package inventory

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

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

// A Plan is what a merge produces (novox/hq ADR 0162): the modules it changed and everything
// standing on them, sorted into tiers, each module's state, and the tier the plan is at. Kept in
// the store so a controller replaced mid-plan resumes it, and so `status` can say what a merge
// still waits for.
type Plan struct {
	ID         string `json:"id"`
	Repository string `json:"repository"`
	// Branch is the branch the merge went into (novox/hq issue 254): a newer plan supersedes the open
	// ones of the same repository and branch. Empty for a plan from before it was kept.
	Branch  string                 `json:"branch,omitempty"`
	Commit  string                 `json:"commit"`
	Created time.Time              `json:"created"`
	Updated time.Time              `json:"updated"`
	State   string                 `json:"state"`
	Tier    int                    `json:"tier"`
	Tiers   [][]string             `json:"tiers"`
	Modules map[string]*PlanModule `json:"modules"`
	Note    string                 `json:"note,omitempty"`
	// TierEntered is when the plan entered the tier it is at (novox/hq to-be 45 Phase 0), read and
	// never written from here: a save measures the tier it leaves and stamps the next. What the
	// watchdog of a plan's progress (S3) reads.
	TierEntered time.Time `json:"tier_entered,omitempty"`
	// Revision is the plan's as it was read, and the one a save must find (novox/hq to-be 45 §6): a
	// plan is written by compare-and-set, so a write against a plan another writer moved since is
	// refused rather than laid over it. Zero is a plan never saved. SavePlan moves it.
	Revision int64 `json:"revision"`
	// Epoch is the controller lease epoch that wrote it last; zero for a write that claimed none.
	Epoch uint64 `json:"epoch,omitempty"`
}

// ErrPlanMoved is a save against a plan written by somebody else since it was read.
var ErrPlanMoved = errors.New("the plan was written by somebody else since it was read")

// PlanModule is one module's state within a plan.
type PlanModule struct {
	// State: asked, built, failed; empty for a module whose tier has not been asked yet.
	State   string     `json:"state,omitempty"`
	AskedAt *time.Time `json:"asked_at,omitempty"`
	BuiltAt *time.Time `json:"built_at,omitempty"`
	// SentAt is when the plan sent the machines running this module its new build, because a
	// later tier is built by it (ADR 0163's gate): the reports that open the gate are the ones
	// after this.
	SentAt *time.Time `json:"sent_at,omitempty"`
	// First is the machines the plan sent the new build to first, and FirstAt when (novox/hq issue
	// 249, ADR 0218): unless the module's policy rolls it out together, one machine takes it before
	// the rest, and the rest are sent once that one reports it applied. Kept so a controller
	// replaced while the plan waits on that report resumes the wait rather than sending again. The
	// machine holding the bus is among them when its user list had to go first.
	First   []string   `json:"first,omitempty"`
	FirstAt *time.Time `json:"first_at,omitempty"`
	Commit  string     `json:"commit,omitempty"`
	Why     string     `json:"why,omitempty"`
	// Build is the id of the build the plan asked for this module (novox/hq ADR 0219), so the plan
	// matches its outcome by id — the one thing every outcome echoes, a failed one that never learnt
	// its module's name included. Empty in a plan from before it was kept, which is matched by
	// module, or by repository and path, as before.
	Build string `json:"build,omitempty"`
}

// The states a plan passes through.
const (
	PlanBuilding = "building"
	PlanRolling  = "rolling"
	PlanDone     = "done"
	PlanFailed   = "failed"
	// PlanSuperseded is a plan a newer merge of the same repository and branch took over (novox/hq
	// issue 254, ADR 0218): what it had not built is in the newer plan, and its note names it.
	PlanSuperseded = "superseded"
)

// Open says whether the plan is still being worked.
func (p Plan) Open() bool { return p.State == PlanBuilding || p.State == PlanRolling }

// SavePlan writes a plan, new or changed, whole: the plan is small and read as one thing.
//
// **By compare-and-set on its revision, carrying the epoch** (novox/hq to-be 45 §6): written only if
// the plan is still at the revision it was read at — a new one only if it does not exist — and refused
// with ErrPlanMoved otherwise; and only by a process that may act (ActsUnder), whose epoch it records.
// On success p's revision and epoch are the ones written, so the caller may save it again.
func (i *Inventory) SavePlan(ctx context.Context, p *Plan) error {
	epoch, err := i.actingEpoch(ctx)
	if err != nil {
		return fmt.Errorf("the plan for %s %s is not written: %w", p.Repository, p.Commit, err)
	}
	tiers, err := json.Marshal(p.Tiers)
	if err != nil {
		return err
	}
	modules, err := json.Marshal(p.Modules)
	if err != nil {
		return err
	}
	// **And how long the tier it left took** (novox/hq to-be 45 Phase 0): measured here, where the
	// plan moves, in the same transaction as the move, so no save can move a tier unmeasured or
	// measure one twice.
	tx, err := i.store.Pool().Begin(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback(ctx) }()
	entered, err := planTierLeft(ctx, tx, *p, time.Now())
	if err != nil {
		return err
	}
	var revision int64
	err = tx.QueryRow(ctx,
		`insert into release_plan (id, repository, commit_hash, created, updated, state, tier, tiers, modules, note,
		                           branch, tier_entered, revision, epoch)
		 values ($1, $2, $3, $4, now(), $5, $6, $7, $8, $9, $10, $11, 1, $13)
		 on conflict (id) do update set updated = now(), state = excluded.state, tier = excluded.tier,
		        tiers = excluded.tiers, modules = excluded.modules, note = excluded.note, branch = excluded.branch,
		        tier_entered = excluded.tier_entered, revision = release_plan.revision + 1, epoch = excluded.epoch
		  where release_plan.revision = $12
		 returning revision`,
		p.ID, p.Repository, p.Commit, p.Created, p.State, p.Tier, tiers, modules, p.Note, p.Branch, entered,
		p.Revision, epoch).Scan(&revision)
	if errors.Is(err, pgx.ErrNoRows) {
		// The row is there and at another revision — moved since this was read, or there already
		// when this one is new: either way not this writer's to overwrite. (A plan saved before plans
		// had revisions is at zero, and its first save here is from a read at zero.)
		return fmt.Errorf("the plan for %s %s (%s) is not written: %w", p.Repository, short(p.Commit), p.ID, ErrPlanMoved)
	}
	if err != nil {
		return err
	}
	if err := tx.Commit(ctx); err != nil {
		return err
	}
	p.Revision, p.TierEntered = revision, entered
	if epoch != nil {
		p.Epoch = uint64(*epoch)
	} else {
		p.Epoch = 0
	}
	return nil
}

// short is a commit as a person reads it.
func short(commit string) string {
	if len(commit) > 8 {
		return commit[:8]
	}
	return commit
}

// OpenPlans is every plan still being worked, oldest first.
func (i *Inventory) OpenPlans(ctx context.Context) ([]Plan, error) {
	return i.plans(ctx, `where state in ('building', 'rolling') order by created`)
}

// RecentPlans is the last few plans, newest first, open or not — what the overview shows.
func (i *Inventory) RecentPlans(ctx context.Context, limit int) ([]Plan, error) {
	return i.plans(ctx, fmt.Sprintf(`order by created desc limit %d`, limit))
}

// PlanByID is one plan.
func (i *Inventory) PlanByID(ctx context.Context, id string) (Plan, error) {
	plans, err := i.plans(ctx, `where id = '`+id+`'`)
	if err != nil {
		return Plan{}, err
	}
	if len(plans) == 0 {
		return Plan{}, fmt.Errorf("no plan %s", id)
	}
	return plans[0], nil
}

func (i *Inventory) plans(ctx context.Context, tail string) ([]Plan, error) {
	rows, err := i.store.Pool().Query(ctx,
		`select id, repository, commit_hash, created, updated, state, tier, tiers, modules, note, branch,
		        coalesce(tier_entered, created), revision, coalesce(epoch, 0)
		   from release_plan `+tail)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []Plan
	for rows.Next() {
		var p Plan
		var tiers, modules []byte
		var epoch int64
		if err := rows.Scan(&p.ID, &p.Repository, &p.Commit, &p.Created, &p.Updated, &p.State,
			&p.Tier, &tiers, &modules, &p.Note, &p.Branch, &p.TierEntered, &p.Revision, &epoch); err != nil {
			return nil, err
		}
		p.Epoch = uint64(epoch)
		if err := json.Unmarshal(tiers, &p.Tiers); err != nil {
			return nil, err
		}
		if err := json.Unmarshal(modules, &p.Modules); err != nil {
			return nil, err
		}
		if p.Modules == nil {
			p.Modules = map[string]*PlanModule{}
		}
		out = append(out, p)
	}
	if errors.Is(rows.Err(), pgx.ErrNoRows) {
		return nil, nil
	}
	return out, rows.Err()
}