package module

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"strings"

	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/routing"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/server"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/store"
)

// Sentinel errors.
var (
	// ErrUnknownModule is returned for a name that names no discovered module.
	ErrUnknownModule = errors.New("module: unknown module")
	// ErrRequiredModule is returned when a required module would be disabled
	// (D-038, AC-4).
	ErrRequiredModule = errors.New("module: required modules cannot be disabled")
	// ErrDuplicateModule is returned when two directories claim the same name.
	ErrDuplicateModule = errors.New("module: duplicate module name")
	// ErrCoreDispatchName is returned when a discovered module claims a name the
	// CORE dispatches for itself — either a core dispatch module (auth · setup ·
	// recovery · core, SPEC-008 §9 D-9) or a reserved level-1 workflow (access ·
	// setup · api · static · media · ws · dev, SPEC-009 §13 Q-1). The name would
	// silently lose precedence — or silently shadow the core — so the module
	// FAILS TO LOAD. `home` is the sole exception (SPEC-009 §13 D-2).
	ErrCoreDispatchName = errors.New("module: name is reserved by the core")
)

// CoreDispatchNames are the module (PARAM2 / `do`) names the CORE registers into
// the door's dispatch registry (SPEC-008 §9 D-9, SPEC-009 §8):
//
//	auth      — the SPEC-006 enroll/login flow + the SPEC-007 `recover` action
//	setup     — the SPEC-005 wizard's steps
//	recovery  — the SPEC-007 approve/deny actions
//	core      — the SPEC-008 Modules page
//	account   — the SPEC-010 account page (factors · add a passkey · opt out)
//	users     — the SPEC-010 admin Users page (list · create + invite)
//
// A discovered module may not claim one of them: the door would either drop the
// discovered module (RegisterModule overwrites by name) or the discovered module
// would shadow the core. Either way it would be a SILENT loss of precedence, so
// the load fails closed instead.
var CoreDispatchNames = []string{"auth", "setup", "recovery", "core", "account", "users"}

// ReservedWorkflowNames are the reserved level-1 workflows (SPEC-002 §4) that a
// discovered module may NOT claim (SPEC-009 §13 Q-1). It is DERIVED from
// routing.ReservedWorkflows — the ONE source for the reserved names (D-004) —
// with `home` removed (SPEC-009 §13 D-2).
//
// `home` is deliberately EXCLUDED. `home` is both a reserved level-1 workflow
// AND the PARAM2 dashboard module, and the dashboard *is* a discovered module
// (internal/modules/home — the reference module, SPEC-008 AC-1): the two are
// separate switches, not a collision (SPEC-002 §4.4). The core registers no
// `home` *module*, so nothing can be shadowed. The derived set is therefore
// access · setup · api · static · media · ws · dev.
var ReservedWorkflowNames = reservedWorkflowNames()

// ReservedModuleNames is the full guarded set — the core dispatch modules plus
// the reserved level-1 workflows (minus `home`). A discovered module claiming
// any of these names FAILS TO LOAD (SPEC-008 §9 D-9, SPEC-009 §13 Q-1).
var ReservedModuleNames = unionNames(CoreDispatchNames, ReservedWorkflowNames)

// reservedWorkflowNames derives the guarded reserved-workflow set from the one
// source (routing.ReservedWorkflows), excluding the `home` exception.
func reservedWorkflowNames() []string {
	out := make([]string, 0, len(routing.ReservedWorkflows))
	for _, n := range routing.ReservedWorkflows {
		if n == "home" {
			continue // the exception — the reference dashboard module IS `home`
		}
		out = append(out, n)
	}
	return out
}

// unionNames concatenates name lists, dropping duplicates, preserving order.
func unionNames(lists ...[]string) []string {
	var out []string
	seen := make(map[string]bool)
	for _, l := range lists {
		for _, n := range l {
			if !seen[n] {
				seen[n] = true
				out = append(out, n)
			}
		}
	}
	return out
}

// IsCoreDispatchName reports whether name is a core dispatch module name — the
// core dispatch set above (SPEC-008 §9 D-9).
func IsCoreDispatchName(name string) bool {
	name = strings.TrimSpace(name)
	for _, n := range CoreDispatchNames {
		if n == name {
			return true
		}
	}
	return false
}

// IsReservedWorkflowName reports whether name is a reserved level-1 workflow a
// discovered module may not claim — home excluded (SPEC-009 §13 Q-1).
func IsReservedWorkflowName(name string) bool {
	name = strings.TrimSpace(name)
	for _, n := range ReservedWorkflowNames {
		if n == name {
			return true
		}
	}
	return false
}

// IsReservedModuleName reports whether name is reserved by the core — the guard
// consulted by Add. It is true for a core dispatch module OR a reserved level-1
// workflow (`home` excepted) — SPEC-008 §9 D-9, SPEC-009 §13 Q-1.
func IsReservedModuleName(name string) bool {
	name = strings.TrimSpace(name)
	for _, n := range ReservedModuleNames {
		if n == name {
			return true
		}
	}
	return false
}

// Registry is the runtime module registry: the discovered modules, in
// registration order, together with their enabled state (D-038).
//
// A disabled module is NOT in the registry (SPEC-008 §6): it is not mounted, so
// its routes 404 and its nav entry is hidden. Disabling never deletes data.
type Registry struct {
	order   []Module
	byName  map[string]Module
	enabled map[string]bool
}

// NewRegistry returns an empty registry.
func NewRegistry() *Registry {
	return &Registry{
		byName:  make(map[string]Module),
		enabled: make(map[string]bool),
	}
}

// Load discovers the modules self-registered in this binary and builds the
// runtime registry, applying the `modules:` map from config (D-038). A module
// absent from cfg keeps its default: required modules are always on, every
// other module defaults to on.
//
// A discovered module with a name reserved by the core FAILS THE LOAD
// (SPEC-008 §9 D-9, SPEC-009 §13 Q-1): the error is returned AND logged, so a
// silent loss of precedence is impossible.
func Load(cfg map[string]bool) (*Registry, error) {
	r, err := LoadModules(Discovered(), cfg)
	if err != nil {
		slog.Default().Error("module: refusing to load the discovered module set", "error", err)
		return nil, err
	}
	return r, nil
}

// LoadModules builds a registry from an explicit module set. Load uses it with
// Discovered(); tests use it with fakes.
func LoadModules(mods []Module, cfg map[string]bool) (*Registry, error) {
	r := NewRegistry()
	for _, m := range mods {
		if err := m.Register(r); err != nil {
			return nil, fmt.Errorf("module: register %s: %w", moduleName(m), err)
		}
	}
	for _, m := range r.order {
		if m.Required() {
			r.enabled[m.Name()] = true
			continue
		}
		on := true // default on; an explicit config value wins
		if v, ok := cfg[m.Name()]; ok {
			on = v
		}
		r.enabled[m.Name()] = on
	}
	return r, nil
}

// Add records a module. It is called by a module's Register method. It fails
// closed on a nil module, an empty name, a name reserved by the core (a core
// dispatch module or a reserved level-1 workflow — SPEC-008 §9 D-9, SPEC-009
// §13 Q-1), a duplicate name, or a malformed route/action set.
func (r *Registry) Add(m Module) error {
	if m == nil {
		return errors.New("module: nil module")
	}
	name := strings.TrimSpace(m.Name())
	if name == "" {
		return errors.New("module: empty module name")
	}
	// The guard runs BEFORE the registry is touched: a discovered module with a
	// reserved name must fail to load, never silently lose (or steal) precedence.
	if IsReservedModuleName(name) {
		return fmt.Errorf("%w: %q", ErrCoreDispatchName, name)
	}
	if _, dup := r.byName[name]; dup {
		return fmt.Errorf("%w: %q", ErrDuplicateModule, name)
	}
	if err := validate(name, m.Routes(), m.Actions()); err != nil {
		return err
	}
	r.order = append(r.order, m)
	r.byName[name] = m
	r.enabled[name] = true // default on; Load applies config, SetEnabled overrides
	return nil
}

// Modules returns every registered module in registration order (deterministic
// — never map iteration, AC-2).
func (r *Registry) Modules() []Module {
	out := make([]Module, len(r.order))
	copy(out, r.order)
	return out
}

// Get returns the registered module by name.
func (r *Registry) Get(name string) (Module, bool) {
	m, ok := r.byName[strings.TrimSpace(name)]
	return m, ok
}

// Enabled reports whether a module is mounted. An unknown module is not
// enabled.
func (r *Registry) Enabled(name string) bool { return r.enabled[strings.TrimSpace(name)] }

// Required reports whether the named module is required.
func (r *Registry) Required(name string) bool {
	m, ok := r.Get(name)
	return ok && m.Required()
}

// SetEnabled turns a module on or off. It refuses an unknown module and a
// required module being turned off (D-038, AC-4). It changes the RUNTIME state
// only; the config file is written by the Modules page (applies at next start).
func (r *Registry) SetEnabled(name string, on bool) error {
	name = strings.TrimSpace(name)
	m, ok := r.byName[name]
	if !ok {
		return fmt.Errorf("%w: %q", ErrUnknownModule, name)
	}
	if !on && m.Required() {
		return fmt.Errorf("%w: %q", ErrRequiredModule, name)
	}
	r.enabled[name] = on
	return nil
}

// Nav returns the names of the enabled modules, in registration order — the
// navigation the shell renders. A disabled module is absent (AC-3: its nav
// hides). Rendering is SPEC-009 (web layer); this is the seam the shell reads.
func (r *Registry) Nav() []string {
	out := make([]string, 0, len(r.order))
	for _, m := range r.order {
		if r.enabled[m.Name()] {
			out = append(out, m.Name())
		}
	}
	return out
}

// Migrations returns the migrations of every ENABLED module, in registration
// order, with each version prefixed by the module name. The core owns the
// runner (AC-5); the prefix keeps module schemas from colliding with the core
// schema or with each other.
//
// A disabled module's migrations are not applied — it is not mounted — but
// disabling never drops the tables an earlier run created (AC-3).
func (r *Registry) Migrations() []store.Migration {
	var out []store.Migration
	for _, m := range r.order {
		if !r.enabled[m.Name()] {
			continue
		}
		for _, mig := range m.Migrations() {
			out = append(out, store.Migration{
				Version: m.Name() + "/" + mig.Version,
				SQL:     mig.SQL,
			})
		}
	}
	return out
}

// Mount registers every ENABLED module's routes and actions into the door's
// dispatch registry. A disabled module is skipped, so the pure model reports it
// as not found and its routes 404 (SPEC-008 §6, AC-3).
func (r *Registry) Mount(dst *server.MapRegistry) {
	if dst == nil {
		return
	}
	for _, m := range r.order {
		if !r.enabled[m.Name()] {
			continue
		}
		mm := server.NewModule(m.Name())
		for _, rt := range m.Routes() {
			if rt.Default {
				mm.SetDefault(rt.Function, rt.Handler)
				continue
			}
			mm.AddRoute(rt.Name, rt.Function, rt.Handler)
		}
		for _, a := range m.Actions() {
			mm.AddAction(a.Name, a.Function, a.Handler)
		}
		dst.RegisterModule(mm)
	}
}

// Start runs every enabled module's optional background work, in registration
// order. The first failure stops the sequence.
func (r *Registry) Start(ctx context.Context) error {
	for _, m := range r.order {
		if !r.enabled[m.Name()] {
			continue
		}
		if err := m.Start(ctx); err != nil {
			return fmt.Errorf("module: start %s: %w", m.Name(), err)
		}
	}
	return nil
}

// LogLoaded writes the loaded module set at startup (D-028 guardrail: "log the
// loaded set — a visible registry beats hidden magic", AC-2).
func (r *Registry) LogLoaded(l *slog.Logger) {
	if l == nil {
		l = slog.Default()
	}
	all := make([]string, 0, len(r.order))
	on := make([]string, 0, len(r.order))
	off := make([]string, 0, len(r.order))
	for _, m := range r.order {
		all = append(all, m.Name())
		if r.enabled[m.Name()] {
			on = append(on, m.Name())
		} else {
			off = append(off, m.Name())
		}
	}
	l.Info("myday: modules loaded",
		"count", len(all), "loaded", all, "enabled", on, "disabled", off)
}

// validate rejects a malformed route/action set so a broken module fails at
// startup, not at request time.
func validate(name string, routes []Route, actions []Action) error {
	seenRoutes := make(map[string]bool, len(routes))
	defaults := 0
	for _, rt := range routes {
		if rt.Default {
			defaults++
			if defaults > 1 {
				return fmt.Errorf("module: %s declares more than one default route", name)
			}
		} else {
			key := strings.TrimSpace(rt.Name)
			if key == "" {
				return fmt.Errorf("module: %s has a route with an empty name", name)
			}
			if seenRoutes[key] {
				return fmt.Errorf("module: %s declares route %q twice", name, key)
			}
			seenRoutes[key] = true
		}
		if strings.TrimSpace(rt.Function) == "" {
			return fmt.Errorf("module: %s has a route with an empty function", name)
		}
		if rt.Handler == nil {
			return fmt.Errorf("module: %s route %q has no handler", name, rt.Name)
		}
	}

	seenActions := make(map[string]bool, len(actions))
	for _, a := range actions {
		key := strings.TrimSpace(a.Name)
		if key == "" {
			return fmt.Errorf("module: %s has an action with an empty name", name)
		}
		if seenActions[key] {
			return fmt.Errorf("module: %s declares action %q twice", name, key)
		}
		seenActions[key] = true
		if strings.TrimSpace(a.Function) == "" {
			return fmt.Errorf("module: %s action %q has an empty function", name, key)
		}
		if a.Handler == nil {
			return fmt.Errorf("module: %s action %q has no handler", name, key)
		}
	}
	return nil
}

// moduleName is a defensive Name() for error messages (a nil module never gets
// here).
func moduleName(m Module) string {
	if m == nil {
		return "<nil>"
	}
	return m.Name()
}