feat(backend): add Alembic migrations

backend/alembic.ini

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+[alembic]
+script_location = alembic
+prepend_sys_path = .
+version_path_separator = os
+sqlalchemy.url = postgresql+asyncpg://codetutor:codetutor@localhost:5432/codetutor
+
+[post_write_hooks]
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

backend/alembic/env.py

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+"""Alembic migration environment configuration."""
+
+import asyncio
+from logging.config import fileConfig
+
+from alembic import context
+from sqlalchemy import pool
+from sqlalchemy.engine import Connection
+from sqlalchemy.ext.asyncio import async_engine_from_config
+
+from src.config import get_settings
+from src.models import Base
+
+config = context.config
+settings = get_settings()
+
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+target_metadata = Base.metadata
+
+config.set_main_option("sqlalchemy.url", settings.database_url)
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode."""
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def do_run_migrations(connection: Connection) -> None:
+    """Run migrations with connection."""
+    context.configure(connection=connection, target_metadata=target_metadata)
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+async def run_async_migrations() -> None:
+    """Run migrations in async mode."""
+    connectable = async_engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    async with connectable.connect() as connection:
+        await connection.run_sync(do_run_migrations)
+
+    await connectable.dispose()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode."""
+    asyncio.run(run_async_migrations())
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

backend/alembic/script.py.mako

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+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}

backend/alembic/versions/001_initial_schema.py

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+"""Initial schema
+
+Revision ID: 001
+Revises:
+Create Date: 2025-01-30
+
+"""
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+revision: str = "001"
+down_revision: str | None = None
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    # Create difficulty enum
+    difficulty_enum = postgresql.ENUM("easy", "medium", "hard", name="difficulty_enum")
+    difficulty_enum.create(op.get_bind())
+
+    # Create questions table
+    op.create_table(
+        "questions",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column("title", sa.String(255), nullable=False),
+        sa.Column("slug", sa.String(255), unique=True, nullable=False),
+        sa.Column(
+            "difficulty",
+            sa.Enum("easy", "medium", "hard", name="difficulty_enum"),
+            nullable=False,
+        ),
+        sa.Column("description", sa.Text, nullable=False),
+        sa.Column("constraints", sa.Text, nullable=True),
+        sa.Column("examples", postgresql.JSONB, nullable=True),
+        sa.Column("leetcode_id", sa.Integer, unique=True, nullable=True),
+        sa.Column("leetcode_url", sa.String(512), nullable=True),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.func.now(),
+            nullable=False,
+        ),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.func.now(),
+            nullable=False,
+        ),
+    )
+    op.create_index("ix_questions_slug", "questions", ["slug"])
+    op.create_index("ix_questions_difficulty", "questions", ["difficulty"])
+
+    # Create explanations table
+    op.create_table(
+        "explanations",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column(
+            "question_id",
+            postgresql.UUID(as_uuid=True),
+            sa.ForeignKey("questions.id", ondelete="CASCADE"),
+            unique=True,
+            nullable=False,
+        ),
+        sa.Column("approach", sa.Text, nullable=False),
+        sa.Column("intuition", sa.Text, nullable=False),
+        sa.Column("common_pitfalls", postgresql.JSONB, nullable=True),
+        sa.Column("key_takeaways", postgresql.JSONB, nullable=True),
+        sa.Column("time_complexity", sa.String(50), nullable=False),
+        sa.Column("space_complexity", sa.String(50), nullable=False),
+        sa.Column("complexity_explanation", sa.Text, nullable=True),
+    )
+
+    # Create solutions table
+    op.create_table(
+        "solutions",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column(
+            "question_id",
+            postgresql.UUID(as_uuid=True),
+            sa.ForeignKey("questions.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("approach_name", sa.String(100), nullable=False),
+        sa.Column("code", sa.Text, nullable=False),
+        sa.Column("language", sa.String(20), server_default="python", nullable=False),
+        sa.Column("is_optimal", sa.Boolean, server_default="false", nullable=False),
+        sa.Column("explanation", sa.Text, nullable=True),
+    )
+    op.create_index("ix_solutions_question_id", "solutions", ["question_id"])
+
+    # Create categories table
+    op.create_table(
+        "categories",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column("name", sa.String(100), unique=True, nullable=False),
+        sa.Column("slug", sa.String(100), unique=True, nullable=False),
+        sa.Column("description", sa.Text, nullable=True),
+    )
+    op.create_index("ix_categories_slug", "categories", ["slug"])
+
+    # Create patterns table
+    op.create_table(
+        "patterns",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column("name", sa.String(100), unique=True, nullable=False),
+        sa.Column("slug", sa.String(100), unique=True, nullable=False),
+        sa.Column("description", sa.Text, nullable=True),
+        sa.Column("when_to_use", sa.Text, nullable=True),
+    )
+    op.create_index("ix_patterns_slug", "patterns", ["slug"])
+
+    # Create question_categories junction table
+    op.create_table(
+        "question_categories",
+        sa.Column(
+            "question_id",
+            postgresql.UUID(as_uuid=True),
+            sa.ForeignKey("questions.id", ondelete="CASCADE"),
+            primary_key=True,
+        ),
+        sa.Column(
+            "category_id",
+            postgresql.UUID(as_uuid=True),
+            sa.ForeignKey("categories.id", ondelete="CASCADE"),
+            primary_key=True,
+        ),
+    )
+
+    # Create question_patterns junction table
+    op.create_table(
+        "question_patterns",
+        sa.Column(
+            "question_id",
+            postgresql.UUID(as_uuid=True),
+            sa.ForeignKey("questions.id", ondelete="CASCADE"),
+            primary_key=True,
+        ),
+        sa.Column(
+            "pattern_id",
+            postgresql.UUID(as_uuid=True),
+            sa.ForeignKey("patterns.id", ondelete="CASCADE"),
+            primary_key=True,
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("question_patterns")
+    op.drop_table("question_categories")
+    op.drop_table("patterns")
+    op.drop_table("categories")
+    op.drop_table("solutions")
+    op.drop_table("explanations")
+    op.drop_table("questions")
+
+    difficulty_enum = postgresql.ENUM("easy", "medium", "hard", name="difficulty_enum")
+    difficulty_enum.drop(op.get_bind())