %v and %v", first, second)
	}
	if first.Weekday() != time.Monday {
		t.Fatalf("expected Monday run, got %s", first.Weekday())
	}
	clock := time.Duration(first.Hour())*time.Hour +
		time.Duration(first.Minute())*time.Minute +
		time.Duration(first.Second())*time.Second
	if clock < policy.WindowStart || clock >= policy.WindowEnd {
		t.Fatalf("run time %s outside window [%s, %s)", clock, policy.WindowStart, policy.WindowEnd)
	}
}

func TestComputeNextRandomRunSkipsEqualNotBeforeBoundary(t *testing.T) {
	loc := time.Local
	day := time.Date(2026, 5, 18, 0, 0, 0, 0, loc) // Monday
	offset := stableWindowOffset(7, day, time.Hour)
	runAt := day.Add(time.Hour + offset)
	policy := RandomPolicy{
		Days:        []time.Weekday{time.Monday},
		TimeMode:    TimeModeRandomWindow,
		WindowStart: time.Hour,
		WindowEnd:   2 * time.Hour,
		Seed:        7,
	}

	next, err := ComputeNextRandomRun(policy, nil, nil, runAt)
	if err != nil {
		t.Fatalf("ComputeNextRandomRun returned error: %v", err)
	}
	if next == nil {
		t.Fatal("expected next weekly run")
	}
	if !next.After(runAt) {
		t.Fatalf("expected equal boundary to roll forward after %v, got %v", runAt, next)
	}
	if next.Weekday() != time.Monday {
		t.Fatalf("expected next allowed weekday Monday, got %s", next.Weekday())
	}
	if next.Year() == runAt.Year() && next.YearDay() == runAt.YearDay() {
		t.Fatalf("expected equal boundary to skip same day, got %v", next)
	}
}

func TestComputeNextRandomRunHonorsStartAtAndEndAt(t *testing.T) {
	loc := time.Local
	now := time.Date(2026, 5, 18, 0, 0, 0, 0, loc)     // Monday
	startAt := time.Date(2026, 5, 20, 0, 0, 0, 0, loc) // Wednesday
	endAt := time.Date(2026, 5, 20, 5, 0, 0, 0, loc)
	policy := RandomPolicy{
		Days:        []time.Weekday{time.Monday, time.Wednesday},
		TimeMode:    TimeModeRandomWindow,
		WindowStart: time.Hour,
		WindowEnd:   2 * time.Hour,
		Seed:        99,
	}

	next, err := ComputeNextRandomRun(policy, &startAt, &endAt, now)
	if err != nil {
		t.Fatalf("ComputeNextRandomRun returned error: %v", err)
	}
	if next == nil {
		t.Fatal("expected run inside endAt")
	}
	if next.Weekday() != time.Wednesday {
		t.Fatalf("expected Wednesday after startAt, got %s", next.Weekday())
	}
	if next.Before(startAt) || next.After(endAt) {
		t.Fatalf("run %v outside [%v, %v]", next, startAt, endAt)
	}

	endBeforeNextWindow := time.Date(2026, 5, 20, 0, 30, 0, 0, loc)
	next, err = ComputeNextRandomRun(policy, &startAt, &endBeforeNextWindow, now)
	if err != nil {
		t.Fatalf("ComputeNextRandomRun returned error with endAt: %v", err)
	}
	if next != nil {
		t.Fatalf("expected nil when next run exceeds endAt, got %v", next)
	}
}

func TestComputeNextRandomRunRejectsInvalidPolicy(t *testing.T) {
	_, err := ComputeNextRandomRun(RandomPolicy{}, nil, nil, time.Now())
	if err == nil {
		t.Fatal("expected missing days error")
	}

	_, err = ComputeNextRandomRun(RandomPolicy{
		Days:        []time.Weekday{time.Monday},
		TimeMode:    TimeModeRandomWindow,
		WindowStart: 2 * time.Hour,
		WindowEnd:   time.Hour,
	}, nil, nil, time.Now())
	if err == nil {
		t.Fatal("expected invalid window error")
	}
}

func TestComputeNextRandomRunReturnsNilAfterSearchHorizon(t *testing.T) {
	loc := time.Local
	now := time.Date(2026, 5, 18, 23, 0, 0, 0, loc) // Monday after the random window
	policy := RandomPolicy{
		Days:        []time.Weekday{time.Monday},
		TimeMode:    TimeModeRandomWindow,
		WindowStart: time.Hour,
		WindowEnd:   2 * time.Hour,
		Seed:        1,
	}

	next, err := computeNextRandomRun(policy, nil, nil, now, 0)
	if err != nil {
		t.Fatalf("computeNextRandomRun returned error: %v", err)
	}
	if next != nil {
		t.Fatalf("expected nil after exhausting search horizon, got %v", next)
	}
}

func TestStableWindowOffsetIsDeterministicAndBounded(t *testing.T) {
	day := time.Date(2026, 5, 18, 0, 0, 0, 0, time.Local)
	width := 4 * time.Hour

	first := stableWindowOffset(123, day, width)
	second := stableWindowOffset(123, day, width)
	if first != second {
		t.Fatalf("expected deterministic offset, got %s and %s", first, second)
	}
	if first < 0 || first >= width {
		t.Fatalf("offset %s outside width %s", first, width)
	}
	if got := stableWindowOffset(123, day, 0); got != 0 {
		t.Fatalf("expected zero width offset to be 0, got %s", got)
	}
}