// Package db tests — migration dry-run gate.
//
// This is the test that catches mig-N crash-loops before they reach prod.
// The convention since t-paliad-098/099 is that paliad migrations land in
// numeric order on a single trunk; the next deploy runs whichever ones are
// pending against the live `public.paliad_schema_migrations` tracker. A
// migration that compiles cleanly but fails on apply (typo, missing column,
// wrong CHECK shape) crashes the Dokploy container loop before paliad.de
// finishes binding :8080, and the only way to learn about it today is to
// watch the deploy log.
//
// TestMigrations_DryRun closes that gap: for every *.up.sql in this
// directory whose version is greater than the scratch DB's current tracker
// version, it opens a transaction, runs the SQL, and ROLLBACKs. Any error
// fails the test with the file name + Postgres error. Always non-destructive
// — the ROLLBACK runs even on success, so the scratch DB stays at its
// starting version.
//
// Requires TEST_DATABASE_URL (same pattern as the rest of the live-DB
// tests). Skipped without it.
//
// Design: docs/design-paliad-test-strategy-2026-05-19.md §5 Slice 1.

package db

import (
	"database/sql"
	"errors"
	"fmt"
	"os"
	"sort"
	"strconv"
	"strings"
	"testing"

	_ "github.com/lib/pq"
)

// migration is one *.up.sql file from the embedded migrations FS.
type migration struct {
	version  int
	name     string
	filename string
}

// TestMigrations_DryRun walks every pending *.up.sql in numeric order,
// applies each inside its own BEGIN/ROLLBACK against the scratch DB, and
// fails the test on the first SQL error. Reports per-file as a sub-test so
// `go test -v` shows which migration failed.
//
// What "pending" means: greater than the scratch DB's current tracker
// version (or 0 if the tracker doesn't exist yet). In CI against a fresh
// scratch DB, every migration is pending and gets verified. On a developer
// laptop whose scratch DB is already at HEAD, no migrations are pending and
// the test logs the start version and passes — the protection only kicks in
// the moment a new *.up.sql lands in the tree before the developer runs
// `db.ApplyMigrations` against the same scratch DB.
func TestMigrations_DryRun(t *testing.T) {
	url := os.Getenv("TEST_DATABASE_URL")
	if url == "" {
		t.Skip("TEST_DATABASE_URL not set — skipping migration dry-run")
	}

	conn, err := sql.Open("postgres", url)
	if err != nil {
		t.Fatalf("open: %v", err)
	}
	defer conn.Close()
	if err := conn.Ping(); err != nil {
		t.Fatalf("ping: %v", err)
	}

	// The paliad schema must exist before migration 001 runs against it,
	// mirroring the bootstrap step in ApplyMigrations. Without this, a
	// fresh scratch DB would fail migration 001's CREATE TABLE paliad.*
	// statements inside the BEGIN/ROLLBACK probe with "schema paliad does
	// not exist" — a false negative that distracts from real errors.
	if _, err := conn.Exec(`CREATE SCHEMA IF NOT EXISTS paliad`); err != nil {
		t.Fatalf("ensure paliad schema: %v", err)
	}

	startVersion, dirty, err := currentTrackerVersion(conn)
	if err != nil {
		t.Fatalf("read tracker: %v", err)
	}
	if dirty {
		t.Fatalf("tracker is dirty at version %d — fix that first (DROP the tracker row "+
			"or restore from backup); the dry-run cannot trust a dirty starting state",
			startVersion)
	}
	t.Logf("scratch DB tracker at version %d; walking pending migrations from %d upward",
		startVersion, startVersion+1)

	migs, err := loadPendingMigrations(startVersion)
	if err != nil {
		t.Fatalf("load migrations: %v", err)
	}
	if len(migs) == 0 {
		t.Logf("no pending migrations — scratch DB is at HEAD (%d)", startVersion)
		return
	}

	for _, m := range migs {
		t.Run(fmt.Sprintf("%03d_%s", m.version, m.name), func(t *testing.T) {
			body, err := migrationFS.ReadFile("migrations/" + m.filename)
			if err != nil {
				t.Fatalf("read %s: %v", m.filename, err)
			}
			tx, err := conn.Begin()
			if err != nil {
				t.Fatalf("begin: %v", err)
			}
			// Always rollback; the dry-run must not leave the scratch DB
			// at a different version than where it started. Rollback is
			// safe to call even after a failed Exec — Postgres aborts the
			// transaction internally on the first error.
			defer func() { _ = tx.Rollback() }()

			if _, err := tx.Exec(string(body)); err != nil {
				t.Fatalf("migration %s failed dry-run: %v", m.filename, err)
			}
		})
	}
}

// currentTrackerVersion reads the latest version + dirty flag from the
// `public.paliad_schema_migrations` tracker. Returns (0, false, nil) when the
// tracker doesn't exist yet — that's the "fresh scratch DB" path.
//
// We don't use golang-migrate's API to read this because golang-migrate's
// driver locks the tracker row on read; a test runner that calls this while
// the developer has paliad running locally would race. A plain SELECT is
// race-safe and matches what `psql` would show.
func currentTrackerVersion(conn *sql.DB) (version int, dirty bool, err error) {
	const q = `SELECT version, dirty FROM public.paliad_schema_migrations LIMIT 1`
	row := conn.QueryRow(q)
	if scanErr := row.Scan(&version, &dirty); scanErr != nil {
		// Missing table → fresh DB → start at 0. lib/pq surfaces this
		// as `pq.Error.Code = "42P01"` (undefined_table); the simpler
		// sql.ErrNoRows fires if the table exists but is empty (also
		// fresh-DB-shaped).
		if errors.Is(scanErr, sql.ErrNoRows) {
			return 0, false, nil
		}
		if strings.Contains(scanErr.Error(), "does not exist") {
			return 0, false, nil
		}
		return 0, false, scanErr
	}
	return version, dirty, nil
}

// loadPendingMigrations returns every *.up.sql in the embedded FS whose
// version is greater than startVersion, sorted by version ascending. A
// filename like "098_submission_codes_prefix_and_rename.up.sql" yields
// version=98, name="submission_codes_prefix_and_rename".
func loadPendingMigrations(startVersion int) ([]migration, error) {
	entries, err := migrationFS.ReadDir("migrations")
	if err != nil {
		return nil, fmt.Errorf("read migrations dir: %w", err)
	}
	var out []migration
	for _, e := range entries {
		name := e.Name()
		if !strings.HasSuffix(name, ".up.sql") {
			continue
		}
		v, n, ok := parseMigrationName(name)
		if !ok {
			return nil, fmt.Errorf("unparseable migration filename: %s "+
				"(expected NNN_description.up.sql)", name)
		}
		if v <= startVersion {
			continue
		}
		out = append(out, migration{version: v, name: n, filename: name})
	}
	sort.Slice(out, func(i, j int) bool { return out[i].version < out[j].version })
	return out, nil
}

// parseMigrationName splits "NNN_description.up.sql" into (NNN, description).
// Returns ok=false on any deviation from that shape.
func parseMigrationName(filename string) (version int, name string, ok bool) {
	base := strings.TrimSuffix(filename, ".up.sql")
	if base == filename { // suffix wasn't present
		return 0, "", false
	}
	underscore := strings.IndexByte(base, '_')
	if underscore <= 0 {
		return 0, "", false
	}
	v, err := strconv.Atoi(base[:underscore])
	if err != nil {
		return 0, "", false
	}
	return v, base[underscore+1:], true
}