// Package wing decides which brain wing an incoming raw note belongs to
// without the human typing it (hyperguild#205).
//
// The contract is conservative: a note is placed automatically only when the
// decision is explicit, or when two independent opinions (an LLM and a
// deterministic scorer) agree with enough confidence on a wing that is both
// known and eligible. Everything else is an Exception for a human to approve.
// A wing is never created here, and a wing the caller does not mark eligible
// (client wings, anything not deliberately tagged) is never auto-assigned.
package wing

import (
	"context"
	"fmt"
	"strings"
)

// Source says how a Decision was reached.
type Source string

const (
	Explicit   Source = "explicit"   // subfolder or frontmatter named the wing
	Classified Source = "classified" // classifier + scorer agreed, confident
	Exception  Source = "exception"  // needs a human
)

// Note is what the resolver sees of an incoming raw note.
type Note struct {
	Dir             string // first subfolder under raw/, "" when dropped at the top
	FrontmatterWing string // `wing:` from the note's frontmatter, "" if absent
	Text            string
}

// Suggestion is a Classifier's answer. An empty Wing means "none fits".
type Suggestion struct {
	Wing       string
	Confidence float64 // 0..1
	Reason     string
}

// Classifier proposes a wing from the candidates. Implementations must run on
// a local model; the resolver cannot enforce that.
type Classifier interface {
	Classify(ctx context.Context, text string, candidates []string) (Suggestion, error)
}

// Scorer is an independent, deterministic opinion (e.g. BM25 against each
// wing's index). Higher is better; the key is the wing name.
type Scorer interface {
	Score(text string) map[string]float64
}

// Decision is the outcome. For an Exception, Wing holds the proposal when
// there was one (so a reviewer can approve it) and is empty otherwise.
type Decision struct {
	Wing       string
	Source     Source
	Confidence float64
	Reason     string
}

// Resolver holds the policy. Known is every existing wing; Eligible reports
// whether a known wing may be assigned automatically.
type Resolver struct {
	Known      []string
	Eligible   func(wing string) bool
	Classifier Classifier
	Scorer     Scorer
	Threshold  float64
}

// Resolve never returns an error: anything it cannot decide safely is an
// Exception with the reason spelled out.
func (r Resolver) Resolve(ctx context.Context, n Note) Decision {
	dir := norm(n.Dir)
	fm := norm(n.FrontmatterWing)
	switch {
	case dir != "" && fm != "" && dir != fm:
		return exception("", 0, fmt.Sprintf("subfolder %q and frontmatter wing %q disagree", dir, fm))
	case dir != "":
		return r.explicit(dir, "subfolder")
	case fm != "":
		return r.explicit(fm, "frontmatter")
	}
	return r.classify(ctx, n)
}

func (r Resolver) explicit(w, via string) Decision {
	if why := r.refuse(w); why != "" {
		return exception(w, 0, fmt.Sprintf("%s names %q: %s", via, w, why))
	}
	return Decision{Wing: w, Source: Explicit, Confidence: 1, Reason: "named by " + via}
}

func (r Resolver) classify(ctx context.Context, n Note) Decision {
	if r.Classifier == nil {
		return exception("", 0, "no classifier configured")
	}
	s, err := r.Classifier.Classify(ctx, n.Text, r.Known)
	if err != nil {
		return exception("", 0, fmt.Sprintf("classifier failed: %v", err))
	}
	w := norm(s.Wing)
	if w == "" {
		return exception("", s.Confidence, "classifier found no fitting wing")
	}
	if why := r.refuse(w); why != "" {
		return exception(w, s.Confidence, fmt.Sprintf("classifier proposed %q: %s", w, why))
	}
	if s.Confidence < r.Threshold {
		return exception(w, s.Confidence, fmt.Sprintf("confidence %.2f below threshold %.2f", s.Confidence, r.Threshold))
	}
	top, ok := r.scorerTop(n.Text)
	if !ok {
		return exception(w, s.Confidence, "scorer has no clear opinion to cross-check against")
	}
	if top != w {
		return exception(w, s.Confidence, fmt.Sprintf("classifier says %q, scorer says %q", w, top))
	}
	return Decision{Wing: w, Source: Classified, Confidence: s.Confidence,
		Reason: fmt.Sprintf("classifier and scorer agree (%.2f): %s", s.Confidence, s.Reason)}
}

// refuse returns why a wing may not be auto-assigned, or "" if it may.
func (r Resolver) refuse(w string) string {
	if !r.known(w) {
		return "not an existing wing (new wings are never created automatically)"
	}
	if r.Eligible == nil || !r.Eligible(w) {
		return "not eligible for automatic assignment"
	}
	return ""
}

func (r Resolver) known(w string) bool {
	for _, k := range r.Known {
		if norm(k) == w {
			return true
		}
	}
	return false
}

// scorerTop returns the single best-scoring wing; a missing scorer, no scores,
// or a tie at the top is "no clear opinion".
func (r Resolver) scorerTop(text string) (string, bool) {
	if r.Scorer == nil {
		return "", false
	}
	return TopWing(r.Scorer.Score(text))
}

// TopWing returns the unique highest-scoring wing in scores, or false when
// there is none or the top is tied. Shared by the Resolver and the backtest so
// both apply the same notion of "the scorer has an opinion".
func TopWing(scores map[string]float64) (string, bool) {
	best, bestScore, tied := "", 0.0, false
	for k, v := range scores {
		switch {
		case v > bestScore:
			best, bestScore, tied = norm(k), v, false
		case v == bestScore && v > 0:
			tied = true
		}
	}
	if best == "" || tied {
		return "", false
	}
	return best, true
}

func exception(w string, conf float64, reason string) Decision {
	return Decision{Wing: w, Source: Exception, Confidence: conf, Reason: reason}
}

func norm(s string) string { return strings.ToLower(strings.TrimSpace(s)) }