package workspace

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"path/filepath"
	"sort"
	"strings"

	"gitea.maximumdirect.net/eric/notarius/internal/core/artifacts"
	"gitea.maximumdirect.net/eric/notarius/internal/framework/pipeline"
)

const digestPrefixLength = 16

type Fingerprint struct {
	Name  string `json:"name"`
	Value string `json:"value"`
}

type CheckpointIdentityInput struct {
	Pipeline               pipeline.ResolvedPipeline
	InputKey               string
	RawInputDigest         string
	SourceDigest           string
	SelectedLanes          []string
	RuntimeOverrides       []Fingerprint
	References             []artifacts.ReferenceProvenance
	ProvenanceFingerprints []Fingerprint
}

type CheckpointIdentity struct {
	Digest                 string        `json:"digest"`
	PipelineID             string        `json:"pipeline_id"`
	PipelineDigest         string        `json:"pipeline_digest"`
	InputKey               string        `json:"input_key"`
	RawInputDigest         string        `json:"raw_input_digest,omitempty"`
	SourceDigest           string        `json:"source_digest,omitempty"`
	SelectedLanes          []string      `json:"selected_lanes,omitempty"`
	RuntimeOverrides       []Fingerprint `json:"runtime_overrides,omitempty"`
	ReferenceDigests       []Fingerprint `json:"reference_digests,omitempty"`
	ProvenanceFingerprints []Fingerprint `json:"provenance_fingerprints,omitempty"`
}

func NewCheckpointIdentity(input CheckpointIdentityInput) (CheckpointIdentity, error) {
	pipelineID := strings.TrimSpace(input.Pipeline.ID)
	if pipelineID == "" {
		return CheckpointIdentity{}, fmt.Errorf("checkpoint identity pipeline id must not be empty")
	}
	pipelineDigest := strings.TrimSpace(input.Pipeline.Digest)
	if pipelineDigest == "" {
		return CheckpointIdentity{}, fmt.Errorf("checkpoint identity pipeline digest must not be empty")
	}
	inputKey := strings.TrimSpace(input.InputKey)
	if inputKey == "" {
		inputKey = strings.TrimSpace(input.Pipeline.Input.Module)
	}
	if inputKey == "" {
		return CheckpointIdentity{}, fmt.Errorf("checkpoint identity input key must not be empty")
	}

	rawInputDigest := strings.TrimSpace(input.RawInputDigest)
	sourceDigest := strings.TrimSpace(input.SourceDigest)
	if rawInputDigest == "" && sourceDigest == "" {
		return CheckpointIdentity{}, fmt.Errorf("checkpoint identity raw input digest or source digest must be set")
	}

	identity := CheckpointIdentity{
		PipelineID:             pipelineID,
		PipelineDigest:         pipelineDigest,
		InputKey:               inputKey,
		RawInputDigest:         rawInputDigest,
		SourceDigest:           sourceDigest,
		SelectedLanes:          normalizedLanes(input.SelectedLanes, input.Pipeline.ArtifactLanes),
		RuntimeOverrides:       normalizeFingerprints(input.RuntimeOverrides),
		ReferenceDigests:       referenceFingerprints(input.References),
		ProvenanceFingerprints: normalizeFingerprints(input.ProvenanceFingerprints),
	}
	digest, err := identityDigest(identity)
	if err != nil {
		return CheckpointIdentity{}, err
	}
	identity.Digest = digest
	return identity, nil
}

func (s Settings) CheckpointDirectory(identity CheckpointIdentity) (string, error) {
	if !s.ResumeEnabled || strings.TrimSpace(s.CheckpointsRoot) == "" {
		return "", nil
	}
	relative, err := identity.RelativePath()
	if err != nil {
		return "", err
	}
	return SafePath(s.CheckpointsRoot, relative)
}

func (i CheckpointIdentity) RelativePath() (string, error) {
	pipelineID, err := safePathComponent(i.PipelineID)
	if err != nil {
		return "", fmt.Errorf("checkpoint identity pipeline id: %w", err)
	}
	inputKey, err := safePathComponent(i.InputKey)
	if err != nil {
		return "", fmt.Errorf("checkpoint identity input key: %w", err)
	}
	sourceDigest := digestPrefix(i.SourceDigest)
	if sourceDigest == "" {
		sourceDigest = digestPrefix(i.RawInputDigest)
	}
	if sourceDigest == "" {
		return "", fmt.Errorf("checkpoint identity source digest prefix must not be empty")
	}
	pipelineDigest := digestPrefix(i.PipelineDigest)
	if pipelineDigest == "" {
		return "", fmt.Errorf("checkpoint identity pipeline digest prefix must not be empty")
	}
	sourceComponent, err := safePathComponent(sourceDigest)
	if err != nil {
		return "", fmt.Errorf("checkpoint identity source digest: %w", err)
	}
	pipelineComponent, err := safePathComponent(pipelineDigest)
	if err != nil {
		return "", fmt.Errorf("checkpoint identity pipeline digest: %w", err)
	}
	identityDigest := digestPrefix(i.Digest)
	if identityDigest == "" {
		return "", fmt.Errorf("checkpoint identity digest prefix must not be empty")
	}
	identityComponent, err := safePathComponent(identityDigest)
	if err != nil {
		return "", fmt.Errorf("checkpoint identity digest: %w", err)
	}
	return filepath.ToSlash(filepath.Join(pipelineID, inputKey+"-"+sourceComponent, pipelineComponent, identityComponent)), nil
}

func identityDigest(identity CheckpointIdentity) (string, error) {
	payload := identity
	payload.Digest = ""
	data, err := json.Marshal(payload)
	if err != nil {
		return "", fmt.Errorf("marshal checkpoint identity: %w", err)
	}
	sum := sha256.Sum256(data)
	return "sha256:" + hex.EncodeToString(sum[:]), nil
}

func normalizedLanes(selected []string, resolved []pipeline.ResolvedArtifactLane) []string {
	if len(selected) > 0 {
		return normalizeStrings(selected)
	}
	lanes := make([]string, 0, len(resolved))
	for _, lane := range resolved {
		lanes = append(lanes, lane.ID)
	}
	return normalizeStrings(lanes)
}

func normalizeFingerprints(values []Fingerprint) []Fingerprint {
	if len(values) == 0 {
		return nil
	}
	byName := make(map[string]string, len(values))
	for _, value := range values {
		name := strings.TrimSpace(value.Name)
		fingerprint := strings.TrimSpace(value.Value)
		if name == "" || fingerprint == "" {
			continue
		}
		byName[name] = fingerprint
	}
	if len(byName) == 0 {
		return nil
	}
	names := make([]string, 0, len(byName))
	for name := range byName {
		names = append(names, name)
	}
	sort.Strings(names)
	out := make([]Fingerprint, 0, len(names))
	for _, name := range names {
		out = append(out, Fingerprint{Name: name, Value: byName[name]})
	}
	return out
}

func referenceFingerprints(references []artifacts.ReferenceProvenance) []Fingerprint {
	if len(references) == 0 {
		return nil
	}
	values := make([]Fingerprint, 0, len(references))
	for _, reference := range references {
		digest := strings.TrimSpace(reference.Digest)
		if digest == "" {
			continue
		}
		parts := []string{
			strings.TrimSpace(reference.Stage),
			strings.TrimSpace(reference.LaneID),
			strings.TrimSpace(reference.SlotName),
			strings.TrimSpace(reference.OriginURI),
		}
		values = append(values, Fingerprint{
			Name:  strings.Join(parts, ":"),
			Value: digest,
		})
	}
	return normalizeFingerprints(values)
}

func normalizeStrings(values []string) []string {
	if len(values) == 0 {
		return nil
	}
	seen := make(map[string]struct{}, len(values))
	for _, value := range values {
		value = strings.TrimSpace(value)
		if value == "" {
			continue
		}
		seen[value] = struct{}{}
	}
	if len(seen) == 0 {
		return nil
	}
	out := make([]string, 0, len(seen))
	for value := range seen {
		out = append(out, value)
	}
	sort.Strings(out)
	return out
}

func digestPrefix(digest string) string {
	digest = strings.TrimSpace(digest)
	if digest == "" {
		return ""
	}
	if idx := strings.Index(digest, ":"); idx >= 0 {
		digest = digest[idx+1:]
	}
	digest = strings.TrimSpace(digest)
	if len(digest) > digestPrefixLength {
		return digest[:digestPrefixLength]
	}
	return digest
}

func safePathComponent(value string) (string, error) {
	value = strings.TrimSpace(value)
	if value == "" {
		return "", fmt.Errorf("must not be empty")
	}
	var b strings.Builder
	for _, r := range value {
		switch {
		case r >= 'a' && r <= 'z':
			b.WriteRune(r)
		case r >= 'A' && r <= 'Z':
			b.WriteRune(r)
		case r >= '0' && r <= '9':
			b.WriteRune(r)
		case r == '-' || r == '_' || r == '.':
			b.WriteRune(r)
		default:
			b.WriteString(fmt.Sprintf("~%x", r))
		}
	}
	encoded := b.String()
	if encoded == "." || encoded == ".." || strings.Contains(encoded, "..") || strings.ContainsAny(encoded, `/\`) {
		return "", fmt.Errorf("%q is not filesystem safe", value)
	}
	return encoded, nil
}