package link

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strconv"
	"strings"
	"time"

	"github.com/nats-io/nats.go"
	"github.com/nats-io/nats.go/jetstream"

	"github.com/novox/mesh-controller/internal/broker"
)

// A pull request's check is queued by the pull request (novox/hq ADR 0406 §3, §4, issue 974).

// SupersededByKey is the outcome of a check that stopped because its pull request's key moved on: its head or its trunk
// commit is no longer the one it was asked for. Said as the check's failure, as a kill is; nothing is asked of the forge.
const SupersededByKey = "superseded: the pull request's key moved on"

// unsafeToken is what may not stand in a subject token or a key.
var unsafeToken = strings.NewReplacer(".", "_", "*", "_", ">", "_", " ", "_", "/", "_", "\t", "_", "\n", "_")

// tokenOf is a name as one subject token: any dot, wildcard or space replaced by an underscore.
func tokenOf(name string) string {
	if name == "" {
		return "_"
	}
	return unsafeToken.Replace(name)
}

// PullKeyOf is a pull request's key in mesh-delivery's bucket, and the last tokens of the subject its check is asked on:
// `<owner>.<repo>.<number>`, a dot in a name made an underscore.
func PullKeyOf(owner, repo string, number int) string {
	return tokenOf(owner) + "." + tokenOf(repo) + "." + strconv.Itoa(number)
}

// CheckSubjectOf is the subject a check is asked on, and whether it has one of its own: a check of a pull request on
// the ready queue or the other, by the pull request; a delivery group's composed check by `group.<name>`; any other
// check (a branch tried before its pull request) by its own id, so it replaces nothing.
func CheckSubjectOf(seat string, r BuildRequest) (string, bool) {
	c := r.Check
	if seat != broker.TheBuildSeat || c == nil {
		return "", false
	}
	prefix := broker.CheckSubjectPrefix(seat, c.Ready)
	switch {
	case c.Group != "":
		return prefix + "group." + tokenOf(c.Group), true
	case c.Try || c.Number <= 0:
		return prefix + "try." + tokenOf(r.ID), true
	}
	return prefix + PullKeyOf(c.Owner, c.Repo, c.Number), true
}

// WorkSubjectOf is where an ask is put: a check on the build seat on its own queue, anything else on the seat's.
func WorkSubjectOf(seat string, r BuildRequest) string {
	if subject, ok := CheckSubjectOf(seat, r); ok {
		return subject
	}
	return BuildWorkOf(seat)
}

// PullKey is what mesh-delivery keeps of a pull request (ADR 0406 §4): its head, the trunk commit its current check is
// asked against, and its verdict once judged.
type PullKey struct {
	Head    string `json:"head"`
	Trunk   string `json:"trunk"`
	Verdict string `json:"verdict,omitempty"`
}

// sameCommit says two spellings name one commit; either may be short, but not under twelve characters.
func sameCommit(a, b string) bool {
	return a == b || SameHead(a, b)
}

// Moved says a key no longer holds what a check was asked for: its head or its trunk commit differs.
func (k PullKey) Moved(head, trunk string) bool {
	return !sameCommit(k.Head, head) || (trunk != "" && k.Trunk != "" && !sameCommit(k.Trunk, trunk))
}

// Judged says a key holds the verdict of the check of this head against this trunk commit.
func (k PullKey) Judged(head, trunk string) bool {
	return k.Verdict != "" && sameCommit(k.Head, head) && sameCommit(k.Trunk, trunk) && trunk != ""
}

// ReadPullKey reads a pull request's key from mesh-delivery's bucket: false when it has none.
func ReadPullKey(ctx context.Context, conn *nats.Conn, owner, repo string, number int) (PullKey, bool, error) {
	api, err := jetstream.New(conn)
	if err != nil {
		return PullKey{}, false, err
	}
	kv, err := api.KeyValue(ctx, broker.PullsBucket)
	if err != nil {
		return PullKey{}, false, fmt.Errorf("the pull requests' keys: %w", err)
	}
	e, err := kv.Get(ctx, PullKeyOf(owner, repo, number))
	if errors.Is(err, jetstream.ErrKeyNotFound) {
		return PullKey{}, false, nil
	}
	if err != nil {
		return PullKey{}, false, err
	}
	var key PullKey
	if err := json.Unmarshal(e.Value(), &key); err != nil {
		return PullKey{}, false, fmt.Errorf("the key of %s/%s#%d is not a pull request's: %w", owner, repo, number, err)
	}
	return key, true, nil
}

// WatchPull calls moved once when the pull request's key moves on from what this check was asked for — its head or its
// trunk commit differs — and not for a key that only gains its verdict. It hears updates, not the key as it stands: the
// key and the request are written for one announcement by two writers, so a key found older than the request is not
// a move. The check is then stopped by whoever asked for it, without asking the forge (novox/hq issue 726). The stop
// ends the watch.
func WatchPull(ctx context.Context, conn *nats.Conn, r BuildRequest, moved func(PullKey)) (stop func(), err error) {
	c := r.Check
	if c == nil || c.Group != "" || c.Try || c.Number <= 0 {
		return func() {}, nil
	}
	api, err := jetstream.New(conn)
	if err != nil {
		return nil, err
	}
	kv, err := api.KeyValue(ctx, broker.PullsBucket)
	if err != nil {
		return nil, fmt.Errorf("the pull requests' keys: %w", err)
	}
	watching, end := context.WithCancel(ctx)
	w, err := kv.Watch(watching, PullKeyOf(c.Owner, c.Repo, c.Number), jetstream.UpdatesOnly())
	if err != nil {
		end()
		return nil, err
	}
	go func() {
		defer w.Stop()
		for {
			select {
			case <-watching.Done():
				return
			case e, ok := <-w.Updates():
				if !ok {
					return
				}
				if e == nil || e.Operation() != jetstream.KeyValuePut {
					continue
				}
				var key PullKey
				if json.Unmarshal(e.Value(), &key) != nil {
					continue
				}
				if key.Moved(r.Ref, c.Trunk) {
					moved(key)
					return
				}
			}
		}
	}()
	return end, nil
}

// checkTakeWait is how long a taking loop waits on one queue for an ask that is not there, and takeIdleWait how long it
// waits on the first when all three are empty.
const (
	checkTakeWait = 30 * time.Millisecond
	takeIdleWait  = time.Second
)