package reconcile

import (
	"context"
	"fmt"
	"sort"
	"strings"
)

// ── The restore-test's space preflight (R-672, agent v0.133.0) ─────────────────────────────────────
//
// MEASURED 2026-09-24 on demo-hp: the scheduled restore-test restored 9201's archive into `local-lvm`
// — the SAME thin pool that holds 9201 — with no free-space check. The pool reached 100 %
// (`out_of_data_space`, `error_if_no_space`), and 9201's rootfs and data volume remounted READ-ONLY.
// Evidence: felhom.eu `documentation/audits/night-2026-09-24/C-02…C-07`, `audits/r672-2026-09-24/`.
//
// THE THREE RULES, all decided here before ANY mutation (before the scratch entry is even journaled):
//  1. SPACE FIRST. The target storage must have free data ≥ restored × factor + reserve (defaults 1.2 and
//     5 GiB, `backup.restore_test_space_factor` / `backup.restore_test_space_reserve_gib`), and a thin
//     pool's metadata must have room for the same share. `restored` is the UNCOMPRESSED size — the
//     archive FILE is the wrong number: 9201's archive was 6.9 GB and its restore wrote 22.6 GB, so
//     "file × 1.2 + 5 GiB" (14.3 GB) would have let the 2026-09-24 test run into a pool with 23 GB free.
//  2. KEEP OFF THE TESTED GUEST'S POOL when another eligible storage (active, takes `rootdir`, and the
//     agent holds Datastore.AllocateSpace on it) passes rule 1. With only one, rule 1 decides.
//  3. UNKNOWN REFUSES. An unreadable size, an unreadable storage or an unknown thin-pool metadata fill is
//     a skip with its reason, never a guess — the fail-safe direction of every guard in this project.
// A refusal is reported to the hub as the test's RESULT ("skipped: …", pass=false), never as a pass.
// Pinned by restoretest_space_test.go.

// RestoreSpace is the preflight's seam onto the host. Production: internal/restorespace.
type RestoreSpace interface {
	// RestoredBytes is how many bytes restoring `archive` will write (uncompressed), and where that
	// figure came from (for the log and the refusal).
	RestoredBytes(ctx context.Context, archive string) (bytes int64, source string, err error)
	// Free reports the storage's free data bytes and, for a thin pool, its metadata-used fraction.
	Free(ctx context.Context, storage string) (StorageFree, error)
	// Eligible lists the storages a restore-test may target: active, content `rootdir`, and the agent
	// holds Datastore.AllocateSpace there.
	Eligible(ctx context.Context) ([]string, error)
}

// StorageFree is one storage's free space as the preflight judges it.
type StorageFree struct {
	AvailBytes int64
	UsedBytes  int64
	Thin       bool
	// MetaUsedFraction is the thin pool's metadata use (0..1); MetaKnown false = could not be read.
	MetaUsedFraction float64
	MetaKnown        bool
}

// SpacePolicy is rule 1's margin.
type SpacePolicy struct {
	Factor       float64 // ≥ 1
	ReserveBytes int64
}

// DefaultSpacePolicy is 1.2 × restored + 5 GiB.
var DefaultSpacePolicy = SpacePolicy{Factor: 1.2, ReserveBytes: 5 << 30}

// SpaceVerdict is the preflight's answer.
type SpaceVerdict struct {
	OK       bool
	Storage  string // the storage the restore goes to (when OK) or was judged (when not)
	Required int64
	Avail    int64
	Reason   string // empty when OK
	// Avoided is the tested guest's own storage, when rule 2 moved the restore off it.
	Avoided string
}

// requiredBytes is rule 1's figure.
func (p SpacePolicy) requiredBytes(restored int64) int64 {
	f := p.Factor
	if f < 1 {
		f = DefaultSpacePolicy.Factor
	}
	return int64(float64(restored)*f) + p.ReserveBytes
}

// fits judges one storage against rule 1 (data AND thin metadata). An unknown metadata fill on a thin
// pool refuses (rule 3).
func fits(fr StorageFree, required int64) (bool, string) {
	if fr.AvailBytes < required {
		return false, fmt.Sprintf("needs %s free, has %s", gib(required), gib(fr.AvailBytes))
	}
	if fr.Thin {
		if !fr.MetaKnown {
			return false, "thin-pool metadata fill unknown"
		}
		// The metadata a restore of `required` bytes needs, in the pool's own proportion of metadata to
		// data. A pool with no data yet has no proportion to read → only the absolute ceiling applies.
		need := 0.0
		if fr.UsedBytes > 0 {
			need = fr.MetaUsedFraction * float64(required) / float64(fr.UsedBytes)
		}
		if fr.MetaUsedFraction+need > 0.9 {
			return false, fmt.Sprintf("thin-pool metadata would reach %.0f%% (now %.0f%%)", 100*(fr.MetaUsedFraction+need), 100*fr.MetaUsedFraction)
		}
	}
	return true, ""
}

func gib(b int64) string { return fmt.Sprintf("%.1f GiB", float64(b)/(1<<30)) }

// sourceStorages returns the storage ids that hold the ARCHIVED guest's volumes (rootfs and every mpN
// that names a `storage:volume`), read from the archive's own embedded config — the guest under test.
// Bind mounts (a leading "/") carry no storage.
func sourceStorages(rawCfg string) map[string]bool {
	out := map[string]bool{}
	for k, v := range archiveCurrentConfig(rawCfg) {
		if k != "rootfs" && !(strings.HasPrefix(k, "mp") && len(k) > 2 && k[2] >= '0' && k[2] <= '9') {
			continue
		}
		vol := strings.TrimSpace(strings.SplitN(strings.TrimSpace(v), ",", 2)[0])
		if vol == "" || strings.HasPrefix(vol, "/") {
			continue
		}
		if st, _, ok := strings.Cut(vol, ":"); ok && st != "" {
			out[st] = true
		}
	}
	return out
}

// PreflightRestoreSpace applies the three rules. `configured` is `backup.restore_storage`.
func PreflightRestoreSpace(ctx context.Context, space RestoreSpace, policy SpacePolicy, archive, rawCfg, configured string) SpaceVerdict {
	if space == nil {
		return SpaceVerdict{Storage: configured, Reason: "no space check is wired — refusing (fail-closed)"}
	}
	restored, src, err := space.RestoredBytes(ctx, archive)
	if err != nil || restored <= 0 {
		return SpaceVerdict{Storage: configured, Reason: fmt.Sprintf("cannot tell how much the restore writes (%v)", err)}
	}
	required := policy.requiredBytes(restored)
	own := sourceStorages(rawCfg)

	// Rule 2: the configured storage holds the guest under test → try the others first.
	var order []string
	avoided := ""
	if own[configured] {
		eligible, eerr := space.Eligible(ctx)
		if eerr == nil {
			sort.Strings(eligible)
			for _, s := range eligible {
				if s != configured && !own[s] {
					order = append(order, s)
				}
			}
		}
		if len(order) > 0 {
			avoided = configured
		}
	}
	order = append(order, configured)

	var last SpaceVerdict
	for _, s := range order {
		fr, ferr := space.Free(ctx, s)
		if ferr != nil {
			last = SpaceVerdict{Storage: s, Required: required, Reason: fmt.Sprintf("cannot read free space on %s (%v)", s, ferr)}
			continue
		}
		ok, why := fits(fr, required)
		v := SpaceVerdict{OK: ok, Storage: s, Required: required, Avail: fr.AvailBytes}
		if ok {
			if s != configured {
				v.Avoided = avoided
			}
			return v
		}
		v.Reason = fmt.Sprintf("not enough space on %s: restoring %s (%s) %s", s, gib(restored), src, why)
		last = v
	}
	return last
}