// Package config defines PgTidy's formatter (and, later, linter) configuration.
//
// Defaults encode the project house style. A .pgtidy.yaml file discovered by
// walking up from the target directory overrides individual fields.
package config

import (
	"fmt"
	"os"
	"path/filepath"

	"gopkg.in/yaml.v3"
)

// Case controls keyword/identifier casing.
type Case string

const (
	CaseUpper Case = "upper"
	CaseLower Case = "lower"
	// CasePreserve leaves the token text unchanged.
	CasePreserve Case = "preserve"
)

// CommaStyle controls where separators sit in multi-line lists.
type CommaStyle string

const (
	// CommaLeading puts the comma at the start of the continuation line
	// (",col"), the house style.
	CommaLeading CommaStyle = "leading"
	// CommaTrailing puts the comma at the end of the preceding line ("col,").
	CommaTrailing CommaStyle = "trailing"
)

// Style is the formatter configuration.
type Style struct {
	// Indent is one indentation level (default two spaces).
	Indent string
	// Newline is the line terminator emitted by the formatter.
	Newline string
	// KeywordCase controls SQL keyword casing (types excluded — see TypeCase).
	KeywordCase Case
	// IdentCase controls unquoted identifier casing (quoted identifiers are
	// never touched).
	IdentCase Case
	// TypeCase controls built-in type-name casing.
	TypeCase Case
	// Commas controls list separator placement.
	Commas CommaStyle
}

// Default returns the house-style configuration.
func Default() Style {
	return Style{
		Indent:      "  ",
		Newline:     "\n",
		KeywordCase: CaseUpper,
		IdentCase:   CaseLower,
		TypeCase:    CaseLower,
		Commas:      CommaLeading,
	}
}

// yamlFile is the on-disk representation of .pgtidy.yaml.
// All fields are pointers so we can distinguish "not set" from "set to zero value".
type yamlFile struct {
	Indent      *string `yaml:"indent"`
	Newline     *string `yaml:"newline"`
	KeywordCase *string `yaml:"keyword_case"`
	IdentCase   *string `yaml:"ident_case"`
	TypeCase    *string `yaml:"type_case"`
	Commas      *string `yaml:"commas"`
}

// Load discovers and parses the nearest .pgtidy.yaml by walking up from
// startDir. Fields present in the file override the house-style defaults;
// missing fields keep the default value. Returns Default() when no config
// file is found.
func Load(startDir string) (Style, error) {
	st := Default()
	path, err := findConfig(startDir)
	if err != nil || path == "" {
		return st, err
	}

	data, err := os.ReadFile(path)
	if err != nil {
		return st, fmt.Errorf("pgtidy: read %s: %w", path, err)
	}

	var yf yamlFile
	if err := yaml.Unmarshal(data, &yf); err != nil {
		return st, fmt.Errorf("pgtidy: parse %s: %w", path, err)
	}

	if yf.Indent != nil {
		st.Indent = *yf.Indent
	}
	if yf.Newline != nil {
		st.Newline = *yf.Newline
	}
	if yf.KeywordCase != nil {
		c := Case(*yf.KeywordCase)
		if err := validCase(c); err != nil {
			return st, fmt.Errorf("pgtidy: %s: keyword_case: %w", path, err)
		}
		st.KeywordCase = c
	}
	if yf.IdentCase != nil {
		c := Case(*yf.IdentCase)
		if err := validCase(c); err != nil {
			return st, fmt.Errorf("pgtidy: %s: ident_case: %w", path, err)
		}
		st.IdentCase = c
	}
	if yf.TypeCase != nil {
		c := Case(*yf.TypeCase)
		if err := validCase(c); err != nil {
			return st, fmt.Errorf("pgtidy: %s: type_case: %w", path, err)
		}
		st.TypeCase = c
	}
	if yf.Commas != nil {
		cs := CommaStyle(*yf.Commas)
		if cs != CommaLeading && cs != CommaTrailing {
			return st, fmt.Errorf("pgtidy: %s: commas: must be \"leading\" or \"trailing\"", path)
		}
		st.Commas = cs
	}

	return st, nil
}

// findConfig walks parent directories from startDir looking for .pgtidy.yaml.
// Returns ("", nil) when no file is found before reaching the filesystem root.
func findConfig(startDir string) (string, error) {
	dir, err := filepath.Abs(startDir)
	if err != nil {
		return "", err
	}
	for {
		candidate := filepath.Join(dir, ".pgtidy.yaml")
		if _, err := os.Stat(candidate); err == nil {
			return candidate, nil
		}
		parent := filepath.Dir(dir)
		if parent == dir {
			return "", nil
		}
		dir = parent
	}
}

func validCase(c Case) error {
	switch c {
	case CaseUpper, CaseLower, CasePreserve:
		return nil
	}
	return fmt.Errorf("must be \"upper\", \"lower\", or \"preserve\"")
}