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)
}

// Parser is the address parser used by the resolver. It is defined here
// (consumer side) so the resolver can be tested with a stub and so a
// deployment can plug in its own dictionary.
type Parser interface {
	Parse(raw string) address.ParsedAddress
	ParseInCity(raw, city string) address.ParsedAddress
	MatchCity(query string) (address.City, bool)
}

// ResolverOptions tunes optional resolver behaviour.
type ResolverOptions struct {
	// Parser defaults to address.DefaultParser().
	Parser Parser
	// OnRewriteError, when set, observes failures of the optional rewriter.
	// The resolver always keeps the deterministic result, but operators still
	// need to know that the fallback is broken.
	OnRewriteError func(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
	parser         Parser
	onRewriteError func(error)
}

// NewResolver builds a resolver with the default parser and no rewriter
// diagnostics.
func NewResolver(index *Index, rewriter Rewriter) *Resolver {
	return NewResolverWithOptions(index, rewriter, ResolverOptions{})
}

// NewResolverWithOptions builds a resolver with explicit options.
func NewResolverWithOptions(index *Index, rewriter Rewriter, opts ResolverOptions) *Resolver {
	parser := opts.Parser
	if parser == nil {
		parser = address.DefaultParser()
	}
	return &Resolver{
		index:          index,
		rewriter:       rewriter,
		parser:         parser,
		onRewriteError: opts.OnRewriteError,
	}
}

// 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 }

// Cities returns the canonical city names present in the index.
func (r *Resolver) Cities() []string {
	if r.index == nil {
		return nil
	}
	return r.index.Cities()
}

// MatchCity reports whether query is a city name/alias and returns the
// canonical name. It uses the resolver's parser dictionary, not the index, so
// it also recognizes aliases for cities that have no rows yet.
func (r *Resolver) MatchCity(query string) (string, bool) {
	city, ok := r.parser.MatchCity(query)
	if !ok {
		return "", false
	}
	return city.Name, true
}

// Resolve parses raw and resolves it, consulting the rewriter when enabled.
func (r *Resolver) Resolve(ctx context.Context, raw string) Result {
	return r.ResolveInCity(ctx, raw, "")
}

// ResolveInCity is Resolve with an explicit city hint. The hint overrides a
// city found in the address text and lets clients pass the city as a separate
// field.
func (r *Resolver) ResolveInCity(ctx context.Context, raw, city string) Result {
	parsed := r.parse(raw, city)
	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 {
		if r.onRewriteError != nil {
			r.onRewriteError(err)
		}
		return res
	}
	if len(alternatives) == 0 {
		return res
	}

	best := res
	for _, alt := range alternatives {
		variant := r.parse(alt, city)
		// The embedded prompt asks the model to strip administrative words
		// (including the city), so a correct variant often has no city. It
		// inherits the original's city; only a conflicting explicit city is a
		// disqualification. Without this, the rewriter silently contributes
		// nothing in multi-city deployments (where default_city is empty).
		if variant.CityKey == "" && parsed.CityKey != "" {
			variant = r.parser.ParseInCity(alt, parsed.City)
		}
		// 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
}

func (r *Resolver) parse(raw, city string) address.ParsedAddress {
	if strings.TrimSpace(city) != "" {
		return r.parser.ParseInCity(raw, city)
	}
	return r.parser.Parse(raw)
}

// 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 orig.CityKey != variant.CityKey {
		return false
	}
	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
	}
	ra, rb := len([]rune(a)), len([]rune(b))
	if ra == 0 || rb == 0 || ra > maxTokenRunes || rb > maxTokenRunes {
		return false
	}
	minLen := ra
	if rb < minLen {
		minLen = rb
	}
	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 &&
		a.Structure == b.Structure
}

// 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
	}
}