// Package db provides SQLite database initialization and schema management.
package db

import (
	"database/sql"
	_ "embed"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"strings"

	_ "modernc.org/sqlite"
)

//go:embed migrations/001_create_tables.sql
var migration001 string

//go:embed migrations/002_dedup_unique_index.sql
var migration002 string

// DB wraps the sql.DB with connection-level settings.
type DB struct {
	*sql.DB
}

// Open opens the SQLite database at the given path, enables WAL mode,
// and runs all migrations using a schema_version table for tracking.
func Open(path string) (*DB, error) {
	// Ensure the directory exists
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return nil, err
	}

	db, err := sql.Open("sqlite", path)
	if err != nil {
		return nil, err
	}

	// Enable WAL for concurrent read/write performance
	if _, err := db.Exec("PRAGMA journal_mode=WAL"); err != nil {
		db.Close()
		return nil, err
	}

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

	// Ensure schema_version table exists for migration tracking
	if _, err := db.Exec(`CREATE TABLE IF NOT EXISTS schema_version (version INTEGER PRIMARY KEY)`); err != nil {
		db.Close()
		return nil, err
	}

	// Read current schema version (0 if table is empty)
	var currentVersion int
	if err := db.QueryRow(`SELECT COALESCE(MAX(version), 0) FROM schema_version`).Scan(&currentVersion); err != nil {
		db.Close()
		return nil, err
	}

	// Migration definitions: ordered list of (version, sql)
	type migration struct {
		version int
		sql     string
	}
	migrations := []migration{
		{1, migration001},
		{2, migration002},
	}

	for _, m := range migrations {
		if currentVersion >= m.version {
			continue
		}
		log.Printf("Running migration %d for %s...", m.version, path)
		if err := migrate(db, m.sql); err != nil {
			db.Close()
			return nil, fmt.Errorf("migration %d: %w", m.version, err)
		}
		if _, err := db.Exec(`INSERT INTO schema_version (version) VALUES (?)`, m.version); err != nil {
			db.Close()
			return nil, fmt.Errorf("record migration %d: %w", m.version, err)
		}
		log.Printf("Migration %d complete", m.version)
	}

	if currentVersion < len(migrations) {
		log.Println("Migrations complete")
	}

	return &DB{db}, nil
}

// migrate executes a SQL migration string by splitting on semicolons.
func migrate(db *sql.DB, sql string) error {
	statements := splitSQL(sql)
	for _, stmt := range statements {
		stmt = strings.TrimSpace(stmt)
		if stmt == "" {
			continue
		}
		if _, err := db.Exec(stmt); err != nil {
			return err
		}
	}
	return nil
}

// splitSQL splits a SQL string on semicolons, respecting quoted strings
// and stripping SQL line comments (--).
func splitSQL(sql string) []string {
	// First, strip all line comments (--) to prevent them from swallowing
	// subsequent SQL statements when newlines are collapsed.
	sql = stripSQLLineComments(sql)

	var stmts []string
	var current string
	inQuote := false
	quoteChar := rune(0)

	for _, r := range sql {
		if inQuote {
			current += string(r)
			if r == quoteChar {
				inQuote = false
			}
			continue
		}
		switch r {
		case '"', '\'', '`':
			inQuote = true
			quoteChar = r
			current += string(r)
		case ';':
			stmts = append(stmts, current)
			current = ""
		case '\r', '\n', '\t':
			current += " "
		default:
			current += string(r)
		}
	}
	if strings.TrimSpace(current) != "" {
		stmts = append(stmts, current)
	}
	return stmts
}

// stripSQLLineComments removes all -- single-line comments from SQL text.
func stripSQLLineComments(sql string) string {
	var result strings.Builder
	i := 0
	runes := []rune(sql)

	for i < len(runes) {
		r := runes[i]

		// Check for -- comment start
		if r == '-' && i+1 < len(runes) && runes[i+1] == '-' {
			// Skip to end of line
			i += 2
			for i < len(runes) && runes[i] != '\n' && runes[i] != '\r' {
				i++
			}
			// Replace comment with a newline (preserves statement boundaries)
			result.WriteRune('\n')
			continue
		}

		result.WriteRune(r)
		i++
	}

	return result.String()
}