package main

// Writing a record section by section (novox/hq to-be 55 §4, ADR 0592 §17, §19, §20, ADR 0597 §11): a draft is a key of the
// state `drafts` holding its author, the fields of the record and its sections as title, digest and the sequence of the
// write-section that wrote each; `write` puts a section's text into the record's history at once, `submit` makes the
// draft a version through the same rules `propose` is judged by.

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"sort"
	"strings"
	"time"

	stdio "git.novox.be/novox/mesh-sdk/go"
)

// The bounds of a draft (to-be 55 §4).
const (
	MostDraftSections = 64
	MostDraftBytes    = 1 << 20
	// DraftIdle is how long a draft untouched is counted in the health, and DraftDropped when it is dropped.
	DraftIdle    = 7 * 24 * time.Hour
	DraftDropped = 14 * 24 * time.Hour
)

const draftsState = "drafts"

// Draft is a record being written.
type Draft struct {
	Kind    string    `json:"kind"`
	Number  int       `json:"number"`
	Author  string    `json:"author"`
	Opened  time.Time `json:"opened"`
	Touched time.Time `json:"touched"`
	// From is the version the draft starts from (0 for a record not yet proposed).
	From int `json:"from"`
	// Fields are the record's fields and clauses and links as the draft carries them; its sections are Sections.
	Fields   ProposeAsk   `json:"fields"`
	Sections []sectionRef `json:"sections"`
	// TakenOver is the reason of the last take-over, carried in the next version's message.
	TakenOver string `json:"taken-over,omitempty"`
}

// SectionWriter is a store that keeps a section's text the moment it is written: the ledger.
type SectionWriter interface {
	// WriteSection appends the text as a write-section of the record and answers its ref.
	WriteSection(ctx context.Context, k Key, title, text string) (sectionRef, error)
	// SectionText is the text a ref names, held to its digest.
	SectionText(ctx context.Context, k Key, ref sectionRef) (string, error)
	// Working is the refs of the sections of the version a writer works on (the proposed one, else the served one).
	Working(ctx context.Context, k Key) ([]sectionRef, error)
	// Known tells the store the sections already written for a draft, so a version that carries them writes none again.
	Known(k Key, refs []sectionRef)
}

func draftKey(k Key) string { return fmt.Sprintf("%s.%04d", k.Kind, k.Number) }

// writer is the store's section writer, or the refusal that the records are not yet on the ledger.
func (k *KB) writer() (SectionWriter, error) {
	if w, ok := k.Store.(SectionWriter); ok {
		return w, nil
	}
	return nil, errors.New("the records are still kept in the database, which takes a record whole: propose it; writing a draft section by section waits for the move to the ledger")
}

func (k *KB) draftState() (KV, error) {
	if k.States == nil {
		return nil, errors.New("the knowledge base has no state to keep a draft in")
	}
	return k.States.State(draftsState), nil
}

// readDraft is the draft of a record and the revision it was read at; nil when there is none.
func (k *KB) readDraft(key Key) (*Draft, uint64, error) {
	kv, err := k.draftState()
	if err != nil {
		return nil, 0, err
	}
	e, err := kv.Get(draftKey(key))
	if err != nil || e == nil {
		return nil, 0, err
	}
	var d Draft
	if err := json.Unmarshal(e.Value, &d); err != nil {
		return nil, 0, fmt.Errorf("the draft of %s is not a draft: %w", key, err)
	}
	return &d, e.Revision, nil
}

// keepDraft writes the draft at the revision read, retried at most three times on a lost race and then refused with the
// reason (ADR 0597 §12).
func (k *KB) keepDraft(d *Draft, revision uint64) error {
	kv, err := k.draftState()
	if err != nil {
		return err
	}
	key := draftKey(Key{d.Kind, d.Number})
	for try := 0; try < 3; try++ {
		if revision == 0 {
			_, err = kv.Create(key, d)
		} else {
			_, err = kv.Update(key, d, revision)
		}
		if !errors.Is(err, stdio.ErrChanged) {
			return err
		}
		cur, rev, rerr := k.readDraft(Key{d.Kind, d.Number})
		if rerr != nil {
			return rerr
		}
		if cur != nil && cur.Author != d.Author {
			return fmt.Errorf("%s was taken over by %s while this was written", Key{d.Kind, d.Number}, cur.Author)
		}
		revision = rev
	}
	return fmt.Errorf("the draft of %s was written by another writer three times in a row; read it and write again", Key{d.Kind, d.Number})
}

// draftOf is the draft the caller may write: it exists, and the caller is its author.
func (k *KB) draftOf(caller string, key Key, verb string) (*Draft, uint64, error) {
	if !proven(caller) {
		return nil, 0, fmt.Errorf("%s needs a caller the runtime proved; this call is by %s. Nothing was written", verb, caller)
	}
	d, rev, err := k.readDraft(key)
	if err != nil {
		return nil, 0, err
	}
	if d == nil {
		return nil, 0, fmt.Errorf("%s has no draft: open it first. Nothing was written", key)
	}
	if d.Author != caller {
		return nil, 0, fmt.Errorf("%s is a draft by %s: only its author, proven by the runtime, writes it (this call is by %s); take-over makes you its author. Nothing was written", key, d.Author, caller)
	}
	return d, rev, nil
}

// OpenAsk opens or changes a draft: the fields of a proposal, but its sections.
type OpenAsk = ProposeAsk

// Opened is the answer to open.
type Opened struct {
	Record   string   `json:"record"`
	Sections []string `json:"sections,omitempty"`
	Says     string   `json:"says"`
}

// Open opens a draft of a reserved or held record, with its fields, clauses and links; called again by its author it
// changes them. A held record's draft starts from the sections of the version a writer works on.
func (k *KB) Open(caller string, a OpenAsk) (*Opened, error) {
	k.mu.Lock()
	defer k.mu.Unlock()
	if !proven(caller) {
		return nil, fmt.Errorf("open needs a caller the runtime proved; this call is by %s. Nothing was opened", caller)
	}
	w, err := k.writer()
	if err != nil {
		return nil, err
	}
	if !contains(Kinds, a.Kind) {
		return nil, fmt.Errorf("kind is decision or research, not %q; nothing was opened", a.Kind)
	}
	key := Key{a.Kind, a.Number}
	ctx := k.ctxFor(caller)
	held, err := k.Store.Get(ctx, key)
	if err != nil {
		return nil, fmt.Errorf("the knowledge base cannot be read (%v); nothing was opened", err)
	}
	if held == nil {
		return nil, fmt.Errorf("%s is held of none: reserve a number first. Nothing was opened", key)
	}
	if held.Current.Status == StatusReserved && proven(held.Current.ReservedBy) && held.Current.ReservedBy != caller {
		return nil, fmt.Errorf("%s was reserved by %s: only who reserved a number writes under it. Nothing was opened", key, held.Current.ReservedBy)
	}
	d, rev, err := k.readDraft(key)
	if err != nil {
		return nil, err
	}
	now := k.now()
	switch {
	case d != nil && d.Author != caller:
		return nil, fmt.Errorf("%s is a draft by %s: only its author writes it (this call is by %s); take-over makes you its author. Nothing was opened", key, d.Author, caller)
	case d == nil:
		sections, err := w.Working(ctx, key)
		if err != nil {
			return nil, err
		}
		d = &Draft{Kind: key.Kind, Number: key.Number, Author: caller, Opened: now, From: held.Versions, Sections: sections}
	}
	a.Sections = nil
	// A research effort's new version keeps the served title, date and deciders where none are given (issue 1966).
	if s := held.Current; a.Kind == KindResearch && s.Status != StatusReserved {
		if strings.TrimSpace(a.Title) == "" {
			a.Title = s.Title
		}
		if strings.TrimSpace(a.Date) == "" {
			a.Date = s.Date
		}
		if len(a.Deciders) == 0 {
			a.Deciders = append([]string(nil), s.Deciders...)
		}
	}
	d.Fields, d.Touched = a, now
	if err := k.keepDraft(d, rev); err != nil {
		return nil, fmt.Errorf("the draft of %s could not be kept (%v); nothing was opened", key, err)
	}
	k.emit(EventOpened, held.Current, caller, fmt.Sprintf("a draft opened from version %d", d.From), d.From)
	return &Opened{Record: key.String(), Sections: titlesOf(d.Sections), Says: fmt.Sprintf("A draft of %s is open, by you, starting from version %d. Write its sections one call each; submit makes it a version.", key, d.From)}, nil
}

func titlesOf(refs []sectionRef) []string {
	out := make([]string, len(refs))
	for i, r := range refs {
		out[i] = r.Name
	}
	return out
}

// Written is the answer to write, remove and order.
type Written struct {
	Record   string   `json:"record"`
	Sections []string `json:"sections"`
	Bytes    int      `json:"bytes"`
	Says     string   `json:"says"`
}

func (k *KB) draftBytes(w SectionWriter, ctx context.Context, d *Draft) (int, error) {
	n := 0
	for _, r := range d.Sections {
		t, err := w.SectionText(ctx, Key{d.Kind, d.Number}, r)
		if err != nil {
			return 0, err
		}
		n += len(t)
	}
	return n, nil
}

// Write writes one section of the draft: its title and its text, into the record's history at once.
func (k *KB) Write(caller string, key Key, title, text string) (*Written, error) {
	k.mu.Lock()
	defer k.mu.Unlock()
	w, err := k.writer()
	if err != nil {
		return nil, err
	}
	d, rev, err := k.draftOf(caller, key, "write")
	if err != nil {
		return nil, err
	}
	title = strings.TrimSpace(title)
	if title == "" {
		return nil, errors.New("write needs the section's title. Nothing was written")
	}
	if len(text) > MostSectionBytes {
		return nil, fmt.Errorf("the section %q is %d bytes; a section holds at most %d: split it. Nothing was written", title, len(text), MostSectionBytes)
	}
	// A section is a part with a title, never a file: learned on the section just written (to-be 55 §2.2, §4).
	if problems := sectionFormProblems(title, text); len(problems) > 0 {
		return nil, fmt.Errorf("the section is refused, and nothing was written:\n- %s", strings.Join(problems, "\n- "))
	}
	ctx := k.ctxFor(caller)
	at := -1
	for i, r := range d.Sections {
		if r.Name == title {
			at = i
		}
	}
	if at < 0 && len(d.Sections) >= MostDraftSections {
		return nil, fmt.Errorf("a draft holds at most %d sections. Nothing was written", MostDraftSections)
	}
	ref, err := w.WriteSection(ctx, key, title, text)
	if err != nil {
		return nil, fmt.Errorf("the section %q could not be written (%v); nothing was written", title, err)
	}
	if at >= 0 {
		d.Sections[at] = ref
	} else {
		d.Sections = append(d.Sections, ref)
	}
	n, err := k.draftBytes(w, ctx, d)
	if err != nil {
		return nil, err
	}
	if n > MostDraftBytes {
		return nil, fmt.Errorf("a draft holds at most %d bytes; this would hold %d. Nothing was kept in the draft (the section stays in the history, named by no version)", MostDraftBytes, n)
	}
	d.Touched = k.now()
	if err := k.keepDraft(d, rev); err != nil {
		return nil, fmt.Errorf("the draft of %s could not be kept (%v)", key, err)
	}
	k.emit(EventWritten, &Record{Kind: key.Kind, Number: key.Number}, caller, fmt.Sprintf("the section %q, %s", title, ref.Digest), 0)
	return &Written{Record: key.String(), Sections: titlesOf(d.Sections), Bytes: n, Says: fmt.Sprintf("The section %q is written (operation %d).", title, ref.Sequence)}, nil
}

// Remove removes one section from the draft.
func (k *KB) Remove(caller string, key Key, title string) (*Written, error) {
	k.mu.Lock()
	defer k.mu.Unlock()
	w, err := k.writer()
	if err != nil {
		return nil, err
	}
	d, rev, err := k.draftOf(caller, key, "remove")
	if err != nil {
		return nil, err
	}
	var kept []sectionRef
	for _, r := range d.Sections {
		if r.Name != title {
			kept = append(kept, r)
		}
	}
	if len(kept) == len(d.Sections) {
		return nil, fmt.Errorf("the draft of %s has no section %q (it has %s). Nothing was removed", key, title, strings.Join(titlesOf(d.Sections), ", "))
	}
	d.Sections, d.Touched = kept, k.now()
	if err := k.keepDraft(d, rev); err != nil {
		return nil, err
	}
	n, _ := k.draftBytes(w, k.ctxFor(caller), d)
	k.emit(EventRemoved, &Record{Kind: key.Kind, Number: key.Number}, caller, fmt.Sprintf("the section %q", title), 0)
	return &Written{Record: key.String(), Sections: titlesOf(d.Sections), Bytes: n, Says: fmt.Sprintf("The section %q is removed from the draft.", title)}, nil
}

// Order sets the sections' order: every title the draft holds, once.
func (k *KB) Order(caller string, key Key, titles []string) (*Written, error) {
	k.mu.Lock()
	defer k.mu.Unlock()
	w, err := k.writer()
	if err != nil {
		return nil, err
	}
	d, rev, err := k.draftOf(caller, key, "order")
	if err != nil {
		return nil, err
	}
	have := titlesOf(d.Sections)
	a, b := append([]string(nil), have...), append([]string(nil), titles...)
	sort.Strings(a)
	sort.Strings(b)
	if strings.Join(a, "\x00") != strings.Join(b, "\x00") {
		return nil, fmt.Errorf("order names every section of the draft once; the draft holds %s. Nothing was reordered", strings.Join(have, ", "))
	}
	byName := map[string]sectionRef{}
	for _, r := range d.Sections {
		byName[r.Name] = r
	}
	d.Sections = d.Sections[:0:0]
	for _, t := range titles {
		d.Sections = append(d.Sections, byName[t])
	}
	d.Touched = k.now()
	if err := k.keepDraft(d, rev); err != nil {
		return nil, err
	}
	n, _ := k.draftBytes(w, k.ctxFor(caller), d)
	k.emit(EventOrdered, &Record{Kind: key.Kind, Number: key.Number}, caller, strings.Join(titles, ", "), 0)
	return &Written{Record: key.String(), Sections: titles, Bytes: n, Says: "The sections are in the order given."}, nil
}

// Dropped is the answer to drop.
type Dropped struct {
	Record string `json:"record"`
	Says   string `json:"says"`
}

// DropDraft discards the draft; its sections stay in the history, named by no version.
func (k *KB) DropDraft(caller string, key Key, reason string) (*Dropped, error) {
	k.mu.Lock()
	defer k.mu.Unlock()
	if _, err := k.writer(); err != nil {
		return nil, err
	}
	if _, _, err := k.draftOf(caller, key, "drop"); err != nil {
		return nil, err
	}
	return k.dropped(caller, key, strings.TrimSpace(reason), "dropped by its author")
}

func (k *KB) dropped(by string, key Key, reason, what string) (*Dropped, error) {
	kv, err := k.draftState()
	if err != nil {
		return nil, err
	}
	if err := kv.Delete(draftKey(key)); err != nil {
		return nil, err
	}
	if reason != "" {
		what += ": " + reason
	}
	k.emit(EventDropped, &Record{Kind: key.Kind, Number: key.Number}, by, what, 0)
	return &Dropped{Record: key.String(), Says: "The draft of " + key.String() + " is gone."}, nil
}

// TakenOver is the answer to take-over.
type TakenOver struct {
	Record string `json:"record"`
	From   string `json:"from"`
	Says   string `json:"says"`
}

// TakeOver makes the caller the author of a draft or of a proposal, with a reason; the reason is carried in the next
// version's message and the previous author is told by the event `taken-over`. A proposal waiting for the operator's
// Approve is not taken over: its author withdraws it first.
func (k *KB) TakeOver(caller string, key Key, reason string) (*TakenOver, error) {
	k.mu.Lock()
	defer k.mu.Unlock()
	if !proven(caller) {
		return nil, fmt.Errorf("take-over needs a caller the runtime proved; this call is by %s. Nothing was taken over", caller)
	}
	reason = strings.TrimSpace(reason)
	if reason == "" {
		return nil, errors.New("take-over needs the reason, in one line. Nothing was taken over")
	}
	if _, err := k.writer(); err != nil {
		return nil, err
	}
	ctx := k.ctxFor(caller)
	held, err := k.Store.Get(ctx, key)
	if err != nil {
		return nil, err
	}
	if held == nil {
		return nil, fmt.Errorf("%s is held of none. Nothing was taken over", key)
	}
	if held.Working().Ask != nil && held.Working().Ask.Said == "waiting" {
		return nil, fmt.Errorf("%s waits for the operator's Approve: its author withdraws it first. Nothing was taken over", key)
	}
	d, rev, err := k.readDraft(key)
	if err != nil {
		return nil, err
	}
	var from string
	switch {
	case d != nil:
		from = d.Author
		d.Author, d.TakenOver, d.Touched = caller, reason, k.now()
		if err := k.keepDraft(d, rev); err != nil {
			return nil, err
		}
		if held.Current.Status == StatusReserved {
			// Only who reserved a number proposes under it: the number is the new author's.
			w := held.Current.Clone()
			w.ReservedBy = caller
			if err := k.Store.Save(ctx, Version{By: caller, At: k.now(), Why: "taken over from " + from + ": " + reason, Record: w}, true, false, held.Revision); err != nil {
				return nil, fmt.Errorf("the number of %s could not be handed over (%v)", key, err)
			}
		}
	case held.Working().Status == StatusProposed:
		w := held.Working().Clone()
		from = w.Author
		w.Author = caller
		if !contains(w.Writers, caller) {
			w.Writers = append(w.Writers, caller)
		}
		current := held.Pending == nil
		if err := k.Store.Save(ctx, Version{By: caller, At: k.now(), Why: "taken over from " + from + ": " + reason, Record: w}, current, false, held.Revision); err != nil {
			return nil, fmt.Errorf("%s could not be taken over (%v)", key, err)
		}
	default:
		return nil, fmt.Errorf("%s has no draft and is %s, not proposed: there is nothing to take over", key, held.Working().Status)
	}
	if from == caller {
		return nil, fmt.Errorf("%s is already yours", key)
	}
	k.emit(EventTakenOver, held.Current, caller, fmt.Sprintf("from %s: %s", from, reason), held.Versions)
	return &TakenOver{Record: key.String(), From: from, Says: fmt.Sprintf("You are the author of %s now; %s is told. The reason goes in its next version's message.", key, from)}, nil
}

// SubmitDraft makes the draft a version: it is judged by the rules a proposal is, every reason of a refusal named at
// once and the draft kept as it was, and the review asked.
func (k *KB) SubmitDraft(caller string, key Key, why string) (*Proposed, error) {
	w, err := k.writer()
	if err != nil {
		return nil, err
	}
	k.mu.Lock()
	d, _, err := k.draftOf(caller, key, "submit")
	k.mu.Unlock()
	if err != nil {
		return nil, err
	}
	a := d.Fields
	a.Kind, a.Number = key.Kind, key.Number
	if strings.TrimSpace(why) != "" {
		a.Why = why
	} else if d.TakenOver != "" && a.Why == "" {
		a.Why = "revised after a take-over: " + d.TakenOver
	}
	ctx := k.ctxFor(caller)
	for _, r := range d.Sections {
		t, err := w.SectionText(ctx, key, r)
		if err != nil {
			return nil, err
		}
		a.Sections = append(a.Sections, Section{Name: r.Name, Text: t})
	}
	w.Known(key, d.Sections)
	out, err := k.Propose(caller, a)
	if err != nil {
		return nil, err
	}
	k.mu.Lock()
	defer k.mu.Unlock()
	if _, err := k.dropped(caller, key, "", "submitted"); err != nil {
		k.logf("[mesh-knowledge] the draft of %s could not be removed after it was submitted: %v", key, err)
	}
	k.emit(EventSubmitted, &Record{Kind: key.Kind, Number: key.Number, Status: out.Status}, caller, fmt.Sprintf("version %d, %d sections", out.Version, len(a.Sections)), out.Version)
	return out, nil
}