package pipeline

import (
	"context"
	"fmt"

	"gitea.maximumdirect.net/eric/seriatim/internal/artifact"
	"gitea.maximumdirect.net/eric/seriatim/internal/buildinfo"
	"gitea.maximumdirect.net/eric/seriatim/internal/config"
	"gitea.maximumdirect.net/eric/seriatim/internal/model"
	"gitea.maximumdirect.net/eric/seriatim/internal/report"
	"gitea.maximumdirect.net/eric/seriatim/schema"
)

const (
	applicationName = artifact.ApplicationName
)

// Run validates module composition, executes the pipeline, and emits outputs.
func Run(ctx context.Context, cfg config.Config, registry *Registry) error {
	plan, err := resolvePlan(cfg, registry)
	if err != nil {
		return err
	}

	events := make([]report.Event, 0)

	raw, newEvents, err := plan.inputReader.Read(ctx, cfg)
	if err != nil {
		return err
	}
	events = append(events, newEvents...)

	state := PreprocessState{
		State: StateRaw,
		Raw:   raw,
	}
	for _, module := range plan.preprocessors {
		state, newEvents, err = module.Process(ctx, state, cfg)
		if err != nil {
			return err
		}
		events = append(events, newEvents...)
	}
	if state.State != StateCanonical {
		return fmt.Errorf("preprocessing ended in state %q; expected %q", state.State, StateCanonical)
	}

	merged, newEvents, err := plan.merger.Merge(ctx, state.Canonical, cfg)
	if err != nil {
		return err
	}
	events = append(events, newEvents...)

	for _, module := range plan.postprocessors {
		merged, newEvents, err = module.Process(ctx, merged, cfg)
		if err != nil {
			return err
		}
		events = append(events, newEvents...)
	}

	final := finalizeTranscript(cfg, merged)
	rpt := finalizeReport(cfg, events)

	for _, module := range plan.outputWriters {
		newEvents, err = module.Write(ctx, final, rpt, cfg)
		if err != nil {
			return err
		}
		events = append(events, newEvents...)
	}

	rpt = finalizeReport(cfg, events)
	if cfg.ReportFile != "" {
		if err := report.WriteJSON(cfg.ReportFile, rpt); err != nil {
			return err
		}
	}

	return nil
}

type executionPlan struct {
	inputReader    InputReader
	preprocessors  []Preprocessor
	merger         Merger
	postprocessors []Postprocessor
	outputWriters  []OutputWriter
}

func resolvePlan(cfg config.Config, registry *Registry) (executionPlan, error) {
	inputReader, err := registry.resolveInputReader(cfg.InputReader)
	if err != nil {
		return executionPlan{}, err
	}

	preprocessors, err := registry.resolvePreprocessors(cfg.PreprocessingModules)
	if err != nil {
		return executionPlan{}, err
	}
	if err := validatePreprocessors(preprocessors); err != nil {
		return executionPlan{}, err
	}

	merger, err := registry.resolveMerger()
	if err != nil {
		return executionPlan{}, err
	}

	postprocessors, err := registry.resolvePostprocessors(cfg.PostprocessingModules)
	if err != nil {
		return executionPlan{}, err
	}

	outputWriters, err := registry.resolveOutputWriters(cfg.OutputModules)
	if err != nil {
		return executionPlan{}, err
	}

	return executionPlan{
		inputReader:    inputReader,
		preprocessors:  preprocessors,
		merger:         merger,
		postprocessors: postprocessors,
		outputWriters:  outputWriters,
	}, nil
}

func validatePreprocessors(modules []Preprocessor) error {
	state := StateRaw
	for _, module := range modules {
		if module.Requires() != state {
			return fmt.Errorf("preprocessing module %q requires state %q but current state is %q", module.Name(), module.Requires(), state)
		}
		state = module.Produces()
	}
	if state != StateCanonical {
		return fmt.Errorf("preprocessing chain ends in state %q; expected %q", state, StateCanonical)
	}
	return nil
}

func finalizeTranscript(cfg config.Config, merged model.MergedTranscript) schema.Transcript {
	return artifact.FromMerged(cfg, merged)
}

func finalizeReport(cfg config.Config, events []report.Event) report.Report {
	return report.Report{
		Metadata: report.Metadata{
			Application:           applicationName,
			Version:               buildinfo.Version,
			InputReader:           cfg.InputReader,
			InputFiles:            append([]string(nil), cfg.InputFiles...),
			PreprocessingModules:  append([]string(nil), cfg.PreprocessingModules...),
			PostprocessingModules: append([]string(nil), cfg.PostprocessingModules...),
			OutputModules:         append([]string(nil), cfg.OutputModules...),
		},
		Events: append([]report.Event(nil), events...),
	}
}