package database

import (
	"math"
	"strconv"
	"time"

	"gorm.io/gorm"
)

const (
	// DefaultRetentionDays is the event retention period applied to a
	// webhook created without an explicit retention value. It is the
	// single source of truth for that policy and must stay in sync
	// with the `gorm:"default:30"` column default on
	// Webhook.RetentionDays below; a struct tag cannot reference a
	// constant, so a test asserts the two agree.
	DefaultRetentionDays = 30

	// RetentionForeverDays is the sentinel RetentionDays value meaning
	// "retain events forever". Users express that intent as 0, which
	// Webhook.BeforeSave rewrites to this value: the column default
	// substitutes DefaultRetentionDays for a zero value at insert
	// time, so a zero can never survive a round trip to the database.
	// Nothing outside this file may hardcode the number.
	RetentionForeverDays = 365 * 1000

	// MaxFiniteRetentionDays is the largest finite retention period the
	// reaper's cutoff arithmetic can represent, and therefore the
	// largest one a caller may request. It is derived from that
	// arithmetic rather than picked: retentionCutoff computes
	// retentionDays * hoursPerDay * time.Hour, and a time.Duration is
	// an int64 nanosecond count, so math.MaxInt64 nanoseconds divided
	// by an hour and then by a day is the exact ceiling — 106751 days,
	// a little over 292 years.
	//
	// One day more overflows int64, wraps the product negative, and
	// turns the cutoff into a timestamp in the far future that matches
	// every row in the webhook's database. That is why this bound is
	// enforced on input and why retentionCutoff saturates underneath
	// it. Note that RetentionForeverDays deliberately sits above this
	// ceiling: such webhooks are skipped before any cutoff is
	// computed, and never reach the arithmetic at all.
	MaxFiniteRetentionDays = int(
		math.MaxInt64 / int64(time.Hour) / hoursPerDay,
	)
)

// Webhook represents a webhook processing unit that groups entrypoints and targets
//
// Every method below takes a pointer receiver. BeforeSave has to,
// because it mutates the record and GORM only invokes hooks declared
// that way; the display helpers follow suit so the receiver kinds do
// not mix. Handlers therefore put a *Webhook into template data:
// html/template cannot call a pointer method on a value held in a map,
// because a map element is not addressable.
type Webhook struct {
	BaseModel

	UserID      string `gorm:"type:uuid;not null" json:"userId"`
	Name        string `gorm:"not null"           json:"name"`
	Description string `json:"description"`

	// RetentionDays is the number of days to retain events. A value of
	// RetentionForeverDays means retain forever. The column default
	// must equal DefaultRetentionDays.
	RetentionDays int `gorm:"default:30" json:"retentionDays"`

	// Relations
	User        User         `json:"user,omitzero"`
	Entrypoints []Entrypoint `json:"entrypoints,omitempty"`
	Targets     []Target     `json:"targets,omitempty"`
}

// BeforeSave normalises RetentionDays on every insert and update. A
// non-positive value is the user's way of asking for "retain forever",
// which is stored as the RetentionForeverDays sentinel.
//
// This has to happen in a hook rather than at the call sites. GORM
// substitutes the column default (DefaultRetentionDays) for a zero
// value while building the insert statement, which runs after
// BeforeSave; rewriting any later than this loses that race and the
// row lands at 30 days. Living on the model also means a future call
// site — a REST API, a fixture, a migration — cannot bypass it.
func (w *Webhook) BeforeSave(_ *gorm.DB) error {
	if w.RetentionDays <= 0 {
		w.RetentionDays = RetentionForeverDays
	}

	return nil
}

// retainsForever reports whether a stored RetentionDays value means
// "keep events indefinitely". It is the single definition of that
// question, shared by Webhook.RetainsForever and by the reaper's
// cutoff computation so the two cannot disagree about which webhooks
// are exempt from reaping.
//
// It accepts the RetentionForeverDays sentinel written by BeforeSave
// and, defensively, the non-positive values that rows written before
// the sentinel existed may still carry.
func retainsForever(retentionDays int) bool {
	return retentionDays <= 0 ||
		retentionDays >= RetentionForeverDays
}

// RetainsForever reports whether this webhook's events are kept
// indefinitely.
func (w *Webhook) RetainsForever() bool {
	return retainsForever(w.RetentionDays)
}

// RetentionLabel returns the webhook's retention policy as display
// text, so that no template has to know about the sentinel value.
func (w *Webhook) RetentionLabel() string {
	if w.RetainsForever() {
		return "forever"
	}

	if w.RetentionDays == 1 {
		return "1 day"
	}

	return strconv.Itoa(w.RetentionDays) + " days"
}