// Package handler — tablehandler.go: directory-of-YAML table view.
//
// URL convention:
//
//	GET /<dir>/<name>.table.html  → tables.html, only when <dir>/.zddc
//	                                declares tables: { <name>: <spec-path> }
//	                                AND the spec file exists.
//
// Discovery is .zddc-declarative (no auto-mount on file presence). The
// handler's only jobs are:
//
//  1. Recognize the URL — does <dir>/.zddc declare a table named <name>,
//     and does the referenced *.table.yaml spec actually exist? If not,
//     fall through to the static-file pipeline.
//  2. Gate on the cascading ACL at the request directory (read action).
//  3. Serve the static tables.html bytes.
//
// All rendering is client-side. The page (built from tables/) detects
// HTTP vs file:// mode, then walks the directory via shared/zddc-source.js
// (HttpDirectoryHandle in HTTP mode, real FileSystemDirectoryHandle in
// file mode), reads .zddc, parses the spec, and renders rows in the
// browser. The server does not pre-parse the spec, list rows, or compute
// per-row "editable" — the client does, and ACL is enforced naturally:
// HTTP-mode reads/writes go through the cascade-aware file API, and
// local-mode reads/writes are bounded by whatever the OS gave the
// FS-Access handle.
package handler

import (
	_ "embed"
	"log/slog"
	"net/http"
	"path/filepath"
	"strings"

	"codeberg.org/VARASYS/ZDDC/zddc/internal/config"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/policy"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/zddc"
)

//go:embed tables.html
var embeddedTablesHTML []byte

//go:embed default-mdl.table.yaml
var embeddedDefaultMdlTable []byte

//go:embed default-mdl.form.yaml
var embeddedDefaultMdlForm []byte

// DefaultMdlTableYAML returns the embedded default mdl.table.yaml bytes.
// Used by the static-file handler to serve the default spec at
// archive/<party>/mdl.table.yaml when no operator file exists on disk.
func DefaultMdlTableYAML() []byte { return embeddedDefaultMdlTable }

// DefaultMdlFormYAML returns the embedded default mdl.form.yaml bytes.
func DefaultMdlFormYAML() []byte { return embeddedDefaultMdlForm }

// IsDefaultMdlSpec reports whether urlPath is one of the default-MDL
// virtual files served when no operator file exists on disk:
//
//	<project>/archive/<party>/mdl/table.yaml
//	<project>/archive/<party>/mdl/form.yaml
//
// The MDL files live INSIDE the rows-dir along with row YAMLs so the
// whole directory is self-contained — copying mdl/ moves the spec,
// the form, and all rows together. Returns embedded bytes + true when
// the fallback should fire; nil + false when an operator-supplied
// file exists or the path is not eligible.
func IsDefaultMdlSpec(fsRoot, urlPath string) ([]byte, bool) {
	base := strings.ToLower(filepath.Base(urlPath))
	var bytes []byte
	switch base {
	case "table.yaml":
		bytes = embeddedDefaultMdlTable
	case "form.yaml":
		bytes = embeddedDefaultMdlForm
	default:
		return nil, false
	}
	if !isAtArchivePartyMdlLevel(fsRoot, urlPath) {
		return nil, false
	}
	// Operator file wins if it exists on disk.
	rel := strings.TrimPrefix(filepath.ToSlash(urlPath), "/")
	abs := filepath.Join(fsRoot, filepath.FromSlash(rel))
	if !strings.HasPrefix(abs, fsRoot+string(filepath.Separator)) && abs != fsRoot {
		return nil, false
	}
	if fileExists(abs) {
		return nil, false
	}
	return bytes, true
}

// IsDefaultMdlSpecAbs is the abs-path-keyed variant of IsDefaultMdlSpec.
// Used by handlers that hold a filesystem path rather than a URL.
// Returns the embedded default bytes + true when absPath is the
// virtual archive/<party>/{mdl.table.yaml, mdl.form.yaml} fallback.
func IsDefaultMdlSpecAbs(fsRoot, absPath string) ([]byte, bool) {
	if !strings.HasPrefix(absPath, fsRoot+string(filepath.Separator)) && absPath != fsRoot {
		return nil, false
	}
	rel, err := filepath.Rel(fsRoot, absPath)
	if err != nil {
		return nil, false
	}
	urlPath := "/" + filepath.ToSlash(rel)
	return IsDefaultMdlSpec(fsRoot, urlPath)
}

// isAtArchivePartyLevel reports whether urlPath refers to a file
// directly under <project>/archive/<party>/ (depth-3 directory). The
// canonical-folder names are case-folded.
func isAtArchivePartyLevel(fsRoot, urlPath string) bool {
	rel := strings.Trim(filepath.ToSlash(urlPath), "/")
	parts := strings.Split(rel, "/")
	// <project>/archive/<party>/<file> = 4 segments
	if len(parts) != 4 {
		return false
	}
	return strings.EqualFold(parts[1], "archive")
}

// isAtArchivePartyMdlLevel reports whether urlPath refers to a file
// directly under <project>/archive/<party>/mdl/ (depth-4 directory).
// Used by the default-MDL fallback after the spec/form moved INSIDE
// the rows-dir for self-containment.
func isAtArchivePartyMdlLevel(fsRoot, urlPath string) bool {
	rel := strings.Trim(filepath.ToSlash(urlPath), "/")
	parts := strings.Split(rel, "/")
	// <project>/archive/<party>/mdl/<file> = 5 segments
	if len(parts) != 5 {
		return false
	}
	return strings.EqualFold(parts[1], "archive") && strings.EqualFold(parts[3], "mdl")
}

// TableRequest describes a recognized table-system request.
type TableRequest struct {
	// Name is the table's URL stem (the key declared in .zddc tables).
	Name string
	// SpecPath is the absolute filesystem path to the *.table.yaml.
	// Validated to exist at recognition time.
	SpecPath string
	// Dir is the absolute path to the request directory (where the
	// .zddc declared the table).
	Dir string
}

// tableRowsRedirect reports the canonical /<dir>/table.html URL to
// redirect to when (urlPath) names a directory that contains a
// table.yaml (or matches the default-MDL fallback). Returns "" when
// no redirect should fire.
//
// Recognition reuses RecognizeTableRequest by synthesizing the
// equivalent <urlPath>table.html and asking the recognizer whether
// it's a real (or default-MDL) table. Single source of truth for
// validation.
func tableRowsRedirect(fsRoot, urlPath string) string {
	// urlPath is the directory request — e.g. "/proj/archive/Acme/mdl/".
	if urlPath == "" || urlPath == "/" {
		return ""
	}
	if !strings.HasSuffix(urlPath, "/") {
		urlPath += "/"
	}
	synthesized := urlPath + "table.html"
	tr := RecognizeTableRequest(fsRoot, http.MethodGet, synthesized)
	if tr == nil {
		return ""
	}
	// Default-MDL case (no on-disk table.yaml): follow the slash/no-
	// slash convention — slash form serves browse, no-slash serves
	// tables (handled by the dispatcher). Redirecting here would
	// override the convention and force the user into the table view
	// from any /<party>/mdl/ click.
	if !fileExists(tr.SpecPath) {
		return ""
	}
	return synthesized
}

// RecognizeTableRequest classifies r as a table-system request, or
// returns nil if it falls through to other handlers. Discovery is
// presence-based and self-contained: a /<dir>/table.html URL fires
// when <dir>/table.yaml exists on disk, or when the default-MDL
// fallback at archive/<party>/mdl/ applies.
//
// The spec, the row-edit form, and all rows live together in <dir>.
// Copying <dir> elsewhere copies everything needed to re-host the
// table — that's the whole point of the in-dir layout.
//
// The table's "name" is the directory's basename (so the URL
// /<parent>/mdl/table.html names the "mdl" table, with rows in mdl/).
//
// Methods other than GET return nil — the table is read-only at the
// URL level. Writes go through the file API directly.
func RecognizeTableRequest(fsRoot, method, urlPath string) *TableRequest {
	if method != http.MethodGet {
		return nil
	}
	if !strings.HasSuffix(urlPath, "/table.html") && urlPath != "/table.html" {
		return nil
	}

	// Strip /table.html — what remains is the rows-dir.
	rel := strings.TrimSuffix(strings.TrimPrefix(urlPath, "/"), "/table.html")
	rel = strings.TrimSuffix(rel, "table.html") // handles "/table.html" at root → ""
	rel = strings.Trim(rel, "/")
	if rel == "" {
		// /table.html at root has no rows-dir to name.
		return nil
	}
	dirAbs := filepath.Join(fsRoot, filepath.FromSlash(rel))
	if !strings.HasPrefix(dirAbs, fsRoot+string(filepath.Separator)) && dirAbs != fsRoot {
		return nil
	}
	name := filepath.Base(dirAbs)

	specAbs := filepath.Join(dirAbs, "table.yaml")

	// Presence-based discovery: <dir>/table.yaml on disk.
	if fileExists(specAbs) {
		return &TableRequest{Name: name, SpecPath: specAbs, Dir: dirAbs}
	}

	// Default-MDL virtual-spec fallback at archive/<party>/mdl/. The
	// spec bytes come from IsDefaultMdlSpec via the static-file
	// dispatcher when no on-disk file exists at that path; the rows-dir
	// itself doesn't need to exist either (fully virtual archive).
	if isAtArchivePartyMdlDir(fsRoot, dirAbs) {
		return &TableRequest{Name: "mdl", SpecPath: specAbs, Dir: dirAbs}
	}
	return nil
}

// isAtArchivePartyMdlDir reports whether dirAbs is exactly
// <fsRoot>/<project>/archive/<party>/mdl. Used by the default-MDL
// fallback to recognize the virtual rows-dir whether or not it
// exists on disk.
func isAtArchivePartyMdlDir(fsRoot, dirAbs string) bool {
	rel, err := filepath.Rel(fsRoot, dirAbs)
	if err != nil {
		return false
	}
	rel = filepath.ToSlash(rel)
	if strings.HasPrefix(rel, "../") || rel == ".." || rel == "." {
		return false
	}
	parts := strings.Split(rel, "/")
	if len(parts) != 4 {
		return false
	}
	return strings.EqualFold(parts[1], "archive") && strings.EqualFold(parts[3], "mdl")
}

// isNotExistError reports whether err indicates a missing file. Local
// helper to avoid pulling errors.Is into the handler package.
func isNotExistError(err error) bool {
	return err != nil && strings.Contains(err.Error(), "no such file or directory")
}

// ServeTable serves the static tables.html bytes for a recognized
// request. ACL gate is the read action at the request directory; on
// allow, the embedded HTML is written verbatim. The client takes over
// from there — see tables/js/main.js.
func ServeTable(cfg config.Config, req *TableRequest, w http.ResponseWriter, r *http.Request) {
	p := PrincipalFromContext(r)
	decider := DeciderFromContext(r)

	chain, err := zddc.EffectivePolicy(cfg.Root, req.Dir)
	if err != nil {
		slog.Warn("table: policy error", "path", req.Dir, "err", err)
	}
	if allowed, _ := policy.AllowActionFromChainP(r.Context(), decider, chain, p, r.URL.Path, policy.ActionRead); !allowed {
		http.Error(w, "Forbidden", http.StatusForbidden)
		return
	}

	if len(embeddedTablesHTML) == 0 {
		http.Error(w, "table renderer not built into this binary", http.StatusServiceUnavailable)
		return
	}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	_, _ = w.Write(embeddedTablesHTML)
}