// Package classification defines the data-sensitivity taxonomy and the
// per-wing / per-repo tagging the capture server reads to enforce the I1
// sovereignty gate (issue #50, capture spec §4.1).
//
// The single load-bearing property is fail-safe-to-strictest: a target
// with no explicit tag and no known default classifies as Confidential,
// never as something more permissive. A missing tag must never silently
// downgrade — that would turn the I1 gate into theatre.
//
// Classification is read from an optional classification.yaml at the
// brain root. A central, Flux-reconcilable file is deliberate: it is
// auditable in one place (I2/I5), it does not require a live Gitea client
// to classify a repo (so this package has no dependency on the gitea
// tracker work), and it avoids tagging a wing's _index.md frontmatter —
// which BuildWingIndex regenerates and would clobber.
package classification

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"gopkg.in/yaml.v3"
)

// Level is a data-sensitivity tier. Higher is stricter, so the "stricter
// wins" rule (spec §4.1 model C) is a plain max.
type Level int

const (
	Public Level = iota
	Internal
	Confidential
)

// String returns the canonical lowercase token for a level.
func (l Level) String() string {
	switch l {
	case Public:
		return "public"
	case Internal:
		return "internal"
	case Confidential:
		return "confidential"
	default:
		return fmt.Sprintf("level(%d)", int(l))
	}
}

// ParseLevel parses a level token (case-insensitive, surrounding space
// tolerated). An unknown token is an error — callers must decide what to
// do with bad input rather than have it silently coerced.
func ParseLevel(s string) (Level, error) {
	switch strings.ToLower(strings.TrimSpace(s)) {
	case "public":
		return Public, nil
	case "internal":
		return Internal, nil
	case "confidential":
		return Confidential, nil
	default:
		return Confidential, fmt.Errorf("unknown classification level %q (want public/internal/confidential)", s)
	}
}

// Stricter returns the more restrictive of two levels.
func Stricter(a, b Level) Level {
	if a > b {
		return a
	}
	return b
}

// TargetKind distinguishes the two kinds of capture destination.
type TargetKind int

const (
	WingTarget TargetKind = iota // a brain wing (insights land here)
	RepoTarget                   // a Gitea repo (tickets / summaries land here)
)

// Target names a capture destination to classify.
type Target struct {
	Kind TargetKind
	Name string
}

// Config holds the explicit per-wing / per-repo classification tags read
// from classification.yaml. Absent entries fall through to the built-in
// defaults in defaultFor. The zero value (no file) is valid and applies
// defaults to everything.
type Config struct {
	wings map[string]Level
	repos map[string]Level
}

// rawConfig is the on-disk YAML shape: string→string maps, parsed into
// validated levels by Load.
type rawConfig struct {
	Wings map[string]string `yaml:"wings"`
	Repos map[string]string `yaml:"repos"`
}

// Load reads classification.yaml from brainDir. An absent file is not an
// error — it yields an empty config where every target classifies by the
// built-in defaults. A malformed file, or any unparseable level token in
// it, is a hard error: a classification source the server cannot trust
// must fail loud, not degrade silently.
func Load(brainDir string) (*Config, error) {
	cfg := &Config{wings: map[string]Level{}, repos: map[string]Level{}}

	data, err := os.ReadFile(filepath.Join(brainDir, "classification.yaml"))
	if err != nil {
		if os.IsNotExist(err) {
			return cfg, nil
		}
		return nil, fmt.Errorf("read classification.yaml: %w", err)
	}

	var raw rawConfig
	if err := yaml.Unmarshal(data, &raw); err != nil {
		return nil, fmt.Errorf("parse classification.yaml: %w", err)
	}
	for name, lvl := range raw.Wings {
		parsed, perr := ParseLevel(lvl)
		if perr != nil {
			return nil, fmt.Errorf("wing %q: %w", name, perr)
		}
		cfg.wings[normalise(name)] = parsed
	}
	for name, lvl := range raw.Repos {
		parsed, perr := ParseLevel(lvl)
		if perr != nil {
			return nil, fmt.Errorf("repo %q: %w", name, perr)
		}
		cfg.repos[normalise(name)] = parsed
	}
	return cfg, nil
}

// Derive returns the classification for any target — the function the
// capture use-case calls per item.
func (c *Config) Derive(t Target) Level {
	if t.Kind == RepoTarget {
		return c.Repo(t.Name)
	}
	return c.Wing(t.Name)
}

// Wing classifies a brain wing: an explicit tag wins, else defaults.
func (c *Config) Wing(name string) Level {
	if lvl, ok := c.wings[normalise(name)]; ok {
		return lvl
	}
	return defaultFor(name)
}

// Repo classifies a Gitea repo: an explicit tag wins, else defaults.
func (c *Config) Repo(name string) Level {
	if lvl, ok := c.repos[normalise(name)]; ok {
		return lvl
	}
	return defaultFor(name)
}

// defaultFor applies the built-in defaulting rules when a target has no
// explicit tag:
//   - client-* → Confidential (client work is confidential by default)
//   - hyperguild / homelab → Internal (the operator's own infra)
//   - everything else → Confidential (fail safe to strictest)
func defaultFor(name string) Level {
	n := normalise(name)
	if strings.HasPrefix(n, "client-") {
		return Confidential
	}
	switch n {
	case "hyperguild", "homelab":
		return Internal
	default:
		return Confidential
	}
}

// normalise lowercases and trims a wing/repo name so matching and the
// client-* prefix check are case-insensitive.
func normalise(name string) string {
	return strings.ToLower(strings.TrimSpace(name))
}