package run

import (
	"context"
	"errors"
	"fmt"
	"time"

	"gitea.stevedudenhoeffer.com/steve/majordomo/agent"
	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"

	"gitea.stevedudenhoeffer.com/steve/executus/compact"
	"gitea.stevedudenhoeffer.com/steve/executus/tool"
)

// ModelResolver resolves a tier alias or concrete spec to a usable llm.Model
// and an enriched context (for usage attribution). model.ParseModelForContext
// satisfies it.
type ModelResolver func(ctx context.Context, tier string) (context.Context, llm.Model, error)

// Defaults are the executor's fallback caps and loop guards, applied per run
// when the RunnableAgent leaves a field zero.
type Defaults struct {
	MaxIterations            int           // tool-dispatch steps; default 12
	MaxRuntime               time.Duration // wall-clock per run; default 60s
	FallbackTier             string        // tier when the agent's is empty; default "fast"
	MaxConsecutiveToolErrors int           // loop guard; default 3
	MaxSameToolCallRepeats   int           // retry-storm guard; default 3
	CompactionThresholdRatio float64       // fraction of model context to compact at; default 0.7
}

func (d Defaults) withFallbacks() Defaults {
	if d.MaxIterations <= 0 {
		d.MaxIterations = 12
	}
	if d.MaxRuntime <= 0 {
		d.MaxRuntime = 60 * time.Second
	}
	if d.FallbackTier == "" {
		d.FallbackTier = "fast"
	}
	if d.MaxConsecutiveToolErrors <= 0 {
		d.MaxConsecutiveToolErrors = 3
	}
	if d.MaxSameToolCallRepeats <= 0 {
		d.MaxSameToolCallRepeats = 3
	}
	if d.CompactionThresholdRatio <= 0 {
		d.CompactionThresholdRatio = 0.7
	}
	return d
}

// Config wires an Executor. Registry + Models are required; everything else is
// optional and nil-safe — the zero Config beyond those yields a bounded,
// in-memory run with no persistence/audit/budget/critic/delegation/compaction
// (gadfly's case).
type Config struct {
	Registry tool.Registry
	Models   ModelResolver
	Defaults Defaults
	Ports    Ports

	// Compactor mints the per-run context-compaction hook. nil disables
	// compaction. ContextTokens resolves a tier's model context-window (for
	// the compaction threshold); nil — or a zero return — also disables it.
	Compactor     compact.CompactorFactory
	ContextTokens func(tier string) int

	// SystemHeader is an optional platform header prepended to every agent's
	// system prompt.
	SystemHeader string
}

// Executor runs a RunnableAgent through majordomo's agent loop with the wired
// Ports. Construct with New; safe for concurrent use across runs.
type Executor struct {
	cfg Config
}

// New builds an Executor. It panics if Registry or Models is nil — those are
// structural, not runtime, errors.
func New(cfg Config) *Executor {
	if cfg.Registry == nil || cfg.Models == nil {
		panic("run.New: Registry and Models are required")
	}
	cfg.Defaults = cfg.Defaults.withFallbacks()
	return &Executor{cfg: cfg}
}

// Result is one run's outcome. Err carries the run failure (if any); the other
// fields are populated best-effort even on error (partial output/steps/usage).
type Result struct {
	RunID  string
	Output string
	Steps  []tool.Step
	Usage  llm.Usage
	Err    error
}

// Run executes ra with the given invocation + input and returns the Result. It
// never propagates a panic; failures surface in Result.Err.
func (e *Executor) Run(ctx context.Context, ra RunnableAgent, inv tool.Invocation, input string) Result {
	started := time.Now()
	res := Result{RunID: inv.RunID}

	tier := ra.ModelTier
	if tier == "" {
		tier = e.cfg.Defaults.FallbackTier
	}
	maxIter := ra.MaxIterations
	if maxIter <= 0 {
		maxIter = e.cfg.Defaults.MaxIterations
	}
	maxRuntime := ra.MaxRuntime
	if maxRuntime <= 0 {
		maxRuntime = e.cfg.Defaults.MaxRuntime
	}

	// Budget gate (pre-run): a rejected run makes no model call.
	if e.cfg.Ports.Budget != nil {
		if err := e.cfg.Ports.Budget.Check(ctx, inv.CallerID); err != nil {
			res.Err = err
			return res
		}
	}

	// Resolve the model (enriches ctx for usage attribution).
	modelCtx, model, err := e.cfg.Models(ctx, tier)
	if err != nil {
		res.Err = fmt.Errorf("resolve model %q: %w", tier, err)
		return res
	}
	if model == nil {
		// A resolver returning (ctx, nil, nil) would otherwise nil-panic inside
		// the agent loop; surface it as a clean error (Run never panics out).
		res.Err = fmt.Errorf("resolve model %q: resolver returned a nil model", tier)
		return res
	}
	ctx = modelCtx

	// Audit start (optional). The recorder satisfies RunTally; stamp it on the
	// invocation so a self-status tool can read live progress.
	var rec RunRecorder
	var stateAcc *RunStateAccessor
	if e.cfg.Ports.Audit != nil {
		rec = e.cfg.Ports.Audit.StartRun(ctx, RunInfo{
			RunID:       inv.RunID,
			SubjectID:   ra.ID,
			Name:        ra.Name,
			CallerID:    inv.CallerID,
			ChannelID:   inv.ChannelID,
			ParentRunID: inv.ParentRunID,
			Inputs:      inv.SkillInputs,
			StartedAt:   started,
		})
	}
	if rec != nil {
		stateAcc = NewRunStateAccessor(rec, maxIter, 0, started)
		inv.RunState = stateAcc
	}

	// Build the toolbox from the agent's low-level tools.
	toolbox, err := e.cfg.Registry.Build(ra.LowLevelTools, inv, tool.Visibility("private"), nil)
	if err != nil {
		res.Err = fmt.Errorf("build toolbox: %w", err)
		e.finishAudit(ctx, rec, "error", res, started, res.Err)
		return res
	}

	// Run context: bound by MaxRuntime, detached from the caller's deadline so a
	// lane/queue wait doesn't eat the run budget (mort's V10 lesson). Caller
	// cancellation still propagates via MergeCancellation. Created BEFORE the
	// step observer so the observer forwards the merged run context (not a
	// possibly-cancelled caller ctx) to OnStep consumers.
	runCtx, cancel := context.WithTimeout(context.WithoutCancel(ctx), maxRuntime)
	defer cancel()
	runCtx, mergeCancel := MergeCancellation(runCtx, ctx)
	defer mergeCancel()

	// Step instrumentation: accumulate Result.Steps + fire inv.OnStep, feed the
	// audit recorder, and keep the live iteration counter fresh. majordomo's
	// step observer hands us each completed iteration; we zip the model's tool
	// calls with their executed results PAIRWISE — a result without a matching
	// call (or a call without a result) is skipped rather than recorded as an
	// empty-name "ghost" step.
	emitter := newStepEmitter(inv.OnStep)
	stepObserver := func(s agent.Step) {
		if stateAcc != nil {
			stateAcc.SetIteration(s.Index)
		}
		if rec != nil {
			rec.OnStep(s.Index, s.Response)
		}
		var calls []llm.ToolCall
		if s.Response != nil {
			calls = s.Response.ToolCalls
		}
		n := len(s.Results)
		if len(calls) < n {
			n = len(calls)
		}
		for i := 0; i < n; i++ {
			call, r := calls[i], s.Results[i]
			emitter.toolStart(runCtx, call.Name, call.Arguments)
			emitter.toolEnd(runCtx, call, r.Content, r.IsError)
			if rec != nil {
				rec.OnTool(call, r.Content)
			}
		}
	}

	opts := []agent.Option{
		agent.WithToolbox(toolbox),
		agent.WithMaxSteps(maxIter),
		agent.WithToolErrorLimits(e.cfg.Defaults.MaxConsecutiveToolErrors, e.cfg.Defaults.MaxSameToolCallRepeats),
		agent.WithStepObserver(stepObserver),
	}
	if e.cfg.Compactor != nil && e.cfg.ContextTokens != nil {
		if threshold := e.compactionThreshold(tier); threshold > 0 {
			// Forward compaction events to the audit log (makes the
			// CompactionEvent doc's "logged to the run trace" promise true).
			var onFire func(compact.CompactionEvent)
			if rec != nil {
				onFire = func(ev compact.CompactionEvent) {
					rec.LogEvent("compaction_fired", map[string]any{
						"messages_before": ev.MessagesBefore,
						"messages_after":  ev.MessagesAfter,
						"tokens_before":   ev.TokensBefore,
						"tokens_after":    ev.TokensAfter,
					})
				}
			}
			opts = append(opts, agent.WithCompactor(e.cfg.Compactor(threshold, onFire)))
		}
	}

	ag := agent.New(model, e.systemPrompt(ra), opts...)
	runRes, runErr := ag.Run(runCtx, input)

	status := statusFor(runErr)
	if runRes != nil {
		res.Output = runRes.Output
		res.Usage = runRes.Usage
	}
	res.Steps = emitter.snapshot()
	res.Err = runErr

	e.finishAudit(ctx, rec, status, res, started, runErr)
	if e.cfg.Ports.Budget != nil {
		e.cfg.Ports.Budget.Commit(detach(ctx), inv.CallerID, time.Since(started).Seconds())
	}
	return res
}

// statusFor maps a run error to a RunStats.Status, distinguishing a deadline
// (timeout) and a cancellation (cancelled — caller cancel or shutdown) from a
// generic error so audit consumers can tell them apart.
func statusFor(runErr error) string {
	switch {
	case runErr == nil:
		return "ok"
	case errors.Is(runErr, context.DeadlineExceeded):
		return "timeout"
	case errors.Is(runErr, context.Canceled):
		return "cancelled"
	default:
		return "error"
	}
}

// finishAudit writes the terminal roll-up on a detached context so a cancelled
// run still records (mort's CleanupContextTimeout lesson).
func (e *Executor) finishAudit(ctx context.Context, rec RunRecorder, status string, res Result, started time.Time, runErr error) {
	if rec == nil {
		return
	}
	stats := RunStats{
		Status:         status,
		Output:         res.Output,
		ToolCalls:      rec.ToolCallsCount(),
		RuntimeSeconds: time.Since(started).Seconds(),
	}
	if runErr != nil {
		stats.Error = runErr.Error()
	}
	stats.InputTokens, stats.OutputTokens, stats.ThinkingTokens = rec.TokenStats()
	rec.Close(detach(ctx), stats)
}

func (e *Executor) systemPrompt(ra RunnableAgent) string {
	if e.cfg.SystemHeader == "" {
		return ra.SystemPrompt
	}
	if ra.SystemPrompt == "" {
		return e.cfg.SystemHeader
	}
	return e.cfg.SystemHeader + "\n\n" + ra.SystemPrompt
}

// compactionThreshold returns the token threshold for the tier's model context
// window (ratio × limit), or 0 when the limit is unknown.
func (e *Executor) compactionThreshold(tier string) int {
	max := e.cfg.ContextTokens(tier)
	if max <= 0 {
		return 0
	}
	return int(float64(max) * e.cfg.Defaults.CompactionThresholdRatio)
}

// detach derives a bounded cleanup context off ctx, detached from its
// cancellation, for post-run writes. The cancel is intentionally not returned;
// CleanupContextTimeout bounds the lifetime.
func detach(ctx context.Context) context.Context {
	c, cancel := context.WithTimeout(context.WithoutCancel(ctx), CleanupContextTimeout)
	_ = cancel // bounded by the timeout; nothing to cancel early
	return c
}