package video

import (
	"errors"
	"fmt"
	"log"

	"mxl-pattern-generator/internal/generator"
)

type generatorFactory func() (generator.FrameGenerator, error)

func newFrameGenerator(cfg Config, pattern pattern) (generator.FrameGenerator, Backend, error) {
	newGPU := func() (generator.FrameGenerator, error) {
		return generator.NewWGPUGenerator(cfg.Width(), cfg.Height(), pattern.kernelSource)
	}
	newCPU := func() (generator.FrameGenerator, error) {
		return generator.NewCPUPatternGenerator(cfg.Width(), cfg.Height(), cfg.Pattern)
	}
	fill, backend, err := selectFrameGenerator(cfg.Backend, newGPU, newCPU)
	if err != nil {
		return nil, "", err
	}
	gen, err := wrapAlphaGenerator(cfg, fill, pattern.dynamic)
	if err != nil {
		return nil, "", err
	}
	return gen, backend, nil
}

func wrapAlphaGenerator(
	cfg Config,
	fill generator.FrameGenerator,
	fillDynamic bool,
) (generator.FrameGenerator, error) {
	if !cfg.HasAlpha() {
		return fill, nil
	}

	gen, err := generator.NewV210AGenerator(fill, cfg.Width(), cfg.Height(), fillDynamic)
	if err != nil {
		closeErr := fill.Close()
		return nil, errors.Join(
			fmt.Errorf("initialize v210a generator: %w", err),
			closeErr,
		)
	}
	return gen, nil
}

func selectFrameGenerator(
	backend Backend,
	newGPU, newCPU generatorFactory,
) (generator.FrameGenerator, Backend, error) {
	switch backend {
	case BackendGPU:
		gen, err := newGPU()
		if err != nil {
			return nil, "", fmt.Errorf("initialize GPU video generator: %w", err)
		}
		return gen, BackendGPU, nil

	case BackendCPU:
		gen, err := newCPU()
		if err != nil {
			return nil, "", fmt.Errorf("initialize CPU video generator: %w", err)
		}
		return gen, BackendCPU, nil

	case "", BackendAuto:
		gpuGen, gpuErr := newGPU()
		if gpuErr == nil {
			return gpuGen, BackendGPU, nil
		}
		log.Printf("GPU video generator unavailable, falling back to CPU: %v", gpuErr)

		cpuGen, cpuErr := newCPU()
		if cpuErr == nil {
			return cpuGen, BackendCPU, nil
		}
		return nil, "", errors.Join(
			fmt.Errorf("initialize GPU video generator: %w", gpuErr),
			fmt.Errorf("initialize CPU video generator: %w", cpuErr),
		)

	default:
		return nil, "", fmt.Errorf("unsupported video backend %q", backend)
	}
}