Add mentorship tables and constraints

cgen-f533dcc61f814b049442dd716407ac7d

supabase/migrations/20251018_mentorship.sql

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+create extension if not exists "pgcrypto";
+
+-- Mentors registry
+create table if not exists public.mentors (
+  user_id uuid primary key references public.user_profiles(id) on delete cascade,
+  bio text,
+  expertise text[] not null default '{}',
+  available boolean not null default true,
+  hourly_rate numeric(10,2),
+  created_at timestamptz not null default now(),
+  updated_at timestamptz not null default now()
+);
+
+create index if not exists mentors_available_idx on public.mentors (available);
+create index if not exists mentors_expertise_gin on public.mentors using gin (expertise);
+
+-- Mentorship requests
+create table if not exists public.mentorship_requests (
+  id uuid primary key default gen_random_uuid(),
+  mentor_id uuid not null references public.user_profiles(id) on delete cascade,
+  mentee_id uuid not null references public.user_profiles(id) on delete cascade,
+  message text,
+  status text not null default 'pending' check (status in ('pending','accepted','rejected','cancelled')),
+  created_at timestamptz not null default now(),
+  updated_at timestamptz not null default now()
+);
+
+create index if not exists mentorship_requests_mentor_idx on public.mentorship_requests (mentor_id);
+create index if not exists mentorship_requests_mentee_idx on public.mentorship_requests (mentee_id);
+create index if not exists mentorship_requests_status_idx on public.mentorship_requests (status);
+
+-- Prevent duplicate pending requests between same pair
+create unique index if not exists mentorship_requests_unique_pending on public.mentorship_requests (mentor_id, mentee_id) where status = 'pending';
+
+-- Simple trigger to maintain updated_at
+create or replace function public.set_updated_at()
+returns trigger as $$
+begin
+  new.updated_at = now();
+  return new;
+end;
+$$ language plpgsql;
+
+create trigger mentors_set_updated_at
+  before update on public.mentors
+  for each row execute function public.set_updated_at();
+
+create trigger mentorship_requests_set_updated_at
+  before update on public.mentorship_requests
+  for each row execute function public.set_updated_at();