package catalogue

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path"
	"path/filepath"
	"strings"
	"unicode/utf8"
)

// TemplateField is the key a file resource names its template file by.
const TemplateField = "template"

// DefaultTemplatesDir is the directory a module's template files are kept in, and its templates archive is built
// from, when its manifest names none (Manifest.Templates, issue 731).
const DefaultTemplatesDir = "files"

// TemplatesDir is the module's directory its template files are kept in, and the directory its templates archive is
// built from: the one its manifest names, else files/.
func (m Manifest) TemplatesDir() string {
	if m.Templates != "" {
		return m.Templates
	}
	return DefaultTemplatesDir
}

// Templated is whether any of the manifest's resources, or any item it contributes (collections.go), names a
// template.
func (m Manifest) Templated() bool {
	for _, r := range m.Resources {
		if _, has := r[TemplateField]; has {
			return true
		}
	}
	for _, it := range m.Items {
		if it.Template != "" {
			return true
		}
	}
	return false
}

// TemplatesArtifact is the name of the archive artifact the module packs its templates into — the one built from its
// templates directory (TemplatesDir) — or "" when it declares none, or more than one (both refused by templateProblems
// for a module naming a template).
func TemplatesArtifact(m Manifest) string {
	found := templatesArtifacts(m)
	if len(found) != 1 {
		return ""
	}
	return found[0]
}

func templatesArtifacts(m Manifest) []string {
	if m.Build == nil {
		return nil
	}
	var found []string
	for _, a := range m.Build.Artifacts {
		if a.Kind == ArtifactArchive && a.URL == "" && cleanFrom(a.From) == m.TemplatesDir() {
			found = append(found, a.Name)
		}
	}
	return found
}

// cleanFrom is an artifact's directory as one relative path: "./files/" is "files".
func cleanFrom(from string) string {
	c := path.Clean(strings.TrimSpace(from))
	return strings.TrimPrefix(c, "./")
}

// templateOf is the template a resource names, whether it names one, and what is wrong with it ("" when nothing):
// dir is the module's templates directory.
func templateOf(module, dir string, r map[string]any) (string, bool, string) {
	raw, has := r[TemplateField]
	if !has {
		return "", false, ""
	}
	id := fmt.Sprint(r["id"])
	if t := fmt.Sprint(r["type"]); t != "file" {
		return "", true, fmt.Sprintf("%s: %s is a %s and names a template; only a file takes its text from one "+
			"(novox/hq ADR 0349 §2)", module, id, t)
	}
	name, ok := raw.(string)
	if !ok || strings.TrimSpace(name) == "" {
		return "", true, fmt.Sprintf("%s: %s names a template that is not a path: %v; a template is %q",
			module, id, raw, dir+"/<name>")
	}
	if _, both := r["content"]; both {
		return name, true, fmt.Sprintf("%s: %s names the template %q and says its content too; a file's text is "+
			"in one place, the template or the content, never both (novox/hq ADR 0349 §2)", module, id, name)
	}
	if strings.HasPrefix(name, "/") || path.Clean(name) != name || !strings.HasPrefix(name, dir+"/") ||
		strings.Contains(name, "\\") {
		return name, true, fmt.Sprintf("%s: %s names the template %q, which is not a file under %s/ of its own "+
			"repository: a template is %q, a plain relative path, and the build packs only %s/",
			module, id, name, dir, dir+"/<name>", dir)
	}
	return name, true, ""
}

// fillTemplates is resources with each template's text as its content and the template key dropped: text says the text
// of a template by its path ("<templates directory>/<name>"), and whether it has one. A template it has no text for, or
// text that is not UTF-8, is refused by name. Every resource is copied; the manifest's own are left as they were.
func fillTemplates(module, dir string, resources []map[string]any, text func(string) (string, bool),
	where string) ([]map[string]any, error) {
	out := make([]map[string]any, 0, len(resources))
	var problems []string
	for _, r := range resources {
		name, has, wrong := templateOf(module, dir, r)
		if !has {
			out = append(out, r)
			continue
		}
		if wrong != "" {
			problems = append(problems, wrong)
			continue
		}
		body, ok := text(name)
		if !ok {
			problems = append(problems, fmt.Sprintf("%s: %v names the template %q, and %s holds no such file",
				module, r["id"], name, where))
			continue
		}
		if !utf8.ValidString(body) {
			// A manifest is JSON: text that is not UTF-8 would be changed on the way, silently.
			problems = append(problems, fmt.Sprintf("%s: %v names the template %q, which is not UTF-8 text; a "+
				"file's text is carried as JSON and would not reach the machine as written", module, r["id"], name))
			continue
		}
		filled := make(map[string]any, len(r))
		for k, v := range r {
			filled[k] = v
		}
		delete(filled, TemplateField)
		filled["content"] = body
		out = append(out, filled)
	}
	if len(problems) > 0 {
		return nil, errors.New(strings.Join(problems, "; "))
	}
	return out, nil
}

// fillItemTemplates is items with each template's text as its content and the template dropped, as fillTemplates
// does for files (collections.go).
func fillItemTemplates(m Manifest, items []Item, text func(string) (string, bool), where string) ([]Item, error) {
	if len(items) == 0 {
		return items, nil
	}
	out := make([]Item, 0, len(items))
	var problems []string
	for _, it := range items {
		if it.Template == "" {
			out = append(out, it)
			continue
		}
		if wrong := itemTemplateProblem(m, it.Template); wrong != "" {
			problems = append(problems, fmt.Sprintf("%s's item of %s: %s", m.Module, it.Collection, wrong))
			continue
		}
		body, ok := text(it.Template)
		switch {
		case !ok:
			problems = append(problems, fmt.Sprintf("%s: its item of %s names the template %q, and %s holds no "+
				"such file", m.Module, it.Collection, it.Template, where))
			continue
		case !utf8.ValidString(body):
			problems = append(problems, fmt.Sprintf("%s: its item of %s names the template %q, which is not UTF-8 "+
				"text", m.Module, it.Collection, it.Template))
			continue
		}
		it.Template, it.Content = "", body
		out = append(out, it)
	}
	if len(problems) > 0 {
		return nil, errors.New(strings.Join(problems, "; "))
	}
	return out, nil
}

// ReadTemplates is the text of each template the manifest names, read from the module's directory in a repository tree,
// by template path. Refused by name: a template the directory lacks, and anything under its templates directory
// (TemplatesDir) the build's packing refuses — that directory itself, or any directory or file under it, that is a
// symlink or not a plain file — so nothing judged here can be read from outside the tree, and no tree passes here that
// the build would refuse. Each template is read through an os.Root of the module's directory besides, which no path
// element can leave.
func ReadTemplates(m Manifest, dir string) (map[string]string, error) {
	problems := templatesTreeProblems(m.Module, dir, m.TemplatesDir())
	root, err := os.OpenRoot(dir)
	if err != nil {
		return nil, fmt.Errorf("%s: the module's directory cannot be opened to read its templates: %w", m.Module, err)
	}
	defer root.Close()
	texts := map[string]string{}
	type named struct {
		id       any
		template string
		wrong    string
	}
	var templates []named
	for _, r := range m.Resources {
		name, has, wrong := templateOf(m.Module, m.TemplatesDir(), r)
		if has {
			templates = append(templates, named{r["id"], name, wrong})
		}
	}
	for _, it := range m.Items {
		if it.Template != "" {
			templates = append(templates, named{"its item of " + it.key(), it.Template,
				itemTemplateProblem(m, it.Template)})
		}
	}
	for _, t := range templates {
		r := map[string]any{"id": t.id}
		name, wrong := t.template, t.wrong
		if wrong != "" {
			problems = append(problems, wrong)
			continue
		}
		if _, read := texts[name]; read {
			continue
		}
		info, err := root.Lstat(name)
		switch {
		case errors.Is(err, fs.ErrNotExist):
			problems = append(problems, fmt.Sprintf("%s: %v names the template %q, and the module's directory "+
				"has no such file", m.Module, r["id"], name))
			continue
		case err != nil:
			problems = append(problems, fmt.Sprintf("%s: %v names the template %q, which cannot be read: %v",
				m.Module, r["id"], name, err))
			continue
		case !info.Mode().IsRegular():
			problems = append(problems, fmt.Sprintf("%s: %v names the template %q, which is not a plain file; "+
				"the build packs only files", m.Module, r["id"], name))
			continue
		}
		body, err := root.ReadFile(name)
		if err != nil {
			problems = append(problems, fmt.Sprintf("%s: %v names the template %q, which cannot be read: %v",
				m.Module, r["id"], name, err))
			continue
		}
		texts[name] = string(body)
	}
	if len(problems) > 0 {
		return nil, errors.New(strings.Join(problems, "; "))
	}
	return texts, nil
}

// templatesTreeProblems is everything under the module's templates directory (templates, inside dir) that the
// build's packing refuses: that directory itself not a plain directory, and any entry under it that is neither a
// directory nor a plain file — a symlink, to a file or a directory, a device, a pipe. Each said by its path. A
// templates directory that does not exist is no problem here: each template it would have held is refused as missing.
func templatesTreeProblems(module, dir, templates string) []string {
	top := filepath.Join(dir, filepath.FromSlash(templates))
	info, err := os.Lstat(top)
	if errors.Is(err, fs.ErrNotExist) {
		return nil
	}
	if err != nil {
		return []string{fmt.Sprintf("%s: %s/ cannot be read: %v", module, templates, err)}
	}
	if !info.IsDir() {
		return []string{fmt.Sprintf("%s: %s/ is %s, not a directory of the module's own; its templates are read "+
			"only from inside the repository, and the build packs only directories and files", module, templates,
			kindOf(info.Mode()))}
	}
	var problems []string
	err = filepath.WalkDir(top, func(at string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() || d.Type().IsRegular() {
			return nil
		}
		rel, _ := filepath.Rel(dir, at)
		problems = append(problems, fmt.Sprintf("%s: %s is %s; the build packs only directories and files, so "+
			"%s/ holds nothing else", module, filepath.ToSlash(rel), kindOf(d.Type()), templates))
		return nil
	})
	if err != nil {
		problems = append(problems, fmt.Sprintf("%s: %s/ cannot be read: %v", module, templates, err))
	}
	return problems
}

// kindOf says what a file that is not a plain file is.
func kindOf(mode fs.FileMode) string {
	switch {
	case mode&fs.ModeSymlink != 0:
		return "a symlink"
	case mode&fs.ModeDevice != 0:
		return "a device"
	case mode&fs.ModeNamedPipe != 0:
		return "a named pipe"
	case mode&fs.ModeSocket != 0:
		return "a socket"
	case mode.IsDir():
		return "a directory"
	}
	return "not a plain file"
}

// WithTemplatesFrom is the manifest with each template's text read from the module's directory in a repository
// tree as its content: what `module check`, the merge gate and `module add` judge, where nothing was built. Read
// again strictly afterwards, so every rule about a file's text judges the template's text exactly as it judges
// inline content. A manifest naming no template is returned as it is.
func WithTemplatesFrom(m Manifest, dir string) (Manifest, error) {
	if !m.Templated() {
		return m, nil
	}
	texts, err := ReadTemplates(m, dir)
	if err != nil {
		return Manifest{}, err
	}
	filled, err := fillTemplates(m.Module, m.TemplatesDir(), m.Resources, func(name string) (string, bool) {
		t, ok := texts[name]
		return t, ok
	}, "the module's directory")
	if err != nil {
		return Manifest{}, err
	}
	items, err := fillItemTemplates(m, m.Items, func(name string) (string, bool) {
		t, ok := texts[name]
		return t, ok
	}, "the module's directory")
	if err != nil {
		return Manifest{}, err
	}
	out := m
	out.Resources = filled
	out.Items = items
	// Nothing names a template now, so nothing names its directory.
	out.Templates = ""
	// A moved module's mark was judged above, while it still named its templates; read again with its text inline,
	// it is judged as it composes without its build's templates archive — as before, nothing handed (handed.go).
	out.Moved = false
	raw, err := json.Marshal(out)
	if err != nil {
		return Manifest{}, err
	}
	// Decoded again, never judged (novox/hq ADR 0578 §3): the judge judges what this answers where it judges.
	again, err := Decode(raw)
	if err != nil {
		return Manifest{}, err
	}
	again.predefined = m.predefined
	again.Moved = m.Moved
	return again, nil
}