package atproto

import (
	"context"
	"errors"
	"fmt"
	"io"
	"net"
	"net/http"
	"strings"
	"time"

	"github.com/bluesky-social/indigo/atproto/identity"
	"github.com/bluesky-social/indigo/atproto/syntax"
)

// ErrHoldDIDPermanent marks a hold-DID resolution failure that no retry can
// fix: a malformed identifier, or a DID whose document does not exist. It is a
// fact about stored data — typically a stale or hand-edited sailor profile
// defaultHold — rather than a fault on our side, so callers can log it quietly
// instead of at ERROR and avoid burying real faults. Transient failures (a PLC
// blip, a network error) deliberately do not carry it.
var ErrHoldDIDPermanent = errors.New("hold DID is not resolvable")

// didWebHostUnusable reports whether a did:web identifier names something the
// identity directory can never resolve. The directory requires a plain
// hostname and rejects ports (percent-encoded as %3A), bare IPs, and
// localhost. Detecting those here, rather than string-matching the directory's
// error prose, is what lets ResolveHoldDIDToURL classify the failure as
// permanent. Conservative by design: anything not clearly hopeless is left to
// the transient path, so an unfamiliar failure still surfaces loudly.
//
// A `-tags testmode` build resolves exactly these identifiers over plain HTTP
// (see indigo_local.go), so there a failure means the local service is down
// rather than unresolvable; the quieter classification is harmless in dev.
func didWebHostUnusable(did string) bool {
	host, ok := strings.CutPrefix(did, "did:web:")
	if !ok {
		return false
	}
	if i := strings.IndexByte(host, ':'); i != -1 { // path-qualified did:web
		host = host[:i]
	}
	if strings.Contains(host, "%3A") || strings.Contains(host, "%3a") {
		return true // a port survived encoding, e.g. localhost%3A8080
	}
	if host == "" || host == "localhost" || strings.HasSuffix(host, ".localhost") {
		return true
	}
	return net.ParseIP(host) != nil
}

// holdDIDResolveClient bounds the /.well-known/atproto-did fetch so an
// unreachable or slow hold can't stall /auth/token (this resolution runs on the
// hot gate + fetch path) past Docker's token-fetch timeout. It's a plain
// idempotent GET, so a hard timeout is safe.
var holdDIDResolveClient = &http.Client{Timeout: 10 * time.Second}

// ResolveHoldURL converts a hold identifier (DID or URL) to an HTTP/HTTPS URL.
// For DIDs (both did:web and did:plc), resolves via the indigo identity directory
// which caches results (24h TTL). Prefers the #atcr_hold service endpoint,
// falls back to #atproto_pds.
//
// Supported formats:
//   - URL: https://hold.example.com → passthrough
//   - DID: did:web:hold01.atcr.io → resolved via /.well-known/did.json
//   - DID: did:plc:abc123 → resolved via PLC directory
func ResolveHoldURL(ctx context.Context, holdIdentifier string) (string, error) {
	// If it's already a URL (has scheme), return as-is
	if strings.HasPrefix(holdIdentifier, "http://") || strings.HasPrefix(holdIdentifier, "https://") {
		return holdIdentifier, nil
	}

	// If it's a DID, resolve via identity directory
	if strings.HasPrefix(holdIdentifier, "did:") {
		return ResolveHoldDIDToURL(ctx, holdIdentifier)
	}

	// Fallback: assume it's a hostname and use HTTPS
	return "https://" + holdIdentifier, nil
}

// ResolveHoldDID resolves a hold identifier (DID, URL, or hostname) to its actual DID.
// If the input is already a DID, it is returned as-is.
// If the input is a URL or hostname, the hold's /.well-known/atproto-did endpoint is
// fetched to discover the real DID (which may be did:web or did:plc).
func ResolveHoldDID(ctx context.Context, holdIdentifier string) (string, error) {
	if holdIdentifier == "" {
		return "", fmt.Errorf("empty hold identifier")
	}

	// If already a DID, return as-is
	if _, err := syntax.ParseDID(holdIdentifier); err == nil {
		return holdIdentifier, nil
	}

	// Normalize to a full URL
	holdURL := holdIdentifier
	if !strings.HasPrefix(holdURL, "http://") && !strings.HasPrefix(holdURL, "https://") {
		holdURL = "https://" + holdURL
	}
	holdURL = strings.TrimSuffix(holdURL, "/")

	// Fetch /.well-known/atproto-did to discover the hold's actual DID
	req, err := http.NewRequestWithContext(ctx, "GET", holdURL+"/.well-known/atproto-did", nil)
	if err != nil {
		return "", fmt.Errorf("failed to create request for hold DID resolution: %w", err)
	}

	resp, err := holdDIDResolveClient.Do(req)
	if err != nil {
		return "", fmt.Errorf("failed to fetch hold DID from %s: %w", holdURL, err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("hold at %s returned status %d for DID resolution", holdURL, resp.StatusCode)
	}

	body, err := io.ReadAll(io.LimitReader(resp.Body, 256))
	if err != nil {
		return "", fmt.Errorf("failed to read hold DID response: %w", err)
	}

	did := strings.TrimSpace(string(body))
	if _, err := syntax.ParseDID(did); err != nil {
		return "", fmt.Errorf("hold at %s returned invalid DID: %q", holdURL, did)
	}

	return did, nil
}

// ResolveHoldDIDToURL resolves a hold DID to its HTTP service endpoint.
// Prefers the #atcr_hold service endpoint, falls back to #atproto_pds.
// Uses the shared identity directory with cache TTL and event-driven invalidation.
func ResolveHoldDIDToURL(ctx context.Context, did string) (string, error) {
	directory := GetDirectory()
	didParsed, err := syntax.ParseDID(did)
	if err != nil {
		return "", fmt.Errorf("invalid hold DID %q: %w: %w", did, ErrHoldDIDPermanent, err)
	}

	ident, err := directory.LookupDID(ctx, didParsed)
	if err != nil {
		// A missing DID document or a structurally unusable did:web will fail
		// identically on every retry, so mark it permanent and let callers pick
		// a quieter log level.
		if errors.Is(err, identity.ErrDIDNotFound) || didWebHostUnusable(did) {
			return "", fmt.Errorf("failed to resolve hold DID %s: %w: %w", did, ErrHoldDIDPermanent, err)
		}
		return "", fmt.Errorf("failed to resolve hold DID %s: %w", did, err)
	}

	// Prefer #atcr_hold service (hold-specific endpoint)
	if url := ident.GetServiceEndpoint("atcr_hold"); url != "" {
		return url, nil
	}

	// Fall back to #atproto_pds (hold publishes both with same URL)
	if url := ident.PDSEndpoint(); url != "" {
		return url, nil
	}

	return "", fmt.Errorf("no hold or PDS service endpoint found for DID %s", did)
}

// HasHoldService reports whether a DID's identity document advertises an
// #atcr_hold service endpoint, i.e. whether the DID actually runs a hold
// service. Any ATProto account can publish io.atcr.hold.captain records, but
// only real holds publish the atcr_hold service in their DID document — use
// this to verify captain records discovered on the network before caching.
// Resolution goes through the shared identity directory (cached, 24h TTL).
func HasHoldService(ctx context.Context, did string) (bool, error) {
	didParsed, err := syntax.ParseDID(did)
	if err != nil {
		return false, fmt.Errorf("invalid hold DID %q: %w", did, err)
	}

	ident, err := GetDirectory().LookupDID(ctx, didParsed)
	if err != nil {
		return false, fmt.Errorf("failed to resolve DID %s: %w", did, err)
	}

	return ident.GetServiceEndpoint("atcr_hold") != "", nil
}

// NormalizeDID ensures did:web DIDs use %3A encoding for port separators
// per the did:web spec. Other DID methods are returned as-is.
// e.g., "did:web:172.28.0.3:8080" → "did:web:172.28.0.3%3A8080"
func NormalizeDID(did string) string {
	if !strings.HasPrefix(did, "did:web:") {
		return did
	}
	host := strings.TrimPrefix(did, "did:web:")
	// Only fix bare colons — skip if already percent-encoded
	if !strings.Contains(host, "%3A") && strings.Contains(host, ":") {
		host = strings.Replace(host, ":", "%3A", 1)
	}
	return "did:web:" + host
}

// ResolveDIDToPDS resolves a DID to its PDS endpoint.
// Uses the shared identity directory with cache TTL and event-driven invalidation.
func ResolveDIDToPDS(ctx context.Context, did string) (string, error) {
	directory := GetDirectory()
	didParsed, err := syntax.ParseDID(did)
	if err != nil {
		return "", fmt.Errorf("invalid DID: %w", err)
	}

	ident, err := directory.LookupDID(ctx, didParsed)
	if err != nil {
		return "", fmt.Errorf("failed to resolve DID: %w", err)
	}

	pdsEndpoint := ident.PDSEndpoint()
	if pdsEndpoint == "" {
		return "", fmt.Errorf("no PDS endpoint found for DID")
	}

	return pdsEndpoint, nil
}

// ResolveIdentity resolves an ATProto identifier (handle or DID) to DID, handle, and PDS endpoint.
// Uses the shared identity directory with cache TTL and event-driven invalidation.
//
// If the handle is invalid (handle.invalid), it returns the DID as the handle for display purposes.
// Returns: did, handle, pdsEndpoint, error
func ResolveIdentity(ctx context.Context, identifier string) (string, string, string, error) {
	directory := GetDirectory()
	atID, err := syntax.ParseAtIdentifier(identifier)
	if err != nil {
		return "", "", "", fmt.Errorf("invalid identifier %q: %w", identifier, err)
	}

	ident, err := directory.Lookup(ctx, atID)
	if err != nil {
		return "", "", "", fmt.Errorf("failed to resolve identity %q: %w", identifier, err)
	}

	did := ident.DID.String()
	handle := ident.Handle.String()
	pdsEndpoint := ident.PDSEndpoint()

	// If handle is invalid, use DID as display name
	if handle == "handle.invalid" || handle == "" {
		handle = did
	}

	// PDS endpoint is required for XRPC calls
	if pdsEndpoint == "" {
		return "", "", "", fmt.Errorf("no PDS endpoint found for identifier %q", identifier)
	}

	return did, handle, pdsEndpoint, nil
}

// ResolveHandleToDID resolves a handle or DID to just the DID.
// Uses the shared identity directory with cache TTL and event-driven invalidation.
// This is useful when you only need the DID and don't care about handle/PDS.
func ResolveHandleToDID(ctx context.Context, identifier string) (string, error) {
	directory := GetDirectory()
	atID, err := syntax.ParseAtIdentifier(identifier)
	if err != nil {
		return "", fmt.Errorf("invalid identifier: %w", err)
	}

	ident, err := directory.Lookup(ctx, atID)
	if err != nil {
		return "", err
	}

	return ident.DID.String(), nil
}

// InvalidateIdentity purges cached identity data for a DID or handle.
// This should be called when identity changes are detected (e.g., via Jetstream events)
// to ensure the cache is refreshed on the next lookup.
//
// Use cases:
// - Handle changes (identity events from Jetstream)
// - Account deactivation/migration (account events from Jetstream)
// - PDS migrations (deactivation followed by reactivation at new PDS)
func InvalidateIdentity(ctx context.Context, identifier string) error {
	directory := GetDirectory()
	atID, err := syntax.ParseAtIdentifier(identifier)
	if err != nil {
		return fmt.Errorf("invalid identifier for cache invalidation: %w", err)
	}

	return directory.Purge(ctx, atID)
}