package wing

import (
	"context"
	"fmt"
	"regexp"
	"slices"
	"strings"
)

// Placer decides where a raw note goes. Router is the production
// implementation; the interface lets the watcher stay ignorant of how.
type Placer interface {
	Resolve(ctx context.Context, n Note) Decision
}

// Router places a note with rules only, no model (hyperguild#208):
//
//  1. A subfolder or frontmatter `wing:` is the owner's deliberate choice. It
//     must name a plain, EXISTING wing (a typo never creates one) and then it
//     places, whatever the wing is: extraction runs on the local model, and it
//     is the owner who dropped the note there. Two signals that disagree park.
//  2. With no signal, a note whose text matches ClientBlock is parked; any
//     other note goes to Default, the one wing that is created on first use.
//
// Wings are read from disk on every decision, so a wing created while the
// server runs is usable at once.
type Router struct {
	BrainDir    string
	Default     string
	ClientBlock *regexp.Regexp // nil = no content check
}

// Resolve implements Placer. It never returns an error: anything it cannot
// decide safely is an Exception with the reason spelled out.
func (r Router) Resolve(_ context.Context, n Note) Decision {
	dir, fm := norm(n.Dir), 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")
	}
	if r.ClientBlock != nil && r.ClientBlock.MatchString(n.Text) {
		return exception("", 0, "text matches the client-content marker; not defaulted into a shared wing")
	}
	if r.Default == "" || !plainWingName(r.Default) {
		return exception("", 0, "no valid default wing configured")
	}
	return Decision{Wing: r.Default, Source: Default, Confidence: 1, Reason: "no wing named; default wing"}
}

func (r Router) explicit(w, via string) Decision {
	if !plainWingName(w) {
		return exception("", 0, fmt.Sprintf("%s names %q, which is not a plain wing name", via, w))
	}
	if w == r.Default && plainWingName(w) {
		return Decision{Wing: w, Source: Explicit, Confidence: 1, Reason: "named by " + via}
	}
	known, err := KnownWings(r.BrainDir)
	if err != nil {
		return exception(w, 0, fmt.Sprintf("cannot list wings: %v", err))
	}
	if !slices.Contains(known, w) {
		return exception(w, 0, fmt.Sprintf("%s names %q: not an existing wing (new wings are never created from a folder name)", via, strings.TrimSpace(w)))
	}
	return Decision{Wing: w, Source: Explicit, Confidence: 1, Reason: "named by " + via}
}