import sqlite3
import json
from collections import namedtuple

Column = namedtuple('Column', ['name', 'type', 'notnull', 'dflt_value'])
ErrorReport = {
    'schema_errors': [],
    'data_errors': []
}

def get_tables(conn):
    cursor = conn.cursor()
    cursor.execute("SELECT name FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%';")
    return [row[0] for row in cursor.fetchall()]

def get_columns(conn, table_name):
    cursor = conn.execute(f"PRAGMA table_info('{table_name}')")
    columns = []
    for row in cursor:
        columns.append(Column(row[1], row[2], bool(row[3]), row[4]))
    return columns

def compare_and_alter_schema(source_conn, target_conn):
    source_tables = get_tables(source_conn)
    target_tables = get_tables(target_conn)

    for table in source_tables:
        if table not in target_tables:
            try:
                create_stmt = source_conn.execute(
                    "SELECT sql FROM sqlite_master WHERE type='table' AND name=?;",
                    (table,)
                ).fetchone()[0]
                target_conn.execute(create_stmt)
                target_conn.commit()
            except Exception as e:
                ErrorReport['schema_errors'].append(f"Failed to create table {table}: {str(e)}")
            continue

        source_cols = get_columns(source_conn, table)
        target_cols = get_columns(target_conn, table)
        target_col_names = [col.name for col in target_cols]

        for col in source_cols:
            if col.name not in target_col_names:
                try:
                    alter_sql = f'ALTER TABLE "{table}" ADD COLUMN "{col.name}" {col.type}'
                    if col.notnull:
                        alter_sql += ' NOT NULL'
                    if col.dflt_value is not None:
                        alter_sql += f' DEFAULT {col.dflt_value}'
                    target_conn.execute(alter_sql)
                    target_conn.commit()
                except Exception as e:
                    ErrorReport['schema_errors'].append(
                        f"Table {table}: Failed to add column {col.name}: {str(e)}"
                    )

        for tcol in target_cols:
            if tcol.name not in [col.name for col in source_cols]:
                if tcol.notnull and tcol.dflt_value is None:
                    ErrorReport['schema_errors'].append(
                        f"Table {table}: Target column '{tcol.name}' is NOT NULL with no default but missing in source"
                    )

def generate_data_migration_script(source_conn, filename='migration_script.sql'):
    with open(filename, 'w') as f:
        tables = get_tables(source_conn)
        for table in tables:
            cols = get_columns(source_conn, table)
            col_names = [f'"{col.name}"' for col in cols]
            cols_str = ', '.join(col_names)
            f.write(f'INSERT INTO "{table}" ({cols_str})\n')
            f.write(f'SELECT {cols_str} FROM source_db."{table}";\n\n')

def migrate_data(source_conn, target_conn):
    source_tables = get_tables(source_conn)
    
    for table in source_tables:
        try:
            source_cols = get_columns(source_conn, table)
            col_names = [col.name for col in source_cols]
            placeholders = ', '.join(['?'] * len(col_names))
            insert_sql = f'INSERT INTO "{table}" ({", ".join(col_names)}) VALUES ({placeholders})'
            
            source_cur = source_conn.cursor()
            source_cur.execute(f'SELECT * FROM "{table}"')
            
            target_cur = target_conn.cursor()
            
            while True:
                rows = source_cur.fetchmany(100)
                if not rows:
                    break
                
                for row in rows:
                    try:
                        target_cur.execute(insert_sql, row)
                        target_conn.commit()
                    except sqlite3.Error as e:
                        ErrorReport['data_errors'].append({
                            'table': table,
                            'row_data': row,
                            'error': str(e)
                        })
                        target_conn.rollback()
        except sqlite3.Error as e:
            ErrorReport['data_errors'].append({
                'table': table,
                'error': f"General migration error: {str(e)}"
            })

def save_error_report(filename='migration_errors.json'):
    with open(filename, 'w') as f:
        json.dump(ErrorReport, f, indent=2)

def main(source_db, target_db):
    source_conn = sqlite3.connect(source_db)
    target_conn = sqlite3.connect(target_db)
    
    # Attach source DB to target connection for SQL script generation
    target_conn.execute(f"ATTACH DATABASE '{source_db}' AS source_db")
    
    compare_and_alter_schema(source_conn, target_conn)
    generate_data_migration_script(source_conn)
    migrate_data(source_conn, target_conn)
    save_error_report()
    
    source_conn.close()
    target_conn.close()

if __name__ == '__main__':
    import sys
    if len(sys.argv) != 3:
        print("Usage: python migrate_db.py <source.db> <target.db>")
        sys.exit(1)
    
    main(sys.argv[1], sys.argv[2])