// Package docs creates and checks the ADR and plan records described in docs/docs-format.md.
package docs

import (
	"bytes"
	"embed"
	"fmt"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"unicode/utf8"
)

//go:embed templates/*.md
var templates embed.FS

var dirs = []struct{ kind, dir string }{{"adr", "docs/adr"}, {"plan", "docs/plans"}}

// Problem is one violation of the format. Line is 1 for file-level problems.
type Problem struct {
	Path string
	Line int
	Msg  string
}

func (p Problem) String() string { return fmt.Sprintf("%s:%d: %s", p.Path, p.Line, p.Msg) }

// Result is the outcome of Check: the number of records read and the sorted problems.
type Result struct {
	Records  int
	Problems []Problem
}

type record struct {
	path, kind, stem, date string
	status                 string
	lists                  map[string][]item
	fm                     *fm
}

type checker struct {
	root, realRoot string
	problems       []Problem
}

func (c *checker) add(path string, line int, format string, args ...any) {
	c.problems = append(c.problems, Problem{path, line, fmt.Sprintf(format, args...)})
}

// Check validates every record under root. The error is for I/O failures only.
func Check(root string) (Result, error) {
	real, err := filepath.EvalSymlinks(root)
	if err != nil {
		return Result{}, err
	}
	c := &checker{root: root, realRoot: real}
	var recs []*record
	for _, d := range dirs {
		if st, err := os.Lstat(filepath.Join(root, d.dir)); os.IsNotExist(err) {
			continue
		} else if err == nil && !st.IsDir() {
			c.add(d.dir, 1, "must be a real directory (symlinks are not allowed)")
			continue
		}
		entries, err := os.ReadDir(filepath.Join(root, d.dir))
		if err != nil {
			return Result{}, err
		}
		for _, e := range entries {
			name := e.Name()
			if strings.HasPrefix(name, ".") || name == "README.md" {
				continue
			}
			rel := d.dir + "/" + name
			if !e.Type().IsRegular() {
				c.add(rel, 1, "must be a regular file (subdirectories, symlinks and other entries are not allowed)")
				continue
			}
			stem, at, msg := parseName(name)
			if msg != "" {
				c.add(rel, 1, "%s", msg)
				continue
			}
			r := &record{path: rel, kind: d.kind, stem: stem, date: at.Format("2006-01-02"), lists: map[string][]item{}}
			if err := c.record(r); err != nil {
				return Result{}, err
			}
			recs = append(recs, r)
		}
	}
	c.graph(recs)
	slices.SortFunc(c.problems, func(a, b Problem) int {
		return strings.Compare(fmt.Sprintf("%s\x00%09d\x00%s", a.Path, a.Line, a.Msg), fmt.Sprintf("%s\x00%09d\x00%s", b.Path, b.Line, b.Msg))
	})
	return Result{len(recs), c.problems}, nil
}

func (c *checker) record(r *record) error {
	data, err := os.ReadFile(filepath.Join(c.root, filepath.FromSlash(r.path)))
	if err != nil {
		return err
	}
	if bytes.HasPrefix(data, []byte("\xef\xbb\xbf")) {
		c.add(r.path, 1, "file must not start with a byte order mark")
		return nil
	}
	if !utf8.Valid(data) {
		c.add(r.path, 1, "file must be valid UTF-8")
		return nil
	}
	src := strings.ReplaceAll(string(data), "\r\n", "\n")
	front, body, bodyLine, msg := splitFrontmatter(src)
	if msg != "" {
		c.add(r.path, 1, "%s", msg)
		return nil
	}
	m, ok := c.parseFrontmatter(r, front)
	if !ok {
		return nil
	}
	r.fm = m
	var title string
	var titleOK bool
	if r.kind == "adr" {
		title, titleOK = c.adr(r, m)
	} else {
		c.plan(r, m)
	}
	c.body(r, body, bodyLine, title, titleOK)
	return nil
}