! db.f90
module db
    !! Database abstraction layer.
    use, intrinsic :: iso_c_binding
    use :: sqlite3
    implicit none
    private

    integer, parameter, public :: DB_OK = SQLITE_OK

    type, public :: db_type
        type(c_ptr) :: ptr = c_null_ptr
    end type db_type

    public :: db_close
    public :: db_open
    public :: db_create_users
    public :: db_get_users
    public :: db_add_user
    public :: db_delete_user

    private :: db_error
    private :: db_exec
contains


    integer function db_open(db, path) result(rc)
        !! Opens database.
        type(db_type),    intent(inout) :: db
        character(len=*), intent(in)    :: path

        rc = sqlite3_open(path, db%ptr)
        call db_error(rc, 'sqlite3_open()')
    end function db_open

    integer function db_exec(db, query) result(rc)
        !! Executes SQLite query.
        type(db_type),    intent(inout) :: db
        character(len=*), intent(in)    :: query
        character(len=:), allocatable   :: err_msg

        rc = sqlite3_exec(db%ptr, query, c_null_ptr, c_null_ptr, err_msg)
        call db_error(rc, 'sqlite3_exec()', err_msg)
    end function db_exec

    integer function db_close(db) result(rc)
        !! Closes database.
        type(db_type), intent(inout) :: db

        rc = sqlite3_close(db%ptr)
        call db_error(rc, 'sqlite3_close()')
    end function db_close

    integer function db_create_users(db) result(rc)
        !! Creates database tables.
        type(db_type), intent(inout) :: db

        ! Create table "users".
        rc = db_exec(db, "CREATE TABLE users " &
        // "(id INTEGER PRIMARY KEY ASC, " &
        // "username TEXT, password TEXT, " &
        // "apperance TEXT, x_pos INTEGER, " &
        // "y_pos INTEGER, last_login INTEGER, " &
        // "created INTEGER);")
        if (rc /= SQLITE_OK) return
    end function db_create_users

    integer function db_add_user(db, name) result(rc)
        !! Adds student to database.
        type(db_type),    intent(inout) :: db
        character(len=:), intent(in)    :: username
        character(len=:), intent(in)    :: password
        character(len=:), intent(in)    :: apperance
        integer, intent(in)             :: x_pos
        integer, intent(in)             :: y_pos
        integer, intent(in)    :: last_login
        integer, intent(in)             :: created
        type(c_ptr)                     :: stmt

        ! Insert values through prepared statement.
        rc = sqlite3_prepare_v2(db%ptr, "INSERT INTO users(username, password, "
        //"apperance, x_pos, y_pos, last_login, created) VALUES (?,?,?,?,?,?,?)", stmt)
        call db_error(rc, 'sqlite3_prepare_v2()')

        rc = sqlite3_bind_text(stmt, 1, username)
        call db_error(rc, 'sqlite3_bind_text()')
        rc = sqlite3_bind_text(stmt, 2, password)
        call db_error(rc, 'sqlite3_bind_text()')
        rc = sqlite3_bind_text(stmt, 3, apperance)
        call db_error(rc, 'sqlite3_bind_text()')
        rc = sqlite3_bind_integer(stmt, 4, x_pos)
        call db_error(rc, 'sqlite3_bind_integer()')
        rc = sqlite3_bind_integer(stmt, 5, y_pos)
        call db_error(rc, 'sqlite3_bind_integer()')
        rc = sqlite3_bind_integer(stmt, 6, last_login)
        call db_error(rc, 'sqlite3_bind_integer()')
        rc = sqlite3_bind_integer(stmt, 7, created)
        call db_error(rc, 'sqlite3_bind_integer()')

        ! Insert bound value into database.
        rc = sqlite3_step(stmt)
        call db_error(rc, 'sqlite3_step()')

        ! Clean-up prepared statement.
        rc = sqlite3_finalize(stmt)
        call db_error(rc, 'sqlite3_finalize()')
    end function db_add_student

    integer function db_get_users(db) result(rc)
        !! Prints number of courses per student to standard output.
        type(db_type), intent(inout) :: db

        type(c_ptr)      :: stmt
        character(len=24) :: username
        character(len=24) :: password

        rc = sqlite3_prepare_v2(db%ptr, &
                "SELECT username " // &
                "FROM users;", stmt)
        call db_error(rc, 'sqlite3_prepare_v2()')

        step_loop: do
            rc = sqlite3_step(stmt)

            select case (rc)
                case (SQLITE_ROW)
                    username  = sqlite3_column_text(stmt, 0)
                    password  = sqlite3_column_text(stmt, 1)
                    print '(a),(a)', username, password

                case (SQLITE_DONE)
                    exit step_loop

                case default
                    call db_error(rc, 'sqlite3_step()')
                    exit step_loop
            end select
        end do step_loop

        rc = sqlite3_finalize(stmt)
        call db_error(rc, 'sqlite3_finalize()')
    end function db_get_users
    
    subroutine db_error(code, proc, err_msg)
        !! Prints error message.
        integer,          intent(in)           :: code
        character(len=*), intent(in), optional :: proc
        character(len=*), intent(in), optional :: err_msg

        if (code == SQLITE_OK .or. code == SQLITE_DONE) return

        if (present(proc) .and. present(err_msg)) then
            print '(a, ": ", a, " (", i0, ")")', proc, err_msg, code
            return
        end if

        if (present(proc)) then
            print '(a, ": ", i0)', proc, code
            return
        end if

        print '("unknown error: ", i0)', code
    end subroutine db_error
end module db