// Package impact maps a change in the Puppet control repo onto the hosts whose
// catalogs that change can alter.
package impact

import (
	"context"
	"fmt"
	"sort"
	"strings"

	"git.unkin.net/unkin/puppet-catalog-tools/internal/puppetdb"
)

// FactNames are the facts every selector is evaluated against. They are
// fetched for the whole estate in one query.
var FactNames = []string{
	"enc_role",
	"enc_role_tier1",
	"enc_role_tier2",
	"enc_role_tier3",
	"country",
	"region",
	"virtual",
	"os",
}

// Node is the slice of a node's facts the hiera hierarchy keys off.
type Node struct {
	Certname string
	Role     string
	Tier1    string
	Tier2    string
	Tier3    string
	Country  string
	Region   string
	Virtual  string
	OSName   string
	OSMajor  string
	OSMinor  string
}

// Tiers returns the role tiers as a slice, truncated at the first empty one.
func (n Node) Tiers() []string {
	tiers := make([]string, 0, 3)
	for _, t := range []string{n.Tier1, n.Tier2, n.Tier3} {
		if t == "" {
			break
		}
		tiers = append(tiers, t)
	}
	return tiers
}

// FactSource supplies the estate-wide fact table.
type FactSource interface {
	FactsByName(ctx context.Context, names []string) ([]puppetdb.FactRecord, error)
}

// NodeWarning is one report of fact records that never reached the estate
// table, with the number of records it accounts for. One warning can stand for
// many records, so the count travels with the message rather than being
// inferred from it.
type NodeWarning struct {
	Message string
	Records int
}

// NodeWarningMessages renders warnings one line each.
func NodeWarningMessages(warnings []NodeWarning) []string {
	out := make([]string, 0, len(warnings))
	for _, w := range warnings {
		out = append(out, w.Message)
	}
	return out
}

// DroppedRecords totals the records the warnings account for.
func DroppedRecords(warnings []NodeWarning) int {
	total := 0
	for _, w := range warnings {
		total += w.Records
	}
	return total
}

// LoadNodes fetches FactNames for every node and folds them into a sorted
// table. Nodes without an enc_role are kept: they still match country, os and
// virtual selectors. A record with no certname belongs to no host and cannot
// be kept, so it is returned as a warning rather than dropped in silence.
// Warnings are returned alongside a failure too: they are usually what
// explains it.
func LoadNodes(ctx context.Context, src FactSource) ([]Node, []NodeWarning, error) {
	records, err := src.FactsByName(ctx, FactNames)
	if err != nil {
		return nil, nil, err
	}

	byName := map[string]*Node{}
	anonymous := map[string]int{}
	for _, r := range records {
		if r.Certname == "" {
			anonymous[r.Name]++
			continue
		}
		n, ok := byName[r.Certname]
		if !ok {
			n = &Node{Certname: r.Certname}
			byName[r.Certname] = n
		}
		applyFact(n, r.Name, r.Value)
	}

	nodes := make([]Node, 0, len(byName))
	for _, n := range byName {
		nodes = append(nodes, *n)
	}
	sort.Slice(nodes, func(i, j int) bool { return nodes[i].Certname < nodes[j].Certname })
	if len(nodes) == 0 {
		return nil, anonymousWarnings(anonymous), fmt.Errorf("puppetdb returned no nodes")
	}
	return nodes, anonymousWarnings(anonymous), nil
}

// anonymousWarnings renders the dropped-record tally one line per fact.
func anonymousWarnings(counts map[string]int) []NodeWarning {
	names := make([]string, 0, len(counts))
	for name := range counts {
		names = append(names, name)
	}
	sort.Strings(names)
	out := make([]NodeWarning, 0, len(names))
	for _, name := range names {
		out = append(out, NodeWarning{
			Message: fmt.Sprintf("fact %q: %d record(s) had no certname and were dropped", name, counts[name]),
			Records: counts[name],
		})
	}
	return out
}

func applyFact(n *Node, name string, value any) {
	switch name {
	case "enc_role":
		n.Role = str(value)
	case "enc_role_tier1":
		n.Tier1 = str(value)
	case "enc_role_tier2":
		n.Tier2 = str(value)
	case "enc_role_tier3":
		n.Tier3 = str(value)
	case "country":
		n.Country = str(value)
	case "region":
		n.Region = str(value)
	case "virtual":
		n.Virtual = str(value)
	case "os":
		os, ok := value.(map[string]any)
		if !ok {
			return
		}
		n.OSName = str(os["name"])
		release, ok := os["release"].(map[string]any)
		if !ok {
			return
		}
		n.OSMajor = str(release["major"])
		n.OSMinor = str(release["minor"])
	}
}

func str(v any) string {
	switch t := v.(type) {
	case string:
		return t
	case nil:
		return ""
	default:
		return strings.TrimSpace(fmt.Sprint(t))
	}
}