package scraper

import (
	"context"
	"fmt"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

// GitHubScraper scrapes documentation from GitHub repositories.
type GitHubScraper struct {
	config *Config
}

// NewGitHubScraper creates a new GitHub scraper.
func NewGitHubScraper(config *Config) *GitHubScraper {
	return &GitHubScraper{config: config}
}

// Scrape clones and parses documents from a GitHub repository.
func (s *GitHubScraper) Scrape(ctx context.Context, source *Source) ([]*Document, error) {
	if source == nil {
		return nil, fmt.Errorf("source is required")
	}

	repoURL, repoName, err := s.resolveRepo(source)
	if err != nil {
		return nil, fmt.Errorf("resolve github repository: %w", err)
	}

	tmpDir, err := os.MkdirTemp("", "devour-github-*")
	if err != nil {
		return nil, fmt.Errorf("create temporary clone directory: %w", err)
	}
	defer os.RemoveAll(tmpDir)

	cloneArgs := []string{"clone", "--depth", "1", "--filter=blob:none", "--sparse", repoURL, tmpDir}
	if branch := strings.TrimSpace(source.Branch); branch != "" {
		cloneArgs = []string{"clone", "--depth", "1", "--filter=blob:none", "--sparse", "--branch", branch, repoURL, tmpDir}
	}

	cmd := exec.CommandContext(ctx, "git", cloneArgs...)
	output, err := cmd.CombinedOutput()
	if err != nil {
		return nil, fmt.Errorf("git clone failed: %v (%s)", err, strings.TrimSpace(string(output)))
	}

	if len(source.Include) == 0 {
		// Try sparse checkout for common docs locations to reduce clone and parse cost.
		sparse := exec.CommandContext(ctx, "git", "-C", tmpDir, "sparse-checkout", "set", "--skip-checks",
			"docs", "doc", "src/routes", "website/docs", "packages/*/docs")
		if sparseOut, sparseErr := sparse.CombinedOutput(); sparseErr != nil {
			_ = sparseOut
			_ = exec.CommandContext(ctx, "git", "-C", tmpDir, "sparse-checkout", "disable").Run()
		}
	} else {
		_ = exec.CommandContext(ctx, "git", "-C", tmpDir, "sparse-checkout", "disable").Run()
	}

	localSource := &Source{
		Name:     coalesce(source.Name, repoName),
		Type:     SourceTypeLocal,
		Path:     tmpDir,
		Include:  append([]string(nil), source.Include...),
		Exclude:  append([]string(nil), source.Exclude...),
		Schedule: source.Schedule,
	}

	if len(localSource.Include) == 0 {
		localSource.Include = []string{
			`(?i)(^|/)readme\.md$`,
			`(?i)(^|/)docs?/`,
			`(?i)\.md$`,
			`(?i)\.mdx$`,
		}
	}

	local := NewLocalScraper(s.config)
	docs, err := local.Scrape(ctx, localSource)
	if err != nil {
		return nil, fmt.Errorf("scrape repository docs: %w", err)
	}
	if len(docs) == 0 && len(source.Include) == 0 {
		// Sparse patterns did not match this repository layout; retry full checkout.
		_ = exec.CommandContext(ctx, "git", "-C", tmpDir, "sparse-checkout", "disable").Run()
		docs, err = local.Scrape(ctx, localSource)
		if err != nil {
			return nil, fmt.Errorf("scrape repository docs after sparse fallback: %w", err)
		}
	}

	for _, doc := range docs {
		if doc == nil {
			continue
		}
		branchForURL := strings.TrimSpace(source.Branch)
		if branchForURL == "" {
			branchForURL = "HEAD"
		}
		if doc.Metadata == nil {
			doc.Metadata = map[string]interface{}{}
		}
		if rawPath, ok := doc.Metadata["path"].(string); ok {
			if relPath, relErr := filepath.Rel(tmpDir, rawPath); relErr == nil {
				relPath = filepath.ToSlash(relPath)
				relPath = strings.TrimPrefix(relPath, "./")
				if relPath != "" && relPath != "." {
					doc.URL = fmt.Sprintf("https://github.com/%s/blob/%s/%s", repoName, branchForURL, relPath)
					doc.ID = generateDocID(doc.URL)
					doc.Metadata["path"] = relPath
				}
			}
		}
		doc.Type = "github-document"
		doc.Metadata["repo"] = repoName
		doc.Metadata["repo_url"] = repoURL
		doc.Metadata["source_type"] = "github"
	}
	return docs, nil
}

// DetectChanges checks if the repository has new commits.
func (s *GitHubScraper) DetectChanges(ctx context.Context, source *Source, lastHash string) (bool, string, error) {
	if source == nil {
		return false, "", fmt.Errorf("source is required")
	}
	_, repoName, err := s.resolveRepo(source)
	if err != nil {
		return false, "", fmt.Errorf("resolve github repository: %w", err)
	}

	remote := "https://github.com/" + strings.TrimSuffix(repoName, ".git") + ".git"
	branch := strings.TrimSpace(source.Branch)
	if branch == "" {
		branch = "HEAD"
	}

	cmd := exec.CommandContext(ctx, "git", "ls-remote", remote, branch)
	output, err := cmd.Output()
	if err != nil {
		return false, "", fmt.Errorf("run git ls-remote for %s (%s): %w", remote, branch, err)
	}
	line := strings.TrimSpace(string(output))
	if line == "" {
		return false, "", fmt.Errorf("empty ls-remote output")
	}
	parts := strings.Fields(line)
	if len(parts) == 0 {
		return false, "", fmt.Errorf("unexpected ls-remote output")
	}
	hash := parts[0]
	return hash != lastHash, hash, nil
}

func (s *GitHubScraper) resolveRepo(source *Source) (repoURL string, repoName string, err error) {
	if strings.TrimSpace(source.Repo) != "" {
		repoName = strings.Trim(strings.TrimSpace(source.Repo), "/")
		repoName = strings.TrimSuffix(repoName, ".git")
		return "https://github.com/" + repoName + ".git", repoName, nil
	}

	raw := strings.TrimSpace(source.URL)
	if raw == "" {
		return "", "", fmt.Errorf("github source requires repo or url")
	}

	u, err := url.Parse(raw)
	if err != nil {
		return "", "", fmt.Errorf("parse github url %q: %w", raw, err)
	}
	if !strings.Contains(strings.ToLower(u.Host), "github.com") {
		return "", "", fmt.Errorf("not a github url: %s", raw)
	}
	parts := strings.Split(strings.Trim(u.Path, "/"), "/")
	if len(parts) < 2 {
		return "", "", fmt.Errorf("invalid github repo url: %s", raw)
	}
	repoName = parts[0] + "/" + strings.TrimSuffix(parts[1], ".git")
	repoURL = "https://github.com/" + repoName + ".git"
	return repoURL, repoName, nil
}

func coalesce(primary, fallback string) string {
	if strings.TrimSpace(primary) != "" {
		return primary
	}
	if strings.TrimSpace(fallback) != "" {
		return filepath.Base(fallback)
	}
	return "github"
}