-- Migration: Add comment threading support
-- Adds parent_comment_id for reply/thread functionality

-- Add parent_comment_id column for threaded comments
ALTER TABLE ticket_comments
ADD COLUMN parent_comment_id INT NULL DEFAULT NULL AFTER comment_id;

-- Add foreign key constraint (self-referencing for thread hierarchy)
ALTER TABLE ticket_comments
ADD CONSTRAINT fk_parent_comment
FOREIGN KEY (parent_comment_id) REFERENCES ticket_comments(comment_id)
ON DELETE CASCADE;

-- Add index for efficient thread retrieval
CREATE INDEX idx_parent_comment ON ticket_comments(parent_comment_id);

-- Add thread_depth column to track nesting level (prevents infinite recursion issues)
ALTER TABLE ticket_comments
ADD COLUMN thread_depth TINYINT UNSIGNED NOT NULL DEFAULT 0 AFTER parent_comment_id;