//go:build mage

package main

import (
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"text/template"
)

const templateExtension string = ".gotmpl"

// Templates generates the configuration files in the managed directory from the templates and
// ensures that they the generated files are symlinked correctly to the files in the user's home
// configuration directory.
func Templates() error {
	homeConfigDirectory, err := os.UserConfigDir()
	if err != nil {
		return fmt.Errorf("unable to get the user's home configuration directory: %w", err)
	}

	config, err := newConfig()
	if err != nil {
		return fmt.Errorf("unable to load the configuration: %w", err)
	}

	managedConfig := managedConfigSet(config.ManagedConfigurations)

	if err = filepath.WalkDir(rootTemplateDir, manageTemplatesFunc(homeConfigDirectory, config, managedConfig)); err != nil {
		return fmt.Errorf("received an error while processing the templates: %w", err)
	}

	return nil
}

func manageTemplatesFunc(homeConfigDirectory string, config config, managedConfig map[string]struct{}) fs.WalkDirFunc {
	funcMap := template.FuncMap{
		"env": env,
	}

	return func(templatePath string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}

		if templatePath == rootTemplateDir {
			return nil
		}

		relativePath := strings.TrimPrefix(templatePath, rootTemplateDir+"/")

		appConfigName := strings.SplitN(relativePath, "/", 2)[0]

		if _, exists := managedConfig[appConfigName]; !exists {
			return nil
		}

		if d.IsDir() {
			managedDir := filepath.Join(rootManagedDir, relativePath)
			configDir := filepath.Join(homeConfigDirectory, relativePath)

			dirs := []string{managedDir, configDir}

			for _, dir := range slices.All(dirs) {
				if err := ensureDirectory(dir); err != nil {
					return fmt.Errorf("unable to ensure the existence of the directory %q: %w", dir, err)
				}
			}

			return nil
		}

		if !strings.HasSuffix(templatePath, templateExtension) {
			return fmt.Errorf(
				"the template %s does not have the %q file extension",
				templatePath,
				templateExtension,
			)
		}

		managedPath := filepath.Join(rootManagedDir, strings.TrimSuffix(relativePath, templateExtension))
		configPath := filepath.Join(homeConfigDirectory, strings.TrimSuffix(relativePath, templateExtension))

		fmt.Println("Processing template:", relativePath)

		if err := renderTemplate(config, templatePath, managedPath, funcMap); err != nil {
			return fmt.Errorf(
				"unable to generate %s from template %s: %w",
				managedPath,
				templatePath,
				err,
			)
		}

		if err := ensureSymlink(managedPath, configPath); err != nil {
			return err
		}

		return nil
	}
}

func renderTemplate(config config, templatePath, managedPath string, funcMap template.FuncMap) error {
	name := filepath.Base(templatePath)

	tmpl, err := template.New(name).Funcs(funcMap).ParseFiles(templatePath)
	if err != nil {
		return fmt.Errorf("unable to create a new template value from %s: %w", templatePath, err)
	}

	output, err := os.Create(managedPath)
	if err != nil {
		return fmt.Errorf("unable to create %s: %w", managedPath, err)
	}
	defer output.Close()

	if err := tmpl.Execute(output, config); err != nil {
		return fmt.Errorf("unable to render the template to %s: %w", managedPath, err)
	}

	return nil
}

func env(value string) string {
	return os.Getenv(value)
}