package runtime

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"sync"

	"github.com/novox/mesh-tools/node-tools/internal/bus"
)

// A module's code reads its values at runtime (novox/hq ADR 0349 clause 14 as ADR 0370 changes it, issue 685).
//
// A bundle asks `mesh/provision.get` and `mesh/provision.watch` with `{kind, key}`; the runtime asks its machine's
// provisioner client **as the module whose bundle asks** — the module this bus was made for, from the bundle it
// launched, never a name the bundle sent (ADR 0370 §4) — and hands the answer back. A watch hands the current value
// first and then each change: the client says which value moved, and the runtime asks again. A secret is refused
// here, with the reason, and never asked: the client serves no secret on the tool runner's word (§2), and a module
// under an account of its own asks the vault itself, which waits on issue 569.

// The kinds a bundle may ask.
const (
	provisionConfig = "config"
	provisionBound  = "bound"
	provisionSecret = "secret"
)

// provisionAsked is what a bundle names. Anything else it sends, a module's name among it, is not read.
type provisionAsked struct {
	Kind string `json:"kind"`
	Key  string `json:"key"`
}

// ProvisionChange is what a watch hands a bundle: the value, or, when it is no longer answered, why.
type ProvisionChange struct {
	Kind  string          `json:"kind"`
	Key   string          `json:"key"`
	Value json.RawMessage `json:"value,omitempty"`
	// Refused is why the value is no longer answered: the module taken off the machine, the key no longer declared.
	Refused string `json:"refused,omitempty"`
}

func readProvisionAsked(verb string, params json.RawMessage) (provisionAsked, error) {
	var asked provisionAsked
	if err := json.Unmarshal(params, &asked); err != nil || asked.Kind == "" || asked.Key == "" {
		return asked, fmt.Errorf("mesh/provision.%s names no value: {kind, key}", verb)
	}
	switch asked.Kind {
	case provisionConfig, provisionBound:
		return asked, nil
	case provisionSecret:
		return asked, fmt.Errorf("the secret %s is not asked for at runtime while the module's code runs in the "+
			"tool runner: the vault hands a secret only to a caller the bus proves, and the bus proves only the tool "+
			"runner here (novox/hq ADR 0370 §2, ADR 0349 §11); the module's secrets reach it through its files, "+
			"until it runs under a bus account of its own (issue 569)", asked.Key)
	}
	return asked, fmt.Errorf("mesh/provision.%s: %q is not a kind of value a module reads at runtime: config or bound",
		verb, asked.Kind)
}

// Provision answers a bundle's `get` of one of its module's values.
func (b *moduleBus) Provision(verb string, params json.RawMessage) (json.RawMessage, error) {
	if verb != "get" {
		return nil, fmt.Errorf("the runtime answers no mesh/provision.%s", verb)
	}
	asked, err := readProvisionAsked(verb, params)
	if err != nil {
		return nil, err
	}
	return b.all.conn.AskProvisioner(b.module, asked.Kind, asked.Key)
}

// ProvisionWatch hands deliver the value now and each change after, until stopped. A value not answered now is
// refused now, with the client's reason.
func (b *moduleBus) ProvisionWatch(params json.RawMessage, deliver func(json.RawMessage) error) (func(), error) {
	asked, err := readProvisionAsked("watch", params)
	if err != nil {
		return nil, err
	}
	value, err := b.all.conn.AskProvisioner(b.module, asked.Kind, asked.Key)
	if err != nil {
		return nil, err
	}
	w := &provisionWatch{bus: b, asked: asked, deliver: deliver, last: value}
	if err := w.hand(ProvisionChange{Kind: asked.Kind, Key: asked.Key, Value: value}); err != nil {
		return nil, err
	}
	stop, err := b.all.provisioned.add(b.all, b.module, w)
	if err != nil {
		return nil, err
	}
	return stop, nil
}

// provisionWatch is one watch a bundle holds: what it asked, and what it was handed last.
type provisionWatch struct {
	bus     *moduleBus
	asked   provisionAsked
	deliver func(json.RawMessage) error
	mu      sync.Mutex // one change at a time, in order
	last    json.RawMessage
	refused string
	stopped bool
}

func (w *provisionWatch) hand(change ProvisionChange) error {
	raw, err := json.Marshal(change)
	if err != nil {
		return err
	}
	return w.deliver(raw)
}

// again asks once more after the client said something moved, and hands the bundle what changed.
func (w *provisionWatch) again() {
	w.mu.Lock()
	defer w.mu.Unlock()
	if w.stopped {
		return
	}
	value, err := w.bus.all.conn.AskProvisioner(w.bus.module, w.asked.Kind, w.asked.Key)
	change := ProvisionChange{Kind: w.asked.Kind, Key: w.asked.Key}
	var refused *bus.ProvisionRefused
	switch {
	case errors.As(err, &refused):
		if w.refused == refused.Reason {
			return
		}
		change.Refused = refused.Reason
	case err != nil:
		// The client not reached: asked again on its next word, which it says whenever it comes up.
		w.bus.all.logf("[mesh-tools] %s's watch of its %s %s could not ask again: %v", w.bus.module, w.asked.Kind,
			w.asked.Key, err)
		return
	default:
		if w.refused == "" && bytes.Equal(value, w.last) {
			return
		}
		change.Value = value
	}
	if err := w.hand(change); err != nil {
		w.bus.all.logf("[mesh-tools] %s did not take a change of its %s %s: %v", w.bus.module, w.asked.Kind,
			w.asked.Key, err)
		return
	}
	w.last, w.refused = value, change.Refused
}

// provisionWatches is every watch on this runtime, by module, and the one subscription that hears the client.
type provisionWatches struct {
	mu   sync.Mutex
	of   map[string]map[*provisionWatch]bool
	stop func()
}

func (p *provisionWatches) add(all *consumers, module string, w *provisionWatch) (func(), error) {
	p.mu.Lock()
	defer p.mu.Unlock()
	if p.stop == nil {
		stop, err := all.conn.OnProvisionChanged(func(module string, changed bus.ProvisionChanged) {
			for _, w := range p.told(module, changed) {
				go w.again()
			}
		})
		if err != nil {
			return nil, fmt.Errorf("the runtime cannot hear its machine's provisioner client: %w", err)
		}
		p.stop = stop
	}
	if p.of == nil {
		p.of = map[string]map[*provisionWatch]bool{}
	}
	if p.of[module] == nil {
		p.of[module] = map[*provisionWatch]bool{}
	}
	p.of[module][w] = true
	return func() {
		w.mu.Lock()
		w.stopped = true
		w.mu.Unlock()
		p.mu.Lock()
		defer p.mu.Unlock()
		delete(p.of[module], w)
	}, nil
}

// told is the watches of module that what moved concerns.
func (p *provisionWatches) told(module string, changed bus.ProvisionChanged) []*provisionWatch {
	p.mu.Lock()
	defer p.mu.Unlock()
	var out []*provisionWatch
	for w := range p.of[module] {
		if w.asked.Kind == changed.Kind && (changed.Key == "" || changed.Key == w.asked.Key) {
			out = append(out, w)
		}
	}
	return out
}

func (p *provisionWatches) stopAll() {
	p.mu.Lock()
	defer p.mu.Unlock()
	for _, ws := range p.of {
		for w := range ws {
			w.mu.Lock()
			w.stopped = true
			w.mu.Unlock()
		}
	}
	p.of = nil
	if p.stop != nil {
		p.stop()
		p.stop = nil
	}
}