package inventory

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

	"github.com/jackc/pgx/v5"
)

// The assignment generation and the record of every send (novox/hq issue 234, migration 0094).
//
// A declaration carries the generation of the assignments it was composed from, and a machine refuses one
// composed from an older generation than it applied — the sequence orders arrival and cannot tell a later
// send carrying an older view. And every send is written down with who sent it, from which generation and
// naming which modules, so what a machine was last told, by whom, is read back rather than guessed at.

// sendsKept is how many sends are kept per machine: the newest. Enough to read back a morning of pushes
// on a busy machine; the record is for finding who sent what, not an archive.
const sendsKept = 200

// AssignmentGeneration is the mesh's assignment generation now: raised by the store itself in the same
// transaction as every change to what is assigned where (a trigger on the assignment table).
func (i *Inventory) AssignmentGeneration(ctx context.Context) (int64, error) {
	var g int64
	if err := i.store.Pool().QueryRow(ctx, `select generation from assignment_generation`).Scan(&g); err != nil {
		return 0, fmt.Errorf("reading the assignment generation: %w", err)
	}
	return g, nil
}

// RaiseAssignmentGeneration raises the generation past one a machine applied, and answers it: one more
// than that, or what it already was when it is past it. It never lowers it.
//
// For one case only: a machine refused a send composed from the generation the mesh holds now, so the
// machine applied a higher one than the mesh's counter — a store put back from a backup. Every send after
// would be refused for ever; raised past it, the next send carries a generation the machine takes, composed
// from the assignments the store holds now. A stale sender never meets this: its generation is below the
// counter, and the counter is not touched for it.
func (i *Inventory) RaiseAssignmentGeneration(ctx context.Context, past int64) (int64, error) {
	var g int64
	err := i.store.Pool().QueryRow(ctx,
		`update assignment_generation set generation = greatest(generation, $1 + 1) returning generation`, past).Scan(&g)
	if err != nil {
		return 0, fmt.Errorf("raising the assignment generation past %d: %w", past, err)
	}
	return g, nil
}

// SentGeneration is the generation a machine was last sent, by its id; zero for one sent without. What the
// mesh WOULD send is stamped with it, so it reads as byte for byte what it DID send when nothing else changed.
func (i *Inventory) SentGeneration(ctx context.Context, id string) (int64, error) {
	var g *int64
	if err := i.store.Pool().QueryRow(ctx, `select sent_generation from node where id = $1`, id).Scan(&g); err != nil {
		return 0, fmt.Errorf("reading the generation %s was last sent: %w", id, err)
	}
	if g == nil {
		return 0, nil
	}
	return *g, nil
}

// ReadsGeneration says a machine's node-engine said it reads a generation in a declaration, by its id.
func (i *Inventory) ReadsGeneration(ctx context.Context, id string) (bool, error) {
	var reads bool
	if err := i.store.Pool().QueryRow(ctx, `select reads_generation from node where id = $1`, id).Scan(&reads); err != nil {
		return false, fmt.Errorf("reading whether %s reads a generation: %w", id, err)
	}
	return reads, nil
}

// RecordReadsGeneration keeps what a machine's latest report said of reading a generation.
func (i *Inventory) RecordReadsGeneration(ctx context.Context, id string, reads bool) error {
	_, err := i.store.Pool().Exec(ctx, `update node set reads_generation = $2 where id = $1`, id, reads)
	return err
}

// Send is one declaration sent to a machine, as the mesh records it.
type Send struct {
	// Node is the machine's id; NodeName its name, filled where it is read back.
	Node     string
	NodeName string
	Sequence int64
	// Epoch is the lease epoch its sender acted under, zero for one that acted under none.
	Epoch int64
	// Sender is who sent it, in words: the caller, and the process and build that composed it.
	Sender string
	// Generation is the assignment generation it was composed from, zero when not known.
	Generation int64
	Digest     string
	// Modules are the modules it named.
	Modules []string
	SentAt  time.Time
	// RefusedAt is when the machine refused it for its generation, nil when it did not; RefusedApplied the
	// generation the machine said it had applied then; CounterRaisedTo what the mesh's counter was raised to
	// because the refusal showed it behind the machine, zero when it was not.
	RefusedAt       *time.Time
	RefusedApplied  int64
	CounterRaisedTo int64
	// Recorded is false for a refusal of a sequence the mesh has no send for: its sender is unknown.
	Recorded bool
}

// unknownSender is the sender of a refused sequence the mesh has no record of sending.
const unknownSender = "a sender the mesh has no record of (no send of this sequence was recorded: sent by " +
	"hand, before sends were recorded, or by a controller whose record was not written)"

// SendNotRecordedError is a send whose machine's record was written — its digest and the generation it
// carried — and whose record of who sent it was not. The send is away and the machine's record stands; the
// caller says this loudly and does not take the send for failed.
type SendNotRecordedError struct{ Err error }

func (e *SendNotRecordedError) Error() string {
	return "the record of the send was not written: " + e.Err.Error()
}
func (e *SendNotRecordedError) Unwrap() error { return e.Err }

// RecordSentWith writes down what a machine was just sent — its digest, the builds it carried, the epoch and
// the generation on the wire — and the send itself, who sent it and from which generation (novox/hq issue
// 234), in one transaction. The digest and the generation are written together, so the would-send is never
// stamped with a generation the machine was not sent. The send's own record is written under a savepoint: if
// it cannot be, the machine's record is still committed and a *SendNotRecordedError says so. The oldest
// sends beyond the newest 200 for the machine are let go.
func (i *Inventory) RecordSentWith(ctx context.Context, node, digest string, builds map[string]string, epoch uint64,
	generation int64, s Send) error {
	var sentEpoch *int64
	if epoch > 0 {
		e := int64(epoch)
		sentEpoch = &e
	}
	var carried *string
	if builds != nil {
		raw, err := json.Marshal(builds)
		if err != nil {
			return err
		}
		text := string(raw)
		carried = &text
	}
	tx, err := i.store.Pool().Begin(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback(ctx) }()
	if _, err := tx.Exec(ctx,
		`update node set sent = $2, sent_at = now(), sent_builds = $3::jsonb, sent_epoch = $4, sent_generation = $5
		  where id = $1`, node, digest, carried, sentEpoch, nullIfZero(generation)); err != nil {
		return err
	}
	recordErr := recordSend(ctx, tx, node, s)
	if err := tx.Commit(ctx); err != nil {
		return err
	}
	if recordErr != nil {
		return &SendNotRecordedError{Err: recordErr}
	}
	return nil
}

// recordSend writes one send under a savepoint of tx, which it rolls back when the send cannot be written.
func recordSend(ctx context.Context, tx pgx.Tx, node string, s Send) error {
	sp, err := tx.Begin(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = sp.Rollback(ctx) }()
	modules := s.Modules
	if modules == nil {
		modules = []string{}
	}
	if _, err := sp.Exec(ctx,
		`insert into declaration_send (node, sequence, epoch, sender, generation, digest, modules)
		 values ($1, $2, $3, $4, $5, $6, $7)`,
		node, nullIfZero(s.Sequence), nullIfZero(s.Epoch), s.Sender, nullIfZero(s.Generation), s.Digest,
		modules); err != nil {
		return err
	}
	if err := pruneSends(ctx, sp, node); err != nil {
		return err
	}
	return sp.Commit(ctx)
}

// pruneSends lets go of a machine's sends beyond the newest 200.
func pruneSends(ctx context.Context, q queries, node string) error {
	_, err := q.Exec(ctx,
		`delete from declaration_send where node = $1 and id not in
		   (select id from declaration_send where node = $1 order by id desc limit $2)`, node, sendsKept)
	return err
}

// sendColumns are a send's columns as scanSends reads them.
const sendColumns = `s.node, n.name, coalesce(s.sequence, 0), coalesce(s.epoch, 0), s.sender, coalesce(s.generation, 0),
	s.digest, s.modules, s.sent_at, s.refused_at, coalesce(s.refused_applied, 0), coalesce(s.counter_raised_to, 0),
	s.recorded`

func scanSends(rows pgx.Rows) ([]Send, error) {
	defer rows.Close()
	var out []Send
	for rows.Next() {
		var s Send
		if err := rows.Scan(&s.Node, &s.NodeName, &s.Sequence, &s.Epoch, &s.Sender, &s.Generation, &s.Digest,
			&s.Modules, &s.SentAt, &s.RefusedAt, &s.RefusedApplied, &s.CounterRaisedTo, &s.Recorded); err != nil {
			return nil, err
		}
		out = append(out, s)
	}
	return out, rows.Err()
}

// LastSend is the last declaration a machine was sent, by its name; false when none was recorded. A refusal
// of a sequence the mesh has no send for is not a send, and is not it.
func (i *Inventory) LastSend(ctx context.Context, name string) (Send, bool, error) {
	rows, err := i.store.Pool().Query(ctx, `select `+sendColumns+`
		  from declaration_send s join node n on n.id = s.node
		 where n.name = $1 and s.recorded order by s.id desc limit 1`, name)
	if err != nil {
		return Send{}, false, err
	}
	sends, err := scanSends(rows)
	if err != nil || len(sends) == 0 {
		return Send{}, false, err
	}
	return sends[0], true, nil
}

// RefusedSend keeps a machine's refusal of the send of a sequence for the generation it came from, and
// answers that send, sender and all; false when no send of that sequence was recorded (RecordUnrecordedRefusal
// keeps that one). The newest of that sequence when there are several: a declaration a person sent by hand may
// repeat one. raisedTo is what the mesh's counter was raised to for it, zero for none.
func (i *Inventory) RefusedSend(ctx context.Context, node string, sequence, applied, raisedTo int64) (Send, bool, error) {
	rows, err := i.store.Pool().Query(ctx, `with refused as (
		update declaration_send set refused_at = now(), refused_applied = $3, counter_raised_to = $4
		 where id = (select id from declaration_send where node = $1 and sequence = $2 and recorded
		              order by id desc limit 1)
		returning *)
		select `+sendColumns+` from refused s join node n on n.id = s.node`, node, sequence, applied,
		nullIfZero(raisedTo))
	if err != nil {
		return Send{}, false, err
	}
	sends, err := scanSends(rows)
	if err != nil || len(sends) == 0 {
		return Send{}, false, err
	}
	return sends[0], true, nil
}

// RecordUnrecordedRefusal keeps a machine's refusal of a sequence the mesh has no send for, as a row of its
// own whose sender is unknown, and answers it: S20 raises it like any other, because a refusal nobody can
// attribute is no quieter for that. s carries the machine, the sequence, epoch, generation and digest the
// refused declaration carried, and the refusal's applied generation and counter raise.
func (i *Inventory) RecordUnrecordedRefusal(ctx context.Context, s Send) (Send, error) {
	rows, err := i.store.Pool().Query(ctx, `with refused as (
		insert into declaration_send (node, sequence, epoch, sender, generation, digest, refused_at, refused_applied,
		                              counter_raised_to, recorded)
		values ($1, $2, $3, $4, $5, $6, now(), $7, $8, false) returning *)
		select `+sendColumns+` from refused s join node n on n.id = s.node`,
		s.Node, nullIfZero(s.Sequence), nullIfZero(s.Epoch), unknownSender, nullIfZero(s.Generation), s.Digest,
		s.RefusedApplied, nullIfZero(s.CounterRaisedTo))
	if err != nil {
		return Send{}, err
	}
	sends, err := scanSends(rows)
	if err != nil {
		return Send{}, err
	}
	if len(sends) == 0 {
		return Send{}, fmt.Errorf("the refusal of sequence %d was not kept", s.Sequence)
	}
	if err := pruneSends(ctx, i.store.Pool(), s.Node); err != nil {
		return Send{}, err
	}
	return sends[0], nil
}

// RefusedSendsSince is every send refused for its generation since a moment, newest first.
func (i *Inventory) RefusedSendsSince(ctx context.Context, since time.Time) ([]Send, error) {
	rows, err := i.store.Pool().Query(ctx, `select `+sendColumns+`
		  from declaration_send s join node n on n.id = s.node
		 where s.refused_at >= $1 order by s.refused_at desc`, since)
	if err != nil {
		return nil, err
	}
	return scanSends(rows)
}