package app

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"io"
	"sort"
	"strings"

	"gitea.maximumdirect.net/eric/narratio/internal/config"
)

type configDiffFlags struct {
	pipelinePath     singletonStringFlag
	campaignPath     singletonStringFlag
	campaignFilePath singletonStringFlag
}

type configDiffRequest struct {
	leftProfile  string
	rightProfile string
	flags        configDiffFlags
}

type configDiffResolved struct {
	left  *inspectionConfig
	right *inspectionConfig
}

type configDiffRecord struct {
	Kind  string
	Path  string
	Left  string
	Right string
}

// ConfigDiff compares two explicitly selected profiles through the same
// read-only configuration resolution boundary used by config validate, show,
// and sources. Differences describe normalized effective values rather than
// the layout of root, import, or overlay files.
func ConfigDiff(_ context.Context, args []string, out io.Writer) error {
	request, err := parseConfigDiffRequest(args, out)
	if err != nil {
		if errors.Is(err, flag.ErrHelp) {
			return nil
		}
		return err
	}
	resolved, err := resolveConfigDiff(request)
	if err != nil {
		return fmt.Errorf("config diff: %w", err)
	}
	leftValues, err := config.EffectivePipelineValues(resolved.left.Pipeline)
	if err != nil {
		return fmt.Errorf("config diff: project left effective configuration: %w", err)
	}
	rightValues, err := config.EffectivePipelineValues(resolved.right.Pipeline)
	if err != nil {
		return fmt.Errorf("config diff: project right effective configuration: %w", err)
	}
	records, err := diffEffectivePipelineValues(leftValues, rightValues)
	if err != nil {
		return fmt.Errorf("config diff: %w", err)
	}
	leftDigest := config.EffectivePipelineDigest(resolved.left.Pipeline)
	rightDigest := config.EffectivePipelineDigest(resolved.right.Pipeline)
	if len(records) == 0 {
		if leftDigest != rightDigest {
			return fmt.Errorf("internal error: effective pipeline digests differ without a semantic difference")
		}
		_, err := fmt.Fprintln(out, "no differences")
		return err
	}
	for _, record := range records {
		switch record.Kind {
		case "added":
			if _, err := fmt.Fprintf(out, "added\t%s\t%s\n", record.Path, record.Right); err != nil {
				return err
			}
		case "removed":
			if _, err := fmt.Fprintf(out, "removed\t%s\t%s\n", record.Path, record.Left); err != nil {
				return err
			}
		case "changed":
			if _, err := fmt.Fprintf(out, "changed\t%s\t%s\t%s\n", record.Path, record.Left, record.Right); err != nil {
				return err
			}
		default:
			return fmt.Errorf("internal error: unsupported difference kind %q", record.Kind)
		}
	}
	return nil
}

func parseConfigDiffRequest(args []string, out io.Writer) (configDiffRequest, error) {
	profiles, flagArgs := splitConfigDiffArguments(args)
	fs := flag.NewFlagSet("config diff", flag.ContinueOnError)
	fs.SetOutput(out)
	var request configDiffRequest
	request.flags.pipelinePath.name = "config"
	request.flags.campaignPath.name = "campaign"
	request.flags.campaignFilePath.name = "campaign-file"
	fs.Var(&request.flags.pipelinePath, "config", "path to pipeline.yml (optional; defaults searched)")
	fs.Var(&request.flags.campaignPath, "campaign", "campaign ID")
	fs.Var(&request.flags.campaignFilePath, "campaign-file", "path to campaign.yml")
	fs.Usage = func() {
		fmt.Fprintln(out, "Usage: narratio config diff <left-profile> <right-profile> [--config <pipeline.yml>] [--campaign <id> | --campaign-file <campaign.yml>]")
		fmt.Fprintln(out)
		fmt.Fprintln(out, "Compares fully resolved profiles without a session, workspace, manifest, adapters, or external services.")
		fmt.Fprintln(out)
		fmt.Fprintln(out, "Flags:")
		fs.PrintDefaults()
	}
	if err := fs.Parse(flagArgs); err != nil {
		return configDiffRequest{}, fmt.Errorf("config diff: invalid flags: %w", err)
	}
	profiles = append(profiles, fs.Args()...)
	if len(profiles) != 2 || strings.TrimSpace(profiles[0]) == "" || strings.TrimSpace(profiles[1]) == "" {
		return configDiffRequest{}, fmt.Errorf("config diff: exactly two non-empty profile names are required")
	}
	if request.flags.campaignPath.set && request.flags.campaignFilePath.set {
		return configDiffRequest{}, fmt.Errorf("config diff: --campaign and --campaign-file are mutually exclusive")
	}
	request.leftProfile = profiles[0]
	request.rightProfile = profiles[1]
	return request, nil
}

// splitConfigDiffArguments accepts the documented positional-first syntax and
// also permits flags before or between profile names. Values belonging to the
// supported string flags stay with their flag so they are not mistaken for
// profile names.
func splitConfigDiffArguments(args []string) (profiles, flagArgs []string) {
	for index := 0; index < len(args); index++ {
		argument := args[index]
		if !strings.HasPrefix(argument, "-") || argument == "-" {
			profiles = append(profiles, argument)
			continue
		}
		flagArgs = append(flagArgs, argument)
		name, hasValue := strings.CutPrefix(argument, "--")
		if !hasValue {
			continue
		}
		name, _, hasInlineValue := strings.Cut(name, "=")
		if hasInlineValue || !configDiffStringFlag(name) || index+1 >= len(args) {
			continue
		}
		index++
		flagArgs = append(flagArgs, args[index])
	}
	return profiles, flagArgs
}

func configDiffStringFlag(name string) bool {
	switch name {
	case "config", "campaign", "campaign-file", "profile":
		return true
	default:
		return false
	}
}

func resolveConfigDiff(request configDiffRequest) (*configDiffResolved, error) {
	pipelinePath, err := resolvePipelineConfigPath(request.flags.pipelinePath.value)
	if err != nil {
		return nil, err
	}
	leftPipeline, rightPipeline, err := config.LoadPipelineProfilePair(pipelinePath, request.leftProfile, request.rightProfile)
	if err != nil {
		return nil, err
	}
	needsCampaign := pipelineHasArtifactFamilies(leftPipeline) || pipelineHasArtifactFamilies(rightPipeline)
	hasCampaignSelection := request.flags.campaignPath.set || request.flags.campaignFilePath.set
	if !needsCampaign && !hasCampaignSelection {
		if err := validateInspectionPipeline(pipelinePath, leftPipeline); err != nil {
			return nil, err
		}
		if err := validateInspectionPipeline(pipelinePath, rightPipeline); err != nil {
			return nil, err
		}
		return &configDiffResolved{
			left:  &inspectionConfig{PipelinePath: pipelinePath, Pipeline: leftPipeline},
			right: &inspectionConfig{PipelinePath: pipelinePath, Pipeline: rightPipeline},
		}, nil
	}

	campaignPath, err := resolveSharedDiffCampaignPath(leftPipeline, rightPipeline, request.flags)
	if err != nil {
		if needsCampaign {
			return nil, fmt.Errorf("pipeline.scriptorium.artifact_families requires one shared campaign: %w", err)
		}
		return nil, err
	}
	campaign, err := config.LoadCampaign(campaignPath)
	if err != nil {
		return nil, err
	}
	if request.flags.campaignPath.set && !request.flags.campaignFilePath.set {
		if got := config.CampaignID(campaign); got != request.flags.campaignPath.value {
			return nil, fmt.Errorf("campaign config %q invalid: campaign_id %q does not match selected campaign %q", campaignPath, got, request.flags.campaignPath.value)
		}
	}
	leftLoaded, err := config.LoadPipelineCampaign(pipelinePath, leftPipeline, campaignPath, campaign)
	if err != nil {
		return nil, err
	}
	rightLoaded, err := config.LoadPipelineCampaignWithParty(pipelinePath, rightPipeline, campaignPath, campaign, leftLoaded.Party)
	if err != nil {
		return nil, err
	}
	if err := validateInspectionPipeline(leftLoaded.PipelinePath, leftLoaded.Pipeline); err != nil {
		return nil, err
	}
	if err := validateInspectionPipeline(rightLoaded.PipelinePath, rightLoaded.Pipeline); err != nil {
		return nil, err
	}
	if err := validateInspectionCampaign(campaignPath, campaign); err != nil {
		return nil, err
	}
	return &configDiffResolved{
		left: &inspectionConfig{
			PipelinePath: leftLoaded.PipelinePath,
			Pipeline:     leftLoaded.Pipeline,
			CampaignPath: leftLoaded.CampaignPath,
			Campaign:     campaign,
			Party:        leftLoaded.Party,
		},
		right: &inspectionConfig{
			PipelinePath: rightLoaded.PipelinePath,
			Pipeline:     rightLoaded.Pipeline,
			CampaignPath: rightLoaded.CampaignPath,
			Campaign:     campaign,
			Party:        rightLoaded.Party,
		},
	}, nil
}

func resolveSharedDiffCampaignPath(left, right *config.PipelineConfig, flags configDiffFlags) (string, error) {
	leftPath, leftErr := resolveCampaignConfigPath(left, flags.campaignPath.value, flags.campaignFilePath.value)
	if leftErr != nil {
		return "", leftErr
	}
	rightPath, rightErr := resolveCampaignConfigPath(right, flags.campaignPath.value, flags.campaignFilePath.value)
	if rightErr != nil {
		return "", rightErr
	}
	if leftPath != rightPath {
		return "", fmt.Errorf("profile selections resolve different campaign files; specify --campaign-file to compare one campaign")
	}
	return leftPath, nil
}

func diffEffectivePipelineValues(left, right []config.EffectivePipelineValueRecord) ([]configDiffRecord, error) {
	leftByPath, err := effectivePipelineValueMap("left", left)
	if err != nil {
		return nil, err
	}
	rightByPath, err := effectivePipelineValueMap("right", right)
	if err != nil {
		return nil, err
	}
	paths := make([]string, 0, len(leftByPath)+len(rightByPath))
	seen := make(map[string]struct{}, len(leftByPath)+len(rightByPath))
	for path := range leftByPath {
		seen[path] = struct{}{}
		paths = append(paths, path)
	}
	for path := range rightByPath {
		if _, exists := seen[path]; !exists {
			paths = append(paths, path)
		}
	}
	sort.Strings(paths)
	records := make([]configDiffRecord, 0)
	for _, path := range paths {
		leftValue, leftExists := leftByPath[path]
		rightValue, rightExists := rightByPath[path]
		switch {
		case !leftExists:
			records = append(records, configDiffRecord{Kind: "added", Path: path, Right: rightValue})
		case !rightExists:
			records = append(records, configDiffRecord{Kind: "removed", Path: path, Left: leftValue})
		case leftValue != rightValue:
			records = append(records, configDiffRecord{Kind: "changed", Path: path, Left: leftValue, Right: rightValue})
		}
	}
	return records, nil
}

func effectivePipelineValueMap(side string, records []config.EffectivePipelineValueRecord) (map[string]string, error) {
	values := make(map[string]string, len(records))
	for _, record := range records {
		if _, exists := values[record.Path]; exists {
			return nil, fmt.Errorf("internal error: %s effective configuration has duplicate path %q", side, record.Path)
		}
		values[record.Path] = record.Value
	}
	return values, nil
}