package monitoring

import (
	"crypto/sha1"
	"encoding/hex"
	"fmt"
	"strings"
	"unicode"

	"github.com/rcourtman/pulse-go-rewrite/internal/config"
	"github.com/rcourtman/pulse-go-rewrite/internal/unifiedresources"
	agentsdocker "github.com/rcourtman/pulse-go-rewrite/pkg/agents/docker"
)

// tokenHintFromRecord returns a redacted token hint for display purposes.
func tokenHintFromRecord(record *config.APITokenRecord) string {
	if record == nil {
		return ""
	}
	switch {
	case record.Prefix != "" && record.Suffix != "":
		return fmt.Sprintf("%s…%s", record.Prefix, record.Suffix)
	case record.Prefix != "":
		return record.Prefix + "…"
	case record.Suffix != "":
		return "…" + record.Suffix
	default:
		return ""
	}
}

// resolveDockerHostIdentifier determines a unique identifier for a Docker host
// based on its report and existing hosts. Returns the identifier, fallback identifiers,
// the existing host (if matched), and whether a match was found. machineRevisit
// (optional) reports whether folding the report's machine ID into a candidate
// identity would alternate back to a machine already seen behind it; see
// findMatchingDockerHost.
func resolveDockerHostIdentifier(report agentsdocker.Report, tokenRecord *config.APITokenRecord, hosts []*unifiedresources.DockerHostView, machineRevisit func(identifier, machineID string) bool) (string, []string, *unifiedresources.DockerHostView, bool) {
	base := strings.TrimSpace(report.AgentKey())
	fallbacks := uniqueNonEmptyStrings(
		base,
		strings.TrimSpace(report.Agent.ID),
		strings.TrimSpace(report.Host.MachineID),
		strings.TrimSpace(report.Host.Hostname),
	)

	if existing, ok := findMatchingDockerHost(hosts, report, tokenRecord, machineRevisit); ok {
		return dockerHostStableID(existing), fallbacks, existing, true
	}

	identifier := base
	if identifier == "" {
		identifier = strings.TrimSpace(report.Host.MachineID)
	}
	if identifier == "" {
		identifier = strings.TrimSpace(report.Host.Hostname)
	}
	if identifier == "" {
		identifier = strings.TrimSpace(report.Agent.ID)
	}
	if identifier == "" {
		identifier = fallbackDockerHostID(report, tokenRecord)
	}
	if identifier == "" {
		identifier = "docker-host"
	}

	if dockerHostIDExists(identifier, hosts) {
		identifier = generateDockerHostIdentifier(identifier, report, tokenRecord, hosts)
	}

	return identifier, fallbacks, nil, false
}

// findMatchingDockerHost searches for an existing host that matches the report.
//
// The hostname-based fallbacks deliberately fold a report whose machine ID
// disagrees with the candidate record: containerized agents regenerate
// /etc/machine-id on recreation and must keep their identity. But two live
// machines reusing one short hostname and one shared install token also land
// in those fallbacks, and folding them collapses two sites into one
// flip-flopping record (the Docker analog of #1753). machineRevisit is the
// discriminator: a recreated container transitions to its new machine ID
// exactly once, while two live machines alternate, so a report whose machine
// ID *returns* to a value already seen behind the candidate identity is proof
// of a second machine and must not be folded.
func findMatchingDockerHost(hosts []*unifiedresources.DockerHostView, report agentsdocker.Report, tokenRecord *config.APITokenRecord, machineRevisit func(identifier, machineID string) bool) (*unifiedresources.DockerHostView, bool) {
	agentID := strings.TrimSpace(report.Agent.ID)
	tokenID := ""
	if tokenRecord != nil {
		tokenID = strings.TrimSpace(tokenRecord.ID)
	}
	machineID := strings.TrimSpace(report.Host.MachineID)
	hostname := strings.TrimSpace(report.Host.Hostname)

	if agentID != "" {
		for _, host := range hosts {
			if host == nil || strings.TrimSpace(host.AgentID()) != agentID {
				continue
			}

			existingToken := strings.TrimSpace(host.TokenID())
			if tokenID == "" || existingToken == tokenID {
				if dockerHostIdentityConflicts(host, report) {
					continue
				}
				return host, true
			}
		}
	}

	if machineID != "" && hostname != "" {
		for _, host := range hosts {
			if host == nil {
				continue
			}
			if strings.TrimSpace(host.MachineID()) == machineID &&
				unifiedresources.HostnamesEquivalent(host.Hostname(), hostname) {
				if tokenID == "" || strings.TrimSpace(host.TokenID()) == tokenID {
					return host, true
				}
			}
		}
	}

	// Fallback: match by Hostname and Token only (when MachineID is missing)
	// This fixes issues where containerized agents without persistent machine-id
	// reconnect with the same token but are treated as new agents.
	if hostname != "" && tokenID != "" {
		for _, host := range hosts {
			if host == nil {
				continue
			}
			if unifiedresources.HostnamesEquivalent(host.Hostname(), hostname) &&
				strings.TrimSpace(host.TokenID()) == tokenID {
				if dockerHostMachineIDRevisits(host, agentID, machineID, machineRevisit) {
					continue
				}
				return host, true
			}
		}
	}

	if machineID != "" && tokenID == "" {
		for _, host := range hosts {
			if host == nil {
				continue
			}
			if strings.TrimSpace(host.MachineID()) == machineID && strings.TrimSpace(host.TokenID()) == "" {
				return host, true
			}
		}
	}

	if hostname != "" && tokenID == "" {
		for _, host := range hosts {
			if host == nil {
				continue
			}
			if unifiedresources.HostnamesEquivalent(host.Hostname(), hostname) &&
				strings.TrimSpace(host.TokenID()) == "" {
				if dockerHostMachineIDRevisits(host, agentID, machineID, machineRevisit) {
					continue
				}
				return host, true
			}
		}
	}

	return nil, false
}

// dockerHostMachineIDRevisits reports whether folding a report with the given
// machine ID into the candidate host would return the record to a machine
// identity it has already alternated away from - two live machines behind one
// hostname, not one recreated container. See findMatchingDockerHost.
//
// A record whose stable ID is derived from the report's own machine or agent
// ID belongs to the reporting machine: the returning owner reclaims it, and
// the *other* machine is the one that splits off to its own identity. This
// keeps each site on the record its identifiers minted, so removing one
// site's record never blocks the sibling through a shared alias.
func dockerHostMachineIDRevisits(host *unifiedresources.DockerHostView, agentID, machineID string, machineRevisit func(identifier, machineID string) bool) bool {
	if machineRevisit == nil || host == nil || machineID == "" {
		return false
	}
	existingMachineID := strings.TrimSpace(host.MachineID())
	if existingMachineID == "" || existingMachineID == machineID {
		return false
	}
	stableID := dockerHostStableID(host)
	if stableID != "" && (stableID == machineID || (agentID != "" && stableID == agentID)) {
		return false
	}
	return machineRevisit(stableID, machineID)
}

// dockerHostIdentityConflicts reports whether an incoming report is clearly from
// a different physical/swarm node than the existing Docker host record, so a
// shared token+agentID reused from another node is not collapsed into one host.
func dockerHostIdentityConflicts(existing *unifiedresources.DockerHostView, report agentsdocker.Report) bool {
	if existing == nil {
		return false
	}

	existingMachineID := strings.TrimSpace(existing.MachineID())
	reportMachineID := strings.TrimSpace(report.Host.MachineID)
	if existingMachineID != "" && reportMachineID != "" && existingMachineID != reportMachineID {
		return true
	}

	existingSwarmNodeID := ""
	if sw := existing.Swarm(); sw != nil {
		existingSwarmNodeID = strings.TrimSpace(sw.NodeID)
	}
	reportSwarmNodeID := ""
	if report.Host.Swarm != nil {
		reportSwarmNodeID = strings.TrimSpace(report.Host.Swarm.NodeID)
	}
	if existingSwarmNodeID != "" && reportSwarmNodeID != "" && existingSwarmNodeID != reportSwarmNodeID {
		return true
	}

	// Without stronger stable IDs, a hostname change is ambiguous and should not
	// be treated as the same reporting host automatically.
	existingHostname := strings.TrimSpace(existing.Hostname())
	reportHostname := strings.TrimSpace(report.Host.Hostname)
	if existingMachineID == "" && reportMachineID == "" &&
		existingSwarmNodeID == "" && reportSwarmNodeID == "" &&
		existingHostname != "" && reportHostname != "" &&
		!unifiedresources.HostnamesEquivalent(existingHostname, reportHostname) {
		return true
	}

	return false
}

func dockerHostStableID(host *unifiedresources.DockerHostView) string {
	if host == nil {
		return ""
	}
	if id := strings.TrimSpace(host.HostSourceID()); id != "" {
		return id
	}
	return strings.TrimSpace(host.ID())
}

func resolveDockerTokenBindingIdentity(identifier string, report agentsdocker.Report, previous *unifiedresources.DockerHostView, hasPrevious bool) (string, []string) {
	preferred := ""
	if hasPrevious {
		preferred = dockerHostStableID(previous)
	}
	if preferred == "" {
		preferred = strings.TrimSpace(report.Agent.ID)
	}
	if preferred == "" {
		preferred = strings.TrimSpace(identifier)
	}
	if preferred == "" {
		preferred = strings.TrimSpace(report.Host.MachineID)
	}
	if preferred == "" {
		preferred = strings.TrimSpace(report.Host.Hostname)
	}

	aliases := uniqueNonEmptyStrings(
		preferred,
		identifier,
		report.Agent.ID,
		report.Host.MachineID,
		report.Host.Hostname,
	)
	if previous != nil {
		aliases = uniqueNonEmptyStrings(append(aliases,
			dockerHostStableID(previous),
			previous.AgentID(),
			previous.MachineID(),
			previous.Hostname(),
		)...)
	}

	return preferred, aliases
}

func dockerTokenBindingMatches(boundAgentID string, aliases []string) bool {
	boundAgentID = strings.TrimSpace(boundAgentID)
	if boundAgentID == "" {
		return false
	}
	for _, alias := range aliases {
		if boundAgentID == strings.TrimSpace(alias) {
			return true
		}
	}
	return false
}

// dockerHostIDExists checks if a host ID is already in use.
func dockerHostIDExists(id string, hosts []*unifiedresources.DockerHostView) bool {
	if strings.TrimSpace(id) == "" {
		return false
	}
	for _, host := range hosts {
		if dockerHostStableID(host) == id {
			return true
		}
	}
	return false
}

// generateDockerHostIdentifier creates a unique identifier by appending suffixes.
func generateDockerHostIdentifier(base string, report agentsdocker.Report, tokenRecord *config.APITokenRecord, hosts []*unifiedresources.DockerHostView) string {
	if strings.TrimSpace(base) == "" {
		base = fallbackDockerHostID(report, tokenRecord)
	}
	if strings.TrimSpace(base) == "" {
		base = "docker-host"
	}

	used := make(map[string]struct{}, len(hosts))
	for _, host := range hosts {
		if id := dockerHostStableID(host); id != "" {
			used[id] = struct{}{}
		}
	}

	suffixes := dockerHostSuffixCandidates(report, tokenRecord)
	for _, suffix := range suffixes {
		candidate := fmt.Sprintf("%s::%s", base, suffix)
		if _, exists := used[candidate]; !exists {
			return candidate
		}
	}

	seed := strings.Join(suffixes, "|")
	if strings.TrimSpace(seed) == "" {
		seed = base
	}
	sum := sha1.Sum([]byte(seed))
	hashSuffix := fmt.Sprintf("hash-%s", hex.EncodeToString(sum[:6]))
	candidate := fmt.Sprintf("%s::%s", base, hashSuffix)
	if _, exists := used[candidate]; !exists {
		return candidate
	}

	for idx := 2; ; idx++ {
		candidate = fmt.Sprintf("%s::%d", base, idx)
		if _, exists := used[candidate]; !exists {
			return candidate
		}
	}
}

// dockerHostSuffixCandidates returns candidate suffixes for generating unique IDs.
func dockerHostSuffixCandidates(report agentsdocker.Report, tokenRecord *config.APITokenRecord) []string {
	candidates := make([]string, 0, 5)

	if tokenRecord != nil {
		if sanitized := sanitizeDockerHostSuffix(tokenRecord.ID); sanitized != "" {
			candidates = append(candidates, "token-"+sanitized)
		}
	}

	if agentID := sanitizeDockerHostSuffix(report.Agent.ID); agentID != "" {
		candidates = append(candidates, "agent-"+agentID)
	}

	if machineID := sanitizeDockerHostSuffix(report.Host.MachineID); machineID != "" {
		candidates = append(candidates, "machine-"+machineID)
	}

	hostNameSanitized := sanitizeDockerHostSuffix(report.Host.Hostname)
	if hostNameSanitized != "" {
		candidates = append(candidates, "host-"+hostNameSanitized)
	}

	hostDisplay := sanitizeDockerHostSuffix(report.Host.Name)
	if hostDisplay != "" && hostDisplay != hostNameSanitized {
		candidates = append(candidates, "name-"+hostDisplay)
	}

	return uniqueNonEmptyStrings(candidates...)
}

// sanitizeDockerHostSuffix cleans a string for use as a host ID suffix.
func sanitizeDockerHostSuffix(value string) string {
	value = strings.ToLower(strings.TrimSpace(value))
	if value == "" {
		return ""
	}

	var builder strings.Builder
	builder.Grow(len(value))
	lastHyphen := false
	runeCount := 0

	for _, r := range value {
		if runeCount >= 48 {
			break
		}

		switch {
		case unicode.IsLetter(r) || unicode.IsDigit(r):
			builder.WriteRune(r)
			lastHyphen = false
			runeCount++
		default:
			if !lastHyphen {
				builder.WriteRune('-')
				lastHyphen = true
				runeCount++
			}
		}
	}

	result := strings.Trim(builder.String(), "-")
	if result == "" {
		return ""
	}
	return result
}

// fallbackDockerHostID generates a hash-based ID when no better identifier exists.
func fallbackDockerHostID(report agentsdocker.Report, tokenRecord *config.APITokenRecord) string {
	seedParts := dockerHostSuffixCandidates(report, tokenRecord)
	if len(seedParts) == 0 {
		seedParts = uniqueNonEmptyStrings(
			report.Host.Hostname,
			report.Host.MachineID,
			report.Agent.ID,
		)
	}
	if len(seedParts) == 0 {
		return ""
	}
	seed := strings.Join(seedParts, "|")
	sum := sha1.Sum([]byte(seed))
	return fmt.Sprintf("docker-host-%s", hex.EncodeToString(sum[:6]))
}

// uniqueNonEmptyStrings returns unique non-empty strings in order of first appearance.
func uniqueNonEmptyStrings(values ...string) []string {
	seen := make(map[string]struct{}, len(values))
	result := make([]string, 0, len(values))
	for _, value := range values {
		value = strings.TrimSpace(value)
		if value == "" {
			continue
		}
		if _, ok := seen[value]; ok {
			continue
		}
		seen[value] = struct{}{}
		result = append(result, value)
	}
	return result
}