package db

import (
	"context"
	"fmt"
	"log/slog"

	"github.com/jackc/pgx/v5/pgxpool"
)

// migration holds a SQL statement and a human-readable name.
// We run them in order and track which ones have already run.
type migration struct {
	name string
	sql  string
}

var migrations = []migration{
	{
		name: "create_receipts",
		sql: `
			CREATE TABLE IF NOT EXISTS receipts (
				id           UUID PRIMARY KEY DEFAULT gen_random_uuid(),
				store_name   TEXT,
				receipt_date DATE NOT NULL,
				image_path   TEXT,
				city         TEXT,
				country      TEXT DEFAULT 'US',
				submitted_at TIMESTAMPTZ NOT NULL DEFAULT now()
			);
		`,
	},
	{
		name: "create_canonical_items",
		sql: `
			-- The "dictionary" of known items we track.
			-- User submissions get mapped to these via fuzzy matching.
			CREATE TABLE IF NOT EXISTS canonical_items (
				name        TEXT PRIMARY KEY,      -- e.g. "milk_whole_1gal"
				display_name TEXT NOT NULL,        -- e.g. "Whole Milk, 1 Gallon"
				category    TEXT NOT NULL,         -- e.g. "dairy"
				unit        TEXT,                  -- e.g. "gallon", "lb", "dozen"
				aliases     TEXT[] DEFAULT '{}'    -- ["1 gal whole milk", "milk whole gal"]
			);
		`,
	},
	{
		name: "create_line_items",
		sql: `
			CREATE TABLE IF NOT EXISTS line_items (
				id                UUID PRIMARY KEY DEFAULT gen_random_uuid(),
				receipt_id        UUID NOT NULL REFERENCES receipts(id) ON DELETE CASCADE,
				raw_name          TEXT NOT NULL,
				canonical_name    TEXT REFERENCES canonical_items(name),
				price_cents       INT NOT NULL CHECK (price_cents > 0),
				quantity          NUMERIC(8,3) NOT NULL DEFAULT 1,
				-- Stored computed column: unit price in cents
				unit_price_cents  INT GENERATED ALWAYS AS
				                    (ROUND(price_cents / quantity)::INT) STORED
			);

			CREATE INDEX IF NOT EXISTS line_items_receipt_id ON line_items(receipt_id);
			CREATE INDEX IF NOT EXISTS line_items_canonical  ON line_items(canonical_name);
		`,
	},
	{
		name: "create_price_snapshots",
		sql: `
			-- Pre-aggregated monthly averages, rebuilt by a background job.
			-- Charts read from here rather than scanning all line_items each time.
			CREATE TABLE IF NOT EXISTS price_snapshots (
				canonical_name   TEXT NOT NULL REFERENCES canonical_items(name),
				year_month       DATE NOT NULL,  -- always the 1st of the month
				avg_price_cents  INT  NOT NULL,
				sample_count     INT  NOT NULL DEFAULT 0,
				PRIMARY KEY (canonical_name, year_month)
			);
		`,
	},
	{
		name: "seed_canonical_items",
		sql: `
			INSERT INTO canonical_items (name, display_name, category, unit, aliases) VALUES
				('milk_whole_1gal',  'Whole Milk, 1 Gallon',    'dairy',   'gallon',
				 ARRAY['whole milk gallon', '1 gal whole milk', 'milk whl gal']),
				('eggs_large_dozen', 'Large Eggs, 1 Dozen',     'dairy',   'dozen',
				 ARRAY['large eggs 12ct', 'eggs large dozen', 'grade a large eggs']),
				('bread_white_loaf', 'White Bread, 1 Loaf',     'bakery',  'loaf',
				 ARRAY['white bread', 'sandwich bread', 'bread loaf']),
				('ground_beef_1lb',  'Ground Beef, 1 lb (80%)', 'meat',    'lb',
				 ARRAY['ground beef lb', '80/20 ground beef', 'hamburger meat']),
				('olive_oil_16oz',   'Olive Oil, 16 oz',        'pantry',  'bottle',
				 ARRAY['olive oil 16oz', 'extra virgin olive oil', 'evoo 16oz']),
				('butter_salted_1lb','Salted Butter, 1 lb',     'dairy',   'lb',
				 ARRAY['butter salted pound', 'salted butter 4 sticks']),
				('chicken_breast_1lb','Chicken Breast, 1 lb',   'meat',    'lb',
				 ARRAY['boneless chicken breast', 'chicken breast lb']),
				('orange_juice_52oz','Orange Juice, 52 oz',     'beverages','carton',
				 ARRAY['oj 52oz', 'orange juice carton', 'florida natural oj'])
			ON CONFLICT (name) DO NOTHING;
		`,
	},
}

// Migrate runs all pending migrations in order.
// It creates a simple tracking table on first run.
func Migrate(pool *pgxpool.Pool) error {
	ctx := context.Background()

	// Create the migrations tracking table if it doesn't exist
	_, err := pool.Exec(ctx, `
		CREATE TABLE IF NOT EXISTS schema_migrations (
			name       TEXT PRIMARY KEY,
			applied_at TIMESTAMPTZ NOT NULL DEFAULT now()
		);
	`)
	if err != nil {
		return fmt.Errorf("create migrations table: %w", err)
	}

	for _, m := range migrations {
		// Check if already applied
		var exists bool
		err := pool.QueryRow(ctx,
			"SELECT EXISTS(SELECT 1 FROM schema_migrations WHERE name = $1)", m.name,
		).Scan(&exists)
		if err != nil {
			return fmt.Errorf("check migration %s: %w", m.name, err)
		}

		if exists {
			continue
		}

		// Run the migration inside a transaction so it's atomic
		tx, err := pool.Begin(ctx)
		if err != nil {
			return fmt.Errorf("begin migration %s: %w", m.name, err)
		}

		if _, err := tx.Exec(ctx, m.sql); err != nil {
			_ = tx.Rollback(ctx)
			return fmt.Errorf("run migration %s: %w", m.name, err)
		}

		if _, err := tx.Exec(ctx,
			"INSERT INTO schema_migrations (name) VALUES ($1)", m.name,
		); err != nil {
			_ = tx.Rollback(ctx)
			return fmt.Errorf("record migration %s: %w", m.name, err)
		}

		if err := tx.Commit(ctx); err != nil {
			return fmt.Errorf("commit migration %s: %w", m.name, err)
		}

		slog.Info("migration applied", "name", m.name)
	}

	return nil
}