package transcribe

import (
	"context"
	"errors"
	"fmt"

	"git.d-ma.be/mathias/tapir/internal/domain"
	"git.d-ma.be/mathias/tapir/internal/errkind"
	"git.d-ma.be/mathias/tapir/internal/progress"
	"git.d-ma.be/mathias/tapir/internal/reconcile"
)

// Ensemble transcribes the same WAV with two engines, one after the other, and has a
// local model reconcile their disagreements (ADR-034). It satisfies uploads.Transcriber,
// so the worker neither knows nor cares that two engines were involved.
//
// It degrades in steps and never turns a recoverable problem into a failed job:
// one engine down → the other's text, said so on the result; the model down → the
// base text unreconciled; both engines down → the cloud fallback, if configured, and
// recorded as such. A cancelled job stops everything and never reaches the cloud.
type Ensemble struct {
	base, alt Backend
	fallback  Backend // nil = no cloud fallback
	adj       reconcile.Adjudicator
	opts      reconcile.Options
}

// NewEnsemble builds an Ensemble. base is the engine whose text stands where the two
// disagree and is the faster one, so it runs first; alt supplies the other reading.
func NewEnsemble(base, alt, fallback Backend, adj reconcile.Adjudicator, opts reconcile.Options) *Ensemble {
	return &Ensemble{base: base, alt: alt, fallback: fallback, adj: adj, opts: opts}
}

// Plan implements uploads.Planner: the phases this ensemble reports, so the page can
// show them before they run. The fallback is a phase only when one is configured.
func (e *Ensemble) Plan() []progress.Planned {
	plan := []progress.Planned{
		{Key: "engine_a", Label: "Transcribing with " + e.base.Name()},
		{Key: "engine_b", Label: "Transcribing with " + e.alt.Name()},
		{Key: "compare", Label: "Comparing the two transcripts"},
		{Key: "decide", Label: "Deciding the differences"},
	}
	if e.fallback != nil {
		plan = append(plan, progress.Planned{Key: "fallback", Label: "Cloud fallback (" + e.fallback.Name() + ")"})
	}
	return plan
}

// Transcribe implements uploads.Transcriber. Each phase is reported through the
// progress.Reporter in ctx (a no-op when nobody listens).
func (e *Ensemble) Transcribe(ctx context.Context, wavPath string) (domain.Transcription, error) {
	rep := progress.From(ctx)
	b, berr := e.run(ctx, rep, "engine_a", e.base, wavPath)
	if err := ctx.Err(); err != nil {
		return domain.Transcription{}, err
	}
	a, aerr := e.run(ctx, rep, "engine_b", e.alt, wavPath)
	if err := ctx.Err(); err != nil {
		return domain.Transcription{}, err
	}

	switch {
	case berr == nil && aerr == nil:
		out, err := reconcile.Reconcile(ctx, b, a, e.adj, e.opts)
		if err != nil {
			return domain.Transcription{}, err
		}
		out.Endpoint = fmt.Sprintf("%s + %s, reconciled by %s", e.base.Name(), e.alt.Name(), e.opts.Reconciler)
		if rc := out.Reconciliation; rc != nil {
			rep.Note("reconciled", "status", string(rc.Status), "disputes", rc.Disputes, "auto_resolved", rc.AutoResolved,
				"adjudicated", rc.Adjudicated, "changed", rc.Changed, "unsure", rc.Unsure, "errors", rc.Errors)
		}
		return out, nil
	case berr == nil:
		return e.single(b, e.base.Name(), fmt.Sprintf("%s failed (%s)", e.alt.Name(), errkind.Of(aerr))), nil
	case aerr == nil:
		return e.single(a, e.alt.Name(), fmt.Sprintf("%s failed (%s)", e.base.Name(), errkind.Of(berr))), nil
	}

	both := errors.Join(fmt.Errorf("%s: %w", e.base.Name(), berr), fmt.Errorf("%s: %w", e.alt.Name(), aerr))
	if e.fallback == nil {
		return domain.Transcription{}, both
	}
	f, ferr := e.run(ctx, rep, "fallback", e.fallback, wavPath)
	if ferr != nil {
		return domain.Transcription{}, errors.Join(both, fmt.Errorf("%s: %w", e.fallback.Name(), ferr))
	}
	return e.single(f, e.fallback.Name(), "both local engines failed"), nil
}

// run is one engine call, reported as a phase. A job that was stopped is not a broken
// engine, so a cancelled context is never reported as a failed phase.
func (e *Ensemble) run(ctx context.Context, rep progress.Reporter, key string, be Backend, wav string) (domain.Transcription, error) {
	rep.Begin(key, 0)
	t, err := be.Transcribe(ctx, wav)
	switch {
	case err == nil:
		rep.Done(key)
	case ctx.Err() == nil:
		rep.Fail(key, err)
	}
	return t, err
}

// single is a transcript from one engine only: nothing to reconcile, and the result
// says why, because a reader should know the second opinion was missing.
func (e *Ensemble) single(t domain.Transcription, engine, reason string) domain.Transcription {
	t.Endpoint = engine
	t.Reconciliation = &domain.Reconciliation{
		Status: domain.ReconcileSingle, Reason: reason, Base: e.opts.BaseEngine, Alt: e.opts.AltEngine, Reconciler: e.opts.Reconciler,
	}
	return t
}