package config

import (
	"context"
	"fmt"
	"html/template"
	"strings"

	"github.com/BurntSushi/toml"

	"code.hackerspace.pl/hscloud/devtools/hackdoc/source"
)

// Config is a configuration concerning a given path of the source. It is built
// from files present in the source, and from global configuration.
type Config struct {
	// DefaultIndex is the filenames that should attempt to be rendered if no exact path is given
	DefaultIndex []string
	// Templates are the templates available to render markdown files, keyed by template name.
	Templates map[string]*template.Template

	// Errors that occured while building this config (due to config file errors, etc).
	Errors map[string]error
}

type configToml struct {
	DefaultIndex []string                       `toml:"default_index"`
	Templates    map[string]*configTomlTemplate `toml:"template"`
}

type configTomlTemplate struct {
	Sources []string `toml:"sources"`
}

func parseToml(data []byte) (*configToml, error) {
	var c configToml
	err := toml.Unmarshal(data, &c)
	if err != nil {
		return nil, err
	}
	if c.Templates == nil {
		c.Templates = make(map[string]*configTomlTemplate)
	}
	return &c, nil
}

func configFileLocations(path string) []string {
	// Support for unix-style filesystem prefix (/foo/bar/baz) and
	// perforce-depot-style prefix (//foo/bar/baz).
	// Also support relative paths.
	pathTrimmed := strings.TrimLeft(path, "/")
	prefixLen := len(path) - len(pathTrimmed)
	prefix := path[:prefixLen]
	path = pathTrimmed
	if len(prefix) > 2 {
		return nil
	}

	// Turn path into possible directory names, including root.
	path = strings.Trim(path, "/")
	parts := strings.Split(path, "/")
	if parts[0] != "" {
		parts = append([]string{""}, parts...)
	}

	locations := []string{}
	for i, _ := range parts {
		p := strings.Join(parts[:i+1], "/")
		p += "/hackdoc.toml"
		p = prefix + strings.Trim(p, "/")
		locations = append(locations, p)
	}
	return locations
}

func ForPath(ctx context.Context, s source.Source, path string) (*Config, error) {
	if path != "//" {
		path = strings.TrimRight(path, "/")
	}

	cfg := &Config{
		Templates: make(map[string]*template.Template),
		Errors:    make(map[string]error),
	}

	tomlPaths := configFileLocations(path)
	for _, p := range tomlPaths {
		file, err := s.IsFile(ctx, p)
		if err != nil {
			return nil, fmt.Errorf("IsFile(%q): %w", path, err)
		}
		if !file {
			continue
		}
		data, err := s.ReadFile(ctx, p)
		if err != nil {
			return nil, fmt.Errorf("ReadFile(%q): %w", path, err)
		}

		c, err := parseToml(data)
		if err != nil {
			cfg.Errors[p] = err
			continue
		}

		err = cfg.updateFromToml(ctx, p, s, c)
		if err != nil {
			return nil, fmt.Errorf("updating from %q: %w", p, err)
		}
	}

	return cfg, nil
}

func (c *Config) updateFromToml(ctx context.Context, p string, s source.Source, t *configToml) error {
	if t.DefaultIndex != nil {
		c.DefaultIndex = t.DefaultIndex
	}

	for k, v := range t.Templates {
		tmpl := template.New(k)

		for _, source := range v.Sources {
			data, err := s.ReadFile(ctx, source)
			if err != nil {
				c.Errors[p] = fmt.Errorf("reading template file %q: %w", source, err)
				return nil
			}
			tmpl, err = tmpl.Parse(string(data))
			if err != nil {
				c.Errors[p] = fmt.Errorf("parsing template file %q: %w", source, err)
				return nil
			}
		}
		c.Templates[k] = tmpl
	}

	return nil
}