// Package kbclient is a typed HTTP client for the HarborForge.Backend
// knowledge-base REST API. Used by the dynamic-kb-* tools to power
// agent browse + cache flows.
//
// Route shapes verified against
// HarborForge.Backend/app/api/routers/knowledge.py:
//
//	GET /knowledge-bases[?project=<code>]               list KBs
//	GET /knowledge-bases/{kb_id_or_code}/topics          list topics in a KB
//	GET /knowledge-bases/{kb_id_or_code}/tree            full hierarchy
//	GET /knowledge-facts/{fact_id}                       single fact
//
// HF's KB hierarchy is KB → Topics → Categories → Facts. ListFacts
// uses the /tree endpoint and filters client-side to the requested
// topic ids (the backend has no flat per-topic-facts route as of
// the route audit on 2026-06-08).
//
// Auth: v1 uses plugin-level APIKey via Bearer header. Per-agent
// token resolution (matching agent's hf-token from secret-mgr) is a
// TODO — needs SDK extension for plugin → secret-mgr access.
package kbclient

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"
)

// Client is the HTTP wrapper. Construct once at plugin init; safe to
// share across goroutines.
type Client struct {
	BaseURL string
	APIKey  string
	HTTP    *http.Client
}

// New returns a client with a 30s default timeout. BaseURL has any
// trailing slash trimmed.
func New(baseURL, apiKey string) *Client {
	return &Client{
		BaseURL: strings.TrimRight(baseURL, "/"),
		APIKey:  apiKey,
		HTTP:    &http.Client{Timeout: 30 * time.Second},
	}
}

// ---- Payload types matching HF backend response shapes ----

// KBSummary is one row from GET /knowledge-bases.
type KBSummary struct {
	ID                int    `json:"id"`
	KnowledgeBaseCode string `json:"knowledge_base_code"`
	Title             string `json:"title"`
	Description       string `json:"description"`
}

// TopicSummary is one row from GET /knowledge-bases/{id}/topics.
type TopicSummary struct {
	ID          int    `json:"id"`
	Topic       string `json:"topic"`
	Description string `json:"description"`
}

// FactSummary is one item the dynamic-kb-list-facts tool surfaces to
// the agent. Built client-side from the tree response — title + a
// snippet of the content. Kept light so list-facts output stays
// scan-able even on large KBs.
type FactSummary struct {
	ID         int    `json:"id"`
	TopicID    int    `json:"topic_id"`
	TopicSlug  string `json:"topic_slug"`
	Title      string `json:"title"`
	Snippet    string `json:"snippet"`
}

// Fact is the full fact body fetched by dynamic-kb-cache before
// writing into kb-block.json.
type Fact struct {
	ID        int    `json:"id"`
	KBCode    string `json:"kb_code"`
	TopicSlug string `json:"topic_slug"`
	Content   string `json:"content"`
}

// ---- HTTP methods ----

// ListKBs hits GET /knowledge-bases[?project=<code>]. Empty
// projectCode = unfiltered.
func (c *Client) ListKBs(ctx context.Context, projectCode string) ([]KBSummary, error) {
	path := "/knowledge-bases"
	if projectCode != "" {
		path += "?project=" + url.QueryEscape(projectCode)
	}
	var out []KBSummary
	if err := c.getJSON(ctx, path, &out); err != nil {
		return nil, err
	}
	return out, nil
}

// ListTopics hits GET /knowledge-bases/{kbCode}/topics. kbCode is the
// human KB code (e.g. "KB-PAYROT"); the backend resolves either int
// id or code in the same path slot.
func (c *Client) ListTopics(ctx context.Context, kbCode string) ([]TopicSummary, error) {
	if kbCode == "" {
		return nil, fmt.Errorf("kbclient: kb-code required")
	}
	path := "/knowledge-bases/" + url.PathEscape(kbCode) + "/topics"
	var out []TopicSummary
	if err := c.getJSON(ctx, path, &out); err != nil {
		return nil, err
	}
	return out, nil
}

// kbTree mirrors the shape of GET /knowledge-bases/{id}/tree. We only
// pull the fields we need to build FactSummary; unknown fields are
// dropped silently.
type kbTree struct {
	KnowledgeBaseCode string     `json:"knowledge_base_code"`
	Topics            []treeNode `json:"topics"`
}

type treeNode struct {
	ID          int        `json:"id"`
	Topic       string     `json:"topic"`         // topic-level
	Category    string     `json:"category"`      // category-level
	Title       string     `json:"title"`         // fact-level
	Content     string     `json:"content"`       // fact-level
	Categories  []treeNode `json:"categories"`    // children of topic / category
	Facts       []treeNode `json:"facts"`         // fact children
}

// ListFacts hits GET /knowledge-bases/{kbCode}/tree, walks the tree,
// and flattens facts under the requested topic ids into FactSummary
// rows. Snippet = first 120 chars of content (UTF-8 safe-truncated).
func (c *Client) ListFacts(ctx context.Context, kbCode string, topicIDs []int) ([]FactSummary, error) {
	if kbCode == "" {
		return nil, fmt.Errorf("kbclient: kb-code required")
	}
	if len(topicIDs) == 0 {
		return nil, fmt.Errorf("kbclient: topic-ids required")
	}
	path := "/knowledge-bases/" + url.PathEscape(kbCode) + "/tree"
	var tree kbTree
	if err := c.getJSON(ctx, path, &tree); err != nil {
		return nil, err
	}
	wantTopic := map[int]bool{}
	for _, id := range topicIDs {
		wantTopic[id] = true
	}
	var out []FactSummary
	for _, topic := range tree.Topics {
		if !wantTopic[topic.ID] {
			continue
		}
		walkFactsInto(&out, topic.ID, topic.Topic, topic.Categories, topic.Facts)
	}
	return out, nil
}

// walkFactsInto descends category subtree, collecting facts. cur is
// the topic context (id + slug) for tagging.
func walkFactsInto(out *[]FactSummary, topicID int, topicSlug string, cats, facts []treeNode) {
	for _, f := range facts {
		*out = append(*out, FactSummary{
			ID:        f.ID,
			TopicID:   topicID,
			TopicSlug: topicSlug,
			Title:     f.Title,
			Snippet:   snippet(f.Content, 120),
		})
	}
	for _, c := range cats {
		walkFactsInto(out, topicID, topicSlug, c.Categories, c.Facts)
	}
}

// GetFacts pulls each fact's full content by ID. Calls
// /knowledge-facts/{id} per fact; rate-limited to sequential issue
// (small N expected — agents cache a handful per call). Pass kbCode
// for tagging the returned Fact records; backend doesn't return it.
func (c *Client) GetFacts(ctx context.Context, kbCode string, factIDs []int) ([]Fact, error) {
	if kbCode == "" {
		return nil, fmt.Errorf("kbclient: kb-code required")
	}
	out := make([]Fact, 0, len(factIDs))
	for _, id := range factIDs {
		path := "/knowledge-facts/" + strconv.Itoa(id)
		var node struct {
			ID         int    `json:"id"`
			Title      string `json:"title"`
			Content    string `json:"content"`
			TopicID    int    `json:"topic_id"`
			TopicSlug  string `json:"topic"`
			CategoryID int    `json:"category_id"`
		}
		if err := c.getJSON(ctx, path, &node); err != nil {
			// 404 → skip silently; other errors fail the batch
			if isNotFound(err) {
				continue
			}
			return nil, err
		}
		out = append(out, Fact{
			ID:        node.ID,
			KBCode:    kbCode,
			TopicSlug: node.TopicSlug,
			Content:   node.Content,
		})
	}
	return out, nil
}

// ---- transport plumbing ----

func (c *Client) getJSON(ctx context.Context, path string, out any) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.BaseURL+path, nil)
	if err != nil {
		return err
	}
	if c.APIKey != "" {
		req.Header.Set("Authorization", "Bearer "+c.APIKey)
	}
	req.Header.Set("Accept", "application/json")
	res, err := c.HTTP.Do(req)
	if err != nil {
		return fmt.Errorf("GET %s: %w", path, err)
	}
	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)
	if res.StatusCode == 404 {
		return notFoundErr{path: path}
	}
	if res.StatusCode >= 400 {
		return fmt.Errorf("GET %s: HTTP %d: %s", path, res.StatusCode, truncate(body, 200))
	}
	if len(body) == 0 {
		return nil
	}
	if err := json.Unmarshal(body, out); err != nil {
		return fmt.Errorf("GET %s decode: %w (body=%q)", path, err, truncate(body, 200))
	}
	return nil
}

type notFoundErr struct{ path string }

func (e notFoundErr) Error() string { return "GET " + e.path + ": 404 not found" }

func isNotFound(err error) bool {
	_, ok := err.(notFoundErr)
	return ok
}

func truncate(b []byte, n int) string {
	if len(b) > n {
		return string(b[:n]) + "..."
	}
	return string(b)
}

// snippet returns the first n bytes of s, padded with "..." if cut.
// Naive byte slice; HF content is UTF-8 and we accept the small risk
// of cutting mid-rune for log-level rendering (the agent gets full
// content via GetFacts before caching).
func snippet(s string, n int) string {
	s = strings.TrimSpace(s)
	if len(s) <= n {
		return s
	}
	return s[:n] + "..."
}

// Compile-time guard: caller code expected to wrap bytes.Buffer usage
// (currently unused but here for future POST/PATCH endpoints).
var _ = bytes.NewReader([]byte{})