package server

import (
	"database/sql"
	"strconv"
	"strings"
)

// dbx is the database the server talks to: SQLite, or PostgreSQL. The
// queries are written once, for SQLite; on PostgreSQL each is rewritten
// (pgSQL) on its way.
type dbx struct {
	*sql.DB
	pg bool
}

func (d *dbx) q(query string) string {
	if d.pg {
		return pgSQL(query)
	}
	return query
}

func (d *dbx) Exec(query string, args ...any) (sql.Result, error) {
	return d.DB.Exec(d.q(query), args...)
}
func (d *dbx) Query(query string, args ...any) (*sql.Rows, error) {
	return d.DB.Query(d.q(query), args...)
}
func (d *dbx) QueryRow(query string, args ...any) *sql.Row {
	return d.DB.QueryRow(d.q(query), args...)
}
func (d *dbx) Begin() (*txx, error) {
	tx, err := d.DB.Begin()
	return &txx{Tx: tx, pg: d.pg}, err
}

// insert runs an INSERT and gives the new row's id (LastInsertId on SQLite,
// RETURNING id on PostgreSQL, which has no LastInsertId).
func (d *dbx) insert(query string, args ...any) (int64, error) {
	if d.pg {
		var id int64
		err := d.DB.QueryRow(pgSQL(query)+" RETURNING id", args...).Scan(&id)
		return id, err
	}
	res, err := d.DB.Exec(query, args...)
	if err != nil {
		return 0, err
	}
	return res.LastInsertId()
}

type txx struct {
	*sql.Tx
	pg bool
}

func (t *txx) Exec(query string, args ...any) (sql.Result, error) {
	if t.pg {
		query = pgSQL(query)
	}
	return t.Tx.Exec(query, args...)
}

// pgSQL rewrites a query for SQLite into PostgreSQL's: $n placeholders,
// INSERT OR IGNORE as ON CONFLICT DO NOTHING, and in table definitions
// BIGSERIAL keys, BIGINT numbers (times are Unix seconds), BYTEA blobs and
// ADD COLUMN IF NOT EXISTS.
func pgSQL(q string) string {
	if strings.HasPrefix(q, "INSERT OR IGNORE ") {
		q = "INSERT " + strings.TrimPrefix(q, "INSERT OR IGNORE ") + " ON CONFLICT DO NOTHING"
	}
	if strings.Contains(q, "CREATE TABLE") || strings.Contains(q, "ALTER TABLE") {
		q = strings.ReplaceAll(q, "INTEGER PRIMARY KEY AUTOINCREMENT", "BIGSERIAL PRIMARY KEY")
		q = strings.ReplaceAll(q, "INTEGER", "BIGINT")
		q = strings.ReplaceAll(q, "BLOB", "BYTEA")
		q = strings.ReplaceAll(q, "ADD COLUMN ", "ADD COLUMN IF NOT EXISTS ")
	}
	var b strings.Builder
	n, quoted := 0, false
	for _, r := range q {
		switch {
		case r == '\'':
			quoted = !quoted
		case r == '?' && !quoted:
			n++
			b.WriteString("$" + strconv.Itoa(n))
			continue
		}
		b.WriteRune(r)
	}
	return b.String()
}