package observation

import (
	"sort"
	"strings"
	"time"

	"github.com/tegwick/fluid-core/internal/contract"
)

// Interaction is one consumer's ordered call chain.
//
// ArchitectureBlueprint.md section 6.4: the analyzer looks beyond individual
// requests, because interaction topologies are often more informative than
// simple error counts. A single 200 tells you nothing; the same 200 fetched
// forty times to find one record tells you the interface is missing a concept.
type Interaction struct {
	ConsumerRef string
	Cohort      contract.CohortID
	Started     time.Time
	Ended       time.Time
	Steps       []Step
}

// Step is one call within an interaction.
type Step struct {
	Route  string
	Method string
	Status int64
	Error  contract.FluidTelemetryErrorClass
}

// Signature renders an interaction as a comparable shape.
//
// Routes are used rather than concrete URLs so that two consumers doing the
// same thing to different resources produce the same signature. Without that
// normalization every chain is unique and no pattern is ever detected twice.
func (i Interaction) Signature() string {
	parts := make([]string, 0, len(i.Steps))
	for _, s := range i.Steps {
		part := s.Method + " " + s.Route
		if s.Error != "" {
			part += " !" + string(s.Error)
		}
		parts = append(parts, part)
	}
	return strings.Join(parts, " -> ")
}

// Pattern is a recurring interaction shape observed across consumers.
type Pattern struct {
	Signature string              `json:"signature"`
	Steps     int                 `json:"steps"`
	Count     int                 `json:"occurrences"`
	Consumers int                 `json:"independent_consumers"`
	Cohorts   []contract.CohortID `json:"cohorts"`
	// RepeatedStep names a route called more than once in the same chain, which
	// is the usual shape of a consumer compensating for a missing capability.
	RepeatedStep string `json:"repeated_step,omitempty"`
	// MaxRepeats is how many times that route appeared in the worst chain.
	MaxRepeats int `json:"max_repeats,omitempty"`
	// RecoveredError names an error the consumer hit and then worked past,
	// which distinguishes a recoverable misunderstanding from a hard failure.
	RecoveredError contract.FluidTelemetryErrorClass `json:"recovered_error,omitempty"`
	FirstSeen      time.Time                         `json:"first_seen"`
	LastSeen       time.Time                         `json:"last_seen"`
}

// TopologyAnalyzer groups telemetry into interactions and finds patterns.
type TopologyAnalyzer struct {
	// ChainGap is the idle time after which a consumer's next call starts a new
	// interaction rather than continuing the previous one.
	ChainGap time.Duration
	// MinOccurrences is how often a shape must appear before it is a pattern.
	MinOccurrences int
	// MinConsumers is how many independent consumers must show the shape.
	// One consumer repeating itself is a client bug; several independent
	// consumers converging on the same workaround is interface pressure.
	MinConsumers int
}

// NewTopologyAnalyzer returns an analyzer with workable defaults.
func NewTopologyAnalyzer() *TopologyAnalyzer {
	return &TopologyAnalyzer{
		ChainGap:       30 * time.Second,
		MinOccurrences: 3,
		MinConsumers:   2,
	}
}

// Interactions groups events into per-consumer call chains.
//
// Grouping prefers an explicit chain id when the consumer supplied one, and
// falls back to time-bounded sessions per consumer. The fallback is a heuristic
// and is why chain ids are worth asking agentic consumers for.
func (a *TopologyAnalyzer) Interactions(events []contract.FluidTelemetry) []Interaction {
	ordered := make([]contract.FluidTelemetry, len(events))
	copy(ordered, events)
	sort.SliceStable(ordered, func(i, j int) bool {
		return ordered[i].OccurredAt.Before(ordered[j].OccurredAt)
	})

	type key struct{ consumer, chain string }
	open := map[key]*Interaction{}
	var done []Interaction

	for _, ev := range ordered {
		if ev.Request == nil && ev.Error == nil {
			continue
		}

		consumer := ev.ConsumerRef
		if consumer == "" {
			consumer = ev.CorrelationID
		}
		if consumer == "" {
			continue
		}

		chain := ""
		if ev.Sequence != nil {
			chain = ev.Sequence.ChainID
		}
		k := key{consumer: consumer, chain: chain}

		current, ok := open[k]
		// With no explicit chain id, an idle gap ends the interaction.
		if ok && chain == "" && ev.OccurredAt.Sub(current.Ended) > a.ChainGap {
			done = append(done, *current)
			ok = false
		}
		if !ok {
			cohort := contract.CohortID("")
			if ev.Cohort != nil {
				cohort = *ev.Cohort
			}
			current = &Interaction{
				ConsumerRef: consumer,
				Cohort:      cohort,
				Started:     ev.OccurredAt,
			}
			open[k] = current
		}

		current.Ended = ev.OccurredAt
		current.Steps = append(current.Steps, stepOf(ev))
	}

	for _, in := range open {
		done = append(done, *in)
	}
	sort.Slice(done, func(i, j int) bool { return done[i].Started.Before(done[j].Started) })
	return done
}

func stepOf(ev contract.FluidTelemetry) Step {
	var s Step
	if ev.Request != nil {
		s.Route = ev.Request.Route
		s.Method = ev.Request.Method
		if ev.Request.Status != nil {
			s.Status = *ev.Request.Status
		}
	}
	if ev.Error != nil {
		s.Error = ev.Error.Class
	}
	if s.Route == "" {
		s.Route = "(unknown)"
	}
	return s
}

// Patterns reports recurring interaction shapes.
func (a *TopologyAnalyzer) Patterns(events []contract.FluidTelemetry) []Pattern {
	interactions := a.Interactions(events)

	type acc struct {
		count      int
		consumers  map[string]struct{}
		cohorts    map[contract.CohortID]struct{}
		steps      int
		repeated   string
		maxRepeats int
		recovered  contract.FluidTelemetryErrorClass
		first      time.Time
		last       time.Time
	}
	groups := map[string]*acc{}

	for _, in := range interactions {
		if len(in.Steps) == 0 {
			continue
		}
		sig := in.Signature()

		g, ok := groups[sig]
		if !ok {
			g = &acc{
				consumers: map[string]struct{}{},
				cohorts:   map[contract.CohortID]struct{}{},
				steps:     len(in.Steps),
				first:     in.Started,
				last:      in.Ended,
			}
			groups[sig] = g
		}

		g.count++
		g.consumers[in.ConsumerRef] = struct{}{}
		if in.Cohort != "" {
			g.cohorts[in.Cohort] = struct{}{}
		}
		if in.Started.Before(g.first) {
			g.first = in.Started
		}
		if in.Ended.After(g.last) {
			g.last = in.Ended
		}

		if route, n := repeatedRoute(in); n > g.maxRepeats {
			g.repeated, g.maxRepeats = route, n
		}
		if class, ok := recoveredError(in); ok {
			g.recovered = class
		}
	}

	out := make([]Pattern, 0, len(groups))
	for sig, g := range groups {
		if g.count < a.MinOccurrences || len(g.consumers) < a.MinConsumers {
			continue
		}
		cohorts := make([]contract.CohortID, 0, len(g.cohorts))
		for c := range g.cohorts {
			cohorts = append(cohorts, c)
		}
		sort.Slice(cohorts, func(i, j int) bool { return cohorts[i] < cohorts[j] })

		p := Pattern{
			Signature: sig,
			Steps:     g.steps,
			Count:     g.count,
			Consumers: len(g.consumers),
			Cohorts:   cohorts,
			FirstSeen: g.first,
			LastSeen:  g.last,
		}
		if g.maxRepeats > 1 {
			p.RepeatedStep, p.MaxRepeats = g.repeated, g.maxRepeats
		}
		p.RecoveredError = g.recovered
		out = append(out, p)
	}

	// Most frequent first: an analyst reading this wants the biggest signal at
	// the top, and a stable tiebreak keeps the output diffable.
	sort.Slice(out, func(i, j int) bool {
		if out[i].Count != out[j].Count {
			return out[i].Count > out[j].Count
		}
		return out[i].Signature < out[j].Signature
	})
	return out
}

// repeatedRoute finds the most-repeated route within one interaction.
func repeatedRoute(in Interaction) (string, int) {
	counts := map[string]int{}
	for _, s := range in.Steps {
		counts[s.Method+" "+s.Route]++
	}

	best, bestN := "", 0
	routes := make([]string, 0, len(counts))
	for r := range counts {
		routes = append(routes, r)
	}
	sort.Strings(routes)
	for _, r := range routes {
		if counts[r] > bestN {
			best, bestN = r, counts[r]
		}
	}
	return best, bestN
}

// recoveredError reports an error the consumer hit and then got past.
//
// This is the shape Blueprint 6.4 calls out as a recoverable misunderstanding:
// invalid request, schema lookup, retry with a corrected request. It is a
// different problem from a chain that simply fails, and conflating the two
// would send the wrong hypothesis to the Daimon.
func recoveredError(in Interaction) (contract.FluidTelemetryErrorClass, bool) {
	var seen contract.FluidTelemetryErrorClass
	for _, s := range in.Steps {
		if s.Error != "" {
			seen = s.Error
			continue
		}
		if seen != "" && s.Status >= 200 && s.Status < 300 {
			return seen, true
		}
	}
	return "", false
}