package staffing

import (
	"context"
	"errors"
	"fmt"
	"strings"

	"github.com/missionworkforce/missionmatch/internal/modules/ai"
	"github.com/missionworkforce/missionmatch/internal/platform/inference"
)

// narrate produces the natural language rationale for one recommendation and records its source. It is
// the ONLY place a model is used, and the recommendation never depends on it: the model writes prose
// grounded strictly in the deterministic evidence, the faithfulness gate confirms the prose asserts
// nothing the evidence does not support, and any failure (no plane, circuit open, timeout, or an
// unconfirmed answer) falls back to a deterministic template assembled from the same facts. The fallback
// reason is recorded in the evidence (never in an audit payload) for later narration tuning.
//
// No candidate name, email, or any demographic field is ever sent to the plane; the facts are the action,
// the engine score and band, skill names, requirement ids, and the computed counterfactual numbers. Every
// string is passed through ai.ForbidEEO before it leaves the process.
func (s *Service) narrate(ctx context.Context, action Action, ev Evidence) (rationale string, source RationaleSource, fallbackReason string) {
	facts := evidenceStatements(action, ev)
	deterministic := strings.Join(facts, " ")
	if deterministic == "" {
		deterministic = "Recommended by the deterministic engine."
	}

	if s.infer == nil {
		return deterministic, RationaleDeterministic, "generation_disabled"
	}

	system := "You write a one or two sentence staffing rationale for a government contractor. Use ONLY the facts provided, assert nothing not present in them, never mention demographics, and never invent a number."
	prompt := "Facts:\n" + strings.Join(facts, "\n") + "\nWrite the rationale for the " + string(action) + " recommendation."
	for _, str := range append([]string{system, prompt}, facts...) {
		if err := ai.ForbidEEO(str); err != nil {
			return deterministic, RationaleDeterministic, "eeo_guard"
		}
	}

	gen, err := s.infer.Generate(ctx, inference.GenerateRequest{System: system, Prompt: prompt, MaxTokens: 120, Temperature: 0})
	if err != nil {
		return deterministic, RationaleDeterministic, fallbackReason2(err)
	}
	answer := strings.TrimSpace(gen.Text)
	if answer == "" {
		return deterministic, RationaleDeterministic, "empty_generation"
	}
	// Defense in depth: if the model echoed an eeo reference, refuse the prose.
	if ai.ForbidEEO(answer) != nil {
		return deterministic, RationaleDeterministic, "eeo_guard"
	}
	fr, err := s.infer.CheckFaithfulness(ctx, answer, facts)
	if err != nil {
		return deterministic, RationaleDeterministic, fallbackReason2(err)
	}
	if !fr.Supported {
		return deterministic, RationaleDeterministic, "could_not_confirm"
	}
	return answer, RationaleAIFaithful, ""
}

// evidenceStatements renders the deterministic facts a rationale may assert, from the structured evidence.
// These are also the evidence array the faithfulness gate checks the generated prose against.
func evidenceStatements(action Action, ev Evidence) []string {
	var out []string
	if ev.EngineTotal != "" {
		band := ev.Band
		if band == "" {
			band = "n/a"
		}
		out = append(out, "Engine total score is "+ev.EngineTotal+" out of 100, band "+band+".")
	}
	switch action {
	case ActionAssign:
		out = append(out, "The candidate is available and clears the staffing floor.")
	case ActionReassign:
		if ev.Reassign != nil {
			out = append(out, "The candidate is committed to requirement "+ev.Reassign.FromRequirementID+"; the target gap is higher priority by "+ev.Reassign.PriorityDelta.String()+".")
		}
	case ActionReskill:
		if ev.Reskill != nil {
			out = append(out, "The candidate holds "+ev.Reskill.HeldSkill+", adjacent to the missing required skill "+ev.Reskill.MissingSkill+" at cosine distance "+ev.Reskill.Distance.String()+".")
		}
	case ActionSource:
		if ev.OpenSlots != nil {
			out = append(out, fmt.Sprintf("No qualified, available bench candidate exists for %d open slot(s); external sourcing is required.", *ev.OpenSlots))
		}
	}
	if cf := ev.Counterfactual; cf != nil {
		out = append(out, "The assigned candidate's engine total for this requirement is "+cf.AssignedTotal+".")
		if cf.CandidateNextRequirement != "" {
			out = append(out, "Their next best alternative is requirement "+cf.CandidateNextRequirement+".")
		}
		if cf.RequirementNextCandidate != "" {
			out = append(out, "If reassigned, this requirement's next best candidate is "+cf.RequirementNextCandidate+".")
		}
	}
	if ev.Trigger != nil {
		out = append(out, "This alert was raised by a "+ev.Trigger.Kind+" change.")
	}
	return out
}

func fallbackReason2(err error) string {
	switch {
	case errors.Is(err, inference.ErrCircuitOpen):
		return "circuit_open"
	case errors.Is(err, context.DeadlineExceeded):
		return "plane_timeout"
	default:
		return "plane_error"
	}
}