package main

import (
	"database/sql"
	"errors"
	"fmt"
	"strings"
	"time"

	_ "github.com/lib/pq"
	"go-mod.ewintr.nl/planner/item"
)

const (
	timestampFormat = "2006-01-02 15:04:05"
)

var migrations = []string{
	`CREATE TABLE items (id TEXT PRIMARY KEY, kind TEXT, updated TIMESTAMP, deleted BOOLEAN, body TEXT)`,
	`CREATE INDEX idx_items_updated ON items(updated)`,
	`CREATE INDEX idx_items_kind ON items(kind)`,
	`ALTER TABLE items ADD COLUMN recurrer JSONB, ADD COLUMN recur_next TIMESTAMP`,
	`ALTER TABLE items ALTER COLUMN recurrer TYPE TEXT USING recurrer::TEXT,
	    ALTER COLUMN recurrer SET NOT NULL,
	    ALTER COLUMN recurrer SET DEFAULT ''`,
	`ALTER TABLE items ALTER COLUMN recur_next TYPE TEXT USING TO_CHAR(recur_next, 'YYYY-MM-DD'),
	    ALTER COLUMN recur_next SET NOT NULL,
	    ALTER COLUMN recur_next SET DEFAULT ''`,
	`ALTER TABLE items ADD COLUMN date TEXT NOT NULL DEFAULT ''`,
}

var (
	ErrInvalidConfiguration     = errors.New("invalid configuration")
	ErrIncompatibleSQLMigration = errors.New("incompatible migration")
	ErrNotEnoughSQLMigrations   = errors.New("already more migrations than wanted")
	ErrPostgresFailure          = errors.New("postgres returned an error")
)

type Postgres struct {
	db *sql.DB
}

func NewPostgres(host, port, dbname, user, password string) (*Postgres, error) {
	connStr := fmt.Sprintf("host=%s port=%s dbname=%s user=%s password=%s sslmode=disable", host, port, dbname, user, password)
	db, err := sql.Open("postgres", connStr)
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrInvalidConfiguration, err)
	}
	if err := db.Ping(); err != nil {
		return nil, fmt.Errorf("%w: %v", ErrInvalidConfiguration, err)
	}

	p := &Postgres{
		db: db,
	}

	if err := p.migrate(migrations); err != nil {
		return nil, err
	}

	return p, nil
}

func (p *Postgres) Update(i item.Item, ts time.Time) error {
	if i.Recurrer != nil && i.RecurNext.IsZero() {
		i.RecurNext = i.Recurrer.First()
	}
	var recurStr string
	if i.Recurrer != nil {
		recurStr = i.Recurrer.String()
	}
	if _, err := p.db.Exec(`
		INSERT INTO items (id, kind, updated, deleted, date, recurrer, recur_next, body)
		VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
		ON CONFLICT (id) DO UPDATE
		SET kind = EXCLUDED.kind,
			updated = EXCLUDED.updated,
			deleted = EXCLUDED.deleted,
			date = EXCLUDED.date,
			recurrer = EXCLUDED.recurrer,
			recur_next = EXCLUDED.recur_next,
			body = EXCLUDED.body`,
		i.ID, i.Kind, ts, i.Deleted, i.Date.String(), recurStr, i.RecurNext.String(), i.Body); err != nil {
		return fmt.Errorf("%w: %v", ErrPostgresFailure, err)
	}
	return nil
}

func (p *Postgres) Updated(ks []item.Kind, t time.Time) ([]item.Item, error) {
	query := `
		SELECT id, kind, updated, deleted, date, recurrer, recur_next, body
		FROM items
		WHERE updated > $1`
	args := []interface{}{t}
	if len(ks) > 0 {
		placeholder := make([]string, len(ks))
		for i := range ks {
			placeholder[i] = fmt.Sprintf("$%d", i+2)
			args = append(args, string(ks[i]))
		}
		query += fmt.Sprintf(" AND kind = ANY(ARRAY[%s])", strings.Join(placeholder, ","))
	}

	rows, err := p.db.Query(query, args...)
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrPostgresFailure, err)
	}
	defer rows.Close()

	result := make([]item.Item, 0)
	for rows.Next() {
		var i item.Item
		var date, recurrer, recurNext string
		if err := rows.Scan(&i.ID, &i.Kind, &i.Updated, &i.Deleted, &date, &recurrer, &recurNext, &i.Body); err != nil {
			return nil, fmt.Errorf("%w: %v", ErrPostgresFailure, err)
		}
		i.Date = item.NewDateFromString(date)
		i.Recurrer = item.NewRecurrer(recurrer)
		i.RecurNext = item.NewDateFromString(recurNext)
		result = append(result, i)
	}

	return result, nil
}

func (p *Postgres) ShouldRecur(date item.Date) ([]item.Item, error) {
	query := `
		SELECT id, kind, updated, deleted, date, recurrer, recur_next, body
		FROM items
		WHERE
		  NOT deleted 
		  AND recurrer <> ''
		  AND recur_next <= $1`
	rows, err := p.db.Query(query, date.String())
	if err != nil {
		return nil, fmt.Errorf("%w: %v", ErrPostgresFailure, err)
	}
	defer rows.Close()

	result := make([]item.Item, 0)
	for rows.Next() {
		var i item.Item
		var date, recurrer, recurNext string
		if err := rows.Scan(&i.ID, &i.Kind, &i.Updated, &i.Deleted, &date, &recurrer, &recurNext, &i.Body); err != nil {
			return nil, fmt.Errorf("%w: %v", ErrPostgresFailure, err)
		}
		i.Date = item.NewDateFromString(date)
		i.Recurrer = item.NewRecurrer(recurrer)
		i.RecurNext = item.NewDateFromString(recurNext)
		result = append(result, i)
	}

	return result, nil
}

func (p *Postgres) migrate(wanted []string) error {
	// Create migration table if not exists
	_, err := p.db.Exec(`
		CREATE TABLE IF NOT EXISTS migration
		(id SERIAL PRIMARY KEY, query TEXT)
	`)
	if err != nil {
		return fmt.Errorf("%w: %v", ErrPostgresFailure, err)
	}

	// Find existing migrations
	rows, err := p.db.Query(`SELECT query FROM migration ORDER BY id`)
	if err != nil {
		return fmt.Errorf("%w: %v", ErrPostgresFailure, err)
	}
	defer rows.Close()

	var existing []string
	for rows.Next() {
		var query string
		if err := rows.Scan(&query); err != nil {
			return fmt.Errorf("%w: %v", ErrPostgresFailure, err)
		}
		existing = append(existing, query)
	}

	// Compare and execute missing migrations
	missing, err := compareMigrations(wanted, existing)
	if err != nil {
		return fmt.Errorf("%w: %v", ErrPostgresFailure, err)
	}

	for _, query := range missing {
		if _, err := p.db.Exec(query); err != nil {
			return fmt.Errorf("%w: %v", ErrPostgresFailure, err)
		}

		// Register migration
		if _, err := p.db.Exec(`
			INSERT INTO migration (query) VALUES ($1)
		`, query); err != nil {
			return fmt.Errorf("%w: %v", ErrPostgresFailure, err)
		}
	}

	return nil
}

func compareMigrations(wanted, existing []string) ([]string, error) {
	var needed []string
	if len(wanted) < len(existing) {
		return nil, ErrNotEnoughSQLMigrations
	}

	for i, want := range wanted {
		switch {
		case i >= len(existing):
			needed = append(needed, want)
		case want == existing[i]:
			// do nothing
		case want != existing[i]:
			return nil, fmt.Errorf("%w: %v", ErrIncompatibleSQLMigration, want)
		}
	}

	return needed, nil
}