package model

import (
	"fmt"
	"sort"
	"strings"
	"sync"
	"time"

	"gitea.stevedudenhoeffer.com/steve/executus/config"
)

// tierResolver expands tier aliases (e.g. "fast", "thinking", "agent-working")
// into a concrete model spec or a comma-separated failover chain. The set of
// tier names and their FALLBACK specs are host-supplied (a map passed at
// Configure time); the live value of each tier is read from a config.Source
// under the key "model.tier.<name>", so a host whose config backend mutates at
// runtime (mort's convar) re-targets tiers without a restart, while a static
// host (gadfly's env) just gets the fallback. A small in-process cache (TTL
// from "model.tier.cache_ttl_seconds", default 30s) saves config round-trips on
// the hot path; ReloadTiers clears it.
//
// This is executus's inversion of mort's convar-bound resolver: the MECHANISM
// (tier lookup, reasoning-suffix dialect, chain validation, cache) is generic;
// the tier MAP content (which tiers exist + their default specs) is host config.
type tierResolver struct {
	cfg      config.Source
	defaults map[string]string // tier name -> fallback spec
	ttl      time.Duration
	mu       sync.RWMutex
	cache    map[string]tierEntry
	now      func() time.Time // overridable for tests
}

type tierEntry struct {
	spec      string
	reasoning string
	expires   time.Time
}

const tierConfigPrefix = "model.tier."

// NewTierResolver builds a resolver over cfg with the given tier defaults
// (name -> fallback spec). cfg may be nil (the fallbacks are then always used).
// ttl<=0 reads "model.tier.cache_ttl_seconds" (default 30s).
func NewTierResolver(cfg config.Source, defaults map[string]string, ttl time.Duration) *tierResolver {
	if ttl <= 0 {
		ttl = time.Duration(config.Int(cfg, tierConfigPrefix+"cache_ttl_seconds", 30)) * time.Second
	}
	if ttl <= 0 {
		ttl = 30 * time.Second
	}
	cp := make(map[string]string, len(defaults))
	for k, v := range defaults {
		cp[k] = v
	}
	return &tierResolver{
		cfg:      cfg,
		defaults: cp,
		ttl:      ttl,
		cache:    make(map[string]tierEntry),
		now:      time.Now,
	}
}

func (r *tierResolver) has(name string) bool {
	_, ok := r.defaults[name]
	return ok
}

func (r *tierResolver) names() []string {
	out := make([]string, 0, len(r.defaults))
	for k := range r.defaults {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

// Resolve returns the current model spec and default reasoning level for a tier
// name. ok=false if name is not a registered tier. Legacy reasoning suffixes
// (":low/:medium/:high") are stripped per chain element; the first non-empty
// level becomes the tier's default reasoning level (ollama tags like ":cloud"
// pass through). The live value is read from config with the host-supplied
// fallback; an empty resolved value yields ok=true with an empty spec
// (ParseModelRequest surfaces a clear error in that path).
func (r *tierResolver) Resolve(name string) (string, string, bool) {
	if !r.has(name) {
		return "", "", false
	}
	now := r.now()

	r.mu.RLock()
	if e, hit := r.cache[name]; hit && now.Before(e.expires) {
		r.mu.RUnlock()
		return e.spec, e.reasoning, true
	}
	r.mu.RUnlock()

	r.mu.Lock()
	defer r.mu.Unlock()
	if e, hit := r.cache[name]; hit && now.Before(e.expires) {
		return e.spec, e.reasoning, true
	}

	raw := strings.TrimSpace(config.String(r.cfg, tierConfigPrefix+name, r.defaults[name]))
	spec, level := splitReasoningSpec(raw)
	r.cache[name] = tierEntry{spec: spec, reasoning: level, expires: now.Add(r.ttl)}
	return spec, level, true
}

// Reload clears the cache so the next Resolve fetches fresh from config.
func (r *tierResolver) Reload() {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.cache = make(map[string]tierEntry)
}

// --- package-level resolver + facade ---

// defaultResolver is initialized as a package-level var (not in init()) so it
// is ready before any other file's init runs — buildRegistry's delegating
// resolver closure reads it at Resolve time. It starts with no tiers; a host
// installs its tier table via Configure.
var defaultResolver = NewTierResolver(nil, nil, 0)

// Configure installs the host's tier table. cfg is the live config source
// (nil = fallbacks only); defaults maps each tier name to its fallback spec;
// ttl<=0 uses the config'd / 30s default. The package registry's delegating
// resolver reads defaultResolver at Resolve time, so swapping it here is
// sufficient — no registry rebuild needed.
func Configure(cfg config.Source, defaults map[string]string, ttl time.Duration) {
	defaultResolver = NewTierResolver(cfg, defaults, ttl)
}

// TierNames returns the registered tier alias names (sorted). Exported so UI
// layers can populate tier dropdowns without hardcoding.
func TierNames() []string { return defaultResolver.names() }

// IsTierName reports whether s is a registered tier alias.
func IsTierName(s string) bool { return defaultResolver.has(s) }

// ReloadTiers clears the package resolver's cache so the next request resolves
// freshly from config.
func ReloadTiers() { defaultResolver.Reload() }

// ValidateTierValue returns an error if value cannot be used as a tier spec —
// specifically, when a chain entry is itself a tier name (which would form a
// resolution loop). Chain entries must be concrete provider/model specs.
func ValidateTierValue(value string) error {
	for _, part := range strings.Split(value, ",") {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		spec, _ := splitReasoning(part)
		if IsTierName(spec) {
			return fmt.Errorf("tier value %q contains tier alias %q (chains must use concrete provider/model specs, not nested tiers)", value, spec)
		}
	}
	return nil
}