package impact

import (
	"fmt"
	"strings"
)

// Selector is a conjunction of fact constraints. Every field left at its zero
// value is unconstrained, so an empty Selector with All unset matches nothing
// and is treated as a programming error by the callers that build them.
type Selector struct {
	// All matches the whole estate (hieradata/common.yaml, repo-global files).
	All bool
	// Certname pins one host (hieradata/nodes/<certname>.yaml).
	Certname string
	// RoleTiers is a prefix match on enc_role_tier1..3, so a two-tier
	// hieradata file covers every role nested under it.
	RoleTiers []string
	// RoleExact matches enc_role verbatim, which is how a role class maps to
	// hosts.
	RoleExact string
	Country   string
	Region    string
	Virtual   string
	OSName    string
	OSMajor   string
	OSMinor   string
}

// Match reports whether the node satisfies every constraint set on s.
func (s Selector) Match(n Node) bool {
	if s.All {
		return true
	}
	if s.Certname != "" && s.Certname != n.Certname {
		return false
	}
	if s.RoleExact != "" && s.RoleExact != n.Role {
		return false
	}
	if s.Country != "" && s.Country != n.Country {
		return false
	}
	if s.Region != "" && s.Region != n.Region {
		return false
	}
	if s.Virtual != "" && s.Virtual != n.Virtual {
		return false
	}
	if s.OSName != "" && !strings.EqualFold(s.OSName, n.OSName) {
		return false
	}
	if s.OSMajor != "" && s.OSMajor != n.OSMajor {
		return false
	}
	if s.OSMinor != "" && s.OSMinor != n.OSMinor {
		return false
	}
	if len(s.RoleTiers) > 0 {
		tiers := n.Tiers()
		if len(tiers) < len(s.RoleTiers) {
			return false
		}
		for i, want := range s.RoleTiers {
			if tiers[i] != want {
				return false
			}
		}
	}
	return true
}

// Select returns the certnames of every matching node, sorted.
func (s Selector) Select(nodes []Node) []string {
	var out []string
	for _, n := range nodes {
		if s.Match(n) {
			out = append(out, n.Certname)
		}
	}
	return out
}

// String renders the selector the way --explain prints it.
func (s Selector) String() string {
	if s.All {
		return "all hosts"
	}
	var parts []string
	add := func(k, v string) {
		if v != "" {
			parts = append(parts, k+"="+v)
		}
	}
	add("certname", s.Certname)
	add("enc_role", s.RoleExact)
	if len(s.RoleTiers) > 0 {
		parts = append(parts, "role-prefix="+strings.Join(s.RoleTiers, "::"))
	}
	add("country", s.Country)
	add("region", s.Region)
	add("virtual", s.Virtual)
	add("os.name", s.OSName)
	add("os.release.major", s.OSMajor)
	add("os.release.minor", s.OSMinor)
	if len(parts) == 0 {
		return "nothing"
	}
	return strings.Join(parts, " ")
}

// target is one resolved "this file reaches these hosts, for this reason".
type target struct {
	sel    Selector
	rule   string
	detail string
}

func allTarget(rule, detail string) target {
	return target{sel: Selector{All: true}, rule: rule, detail: detail}
}

func fmtDetail(format string, args ...any) string { return fmt.Sprintf(format, args...) }