// Package match resolves a ParsedAddress against a canonical registry index.
//
// It is the deterministic heart of addrkit. It knows nothing about storage,
// HTTP or LLMs: it operates on an in-memory index built from []address.Entry
// and always answers from that data. A wrong house number is never invented —
// when the exact house unit is not present the result is "partial", and when
// several streets are plausible the result is "ambiguous".
package match

import (
	"sort"

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

// Candidate is one plausible match, returned alongside a non-"found" result so
// the caller (or an operator) can see what the resolver was choosing between.
type Candidate struct {
	Address  string  `json:"address"`
	District string  `json:"district,omitempty"`
	House    string  `json:"house,omitempty"`
	Score    float64 `json:"score"`
}

// Result is the outcome of a resolution.
type Result struct {
	Status      address.Status `json:"status"`
	Address     string         `json:"address,omitempty"`
	District    string         `json:"district,omitempty"`
	Confidence  float64        `json:"confidence"`
	Candidates  []Candidate    `json:"candidates,omitempty"`
	DataVersion string         `json:"data_version,omitempty"`
}

// Options tunes matching behaviour.
type Options struct {
	// FuzzyThreshold is the minimum similarity (0..1) for a street to be
	// accepted as a typo-tolerant match. Below it the result is not_found.
	FuzzyThreshold float64
	// AmbiguityMargin: streets within this similarity of the best match make
	// the result ambiguous instead of silently picking one.
	AmbiguityMargin float64
	// MaxCandidates caps the candidates returned to the caller.
	MaxCandidates int
}

// DefaultOptions returns conservative defaults.
//
// The ambiguity margin is deliberately generous relative to the token scores:
// a one-edit match scores 0.95 and a two-edit match 0.90, so a 0.06 margin
// makes near-collisions (e.g. "Елоховская" vs "Волховская") ambiguous rather
// than silently picking the closer-but-wrong street.
func DefaultOptions() Options {
	return Options{
		FuzzyThreshold:  0.82,
		AmbiguityMargin: 0.06,
		MaxCandidates:   5,
	}
}

type streetRef struct {
	key        string
	ordinal    string
	nameKey    string
	streetType string
}

// Index is an immutable, in-memory registry index. It is safe for concurrent
// reads once constructed.
type Index struct {
	version string
	opts    Options
	byKey   map[string][]address.Entry
	streets []streetRef
}

// NewIndex builds an index from canonical entries. Entries sharing a StreetKey
// are grouped; distinct streets are collected for typo-tolerant matching.
func NewIndex(version string, entries []address.Entry, opts Options) *Index {
	ix := &Index{
		version: version,
		opts:    opts,
		byKey:   make(map[string][]address.Entry, len(entries)),
	}
	seen := make(map[string]struct{}, len(entries))
	for _, e := range entries {
		ix.byKey[e.StreetKey] = append(ix.byKey[e.StreetKey], e)
		if _, ok := seen[e.StreetKey]; !ok {
			seen[e.StreetKey] = struct{}{}
			ix.streets = append(ix.streets, streetRef{
				key:        e.StreetKey,
				ordinal:    e.Ordinal,
				nameKey:    e.NameKey,
				streetType: e.StreetType,
			})
		}
	}
	sort.Slice(ix.streets, func(i, j int) bool { return ix.streets[i].key < ix.streets[j].key })
	return ix
}

// Version returns the data version the index was built from.
func (ix *Index) Version() string { return ix.version }

// Size returns the number of indexed entries.
func (ix *Index) Size() int {
	n := 0
	for _, v := range ix.byKey {
		n += len(v)
	}
	return n
}

// Resolve resolves a parsed address. It never returns an address that is not
// present in the index.
func (ix *Index) Resolve(p address.ParsedAddress) Result {
	res := Result{DataVersion: ix.version}

	entries := ix.byKey[p.StreetKey]
	similarity := 1.0

	if len(entries) == 0 {
		var ambiguousKeys []string
		entries, similarity, ambiguousKeys = ix.fuzzyStreets(p)
		if len(ambiguousKeys) > 0 {
			res.Status = address.StatusAmbiguous
			res.Confidence = similarity
			res.Candidates = ix.representatives(ambiguousKeys, similarity)
			return res
		}
	}
	if len(entries) == 0 {
		res.Status = address.StatusNotFound
		return res
	}

	if !p.HasHouse {
		// Street is known but the caller did not supply a house: safe but
		// incomplete.
		res.Status = address.StatusPartial
		res.Confidence = clamp01(similarity * 0.8)
		res.Candidates = candidates(entries, similarity, ix.opts.MaxCandidates)
		return res
	}

	matched := matchHouseUnit(entries, p)
	switch len(matched) {
	case 1:
		res.Status = address.StatusFound
		res.Address = matched[0].Address
		res.District = matched[0].District
		res.Confidence = clamp01(similarity)
		return res
	case 0:
		// Street recognised, exact house unit absent, or several units share
		// the same number (ambiguous at the unit level).
		if sameHouseSeveral(entries, p) {
			res.Status = address.StatusAmbiguous
			res.Confidence = clamp01(similarity * 0.9)
			res.Candidates = candidates(matchHouseUnitAll(entries, p), similarity, ix.opts.MaxCandidates)
			return res
		}
		res.Status = address.StatusPartial
		res.Confidence = clamp01(similarity * 0.9)
		res.Candidates = candidates(entries, similarity, ix.opts.MaxCandidates)
		return res
	default:
		res.Status = address.StatusAmbiguous
		res.Confidence = clamp01(similarity * 0.9)
		res.Candidates = candidates(matched, similarity, ix.opts.MaxCandidates)
		return res
	}
}

// fuzzyStreets finds streets similar to the query. It returns the entries of
// the best street when the match is unambiguous, or the list of competing
// street keys when several are within the ambiguity margin.
func (ix *Index) fuzzyStreets(p address.ParsedAddress) (entries []address.Entry, similarity float64, ambiguousKeys []string) {
	if p.NameKey == "" {
		return nil, 0, nil
	}
	best := 0.0
	bestKey := ""
	for _, s := range ix.streets {
		// If both sides carry an ordinal and they differ, the streets are
		// different even if the names rhyme.
		if p.Ordinal != "" && s.ordinal != "" && p.Ordinal != s.ordinal {
			continue
		}
		if sim := nameSimilarity(p.NameKey, s.nameKey); sim > best {
			best = sim
			bestKey = s.key
		}
	}
	if best < ix.opts.FuzzyThreshold {
		return nil, best, nil
	}

	for _, s := range ix.streets {
		if p.Ordinal != "" && s.ordinal != "" && p.Ordinal != s.ordinal {
			continue
		}
		if nameSimilarity(p.NameKey, s.nameKey) >= best-ix.opts.AmbiguityMargin {
			ambiguousKeys = append(ambiguousKeys, s.key)
		}
	}
	if len(ambiguousKeys) > 1 {
		return nil, best, ambiguousKeys
	}
	return ix.byKey[bestKey], best, nil
}

// representatives returns one candidate per competing street, which is far
// more useful to a user than five houses of a single street.
func (ix *Index) representatives(keys []string, score float64) []Candidate {
	sort.Strings(keys)
	out := make([]Candidate, 0, len(keys))
	for _, k := range keys {
		es := ix.byKey[k]
		if len(es) == 0 {
			continue
		}
		e := es[0]
		out = append(out, Candidate{
			Address:  e.Address,
			District: e.District,
			House:    e.House,
			Score:    clamp01(score),
		})
		if len(out) == ix.opts.MaxCandidates {
			break
		}
	}
	return out
}

// matchHouseUnit returns entries whose house unit equals p's, exactly.
func matchHouseUnit(entries []address.Entry, p address.ParsedAddress) []address.Entry {
	var out []address.Entry
	for _, e := range entries {
		if houseUnitEqual(e, p) {
			out = append(out, e)
		}
	}
	return out
}

// matchHouseUnitAll returns all entries for entries that share the same house
// number as p (used to surface ambiguity).
func matchHouseUnitAll(entries []address.Entry, p address.ParsedAddress) []address.Entry {
	var out []address.Entry
	for _, e := range entries {
		if e.House == p.House && e.HouseFrac == p.HouseFrac && e.HouseLetter == p.HouseLetter {
			out = append(out, e)
		}
	}
	return out
}

// sameHouseSeveral reports whether more than one entry matches the house
// number but with differing buildings/letters, i.e. the unit is ambiguous.
func sameHouseSeveral(entries []address.Entry, p address.ParsedAddress) bool {
	return len(matchHouseUnitAll(entries, p)) > 1
}

// houseUnitEqual compares the parts of a house unit. Unspecified (empty) parts
// must also be empty on the entry side, so "60/1" never matches "60/1 к148".
func houseUnitEqual(e address.Entry, p address.ParsedAddress) bool {
	return e.House == p.House &&
		e.HouseFrac == p.HouseFrac &&
		e.HouseLetter == p.HouseLetter &&
		e.Building == p.Building &&
		e.BuildingFrac == p.BuildingFrac &&
		e.BuildingLetter == p.BuildingLetter
}

func candidates(entries []address.Entry, score float64, limit int) []Candidate {
	if limit <= 0 || len(entries) == 0 {
		return nil
	}
	out := make([]Candidate, 0, len(entries))
	for _, e := range entries {
		out = append(out, Candidate{
			Address:  e.Address,
			District: e.District,
			House:    e.House,
			Score:    clamp01(score),
		})
		if len(out) == limit {
			break
		}
	}
	return out
}

func clamp01(v float64) float64 {
	if v < 0 {
		return 0
	}
	if v > 1 {
		return 1
	}
	return v
}