// Package migrate provides functions for managing database migrations
package migrate

import (
	"bufio"
	"context"
	"fmt"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"text/tabwriter"
	"time"

	"git.haelnorr.com/h/oslstats/internal/config"
	"git.haelnorr.com/h/oslstats/internal/db"
	"git.haelnorr.com/h/oslstats/internal/db/migrations"
	"github.com/pkg/errors"
	"github.com/uptrace/bun/migrate"
)

// RunMigrations executes database migrations
func RunMigrations(ctx context.Context, cfg *config.Config, command string, countStr string) error {
	conn := db.NewDB(cfg.DB)
	defer func() { _ = conn.Close() }()

	migrator := migrate.NewMigrator(conn.DB, migrations.Migrations)

	// Initialize migration tables
	if err := migrator.Init(ctx); err != nil {
		return errors.Wrap(err, "migrator.Init")
	}

	switch command {
	case "up":
		err := migrateUp(ctx, migrator, conn, cfg, countStr)
		if err != nil {
			// On error, automatically rollback the migrations that were just applied
			fmt.Println("[WARN] Migration failed, attempting automatic rollback...")
			// We need to figure out how many migrations were applied in this batch
			// For now, we'll skip automatic rollback since it's complex with the new count system
			// The user can manually rollback if needed
			return err
		}
		return err
	case "rollback":
		return migrateRollback(ctx, migrator, conn, cfg, countStr)
	case "status":
		return migrateStatus(ctx, migrator)
	default:
		return fmt.Errorf("unknown migration command: %s", command)
	}
}

// migrateUp runs pending migrations
func migrateUp(ctx context.Context, migrator *migrate.Migrator, conn *db.DB, cfg *config.Config, countStr string) error {
	// Parse count parameter
	count, all, err := parseMigrationCount(countStr)
	if err != nil {
		return errors.Wrap(err, "parse migration count")
	}

	fmt.Println("[INFO] Step 1/5: Validating migrations...")
	if err := validateMigrations(ctx); err != nil {
		return err
	}
	fmt.Println("[INFO] Migration validation passed ✓")

	fmt.Println("[INFO] Step 2/5: Checking for pending migrations...")
	// Check for pending migrations using MigrationsWithStatus (read-only)
	ms, err := migrator.MigrationsWithStatus(ctx)
	if err != nil {
		return errors.Wrap(err, "get migration status")
	}

	unapplied := ms.Unapplied()
	if len(unapplied) == 0 {
		fmt.Println("[INFO] No pending migrations")
		return nil
	}

	// Select which migrations to apply
	toApply := selectMigrationsToApply(unapplied, count, all)
	if len(toApply) == 0 {
		fmt.Println("[INFO] No migrations to run")
		return nil
	}

	// Print what we're about to do
	if all {
		fmt.Printf("[INFO] Running all %d pending migration(s):\n", len(toApply))
	} else {
		fmt.Printf("[INFO] Running %d migration(s):\n", len(toApply))
	}
	for _, m := range toApply {
		fmt.Printf("  📋 %s\n", m.Name)
	}

	// Create backup unless --no-backup flag is set
	if !cfg.Flags.MigrateNoBackup {
		fmt.Println("[INFO] Step 3/5: Creating backup...")
		_, err := db.CreateBackup(ctx, cfg.DB, "migration")
		if err != nil {
			return errors.Wrap(err, "create backup")
		}

		// Clean old backups
		if err := db.CleanOldBackups(cfg.DB, cfg.DB.BackupRetention); err != nil {
			fmt.Printf("[WARN] Failed to clean old backups: %v\n", err)
		}
	} else {
		fmt.Println("[INFO] Step 3/5: Skipping backup (--no-backup flag set)")
	}

	// Acquire migration lock
	fmt.Println("[INFO] Step 4/5: Acquiring migration lock...")
	if err := acquireMigrationLock(ctx, conn); err != nil {
		return errors.Wrap(err, "acquire migration lock")
	}
	defer releaseMigrationLock(ctx, conn)
	fmt.Println("[INFO] Migration lock acquired")

	// Run migrations
	fmt.Println("[INFO] Step 5/5: Applying migrations...")
	group, err := executeUpMigrations(ctx, migrator, toApply)
	if err != nil {
		return errors.Wrap(err, "execute migrations")
	}

	if group.IsZero() {
		fmt.Println("[INFO] No migrations to run")
		return nil
	}

	fmt.Printf("[INFO] Migrated to group %d\n", group.ID)
	for _, migration := range group.Migrations {
		fmt.Printf("  ✅ %s\n", migration.Name)
	}

	return nil
}

// migrateRollback rolls back migrations
func migrateRollback(ctx context.Context, migrator *migrate.Migrator, conn *db.DB, cfg *config.Config, countStr string) error {
	// Parse count parameter
	count, all, err := parseMigrationCount(countStr)
	if err != nil {
		return errors.Wrap(err, "parse migration count")
	}

	// Get all migrations with status
	ms, err := migrator.MigrationsWithStatus(ctx)
	if err != nil {
		return errors.Wrap(err, "get migration status")
	}

	applied := ms.Applied()
	if len(applied) == 0 {
		fmt.Println("[INFO] No migrations to rollback")
		return nil
	}

	// Select which migrations to rollback
	toRollback := selectMigrationsToRollback(applied, count, all)
	if len(toRollback) == 0 {
		fmt.Println("[INFO] No migrations to rollback")
		return nil
	}

	// Print what we're about to do
	if all {
		fmt.Printf("[INFO] Rolling back all %d migration(s):\n", len(toRollback))
	} else {
		fmt.Printf("[INFO] Rolling back %d migration(s):\n", len(toRollback))
	}
	for _, m := range toRollback {
		fmt.Printf("  📋 %s (group %d)\n", m.Name, m.GroupID)
	}

	// Create backup unless --no-backup flag is set
	if !cfg.Flags.MigrateNoBackup {
		fmt.Println("[INFO] Creating backup before rollback...")
		_, err := db.CreateBackup(ctx, cfg.DB, "rollback")
		if err != nil {
			return errors.Wrap(err, "create backup")
		}

		// Clean old backups
		if err := db.CleanOldBackups(cfg.DB, cfg.DB.BackupRetention); err != nil {
			fmt.Printf("[WARN] Failed to clean old backups: %v\n", err)
		}
	} else {
		fmt.Println("[INFO] Skipping backup (--no-backup flag set)")
	}

	// Acquire migration lock
	fmt.Println("[INFO] Acquiring migration lock...")
	if err := acquireMigrationLock(ctx, conn); err != nil {
		return errors.Wrap(err, "acquire migration lock")
	}
	defer releaseMigrationLock(ctx, conn)
	fmt.Println("[INFO] Migration lock acquired")

	// Rollback
	fmt.Println("[INFO] Executing rollback...")
	rolledBack, err := executeDownMigrations(ctx, migrator, toRollback)
	if err != nil {
		return errors.Wrap(err, "execute rollback")
	}

	fmt.Printf("[INFO] Successfully rolled back %d migration(s)\n", len(rolledBack))
	for _, migration := range rolledBack {
		fmt.Printf("  ↩️  %s\n", migration.Name)
	}

	return nil
}

// migrateStatus shows migration status
func migrateStatus(ctx context.Context, migrator *migrate.Migrator) error {
	ms, err := migrator.MigrationsWithStatus(ctx)
	if err != nil {
		return errors.Wrap(err, "get migration status")
	}

	fmt.Println("╔══════════════════════════════════════════════════════════╗")
	fmt.Println("║               DATABASE MIGRATION STATUS                  ║")
	fmt.Println("╚══════════════════════════════════════════════════════════╝")

	w := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ', 0)
	_, _ = fmt.Fprintln(w, "STATUS\tMIGRATION\tGROUP\tCOMMENT")
	_, _ = fmt.Fprintln(w, "----------\t---------------\t-----\t---------------------------")

	appliedCount := 0
	for _, m := range ms {
		status := "⏳ Pending"
		group := "-"

		if m.GroupID > 0 {
			status = "✅ Applied"
			appliedCount++
			group = fmt.Sprint(m.GroupID)
		}

		_, _ = fmt.Fprintf(w, "%s\t%s\t%s\t%s\n", status, m.Name, group, m.Comment)
	}

	_ = w.Flush()

	fmt.Printf("\n📊 Summary: %d applied, %d pending\n\n",
		appliedCount, len(ms)-appliedCount)

	return nil
}

// validateMigrations ensures migrations compile before running
func validateMigrations(ctx context.Context) error {
	cmd := exec.CommandContext(ctx, "go", "build",
		"-o", "/dev/null", "./internal/db/migrations")

	output, err := cmd.CombinedOutput()
	if err != nil {
		fmt.Println("[ERROR] Migration validation failed!")
		fmt.Println(string(output))
		return errors.Wrap(err, "migration build failed")
	}

	return nil
}

// acquireMigrationLock prevents concurrent migrations using PostgreSQL advisory lock
func acquireMigrationLock(ctx context.Context, conn *db.DB) error {
	const lockID = 1234567890  // Arbitrary unique ID for migration lock
	const timeoutSeconds = 300 // 5 minutes

	// Set statement timeout for this session
	_, err := conn.ExecContext(ctx,
		fmt.Sprintf("SET statement_timeout = '%ds'", timeoutSeconds))
	if err != nil {
		return errors.Wrap(err, "set timeout")
	}

	var acquired bool
	err = conn.NewRaw("SELECT pg_try_advisory_lock(?)", lockID).
		Scan(ctx, &acquired)
	if err != nil {
		return errors.Wrap(err, "pg_try_advisory_lock")
	}

	if !acquired {
		return errors.New("migration already in progress (could not acquire lock)")
	}

	return nil
}

// releaseMigrationLock releases the migration lock
func releaseMigrationLock(ctx context.Context, conn *db.DB) {
	const lockID = 1234567890

	_, err := conn.NewRaw("SELECT pg_advisory_unlock(?)", lockID).Exec(ctx)
	if err != nil {
		fmt.Printf("[WARN] Failed to release migration lock: %v\n", err)
	} else {
		fmt.Println("[INFO] Migration lock released")
	}
}

// CreateMigration generates a new migration file
func CreateMigration(name string) error {
	if name == "" {
		return errors.New("migration name cannot be empty")
	}

	// Sanitize name (replace spaces with underscores, lowercase)
	name = strings.ToLower(strings.ReplaceAll(name, " ", "_"))

	// Generate timestamp
	timestamp := time.Now().Format("20060102150405")
	filename := fmt.Sprintf("internal/db/migrations/%s_%s.go", timestamp, name)

	// Template
	template := `package migrations

import (
	"context"
	"github.com/uptrace/bun"
)

func init() {
	Migrations.MustRegister(
		// UP migration
		func(ctx context.Context, conn *bun.DB) error {
			// Add your migration code here
			return nil
		},
		// DOWN migration
		func(ctx context.Context, conn *bun.DB) error {
			// Add your rollback code here
			return nil
		},
	)
}
`

	// Write file
	if err := os.WriteFile(filename, []byte(template), 0o644); err != nil {
		return errors.Wrap(err, "write migration file")
	}

	fmt.Printf("✅ Created migration: %s\n", filename)
	fmt.Println("📝 Next steps:")
	fmt.Println("   1. Edit the file and implement the UP and DOWN functions")
	fmt.Println("   2. Run: just migrate up")

	return nil
}

// parseMigrationCount parses a migration count string
// Returns: (count, all, error)
// - "" (empty) → (1, false, nil) - default to 1
// - "all" → (0, true, nil) - special case for all
// - "5" → (5, false, nil) - specific count
// - "invalid" → (0, false, error)
func parseMigrationCount(value string) (int, bool, error) {
	// Default to 1 if empty
	if value == "" {
		return 1, false, nil
	}

	// Special case for "all"
	if value == "all" {
		return 0, true, nil
	}

	// Parse as integer
	count, err := strconv.Atoi(value)
	if err != nil {
		return 0, false, errors.New("migration count must be a positive integer or 'all'")
	}
	if count < 1 {
		return 0, false, errors.New("migration count must be a positive integer (1 or greater)")
	}

	return count, false, nil
}

// selectMigrationsToApply returns the subset of unapplied migrations to run
func selectMigrationsToApply(unapplied migrate.MigrationSlice, count int, all bool) migrate.MigrationSlice {
	if all {
		return unapplied
	}

	count = min(count, len(unapplied))
	return unapplied[:count]
}

// selectMigrationsToRollback returns the subset of applied migrations to rollback
// Returns migrations in reverse chronological order (most recent first)
func selectMigrationsToRollback(applied migrate.MigrationSlice, count int, all bool) migrate.MigrationSlice {
	if len(applied) == 0 || all {
		return applied
	}
	count = min(count, len(applied))
	return applied[:count]
}

// executeUpMigrations executes a subset of UP migrations
func executeUpMigrations(ctx context.Context, migrator *migrate.Migrator, migrations migrate.MigrationSlice) (*migrate.MigrationGroup, error) {
	if len(migrations) == 0 {
		return &migrate.MigrationGroup{}, nil
	}

	// Get the next group ID
	ms, err := migrator.MigrationsWithStatus(ctx)
	if err != nil {
		return nil, errors.Wrap(err, "get migration status")
	}

	lastGroup := ms.LastGroup()
	groupID := int64(1)
	if lastGroup.ID > 0 {
		groupID = lastGroup.ID + 1
	}

	// Create the migration group
	group := &migrate.MigrationGroup{
		ID:         groupID,
		Migrations: make(migrate.MigrationSlice, 0, len(migrations)),
	}

	// Execute each migration
	for i := range migrations {
		migration := &migrations[i]
		migration.GroupID = groupID

		// Mark as applied before execution (Bun's default behavior)
		if err := migrator.MarkApplied(ctx, migration); err != nil {
			return group, errors.Wrap(err, "mark applied")
		}

		// Add to group
		group.Migrations = append(group.Migrations, *migration)

		// Execute the UP function
		if migration.Up != nil {
			if err := migration.Up(ctx, migrator, migration); err != nil {
				return group, errors.Wrap(err, fmt.Sprintf("migration %s failed", migration.Name))
			}
		}
	}

	return group, nil
}

// executeDownMigrations executes a subset of DOWN migrations
func executeDownMigrations(ctx context.Context, migrator *migrate.Migrator, migrations migrate.MigrationSlice) (migrate.MigrationSlice, error) {
	rolledBack := make(migrate.MigrationSlice, 0, len(migrations))

	// Execute each migration in order (already reversed)
	for i := range migrations {
		migration := &migrations[i]

		// Execute the DOWN function
		if migration.Down != nil {
			if err := migration.Down(ctx, migrator, migration); err != nil {
				return rolledBack, errors.Wrap(err, fmt.Sprintf("rollback %s failed", migration.Name))
			}
		}

		// Mark as unapplied after execution
		if err := migrator.MarkUnapplied(ctx, migration); err != nil {
			return rolledBack, errors.Wrap(err, "mark unapplied")
		}

		rolledBack = append(rolledBack, *migration)
	}

	return rolledBack, nil
}

// ResetDatabase drops and recreates all tables (destructive)
func ResetDatabase(ctx context.Context, cfg *config.Config) error {
	fmt.Println("⚠️  WARNING - This will DELETE ALL DATA in the database!")
	fmt.Print("Type 'yes' to continue: ")

	reader := bufio.NewReader(os.Stdin)
	response, err := reader.ReadString('\n')
	if err != nil {
		return errors.Wrap(err, "read input")
	}

	response = strings.TrimSpace(response)
	if response != "yes" {
		fmt.Println("❌ Reset cancelled")
		return nil
	}
	conn := db.NewDB(cfg.DB)
	defer func() { _ = conn.Close() }()

	models := conn.RegisterModels()

	for _, model := range models {
		if err := conn.ResetModel(ctx, model); err != nil {
			return errors.Wrap(err, "reset model")
		}
	}

	fmt.Println("✅ Database reset complete")
	return nil
}