// Package templates provides embedded project templates for seeding new repos.
//
// Templates are embedded at compile time from the templates/ subdirectory.
// Each template contains starter files with {{VAR}} placeholders that get
// interpolated when seeding a repository.
package templates

import (
	"context"
	"embed"
	"encoding/base64"
	"fmt"
	"io/fs"
	"log/slog"
	"path/filepath"
	"regexp"
	"strings"

	"code.gitea.io/sdk/gitea"
	"github.com/orchard9/rdev/internal/domain"
	"github.com/orchard9/rdev/internal/port"
)

//go:embed all:templates
var templatesFS embed.FS

// availableTemplates lists all supported project templates.
var availableTemplates = []port.TemplateInfo{
	{Name: "default", Description: "Basic project with Dockerfile", Stack: "generic"},
	{Name: "astro-landing", Description: "Astro landing page with Tailwind", Stack: "astro"},
	{Name: "go-api", Description: "Go REST API with chi router", Stack: "go"},
}

// templateNameRegex validates template names (alphanumeric, dash only).
var templateNameRegex = regexp.MustCompile(`^[a-z][a-z0-9-]*$`)

// Provider implements port.TemplateProvider using embedded templates
// and the Gitea API to seed repositories.
type Provider struct {
	giteaClient *gitea.Client
	logger      *slog.Logger
}

// Ensure Provider implements TemplateProvider.
var _ port.TemplateProvider = (*Provider)(nil)

// NewProvider creates a new template provider.
// giteaClient is used to create files in repositories.
// logger is optional; if nil, slog.Default() is used.
func NewProvider(giteaClient *gitea.Client, logger *slog.Logger) *Provider {
	if logger == nil {
		logger = slog.Default()
	}
	return &Provider{
		giteaClient: giteaClient,
		logger:      logger,
	}
}

// SeedRepo populates a repository with template files.
func (p *Provider) SeedRepo(ctx context.Context, owner, repo, templateName string, vars map[string]string) error {
	// Check for context cancellation
	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
	}

	// Validate template name (prevent path traversal, enforce naming convention)
	if !isValidTemplateName(templateName) {
		return fmt.Errorf("invalid template name: %s (must be lowercase alphanumeric with dashes)", templateName)
	}

	// Validate template exists
	templateDir := "templates/" + templateName
	if _, err := templatesFS.ReadDir(templateDir); err != nil {
		return fmt.Errorf("template not found: %s", templateName)
	}

	p.logger.Info("seeding repo from template",
		"owner", owner,
		"repo", repo,
		"template", templateName,
	)

	// Walk template directory and create files
	var filesCreated int
	err := fs.WalkDir(templatesFS, templateDir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}

		// Read file content
		content, err := templatesFS.ReadFile(path)
		if err != nil {
			return fmt.Errorf("failed to read template file %s: %w", path, err)
		}

		// Interpolate variables
		interpolated := interpolateVars(string(content), vars)

		// Calculate relative path from template root
		relPath, err := filepath.Rel(templateDir, path)
		if err != nil {
			return fmt.Errorf("failed to get relative path: %w", err)
		}

		// Strip .tmpl extension (allows embedding go.mod as go.mod.tmpl)
		relPath = strings.TrimSuffix(relPath, ".tmpl")

		// Create file in repo via Gitea API
		// Gitea expects base64-encoded content
		encodedContent := base64.StdEncoding.EncodeToString([]byte(interpolated))

		// For empty repos (AutoInit: false), the first file must create the branch
		// using NewBranchName. Subsequent files use the existing branch.
		opts := gitea.CreateFileOptions{
			Content: encodedContent,
			FileOptions: gitea.FileOptions{
				Message: "Add " + relPath + " from template",
			},
		}
		if filesCreated == 0 {
			// First file: create the main branch
			opts.NewBranchName = "main"
		} else {
			// Subsequent files: use existing main branch
			opts.BranchName = "main"
		}

		_, _, err = p.giteaClient.CreateFile(owner, repo, relPath, opts)
		if err != nil {
			return fmt.Errorf("failed to create file %s: %w", relPath, err)
		}

		filesCreated++
		return nil
	})

	if err != nil {
		return fmt.Errorf("failed to seed repo from template %s: %w", templateName, err)
	}

	p.logger.Info("repo seeded successfully",
		"owner", owner,
		"repo", repo,
		"template", templateName,
		"files_created", filesCreated,
	)

	return nil
}

// isValidTemplateName validates that a template name is safe.
func isValidTemplateName(name string) bool {
	if name == "" || len(name) > 64 {
		return false
	}
	return templateNameRegex.MatchString(name)
}

// ListTemplates returns available templates.
func (p *Provider) ListTemplates(ctx context.Context) ([]port.TemplateInfo, error) {
	// Check for context cancellation
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	default:
	}

	result := make([]port.TemplateInfo, len(availableTemplates))
	for i, t := range availableTemplates {
		result[i] = t
		// Populate files list
		files, err := listTemplateFiles(t.Name)
		if err == nil {
			result[i].Files = files
		}
	}
	return result, nil
}

// GetTemplate returns info about a specific template.
func (p *Provider) GetTemplate(ctx context.Context, name string) (*port.TemplateInfo, error) {
	// Check for context cancellation
	select {
	case <-ctx.Done():
		return nil, ctx.Err()
	default:
	}

	for _, t := range availableTemplates {
		if t.Name == name {
			result := t
			files, err := listTemplateFiles(name)
			if err == nil {
				result.Files = files
			}
			return &result, nil
		}
	}
	return nil, fmt.Errorf("%w: %s", domain.ErrTemplateNotFound, name)
}

// interpolateVars replaces {{VAR_NAME}} placeholders with values.
func interpolateVars(content string, vars map[string]string) string {
	result := content
	for key, value := range vars {
		placeholder := "{{" + key + "}}"
		result = strings.ReplaceAll(result, placeholder, value)
	}
	return result
}

// listTemplateFiles returns the list of files in a template.
func listTemplateFiles(templateName string) ([]string, error) {
	templateDir := "templates/" + templateName
	var files []string

	err := fs.WalkDir(templatesFS, templateDir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		relPath, err := filepath.Rel(templateDir, path)
		if err != nil {
			return err
		}
		// Strip .tmpl extension for display
		relPath = strings.TrimSuffix(relPath, ".tmpl")
		files = append(files, relPath)
		return nil
	})

	return files, err
}