package compose

import (
	"errors"
	"fmt"
	"sort"

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

// notResolvable marks the one failure in a node's resolution that is a statement about the node: its assigned modules
// do not compose. Every other failure means the mesh could not be asked. Whoever gathers across the mesh skips a node
// that cannot resolve and never a node that could not be read (novox/hq 04-ISSUES/152).
type notResolvable struct{ err error }

func (n notResolvable) Error() string { return n.err.Error() }
func (n notResolvable) Unwrap() error { return n.err }

// unresolvable reports whether err is a node's own set failing to compose.
func unresolvable(err error) bool {
	var n notResolvable
	return errors.As(err, &n)
}

// Passes is what a composition found that the mesh must record, and did not: each seat held once whose holder on record
// is assigned nowhere that exactly one claimant takes over (novox/hq ADR 0449 clause 4), and the lines that say what was
// found. The caller records a pass and writes its hand act; this package does neither.
type Passes struct {
	// Passes are the seats to pass, in the order they were found.
	Passes []catalogue.SeatPass
	// Said are the lines the finding says (a seat two claimants could take, one nothing can).
	Said []string
}

// LeftOut is a node that does not resolve in the view of the rest of the mesh, with why: it offers nothing and holds
// nothing as far as every other machine's plan can tell (novox/hq issue 188).
type LeftOut struct {
	Node string
	Err  error
}

// String is the line the controller says of it.
func (l LeftOut) String() string {
	return fmt.Sprintf("%s is left out of the rest of the mesh: it does not resolve: %v", l.Node, l.Err)
}

// TheRestOfTheMesh is what every other node holds and offers, as the controller works it out (plan.go theRestOfTheMesh):
// two passes over the others, because what a node offers needs it resolved and resolving it may need what the mesh
// offers. The first takes brokered requirements on trust and answers only what each node offers; the second answers
// everything with that in hand. Nothing is declared from the first.
//
// It writes nothing. A seat the mesh passes on is returned in Passes for the caller to record; the World carries the
// holdings as they stand after the passes, and Input's own are unchanged. A node left out is returned with its reason, in
// the order the controller said them (the first pass's, then the second's when no node is excluded).
func TheRestOfTheMesh(in Input, exclude string) (catalogue.World, Passes, []LeftOut, error) {
	c := newComposer(in)
	return c.theRestOfTheMesh(exclude)
}

func (c *composer) theRestOfTheMesh(exclude string) (catalogue.World, Passes, []LeftOut, error) {
	shelf := c.in.Catalogue
	holdings := append([]catalogue.Held(nil), c.in.Holdings...)
	nodes := c.in.sorted()

	onNetwork, err := c.whereEveryoneIs()
	if err != nil {
		return catalogue.World{}, Passes{}, nil, err
	}

	type candidate struct {
		node     catalogue.Node
		assigned []string
		pins     map[string]catalogue.Chosen
		shelf    map[string]catalogue.Manifest
	}
	var others []candidate
	// Every machine's assignments, before the holdings are read by any resolution (novox/hq ADR 0449 clause 4): a seat
	// held once whose holder on record is assigned on no machine passes to its only claimant here.
	everyAssigned := map[string][]string{}
	for _, n := range nodes {
		if len(n.Assigned) > 0 {
			everyAssigned[n.Name] = n.Assigned
		}
	}
	var passes Passes
	holdings, passes = passSeatsOn(holdings, assignmentsOf(shelf, everyAssigned))
	for _, n := range nodes {
		if n.Name == exclude {
			continue
		}
		theirs := everyAssigned[n.Name]
		if len(theirs) == 0 {
			continue
		}
		others = append(others, candidate{
			node: catalogue.Node{Name: n.Name, Site: n.Place.Site, Capabilities: n.Capabilities,
				At: onNetwork[n.Name], PublicDomain: n.PublicDomain},
			assigned: theirs, pins: n.Pins, shelf: c.shelfFor(n)})
	}

	var left []LeftOut
	offered := map[string][]catalogue.Provider{}
	var firstHeld []catalogue.Held
	for _, o := range others {
		got, err := catalogue.Resolve(o.shelf, o.assigned, o.node, catalogue.World{Unchecked: true, Holdings: holdings})
		if err != nil {
			// Said, not skipped: a machine dropped here offers nothing and holds nothing.
			left = append(left, LeftOut{Node: o.node.Name, Err: err})
			continue
		}
		firstHeld = append(firstHeld, got.Claims...)
		for _, m := range got.Modules {
			for _, name := range m.OffersAt(catalogue.ScopeMesh) {
				// What that module says a consumer needs to know, with that node's settings on it.
				serves, layers, err := c.servedOnNode(o.node.Name, m, name)
				if err != nil {
					return catalogue.World{}, Passes{}, nil, err
				}
				// And its own composed names, as that node composes them (novox/hq ADR 0346).
				serves, leftOut, err := got.ServedOwnNames(m, name, serves, catalogue.WithDefaults(m, layers))
				if err != nil {
					return catalogue.World{}, Passes{}, nil, err
				}
				offered[name] = append(offered[name], catalogue.Provider{
					Node: o.node.Name, At: o.node.At, Serves: serves, Module: m.Module, LeftOut: leftOut})
			}
		}
	}
	for k := range offered {
		sort.Slice(offered[k], func(i, j int) bool {
			return offered[k][i].Node < offered[k][j].Node
		})
	}

	// The second pass is given the first pass's holdings (novox/hq ADR 0110).
	world := catalogue.World{Offered: offered, Held: firstHeld, Holdings: holdings}
	var held []catalogue.Held
	for _, o := range others {
		// Each machine is resolved with its own pins, as its plan is.
		theirs := world
		theirs.Pinned = o.pins
		got, err := catalogue.Resolve(o.shelf, o.assigned, o.node, theirs)
		if err != nil {
			// Said only for the whole-mesh view: with one machine excluded, the view is partial by design.
			if exclude == "" {
				left = append(left, LeftOut{Node: o.node.Name, Err: err})
			}
			continue
		}
		held = append(held, got.Claims...)
	}
	world.Held = held
	return world, passes, left, nil
}

// passSeatsOn finds, in the composition that finds it, the new holder of each seat held once whose holder on record is
// assigned nowhere and which has exactly one claimant able to hold it (novox/hq ADR 0449 clause 4), and answers the
// holdings as they are after it, with the passes. Nothing is recorded.
func passSeatsOn(holdings []catalogue.Held, assignments []catalogue.Assignment) ([]catalogue.Held, Passes) {
	passes, said := catalogue.SeatsToPassOn(holdings, assignments)
	out := Passes{Said: said}
	for _, p := range passes {
		out.Passes = append(out.Passes, p)
		var next []catalogue.Held
		for _, h := range holdings {
			if hs, ok := catalogue.SeatNamed(h.Claim); ok && hs.Name == p.Seat.Name {
				continue
			}
			next = append(next, h)
		}
		p.To.Site = p.From.Site
		holdings = append(next, p.To)
	}
	return holdings, out
}

// assignmentsOf are the assignments of every machine, as the passing of a seat reads them. A module assigned and
// missing from the shelf is still assigned: an assignment with no claims, so its holder is not taken for gone.
func assignmentsOf(shelf map[string]catalogue.Manifest, assigned map[string][]string) []catalogue.Assignment {
	var out []catalogue.Assignment
	names := make([]string, 0, len(assigned))
	for node := range assigned {
		names = append(names, node)
	}
	sort.Strings(names)
	for _, node := range names {
		for _, module := range assigned[node] {
			m, ok := shelf[module]
			if !ok {
				m = catalogue.Manifest{Module: module}
			}
			out = append(out, catalogue.Assignment{Node: node, Manifest: m})
		}
	}
	return out
}

// servedOnNode is what a module on a node tells a consumer of one of its provisions, with THAT node's ports on it: the
// port the node was given over the one the mesh assigned over the manifest's own, settled with the node's settings
// layers. The one derivation for every reader of a provider's address.
func (c *composer) servedOnNode(node string, m catalogue.Manifest, provision string) (map[string]any, []catalogue.Layer, error) {
	ports, layers, err := c.portsGivenOn(node, m)
	if err != nil {
		return nil, nil, err
	}
	serves := catalogue.ServedOn(m, provision, ports)
	if len(serves) > 0 {
		serves, err = catalogue.Settle(serves, catalogue.WithDefaults(m, layers))
		if err != nil {
			return nil, nil, err
		}
	}
	return serves, layers, nil
}

// portsGivenOn is where a node puts a module's ports — assigned, then given over them — and the node's settings layers
// for the module.
func (c *composer) portsGivenOn(node string, m catalogue.Manifest) (map[int]int, []catalogue.Layer, error) {
	n, err := c.in.node(node)
	if err != nil {
		return nil, nil, err
	}
	ports := map[int]int{}
	for wanted, at := range n.Ports[m.Module] {
		ports[wanted] = at
	}
	layers := n.Settings[m.Module]
	if given, err := catalogue.GivenPorts(m, layers); err == nil {
		for wanted, at := range given {
			ports[wanted] = at
		}
	}
	return ports, layers, nil
}