package inventory

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

	"github.com/jackc/pgx/v5"
	"github.com/novox/mesh-control/internal/catalogue"
)

// ErrNoSuchModule is what the mesh says about a module it has never been told about.
var ErrNoSuchModule = errors.New("no module of that name")

// ErrStillAssigned is why a module cannot be forgotten.
//
// Its own error because it is not a fault: it means a machine is running that module now, and
// removing the record would leave the mesh unable to describe what is on it.
var ErrStillAssigned = errors.New("that module is still assigned to nodes")

// Source is where a module comes from and what has been built from it.
type Source struct {
	Repository string
	Ref        string
	// BuiltFrom is the commit the manifest the mesh holds was read at.
	BuiltFrom string
	// Head is the newest commit the source is known to have.
	Head string
}

// Current reports whether what the mesh holds is what the source last had.
//
// A module with no source is always current: it was handed over directly, and there is nothing
// it could be behind. Saying "out of date" about it would be inventing a comparison.
func (s Source) Current() bool {
	if s.Repository == "" || s.Head == "" {
		return true
	}
	return s.BuiltFrom == s.Head
}

// RegisterModule records a module, replacing what was there.
//
// Replacing rather than refusing, because a manifest changing is the ordinary case -- a module
// gains a requirement, a claim, a resource. What matters is that the change is visible the next
// time a node is resolved, which it is.
func (i *Inventory) RegisterModule(ctx context.Context, m catalogue.Manifest, from Source) error {
	raw, err := json.Marshal(m)
	if err != nil {
		return err
	}

	// A module registered without provenance keeps whatever it had. Handing over a manifest by
	// hand is a legitimate way to fix something in a hurry, and it should not silently erase the
	// record of where the module normally comes from — which is the only thing that would say,
	// afterwards, that the machine is running something nobody can rebuild.
	_, err = i.store.Pool().Exec(ctx,
		`insert into module (name, manifest, version, source, ref, built_from, source_head)
		 values ($1, $2, nullif($3,''), nullif($4,''), nullif($5,''), nullif($6,''), nullif($6,''))
		 on conflict (name) do update set
		     manifest   = excluded.manifest,
		     version    = excluded.version,
		     registered = now(),
		     source     = coalesce(excluded.source, module.source),
		     ref        = coalesce(excluded.ref, module.ref),
		     built_from = coalesce(excluded.built_from, module.built_from),
		     source_head = coalesce(excluded.built_from, module.source_head)`,
		m.Module, raw, m.Version, from.Repository, from.Ref, from.BuiltFrom)
	return err
}

// SourceMoved records that a module's source has a newer commit than the mesh has built.
//
// This is the whole of noticing. Nothing here builds anything — it writes down that the two
// halves differ, which is what makes *is this current?* answerable without building, and what
// makes a module that nobody rebuilt visible rather than silent.
func (i *Inventory) SourceMoved(ctx context.Context, module, head string) error {
	tag, err := i.store.Pool().Exec(ctx,
		`update module set source_head = $2, source_seen = now() where name = $1`, module, head)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return fmt.Errorf("%w: %s", ErrNoSuchModule, module)
	}
	return nil
}

// SourceOf is where a module came from and whether the mesh is behind it.
func (i *Inventory) SourceOf(ctx context.Context, module string) (Source, error) {
	var s Source
	var repo, ref, built, head *string
	err := i.store.Pool().QueryRow(ctx,
		`select source, ref, built_from, source_head from module where name = $1`,
		module).Scan(&repo, &ref, &built, &head)
	if errors.Is(err, pgx.ErrNoRows) {
		return Source{}, fmt.Errorf("%w: %s", ErrNoSuchModule, module)
	}
	if err != nil {
		return Source{}, err
	}
	for _, pair := range []struct {
		from *string
		to   *string
	}{{repo, &s.Repository}, {ref, &s.Ref}, {built, &s.BuiltFrom}, {head, &s.Head}} {
		if pair.from != nil {
			*pair.to = *pair.from
		}
	}
	return s, nil
}

// Behind is every module the mesh has not built from what its source now has, with the nodes
// running the old one.
//
// The nodes are the point. "Is this module out of date" is a fact about the catalogue; "which
// machines are running last week's version" is the question somebody actually has, and it is the
// one novox/hq ADR 0010 names as the thing that must not be lost.
func (i *Inventory) Behind(ctx context.Context) (map[string][]string, error) {
	rows, err := i.store.Pool().Query(ctx,
		`select m.name, coalesce(n.name, '')
		   from module m
		   left join assignment a on a.module = m.name
		   left join node n on n.id = a.node
		  where m.source is not null
		    and m.source_head is not null
		    and coalesce(m.built_from, '') is distinct from m.source_head
		  order by m.name, n.name`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	out := map[string][]string{}
	for rows.Next() {
		var module, node string
		if err := rows.Scan(&module, &node); err != nil {
			return nil, err
		}
		if _, seen := out[module]; !seen {
			out[module] = nil
		}
		if node != "" {
			out[module] = append(out[module], node)
		}
	}
	return out, rows.Err()
}

// Catalogue is every module the mesh knows about, which is what resolution needs: the question
// "how many modules provide this" cannot be asked of a subset.
func (i *Inventory) Catalogue(ctx context.Context) (map[string]catalogue.Manifest, error) {
	rows, err := i.store.Pool().Query(ctx, `select manifest from module order by name`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	out := map[string]catalogue.Manifest{}
	for rows.Next() {
		var raw []byte
		if err := rows.Scan(&raw); err != nil {
			return nil, err
		}
		var m catalogue.Manifest
		if err := json.Unmarshal(raw, &m); err != nil {
			return nil, err
		}
		out[m.Module] = m
	}
	return out, rows.Err()
}

// Provide records a module the control plane ships with itself.
//
// The mesh's own private network is one: what computes its files is in this binary, so the
// manifest is too. Marked so it can be told apart from a module somebody wrote — not because it
// behaves differently, but because "where did this come from" must have an answer for everything
// in the catalogue, and "it came with the control plane" is that answer.
func (i *Inventory) Provide(ctx context.Context, m catalogue.Manifest) error {
	raw, err := json.Marshal(m)
	if err != nil {
		return err
	}
	_, err = i.store.Pool().Exec(ctx,
		`insert into module (name, manifest, version, source)
		 values ($1, $2, $3, 'the control plane')
		 on conflict (name) do update set manifest = excluded.manifest,
		   version = excluded.version, source = 'the control plane'`,
		m.Module, raw, m.Version)
	return err
}

// Provided reports whether a module came with the control plane rather than from a repository.
func (i *Inventory) Provided(ctx context.Context, name string) (bool, error) {
	var source *string
	err := i.store.Pool().QueryRow(ctx,
		`select source from module where name = $1`, name).Scan(&source)
	if err != nil {
		return false, err
	}
	return source != nil && *source == "the control plane", nil
}

// ForgetModule removes a module, unless a machine is running it, and never one the control plane
// provides.
func (i *Inventory) ForgetModule(ctx context.Context, name string) error {
	provided, err := i.Provided(ctx, name)
	if err != nil {
		return err
	}
	if provided {
		// Refused rather than removed and re-created on the next migrate, which would look like
		// it worked and quietly come back. Taking it off a machine is what "I do not want this"
		// means, and that is what unassign is for.
		return fmt.Errorf(
			"%s comes with the control plane and cannot be forgotten; unassign it instead", name)
	}

	var on []string
	rows, err := i.store.Pool().Query(ctx,
		`select n.name from assignment a join node n on n.id = a.node where a.module = $1
		 order by n.name`, name)
	if err != nil {
		return err
	}
	for rows.Next() {
		var node string
		if err := rows.Scan(&node); err != nil {
			rows.Close()
			return err
		}
		on = append(on, node)
	}
	rows.Close()
	if len(on) > 0 {
		return fmt.Errorf("%w: %s. Unassign it first", ErrStillAssigned, strings.Join(on, ", "))
	}

	tag, err := i.store.Pool().Exec(ctx, `delete from module where name = $1`, name)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return fmt.Errorf("%w: %s", ErrNoSuchModule, name)
	}
	return nil
}

// Assign puts a module on a node.
//
// Records the intention and checks nothing. Whether the set of assignments can actually become a
// declaration is resolution's question, asked over the whole set at once — and asking it here,
// one module at a time, would let an assignment look accepted and then refuse when a second
// arrives.
func (i *Inventory) Assign(ctx context.Context, nodeName, module string) error {
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return err
	}
	_, err = i.store.Pool().Exec(ctx,
		`insert into assignment (node, module) values ($1, $2) on conflict do nothing`,
		node.ID, module)
	if err != nil && strings.Contains(err.Error(), "assignment_module_fkey") {
		return fmt.Errorf("%w: %s", ErrNoSuchModule, module)
	}
	return err
}

// Unassign takes a module off a node.
func (i *Inventory) Unassign(ctx context.Context, nodeName, module string) error {
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return err
	}
	tag, err := i.store.Pool().Exec(ctx,
		`delete from assignment where node = $1 and module = $2`, node.ID, module)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return fmt.Errorf("%s is not assigned to %s", module, nodeName)
	}
	return nil
}

// Assigned is what a person put on this node, which is not the same as what it runs: resolution
// adds whatever those modules require.
func (i *Inventory) Assigned(ctx context.Context, nodeName string) ([]string, error) {
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return nil, err
	}
	rows, err := i.store.Pool().Query(ctx,
		`select module from assignment where node = $1 order by module`, node.ID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var out []string
	for rows.Next() {
		var m string
		if err := rows.Scan(&m); err != nil {
			return nil, err
		}
		out = append(out, m)
	}
	return out, rows.Err()
}

// ProfileOf is what a node last said it can do, as resolution needs it: the capabilities that are
// present, and nothing else.
func (i *Inventory) ProfileOf(ctx context.Context, nodeName string) (map[string]bool, error) {
	var raw []byte
	err := i.store.Pool().QueryRow(ctx,
		`select profile from node where name = $1`, nodeName).Scan(&raw)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, fmt.Errorf("%w: %s", ErrNoSuchNode, nodeName)
	}
	if err != nil {
		return nil, err
	}

	out := map[string]bool{}
	if len(raw) == 0 {
		// A node that has never reported. Not an error, and not an empty machine either — every
		// capability will read as absent, so anything requiring one is refused with "the wrong
		// machine", which is wrong but visible. Better than assuming it can do everything.
		return out, nil
	}
	var reported struct {
		Capabilities []struct {
			Name    string `json:"name"`
			Present bool   `json:"present"`
		} `json:"capabilities"`
	}
	if err := json.Unmarshal(raw, &reported); err != nil {
		return nil, err
	}
	for _, c := range reported.Capabilities {
		if c.Present {
			out[c.Name] = true
		}
	}
	return out, nil
}

// SetSettings records what somebody wants a module's configuration to say.
//
// An empty node name means the whole mesh. Replacing rather than merging what is already there:
// this is a statement of the whole layer, so removing a key is done by leaving it out, which is
// the only way removing one could work at all.
func (i *Inventory) SetSettings(ctx context.Context, nodeName, module string, values map[string]any) error {
	raw, err := json.Marshal(values)
	if err != nil {
		return err
	}
	if nodeName == "" {
		_, err = i.store.Pool().Exec(ctx,
			`insert into settings (node, module, values) values (null, $1, $2)
			 on conflict (module) where node is null
			 do update set values = excluded.values, set_at = now()`, module, raw)
		return wrapModule(err, module)
	}
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return err
	}
	_, err = i.store.Pool().Exec(ctx,
		`insert into settings (node, module, values) values ($1, $2, $3)
		 on conflict (node, module) where node is not null
		 do update set values = excluded.values, set_at = now()`, node.ID, module, raw)
	return wrapModule(err, module)
}

func wrapModule(err error, module string) error {
	if err != nil && strings.Contains(err.Error(), "settings_module_fkey") {
		return fmt.Errorf("%w: %s", ErrNoSuchModule, module)
	}
	return err
}

// ClearSettings removes a layer.
func (i *Inventory) ClearSettings(ctx context.Context, nodeName, module string) error {
	if nodeName == "" {
		_, err := i.store.Pool().Exec(ctx,
			`delete from settings where module = $1 and node is null`, module)
		return err
	}
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return err
	}
	_, err = i.store.Pool().Exec(ctx,
		`delete from settings where module = $1 and node = $2`, module, node.ID)
	return err
}

// SettingsFor is the layers that apply to one module on one node, in the order they are applied.
//
// The mesh's first, then the node's, so a node that differs is expressed by differing rather
// than by restating everything the rest of the mesh already says.
func (i *Inventory) SettingsFor(ctx context.Context, nodeName, module string) ([]catalogue.Layer, error) {
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return nil, err
	}
	rows, err := i.store.Pool().Query(ctx,
		`select node is null, values from settings
		  where module = $1 and (node is null or node = $2)
		  order by node is null desc`, module, node.ID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var layers []catalogue.Layer
	for rows.Next() {
		var meshWide bool
		var raw []byte
		if err := rows.Scan(&meshWide, &raw); err != nil {
			return nil, err
		}
		values := map[string]any{}
		if err := json.Unmarshal(raw, &values); err != nil {
			return nil, err
		}
		from := nodeName
		if meshWide {
			from = "the mesh"
		}
		layers = append(layers, catalogue.Layer{From: from, Values: values})
	}
	return layers, rows.Err()
}

// PinProvision records which node a machine gets a provision from.
//
// Only needed when more than one node could answer. Recordable before that, because a mesh with
// one database should not change where an existing machine gets its data the day a second
// arrives.
func (i *Inventory) PinProvision(ctx context.Context, nodeName, provision, provider string) error {
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return err
	}
	from, err := i.NodeByName(ctx, provider)
	if err != nil {
		return err
	}
	_, err = i.store.Pool().Exec(ctx,
		`insert into provision_pin (node, name, provider) values ($1, $2, $3)
		 on conflict (node, name) do update set provider = excluded.provider, pinned_at = now()`,
		node.ID, provision, from.ID)
	return err
}

// UnpinProvision removes a choice, putting the question back.
func (i *Inventory) UnpinProvision(ctx context.Context, nodeName, provision string) error {
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return err
	}
	tag, err := i.store.Pool().Exec(ctx,
		`delete from provision_pin where node = $1 and name = $2`, node.ID, provision)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return fmt.Errorf("%s was not told where to get %q from", nodeName, provision)
	}
	return nil
}

// PinsFor is what a node was told about where its provisions come from.
func (i *Inventory) PinsFor(ctx context.Context, nodeName string) (map[string]string, error) {
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return nil, err
	}
	rows, err := i.store.Pool().Query(ctx,
		`select p.name, n.name from provision_pin p join node n on n.id = p.provider
		 where p.node = $1`, node.ID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	out := map[string]string{}
	for rows.Next() {
		var name, provider string
		if err := rows.Scan(&name, &provider); err != nil {
			return nil, err
		}
		out[name] = provider
	}
	return out, rows.Err()
}

// pinRows is how many pins a node holds, counted in the table rather than through the join that
// reads them.
//
// For a test that would otherwise pass for the wrong reason: PinsFor joins on the provider, so a
// pin left behind by a departed node is invisible through it whether it was cleaned up or not.
func (i *Inventory) pinRows(ctx context.Context, nodeName string) (int, error) {
	node, err := i.NodeByName(ctx, nodeName)
	if err != nil {
		return 0, err
	}
	var n int
	err = i.store.Pool().QueryRow(ctx,
		`select count(*) from provision_pin where node = $1`, node.ID).Scan(&n)
	return n, err
}

// Entry is one module as a catalogue shows it: what it is, where it came from, and who runs it.
type Entry struct {
	Manifest catalogue.Manifest
	Source   Source
	// On is every node this module is assigned to, sorted.
	On []string
	// Provided is true when the module came with the control plane rather than from a repository.
	Provided bool
}

// Catalogued is every module the mesh knows about, with everything a person asks about one.
//
// **One query rather than a call per module.** A catalogue that costs a round trip per row is a
// catalogue nobody lists, and the questions here — what is this, where did it come from, who is
// running it — are asked together every time.
func (i *Inventory) Catalogued(ctx context.Context) ([]Entry, error) {
	rows, err := i.store.Pool().Query(ctx,
		`select m.name, m.manifest,
		        coalesce(m.source, ''), coalesce(m.ref, ''),
		        coalesce(m.built_from, ''), coalesce(m.source_head, ''),
		        coalesce(array_agg(n.name order by n.name) filter (where n.name is not null), '{}')
		 from module m
		 left join assignment a on a.module = m.name
		 left join node n on n.id = a.node
		 group by m.name, m.manifest, m.source, m.ref, m.built_from, m.source_head
		 order by m.name`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var out []Entry
	for rows.Next() {
		var raw []byte
		var name string
		var source Source
		var on []string
		if err := rows.Scan(&name, &raw, &source.Repository, &source.Ref,
			&source.BuiltFrom, &source.Head, &on); err != nil {
			return nil, err
		}
		var m catalogue.Manifest
		if err := json.Unmarshal(raw, &m); err != nil {
			return nil, err
		}
		entry := Entry{Manifest: m, Source: source, On: on}
		if source.Repository == providedBy {
			// It came with the control plane. Not a repository, and showing it as one would have
			// somebody go looking for it.
			entry.Provided = true
			entry.Source = Source{}
		}
		out = append(out, entry)
	}
	return out, rows.Err()
}

// providedBy is what the source column says for a module the control plane ships.
const providedBy = "the control plane"