package core

import (
	"context"
	"path/filepath"
	"regexp"
	"strings"
	"testing"
	"time"
)

// stampShape is exactly: YYYY-MM-DDTHH:MM:SS.fffZ — three fractional digits and
// a literal Z, which is the shape SQLite's strftime('%Y-%m-%dT%H:%M:%fZ','now')
// emits.
var stampShape = regexp.MustCompile(`^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$`)

// (a) Stamp is fixed-width: exactly 3 fractional digits and a trailing Z, even
// for a fraction RFC3339Nano would trim.
func TestStampFixedWidth(t *testing.T) {
	tm := time.Date(2026, 10, 11, 12, 0, 0, 500_000_000, time.UTC)

	got := Stamp(tm)
	if want := "2026-10-11T12:00:00.500Z"; got != want {
		t.Fatalf("Stamp = %q, want %q", got, want)
	}
	if !strings.HasSuffix(got, "Z") {
		t.Errorf("Stamp %q does not end in Z", got)
	}
	if !stampShape.MatchString(got) {
		t.Errorf("Stamp %q is not fixed-width with exactly 3 fractional digits", got)
	}

	// The premise: RFC3339Nano trims the trailing zeros, which is why it cannot
	// be used for a lexicographically sortable column.
	if rfc := tm.Format(time.RFC3339Nano); rfc != "2026-10-11T12:00:00.5Z" {
		t.Fatalf("RFC3339Nano = %q; test premise (trailing-zero trimming) is wrong", rfc)
	}
}

// (b) Two Stamps 1ms apart must compare in the same order as the instants.
func TestStampOrdersChronologically(t *testing.T) {
	a := time.Date(2026, 10, 11, 12, 0, 0, 0, time.UTC)
	b := a.Add(time.Millisecond)

	sa, sb := Stamp(a), Stamp(b)
	if !(sa < sb) {
		t.Errorf("Stamp %q is not < %q; string order != chronological order", sa, sb)
	}
}

// (c) The exact case that was broken: .500s sorts BEFORE .550s as a string.
// With RFC3339Nano the opposite happens (".5Z" > ".55Z").
func TestStampBrokenCaseSortsCorrectly(t *testing.T) {
	a := time.Date(2026, 10, 11, 12, 0, 0, 500_000_000, time.UTC) // .500s
	b := time.Date(2026, 10, 11, 12, 0, 0, 550_000_000, time.UTC) // .550s

	sa, sb := Stamp(a), Stamp(b)
	if !(sa < sb) {
		t.Errorf("Stamp %q should sort before %q", sa, sb)
	}

	// Demonstrate that the old format really was misordered, so this test is
	// guarding a real regression rather than a tautology.
	ra, rb := a.Format(time.RFC3339Nano), b.Format(time.RFC3339Nano)
	if !(ra > rb) {
		t.Fatalf("premise: RFC3339Nano %q,%q should compare backwards", ra, rb)
	}
}

// (d) Stamp's output shape matches SQLite's own default byte-for-byte.
func TestStampMatchesSQLiteDefault(t *testing.T) {
	db, err := OpenDB(filepath.Join(t.TempDir(), "stamp.db"))
	if err != nil {
		t.Fatalf("OpenDB: %v", err)
	}
	defer db.Close()

	// A fixed second keeps the comparison deterministic. The format literal is
	// copied verbatim from the column DEFAULTs in the migrations.
	var sqliteStamp string
	if err := db.QueryRowContext(context.Background(),
		`SELECT strftime('%Y-%m-%dT%H:%M:%fZ','2026-10-11 12:00:00.500')`,
	).Scan(&sqliteStamp); err != nil {
		t.Fatalf("strftime: %v", err)
	}
	if !stampShape.MatchString(sqliteStamp) {
		t.Fatalf("SQLite strftime output %q has an unexpected shape", sqliteStamp)
	}

	got := Stamp(time.Date(2026, 10, 11, 12, 0, 0, 500_000_000, time.UTC))
	if got != sqliteStamp {
		t.Fatalf("Stamp = %q, SQLite strftime = %q; they must match byte-for-byte", got, sqliteStamp)
	}
}