package run

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"text/template"

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

// The multi-step phase runner. A phased RunnableAgent (ra.Phases non-empty) runs
// its phases in order; each phase is a fresh majordomo agent loop (or a single
// bare LLM call for IsRunFunc phases) with its own template-expanded system
// prompt, model tier, step cap, and tool subset. Phase outputs feed later phases
// through {{.<PhaseName>}} template variables; {{.Query}} is the original input.
// The final phase's output is the run's output.
//
// Ported from mort's agentexec pipeline so the executus kernel — which already
// carries RunnableAgent.Phases as a DTO — actually EXECUTES them (it previously
// ignored the slice and ran a single loop with the base prompt). It reuses the
// shared run machinery built once in Run: the same stepObserver (so audit/steps/
// critic accumulate across every phase), the same critic steer, and the same
// compaction option.
//
// Semantics preserved from mort's pipeline:
//   - phases run sequentially; ctx cancellation between phases aborts the run.
//   - IsRunFunc = one bare LLM call, no tools, no loop.
//   - Optional phases swallow errors and substitute FallbackMessage.
//   - a non-optional phase that merely exhausts its step/tool budget is NOT fatal:
//     its partial transcript is salvaged and the pipeline continues (so a long
//     verify phase never discards every earlier phase's work). A hard error
//     (cancellation, model failure) still aborts.
//   - per-phase ModelTier resolve failures fall back to the base model with a WARN.
//
// Deliberately NOT carried over (kernel is leaner than mort's legacy pipeline):
// the legacy `submit` capture tool (the kernel relies on majordomo's
// no-tool-call-is-final-answer termination, like its single-loop path), and the
// critic's dynamic iteration ceiling (per-phase caps are fixed at phase start —
// the run-level critic's steer + hard deadline still apply across phases).

// phaseDeps carries the per-run state the phase runner shares with Run: the base
// model + tier, the full decorated toolbox (filtered per phase), the base step
// cap, the shared agent options (tool-error limits + step observer + compactor),
// the critic/session steer, and the audit recorder (phase events).
type phaseDeps struct {
	baseModel   llm.Model
	baseTier    string
	baseToolbox *llm.Toolbox
	baseMaxIter int
	sharedOpts  []agent.Option
	steer       func() []llm.Message
	rec         RunRecorder
}

// runPhases executes ra.Phases sequentially and returns a synthetic agent.Result
// whose Output is the final phase's output, with Usage aggregated across phases
// and Messages set to the last phase's transcript (for the PostRun hook). A hard
// (non-optional, non-budget) phase failure returns the error.
func (e *Executor) runPhases(runCtx context.Context, ra RunnableAgent, deps phaseDeps, query string, images []llm.ImagePart) (*agent.Result, error) {
	outputs := make(map[string]string, len(ra.Phases))
	var lastResult *agent.Result
	var lastOutput string
	var totalUsage llm.Usage

	for i, phase := range ra.Phases {
		// A killed/timed-out/cancelled run must not start its next phase.
		if err := runCtx.Err(); err != nil {
			return lastResult, err
		}

		instructions := expandPhaseTemplate(phase.SystemPrompt, query, outputs)
		if deps.rec != nil {
			deps.rec.LogEvent("phase_start", map[string]any{"phase": phase.Name})
		}

		output, res, err := e.runOnePhase(runCtx, ra, deps, phase, instructions, query, images)
		if res != nil {
			lastResult = res
			totalUsage = addUsage(totalUsage, res.Usage)
		}
		if err != nil {
			isLast := i == len(ra.Phases)-1
			switch {
			case phase.Optional:
				output = phase.FallbackMessage
				if output == "" {
					output = fmt.Sprintf("(Phase %q encountered an error -- proceeding without its results)", phase.Name)
				}
				slog.Warn("run: optional pipeline phase failed",
					"agent", ra.Name, "phase", phase.Name, "error", err)
				if deps.rec != nil {
					deps.rec.LogEvent("phase_failed_optional", map[string]any{"phase": phase.Name, "error": err.Error()})
				}

			case isPhaseBudgetExhaustion(err) && (!isLast || strings.TrimSpace(output) != ""):
				// Soft stop: the phase ran out of its step/tool budget before
				// composing a final answer. Not fatal — it did real work
				// (runOnePhase salvaged its partial transcript into output), and
				// aborting would discard every completed phase before it. Degrade
				// gracefully and continue.
				if strings.TrimSpace(output) == "" {
					output = fmt.Sprintf("(Phase %q reached its step budget before producing a consolidated result; continuing with its partial findings.)", phase.Name)
				} else {
					output += fmt.Sprintf("\n\n(Note: phase %q reached its step budget before fully completing; the above is its partial output.)", phase.Name)
				}
				slog.Warn("run: pipeline phase exhausted its budget; salvaging partial output and continuing",
					"agent", ra.Name, "phase", phase.Name, "last_phase", isLast, "error", err)
				if deps.rec != nil {
					deps.rec.LogEvent("phase_budget_exhausted", map[string]any{"phase": phase.Name, "error": err.Error(), "last_phase": isLast})
				}

			default:
				return lastResult, fmt.Errorf("pipeline phase %q: %w", phase.Name, err)
			}
		}

		outputs[phase.Name] = output
		lastOutput = output
	}

	// Synthesize the run result: the final phase's output, usage aggregated over
	// all phases, and the last phase's transcript for the PostRun hook.
	if lastResult == nil {
		lastResult = &agent.Result{}
	}
	lastResult.Output = lastOutput
	lastResult.Usage = totalUsage
	return lastResult, nil
}

// runOnePhase runs a single phase: a bare LLM call for IsRunFunc phases, a fresh
// agent loop otherwise. Returns the phase output, the loop result (nil for a
// failed bare call), and any error. On a budget-exhaustion error the loop's
// partial transcript is salvaged into the returned output.
func (e *Executor) runOnePhase(runCtx context.Context, ra RunnableAgent, deps phaseDeps, phase Phase, instructions, query string, images []llm.ImagePart) (string, *agent.Result, error) {
	model := e.phaseModel(runCtx, deps, ra, phase)
	// The phase's expanded instructions are the system prompt (with the platform
	// header so tools keep their run ids); the original query is the user message.
	system := e.systemPromptWithBody(instructions)

	if phase.IsRunFunc {
		// Bare LLM call: no tool loop, no tools array (some models 400 on an empty
		// tools list). The response still lands in the audit token tally.
		msgs := []llm.Message{phaseUserMessage(query, images)}
		resp, err := model.Generate(runCtx, llm.Request{System: system, Messages: msgs})
		if err != nil {
			return "", nil, fmt.Errorf("phase %q model call: %w", phase.Name, err)
		}
		if deps.rec != nil {
			deps.rec.OnStep(1, resp)
		}
		return resp.Text(), &agent.Result{
			Output:   resp.Text(),
			Usage:    resp.Usage,
			Messages: append(msgs, resp.Message()),
		}, nil
	}

	toolbox := filterToolbox(deps.baseToolbox, phase.Tools)
	maxIter := phase.MaxIterations
	if maxIter <= 0 {
		maxIter = deps.baseMaxIter
	}
	// Per-phase opts: a fixed step ceiling for this phase (the critic's dynamic
	// ceiling is intentionally not propagated to phases) + the phase toolbox, on
	// top of the shared opts (tool-error limits, step observer, compactor).
	opts := append([]agent.Option{
		agent.WithToolbox(toolbox),
		agent.WithMaxSteps(maxIter),
	}, deps.sharedOpts...)
	ag := agent.New(model, system, opts...)

	res, runErr := runAgent(runCtx, ag, query, images, agent.WithSteer(deps.steer))
	output := ""
	if res != nil {
		output = res.Output
	}
	// Budget/guard exhaustion leaves a usable partial transcript but an empty
	// final answer; salvage the narrated work so the pipeline can carry it forward.
	if runErr != nil && isPhaseBudgetExhaustion(runErr) {
		if salvaged := salvagePhaseTranscript(res); salvaged != "" {
			output = salvaged
		}
	}
	return output, res, runErr
}

// phaseModel resolves the phase's model tier, falling back to the base model on
// an empty tier or a resolution failure (WARN — visible, non-fatal).
func (e *Executor) phaseModel(ctx context.Context, deps phaseDeps, ra RunnableAgent, phase Phase) llm.Model {
	if phase.ModelTier == "" {
		return deps.baseModel
	}
	_, m, err := e.cfg.Models(ctx, phase.ModelTier)
	if err != nil || m == nil {
		slog.Warn("run: pipeline phase model resolve failed; using base model",
			"agent", ra.Name, "phase", phase.Name, "tier", phase.ModelTier, "error", err)
		return deps.baseModel
	}
	return m
}

// isPhaseBudgetExhaustion reports whether err is a soft budget/guard stop (the
// loop hit its step cap or tripped a tool-error guard) — which leaves a usable
// partial transcript — as opposed to a hard error (cancellation, model failure).
func isPhaseBudgetExhaustion(err error) bool {
	return errors.Is(err, agent.ErrMaxSteps) || errors.Is(err, agent.ErrToolLoop)
}

// salvagePhaseTranscript reconstructs a best-effort phase output from a loop that
// ended without a final answer: the assistant's narrated text across every step,
// tail-trimmed to a bound. Returns "" when the model wrote no prose.
func salvagePhaseTranscript(res *agent.Result) string {
	if res == nil {
		return ""
	}
	var b strings.Builder
	for _, step := range res.Steps {
		if step.Response == nil {
			continue
		}
		if t := strings.TrimSpace(step.Response.Text()); t != "" {
			if b.Len() > 0 {
				b.WriteString("\n\n")
			}
			b.WriteString(t)
		}
	}
	out := strings.TrimSpace(b.String())
	const maxSalvage = 8000
	if len(out) > maxSalvage {
		out = "...(earlier reasoning trimmed)...\n" + out[len(out)-maxSalvage:]
	}
	return out
}

// phaseUserMessage builds a phase's user message: the original query text plus
// any inline images. Mirrors the single-loop multimodal seeding in runAgent.
func phaseUserMessage(query string, images []llm.ImagePart) llm.Message {
	if len(images) == 0 {
		return llm.UserText(query)
	}
	parts := make([]llm.Part, 0, len(images)+1)
	if strings.TrimSpace(query) != "" {
		parts = append(parts, llm.Text(query))
	}
	for _, img := range images {
		parts = append(parts, img)
	}
	return llm.UserParts(parts...)
}

// expandPhaseTemplate applies Go text/template substitution to a phase prompt,
// replacing {{.Query}} with the original query and {{.<PhaseName>}} with a prior
// phase's output. Returns the original string unchanged if parsing or execution
// fails (best-effort, not fatal).
func expandPhaseTemplate(tmpl, query string, priorOutputs map[string]string) string {
	t, err := template.New("phase").Option("missingkey=zero").Parse(tmpl)
	if err != nil {
		return tmpl
	}
	data := map[string]string{"Query": query}
	for k, v := range priorOutputs {
		data[k] = v
	}
	var buf bytes.Buffer
	if err := t.Execute(&buf, data); err != nil {
		return tmpl
	}
	return buf.String()
}

// filterToolbox returns a new toolbox restricted to the named tools (preserving
// palette order). Empty names = the full palette. Unknown names are skipped with
// a WARN — a typo'd phase tool list should not abort a run mid-pipeline.
func filterToolbox(box *llm.Toolbox, names []string) *llm.Toolbox {
	out := llm.NewToolbox(box.Name())
	if len(names) == 0 {
		for _, t := range box.Tools() {
			_ = out.Add(t)
		}
		return out
	}
	for _, name := range names {
		t, ok := box.Get(name)
		if !ok {
			slog.Warn("run: pipeline phase references unknown tool; skipping", "tool", name)
			continue
		}
		if err := out.Add(t); err != nil {
			slog.Warn("run: pipeline phase tool duplicated; skipping", "tool", name, "error", err)
		}
	}
	return out
}

// addUsage sums two llm.Usage tallies field-by-field so a phased run reports the
// total tokens across all phases.
func addUsage(a, b llm.Usage) llm.Usage {
	a.InputTokens += b.InputTokens
	a.OutputTokens += b.OutputTokens
	a.CacheReadTokens += b.CacheReadTokens
	a.CacheWriteTokens += b.CacheWriteTokens
	a.ReasoningTokens += b.ReasoningTokens
	return a
}