import utime


class Transition:
    def __init__(self, driver):
        self.driver = driver

    def run(self, preset):
        """Transition between colors, blending over `delay` ms."""
        colors = preset.c
        if not colors:
            self.driver.off()
            yield
            return

        # Only one color: just keep it on
        if len(colors) == 1:
            while True:
                self.driver.fill(self.driver.apply_brightness(colors[0], preset.b))
                yield
            return

        color_index = 0
        start_time = utime.ticks_ms()

        while True:
            if not colors:
                break

            # Get current and next color based on live list
            c1 = colors[color_index % len(colors)]
            c2 = colors[(color_index + 1) % len(colors)]

            duration = max(10, int(preset.d))  # At least 10ms
            now = utime.ticks_ms()
            elapsed = utime.ticks_diff(now, start_time)

            if elapsed >= duration:
                # End of this transition step
                if not preset.a:
                    # One-shot: transition from first to second color only
                    self.driver.fill(self.driver.apply_brightness(c2, preset.b))
                    break
                # Auto: move to next pair
                color_index = (color_index + 1) % len(colors)
                start_time = now
                yield
                continue

            # Interpolate between c1 and c2
            factor = elapsed / duration
            interpolated = tuple(
                int(c1[i] + (c2[i] - c1[i]) * factor) for i in range(3)
            )
            self.driver.fill(self.driver.apply_brightness(interpolated, preset.b))

            yield