package main

// The reconcile loop every provider shares, as the TypeScript SDK's runProvisioner runs it
// (@novox/mesh-sdk/provisioner, 0.1.10). The Go SDK has no provisioner yet, so this module carries
// the loop itself, line for line in behaviour; when the Go SDK grows one, this file is what moves
// there (novox/hq ADR 0039: the loop is the SDK's, the adapter is the module's).
//
// Read the contributions the mesh delivered; bring each consumer's resource into being through the
// adapter, under the login and password the mesh minted; withdraw what the mesh no longer asks for.
// **A provider creates the credential the mesh minted, and seals nothing (novox/hq ADR 0048).**

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/url"
	"os"
	"strings"
	"time"
)

// Provision is one consumer's resource to bring into being — everything the mesh derived and delivered.
type Provision struct {
	// As is the login the mesh derived and gave the consumer to present.
	As string
	// Password is the one the mesh minted, read from the file the host unsealed.
	Password string
	// Values are what the consumer contributed (e.g. {"name": "letta", "extensions": ["vector"]}).
	Values map[string]any
	// Derived is what this provider's own definition derives for the consumer (novox/hq ADR 0201).
	Derived map[string]any
	// At is where the consumer is; Consumer is its node.
	At       string
	Consumer string
}

// Adapter is the per-service half.
type Adapter interface {
	Create(ctx context.Context, p Provision) error
	// Remove withdraws what Create made; derived is what the mesh last derived, remembered here.
	Remove(ctx context.Context, as string, derived map[string]any) error
	// Holds says whether the backend still holds the consumer exactly as p says. Read-only.
	Holds(ctx context.Context, p Provision) (bool, error)
}

// Harness is the loop's settings and memory.
type Harness struct {
	Resource     string
	Receives     string
	Adapter      Adapter
	Every        time.Duration // 5s
	VerifyEvery  time.Duration // 60s
	HoldsTimeout time.Duration // 30s
	Log          func(format string, args ...any)
	Now          func() time.Time

	verifiedAt  time.Time
	applied     map[string]appliedEntry
	lost        map[string]brake
	waiting     map[string]int
	failing     map[string]failure
	lastWarning string
}

type appliedEntry struct {
	hash    string
	derived map[string]any
}

type brake struct {
	times  int
	nextAt time.Time
}

type failure struct {
	text  string
	times int
}

// The longest a consumer whose create keeps failing to satisfy holds waits between checks.
const maxBackoff = time.Hour

// How many passes a secret may be unreadable before it stops being called a race (issue 225), and
// once said loudly, how often it is repeated. The same cadence quiets a create that keeps failing
// the same way.
const (
	patiently   = 12
	loudlyEvery = 240
)

type contribution struct {
	As      string         `json:"as"`
	Secret  string         `json:"secret"`
	Node    string         `json:"node"`
	At      string         `json:"at"`
	Values  map[string]any `json:"values"`
	Derived map[string]any `json:"derived"`
}

func (h *Harness) init() {
	if h.Every == 0 {
		h.Every = 5 * time.Second
	}
	if h.VerifyEvery == 0 {
		h.VerifyEvery = time.Minute
	}
	if h.HoldsTimeout == 0 {
		h.HoldsTimeout = 30 * time.Second
	}
	if h.Now == nil {
		h.Now = time.Now
	}
	if h.Log == nil {
		h.Log = func(format string, args ...any) { fmt.Fprintf(os.Stderr, format+"\n", args...) }
	}
	if h.applied == nil {
		h.applied = map[string]appliedEntry{}
		h.lost = map[string]brake{}
		h.waiting = map[string]int{}
		h.failing = map[string]failure{}
	}
}

// Run reconciles until ctx ends. One consumer's failure never stops the others'.
func (h *Harness) Run(ctx context.Context) {
	h.init()
	for {
		h.Reconcile(ctx)
		select {
		case <-ctx.Done():
			return
		case <-time.After(h.Every):
		}
	}
}

func (h *Harness) say(format string, args ...any) {
	h.Log("[provisioner:"+h.Resource+"] "+format, args...)
}

func (h *Harness) warn(why string) {
	if why == h.lastWarning {
		return
	}
	if why != "" {
		h.say("%s; nothing applied or removed until it can be read", why)
	} else {
		h.say("contributions file readable again")
	}
	h.lastWarning = why
}

// readContributions answers the consumers asked for, or nil when the file says nothing usable.
// **Nothing read is not nobody asking** (novox/hq issue 241): only a file that was read can withdraw.
func (h *Harness) readContributions() []contribution {
	raw, err := os.ReadFile(h.Receives)
	if err != nil {
		h.warn(fmt.Sprintf("contributions file unreadable (%s): %v", h.Receives, err))
		return nil
	}
	var doc struct {
		Requirement string          `json:"requirement"`
		Given       json.RawMessage `json:"given"`
	}
	if err := json.Unmarshal(raw, &doc); err != nil {
		h.warn(fmt.Sprintf("contributions file is not JSON (%s): %v", h.Receives, err))
		return nil
	}
	if doc.Requirement != "" && doc.Requirement != h.Resource {
		h.warn(fmt.Sprintf("%s is for %s, not %s", h.Receives, doc.Requirement, h.Resource))
		return nil
	}
	var given []contribution
	if len(doc.Given) == 0 || string(doc.Given) == "null" || json.Unmarshal(doc.Given, &given) != nil {
		h.warn(fmt.Sprintf("%s has no given list", h.Receives))
		return nil
	}
	h.warn("")
	out := []contribution{}
	for _, g := range given {
		// No `as` is not a credential grant: nothing to create for it.
		if g.As != "" && g.Secret != "" {
			out = append(out, g)
		}
	}
	return out
}

func hashOf(as, password string, values, derived map[string]any) string {
	// Derived is in the hash: a provider that renames what it derives gave a different resource.
	b, _ := json.Marshal([]any{as, password, orEmpty(values), orEmpty(derived)})
	return string(b)
}

func orEmpty(m map[string]any) map[string]any {
	if m == nil {
		return map[string]any{}
	}
	return m
}

// Reconcile is one pass.
func (h *Harness) Reconcile(ctx context.Context) {
	h.init()
	given := h.readContributions()
	if given == nil {
		return
	}
	want := map[string]bool{}
	for _, g := range given {
		want[g.As] = true
	}
	verifying := h.Now().Sub(h.verifiedAt) >= h.VerifyEvery
	if verifying {
		h.verifiedAt = h.Now()
	}

	for _, g := range given {
		raw, err := os.ReadFile(g.Secret)
		if err != nil {
			// A secret the host has not written yet is a race on the first pass; past a minute it is
			// a person's to look at, and said so (novox/hq issue 225).
			n := h.waiting[g.As] + 1
			h.waiting[g.As] = n
			if n <= patiently {
				h.say("%s: secret not readable yet (%s): %v", g.As, g.Secret, err)
			} else if n == patiently+1 || n%loudlyEvery == 0 {
				h.say("%s: CANNOT READ the secret after %d attempts (%s): %v. This is not a race any more — "+
					"nothing has been provisioned for this consumer and nothing will be until somebody looks. "+
					"Check who owns the file and who this process runs as (novox/hq issue 225)", g.As, n, g.Secret, err)
			}
			continue
		}
		delete(h.waiting, g.As)
		password := strings.TrimSuffix(string(raw), "\n")
		p := Provision{As: g.As, Password: password, Values: orEmpty(g.Values), Derived: orEmpty(g.Derived), At: g.At, Consumer: g.Node}
		hash := hashOf(g.As, password, g.Values, g.Derived)

		reapplying := 0
		if was, ok := h.applied[g.As]; ok && was.hash == hash {
			if !verifying {
				continue
			}
			b, braked := h.lost[g.As]
			if braked && h.Now().Before(b.nextAt) {
				continue
			}
			hctx, cancel := context.WithTimeout(ctx, h.HoldsTimeout)
			held, err := h.Adapter.Holds(hctx, p)
			timedOut := errors.Is(hctx.Err(), context.DeadlineExceeded)
			cancel()
			if err != nil {
				// Unable to ask is not evidence of loss. A backend that timed out will time out for
				// the next consumer too, so the rest of this pass is not asked.
				h.say("%s: could not check the backend, will ask again: %s", g.As, scrub(err, password))
				if timedOut {
					verifying = false
				}
				continue
			}
			if held {
				delete(h.lost, g.As)
				continue
			}
			reapplying = b.times + 1
			if reapplying == 1 {
				h.say("%s: the backend no longer holds it; applying again", g.As)
			} else {
				h.say("%s: still not held after being applied again (%d times in a row) — create does not "+
					"produce what holds checks; applying again", g.As, reapplying)
			}
		}
		if err := h.Adapter.Create(ctx, p); err != nil {
			text := scrub(err, password)
			f := h.failing[g.As]
			if f.text != text {
				f = failure{text: text}
			}
			f.times++
			h.failing[g.As] = f
			// Said each time it changes, and while it stays the same, as rarely as a lost secret.
			if f.times == 1 || f.times%loudlyEvery == 0 {
				h.say("%s: create failed, will retry: %s", g.As, text)
			}
			if reapplying > 0 {
				h.lost[g.As] = brake{times: reapplying - 1}
			}
			continue
		}
		if f, was := h.failing[g.As]; was {
			h.say("%s: created, after %d failed attempt(s)", g.As, f.times)
			delete(h.failing, g.As)
		}
		h.applied[g.As] = appliedEntry{hash: hash, derived: p.Derived}
		if reapplying == 0 {
			delete(h.lost, g.As)
		} else {
			wait := h.VerifyEvery << (reapplying - 1)
			if wait > maxBackoff || wait <= 0 {
				wait = maxBackoff
			}
			h.lost[g.As] = brake{times: reapplying, nextAt: h.Now().Add(wait)}
			if reapplying > 1 {
				h.say("%s: next check in %s", g.As, wait.Round(time.Second))
			}
		}
	}

	// Withdraw every login this process made that the mesh no longer asks for.
	for as, was := range h.applied {
		if want[as] {
			continue
		}
		h.say("%s: no longer in %s; withdrawing it from the backend", as, h.Receives)
		if err := h.Adapter.Remove(ctx, as, was.derived); err != nil {
			h.say("%s: remove failed, will retry: %v", as, err)
			continue
		}
		delete(h.applied, as)
		delete(h.lost, as)
	}
	for as := range h.failing {
		if !want[as] {
			delete(h.failing, as)
		}
	}
}

// scrub is an error's text with the consumer's password removed, raw and URL-encoded.
func scrub(err error, password string) string {
	text := err.Error()
	if password == "" {
		return text
	}
	for _, form := range []string{password, url.QueryEscape(password), url.PathEscape(password)} {
		text = strings.ReplaceAll(text, form, "***")
	}
	return text
}