// Package db provides the database layer for the AppView web UI, including
// SQLite schema initialization, migrations, and query functions for OAuth
// sessions, device flows, repository metadata, stars, pull counts, and
// user profiles.
package db

import (
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"log/slog"
	"path/filepath"
	"sort"
	"strconv"
	"strings"

	_ "github.com/mattn/go-sqlite3"
	"go.yaml.in/yaml/v4"
)

//go:embed migrations/*.yaml
var migrationsFS embed.FS

//go:embed schema.sql
var schemaSQL string

// InitDB initializes the SQLite database with the schema
func InitDB(path string, skipMigrations bool) (*sql.DB, error) {
	db, err := sql.Open("sqlite3", path)
	if err != nil {
		return nil, err
	}

	// Enable foreign keys
	if _, err := db.Exec("PRAGMA foreign_keys = ON"); err != nil {
		return nil, err
	}

	// Create schema from embedded SQL file
	if _, err := db.Exec(schemaSQL); err != nil {
		return nil, err
	}

	// Run migrations unless skipped
	if !skipMigrations {
		if err := runMigrations(db); err != nil {
			return nil, err
		}
	}

	return db, nil
}

// Migration represents a database migration
type Migration struct {
	Version     int
	Name        string
	Description string `yaml:"description"`
	Query       string `yaml:"query"`
}

// runMigrations applies any pending database migrations
func runMigrations(db *sql.DB) error {
	// Load migrations from files
	migrations, err := loadMigrations()
	if err != nil {
		return fmt.Errorf("failed to load migrations: %w", err)
	}

	// Sort migrations by version
	sort.Slice(migrations, func(i, j int) bool {
		return migrations[i].Version < migrations[j].Version
	})

	for _, m := range migrations {
		// Check if migration already applied
		var count int
		err := db.QueryRow("SELECT COUNT(*) FROM schema_migrations WHERE version = ?", m.Version).Scan(&count)
		if err != nil {
			return fmt.Errorf("failed to check migration status: %w", err)
		}

		if count > 0 {
			// Migration already applied
			continue
		}

		// Apply migration in a transaction
		slog.Info("Applying migration", "version", m.Version, "name", m.Name, "description", m.Description)

		tx, err := db.Begin()
		if err != nil {
			return fmt.Errorf("failed to begin transaction for migration %d: %w", m.Version, err)
		}

		// Split query into individual statements and execute each
		// go-sqlite3's Exec() doesn't reliably execute all statements in multi-statement queries
		statements := splitSQLStatements(m.Query)
		for i, stmt := range statements {
			if _, err := tx.Exec(stmt); err != nil {
				tx.Rollback()
				return fmt.Errorf("failed to apply migration %d (%s) statement %d: %w", m.Version, m.Name, i+1, err)
			}
		}

		// Record migration
		if _, err := tx.Exec("INSERT INTO schema_migrations (version) VALUES (?)", m.Version); err != nil {
			tx.Rollback()
			return fmt.Errorf("failed to record migration %d: %w", m.Version, err)
		}

		if err := tx.Commit(); err != nil {
			return fmt.Errorf("failed to commit migration %d: %w", m.Version, err)
		}

		slog.Info("Migration applied successfully", "version", m.Version)
	}

	return nil
}

// loadMigrations loads all migration files from embedded filesystem
func loadMigrations() ([]Migration, error) {
	// Read all migration files from embedded FS
	entries, err := fs.Glob(migrationsFS, "migrations/[0-9][0-9][0-9][0-9]_*.yaml")
	if err != nil {
		return nil, fmt.Errorf("failed to list migration files: %w", err)
	}

	var migrations []Migration
	for _, file := range entries {
		// Parse version and name from filename
		basename := filepath.Base(file)
		version, name, err := parseMigrationFilename(basename)
		if err != nil {
			return nil, fmt.Errorf("invalid migration filename %s: %w", basename, err)
		}

		// Read YAML content from embedded FS
		data, err := migrationsFS.ReadFile(file)
		if err != nil {
			return nil, fmt.Errorf("failed to read migration file %s: %w", file, err)
		}

		var m Migration
		if err := yaml.Unmarshal(data, &m); err != nil {
			return nil, fmt.Errorf("failed to parse migration file %s: %w", file, err)
		}

		// Set version and name from filename
		m.Version = version
		m.Name = name

		// Validate migration
		if m.Query == "" {
			return nil, fmt.Errorf("missing migration 'query' in %s", file)
		}

		migrations = append(migrations, m)
	}

	return migrations, nil
}

// splitSQLStatements splits a SQL query into individual statements.
// It handles semicolons as statement separators and filters out empty statements.
func splitSQLStatements(query string) []string {
	var statements []string

	// Split on semicolons
	parts := strings.Split(query, ";")

	for _, part := range parts {
		// Trim whitespace
		stmt := strings.TrimSpace(part)

		// Skip empty statements (could be trailing semicolon or comment-only)
		if stmt == "" {
			continue
		}

		// Skip comment-only statements
		lines := strings.Split(stmt, "\n")
		hasCode := false
		for _, line := range lines {
			trimmed := strings.TrimSpace(line)
			if trimmed != "" && !strings.HasPrefix(trimmed, "--") {
				hasCode = true
				break
			}
		}

		if hasCode {
			statements = append(statements, stmt)
		}
	}

	return statements
}

// parseMigrationFilename extracts version and name from migration filename
// Expected format: 0001_migration_name.yaml
// Returns: version (int), name (string), error
// Note: Glob pattern ensures format is valid, so minimal validation needed
func parseMigrationFilename(filename string) (int, string, error) {
	// Remove extension (.yaml or .yml)
	ext := filepath.Ext(filename)
	fileNameWithoutExt := filename[:len(filename)-len(ext)]

	// First 4 characters are the version (glob guarantees they're digits)
	version, _ := strconv.Atoi(fileNameWithoutExt[:4])

	// Remainder after position 5 is the name (glob guarantees it exists)
	name := strings.ReplaceAll(fileNameWithoutExt[5:], "_", " ")
	name = strings.TrimSpace(name)

	return version, name, nil
}