package issue

import (
	"context"
	_ "embed"
	"encoding/json"
	"fmt"
	"strings"

	"superwork-tui/internal/gitea"
)

//go:generate cp ../../../vscode/schemas/state-json.schema.json state-json.schema.json

// stateSchema is a copy of the [state schema](vscode/schemas/state-json.schema.json)
// shared with the VS Code extension and the spx CLI; `go generate` refreshes it.
//
//go:embed state-json.schema.json
var stateSchema []byte

// knownStateFields holds the schema's top-level properties; a comment counts as
// state only when its object carries one of them, so ordinary JSON comments
// cannot pass as state.
var knownStateFields = schemaProperties(stateSchema)

const (
	// stateCommentOpen and stateCommentClose wrap the state JSON in an HTML
	// comment, so trackers that render Markdown hide it from the thread.
	stateCommentOpen  = "<!-- spx-state"
	stateCommentClose = "-->"
	// legacyStateMarker prefixes state comments written by the YouTrack integration.
	legacyStateMarker = "<!--spx-state-->"
)

// schemaProperties returns the property names a JSON schema declares at its
// top level; it panics on a malformed schema because the schema is embedded at
// build time.
func schemaProperties(schema []byte) map[string]bool {
	var doc struct {
		Properties map[string]json.RawMessage `json:"properties"`
	}
	if err := json.Unmarshal(schema, &doc); err != nil {
		panic(fmt.Sprintf("parse embedded state schema: %v", err))
	}
	if len(doc.Properties) == 0 {
		panic("embedded state schema declares no properties")
	}
	fields := make(map[string]bool, len(doc.Properties))
	for name := range doc.Properties {
		fields[name] = true
	}
	return fields
}

// ExtractStateJSON returns the state of the newest comment that
// [ParseStateComment] accepts, scanning tail-first so ordinary comments posted
// afterwards cannot shadow it. Returns an empty map when nothing matches.
//
// Exported so tests can call it without a network client.
func ExtractStateJSON(comments []gitea.Comment) map[string]any {
	for i := len(comments) - 1; i >= 0; i-- {
		if obj, ok := ParseStateComment(comments[i].Body); ok {
			return obj
		}
	}
	return map[string]any{}
}

// ParseStateComment returns the state object carried by a comment body, or
// false when the body is not a state comment.
//
// Three forms are accepted: the hidden `<!-- spx-state` … `-->` comment written
// by [FormatStateComment], the YouTrack `<!--spx-state-->` prefix, and a bare
// JSON object left by older writers. The JSON must be an object carrying at
// least one schema field, so review notes and other JSON comments are rejected.
func ParseStateComment(body string) (map[string]any, bool) {
	text := strings.TrimSpace(body)
	switch {
	case strings.HasPrefix(text, stateCommentOpen) && strings.HasSuffix(text, stateCommentClose):
		text = strings.TrimSuffix(strings.TrimPrefix(text, stateCommentOpen), stateCommentClose)
	case strings.HasPrefix(text, legacyStateMarker):
		text = strings.TrimPrefix(text, legacyStateMarker)
	}
	var obj map[string]any
	if err := json.Unmarshal([]byte(strings.TrimSpace(text)), &obj); err != nil || obj == nil {
		return nil, false
	}
	for k := range obj {
		if knownStateFields[k] {
			return obj, true
		}
	}
	return nil, false
}

// FormatStateComment renders `state` as a hidden state comment: compact JSON
// between `<!-- spx-state` and `-->`. [json.Marshal] escapes `<`, `>` and `&`,
// so a value containing `-->` cannot close the comment early.
func FormatStateComment(state map[string]any) (string, error) {
	b, err := json.Marshal(state)
	if err != nil {
		return "", fmt.Errorf("marshal state JSON: %w", err)
	}
	return stateCommentOpen + "\n" + string(b) + "\n" + stateCommentClose, nil
}

// stateCommenter is the subset of gitea.Client used by state-JSON operations.
type stateCommenter interface {
	ListIssueComments(ctx context.Context, owner, repo string, number int) ([]gitea.Comment, error)
	PostIssueComment(ctx context.Context, owner, repo string, number int, body string) (*gitea.Comment, error)
}

// ReadStateJSON fetches issue comments and extracts the latest state blob.
func ReadStateJSON(ctx context.Context, client stateCommenter, owner, repo string, number int) (map[string]any, error) {
	comments, err := client.ListIssueComments(ctx, owner, repo, number)
	if err != nil {
		return nil, fmt.Errorf("list comments for issue %d: %w", number, err)
	}
	return ExtractStateJSON(comments), nil
}

// MergeStateJSON reads the current state blob, merges extra on top, and posts
// a new comment containing the merged JSON.
func MergeStateJSON(ctx context.Context, client stateCommenter, owner, repo string, number int, extra map[string]any) error {
	current, err := ReadStateJSON(ctx, client, owner, repo, number)
	if err != nil {
		return err
	}
	return postMerged(ctx, client, owner, repo, number, current, extra)
}

// MergeStateJSONGuarded is like MergeStateJSON but protects done-column issues
// from having their column overwritten by a stale automated update. When the
// protection strips the only incoming field, no comment is posted.
func MergeStateJSONGuarded(
	ctx context.Context,
	client stateCommenter,
	owner, repo string,
	number int,
	extra map[string]any,
	protectDoneColumn bool,
) (posted bool, protectedDoneColumn bool, err error) {
	current, err := ReadStateJSON(ctx, client, owner, repo, number)
	if err != nil {
		return false, false, err
	}

	merged := make(map[string]any, len(extra))
	for k, v := range extra {
		merged[k] = v
	}

	if protectDoneColumn {
		if col, ok := current["column"]; ok && col == "done" {
			if incomingCol, has := merged["column"]; has && incomingCol != "done" {
				delete(merged, "column")
				protectedDoneColumn = true
			}
		}
	}

	if len(merged) == 0 {
		return false, protectedDoneColumn, nil
	}

	if err := postMerged(ctx, client, owner, repo, number, current, merged); err != nil {
		return false, protectedDoneColumn, err
	}
	return true, protectedDoneColumn, nil
}

// postMerged merges `extra` over `current` and posts the result as a new
// state comment.
func postMerged(ctx context.Context, client stateCommenter, owner, repo string, number int, current, extra map[string]any) error {
	result := make(map[string]any, len(current)+len(extra))
	for k, v := range current {
		result[k] = v
	}
	for k, v := range extra {
		result[k] = v
	}
	body, err := FormatStateComment(result)
	if err != nil {
		return err
	}
	if _, err := client.PostIssueComment(ctx, owner, repo, number, body); err != nil {
		return fmt.Errorf("post state comment on issue %d: %w", number, err)
	}
	return nil
}