package inventory

import (
	"context"
	"encoding/json"
	"strings"

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

// What the artifact store keeps, and what it may let go (novox/hq ADR 0189, issue 108).
//
// The store has never collected anything: every build pushes another layer set and nothing has
// ever removed one. The registry's own answer — collect what no tag names — is wrong here, because
// the mesh pushes each artifact under one moving tag and pins machines by digest, so every build
// but the newest is untagged and some machine may still be running it.
//
// **So the mesh decides, from its own records, and it never has to look in the store to do it.**
// It has never put anything there it did not record, which means every digest it could remove is
// already in a build row. A digest the mesh did not record making is therefore never named here —
// not as a safety margin but as the rule restated, and it is what keeps the sweep away from the
// images genesis pushed before any record existed (04-ISSUES/102, F4).

// KeptBuilds is how many successful builds of each module keep their artifacts, counting the
// newest. The newest is what the mesh hands a machine now; the four behind it are how far back a
// release that turns out wrong can be taken.
const KeptBuilds = 5

// ToCollect is every artifact the mesh made, no longer keeps, and has not already collected.
//
// Three reasons an artifact stays, and nothing else is a reason:
//
//   - **a definition names it** — the reference appears in a module's recorded manifest, which is
//     what the mesh would hand a machine now. No age limit: this is the floor;
//   - **the mesh can still go back to it** — it is an artifact of one of the KeptBuilds most
//     recent successful builds of its module;
//   - it was already collected, in which case there is nothing left to do.
//
// Returned in a stated order so two runs over the same records ask for the same things in the
// same sequence, which is what makes a failed sweep safe to simply run again.
func (i *Inventory) ToCollect(ctx context.Context) ([]string, error) {
	keep, err := i.keptReferences(ctx)
	if err != nil {
		return nil, err
	}
	rows, err := i.store.Pool().Query(ctx,
		// Every artifact of every successful build, oldest first, minus what has already been
		// collected. A failed build published nothing, so it names nothing to remove.
		`select b.made
		   from build b
		  where b.failed = '' and b.module is not null and b.module <> ''
		  order by b.at asc, b.id asc`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	collected, err := i.alreadyCollected(ctx)
	if err != nil {
		return nil, err
	}
	seen := map[string]bool{}
	var out []string
	for rows.Next() {
		var raw []byte
		if err := rows.Scan(&raw); err != nil {
			return nil, err
		}
		var made []Artifact
		if err := json.Unmarshal(raw, &made); err != nil {
			// One unreadable record must not stop the rest being collected — and an artifact this
			// row named is simply not offered, which errs toward keeping.
			continue
		}
		for _, a := range made {
			reference := asRecorded(a.Reference)
			if reference == "" || keep[reference] || collected[reference] || seen[reference] {
				continue
			}
			seen[reference] = true
			out = append(out, reference)
		}
	}
	return out, rows.Err()
}

// keptReferences is every artifact reference the mesh still keeps, for either of the two reasons.
func (i *Inventory) keptReferences(ctx context.Context) (map[string]bool, error) {
	keep := map[string]bool{}

	// **Whatever a definition the mesh holds names.** Read as text rather than by walking the
	// resource shapes: a reference may be a container's image, a bundle's source, or a field some
	// later kind of resource grows, and what matters is only whether the mesh could hand this
	// string to a machine. A manifest that mentions it is a manifest that might.
	manifests, err := i.store.Pool().Query(ctx, `select manifest::text from module where manifest is not null`)
	if err != nil {
		return nil, err
	}
	defer manifests.Close()
	var named []string
	for manifests.Next() {
		var text string
		if err := manifests.Scan(&text); err != nil {
			return nil, err
		}
		named = append(named, text)
	}
	if err := manifests.Err(); err != nil {
		return nil, err
	}

	// The KeptBuilds most recent successful builds of each module, whole.
	recent, err := i.store.Pool().Query(ctx,
		`select made from (
		    select made, row_number() over (partition by module order by at desc, id desc) as back
		      from build
		     where failed = '' and module is not null and module <> ''
		 ) ranked where back <= $1`, KeptBuilds)
	if err != nil {
		return nil, err
	}
	defer recent.Close()
	for recent.Next() {
		var raw []byte
		if err := recent.Scan(&raw); err != nil {
			return nil, err
		}
		var made []Artifact
		if err := json.Unmarshal(raw, &made); err != nil {
			continue
		}
		for _, a := range made {
			if reference := asRecorded(a.Reference); reference != "" {
				keep[reference] = true
			}
		}
	}
	if err := recent.Err(); err != nil {
		return nil, err
	}

	// And anything a manifest mentions. Done after the recent set so the scan runs over the
	// candidates rather than over every reference ever recorded: a manifest holds a reference
	// composed with the store's address or kept bare, so the search is for the digest within it.
	if len(named) > 0 {
		all, err := i.everyReferenceMade(ctx)
		if err != nil {
			return nil, err
		}
		for _, reference := range all {
			if keep[reference] {
				continue
			}
			digest := digestIn(reference)
			if digest == "" {
				// Not something the store holds by digest; nothing here can speak for it, so it
				// is kept rather than guessed about.
				keep[reference] = true
				continue
			}
			for _, text := range named {
				if strings.Contains(text, digest) {
					keep[reference] = true
					break
				}
			}
		}
	}
	return keep, nil
}

// everyReferenceMade is every artifact reference any successful build recorded.
func (i *Inventory) everyReferenceMade(ctx context.Context) ([]string, error) {
	rows, err := i.store.Pool().Query(ctx,
		`select made from build where failed = '' and module is not null and module <> ''`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	seen := map[string]bool{}
	var out []string
	for rows.Next() {
		var raw []byte
		if err := rows.Scan(&raw); err != nil {
			return nil, err
		}
		var made []Artifact
		if err := json.Unmarshal(raw, &made); err != nil {
			continue
		}
		for _, a := range made {
			reference := asRecorded(a.Reference)
			if reference == "" || seen[reference] {
				continue
			}
			seen[reference] = true
			out = append(out, reference)
		}
	}
	return out, rows.Err()
}

// asRecorded is an artifact reference in the one vocabulary the sweep speaks (novox/hq issue 226).
//
// **Every reference here came from a build record, so every one of them is the mesh's own.** That
// is what makes it safe to normalise: references kept before the store's address stopped being
// written are `<host>:<port>/<path>@sha256:…` (04-ISSUES/102), and `Recorded` reads those as the
// `artifact-store://` references the rest of the mesh uses. Done here rather than when the store
// is asked, because `Recorded` cannot tell one registry host from another — only the provenance
// can, and the provenance is here.
//
// The oldest artifacts are exactly the ones recorded the old way, and exactly the ones a
// sweep reaches first. Untranslated, the first of them ended every sweep.
func asRecorded(reference string) string {
	if reference == "" {
		return ""
	}
	return catalogue.Recorded(reference)
}

// digestIn is the `sha256:<hex>` a reference names, empty when it names none.
func digestIn(reference string) string {
	for _, marker := range []string{"@sha256:", "/sha256:"} {
		if _, after, ok := strings.Cut(reference, marker); ok {
			return "sha256:" + after
		}
	}
	return ""
}

// alreadyCollected is what the store has already been asked to let go.
func (i *Inventory) alreadyCollected(ctx context.Context) (map[string]bool, error) {
	rows, err := i.store.Pool().Query(ctx, `select reference from artifact_collected`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := map[string]bool{}
	for rows.Next() {
		var reference string
		if err := rows.Scan(&reference); err != nil {
			return nil, err
		}
		out[reference] = true
	}
	return out, rows.Err()
}

// MarkCollected records that the store no longer holds these.
//
// **A store that answered "not found" is recorded too.** The outcome wanted is that the artifact
// is gone, and it is; retrying it every sweep for ever is the failure this table exists to
// prevent. Only a store that could not be reached, or refused, leaves a reference unmarked — and
// then the next sweep asks again, which is what should happen.
func (i *Inventory) MarkCollected(ctx context.Context, references []string) error {
	for _, reference := range references {
		if _, err := i.store.Pool().Exec(ctx,
			`insert into artifact_collected (reference) values ($1) on conflict (reference) do nothing`,
			reference); err != nil {
			return err
		}
	}
	return nil
}