package shellstream

import (
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"strconv"
	"strings"
)

// Extension key constants — all use the @guildhouse.io vendor suffix.
const (
	ExtSatScope        = "sat-scope@guildhouse.io"
	ExtSatHash         = "sat-hash@guildhouse.io"
	ExtTenantID        = "tenant-id@guildhouse.io"
	ExtRoles           = "roles@guildhouse.io"
	ExtCeremonyID      = "ceremony-id@guildhouse.io"
	ExtCeremonyType    = "ceremony-type@guildhouse.io"
	ExtMerkleRoot      = "merkle-root@guildhouse.io"
	ExtMerkleProof     = "merkle-proof@guildhouse.io"
	ExtGovernanceEpoch = "governance-epoch@guildhouse.io"

	// Vendor suffix for identifying Shellstream extensions.
	VendorSuffix = "@guildhouse.io"
)

// Valid ceremony types.
var validCeremonyTypes = map[string]bool{
	"self_grant":           true,
	"single_approval":      true,
	"quorum_approval":      true,
	"emergency_break_glass": true,
}

// SatScope represents a Substrate Attestation Token scope.
type SatScope struct {
	RegistryType    string   `json:"registry_type"`
	Verbs           []string `json:"verbs"`
	ResourcePattern string   `json:"resource_pattern"`
}

// ShellstreamExtensions holds all Shellstream extension values.
type ShellstreamExtensions struct {
	// SatScope is the authorization scope. Required when SAT is present.
	SatScope *SatScope

	// SatHash is the hex-encoded SHA-256 of the SAT bytes. Required when SatScope is set.
	SatHash string

	// TenantID is the tenant UUID. Required.
	TenantID string

	// Roles is the list of role names. Required (at least one).
	Roles []string

	// CeremonyID is the governance ceremony UUID. Optional (elevated sessions only).
	CeremonyID string

	// CeremonyType is the ceremony type. Required when CeremonyID is set.
	CeremonyType string

	// MerkleRoot is the hex-encoded governance merkle root at issuance. Optional.
	MerkleRoot string

	// MerkleProof is the binary inclusion proof. Optional, requires MerkleRoot.
	MerkleProof []byte

	// GovernanceEpoch is the monotonic governance state counter. Optional.
	GovernanceEpoch uint64

	// Internal tracking for whether epoch was explicitly set (0 is valid).
	hasGovernanceEpoch bool
}

// WithGovernanceEpoch sets the governance epoch and marks it as explicitly set.
func (e *ShellstreamExtensions) WithGovernanceEpoch(epoch uint64) {
	e.GovernanceEpoch = epoch
	e.hasGovernanceEpoch = true
}

// HasGovernanceEpoch returns true if the governance epoch was explicitly set.
func (e *ShellstreamExtensions) HasGovernanceEpoch() bool {
	return e.hasGovernanceEpoch
}

// Encode serializes ShellstreamExtensions into an SSH certificate extensions map.
func Encode(ext *ShellstreamExtensions) (map[string]string, error) {
	if ext == nil {
		return nil, fmt.Errorf("shellstream: nil extensions")
	}

	m := make(map[string]string)

	// Required fields.
	m[ExtTenantID] = ext.TenantID
	m[ExtRoles] = strings.Join(ext.Roles, ",")

	// SAT fields (both or neither).
	if ext.SatScope != nil {
		scopeJSON, err := json.Marshal(ext.SatScope)
		if err != nil {
			return nil, fmt.Errorf("shellstream: marshal sat-scope: %w", err)
		}
		m[ExtSatScope] = string(scopeJSON)
		m[ExtSatHash] = ext.SatHash
	}

	// Ceremony fields.
	if ext.CeremonyID != "" {
		m[ExtCeremonyID] = ext.CeremonyID
		m[ExtCeremonyType] = ext.CeremonyType
	}

	// Merkle fields.
	if ext.MerkleRoot != "" {
		m[ExtMerkleRoot] = ext.MerkleRoot
	}
	if len(ext.MerkleProof) > 0 {
		m[ExtMerkleProof] = base64.StdEncoding.EncodeToString(ext.MerkleProof)
	}

	// Governance epoch.
	if ext.hasGovernanceEpoch {
		m[ExtGovernanceEpoch] = strconv.FormatUint(ext.GovernanceEpoch, 10)
	}

	return m, nil
}

// Decode parses an SSH certificate extensions map into ShellstreamExtensions.
// Unknown extensions (including non-Shellstream keys) are silently ignored.
func Decode(extensions map[string]string) (*ShellstreamExtensions, error) {
	ext := &ShellstreamExtensions{}

	// Required: tenant-id.
	if v, ok := extensions[ExtTenantID]; ok {
		ext.TenantID = v
	}

	// Required: roles.
	if v, ok := extensions[ExtRoles]; ok && v != "" {
		ext.Roles = strings.Split(v, ",")
	}

	// Optional: sat-scope.
	if v, ok := extensions[ExtSatScope]; ok {
		scope := &SatScope{}
		if err := json.Unmarshal([]byte(v), scope); err != nil {
			return nil, fmt.Errorf("shellstream: unmarshal sat-scope: %w", err)
		}
		ext.SatScope = scope
	}

	// Optional: sat-hash.
	if v, ok := extensions[ExtSatHash]; ok {
		ext.SatHash = v
	}

	// Optional: ceremony-id.
	if v, ok := extensions[ExtCeremonyID]; ok {
		ext.CeremonyID = v
	}

	// Optional: ceremony-type.
	if v, ok := extensions[ExtCeremonyType]; ok {
		ext.CeremonyType = v
	}

	// Optional: merkle-root.
	if v, ok := extensions[ExtMerkleRoot]; ok {
		ext.MerkleRoot = v
	}

	// Optional: merkle-proof.
	if v, ok := extensions[ExtMerkleProof]; ok {
		proof, err := base64.StdEncoding.DecodeString(v)
		if err != nil {
			return nil, fmt.Errorf("shellstream: decode merkle-proof: %w", err)
		}
		ext.MerkleProof = proof
	}

	// Optional: governance-epoch.
	if v, ok := extensions[ExtGovernanceEpoch]; ok {
		epoch, err := strconv.ParseUint(v, 10, 64)
		if err != nil {
			return nil, fmt.Errorf("shellstream: parse governance-epoch: %w", err)
		}
		ext.GovernanceEpoch = epoch
		ext.hasGovernanceEpoch = true
	}

	return ext, nil
}

// Validate checks that a ShellstreamExtensions value satisfies all format
// constraints and co-occurrence rules from the specification.
func Validate(ext *ShellstreamExtensions) error {
	if ext == nil {
		return fmt.Errorf("shellstream: nil extensions")
	}

	// Required: tenant-id.
	if ext.TenantID == "" {
		return fmt.Errorf("shellstream: tenant-id is required")
	}
	if !isValidUUID(ext.TenantID) {
		return fmt.Errorf("shellstream: tenant-id is not a valid UUID: %q", ext.TenantID)
	}

	// Required: roles (at least one).
	if len(ext.Roles) == 0 {
		return fmt.Errorf("shellstream: roles is required (at least one role)")
	}
	for _, r := range ext.Roles {
		if r == "" {
			return fmt.Errorf("shellstream: empty role name")
		}
		if strings.ContainsAny(r, ", ") {
			return fmt.Errorf("shellstream: role name must not contain commas or spaces: %q", r)
		}
	}

	// Co-occurrence: sat-scope requires sat-hash and vice versa.
	if ext.SatScope != nil && ext.SatHash == "" {
		return fmt.Errorf("shellstream: sat-scope requires sat-hash")
	}
	if ext.SatHash != "" && ext.SatScope == nil {
		return fmt.Errorf("shellstream: sat-hash requires sat-scope")
	}

	// sat-hash format: 64 lowercase hex characters.
	if ext.SatHash != "" {
		if len(ext.SatHash) != 64 {
			return fmt.Errorf("shellstream: sat-hash must be 64 hex characters, got %d", len(ext.SatHash))
		}
		if _, err := hex.DecodeString(ext.SatHash); err != nil {
			return fmt.Errorf("shellstream: sat-hash is not valid hex: %w", err)
		}
		if ext.SatHash != strings.ToLower(ext.SatHash) {
			return fmt.Errorf("shellstream: sat-hash must be lowercase")
		}
	}

	// sat-scope fields.
	if ext.SatScope != nil {
		if ext.SatScope.RegistryType == "" {
			return fmt.Errorf("shellstream: sat-scope.registry_type is required")
		}
		if len(ext.SatScope.Verbs) == 0 {
			return fmt.Errorf("shellstream: sat-scope.verbs is required (at least one verb)")
		}
	}

	// Co-occurrence: ceremony-id requires ceremony-type.
	if ext.CeremonyID != "" && ext.CeremonyType == "" {
		return fmt.Errorf("shellstream: ceremony-id requires ceremony-type")
	}
	if ext.CeremonyType != "" && ext.CeremonyID == "" {
		return fmt.Errorf("shellstream: ceremony-type requires ceremony-id")
	}

	// ceremony-id format: UUID.
	if ext.CeremonyID != "" {
		if !isValidUUID(ext.CeremonyID) {
			return fmt.Errorf("shellstream: ceremony-id is not a valid UUID: %q", ext.CeremonyID)
		}
	}

	// ceremony-type: must be a known value.
	if ext.CeremonyType != "" {
		if !validCeremonyTypes[ext.CeremonyType] {
			return fmt.Errorf("shellstream: unknown ceremony-type: %q", ext.CeremonyType)
		}
	}

	// merkle-root format: 64 lowercase hex characters.
	if ext.MerkleRoot != "" {
		if len(ext.MerkleRoot) != 64 {
			return fmt.Errorf("shellstream: merkle-root must be 64 hex characters, got %d", len(ext.MerkleRoot))
		}
		if _, err := hex.DecodeString(ext.MerkleRoot); err != nil {
			return fmt.Errorf("shellstream: merkle-root is not valid hex: %w", err)
		}
		if ext.MerkleRoot != strings.ToLower(ext.MerkleRoot) {
			return fmt.Errorf("shellstream: merkle-root must be lowercase")
		}
	}

	// Co-occurrence: merkle-proof requires merkle-root.
	if len(ext.MerkleProof) > 0 && ext.MerkleRoot == "" {
		return fmt.Errorf("shellstream: merkle-proof requires merkle-root")
	}

	return nil
}

// isValidUUID checks if a string is a valid RFC 4122 UUID (lowercase, hyphenated).
func isValidUUID(s string) bool {
	// Format: 8-4-4-4-12 = 36 characters.
	if len(s) != 36 {
		return false
	}
	for i, c := range s {
		switch i {
		case 8, 13, 18, 23:
			if c != '-' {
				return false
			}
		default:
			if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f')) {
				return false
			}
		}
	}
	return true
}