package docs

import (
	"os"
	"path/filepath"
	"strings"
)

// DocFrontmatter is the machine-readable identity header of an API doc page.
// It is the contract the drift gate (drift_test.go) checks against the real
// router registrations and the schema registry (schema.go).
type DocFrontmatter struct {
	Method string // GET|POST|PUT|PATCH|DELETE
	Path   string // Echo syntax, e.g. /api/collections/:id
	Auth   string // none|jwt|jwt+admin|device-token|optional-jwt
	Area   string // sidebar area, e.g. collections
}

// APIDoc is one endpoint doc file: its frontmatter plus the labeled example
// blocks extracted from the body.
type APIDoc struct {
	RelPath            string
	Frontmatter        DocFrontmatter
	ExampleRequest     []byte
	ExampleResponse    []byte
	HasExampleResponse bool
	Unverified         []string // UNVERIFIED markers found in the body
}

// parseFrontmatter splits a leading "---" delimited block of flat key:value
// lines off content. Recognized keys: method, path, auth, area. Returns the
// frontmatter and the remaining body; hasFM is false when no well-formed
// block is present (prose pages like overviews have none and are skipped by
// the gate).
func parseFrontmatter(content string) (fm DocFrontmatter, body string, hasFM bool) {
	lines := strings.Split(content, "\n")
	if len(lines) == 0 || strings.TrimSpace(lines[0]) != "---" {
		return fm, content, false
	}
	end := -1
	for i := 1; i < len(lines); i++ {
		if strings.TrimSpace(lines[i]) == "---" {
			end = i
			break
		}
	}
	if end == -1 {
		return fm, content, false
	}

	for _, line := range lines[1:end] {
		key, value, ok := strings.Cut(line, ":")
		if !ok {
			continue
		}
		key = strings.ToLower(strings.TrimSpace(key))
		value = strings.TrimSpace(value)
		switch key {
		case "method":
			fm.Method = strings.ToUpper(value)
		case "path":
			fm.Path = value
		case "auth":
			fm.Auth = strings.ToLower(value)
		case "area":
			fm.Area = strings.ToLower(value)
		}
	}
	if fm.Method == "" || fm.Path == "" {
		return fm, content, false // identity is the minimum for a gateable doc
	}
	return fm, strings.Join(lines[end+1:], "\n"), true
}

// extractExampleBlocks pulls fenced code blocks tagged
// "json example-request" / "json example-response" out of a doc body, and
// counts UNVERIFIED markers.
func extractExampleBlocks(body string, doc *APIDoc) {
	lines := strings.Split(body, "\n")
	for i := 0; i < len(lines); i++ {
		fence := strings.TrimSpace(lines[i])
		switch {
		case fence == "```json example-request":
			doc.ExampleRequest = extractUntilClose(lines, i+1)
			i = skipBlock(lines, i+1)
		case fence == "```json example-response":
			doc.ExampleResponse = extractUntilClose(lines, i+1)
			doc.HasExampleResponse = true
			i = skipBlock(lines, i+1)
		}
		if strings.Contains(lines[i], "UNVERIFIED:") {
			doc.Unverified = append(doc.Unverified, strings.TrimSpace(lines[i]))
		}
	}
}

func extractUntilClose(lines []string, start int) []byte {
	var b strings.Builder
	for i := start; i < len(lines); i++ {
		if strings.TrimSpace(lines[i]) == "```" {
			break
		}
		b.WriteString(lines[i])
		b.WriteString("\n")
	}
	return []byte(b.String())
}

// skipBlock returns the index of the closing fence line so the outer loop
// resumes after it.
func skipBlock(lines []string, start int) int {
	for i := start; i < len(lines); i++ {
		if strings.TrimSpace(lines[i]) == "```" {
			return i
		}
	}
	return len(lines) - 1
}

// LoadAPIDocs walks dir recursively and returns every markdown file carrying
// well-formed endpoint frontmatter. Prose pages (overviews, contracts) are
// skipped: the gate only checks docs that claim to describe an endpoint.
func LoadAPIDocs(dir string) ([]APIDoc, error) {
	var docs []APIDoc
	err := filepath.WalkDir(dir, func(path string, d os.DirEntry, err error) error {
		if err != nil || d.IsDir() || !strings.HasSuffix(path, ".md") {
			return err
		}
		raw, err := os.ReadFile(path)
		if err != nil {
			return err
		}
		fm, body, hasFM := parseFrontmatter(string(raw))
		if !hasFM {
			return nil
		}
		doc := APIDoc{
			RelPath:     path,
			Frontmatter: fm,
		}
		extractExampleBlocks(body, &doc)
		docs = append(docs, doc)
		return nil
	})
	return docs, err
}