package api

import (
	"net/http"
	"strconv"
	"strings"
	"unicode/utf8"

	"git.golem15.com/golem15/summercms/modules/beachcomber"
	"git.golem15.com/golem15/summercms/modules/wire"
	"git.golem15.com/jakub/sm-bm-plugin/models"
	"gorm.io/gorm"
)

// Material search: the engine (beachcomber, Typesense) answers candidate ids
// only. Visibility, the filters, the total and the paging stay in SQL, and a
// row's snippet is read only once SQL returned that row, so a material the
// caller may not see never reaches the JSON, its count or a snippet.

// minSearchRunes is the shortest query that searches; a shorter one is
// ignored, as the student app does.
const minSearchRunes = 2

// searchQuery returns the trimmed q of in, or "" when it is shorter than
// minSearchRunes.
func searchQuery(in map[string]any) string {
	q := strings.TrimSpace(str(in, "q"))
	if utf8.RuneCountInString(q) < minSearchRunes {
		return ""
	}
	return q
}

// writeSearchUnavailable answers a search the engine cannot serve: it is not
// configured or the call failed. The list without q keeps working.
func writeSearchUnavailable(w http.ResponseWriter) {
	wire.WriteJSON(w, http.StatusServiceUnavailable, map[string]any{"error": true, "message": "Search is unavailable."})
}

// rankOrder orders rows by their position in ids, the engine's rank. The ids
// are parsed integers, so the array literal carries no caller text.
func rankOrder(ids []uint) string {
	parts := make([]string, len(ids))
	for i, id := range ids {
		parts[i] = strconv.FormatUint(uint64(id), 10)
	}
	return "array_position(ARRAY[" + strings.Join(parts, ",") + "]::bigint[], jz_bm_materials.id), jz_bm_materials.id DESC"
}

// segmentJSON is one run of a snippet: the engine's plain text, verbatim,
// and whether it matched the query. It is never markup; the client renders
// it as text.
type segmentJSON struct {
	Text string `json:"text"`
	Hit  bool   `json:"hit"`
}

// snippetJSON is the one excerpt a search result shows. Source is "body" or
// "file" (FileName set); Lead and Trail say whether text was cut before or
// after the excerpt.
type snippetJSON struct {
	Source   string        `json:"source"`
	FileName *string       `json:"file_name"`
	Lead     bool          `json:"lead"`
	Trail    bool          `json:"trail"`
	Segments []segmentJSON `json:"segments"`
}

// pickSnippet returns the snippet of m from hit: the first body snippet,
// mapped one to one, or else the first file_texts snippet, with the name of
// the file at its array index in files (the IndexedFiles of m, in document
// order; nil when the index does not resolve). A file text is long and is
// not loaded for the page, so a file snippet is always cut on both sides.
// It is nil when the hit has neither. Call it only for a row the SQL
// re-gate returned.
func pickSnippet(hit beachcomber.Hit, m models.Material, files []models.IndexedFile) *snippetJSON {
	for _, sn := range hit.Highlights {
		if sn.Field != "body" || len(sn.Segments) == 0 {
			continue
		}
		out := &snippetJSON{Source: "body", Segments: snippetSegments(sn)}
		var joined strings.Builder
		for _, seg := range sn.Segments {
			joined.WriteString(seg.Text)
		}
		body := ""
		if m.Body != nil {
			body = models.MaterialPlainBody(*m.Body)
		}
		text := strings.TrimSpace(joined.String())
		out.Lead = !strings.HasPrefix(body, text)
		out.Trail = !strings.HasSuffix(body, text)
		return out
	}
	for _, sn := range hit.Highlights {
		if sn.Field != fileTextsField || len(sn.Segments) == 0 {
			continue
		}
		out := &snippetJSON{Source: "file", Lead: true, Trail: true, Segments: snippetSegments(sn)}
		if sn.ArrayIndex >= 0 && sn.ArrayIndex < len(files) {
			name := files[sn.ArrayIndex].FileName
			out.FileName = &name
		}
		return out
	}
	return nil
}

// fileTextsField is the document field of the attached files' texts.
const fileTextsField = "file_texts"

// snippetSegments maps the engine's segments one to one.
func snippetSegments(sn beachcomber.Snippet) []segmentJSON {
	out := make([]segmentJSON, 0, len(sn.Segments))
	for _, seg := range sn.Segments {
		out = append(out, segmentJSON{Text: seg.Text, Hit: seg.Match})
	}
	return out
}

// hasFileSnippet reports whether hit carries a file_texts snippet and no
// body one, so its snippet needs the material's file names.
func hasFileSnippet(hit beachcomber.Hit) bool {
	file := false
	for _, sn := range hit.Highlights {
		if len(sn.Segments) == 0 {
			continue
		}
		switch sn.Field {
		case "body":
			return false
		case fileTextsField:
			file = true
		}
	}
	return file
}

// snippetFiles loads, once per page, the indexed files (names only) of the
// rows whose snippet comes from a file. It reads nothing when no row needs
// it. ids are rows SQL returned.
func snippetFiles(db *gorm.DB, ids []uint, hits map[uint]beachcomber.Hit) (map[uint][]models.IndexedFile, error) {
	var need []uint
	for _, id := range ids {
		if hit, ok := hits[id]; ok && hasFileSnippet(hit) {
			need = append(need, id)
		}
	}
	if len(need) == 0 {
		return nil, nil
	}
	return models.IndexedFiles(db, need, false)
}

// flattenSnippet is a snippet as plain text, for MCP: the segment texts
// joined, with an ellipsis where text was cut.
func flattenSnippet(s *snippetJSON) string {
	if s == nil {
		return ""
	}
	var b strings.Builder
	if s.Lead {
		b.WriteString("…")
	}
	for _, seg := range s.Segments {
		b.WriteString(seg.Text)
	}
	if s.Trail {
		b.WriteString("…")
	}
	return b.String()
}

// snippetValue is the snippet key of a row: the struct, a plain string
// through MCP, or nil when there is none (the key is then left out).
func snippetValue(s *snippetJSON, mcp bool) any {
	if s == nil {
		return nil
	}
	if mcp {
		return flattenSnippet(s)
	}
	return s
}