package delivery

import (
	"encoding/json"
	"fmt"
	"reflect"
	"strings"
	"time"
)

// **The merge turns** (novox/hq ADR 0548 clauses 3 and 4). An approved merge holds a turn on each repository it goes into:
// before it reads the checker's verdicts for the merge, the gate writes one key per repository in its bucket turns, naming
// the deliveries that wait in the order of their Approve, the verdict key each waits for and since when. The gate is the
// key's one writer; the checker is granted to read the bucket, reads it absent as empty, and claims no check of a repository
// a turn names, except the check of the waiting delivery's own heads (TurnHolds). The key goes when the last delivery in it
// merged or left.
const (
	// TurnsBucket is the gate's bucket of merge turns.
	TurnsBucket = GateModule + "_turns"
	// TurnsHistory is the revisions the turns bucket keeps per key.
	TurnsHistory = 5
)

// TurnsKey is the key, in TurnsBucket, of a repository's turn: `<owner>.<name>`, lowercase, each part escaped (EscapeName),
// so the key names the repository the checker's verdicts name as a trunk whatever its case.
func TurnsKey(repository string) (string, error) {
	repository = strings.ToLower(repository)
	if _, err := escapeRepository(repository); err != nil {
		return "", err
	}
	owner, name, _ := strings.Cut(repository, "/")
	return EscapeName(owner) + "." + EscapeName(name), nil
}

// ParseTurnsKey is the inverse of TurnsKey: the repository, lowercase.
func ParseTurnsKey(key string) (string, error) {
	owner, name, ok := strings.Cut(key, ".")
	if !ok || owner == "" || name == "" || strings.Contains(name, ".") {
		return "", fmt.Errorf("delivery: %q is not a turns key, <owner>.<name>", key)
	}
	o, err := UnescapeName(owner)
	if err != nil {
		return "", fmt.Errorf("delivery: %q is not a turns key: %w", key, err)
	}
	n, err := UnescapeName(name)
	if err != nil {
		return "", fmt.Errorf("delivery: %q is not a turns key: %w", key, err)
	}
	repository := o + "/" + n
	if again, err := TurnsKey(repository); err != nil || again != key {
		return "", fmt.Errorf("delivery: %q is not a turns key: it does not name a lowercase <owner>/<name>", key)
	}
	return repository, nil
}

// Turn is the value of a turns key: the repository and the approved deliveries that wait to merge into it, in the order of
// their Approve. A turn with no delivery is no value: its key is deleted.
type Turn struct {
	V          int        `json:"v"`
	Repository string     `json:"repository"`
	Waiting    []TurnWait `json:"waiting"`
}

// TurnWait is one approved delivery in a turn: its group (a lone pull request's branch), the hash of the heads the Approve
// covers (the checker's verdict key's hash, HeadsHash over its members), the Approve's ask key, when it was approved and since
// when it waits; and, while a check of another delivery runs on the repository, that check's verdict key, when the gate saw
// it start, and the step the checker says it is at.
type TurnWait struct {
	Group    string    `json:"group"`
	Heads    string    `json:"heads"`
	Ask      string    `json:"ask,omitempty"`
	Approved time.Time `json:"approved"`
	Since    time.Time `json:"since"`
	// WaitsFor is the verdict key (`<group>.<heads hash>`) of the running check the merge waits for; empty when none runs.
	WaitsFor   string    `json:"waits-for,omitempty"`
	WaitsSince time.Time `json:"waits-since,omitzero"`
	Step       string    `json:"step,omitempty"`
}

func (t Turn) check() error {
	repository := strings.ToLower(t.Repository)
	if repository != t.Repository {
		return fmt.Errorf("delivery: the turn's repository %q is not lowercase", t.Repository)
	}
	if _, err := escapeRepository(repository); err != nil {
		return err
	}
	if len(t.Waiting) == 0 {
		return fmt.Errorf("delivery: the turn of %s names no delivery: its key is deleted instead", t.Repository)
	}
	seen := map[string]bool{}
	for i, w := range t.Waiting {
		if w.Group == "" {
			return fmt.Errorf("delivery: a delivery in the turn of %s names no group", t.Repository)
		}
		if !isHex12(w.Heads) {
			return fmt.Errorf("delivery: the heads hash %q in the turn of %s is not 12 lowercase hex digits", w.Heads, t.Repository)
		}
		if seen[w.Heads] {
			return fmt.Errorf("delivery: the turn of %s names the heads %s twice", t.Repository, w.Heads)
		}
		seen[w.Heads] = true
		if w.Approved.IsZero() || w.Since.IsZero() {
			return fmt.Errorf("delivery: the delivery %s in the turn of %s says no time of its Approve or of its wait", w.Group, t.Repository)
		}
		if i > 0 && w.Approved.Before(t.Waiting[i-1].Approved) {
			return fmt.Errorf("delivery: the turn of %s is not in the order of the Approve: %s was approved before %s", t.Repository, w.Group, t.Waiting[i-1].Group)
		}
		if w.WaitsFor != "" {
			if _, _, err := ParseCheckerVerdictKey(w.WaitsFor); err != nil {
				return fmt.Errorf("delivery: the delivery %s in the turn of %s waits for what is not a verdict key: %w", w.Group, t.Repository, err)
			}
		} else if !w.WaitsSince.IsZero() || w.Step != "" {
			return fmt.Errorf("delivery: the delivery %s in the turn of %s says when and where a check runs, and names no check", w.Group, t.Repository)
		}
	}
	return nil
}

// TurnHolds says whether a turn holds off the check of the heads: it names deliveries, and none of them of these heads. A
// turn never holds the check of heads that wait in it (the carry a waiting merge needs): two approved merges in one turn whose
// trunk moved would otherwise each hold the other's carry, and neither would ever merge (review of ADR 0548's build, round 1).
func TurnHolds(t Turn, heads string) bool {
	if len(t.Waiting) == 0 {
		return false
	}
	for _, w := range t.Waiting {
		if w.Heads == heads {
			return false
		}
	}
	return true
}

// EncodeTurn is t as JSON at Version; it refuses a turn with no delivery, a repository that is not lowercase <owner>/<name>,
// a delivery without its group, heads hash or times, the same heads twice, an order other than the Approve's, and a check
// waited for that is not a verdict key.
func EncodeTurn(t Turn) ([]byte, error) {
	if err := t.check(); err != nil {
		return nil, err
	}
	t.V = Version
	return json.Marshal(t)
}

// DecodeTurn reads a turn; it refuses an unknown version (ErrUnknownVersion) and what EncodeTurn refuses.
func DecodeTurn(data []byte) (Turn, error) {
	var t Turn
	if err := decode(data, &t); err != nil {
		return Turn{}, err
	}
	if err := t.check(); err != nil {
		return Turn{}, err
	}
	return t, nil
}

// SameTurn says whether two turns are the same value, so the gate writes only when they differ.
func SameTurn(a, b Turn) bool {
	if len(a.Waiting) != len(b.Waiting) || a.Repository != b.Repository || a.V != b.V {
		return false
	}
	for i := range a.Waiting {
		x, y := a.Waiting[i], b.Waiting[i]
		if !x.Approved.Equal(y.Approved) || !x.Since.Equal(y.Since) || !x.WaitsSince.Equal(y.WaitsSince) {
			return false
		}
		x.Approved, y.Approved, x.Since, y.Since, x.WaitsSince, y.WaitsSince = time.Time{}, time.Time{}, time.Time{}, time.Time{}, time.Time{}, time.Time{}
		if !reflect.DeepEqual(x, y) {
			return false
		}
	}
	return true
}