SET sql_mode = 'STRICT_ALL_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';

-- USERS
CREATE TABLE IF NOT EXISTS users (
  id            BIGINT PRIMARY KEY AUTO_INCREMENT,
  email         VARCHAR(255) NOT NULL UNIQUE,
  pass_bcrypt   VARBINARY(60) NOT NULL,
  created_at    TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB;

-- CONVERSATIONS (one tree-ish DAG per conversation)
CREATE TABLE IF NOT EXISTS conversations (
  id            BIGINT PRIMARY KEY AUTO_INCREMENT,
  owner_id      BIGINT NOT NULL,
  title         VARCHAR(255),
  created_at    TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  CONSTRAINT fk_conversations_owner
    FOREIGN KEY (owner_id) REFERENCES users(id)
      ON DELETE CASCADE
) ENGINE=InnoDB;

-- NODES = commits (plain numeric IDs). author_kind for display only.
CREATE TABLE IF NOT EXISTS nodes (
  id                BIGINT PRIMARY KEY AUTO_INCREMENT,
  conversation_id   BIGINT NOT NULL,
  author_kind       ENUM('user','assistant') NOT NULL,
  content           MEDIUMTEXT NOT NULL,
  created_at        TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  CONSTRAINT fk_nodes_conversation
    FOREIGN KEY (conversation_id) REFERENCES conversations(id)
      ON DELETE CASCADE
) ENGINE=InnoDB;

-- EDGES (parent -> child). Acyclic enforced in application.
CREATE TABLE IF NOT EXISTS edges (
  parent_id   BIGINT NOT NULL,
  child_id    BIGINT NOT NULL,
  PRIMARY KEY (parent_id, child_id),
  CONSTRAINT fk_edges_parent
    FOREIGN KEY (parent_id) REFERENCES nodes(id)
      ON DELETE CASCADE,
  CONSTRAINT fk_edges_child
    FOREIGN KEY (child_id)  REFERENCES nodes(id)
      ON DELETE CASCADE
) ENGINE=InnoDB;

-- BRANCHES (named pointers to any node within a conversation)
CREATE TABLE IF NOT EXISTS branches (
  id                BIGINT PRIMARY KEY AUTO_INCREMENT,
  conversation_id   BIGINT NOT NULL,
  name              VARCHAR(128) NOT NULL,
  head_node_id      BIGINT NOT NULL,
  created_at        TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
  UNIQUE KEY uq_branch_name (conversation_id, name),
  CONSTRAINT fk_branches_conversation
    FOREIGN KEY (conversation_id) REFERENCES conversations(id)
      ON DELETE CASCADE,
  CONSTRAINT fk_branches_head
    FOREIGN KEY (head_node_id) REFERENCES nodes(id)
      ON DELETE CASCADE
) ENGINE=InnoDB;

CREATE INDEX idx_nodes_conv_created ON nodes (conversation_id, created_at, id);
CREATE INDEX idx_edges_child ON edges (child_id);
CREATE INDEX idx_edges_parent ON edges (parent_id);
CREATE INDEX idx_branches_conv_head ON branches (conversation_id, head_node_id);