package frombus

// **The bus read through a module's declared `reads`** (the lead, 2026-10-29: one reader in place of the copies in
// mesh-provisioner and disk-load): a Reader over the states a module reads, by a runtime's Get and Keys (a bundle's
// stdio.State, a process's own), for a holder that composes plans or data items and reads no value: placement, each
// node's record in its own have key, the indexer's modules and manifests, the builder's builds and mesh-config's resolved
// values. No own secret and no credential is read (compose.Planning). Pure as the rest of this package: a bundle's
// runtime states and an HTTP fetch are compose/fromruntime's.

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"strings"
	"time"

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

// The states a module names in its manifest's `reads` to compose through StatesReader.
const (
	PlacementRead = delivery.PlacementRead
	ModulesRead   = delivery.IndexerModule + ".modules"
	ManifestsRead = delivery.IndexerModule + ".manifests"
	BuildsRead    = delivery.BuilderModule + ".builds"
	HaveRead      = "node-engine.have"
	ResolvedRead  = "mesh-config.resolved"
)

// StatesReads are those reads, in a manifest's order.
var StatesReads = []string{PlacementRead, ModulesRead, ManifestsRead, BuildsRead, HaveRead, ResolvedRead}

// States is a module's read states as its runtime gives them: a key's value, false when it has none.
type States interface {
	Get(state, key string) (value []byte, found bool, err error)
	Keys(state string) ([]string, error)
}

// Fetch reads an archive at a URL (fromruntime.HTTPFetch over HTTP).
type Fetch func(ctx context.Context, url string) ([]byte, error)

// StatesReader is the Reader over s; fetch reads a templates archive, nil for a holder that reads none.
func StatesReader(s States, fetch Fetch) Reader { return statesReader{s: s, fetch: fetch} }

type statesReader struct {
	s     States
	fetch Fetch
}

func (r statesReader) each(read string, visit func(key string, value []byte)) error {
	keys, err := r.s.Keys(read)
	if err != nil {
		return fmt.Errorf("%s: %w", read, err)
	}
	for _, k := range keys {
		v, found, err := r.s.Get(read, k)
		if err != nil {
			return fmt.Errorf("%s %s: %w", read, k, err)
		}
		if found {
			visit(k, v)
		}
	}
	return nil
}

func (r statesReader) Placements(context.Context) (map[string]delivery.Placement, error) {
	keys := delivery.NewPlacementKeys()
	err := r.each(PlacementRead, func(k string, v []byte) {
		_, _ = keys.Put(k, v, 0, false) // a key that does not read places nothing, as before
	})
	return keys.All(), err
}

func (r statesReader) Records(context.Context) (map[string]delivery.NodeRecord, error) {
	out := map[string]delivery.NodeRecord{}
	err := r.each(HaveRead, func(k string, v []byte) {
		if node, _, isNode, err := delivery.ParseHaveKey(k); err == nil && isNode {
			if h, err := delivery.DecodeHaveNode(v); err == nil && h.Record != nil {
				out[node] = *h.Record
			}
		}
	})
	return out, err
}

func (r statesReader) Modules(context.Context) (map[string]delivery.Module, error) {
	out := map[string]delivery.Module{}
	err := r.each(ModulesRead, func(k string, v []byte) {
		if module, err := delivery.ParseModulesKey(k); err == nil {
			if m, err := delivery.DecodeModule(v); err == nil {
				out[module] = m
			}
		}
	})
	return out, err
}

func (r statesReader) Manifest(_ context.Context, digest string) ([]byte, error) {
	key, err := delivery.ManifestsKey(digest)
	if err != nil {
		return nil, err
	}
	v, found, err := r.s.Get(ManifestsRead, key)
	if err != nil {
		return nil, err
	}
	if !found {
		return nil, fmt.Errorf("the indexer holds no manifest %s", digest)
	}
	m, err := delivery.DecodeManifest(v)
	if err != nil {
		return nil, err
	}
	return []byte(m.JSON), nil
}

func (r statesReader) Values(_ context.Context, node, module string) (map[string]any, error) {
	var out map[string]any
	prefix := node + "." + module + "."
	err := r.each(ResolvedRead, func(k string, v []byte) {
		name, ok := strings.CutPrefix(k, prefix)
		if !ok || strings.Contains(name, ".") {
			return
		}
		if value, laid := catalogue.LaidValue(v); laid {
			if out == nil {
				out = map[string]any{}
			}
			out[name] = value
		}
	})
	return out, err
}

func (statesReader) OwnSecrets(context.Context, string) ([]compose.OwnSecretRow, error) {
	return nil, nil
}

func (statesReader) Credentials(context.Context, string, []compose.CredentialKey, []compose.CredentialKey) ([]compose.Credential, []compose.Issued, error) {
	return nil, nil, nil
}

func (r statesReader) Build(_ context.Context, module, fp string) (*delivery.BuilderBuild, error) {
	key, err := delivery.BuilderBuildKey(module, fp)
	if err != nil {
		return nil, err
	}
	v, found, err := r.s.Get(BuildsRead, key)
	if err != nil || !found {
		return nil, err
	}
	b, err := delivery.DecodeBuilderBuild(v)
	if err != nil {
		return nil, err
	}
	return &b, nil
}

// archiveWithin bounds one read of a templates archive.
const archiveWithin = 30 * time.Second

func (r statesReader) Archive(ctx context.Context, url, digest string) ([]byte, error) {
	if r.fetch == nil {
		return nil, fmt.Errorf("this holder reads no archive (%s)", url)
	}
	fetching, cancel := context.WithTimeout(ctx, archiveWithin)
	defer cancel()
	body, err := r.fetch(fetching, url)
	if err != nil {
		return nil, err
	}
	sum := sha256.Sum256(body)
	if got := hex.EncodeToString(sum[:]); got != strings.TrimPrefix(digest, "sha256:") {
		return nil, fmt.Errorf("%s was recorded as %s and what arrived is %s", url, digest, got)
	}
	return body, nil
}

func (r statesReader) Served(ctx context.Context, node, module string, keys []string) (map[string]any, error) {
	all, err := r.Values(ctx, node, module)
	var out map[string]any
	for _, k := range keys {
		if v, ok := all[k]; ok {
			if out == nil {
				out = map[string]any{}
			}
			out[k] = v
		}
	}
	return out, err
}