package ckconfig

import (
	"bytes"
	"errors"
	"fmt"
	"io"

	configkit "gitea.maximumdirect.net/eric/ConfigKit"
)

func newConfigExplainCommand[C any](prepared *preparedConfigSuite[C]) (Command, error) {
	flags := configInputFlags(prepared.suite, "text")
	flags = append(flags, ValueFlag[configInput[C]](FlagMeta{
		Name:     "path",
		Usage:    "Configuration path as a JSON Pointer; an empty value selects the root.",
		Required: true,
	}, nil, parseString, func(input *configInput[C], value Supplied[string]) {
		input.Path = value
	}))
	spec := CommandSpec[configInput[C]]{
		Name:    string(ConfigExplain),
		Summary: "Explain the effective and historical value at a configuration path.",
		Flags:   flags,
		CheckInput: func(input configInput[C]) error {
			if _, err := preflightConfig(prepared, input, ConfigExplain); err != nil {
				return err
			}
			if !input.Path.Set {
				return fmt.Errorf("--path is required")
			}
			if _, err := configkit.ParsePath(input.Path.Value); err != nil {
				return fmt.Errorf("invalid configuration path %q: %w", input.Path.Value, err)
			}
			return nil
		},
		Run: func(invocation Invocation, input configInput[C]) Outcome {
			return runConfigExplanation(invocation, prepared, input)
		},
	}
	return NewCommand(spec)
}

type explanationReport struct {
	Scope           string                 `yaml:"scope"`
	Path            string                 `yaml:"path"`
	Effective       snapshotDTO            `yaml:"effective"`
	Origin          explanationOriginDTO   `yaml:"origin"`
	History         []explanationChangeDTO `yaml:"history"`
	SecretReference *secretReferenceDTO    `yaml:"secret_reference"`
}

type snapshotDTO struct {
	Present  bool   `yaml:"present"`
	Redacted bool   `yaml:"redacted"`
	YAML     string `yaml:"yaml"`
}

type explanationOriginDTO struct {
	Layer       string               `yaml:"layer"`
	Locations   []locationDTO        `yaml:"locations"`
	Operation   string               `yaml:"operation"`
	Inheritance []inheritanceStepDTO `yaml:"inheritance"`
}

type inheritanceStepDTO struct {
	From      string        `yaml:"from"`
	To        string        `yaml:"to"`
	Reference string        `yaml:"reference"`
	Locations []locationDTO `yaml:"locations"`
}

type explanationChangeDTO struct {
	Before       snapshotDTO          `yaml:"before"`
	After        snapshotDTO          `yaml:"after"`
	Origin       explanationOriginDTO `yaml:"origin"`
	Reasons      []string             `yaml:"reasons"`
	Dependencies []string             `yaml:"dependencies"`
}

type secretReferenceDTO struct {
	Name string `yaml:"name"`
}

func runConfigExplanation[C any](invocation Invocation, prepared *preparedConfigSuite[C], input configInput[C]) Outcome {
	if err := invocation.Context.Err(); err != nil {
		return Failure(err)
	}
	scopeNames, err := selectConfigScopes(prepared, input, ConfigExplain)
	if err != nil {
		return Failure(err)
	}
	if !input.Path.Set {
		return Failure(fmt.Errorf("--path is required"))
	}
	path, err := configkit.ParsePath(input.Path.Value)
	if err != nil {
		return Usage(fmt.Errorf("invalid configuration path %q: %w", input.Path.Value, err))
	}
	name := scopeNames[0]
	contexts := contextsForScopes(prepared, input, scopeNames)
	scope, ok := findConfigScope(prepared, name)
	if !ok || scope.Acquire == nil {
		return Failure(fmt.Errorf("configuration scope %q has no acquisition callback", name))
	}
	if err := invocation.Context.Err(); err != nil {
		return explanationFailure(err, nil, false)
	}
	acquired, acquireErr := scope.Acquire(invocation.Context, ConfigRequest{Operation: ConfigExplain, Selection: input.Selection}, contexts[name])
	diagnostics := append([]Diagnostic(nil), acquired.Diagnostics...)
	if acquireErr != nil {
		return explanationFailure(acquireErr, diagnostics, false)
	}
	if err := invocation.Context.Err(); err != nil {
		return explanationFailure(err, diagnostics, false)
	}

	if acquired.Value.Explanation == nil {
		return explanationFailure(fmt.Errorf("configuration scope %q did not provide an explanation reader", name), diagnostics, false)
	}
	explanation, found := acquired.Value.Explanation.Explain(path)
	if !found {
		return explanationFailure(fmt.Errorf("configuration path %q is not known in scope %q", path.String(), name), diagnostics, false)
	}
	if err := invocation.Context.Err(); err != nil {
		return explanationFailure(err, diagnostics, false)
	}
	if input.Format != "yaml" {
		return writeNativeExplanation(invocation.Streams.Out, acquired.Value.Explanation, path, diagnostics)
	}
	var report bytes.Buffer
	if err := encodeYAML(&report, makeExplanationReport(name, explanation)); err != nil {
		return explanationFailure(err, diagnostics, false)
	}
	if err := invocation.Context.Err(); err != nil {
		return explanationFailure(err, diagnostics, false)
	}
	if err := writeReport(invocation.Streams.Out, report.Bytes()); err != nil {
		outcome := explanationFailure(err, diagnostics, true)
		outcome.DeliveryError = err
		return outcome
	}
	outcome := Success()
	outcome.Diagnostics = diagnostics
	return outcome
}

func writeNativeExplanation(writer io.Writer, reader ExplanationReader, path configkit.Path, diagnostics []Diagnostic) Outcome {
	checked := &checkedWriter{writer: writer}
	renderErr := reader.WriteExplanation(checked, path)
	if checked.failure != nil {
		if renderErr == nil {
			renderErr = checked.failure
		} else {
			renderErr = errors.Join(renderErr, checked.failure)
		}
	}
	if renderErr != nil {
		outcome := explanationFailure(renderErr, diagnostics, true)
		outcome.DeliveryError = checked.failure
		return outcome
	}
	outcome := Success()
	outcome.Diagnostics = diagnostics
	return outcome
}

func makeExplanationReport(scope string, explanation configkit.Explanation) explanationReport {
	report := explanationReport{
		Scope:     scope,
		Path:      explanation.Path.String(),
		Effective: snapshotReport(explanation.Effective),
		Origin:    originReport(explanation.Origin),
		History:   make([]explanationChangeDTO, 0, len(explanation.History)),
	}
	for _, change := range explanation.History {
		entry := explanationChangeDTO{
			Before:       snapshotReport(change.Before),
			After:        snapshotReport(change.After),
			Origin:       originReport(change.Origin),
			Reasons:      append([]string{}, change.Reasons...),
			Dependencies: make([]string, 0, len(change.Dependencies)),
		}
		for _, dependency := range change.Dependencies {
			entry.Dependencies = append(entry.Dependencies, dependency.String())
		}
		report.History = append(report.History, entry)
	}
	if explanation.SecretReference != nil {
		report.SecretReference = &secretReferenceDTO{Name: explanation.SecretReference.Name}
	}
	return report
}

func snapshotReport(snapshot configkit.ValueSnapshot) snapshotDTO {
	return snapshotDTO{Present: snapshot.Present, Redacted: snapshot.Redacted, YAML: snapshot.YAML}
}

func originReport(origin configkit.Origin) explanationOriginDTO {
	report := explanationOriginDTO{
		Layer:       string(origin.Layer),
		Locations:   locationReports(origin.Locations),
		Operation:   string(origin.Operation),
		Inheritance: make([]inheritanceStepDTO, 0, len(origin.Inheritance)),
	}
	for _, step := range origin.Inheritance {
		report.Inheritance = append(report.Inheritance, inheritanceStepDTO{
			From:      step.From.String(),
			To:        step.To.String(),
			Reference: step.Reference.String(),
			Locations: locationReports(step.Locations),
		})
	}
	return report
}

func locationReports(locations []configkit.Location) []locationDTO {
	report := make([]locationDTO, 0, len(locations))
	for _, location := range locations {
		report = append(report, locationDTO{SourceID: location.SourceID, Line: location.Line, Column: location.Column})
	}
	return report
}

func explanationFailure(cause error, diagnostics []Diagnostic, reportStarted bool) Outcome {
	outcome := Failure(cause)
	outcome.Diagnostics = diagnostics
	outcome.ReportIncomplete = reportStarted
	return outcome
}