package main

import (
	"fmt"
	"path"
	"slices"
	"sort"
	"strings"

	"github.com/novox/mesh-controller/internal/catalogue"
	"github.com/novox/mesh-controller/internal/inventory"
	"github.com/novox/mesh-controller/internal/link"
)

// The change plan (novox/hq ADR 0238): **one commit, one plan** — what a change does to the mesh, computed
// from its diffset (a repository, the branch it merges into, the commit at hand) by the planner, never by
// a mapping of its own. reachOfMerge answers what moves and what follows it; this adds where each module
// goes — the deploy plan, machine by machine in the build plan's order — and what is not an ordinary
// send. A pull request's check posts it with its verdict; the release a merge makes follows the same
// planner, so the two can be compared.

// policyOf is a module's upgrade policy, as the controller holds it; false when it cannot be read.
type policyOf func(module string) (inventory.Upgrade, bool)

// changePlanOf is the change plan of a reach: pure, so it is tested without a store.
func changePlanOf(repository, base, head string, r mergeReach, entries []inventory.Entry, policy policyOf) link.ChangePlan {
	p := link.ChangePlan{Repository: repository, Base: base, Head: head, Moved: r.Moved(), Dependents: r.Dependents(),
		New: r.Added, Unread: r.Unread, Tiers: r.Plan.Tiers}
	byName := map[string]inventory.Entry{}
	for _, e := range entries {
		byName[e.Manifest.Module] = e
	}
	// The machine holding the bus, whose declaration carries every module's grants (novox/hq issue 490).
	holder := ""
	for _, e := range entries {
		if e.Manifest.BusUsers != "" && e.Manifest.ClaimsSeat(catalogue.BrokerSeat) && len(e.On) > 0 {
			holder = e.On[0]
		}
	}
	var granting []string
	machines := map[string]*link.MachinePlan{}
	machine := func(name string) *link.MachinePlan {
		if machines[name] == nil {
			machines[name] = &link.MachinePlan{Machine: name}
		}
		return machines[name]
	}
	for _, tier := range r.Plan.Tiers {
		for _, name := range tier {
			e, held := byName[name]
			if !held {
				continue
			}
			u, known := policy(name)
			waits := known && !u.RollOut
			for _, on := range e.On {
				if waits {
					machine(on).Waits = append(machine(on).Waits, name)
				} else {
					machine(on).Receives = append(machine(on).Receives, name)
				}
			}
			if !waits && holder != "" && !(len(e.On) == 1 && e.On[0] == holder) && len(e.On) > 0 &&
				!slices.Contains(granting, name) {
				granting = append(granting, name)
			}
			switch {
			case (name == "nats" || catalogue.ProvidesBus(e.Manifest)) && len(e.On) > 0:
				// Said before the merge (novox/hq issue 336): a new bus build holds every send to the bus's machine
				// until a person takes the step, so merging it is a promise to take it.
				p.Steps = append(p.Steps, fmt.Sprintf("%s: %s is never sent by an ordinary send, and until %s runs, "+
					"nothing else is sent to %s either — unless the new build turns out the same as the one running there "+
					"(issue 280)", busUpgradeNeeded, name, busUpgradeVerb, strings.Join(e.On, ", ")))
			case name == "nats" || catalogue.ProvidesBus(e.Manifest):
				p.Steps = append(p.Steps, "a planned bus step: the bus is upgraded by `bus upgrade`, never by an ordinary send")
			case waits && len(e.On) > 0 && (u.From == catalogue.FromModule || u.From == catalogue.FromData):
				// Judged per machine by the walk, against the build each was last sent (novox/hq ADR 0377).
				p.Steps = append(p.Steps, fmt.Sprintf("%s waits for a person: its policy records (%s) — unless on a machine "+
					"its move recreates none of its containers and moves none of its data, which the walk judges and then sends",
					name, orNone(u.From)))
			case waits && len(e.On) > 0:
				p.Steps = append(p.Steps, fmt.Sprintf("%s waits for a person: its policy records (%s)", name,
					orNone(u.From)))
			}
			if len(e.Manifest.Provides) > 0 && len(e.On) > 0 {
				var offers []string
				for _, o := range e.Manifest.Provides {
					offers = append(offers, o.Name)
				}
				p.Steps = append(p.Steps, fmt.Sprintf("%s provides %s: its consumers are sent again after it",
					name, strings.Join(offers, ", ")))
			}
			if e.Manifest.Data != nil && len(e.On) > 0 {
				p.Steps = append(p.Steps, fmt.Sprintf("%s keeps data (ADR 0233): what it holds is backed up before it moves", name))
			}
		}
	}
	if len(granting) > 0 {
		// Said before the merge (novox/hq issue 490): what the walk does when the change alters the bus's
		// user list. Whether it does is known only once the builds are registered, so it is said as a rule.
		p.Steps = append(p.Steps, fmt.Sprintf("%s: if this changes what the bus's user list says (a new tool, "+
			"subject or user), %s is sent that list alone, every build there kept, before %s is judged on its first "+
			"machine", grantsStepWord, holder, strings.Join(granting, ", ")))
	}
	var names []string
	for name := range machines {
		names = append(names, name)
	}
	sort.Strings(names)
	for _, name := range names {
		p.Machines = append(p.Machines, *machines[name])
	}
	p.Summary = summaryOf(p)
	p.Class = changeClassOf(p, entries)
	return p
}

// classNone is the class of a change that moves no module: nothing for a walk to move (novox/hq ADR 0313 §2).
const classNone = "none"

// changeClassOf is a change plan's class (novox/hq ADR 0313 §2): that of the slowest-budgeted module it moves,
// itself or as a dependent — core when one is on the controller's own path or holds the mesh's resolver, leaf
// otherwise — and none when it moves nothing. A module it adds a directory for counts by its own class: the
// catalogue names a module's directory by the module, so the directory's last element is its name. The graph holds
// no manifest of it yet, so a new module is core by its name alone (on the controller's own path), never by a
// resolver claim its manifest makes.
func changeClassOf(p link.ChangePlan, entries []inventory.Entry) string {
	if len(p.Moved) == 0 && len(p.Dependents) == 0 && len(p.New) == 0 {
		return classNone
	}
	modules := append(append([]string{}, p.Moved...), p.Dependents...)
	for _, dir := range p.New {
		if name := path.Base(strings.Trim(dir, "/")); name != "." && name != "/" && name != "" {
			modules = append(modules, name)
		}
	}
	return classOfModules(modules, entries)
}

// grantsStepWord names the grants step (novox/hq issue 490): the bus's user list sent alone to the machine
// holding the bus ahead of a walk's gate. Not the bus step, which replaces the bus itself.
const grantsStepWord = "grants step"

// busUpgradeNeeded is how a change plan says that merging it holds the bus's machine for a person's step.
const busUpgradeNeeded = "merging this needs a person's bus upgrade"

// summaryOf is a change plan in one line: what it builds, where it goes, and whether the bus moves.
func summaryOf(p link.ChangePlan) string {
	if len(p.Moved) == 0 && len(p.New) == 0 {
		return "builds nothing: the change touches no module of the mesh's graph"
	}
	var parts []string
	what := strings.Join(p.Moved, ", ")
	if len(p.Dependents) > 0 {
		what += fmt.Sprintf(" (+%d dependent(s))", len(p.Dependents))
	}
	if len(p.New) > 0 {
		if what != "" {
			what += ", "
		}
		what += "new: " + strings.Join(p.New, ", ")
	}
	var to []string
	for _, m := range p.Machines {
		if len(m.Receives) > 0 {
			to = append(to, m.Machine)
		}
	}
	if len(to) > 0 {
		parts = append(parts, "builds "+what+" → "+strings.Join(to, ", "))
	} else {
		parts = append(parts, "builds "+what+", sent nowhere")
	}
	bus := "no bus step"
	for _, s := range p.Steps {
		switch {
		case strings.HasPrefix(s, busUpgradeNeeded):
			bus = busUpgradeNeeded
		case strings.HasPrefix(s, "a planned bus step") && bus == "no bus step":
			bus = "a bus step"
		}
	}
	parts = append(parts, bus)
	waiting := 0
	for _, m := range p.Machines {
		waiting += len(m.Waits)
	}
	if waiting > 0 {
		parts = append(parts, fmt.Sprintf("%d wait(s) for a person", waiting))
	}
	return strings.Join(parts, "; ")
}

// planText is a change plan as a person reads it, for the pull request's comment.
func planText(p link.ChangePlan) string {
	var b strings.Builder
	fmt.Fprintf(&b, "change plan of %s at %.8s into %s: %s\n", p.Repository, p.Head, p.Base, p.Summary)
	for i, tier := range p.Tiers {
		fmt.Fprintf(&b, "  tier %d: %s\n", i, strings.Join(tier, ", "))
	}
	for _, m := range p.Machines {
		line := "  " + m.Machine + ": "
		if len(m.Receives) > 0 {
			line += "receives " + strings.Join(m.Receives, ", ")
		}
		if len(m.Waits) > 0 {
			if len(m.Receives) > 0 {
				line += "; "
			}
			line += "waits for a person: " + strings.Join(m.Waits, ", ")
		}
		b.WriteString(line + "\n")
	}
	for _, s := range p.Steps {
		b.WriteString("  - " + s + "\n")
	}
	if len(p.Unread) > 0 {
		fmt.Fprintf(&b, "  read by no module's build: %s\n", strings.Join(p.Unread, ", "))
	}
	return b.String()
}