package engine

import (
	"fmt"
	"slices"
	"strings"

	"jarl/internal/dnsname"
	"jarl/internal/model"
)

// ViewSet is what one view has for a name and type.
type ViewSet struct {
	View    string   `json:"view"`
	ZoneID  int64    `json:"zone_id"`
	Records []string `json:"records"`          // data (with TTL and "(disabled)" when set), sorted
	IDs     []int64  `json:"ids"`              // the records, in the same order
	Data    []string `json:"data"`             // their data alone, in the same order
	TTL     *uint32  `json:"ttl,omitempty"`    // the first record's own TTL
	Linked  string   `json:"linked,omitempty"` // shared or local, in a linked zone
}

// CompareRow is one name and type across views.
type CompareRow struct {
	Name  string    `json:"name"` // relative to the zone
	FQDN  string    `json:"fqdn"`
	Type  string    `json:"type"`
	Same  bool      `json:"same"`
	Views []ViewSet `json:"views"` // in the order of the zones given
}

// CompareZones lines up the records of zones of the same name in
// different views (docs/views.md#linked-zones), one row per name and type,
// sorted like a zone file.
func CompareZones(st *model.State, zones []*model.Zone) []CompareRow {
	type key struct{ name, typ string }
	sets := make([]map[key][]*model.Record, len(zones))
	var keys []key
	seen := map[key]bool{}
	var all []*model.Record
	for i, z := range zones {
		sets[i] = map[key][]*model.Record{}
		for _, r := range st.ZoneRecords(z.ID) {
			k := key{r.Name, r.Type}
			sets[i][k] = append(sets[i][k], r)
			if !seen[k] {
				seen[k] = true
				keys = append(keys, k)
				all = append(all, r)
			}
		}
	}
	if len(zones) > 0 {
		// Zone file order: the apex first, then by name and type.
		model.SortRecords(all, zones[0])
		keys = keys[:0]
		for _, r := range all {
			keys = append(keys, key{r.Name, r.Type})
		}
	}
	var out []CompareRow
	for _, k := range keys {
		row := CompareRow{FQDN: k.name, Type: k.typ, Same: true}
		if len(zones) > 0 {
			row.Name = relName(k.name, zones[0].Name)
		}
		var first string
		for i, z := range zones {
			vs := ViewSet{View: st.ViewName(z), ZoneID: z.ID, Records: []string{}, IDs: []int64{}, Data: []string{}}
			rs := slices.Clone(sets[i][k])
			slices.SortFunc(rs, func(a, b *model.Record) int { return strings.Compare(strings.ToLower(a.Data), strings.ToLower(b.Data)) })
			for _, r := range rs {
				d := r.Data
				if r.TTL != nil {
					d = fmt.Sprintf("%s (TTL %d)", d, *r.TTL)
				}
				if r.Disabled {
					d += " (disabled)"
				}
				vs.Records = append(vs.Records, d)
				vs.IDs = append(vs.IDs, r.ID)
				vs.Data = append(vs.Data, r.Data)
				if vs.TTL == nil && r.TTL != nil {
					vs.TTL = model.Ptr(*r.TTL)
				}
			}
			if z.LinkGroup != 0 && len(rs) > 0 {
				vs.Linked = "shared"
				if rs[0].SharedID == 0 {
					vs.Linked = "local"
				}
			}
			sig := strings.Join(vs.Records, "\n")
			if i == 0 {
				first = sig
			} else if sig != first {
				row.Same = false
			}
			row.Views = append(row.Views, vs)
		}
		out = append(out, row)
	}
	return out
}

func relName(name, zone string) string {
	if name == zone {
		return "@"
	}
	return strings.TrimSuffix(name, "."+zone)
}

// CompareReport is a zone in one view (the base) next to the same zone in
// other views (docs/views.md#comparing-views): what the other views answer
// differently, the names only some views have, and how much is the same.
type CompareReport struct {
	Zone   string   `json:"zone"`
	Base   string   `json:"base"`   // the view compared from
	Views  []string `json:"views"`  // the base first
	Linked bool     `json:"linked"` // all in one link
	// Summary is, per other view, how it differs from the base.
	Summary []CompareSummary `json:"summary"`
	// Different are names and types more than one view has, with
	// different records.
	Different []CompareRow `json:"different"`
	// Only are the names and types only some views have, by the views
	// that have them.
	Only []CompareOnly `json:"only"`
	Same int           `json:"same"`
	// SameRows are the ones that are the same (when asked for).
	SameRows []CompareRow `json:"same_rows,omitempty"`
}

// CompareSummary counts how a view differs from the base view.
type CompareSummary struct {
	View      string `json:"view"`
	Different int    `json:"different"`  // both have it, with different records
	OnlyBase  int    `json:"only_base"`  // the base has it, this view doesn't
	OnlyOther int    `json:"only_other"` // this view has it, the base doesn't
	Same      int    `json:"same"`
}

// CompareOnly are names and types that only some views have.
type CompareOnly struct {
	Views []string     `json:"views"`
	Rows  []CompareRow `json:"rows"`
}

// CompareFilter narrows a comparison to a name, and optionally a type.
type CompareFilter struct {
	Name string // relative ("www", "@") or absolute
	Type string
	All  bool // include what is the same
}

// Compare builds the report for zones (the base first). Apex NS records are
// left out: they name the servers, which views often list differently on
// purpose.
func Compare(st *model.State, zones []*model.Zone, f CompareFilter) *CompareReport {
	rep := &CompareReport{Zone: dnsname.Display(zones[0].Name), Base: st.ViewName(zones[0]), Different: []CompareRow{}, Only: []CompareOnly{}, Linked: true}
	for _, z := range zones {
		rep.Views = append(rep.Views, st.ViewName(z))
		rep.Linked = rep.Linked && z.LinkGroup != 0 && z.LinkGroup == zones[0].LinkGroup
	}
	for _, v := range rep.Views[1:] {
		rep.Summary = append(rep.Summary, CompareSummary{View: v})
	}
	want := ""
	if f.Name != "" {
		if o, err := dnsname.Owner(f.Name, zones[0].Name); err == nil {
			want = o
		}
	}
	only := map[string]int{}
	for _, row := range CompareZones(st, zones) {
		if row.FQDN == zones[0].Name && row.Type == "NS" {
			continue
		}
		if want != "" && (row.FQDN != want || f.Type != "" && !strings.EqualFold(row.Type, f.Type)) {
			continue
		}
		base := row.Views[0]
		for i, vs := range row.Views[1:] {
			s := &rep.Summary[i]
			switch {
			case len(base.Records) > 0 && len(vs.Records) > 0 && slices.Equal(base.Records, vs.Records):
				s.Same++
			case len(base.Records) > 0 && len(vs.Records) > 0:
				s.Different++
			case len(base.Records) > 0:
				s.OnlyBase++
			case len(vs.Records) > 0:
				s.OnlyOther++
			}
		}
		if row.Same {
			rep.Same++
			if f.All || want != "" {
				rep.SameRows = append(rep.SameRows, row)
			}
			continue
		}
		var having []string
		versions := map[string]bool{}
		for _, vs := range row.Views {
			if len(vs.Records) > 0 {
				having = append(having, vs.View)
				versions[strings.Join(vs.Records, "\n")] = true
			}
		}
		if len(versions) > 1 {
			rep.Different = append(rep.Different, row)
			continue
		}
		k := strings.Join(having, ",")
		i, ok := only[k]
		if !ok {
			i = len(rep.Only)
			only[k] = i
			rep.Only = append(rep.Only, CompareOnly{Views: having})
		}
		rep.Only[i].Rows = append(rep.Only[i].Rows, row)
	}
	// The base's own names first, then by how many views have them.
	slices.SortStableFunc(rep.Only, func(a, b CompareOnly) int {
		ab, bb := slices.Contains(a.Views, rep.Base), slices.Contains(b.Views, rep.Base)
		if ab != bb {
			if ab {
				return -1
			}
			return 1
		}
		return len(b.Views) - len(a.Views)
	})
	return rep
}