package health

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

	"git.novox.be/novox/mesh-sdk/go/catalogue"
)

// **Disk usage readings and peaks per data item** (novox/hq ADR 0571 clause 3, ADR 0233 §21, §27, §34): disk-load, on every
// node, measures each data item the modules of its node declare (catalogue.PlacedDataItem, from compose/frombus.DataItems)
// and keeps the newest reading and the item's largest size in seven days as its own state `readings`, one key
// `<node>.<module>.<item>`, written only when it changes. The node-backup holder, mounts, nfs-server and the self-check's
// probes read it there; the controller keeps none of it. Moved here from mesh-catalog modules/disk-load (b4c237d2).
const (
	DiskLoadModule = "disk-load"
	ReadingsState  = "readings"
	ReadingsBucket = DiskLoadModule + "_" + ReadingsState
	ReadingsRead   = DiskLoadModule + "." + ReadingsState
)

// ReadingVersion is the version of a reading's layout.
const ReadingVersion = 1

// PeakWindow is how far back the peak looks (ADR 0233 §34).
const PeakWindow = 7 * 24 * time.Hour

// Redundancy is the redundant storage an item is on, as read: zfs, md or btrfs, its pool, array or filesystem, and its
// health (nil when it could not be read).
type Redundancy struct {
	Kind    string `json:"kind"`
	Where   string `json:"where"`
	Healthy *bool  `json:"healthy"`
	Said    string `json:"said"`
}

// Measured is what one measurement found. Precision says what the size is: "exact", "dataset <name>: its whole size",
// "partial: ..." (a lower bound, never compared), or "no size: ...".
type Measured struct {
	SizeBytes  *int64      `json:"size_bytes,omitempty"`
	LastWrite  *time.Time  `json:"last_write,omitempty"`
	MeasuredAt *time.Time  `json:"measured_at,omitempty"`
	Precision  string      `json:"precision,omitempty"`
	Error      string      `json:"error,omitempty"`
	Redundancy *Redundancy `json:"redundancy,omitempty"`
}

// Partial says the size is only a lower bound, which a peak is never made of.
func (m Measured) Partial() bool { return strings.HasPrefix(m.Precision, "partial") }

// DaySize is the largest size measured on one UTC day.
type DaySize struct {
	Day   string `json:"day"`
	Bytes int64  `json:"bytes"`
}

// Reading is the value of one key: the item as placed, what was measured, and the largest size in the seven days up to
// it (Peak, measured on PeakAt), read from the day maxima Days.
type Reading struct {
	V    int    `json:"v"`
	Node string `json:"node"`
	catalogue.PlacedDataItem
	Measured
	Peak   *int64    `json:"peak_bytes,omitempty"`
	PeakAt string    `json:"peak_day,omitempty"`
	Days   []DaySize `json:"days,omitempty"`
	// FirstSeen is when the item was first measured on this node, kept by every reading after; RetiredAt and RetiredWhy
	// say its module left the node, written by whoever retires it and carried on unchanged. Each is left out while zero,
	// so a reading written before reads as it did.
	FirstSeen  time.Time `json:"first_seen,omitzero"`
	RetiredAt  time.Time `json:"retired_at,omitzero"`
	RetiredWhy string    `json:"retired_why,omitempty"`
}

// ReadingKey is the key of an item on a node: `<node>.<module>.<item>`.
func ReadingKey(node, module, item string) string { return node + "." + module + "." + item }

// DecodeReading reads a key's value; it refuses another version.
func DecodeReading(raw []byte) (Reading, error) {
	var r Reading
	if err := json.Unmarshal(raw, &r); err != nil {
		return Reading{}, fmt.Errorf("health: a reading is not readable: %w", err)
	}
	if r.V != ReadingVersion {
		return Reading{}, fmt.Errorf("health: a reading of version %d, and this reads %d", r.V, ReadingVersion)
	}
	return r, nil
}

// NextReading is the reading after a measurement, and whether it differs from the one before in anything but the time it
// was taken: a reading that did not change is not written. A measurement with no size (an error, a shallow item) carries
// the last size's days on, so the peak outlives one failed measurement.
func NextReading(prev *Reading, node string, it catalogue.PlacedDataItem, m Measured, now time.Time) (Reading, bool) {
	r := Reading{V: ReadingVersion, Node: node, PlacedDataItem: it, Measured: m, FirstSeen: now.UTC()}
	var days []DaySize
	if prev != nil {
		days = prev.Days
		r.RetiredAt, r.RetiredWhy = prev.RetiredAt, prev.RetiredWhy
		if !prev.FirstSeen.IsZero() {
			r.FirstSeen = prev.FirstSeen
		}
	}
	today := now.UTC().Format("2006-01-02")
	cut := now.UTC().Add(-PeakWindow).Format("2006-01-02")
	var kept []DaySize
	todays := int64(-1)
	for _, d := range days {
		switch {
		case d.Day == today:
			todays = d.Bytes
		case d.Day >= cut:
			kept = append(kept, d)
		}
	}
	if m.SizeBytes != nil && !m.Partial() && *m.SizeBytes > todays {
		todays = *m.SizeBytes
	}
	if todays >= 0 {
		kept = append(kept, DaySize{Day: today, Bytes: todays})
	}
	r.Days = kept
	for _, d := range kept {
		if r.Peak == nil || d.Bytes >= *r.Peak {
			b := d.Bytes
			r.Peak, r.PeakAt = &b, d.Day
		}
	}
	if prev == nil {
		return r, true
	}
	a, b := *prev, r
	a.MeasuredAt, b.MeasuredAt = nil, nil
	return r, !reflect.DeepEqual(a, b)
}

// **Each item's last good night** (novox/hq ADR 0571 clause 3, ADR 0564 §6; the lead, 2026-10-29): the node-backup holder
// restic keeps, from its tools bundle through the runtime on the night's file event (its night's process runs as the
// operator's account and holds no bus account, ADR 0436 §1-2), its own state `good`, one key `<node>.<module>.<item>` for every item a module
// declares that a backup path covers, written when it changes: the item, the path whose snapshot keeps it and the newest
// good night of its module (zero before the first). The self-check's probe of a stale backup reads it there. Moved here
// from mesh-catalog modules/restic (e5ef3bed).
const (
	ResticModule = "restic"
	GoodState    = "good"
	GoodBucket   = ResticModule + "_" + GoodState
	GoodRead     = ResticModule + "." + GoodState
	GoodVersion  = 1
)

// GoodRow is one key of restic's `good`.
type GoodRow struct {
	V         int       `json:"v"`
	Node      string    `json:"node"`
	Module    string    `json:"module"`
	Item      string    `json:"item"`
	CoveredBy string    `json:"covered_by"`
	LastGood  time.Time `json:"last_good,omitzero"`
}

// GoodKey is a row's key: `<node>.<module>.<item>`, as a reading's.
func GoodKey(node, module, item string) string { return ReadingKey(node, module, item) }

// DecodeGoodRow reads a row; it refuses another version.
func DecodeGoodRow(raw []byte) (GoodRow, error) {
	var g GoodRow
	if err := json.Unmarshal(raw, &g); err != nil {
		return GoodRow{}, fmt.Errorf("health: a last good night is not readable: %w", err)
	}
	if g.V != GoodVersion {
		return GoodRow{}, fmt.Errorf("health: a last good night of version %d, and this reads %d", g.V, GoodVersion)
	}
	return g, nil
}