package main

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

// Spec is a parsed source as the user wrote it: a git URL and an optional ref.
type Spec struct {
	URL string
	Ref string
}

var (
	ghShorthand = regexp.MustCompile(`^[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+$`)
	scpLike     = regexp.MustCompile(`^([A-Za-z0-9_.-]+@)?([A-Za-z0-9_.-]+):([^/].*)$`)
	fullRev     = regexp.MustCompile(`^[0-9a-f]{40}$`)
)

// parseSpec turns what a user typed into a git URL. It accepts:
//
//	owner/repo, github:owner/repo     GitHub
//	https://…, ssh://…, git://…, file://…
//	user@host:path                    scp-like, as git understands it
//	./path, /path, ~/path             a local repository
//
// each optionally followed by #ref (a branch, tag or commit).
func parseSpec(s string) (Spec, error) {
	raw, ref, _ := strings.Cut(s, "#")
	if raw == "" {
		return Spec{}, fmt.Errorf("empty source %q", s)
	}
	var url string
	switch {
	case strings.HasPrefix(raw, "github:"):
		url = "https://github.com/" + strings.TrimPrefix(raw, "github:")
	case strings.Contains(raw, "://"):
		// Accept Nix's git+https:// spelling too.
		url = strings.TrimPrefix(raw, "git+")
	case strings.HasPrefix(raw, "/"), strings.HasPrefix(raw, "."), strings.HasPrefix(raw, "~"):
		p := raw
		if strings.HasPrefix(p, "~") {
			home, err := os.UserHomeDir()
			if err != nil {
				return Spec{}, err
			}
			p = filepath.Join(home, strings.TrimPrefix(p, "~"))
		}
		abs, err := filepath.Abs(p)
		if err != nil {
			return Spec{}, err
		}
		url = "file://" + abs
	case scpLike.MatchString(raw):
		// Nix only takes URLs, and the lock is shared with it.
		m := scpLike.FindStringSubmatch(raw)
		url = "ssh://" + m[1] + m[2] + "/" + m[3]
	case ghShorthand.MatchString(raw):
		url = "https://github.com/" + raw
	default:
		return Spec{}, fmt.Errorf("%q is not a source; use owner/repo, a git URL or a path", s)
	}
	return Spec{URL: strings.TrimSuffix(url, "/"), Ref: ref}, nil
}

// defaultSourceName names a source after its only skill, or else after its
// repository.
func defaultSourceName(spec Spec, selected []Skill) string {
	if len(selected) == 1 {
		return selected[0].Name
	}
	u := spec.URL
	if i := strings.LastIndexAny(u, "/:"); i >= 0 {
		u = u[i+1:]
	}
	return strings.TrimSuffix(u, ".git")
}