package main

import (
	"context"
	"fmt"
	"sort"

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

// A recorded build reaches a machine only by a person's push (novox/hq issue 295, ADR 0245).
//
// **A send carries the machine's whole declaration** (ADR 0221), composed from the build the mesh holds
// of every module on it. A module whose upgrade policy records — postgres, mongodb, keycloak, the
// network path — has its new build registered at its merge and sent nowhere, "until a person pushes".
// But every other send to its machine composed it too: on 2026-10-07 a catalogue merge adopting the
// images' health checks rebuilt postgres and mongodb with the rest, and the plan's gated send to the
// control node for mail — and to the anchor for the spreadsheet app — carried both, recreating the
// providers every consumer on those machines drops with. No gate judged them (the gate judges only what
// rolls out), and nobody had pushed.
//
// So **every send but a person's push composes a recorded module at the build its machine was last
// sent**: the manifest of that build, from the build records, in place of the one the mesh holds. The
// machine runs what it ran; the send records that it still carries that build; `status` keeps saying
// the machine is behind, and `push <node>` — a person's word — sends the new one. The bus step is a
// person's too, and carries the bus; any other recorded module waiting on the bus's machine stays.
//
// A recorded module the machine was never sent (a new assignment) is composed as the mesh holds it —
// there is nothing running to keep. One whose kept build is no longer in the records refuses the send,
// said: composing the new build would be the very move this exists to stop.

type keepRecordedKey struct{}

// sendKeeps is the context a send that is not a person's push composes under: every recorded module
// kept at the build its machine runs — except, on the bus step, the bus.
func sendKeeps(ctx context.Context, inv *inventory.Inventory) (context.Context, error) {
	if !busStepSending(ctx) {
		return keepingRecorded(ctx), nil
	}
	bus, err := pendingBus(ctx, inv)
	if err != nil {
		return nil, err
	}
	return keepingRecorded(ctx, bus.module), nil
}

// keepingRecorded is a context whose sends compose every recorded module at the build its machine runs,
// except the modules named (the bus, on the bus step).
func keepingRecorded(ctx context.Context, except ...string) context.Context {
	skip := map[string]bool{}
	for _, m := range except {
		skip[m] = true
	}
	return context.WithValue(ctx, keepRecordedKey{}, skip)
}

// keptExcept is whether this context keeps recorded modules, and the modules it lets move.
func keptExcept(ctx context.Context) (map[string]bool, bool) {
	skip, on := ctx.Value(keepRecordedKey{}).(map[string]bool)
	return skip, on
}

// recordedKept is, for a send under keepingRecorded, every recorded module the machine was last sent a
// build of that the mesh's build is not identical to: module → the commit it keeps. Nil when the context
// keeps nothing, or when what the machine was last sent is not known (it is then held whole elsewhere —
// ADR 0221).
func recordedKept(ctx context.Context, open *stores, node string) (map[string]string, error) {
	skip, on := keptExcept(ctx)
	if !on {
		return nil, nil
	}
	inv := open.inventory
	sent, known, err := inv.SentBuilds(ctx, node)
	if err != nil || !known {
		return nil, err
	}
	current, err := inv.CurrentBuilds(ctx)
	if err != nil {
		return nil, err
	}
	var f *moveFacts
	out := map[string]string{}
	for m, was := range sent {
		now, held := current[m]
		if !held || now.RollOut || skip[m] || was == "" || sameCommit(was, now.Commit) {
			continue
		}
		if f == nil {
			read, err := readMoveFacts(ctx, inv)
			if err != nil {
				return nil, err
			}
			f = &read
		}
		if f.identical(m, was, now.Commit) {
			continue
		}
		out[m] = was
	}
	return out, nil
}

// keepRecorded puts, in a shelf about to be resolved for a machine, the build each recorded module there
// runs in place of the one the mesh holds; it answers what it kept, module → commit.
func keepRecorded(ctx context.Context, open *stores, node string, shelf map[string]catalogue.Manifest) (map[string]string, error) {
	kept, err := recordedKept(ctx, open, node)
	if err != nil || len(kept) == 0 {
		return nil, err
	}
	names := make([]string, 0, len(kept))
	for m := range kept {
		names = append(names, m)
	}
	sort.Strings(names)
	for _, m := range names {
		ran, found, err := open.inventory.ManifestAt(ctx, m, kept[m])
		if err != nil {
			return nil, err
		}
		if !found {
			return nil, fmt.Errorf("%s records rather than rolls out, and %s runs its build %s, which the build "+
				"records no longer hold: this send cannot keep it and does not move it — `push %s` sends the new "+
				"one on a person's word (novox/hq ADR 0245)", m, node, short(kept[m]), node)
		}
		shelf[m] = ran
	}
	return kept, nil
}