package readme

import (
	"fmt"
	"net/url"
	"strings"
)

// Platform represents a supported Git hosting platform
type Platform string

const (
	PlatformGitHub   Platform = "github"
	PlatformGitLab   Platform = "gitlab"
	PlatformTangled  Platform = "tangled"
	PlatformCodeberg Platform = "codeberg"
)

// ParseSourceURL extracts platform, user, and repo from a source repository URL.
// Returns ok=false if the URL is not a recognized pattern.
func ParseSourceURL(sourceURL string) (platform Platform, user, repo string, ok bool) {
	if sourceURL == "" {
		return "", "", "", false
	}

	parsed, err := url.Parse(sourceURL)
	if err != nil {
		return "", "", "", false
	}

	// Normalize: remove trailing slash and .git suffix
	path := strings.TrimSuffix(parsed.Path, "/")
	path = strings.TrimSuffix(path, ".git")
	path = strings.TrimPrefix(path, "/")

	if path == "" {
		return "", "", "", false
	}

	host := strings.ToLower(parsed.Host)

	switch host {
	case "github.com":
		// GitHub: github.com/{user}/{repo}
		parts := strings.SplitN(path, "/", 3)
		if len(parts) < 2 || parts[0] == "" || parts[1] == "" {
			return "", "", "", false
		}
		return PlatformGitHub, parts[0], parts[1], true

	case "gitlab.com":
		// GitLab: gitlab.com/{user}/{repo} or gitlab.com/{group}/{subgroup}/{repo}
		// For nested groups, user = everything except last part, repo = last part
		lastSlash := strings.LastIndex(path, "/")
		if lastSlash == -1 || lastSlash == 0 {
			return "", "", "", false
		}
		user = path[:lastSlash]
		repo = path[lastSlash+1:]
		if user == "" || repo == "" {
			return "", "", "", false
		}
		return PlatformGitLab, user, repo, true

	case "tangled.org", "tangled.sh":
		// Tangled: tangled.org/{user}/{repo} or tangled.sh/@{user}/{repo} (legacy)
		// Strip leading @ from user if present
		path = strings.TrimPrefix(path, "@")
		parts := strings.SplitN(path, "/", 3)
		if len(parts) < 2 || parts[0] == "" || parts[1] == "" {
			return "", "", "", false
		}
		return PlatformTangled, parts[0], parts[1], true

	case "codeberg.org":
		// Codeberg: codeberg.org/{user}/{repo}
		parts := strings.SplitN(path, "/", 3)
		if len(parts) < 2 || parts[0] == "" || parts[1] == "" {
			return "", "", "", false
		}
		return PlatformCodeberg, parts[0], parts[1], true

	default:
		return "", "", "", false
	}
}

// DeriveReadmeURL converts a source repository URL to a raw README URL.
// Returns empty string if platform is not supported.
func DeriveReadmeURL(sourceURL, branch string) string {
	platform, user, repo, ok := ParseSourceURL(sourceURL)
	if !ok {
		return ""
	}

	switch platform {
	case PlatformGitHub:
		// https://raw.githubusercontent.com/{user}/{repo}/refs/heads/{branch}/README.md
		return fmt.Sprintf("https://raw.githubusercontent.com/%s/%s/refs/heads/%s/README.md", user, repo, branch)

	case PlatformGitLab:
		// https://gitlab.com/{user}/{repo}/-/raw/{branch}/README.md
		return fmt.Sprintf("https://gitlab.com/%s/%s/-/raw/%s/README.md", user, repo, branch)

	case PlatformTangled:
		// https://tangled.org/{user}/{repo}/raw/{branch}/README.md
		return fmt.Sprintf("https://tangled.org/%s/%s/raw/%s/README.md", user, repo, branch)

	case PlatformCodeberg:
		// https://codeberg.org/{user}/{repo}/raw/branch/{branch}/README.md
		return fmt.Sprintf("https://codeberg.org/%s/%s/raw/branch/%s/README.md", user, repo, branch)

	default:
		return ""
	}
}