package changeset

import (
	"bytes"
	"fmt"
	"math/rand"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/BurntSushi/toml"
	"gopkg.in/yaml.v3"
)

// BumpType represents a semver bump type.
type BumpType string

const (
	BumpMajor      BumpType = "major"
	BumpMinor      BumpType = "minor"
	BumpPatch      BumpType = "patch"
	BumpPreMajor   BumpType = "premajor"
	BumpPreMinor   BumpType = "preminor"
	BumpPrePatch   BumpType = "prepatch"
	BumpPreRelease BumpType = "prerelease"
)

// ValidBumps is the set of valid bump type strings.
var ValidBumps = []BumpType{
	BumpMajor, BumpMinor, BumpPatch,
	BumpPreMajor, BumpPreMinor, BumpPrePatch, BumpPreRelease,
}

// Changeset represents a single .stamp/*.md file.
type Changeset struct {
	// Slug is the filename without extension.
	Slug string
	// Bumps maps project name to bump type.
	Bumps map[string]BumpType
	// Description is the markdown body of the changeset.
	Description string
}

// frontmatterYAML is the shape parsed from YAML frontmatter.
type frontmatterYAML struct {
	Bumps map[string]string `yaml:"bumps"`
}

// frontmatterTOML is the shape parsed from TOML frontmatter.
type frontmatterTOML struct {
	Bumps map[string]string `toml:"bumps"`
}

// Parse reads a .stamp/*.md file and returns a Changeset.
func Parse(path string) (*Changeset, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("reading %s: %w", path, err)
	}
	return ParseBytes(filepath.Base(strings.TrimSuffix(path, ".md")), data)
}

// ParseBytes parses changeset content from raw bytes.
func ParseBytes(slug string, data []byte) (*Changeset, error) {
	content := strings.TrimSpace(string(data))

	var (
		rawBumps map[string]string
		body     string
		err      error
	)

	switch {
	case strings.HasPrefix(content, "---"):
		rawBumps, body, err = parseYAMLFrontmatter(content)
	case strings.HasPrefix(content, "+++"):
		rawBumps, body, err = parseTOMLFrontmatter(content)
	default:
		return nil, fmt.Errorf("changeset %q: missing frontmatter (expected --- or +++)", slug)
	}
	if err != nil {
		return nil, fmt.Errorf("changeset %q: %w", slug, err)
	}

	bumps := make(map[string]BumpType, len(rawBumps))
	for project, raw := range rawBumps {
		bt := BumpType(strings.ToLower(raw))
		if !isValidBump(bt) {
			return nil, fmt.Errorf("changeset %q: invalid bump type %q for project %q", slug, raw, project)
		}
		bumps[project] = bt
	}

	return &Changeset{
		Slug:        slug,
		Bumps:       bumps,
		Description: strings.TrimSpace(body),
	}, nil
}

func parseYAMLFrontmatter(content string) (map[string]string, string, error) {
	// Strip opening ---
	rest := strings.TrimPrefix(content, "---")
	idx := strings.Index(rest, "\n---")
	if idx < 0 {
		return nil, "", fmt.Errorf("unterminated YAML frontmatter")
	}
	fm := rest[:idx]
	body := strings.TrimSpace(rest[idx+4:]) // skip closing ---\n

	var parsed frontmatterYAML
	if err := yaml.Unmarshal([]byte(fm), &parsed); err != nil {
		return nil, "", fmt.Errorf("invalid YAML frontmatter: %w", err)
	}
	return parsed.Bumps, body, nil
}

func parseTOMLFrontmatter(content string) (map[string]string, string, error) {
	rest := strings.TrimPrefix(content, "+++")
	idx := strings.Index(rest, "\n+++")
	if idx < 0 {
		return nil, "", fmt.Errorf("unterminated TOML frontmatter")
	}
	fm := rest[:idx]
	body := strings.TrimSpace(rest[idx+4:])

	var parsed frontmatterTOML
	if err := toml.Unmarshal([]byte(fm), &parsed); err != nil {
		return nil, "", fmt.Errorf("invalid TOML frontmatter: %w", err)
	}
	return parsed.Bumps, body, nil
}

// Write creates a new .stamp/<slug>.md file in the given directory.
func Write(dir, slug string, bumps map[string]BumpType, description string) error {
	if err := os.MkdirAll(dir, 0755); err != nil {
		return fmt.Errorf("creating %s: %w", dir, err)
	}

	path := filepath.Join(dir, slug+".md")
	content, err := Format(bumps, description)
	if err != nil {
		return err
	}
	return os.WriteFile(path, content, 0644)
}

// Format renders a changeset to YAML-frontmatter markdown bytes.
func Format(bumps map[string]BumpType, description string) ([]byte, error) {
	var buf bytes.Buffer
	buf.WriteString("---\nbumps:\n")
	for project, bump := range bumps {
		fmt.Fprintf(&buf, "  %s: %s\n", project, bump)
	}
	buf.WriteString("---\n\n")
	buf.WriteString(description)
	buf.WriteString("\n")
	return buf.Bytes(), nil
}

// ReadAll reads all .stamp/*.md files from the given directory.
func ReadAll(dir string) ([]*Changeset, error) {
	entries, err := filepath.Glob(filepath.Join(dir, "*.md"))
	if err != nil {
		return nil, err
	}

	var result []*Changeset
	for _, entry := range entries {
		cs, err := Parse(entry)
		if err != nil {
			return nil, err
		}
		result = append(result, cs)
	}
	return result, nil
}

// DeleteAll removes all .stamp/*.md files from the given directory.
func DeleteAll(dir string) error {
	entries, err := filepath.Glob(filepath.Join(dir, "*.md"))
	if err != nil {
		return err
	}
	for _, entry := range entries {
		if err := os.Remove(entry); err != nil {
			return fmt.Errorf("removing %s: %w", entry, err)
		}
	}
	return nil
}

// GenerateSlug returns a random adjective-noun slug, e.g. "brave-river".
func GenerateSlug() string {
	r := rand.New(rand.NewSource(time.Now().UnixNano()))
	adj := adjectives[r.Intn(len(adjectives))]
	noun := nouns[r.Intn(len(nouns))]
	return fmt.Sprintf("%s-%s", adj, noun)
}

func isValidBump(bt BumpType) bool {
	for _, v := range ValidBumps {
		if bt == v {
			return true
		}
	}
	return false
}

var adjectives = []string{
	"brave", "calm", "clean", "dark", "eager", "fast", "fresh",
	"gentle", "happy", "kind", "light", "loud", "neat", "quiet",
	"rapid", "sharp", "silent", "smart", "soft", "sweet", "swift",
	"warm", "wide", "wild", "young",
}

var nouns = []string{
	"bird", "cloud", "dawn", "dew", "dust", "fire", "flame",
	"flash", "frost", "gale", "hill", "lake", "leaf", "moon",
	"rain", "river", "rock", "seed", "shadow", "sky", "snow",
	"star", "storm", "stream", "tide", "tree", "wave", "wind",
}