package wire

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
)

// Repo is one repository, spelled the way a tracker spells it.
type Repo struct {
	Owner string
	Name  string
}

func (r Repo) String() string {
	if r.Zero() {
		return ""
	}
	return r.Owner + "/" + r.Name
}

// Zero reports whether this names no repository. Both halves are required:
// half a name addresses nothing.
func (r Repo) Zero() bool { return r.Owner == "" || r.Name == "" }

// ParseRepo reads owner/name.
func ParseRepo(s string) (Repo, error) {
	owner, name, ok := strings.Cut(strings.TrimSpace(s), "/")
	if !ok || owner == "" || name == "" {
		return Repo{}, fmt.Errorf("repo %q is not owner/name", s)
	}
	return Repo{Owner: owner, Name: name}, nil
}

// Key is a stable cross-repo handle for one issue: owner/repo#42.
//
// It is what the ledger is keyed by and what the `gitea:` metadata field holds,
// so it has to survive being written to a file and read back — which is why it
// is a repository and a number and not a bare number. A number is ambiguous the
// moment a dependency lives in another repository, and dependencies are allowed
// to.
type Key struct {
	// Repo is zero when the caller named a number and nothing else, which is
	// the common case on a command line: "42" means "42 in this project's
	// repository", and which repository that is, is the client's business.
	Repo   Repo
	Number int
}

func (k Key) String() string {
	if k.Repo.Zero() {
		return "#" + strconv.Itoa(k.Number)
	}
	return fmt.Sprintf("%s#%d", k.Repo, k.Number)
}

// In returns this key with r filled in when it names no repository of its own.
func (k Key) In(r Repo) Key {
	if k.Repo.Zero() {
		k.Repo = r
	}
	return k
}

// The four spellings, as patterns.
//
// Digits and only digits after the `#`, which is the test strconv.Atoi is too
// generous to make on its own: it accepts a sign, and `owner/repo#-3` is not a
// handle anybody ever wrote. Anything that is not a key has to be recognizable
// as not a key — a hand-edited metadata line and a number are told apart here
// and nowhere else.
var (
	keyURL       = regexp.MustCompile(`^https?://[^/]+/([^/]+)/([^/]+)/issues/(\d+)/?$`)
	keyQualified = regexp.MustCompile(`^([\w.-]+/[\w.-]+)#(\d+)$`)
	keyNumber    = regexp.MustCompile(`^#?(\d+)$`)
)

// ParseKey reads an issue key: 42, #42, owner/repo#42, or the issue's URL.
//
// All four spellings because all four are what somebody has in hand — a number
// from a receipt, a `#42` copied out of a body, a qualified key out of the
// ledger, a URL pasted from a browser. Refusing three of them buys nothing.
func ParseKey(s string) (Key, error) {
	s = strings.TrimSpace(s)
	if m := keyURL.FindStringSubmatch(s); m != nil {
		n, _ := strconv.Atoi(m[3])
		return Key{Repo: Repo{Owner: m[1], Name: m[2]}, Number: n}, nil
	}
	if m := keyQualified.FindStringSubmatch(s); m != nil {
		repo, err := ParseRepo(m[1])
		if err != nil {
			return Key{}, err
		}
		n, _ := strconv.Atoi(m[2])
		return Key{Repo: repo, Number: n}, nil
	}
	if m := keyNumber.FindStringSubmatch(s); m != nil {
		n, _ := strconv.Atoi(m[1])
		return Key{Number: n}, nil
	}
	return Key{}, fmt.Errorf("cannot parse issue key %q — want 42, #42, owner/repo#42, or an issue URL", s)
}