// Package eval scores nudge phrasing — the sentences the operator actually
// hears. It is the phrasing counterpart to internal/router/eval.
//
// Why a separate package from phraser: the fixture must be scorable by BOTH
// phrasing paths (the deterministic Stub and the resident model) from outside
// the phraser package, and a _test.go file inside phraser cannot be imported.
// So the fixture is embedded here and the scorer takes a Nudger interface.
//
// Why deterministic checks and not model judgement: the resident model is a
// 0.8B. It cannot grade its own tone. Every check in checks.go is a string or
// length test that a human can read and disagree with. A score here is a claim
// about measurable properties, not about whether a sentence is good.
//
// DESIGN.md § "Rules decide, LLM phrases" is why there is no send/veto signal
// anywhere in this package: the rule already decided she speaks. The phraser
// only words it, so a nudge the model refuses to write is a failure, never a
// legitimate outcome.
package eval

import (
	"context"
	_ "embed"
	"encoding/json"
	"fmt"
	"sort"
	"strings"
	"time"

	"github.com/kami/maven/internal/delivery"
	"github.com/kami/maven/internal/loop"
	"github.com/kami/maven/internal/store"
)

//go:embed nudges_v1.json
var fixtureJSON []byte

// SchemaVersion — the version this package understands.
const SchemaVersion = 1

// Case — one nudge situation, as a real tick would present it. The fields are
// the (rule, severity, context) input DESIGN.md names, flattened to JSON.
//
// WantAny is the on-topic contract: at least one of these lowercased fragments
// must appear in the message. A water nudge that never mentions water is a
// failure however charming it reads. Fragments are stems ("вод") so declension
// does not defeat the check, and they list both languages because the Stub is
// still English (see the writeup).
type Case struct {
	ID       string `json:"id"`
	Rule     string `json:"rule"`
	Severity int    `json:"severity"`

	// SinceMinutes — age of the rule's own fact. 0 means "no such fact", which
	// is the branch where the phraser has no duration to name.
	SinceMinutes int `json:"since_minutes"`

	// FactKey/FactValue/FactSource — the aggregate fact behind the ops rules.
	// service_down phrasing reads the key for the service name.
	FactKey    string `json:"fact_key,omitempty"`
	FactValue  string `json:"fact_value,omitempty"`
	FactSource string `json:"fact_source,omitempty"`

	// QuietHours/CalendarBusy — the bad moments. The gate already let this
	// nudge through (ops outranks quiet hours), so the phrasing still has to be
	// short and plain rather than apologetic about the timing.
	QuietHours   bool `json:"quiet_hours,omitempty"`
	CalendarBusy bool `json:"calendar_busy,omitempty"`

	WantAny []string `json:"want_any"`
	Tags    []string `json:"tags,omitempty"`
	Note    string   `json:"note,omitempty"`
}

// Fixture — the versioned envelope. SchemaVersion gates the loader so an older
// binary refuses a fixture it would misread instead of reporting a wrong score.
type Fixture struct {
	SchemaVersion int      `json:"schema_version"`
	Name          string   `json:"name"`
	ReferenceNow  string   `json:"reference_now"`
	Notes         []string `json:"notes"`
	Cases         []Case   `json:"cases"`
}

// Load returns the embedded fixture.
func Load() (Fixture, error) {
	var f Fixture
	if err := json.Unmarshal(fixtureJSON, &f); err != nil {
		return Fixture{}, fmt.Errorf("parse fixture: %w", err)
	}
	if f.SchemaVersion != SchemaVersion {
		return Fixture{}, fmt.Errorf("fixture schema_version %d, want %d", f.SchemaVersion, SchemaVersion)
	}
	if len(f.Cases) == 0 {
		return Fixture{}, fmt.Errorf("fixture has no cases")
	}
	return f, nil
}

// Now — the fixture's reference clock, so fact ages are reproducible.
func (f Fixture) Now() (time.Time, error) {
	t, err := time.Parse(time.RFC3339, f.ReferenceNow)
	if err != nil {
		return time.Time{}, fmt.Errorf("parse reference_now %q: %w", f.ReferenceNow, err)
	}
	return t, nil
}

// Candidate rebuilds the loop.Candidate a tick would hand the phraser.
func (c Case) Candidate(now time.Time) loop.Candidate {
	state := loop.State{
		Now:          now,
		Facts:        map[string]store.Fact{},
		QuietHours:   c.QuietHours,
		CalendarBusy: c.CalendarBusy,
	}
	if c.SinceMinutes > 0 {
		state.Facts[c.Rule] = store.Fact{
			Key: c.Rule,
			Ts:  now.Add(-time.Duration(c.SinceMinutes) * time.Minute),
		}
	}
	if c.FactKey != "" {
		state.Facts[c.Rule] = store.Fact{
			Key:    c.FactKey,
			Value:  c.FactValue,
			Source: c.FactSource,
			Ts:     now.Add(-time.Duration(c.SinceMinutes) * time.Minute),
		}
	}
	sev := loop.Severity(c.Severity)
	return loop.Candidate{
		Rule:     loop.Rule{Name: c.Rule, Severity: sev},
		Severity: sev,
		State:    state,
	}
}

// Nudger — the one thing a phrasing path must do to be scorable. Both
// *phraser.Stub and *phraser.LLMPhraser satisfy it.
type Nudger interface {
	PhraseNudge(ctx context.Context, c loop.Candidate) (delivery.PhrasedNudge, error)
}

// Outcome — one scored case. Failed lists the check names that did not pass,
// Reasons the human-readable detail. Failed is empty exactly when Pass is true.
type Outcome struct {
	Case    Case
	Body    string
	Mood    string
	Err     error
	Latency time.Duration
	Pass    bool
	Failed  []string
	Reasons []string
}

// Report — the aggregate. ByCheck is the useful part: one composite percentage
// hides which property broke, and tuning a prompt needs to know.
type Report struct {
	Name     string
	Total    int
	Passed   int
	Errors   int
	ByCheck  map[string]int
	ByRule   map[string]TagStat
	Outcomes []Outcome
	P50      time.Duration
	P95      time.Duration
	Max      time.Duration
}

// TagStat — passed/total for one slice of the fixture.
type TagStat struct{ Passed, Total int }

// Accuracy — fraction of cases that passed every check.
func (r Report) Accuracy() float64 {
	if r.Total == 0 {
		return 0
	}
	return float64(r.Passed) / float64(r.Total)
}

// Score runs every case through p and aggregates. A phrasing error scores as a
// miss and is counted in Errors — "the model was down" and "the model wrote
// something bad" are different numbers and a prompt change must not be able to
// hide behind the first one.
//
// Latency is wall-clock per PhraseNudge call. On the CPU/iGPU target a nudge
// the model takes a minute to word has already missed its moment.
func Score(ctx context.Context, name string, p Nudger, f Fixture) (Report, error) {
	now, err := f.Now()
	if err != nil {
		return Report{}, err
	}
	rep := Report{
		Name:    name,
		Total:   len(f.Cases),
		ByCheck: map[string]int{},
		ByRule:  map[string]TagStat{},
	}
	for _, name := range CheckNames {
		rep.ByCheck[name] = 0
	}
	lat := make([]time.Duration, 0, len(f.Cases))

	for _, c := range f.Cases {
		start := time.Now()
		pn, err := p.PhraseNudge(ctx, c.Candidate(now))
		o := Outcome{Case: c, Body: pn.Body, Mood: pn.Mood, Err: err, Latency: time.Since(start)}
		lat = append(lat, o.Latency)

		if err != nil {
			rep.Errors++
			o.Failed = append(o.Failed, "call")
			o.Reasons = append(o.Reasons, fmt.Sprintf("phrase error: %v", err))
		} else {
			for _, res := range RunChecks(c, pn.Body, pn.Mood) {
				if res.Pass {
					rep.ByCheck[res.Name]++
					continue
				}
				o.Failed = append(o.Failed, res.Name)
				o.Reasons = append(o.Reasons, res.Name+": "+res.Detail)
			}
		}

		o.Pass = len(o.Failed) == 0
		if o.Pass {
			rep.Passed++
		}
		bump(rep.ByRule, ruleFamily(c.Rule), o.Pass)
		rep.Outcomes = append(rep.Outcomes, o)
	}

	sort.Slice(lat, func(i, j int) bool { return lat[i] < lat[j] })
	rep.P50, rep.P95 = percentile(lat, 0.50), percentile(lat, 0.95)
	if len(lat) > 0 {
		rep.Max = lat[len(lat)-1]
	}
	return rep, nil
}

// ruleFamily collapses "routine:зарядка" to "routine" so the per-rule table
// stays readable however many routines the operator configures.
func ruleFamily(rule string) string {
	if i := strings.IndexByte(rule, ':'); i > 0 {
		return rule[:i]
	}
	return rule
}

func bump(m map[string]TagStat, key string, pass bool) {
	if key == "" {
		return
	}
	s := m[key]
	s.Total++
	if pass {
		s.Passed++
	}
	m[key] = s
}

// percentile — nearest-rank on a pre-sorted slice. No interpolation: with ~15
// samples an interpolated p95 invents a latency no call actually took.
func percentile(sorted []time.Duration, p float64) time.Duration {
	if len(sorted) == 0 {
		return 0
	}
	i := int(p * float64(len(sorted)))
	if i >= len(sorted) {
		i = len(sorted) - 1
	}
	return sorted[i]
}

// String renders the comparison table — composite score, then per-check so a
// regression names the property it broke, then latency.
func (r Report) String() string {
	var b strings.Builder
	fmt.Fprintf(&b, "%s: %d/%d cases pass every check (%.1f%%), %d errors\n",
		r.Name, r.Passed, r.Total, 100*r.Accuracy(), r.Errors)
	for _, name := range CheckNames {
		fmt.Fprintf(&b, "  %-10s %d/%d\n", name, r.ByCheck[name], r.Total)
	}
	fmt.Fprintf(&b, "  latency: p50 %s  p95 %s  max %s\n", r.P50, r.P95, r.Max)
	fmt.Fprintf(&b, "  by rule: %s\n", renderStats(r.ByRule))
	return b.String()
}

// Failures — per-case detail, sorted by ID so two runs diff cleanly.
func (r Report) Failures() string {
	var b strings.Builder
	for _, o := range r.sorted() {
		if o.Pass {
			continue
		}
		fmt.Fprintf(&b, "  %s %q\n    %s\n", o.Case.ID, o.Body, strings.Join(o.Reasons, "; "))
	}
	return b.String()
}

// Messages — every generated message verbatim, pass or fail. This is what a
// human reads to judge tone; the score only says which checks fired.
func (r Report) Messages() string {
	var b strings.Builder
	for _, o := range r.sorted() {
		mark := "ok  "
		if !o.Pass {
			mark = "FAIL"
		}
		fmt.Fprintf(&b, "  %s %-22s [%s] %q\n", mark, o.Case.ID, o.Mood, o.Body)
	}
	return b.String()
}

func (r Report) sorted() []Outcome {
	out := append([]Outcome(nil), r.Outcomes...)
	sort.Slice(out, func(i, j int) bool { return out[i].Case.ID < out[j].Case.ID })
	return out
}

func renderStats(m map[string]TagStat) string {
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	parts := make([]string, 0, len(keys))
	for _, k := range keys {
		parts = append(parts, fmt.Sprintf("%s %d/%d", k, m[k].Passed, m[k].Total))
	}
	return strings.Join(parts, "  ")
}