Invercargill-Sql/src/migrations/alter-table-builder.vala

using Invercargill.DataStructures;
using InvercargillSql.Orm;

namespace InvercargillSql.Migrations {
    
    /**
     * Builder for ALTER TABLE operations that provides a fluent API for modifying existing tables.
     *
     * This builder is used within MigrationBuilder.alter_table() to add, drop, or rename columns,
     * and to create or drop indexes. It follows the builder pattern, returning itself for chaining
     * alter operations.
     *
     * Example usage within a migration:
     * {{{
     * b.alter_table("users", t => {
     *     t.add_column<string>("email", c => c.type_text().not_null())
     *     t.rename_column("old_name", "new_name")
     *     t.drop_column("deprecated_field")
     *     t.create_index("idx_email").on_column("email")
     *     t.drop_index("idx_old_email")
     *     t.drop_foreign_key("fk_users_profile")
     *     t.drop_foreign_key_on("profile_id")
     *     t.drop_index_on("email")
     * });
     * }}}
     */
    public class AlterTableBuilder : Object {
        private MigrationBuilder _parent;
        private string _table_name;
        private Vector<SchemaOperation> _operations;
        private Vector<MigrationColumnBuilder> _column_builders;
        
        /**
         * Creates a new AlterTableBuilder for the specified table.
         *
         * @param parent the parent MigrationBuilder to return to after alterations
         * @param table_name the name of the table to alter
         */
        internal AlterTableBuilder(MigrationBuilder parent, string table_name) {
            _parent = parent;
            _table_name = table_name;
            _operations = new Vector<SchemaOperation>();
            _column_builders = new Vector<MigrationColumnBuilder>();
        }
        
        /**
         * Adds a new column to the table.
         *
         * The generic type T is used to infer the column type. The returned
         * MigrationColumnBuilder can be used to configure additional column properties.
         *
         * Note: The builder is tracked internally to collect FK constraints and index
         * operations when get_operations() is called.
         *
         * @param name the name of the column to add
         * @return a MigrationColumnBuilder for configuring the column
         */
        public MigrationColumnBuilder add_column<T>(string name) {
            var col = new ColumnDefinition() {
                name = name,
                column_type = ColumnType.from_gtype(typeof(T)) ?? ColumnType.TEXT
            };
            // Add the operation immediately - the column builder will modify it in place
            _operations.add(new AddColumnOperation() {
                table_name = _table_name,
                column = col
            });
            var builder = new MigrationColumnBuilder.for_alter(this, _table_name, col);
            _column_builders.add(builder);
            return builder;
        }
        
        /**
         * Creates an index on this table.
         * 
         * Use the returned IndexBuilder to specify columns and uniqueness.
         * 
         * @param name the name of the index
         * @return an IndexBuilder for configuring the index
         * 
         * Example:
         * {{{
         * t.create_index("idx_email").on_column("email")
         * t.create_index("idx_composite").on_columns("email", "name").unique()
         * }}}
         */
        public IndexBuilder create_index(string name) {
            return new IndexBuilder.for_alter(this, _table_name, name);
        }
        
        /**
         * Drops an index from this table.
         *
         * @param name the name of the index to drop
         * @return this builder for method chaining
         */
        public AlterTableBuilder drop_index(string name) {
            _operations.add(new DropIndexOperation() {
                index_name = name,
                table_name = _table_name
            });
            return this;
        }
        
        /**
         * Drops a foreign key constraint by its explicit name.
         *
         * Use this when you know the exact constraint name.
         *
         * @param constraint_name the name of the FK constraint to drop
         * @return this builder for method chaining
         */
        public AlterTableBuilder drop_foreign_key(string constraint_name) {
            var op = new DropForeignKeyOperation(_table_name);
            op.constraint_name = constraint_name;
            _operations.add(op);
            return this;
        }
        
        /**
         * Drops a foreign key constraint by column name.
         *
         * This is useful for auto-generated constraint names (fk_{table}_{column}).
         *
         * @param column_name the column name that has the FK constraint
         * @return this builder for method chaining
         */
        public AlterTableBuilder drop_foreign_key_on(string column_name) {
            var op = new DropForeignKeyOperation(_table_name);
            op.column_name = column_name;
            _operations.add(op);
            return this;
        }
        
        /**
         * Drops an index by column name.
         *
         * This is useful for auto-generated index names (idx_{table}_{column}).
         *
         * @param column_name the column name that has the index
         * @return this builder for method chaining
         */
        public AlterTableBuilder drop_index_on(string column_name) {
            string index_name = @"idx_$(_table_name)_$(column_name)";
            _operations.add(new DropIndexOperation() {
                index_name = index_name,
                table_name = _table_name
            });
            return this;
        }
        
        /**
         * Adds an AddColumnOperation to the operations list.
         * 
         * This is used internally by MigrationColumnBuilder to add the configured
         * column definition to the alter operations.
         * 
         * @param col the column definition to add
         */
        internal void add_column_operation(ColumnDefinition col) {
            _operations.add(new AddColumnOperation() {
                table_name = _table_name,
                column = col
            });
        }
        
        /**
         * Adds an index operation to the operations list.
         * 
         * This is used internally by IndexBuilder.
         * 
         * @param op the index operation to add
         */
        internal void add_index_operation(CreateIndexOperation op) {
            _operations.add(op);
        }
        
        /**
         * Drops a column from the table.
         * 
         * @param name the name of the column to drop
         * @return this builder for method chaining
         */
        public AlterTableBuilder drop_column(string name) {
            _operations.add(new DropColumnOperation() {
                table_name = _table_name,
                column_name = name
            });
            return this;
        }
        
        /**
         * Renames a column in the table.
         * 
         * @param old_name the current name of the column
         * @param new_name the new name for the column
         * @return this builder for method chaining
         */
        public AlterTableBuilder rename_column(string old_name, string new_name) {
            _operations.add(new RenameColumnOperation() {
                table_name = _table_name,
                old_name = old_name,
                new_name = new_name
            });
            return this;
        }
        
        /**
         * Returns to the parent MigrationBuilder.
         * 
         * This method is used by MigrationColumnBuilder to navigate back to the
         * MigrationBuilder after configuring a column.
         * 
         * @return the parent MigrationBuilder
         */
        internal MigrationBuilder return_to_migration() {
            return _parent;
        }
        
        /**
         * Gets all schema operations collected by this builder.
         *
         * This method also collects FK constraints and index operations from column builders.
         * For ALTER TABLE ADD COLUMN, FK constraints are added as separate operations since
         * they need to be applied after the column is added.
         *
         * @return a Vector of SchemaOperation objects representing the ALTER TABLE operations
         */
        internal Vector<SchemaOperation> get_operations() {
            // Process column builders to collect FK and index operations
            // We need to find the corresponding AddColumnOperation for each builder
            // and add FK/index operations as needed
            
            // First, collect all add column operations to match with builders
            Vector<AddColumnOperation> add_col_ops = new Vector<AddColumnOperation>();
            foreach (var op in _operations) {
                if (op is AddColumnOperation) {
                    add_col_ops.add((AddColumnOperation) op);
                }
            }
            
            // Process each column builder
            for (int i = 0; i < (int) _column_builders.length && i < (int) add_col_ops.length; i++) {
                var builder = _column_builders.get(i);
                var add_col_op = add_col_ops.get(i);
                var col = add_col_op.column;
                
                // Collect FK constraint if configured
                // For ALTER TABLE, we need to add the FK as a table constraint
                // Note: SQLite doesn't support ADD CONSTRAINT, so the dialect needs
                // to handle this appropriately (e.g., table recreation)
                var fk_builder = builder.fk_builder;
                if (fk_builder != null) {
                    var constraint = fk_builder.build_constraint(col.name, _table_name);
                    // Store the constraint info for the dialect to use
                    // We add a marker to the AddColumnOperation by storing FK info
                    // The dialect will generate inline REFERENCES clause
                    add_col_op.foreign_key_constraint = constraint;
                }
                
                // Collect index operation if configured
                if (builder.should_create_index) {
                    var index_op = new CreateIndexOperation() {
                        table_name = _table_name,
                        is_unique = col.is_unique
                    };
                    index_op.columns.add(col.name);
                    
                    // Use custom index name or auto-generate
                    index_op.index_name = builder.index_name ?? @"idx_$(_table_name)_$(col.name)";
                    
                    _operations.add(index_op);
                }
            }
            
            return _operations;
        }
    }
}