-- ==========================================
-- Migration 006: Unify Chats → Channels
-- ==========================================
-- "Everything is a channel." Merges the separate chats/channels
-- schema into a single unified channel model.
--
-- The old channels/channel_members/channel_messages tables (from 001)
-- were never populated — safe to drop and rebuild on top of chats.
-- ==========================================

-- ── 1. Drop unused legacy channel tables ────
-- These were placeholders from 001; no data, no handlers.
-- Order matters: drop dependents first.

-- Remove FK references in tool_usage_log before dropping
ALTER TABLE tool_usage_log DROP CONSTRAINT IF EXISTS tool_usage_log_channel_id_fkey;
ALTER TABLE tool_usage_log DROP COLUMN IF EXISTS channel_id;

DROP TABLE IF EXISTS channel_messages CASCADE;
DROP TABLE IF EXISTS channel_members CASCADE;
DROP TABLE IF EXISTS channels CASCADE;

-- Drop the old trigger (will re-create after rename)
DROP TRIGGER IF EXISTS channels_updated_at ON channels;

-- ── 2. Rename chats → channels ──────────────

ALTER TABLE chats RENAME TO channels;
ALTER TABLE chat_messages RENAME TO messages;

-- Rename columns to match new schema
ALTER TABLE messages RENAME COLUMN chat_id TO channel_id;

-- Rename indexes
ALTER INDEX IF EXISTS idx_chats_user RENAME TO idx_channels_user;
ALTER INDEX IF EXISTS idx_chats_updated RENAME TO idx_channels_updated;
ALTER INDEX IF EXISTS idx_chats_tags RENAME TO idx_channels_tags;
ALTER INDEX IF EXISTS idx_chat_messages_chat RENAME TO idx_messages_channel;

-- Rename constraints (PK and FK auto-renamed with table on some PG versions,
-- but let's be explicit for the FK)
-- Note: PG auto-renames PKs but not FKs or check constraints

-- Rename the updated_at trigger
DROP TRIGGER IF EXISTS chats_updated_at ON channels;
CREATE TRIGGER channels_updated_at BEFORE UPDATE ON channels
    FOR EACH ROW EXECUTE FUNCTION update_updated_at();

-- ── 3. Add channel type + description ───────

ALTER TABLE channels ADD COLUMN IF NOT EXISTS type VARCHAR(20) DEFAULT 'direct';
ALTER TABLE channels ADD COLUMN IF NOT EXISTS description TEXT;

COMMENT ON COLUMN channels.type IS 'direct=1:1 AI chat, group=multi-model, channel=named persistent';

-- Backfill: all existing rows are 1:1 AI chats
UPDATE channels SET type = 'direct' WHERE type IS NULL;

-- Index on type for filtered queries
CREATE INDEX IF NOT EXISTS idx_channels_type ON channels(type);

-- ── 4. Add message tree (parent_id) ─────────

ALTER TABLE messages ADD COLUMN IF NOT EXISTS parent_id UUID REFERENCES messages(id) ON DELETE SET NULL;

CREATE INDEX IF NOT EXISTS idx_messages_parent ON messages(parent_id);

-- Backfill linear parent chains on existing messages.
-- Each message's parent is the previous message in the same channel (by created_at).
WITH ordered AS (
    SELECT id, channel_id, created_at,
           LAG(id) OVER (PARTITION BY channel_id ORDER BY created_at) AS prev_id
    FROM messages
)
UPDATE messages m
SET parent_id = o.prev_id
FROM ordered o
WHERE m.id = o.id AND o.prev_id IS NOT NULL AND m.parent_id IS NULL;

-- ── 5. Add participant columns on messages ──
-- Decouples messages from user-only: AI models are participants too.

ALTER TABLE messages ADD COLUMN IF NOT EXISTS participant_type VARCHAR(10) DEFAULT 'user';
ALTER TABLE messages ADD COLUMN IF NOT EXISTS participant_id VARCHAR(255);

COMMENT ON COLUMN messages.participant_type IS 'user or model';
COMMENT ON COLUMN messages.participant_id IS 'user UUID or model identifier string';

-- Backfill: user messages get the channel owner's user_id;
-- assistant messages get the model name as participant_id.
UPDATE messages m
SET participant_type = CASE WHEN m.role = 'assistant' THEN 'model' ELSE 'user' END,
    participant_id = CASE
        WHEN m.role = 'assistant' THEN COALESCE(m.model, 'unknown')
        ELSE (SELECT c.user_id::text FROM channels c WHERE c.id = m.channel_id)
    END
WHERE m.participant_id IS NULL;

-- ── 6. Update model_routing_log FK ──────────

-- The FK column was named chat_id — rename it
ALTER TABLE model_routing_log RENAME COLUMN chat_id TO channel_id;
ALTER INDEX IF EXISTS idx_routing_log_chat RENAME TO idx_routing_log_channel;

-- message_id FK still valid (messages table was renamed, FK follows)

-- ── 7. Update tool_usage_log ────────────────
-- We already dropped the old channel_id column above.
-- Re-add it pointing to the unified channels table.
-- Also rename the old chat_id column.

ALTER TABLE tool_usage_log RENAME COLUMN chat_id TO channel_id;
-- The FK auto-follows the table rename, but let's be safe:
-- (chat_id FK pointed to chats(id), which is now channels(id) — PG handles this)