package match

import (
	"context"
	"strings"

	"git.totmin.ru/en2zmax/addrkit/internal/domain/address"
)

// Rewriter is an optional, pluggable query rewriter. Its only job is to
// propose alternative surface forms of a user address (for example an LLM
// normalising "кошурникова одиннадцать дробь один" to "Кошевого 11/1"). The
// rewriter never decides the answer: every proposal is parsed, validated and
// resolved deterministically, and only entries that exist in the index can be
// returned.
//
// It is defined here (consumer side) so the domain stays free of any transport
// or vendor dependency.
type Rewriter interface {
	Rewrite(ctx context.Context, raw string) ([]string, error)
}

// Resolver wraps an Index with an optional Rewriter.
//
// The deterministic path is always tried first. The rewriter is consulted only
// when the deterministic result is not a confident "found", and its
// suggestions must pass compatibleVariant before being considered, so the
// model cannot substitute a different street or corrupt the house unit.
type Resolver struct {
	index    *Index
	rewriter Rewriter
}

// NewResolver builds a resolver. rewriter may be nil to disable rewriting.
func NewResolver(index *Index, rewriter Rewriter) *Resolver {
	return &Resolver{index: index, rewriter: rewriter}
}

// Version returns the current data version.
func (r *Resolver) Version() string { return r.index.Version() }

// Ready reports whether the resolver has a usable index.
func (r *Resolver) Ready() bool { return r.index != nil && r.index.Size() > 0 }

// Resolve parses raw and resolves it, consulting the rewriter when enabled.
func (r *Resolver) Resolve(ctx context.Context, raw string) Result {
	parsed := address.Parse(raw)
	res := r.index.Resolve(parsed)

	if res.Status == address.StatusFound || r.rewriter == nil {
		return res
	}
	if res.Status != address.StatusNotFound && res.Status != address.StatusAmbiguous {
		return res
	}

	alternatives, err := r.rewriter.Rewrite(ctx, raw)
	if err != nil || len(alternatives) == 0 {
		return res
	}

	best := res
	for _, alt := range alternatives {
		variant := address.Parse(alt)
		// The model may fix the spelling of the street, nothing else.
		if !compatibleVariant(parsed, variant) {
			continue
		}
		candidate := r.index.Resolve(variant)
		if better(candidate, best) {
			best = candidate
		}
	}
	return best
}

// compatibleVariant reports whether an LLM rewrite may be considered. A rewrite
// is acceptable only when it:
//   - keeps the exact house unit (number, fraction, letter, corpus, structure
//     ignored) — so an apartment is never turned into a corpus;
//   - keeps the ordinal — so "2-я Сухарная" is not collapsed to "Сухарная";
//   - has the same words in the street name, each within a small edit distance
//     — so a different street can never be substituted.
func compatibleVariant(orig, variant address.ParsedAddress) bool {
	if !sameHouseUnit(orig, variant) {
		return false
	}
	if orig.Ordinal != variant.Ordinal {
		return false
	}
	to := strings.Fields(orig.NameKey)
	tv := strings.Fields(variant.NameKey)
	if len(to) != len(tv) {
		return false
	}
	// NameKey is sorted, so tokens align one-to-one.
	for i := range to {
		if !nearToken(to[i], tv[i]) {
			return false
		}
	}
	return true
}

// nearToken allows a small number of edits (including transpositions) between
// two name tokens, scaled to their length.
func nearToken(a, b string) bool {
	if a == b {
		return true
	}
	minLen := len([]rune(a))
	if lb := len([]rune(b)); lb < minLen {
		minLen = lb
	}
	d := damerau(a, b)
	switch {
	case d <= 1 && minLen >= 4:
		return true
	case d <= 2 && minLen >= 8:
		return true
	default:
		return false
	}
}

func sameHouseUnit(a, b address.ParsedAddress) bool {
	return a.House == b.House &&
		a.HouseFrac == b.HouseFrac &&
		a.HouseLetter == b.HouseLetter &&
		a.Building == b.Building &&
		a.BuildingFrac == b.BuildingFrac &&
		a.BuildingLetter == b.BuildingLetter
}

// better ranks results: a stronger status wins, then higher confidence.
func better(a, b Result) bool {
	ra, rb := statusRank(a.Status), statusRank(b.Status)
	if ra != rb {
		return ra > rb
	}
	return a.Confidence > b.Confidence
}

func statusRank(s address.Status) int {
	switch s {
	case address.StatusFound:
		return 3
	case address.StatusAmbiguous:
		return 2
	case address.StatusPartial:
		return 1
	default:
		return 0
	}
}